A Realization of Network Slices for 5G Networks Using Current IP/MPLS Technologies
draft-ietf-teas-5g-ns-ip-mpls-04
| Document | Type | Active Internet-Draft (teas WG) | |
|---|---|---|---|
| Authors | Krzysztof Grzegorz Szarkowicz , Richard Roberts , Julian Lucek , Mohamed Boucadair , Luis M. Contreras | ||
| Last updated | 2024-04-12 (Latest revision 2024-03-19) | ||
| Replaces | draft-srld-teas-5g-slicing | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-ietf-teas-5g-ns-ip-mpls-04
TEAS K. G. Szarkowicz, Ed.
Internet-Draft R. Roberts, Ed.
Intended status: Informational J. Lucek
Expires: 21 September 2024 Juniper Networks
M. Boucadair, Ed.
Orange
L. M. Contreras
Telefonica
20 March 2024
A Realization of Network Slices for 5G Networks Using Current IP/MPLS
Technologies
draft-ietf-teas-5g-ns-ip-mpls-04
Abstract
Slicing is a feature that was introduced by the 3rd Generation
Partnership Project (3GPP) in mobile networks. Realization of 5G
slicing implies requirements for all mobile domains, including the
Radio Access Network (RAN), Core Network (CN), and Transport Network
(TN).
This document describes a Network Slice realization model for IP/MPLS
networks with a focus on the Transport Network fulfilling 5G slicing
connectivity service objectives. The realization model reuses many
building blocks currently commonly used in service provider networks.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Traffic Engineering
Architecture and Signaling Working Group mailing list
(teas@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/teas/.
Source for this draft and an issue tracker can be found at
https://github.com/boucadair/5g-slice-realization.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 21 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. 5G Network Slicing Integration in Transport Networks . . . . 4
3.1. Scope of the Transport Network . . . . . . . . . . . . . 4
3.2. 5G Network Slicing versus Transport Network Slicing . . . 6
3.3. Transport Network Reference Design . . . . . . . . . . . 6
3.3.1. Distributed PE and CE . . . . . . . . . . . . . . . . 8
3.3.2. Co-Managed CE . . . . . . . . . . . . . . . . . . . . 10
3.3.3. Service-aware CE . . . . . . . . . . . . . . . . . . 11
3.4. Orchestration Overview . . . . . . . . . . . . . . . . . 11
3.4.1. End-to-End 5G Slice Orchestration Architecture . . . 11
3.4.2. Transport Network Segments and Network Slice
Instantiation . . . . . . . . . . . . . . . . . . . . 14
3.4.3. Additional Segmentation and Domains . . . . . . . . . 16
3.5. Mapping Schemes Between 5G Network Slices and Transport
Network Slices . . . . . . . . . . . . . . . . . . . . . 16
3.6. First 5G Slice versus Subsequent Slices . . . . . . . . . 19
3.7. Overview of the Transport Network Realization Model . . . 21
4. Hand-off Between Domains . . . . . . . . . . . . . . . . . . 23
4.1. VLAN Hand-off . . . . . . . . . . . . . . . . . . . . . . 23
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4.2. IP Hand-off . . . . . . . . . . . . . . . . . . . . . . . 24
4.3. MPLS Label Hand-off . . . . . . . . . . . . . . . . . . . 27
4.3.1. Option A . . . . . . . . . . . . . . . . . . . . . . 28
4.3.2. Option B . . . . . . . . . . . . . . . . . . . . . . 28
4.3.3. Option C . . . . . . . . . . . . . . . . . . . . . . 30
5. QoS Mapping Realization Models . . . . . . . . . . . . . . . 32
5.1. QoS Layers . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.1. 5G QoS Layer . . . . . . . . . . . . . . . . . . . . 32
5.1.2. TN QoS Layer . . . . . . . . . . . . . . . . . . . . 33
5.2. QoS Realization Models . . . . . . . . . . . . . . . . . 33
5.2.1. 5QI-unaware Model . . . . . . . . . . . . . . . . . . 34
5.2.2. 5QI-aware Model . . . . . . . . . . . . . . . . . . . 41
5.3. Transit Resource Control . . . . . . . . . . . . . . . . 48
6. Transport Planes Mapping Models . . . . . . . . . . . . . . . 48
6.1. 5QI-unaware Model . . . . . . . . . . . . . . . . . . . . 50
6.2. 5QI-aware Model . . . . . . . . . . . . . . . . . . . . . 51
7. Capacity Planning/Management . . . . . . . . . . . . . . . . 52
7.1. Bandwidth Requirements . . . . . . . . . . . . . . . . . 52
7.2. Bandwidth Models . . . . . . . . . . . . . . . . . . . . 56
7.2.1. Scheme 1: Shortest Path Forwarding (SPF) . . . . . . 56
7.2.2. Scheme 2: TE LSPs with Fixed Bandwidth
Reservations . . . . . . . . . . . . . . . . . . . . 57
7.2.3. Scheme 3: TE LSPs without Bandwidth Reservation . . . 58
8. Network Slicing OAM . . . . . . . . . . . . . . . . . . . . . 58
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60
10. Security Considerations . . . . . . . . . . . . . . . . . . . 60
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 61
11.1. Normative References . . . . . . . . . . . . . . . . . . 61
11.2. Informative References . . . . . . . . . . . . . . . . . 62
Appendix A. Acronyms and Abbreviations . . . . . . . . . . . . . 68
Appendix B. An Overview of 5G Networking . . . . . . . . . . . . 71
B.1. Key Building Blocks . . . . . . . . . . . . . . . . . . . 71
B.2. Core Network (CN) . . . . . . . . . . . . . . . . . . . . 73
B.3. Radio Access Network (RAN) . . . . . . . . . . . . . . . 74
B.4. Transport Network (TN) . . . . . . . . . . . . . . . . . 76
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 78
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
1. Introduction
This document focuses on network slicing for 5G networks, covering
the connectivity between Network Functions (NFs) across multiple
domains such as edge clouds, data centers, and the Wide Area Network
(WAN). The document describes a Network Slice realization approach
that fulfills 5G slicing requirements by using existing IP/MPLS
technologies to optimally control Service Level Agreements (SLAs)
offered for 5G slices.
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This work is compatible with the framework defined in [RFC9543] which
describes network slicing in the context of networks built from IETF
technologies.
The realization approach described in this document is typically
triggered by Network Slice Service requests. How a Network Slice
Service request is placed for realization, including how it is
derived from a 5G Slice Service request, is out of scope. Network
Slice Service mapping considerations (e.g., mapping between 3GPP to
IETF service parameters) are discussed, e.g., in
[I-D.ietf-teas-5g-network-slice-application].
Although this document focuses on 5G, the realizations are not
fundamentally constrained by the 5G use case. The document is not
intended to be a BCP and does not claim to specify mandatory
mechanisms to realize network slices. Rather, a key goal of the
document is to provide pragmatic implementation approaches by
leveraging existing readily-available, widely-deployed techniques.
The document is also intended to align the mobile and the IETF
perspectives of slicing.
A brief 5G overview is provided in Appendix B for the reader's
convenience. The reader may refer to [TS-23.501] or [_5G-Book] for
more details about 3GPP network architectures.
2. Definitions
The document uses the terms defined in [RFC9543]. See Section 3.3
for the contextualization of some of these terms.
An extended list of abbreviations used in this document is provided
in Appendix A.
3. 5G Network Slicing Integration in Transport Networks
3.1. Scope of the Transport Network
Appendix B provides an overview of 5G network building blocks: the
Radio Access Network (RAN), Core Network (CN), and Transport Network
(TN). The Transport Network is defined by the 3GPP as the "part
supporting connectivity within and between CN and RAN parts"
(Section 1 of [TS-28.530]).
As discussed in Section 4.4.1 of [TS-28.530], the 3GPP management
system does not directly control the Transport Network: it is
considered as a non-3GPP managed system.
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'The non-3GPP part includes TN parts. The 3GPP management system
provides the network slice requirements to the corresponding
management systems of those non-3GPP parts, e.g. the TN part
supports connectivity within and between CN and AN parts.'
(Section 4.4.1 of [TS-28.530])
In practice, the TN may not map to a monolithic architecture and
management domain. It is frequently segmented, non-uniform, and
managed by different entities. For example, Figure 1 depicts a NF
instance that is deployed in an edge data center (DC) connected to a
NF located in a Public Cloud via a WAN (e.g., MPLS-VPN service). In
this example, the TN can be seen as an abstraction representing an
end-to-end connectivity based upon three distinct domains: DC, WAN,
and Public Cloud. A model for the Transport Network based on
orchestration domains is introduced in Section 3.4. This model
permits to define more precisely where the RFC 9543 Network Slices
apply.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┌───── 5G RAN or CORE Network ├────┐
│ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │
│ │
│ │
▼ ▼
┌──┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┌──┐
│NF├── Transport Network ├──┤NF│
└──┘ └ ─ ┬ ─ ─ ─ ─ ─ ─ ─ ─ ┬ ─ ─ ─ ─ ─ ┬ └──┘
│ │ │
│ │ │
▼ ▼ ▼
┌ ─ Data Center ─ ┌ MPLS VPN─ ┌ Public─
│ Backbone │ Cloud │
│ ┌───┐┌───┐ ┌┴─┐ ┌──┐┌┴─┐
└───┘└───┘ │ └──┘ └─┬┘└──┘ │
│┌──┐┌──┐┌──┐┌──┐ ┌┴─┐ ┌──┐ │
└──┘└──┘└──┘└──┘│ └──┘ └─┬┘ │
└ ─ ─ ─ ─ ─ ─ ─ ─ └ ─ ─ ─ ─ ─ └ ─ ─ ─ ─
Figure 1: An Example of Transport Network Decomposition
The term "Transport Network" is used for disambiguation with 5G
network (e.g., IP, packet-based forwarding vs RAN and CN).
Consequently, the disambiguation applies to Transport Network Slicing
vs. End-to-End 5G Network Slicing (Section 3.2) as well the
management domains: RAN, CN, and TN domains.
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3.2. 5G Network Slicing versus Transport Network Slicing
Network slicing has a different meaning in the 3GPP mobile and
transport worlds. Hence, for the sake of precision and without
seeking to be exhaustive, this section provides a brief description
of the objectives of 5G Network Slicing and Transport Network
Slicing:
* 5G Network Slicing:
Is defined by the 3GPP as an appraoch where logical networks/
partitions are created (called, 5G Network Slices), with
appropriate isolation, resources and optimized topology to serve a
purpose or service category or customers [TS-28.530]. These
resources are from the TN, RAN, CN Network Functions, and the
underlying infrastructure.
* TN Slicing:
The term "TN slice" is used in this document to refer to a slice
in the Transport Network domain of the overall 5G architecture.
The objective of TN Slicing is to isolate, guarantee, or
prioritize Transport Network resources for slices. Examples of
such resources are: buffers, link capacity, or even Routing
Information Base (RIB) and Forwarding Information Base (FIB).
TN Slicing provides various degrees of sharing of resources
between slices. For example, the network capacity can be shared
by all slices, usually with a guaranteed minimum per slice, or
each individual slice can be allocated dedicated network capacity.
Parts of a given network may use the former, while others use the
latter. For example, in order to satisfy local engineering
guidelines and specific service requirements, shared TN resources
could be provided in the backhaul (or midhaul), and dedicated TN
resources could be provided in the midhaul (or backhaul). The
capacity partitioning strategy is deployment specific.
There are different options to implement TN slices based upon
mechanisms such as Virtual Routing and Forwarding instances (VRFs)
for logical separation, Quality of Service (QoS), or Traffic
Engineering (TE).
3.3. Transport Network Reference Design
Figure 2 depicts the reference design used for modelling the
Transport Network based on management perimeters (Customer vs.
Provider).
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Customer Orch. Provider Orch. Customer Orch.
Domain Domain Domain
┌ ─ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─
Customer │ Provider Network Customer │
│ Site 1 │ │ │ Site 2
┌────┐│ ┌────┐ ┌────┐ ┌────┐ │
│┌──┐ │ │ AC ││ │ │ ││ AC ││ NF │
│┌─┴┐─ ─ ─│ CE ├│─ ─ ─ ─│ PE │ │ PE │─ ─ ─ ─ ─│(CE)│ │
│└┤┌─┴┐ │ │ ││ │ │ ││ ││ │
└┤NF│ └────┘│ └────┘ └────┘ └────┘ │
│ └──┘ │ │ │
─ ─ ─ ─ ─ ─ ─ ─ ┘ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
◀─────────────────Transport Network────────────────▶
Figure 2: Reference Design: customer site and Provider Network
The description of the main components shown in Figure 2 are:
Customer: An entity that is responsible for managing and
orchestrating the end-to-end 5G Mobile Network, notably RANs and
CNs.
customer site: A customer manages and deploys 5G NFs (RAN and CN) in
customer sites. On top of 5G NFs (e.g., gNodeB (gNB), 5G Core
(5GC)), a customer may manage additional TN elements (e.g.,
servers, routers, or switches) within a customer site. A customer
site can be either a physical or a virtual location. Examples of
customer sites are a customer private locations (Point of Presence
(PoP), DC), a VPC in a Public Cloud, or servers hosted within the
provider network or colocation service.
The Orchestration of the TN within a customer site involves a set
of controllers for automation purposes (e.g., Network Functions
Virtualization Infrastructure (NFVI), Enhanced Container Network
Interface (CNI), Fabric Managers, or Public Cloud APIs). It is
out of the scope of this document to document how these
controllers are implemented.
Provider: An entity responsible for interconnecting customer sites.
The provider orchestrates and manages a provider network.
Provider Network: A provider uses a provider network to interconnect
customer sites. This document assumes that the provider network
is based on IP or MPLS.
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Customer Edge (CE): A device that provides logical connectivity to
the provider network. The logical connectivity is enforced at
Layer 2 and/or Layer 3 and is denominated an Attachment Circuit
(AC). Examples of CEs include TN components (e.g., router,
switch, or firewalls) and also 5G NFs (i.e., an element of the 5G
domain such as Centralized Unit (CU), Distributed Unit (DU), or
User Plane Function (UPF)).
This document generalizes the definition of a CE with the
introduction of Distributed CEs in Section 3.3.1.
Provider Edge (PE): A device managed by a provider that is connected
to a CE. The connectivity between a CE and a PE is achieved using
one or multiple Attachment Circuit. This document generalizes the
PE definition with the introduction of Distributed PEs in
Section 3.3.1.
Attachment Circuit (AC): The logical connection that attaches a CE
to a PE. A CE is connected to a PE via one or multiple ACs. An
AC is technology-specific. For consistency with the AC data
models terminology (e.g.,
[I-D.ietf-opsawg-teas-attachment-circuit] and
[I-D.ietf-opsawg-ntw-attachment-circuit]), this document assumes
that an AC is configured on a "bearer", which represents the
underlying connectivity.
Examples of ACs are Virtual Local Area Networks (VLANs) (AC)
configured on a physical interface (bearer) or an Overlay VXLAN
EVI (AC) configured on an IP underlay (bearer).
In order to keep the figures simple, only one AC and single-homed
CEs are represented. However, this document does not exclude the
instantiation of multiple ACs between a CE and a PE nor the
presence of CEs that are attached to more than one PE.
3.3.1. Distributed PE and CE
This document uses the concept of distributed CEs and PEs (e.g.,
Section 3.4.3 of [RFC4664]). This approach consolidates a CE/AC/PE
definition that is consistent with the orchestration perimeters. The
CEs and PEs delimit respectively the customer and provider
orchestration domains, while the AC interconnects these domains.
Distributed CE: The logical connectivity is realized by configuring
multiple devices in the customer domain. The CE function is
distributed.
An example of a distributed CE is the realization of an
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interconnection using a L3VPN service based on a distributed CE
composed of a switch (Layer 2) and a router (Layer 3) (case (ii)
in Figure 3).
Distributed PE: The logical connectivity is realized by configuring
multiple devices in the Transport Network (provider orchestration
domain). The PE function is distributed.
An example of a distributed PE is the "Managed CE service". For
example, a provider delivers VPN services using CEs and PEs which
are both managed by the provider (case (iii) in Figure 3). The
managed CE can also be a Data Center Gateway as depicted in the
example (iv) of Figure 3. A provider-managed CE may attach to CEs
of multiple customers. However, this device is part of the
provider network.
Figure 3 depicts the reference model together with examples of
distributed CEs and PEs.
┌ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐
Customer │ Provider
│ Site ┌────┐ ┌──┴─┐ Network │
│ ├──────────────────┤ │
│ │ CE ├ ─ ─ ─ ─AC ─ ─ ─ ─│ PE │ │
│ ├──────────────────┤ │
│ └────┘ └──┬─┘ │
─ ─ ─ ─ ─ ─ ─ ┘ ─ ─ ─ ─ ─ ─ ─ ─
i) Reference Design
┌ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐
Customer │ Provider
│ Site │ Network │
┏━━━━━━━━━━━━━━━┓
│┃ ┌─────┐ ┌────┐┃ ┌──┴─┐ │
┃ │ │ │ ├┃─────────────────┤ │
│┃ │ ├ ┼ ─ ─│┃ ─ ─ ─ AC─ ─ ─ ─ ┤ PE │ │
┃ │ RTR │ │ SW ├┃─────────────────┤ │
│┃ └─────┘ └────┘┃ └──┬─┘ │
┗━━Distributed━━┛
│ CE │ │
─ ─ ─ ─ ─ ─ ─ ┘ ─ ─ ─ ─ ─ ─ ─ ─
ii) Distributed CE
┌ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐
Customer │ Provider
│ Site │ Network │
│ ┏━━━━━━━━━━━━━━━┓
│ ┌────┐ ┃┌──┴─┐ ┌────┐┃ │
│ ├─────────────────┃┤Mngd│ │ │┃
│ │ CE ├ ─ ─ ─ ─AC ─ ─ ─ ┃│ CE ├───┤ PE │┃ │
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│ ├─────────────────┃┤ │ │ │┃
│ └────┘ ┃└──┬─┘ └────┘┃ │
│ ┗━━Distributed━━┛
│ │ PE │
─ ─ ─ ─ ─ ─ ─ ┘ ─ ─ ─ ─ ─ ─ ─ ─
iii) Distributed PE
┌ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐
Customer │ Provider
│ Site │ Network │
┏━━━━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━━━━━┓
│ ┃ IP Fabric ┃ ┃┌──┴─┐ ┌────┐ ┃ │
┃ ┌───┐┌───┐ ┃─────────────╋┤ DC │ │ │ ┃
│ ┃ └───┘└───┘ ┃ ─ ─ ─AC ─ ─ ╋│ GW ├───┤ PE │ ┃ │
┃┌──┐┌──┐┌──┐┌──┐┃─────────────╋┤ │ │ │ ┃
│ ┃└──┘└──┘└──┘└──┘┃ ┃└──┬─┘ └────┘ ┃ │
┗━━━Distributed━━┛ ┗━━Distributed━━━┛
│ CE │ PE │
│
└ ─Data Center─ └ ─ ─ ─ ─ ─ ─ ─ ┘
iv) Distributed PE
and CE
Figure 3: Generic Model vs Distributed CE and PE
In subsequent sections of this document, the terms CE and PE are used
for both single and distributed devices.
3.3.2. Co-Managed CE
A co-managed CE is orchestrated by both the customer and the
provider. In this case, the customer and provider usually have
control on distinct device configuration perimeters. For example,
the customer is responsible for the LAN interfaces, while the
provider is responsible for the WAN interfaces (including routing/
forwarding policies). Considering the generic model, a co-managed CE
has both PE and CE functions and there is no strict AC connection,
although one may consider that the AC stitching logic happens
internally within the CE itself. The provider manages the AC between
the CE and the PE.
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3.3.3. Service-aware CE
While in most cases CEs connect to PEs using IP (e.g., VLANs), a CE
may also connect to the provider network using MPLS -potentially over
IP tunnels- or Segment Routing over IPv6 (SRv6) [RFC8986]. The CE
has awareness of provider services configuration (e.g., control plane
identifiers such as Route Targets (RTs) and Route Distinguishers
(RDs)). An example of such an AC is depicted in Figure 4. This is a
source of confusion since these configurations are typically enforced
on PEs. Notwithstanding, the reference design based on Orchestration
scope prevails: the CE is managed by the customer and the AC is based
on MPLS or SRv6 data plane technologies. Note that the complete
termination of the AC within the provider network may happen on
distinct routers: this is another example of distributed PE.
┌ ─ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐
Customer │ Provider
│ Site │ Network │
│
│ │ │
│ ◀─────MP-BGP─────▶
│ ┌────┐ ┌─┴──┐ │
│ │ MPLS-based AC │ │
│ │ CE ├──────────────────│ PE │ │
┏━━┻━━━━┻━━┓ │ │
│ ┃ VRF foo ┃ └─┬──┘ │
─ ─ ─ ─ ┻━━━━━━━━━━┛ ─ ─ ─ ─ ─ ─ ─ ─
Figure 4: Example of MPLS-based Attachment Circuit
This use case is also referred to in Section 4.3.2 and Section 4.3.3.
3.4. Orchestration Overview
3.4.1. End-to-End 5G Slice Orchestration Architecture
This section introduces a global framework for the orchestration of
an end-to-end 5G slice with a zoom on TN parts. This framework helps
to delimit the realization scope of RFC 9543 Network Slices and
identify interactions that are required for the realization of such
slices.
This framework is consistent with the management coordination
example shown in Figure 4.7.1 of [TS-28.530].
In reference to Figure 5, an end-to-end 5G Network Slice Orchestrator
(5G NSO) is responsible for orchestrating end-to-end 5G slices. The
details of the 5G NSO is out of the scope of this document. The
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realization of the end-to-end 5G slice spans RAN, CN, and TN. As
mentioned in Section 3.1, the RAN and CN are under the responsibility
of the 3GPP Management System, while the TN is not. The
orchestration of the TN is split into two sub-domains in conformance
with the reference design in {#sec-ref-design}:
Provider Network Orchestration domain: As defined in [RFC9543], the
provider relies on a Network Slice Controller (NSC) to manage and
orchestrate RFC 9543 Network Slices in the provider network. This
framework permits to manage connectivity together with SLOs.
Customer Site Orchestration domain: The Orchestration of TN elements
of the customer sites relies upon a variety of controllers (e.g.,
Fabric Manager, Element Management System, or VIM). The
realization of this segment does not involve the Transport Network
Orchestration.
A TN slice relies upon resources that can involve both the provider
and customer TN domains. More details are provided in Section 3.4.2.
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┌───────────┐
│ 5G NSO │
└───────────┘
│ │
│ │
▼ │
┌───────────────┐ │
│ 3GPP domains │ │
┌───────────│ Orchestration │────────────────────────────┐
│ │ (RAN and CN) │ │ │
│ └───────────────┘ │ │
│ │ │
│ ┏ ━ ━ ━ ━ ━ ━ ━ ━ ━ ━ ━ ━│━ ━ ━ ━ ━ ━ ━ ━ ━ ━ ━ ┓ │
│ TN Orchestration │ │
│ ┃ ┌───────────────┼──────────────┐ ┃ │
│ ▼ ▼ ▼ │
│ ┃┌───────────────┐┌───────────┐┌───────────────┐┃ │
│ │ Customer Site ││RFCXXXX NSC││ Customer Site │ │
│ ┃│ Orchestration ││ ││ Orchestration │┃ │
│ └──┬────────────┘└─────┬─────┘└──────────────┬┘ │
│ ┗ ━ ╋ ━ ━ ━ ━ ━ ━ ━ ━ ━ ╋ ━ ━ ━ ━ ━ ━ ━ ━ ━ ━ ╋ ┛ │
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
│ ▼ ▼ ▼ │
┌ ┼ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─│─ ─
│ Provider │ │
│ ▼ │ ┌─┴──┐ Network ┌──┴─┐ ┌┴───┐ │
┌──┐ ┌────┐ AC │ │ │ │ AC │ NF │◀─┘ │
││NF◍ ─ ─ ┤ CE ├ ─ ─ ─■ PE │ │ PE ■ ─ ─ ─◍(CE)│
└──┘ └────┘ │ │ │ │ └────┘ │
│ │ └─┬──┘ └──┬─┘ │
Customer Customer │
│ Site │ │ │ │ Site
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
RFC XXXX
■─────Network Slice───■
◍───────────────────TN Slice───────────────────◍
Figure 5: End-to-end 5G Slice Orchestration with TN
The various orchestration depicted in the figure encompass the
3GPP's Network Slice Subnet Management Function (NSSMF).
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3.4.2. Transport Network Segments and Network Slice Instantiation
In reference to the architecture depicted in Section 3.4.1, the
connectivity between NFs can be decomposed into three main types of
segments that are shown in Figure 6.
Customer Site: Either connects two NFs located in the same customer
site (e.g., NF1-NF2) or connects a NF to a CE (e.g., NF1-CE).
This segment may not be present if the NF is the CE (e.g., NF3):
in this case the AC connects the NF to the PE.
The realization of this segment is driven by the 5G Network
Orchestration and potentially the Customer Site Orchestration.
The realization of this segment does not involve the Transport
Network Orchestration.
Provider Network: Represents the connectivity between two PEs (e.g.,
PE1-PE2). The realization of this segment is controlled by an RFC
9543 NSC.
Attachment Circuit: Represents the connectivity between CEs and PEs
(e.g., CE-PE1 and PE2-NF3). The orchestration of this segment
relies partially upon an RFC 9543 NSC for the configuration of the
AC on the PE customer-facing interfaces and the Customer Site
Orchestration for the configuration of the AC on the CE.
As depicted in Figure 6, the realization of an RFC 9543 Network Slice
(i.e., connectivity with performance commitments) involves the
provider network and partially the AC (the PE-side of the AC). Note
that the provisioning of a new Network Slice may rely on a partial or
full pre-provisioned segment (e.g., a new Network Slice may rely on
an existing AC). The customer site segment is considered as an
extension of the connectivity of the RAN/CN domain without complex
slice-specific performances requirements: the customer site
infrastructure is usually over-provisioned and involves short
distances (low latency) where basic QoS/Scheduling logic is
sufficient to comply with the target SLOs. In other words, the main
focus for the enforcement of end-to-end SLOs is managed at the
Network Slice between PE interfaces connected to the AC.
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├───────────────────────TN Slice─────────────┤
○─────RFC XXXX ─────○
│ Network Slice │
│ │
│ │
▼ ▼
○──CS───□ □───AC──○ □──────PN───────□ ○──AC──○
┌ ─ ─ ─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─
Customer │ Provider Customer │
│ Site 1 │ Network │ │ Site 2
│ ┌────┐ ┌────┐ │
│┌───┐ ┌────┐ AC │ │ │ │ AC ┌─┴─┐
CS │NF1├────┤ CE ├──────┤ PE │ │ PE ├────┤NF3│ │
□ │└─┬─┘ └────┘ │ │ │ │ └─┬─┘
│ │ │ └────┘ └────┘ │
│ │ │ │ │ │
□ ┌─┴─┐ │ │
││NF2│ │ │ │
└───┘ │ │
└ ─ ─ ─ ─ ─ ─ └ ─ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─
□──────□ TN segments:
CS = Customer Segment
AC = Attachment Circuit
PN = Provider Network
Figure 6: Segmentation of the Transport Network
Resource synchronization for AC provisioning: The realization of the
Attachment Circuit is made up of TN resources shared between the
Customer Site Orchestration and the Provider Network Orchestration
(e.g., RFC 9543 NSC). More precisely, a PE and a CE connected via
an AC need to be provisioned with consistent data plane and
control plane information (e.g., VLAN- IDs, IP addresses/subnets,
or BGP Autonomous System (AS) Number). Hence, the realization of
this interconnection is technology-specific and requires
coordination between the Customer Site Orchestration and an NSC.
Automating the provisioning and management of the AC is
recommended. Aligned with [RFC8969], this document assumes that
this coordination is based upon standard YANG data models and
APIs.
Figure 7 is a basic example of a Layer 3 CE-PE link realization
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with shared network resources (such as VLAN-IDs and IP prefixes)
which are passed between Orchestrators via a dedicated interface,
e.g., the RFC 9543 Network Slice Service Interface
[I-D.ietf-teas-ietf-network-slice-nbi-yang] or the Attachment
Circuit Service Interface
([I-D.ietf-opsawg-teas-attachment-circuit].
┌ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─
RFCXXXX NSC │
│ Customer Site │ │
Orchestration IETF APIs/DM (Provider Network │
│ │◀─────────────────▶│ Orchestration)
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
│ │
│ │
┌ ─ ─ ─ ─ ─ ─ ─ ┼ ┐ ┌ ┼ ─ ─ ─ ─ ─ ─ ─ ┐
▼ ▼
│ ┌──┐ ┌──┐.1│ 192.0.2.0/31 │.0┌──┐ │
│NF├──────┤CE├──────────────────────────┤PE│
│ └──┘ └──┘ │ VLAN 100 │ └──┘ │
Customer Provider
│ Site │ │ Network │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└─────────── AC ──────────┘
Figure 7: Coordination of Transport Network Resources for the AC
Provisioning
3.4.3. Additional Segmentation and Domains
More complex scenarios can happen with extra segmentation of the TN
and additional TN Orchestration domains. It is not realistic to
describe any design flavor, however the main concepts presented here
in terms of segmentation (provider/customer) and stitching (AC) can
be reused for the integration of more complex integrations.
3.5. Mapping Schemes Between 5G Network Slices and Transport Network
Slices
There are multiple options for mapping 5G Network Slices to TN
slices:
* 1 to N: A single 5G Network Slice can be mapped to multiple TN
slices (1 to N). For instance, consider the scenario depicted in
Figure 8, illustrating the separation of the 5G Control Plane and
User Plane in TN slices for a single 5G eMBB network slice. It is
important to note that this mapping can serve as an interim step
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to N:M mapping. In this scenario, a subset of the TN slices can
be intended for sharing by multiple 5G network slices (e.g., the
Control Plane TN slice is shared by multiple 5G network Slices).
Further details about this scheme are described in Section 3.6.
* M to 1: Multiple 5G Network Slices may rely upon the same TN
slice. In such a case, the Service Level Agreement (SLA)
differentiation of slices would be entirely controlled at 5G
Control Plane, for example, with appropriate placement strategies:
this use case is represented in Figure 9, where a User Plane
Function (UPF) for the URLLC slice is instantiated at the edge
cloud close to the gNB CU-UP User Plane for better latency/jitter
control, while the 5G Control Plane and the UPF for eMBB slice are
instantiated in the regional cloud.
* M to N: The 5G to TN slice mapping combines both approaches with a
mix of shared and dedicated associations.
In practice, for operational and scaling reasons, typically M to N
would be used, with M >> N.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
│ 5G Slice eMBB │
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
┌─────┐ N3 ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ N3 ┌─────┐
│ │CU-UP├─────── RFC XXXX Network Slice UP_eMBB ───────┤ UPF │ │
└─────┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └─────┘
│ │ │ │
┌─────┐ N2 ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ N2 ┌─────┐
│ │CU-CP├─────── RFC XXXX Network Slice CP ───────┤ AMF │ │
└─────┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └─────┘
└ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ┘
│ │
Transport Network
│ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 8: 1 (5G Slice) to N (RFC 9543 Network Slice) Mapping
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┌ ─ ─ ─ ─ ─ ─ ┐
Edge Cloud
│ │
┌─────────┐
│ │UPF_URLLC│ │
└─────┬───┘
└ ─ ─ ─ │ ─ ─ ┘
┌ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ │ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┌ ─ ─ ┴ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ ┌ ─ ─ ─ ─ ─ ─ ─
│ Cell Site │ │ │ │
│ │ │ Regional
│ ┌───────────┐ │ │ │ Cloud │
│CU-UP_URLLC├─────┤ │ │ ┌──────────┐
│ └───────────┘ │ │ RFC XXXX Network ├─────┤ 5GC CP │ │
│ Slice ALL │ │ └──────────┘
│ ┌───────────┐ │ │ │ │
│CU-UP_eMBB ├─────┤ │ │ ┌──────────┐
│ └───────────┘ │ │ ├─────┤ UPF_eMBB │ │
─ ─ ─ ─ ─ ─ ─ ─ │ │ │ └──────────┘
│ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ │
│ └ ─ ─ ─ ─ ─ ─ ─
│ Transport Network
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 9: N (5G Slice) to 1 (RFC 9543 Network Slice) Mapping
Note that the actual realization of the mapping depends on several
factors, such as the actual business cases, the NF vendor
capabilities, the NF vendor reference designs, as well as service
provider or even legal requirements.
Specifically, the actual mapping is a design choice of service
operators that may be a function of, e.g., the number of instantiated
slices, requested services, or local engineering capabilities and
guidelines. However, operators should carefully consider means to
ease slice migration strategies. For example, a provider may
initially adopt a 1-to-1 mapping if it has to instantiate just a few
Network Slices and accommodate the need of only a few customers.
That provider may decide to move to a N-to-1 mapping for aggregation/
scalability purposes if sustained increased slice demand is observed.
Putting in place adequate automation means to realize Network Slices
(including the adjustment of slice services to Network Slices
mapping) would ease slice migration operations.
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3.6. First 5G Slice versus Subsequent Slices
An operational 5G Network Slice incorporates both 5G Control Plane
and User Plane capabilities. For instance, consider a slice based on
split-CU in the RAN, both CU-UP and CU-CP need to be deployed along
with the associated interfaces E1, F1-c, F1-u, N2, and N3 which are
conveyed in the TN. In this regard, the creation of the "first
slice" can be subject to a specific logic that does not apply to
subsequent slices. Referring to the example in Figure 10, the first
5G slice relies on the deployment of NF-CP and NF-UP functions
together with two TN slices for Control and User Planes (INS-CP and
INS-UP1). Next, the deployment of a second slice relies solely on
the instantiation of a User Plane Function (NF-UP2) together with a
dedicated User Plane TN slice (INS-UP2). The Control Plane of the
first 5G slice is also updated to integrate the second slice: the TN
slice (INS-CP) and Network Functions (NF-CP) are shared.
At the time of writing (2023), Section 6.1.2 of [NG.113] specifies
that the eMBB slice (SST=1 and no Slice Differentiator (SD)) should
be supported globally. This 5G slice would be the first slice in any
5G deployment.
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┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ 1 ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
s S │NF-CP├──────┤ CP TN Slice (TNS-CP) ├──────┤NF-CP│
│ t l └─────┘ └──────────────────────────┘ │ └─────┘ │
i │
│ 5 c ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
G e │NF-UP├──────┤ UP TN Slice (TNS-UP1) ├──────┤NF-UP│
│ └─────┘ └──────────────────────────┘ │ └─────┘ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
│ Transport Network
│
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Deployment of first 5G slice
│ │
│ │
│ │
─┘ └─
╲ ╱
╲ ╱
V
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ 1 ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
s S │NF-CP├──────┤ CP TN Slice (TNS-CP) ├──────┤NF-CP│
│ t l └─────┘ └──────────────────────────┘ │ └─────┘ │
i │
│ 5 c ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
G e │NF-UP├──────┤ UP TN Slice (TNS-UP1) ├──────┤NF-UP│
│ └─────┘ └──────────────────────────┘ │ └─────┘ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
2 │
│ n S ┌──────┐ │ ┌──────────────────────────┐ ┌──────┐ │
d l │NF-UP2├─────┤ UP TN Slice (TNS-UP2) ├─────┤NF-UP2│
│ i └──────┘ │ └──────────────────────────┘ └──────┘ │
5 c │
│ G e │ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─
│
Transport Network │
│
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Deployment of additional 5G slice with shared Control Plane
Figure 10: First and Subsequent Slice Deployment
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Overall, policies might be provided by an operator (e.g., to Network
Slice Controllers) to indicate whether the same or dedicated CP NFs
are allowed when processing a new slice creation request. Providing
such a policy is meant to better automate the realization of 5G
slices and minimize the realization delay that might be induced by
extra cycles to seek for operator validation.
3.7. Overview of the Transport Network Realization Model
The realization model described in this document is depicted in
Figure 11. The following building blocks are used:
* Layer 2 Virtual Private Network (L2VPN) [RFC4664] and/or Layer 3
Virtual Private Network (L3VPN) [RFC4364] service instances for
logical separation:
This realization model of transport for 5G slices assumes Layer 3
delivery for midhaul and backhaul transport connections, and a
Layer 2 or Layer 3 for fronthaul connections. Enhanced Common
Public Radio Interface (eCPRI) supports both delivery models.
L2VPN/L3VPN service instances might be used as a basic form of
logical slice separation. Furthermore, using service instances
results in an additional outer header (as packets are
encapsulated/decapsulated at the nodes hosting service instances)
providing clean discrimination between 5G QoS and TN QoS, as
explained in Section 5.
* Fine-grained resource control at the PE:
This is sometimes called 'admission control' or 'traffic
conditioning'. The main purpose is the enforcement of the
bandwidth contract for the slice right at the edge of the provider
network where the traffic is handed-off between the customer site
and the provider network.
The toolset used here is granular ingress policing (rate limiting)
to enforce contracted bandwidths per slice and, potentially, per
traffic class within the slice. Traffic above the enforced rate
might be immediately dropped, or marked as high drop-probability
traffic, which is more likely to be dropped somewhere inside the
provider network if congestion occurs. In the egress direction at
the PE node, hierarchical schedulers/shapers can be deployed,
providing guaranteed rates per slice, as well as guarantees per
traffic class within each slice.
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For managed CEs, edge admission control can be distributed between
CEs and PEs, where a part of the admission control is implemented
on the CE and other part of the admission control is implemented
on the PE.
* Coarse-grained resource control at the transit (non-attachment
circuits) links in the provider network, using a single NRP,
spanning the entire provider network. Transit nodes in the
provider network do not maintain any state of individual slices.
Instead, only a flat (non-hierarchical) QoS model is used on
transit links in the provider network, with up to 8 traffic
classes. At the PE, traffic-flows from multiple slice services
are mapped to the limited number of traffic classes used on
provider network transit links.
* Capacity planning/management for efficient usage of provider
network resources:
The role of capacity management is to ensure the provider network
capacity can be utilized without causing any bottlenecks. The
toolset used here can range from careful network planning, to
ensure a more or less equal traffic distribution (i.e., equal cost
load balancing), to advanced traffic engineering techniques, with
or without bandwidth reservations, to force more consistent load
distribution even in non-ECMP friendly network topologies.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌──────────┐ base NRP ┌──────────┐
│ PE │ │ PE │
┌ ┼ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─│─
■<───┐│ │ RFC XXXX Network Slice 1 │ ┌┼───>■ │
│ │ │ │ ┌─────┐ ┌─────┐ │ │ │
■<───┤│ │ │ P │ │ P │ │ ├┼───>■ │
├ ┼ ─ ─├────>□<──────>□<───>□<──────>□────>□<──────>□<───┤─ ─ ─│─
■<───┤│ │ │ │ │ │ │ ├┼───>■ │
│ │ │ │ └─────┘ └─────┘ │ │ │
■<───┘│ │ RFC XXXX Network Slice 2 │ └┼───>■ │
└ ┼ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─│─
│ │ │ │ │ │
└──────────┘ └──────────┘
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
■ - SDP, with fine-grained QoS (dedicated resources per TN slice)
□ - coarse-grained QoS, with resources shared by all TN slices
Figure 11: Resource Allocation Slicing Model with a Single NRP
This document does not describe in detail how to manage an L2VPN or
L3VPN, as this is already well-documented.
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4. Hand-off Between Domains
The 5G control plane relies upon the Single Network Slice Selection
Assistance Information (S-NSSAI) 32-bit slice identifier for slice
identification. The S-NSSAI is not visible to the transport domain.
So instead, 5G network functions can expose the 5G slices to the
transport domain by mapping to explicit Layer 2 or Layer 3
identifiers, such as VLAN-IDs, IP addresses, or Differentiated
Services Code Point (DSCP). The realization of the mapping between
customer sites and provider networks is commonly refered to as the
"hand-off".
More details about the mapping between 3GPP and RFC 9543 Network
Slices is provided in [I-D.ietf-teas-5g-network-slice-application].
That document includes additional methods for mapping 5G slices to TN
slices (e.g., source UDP port number), but these methods are not
reproduced here because of the intrinsic shortcomings of these
methods.
4.1. VLAN Hand-off
In this option, the RFC 9543 Network Slice, fulfilling connectivity
requirements between NFs that belong to a 5G slice, is represented at
the Service Demarcation Point (SDP) by a VLAN ID (or double VLAN IDs,
commonly known as QinQ), as depicted in Figure 12.
Each VLAN represents a distinct logical interface on the ACs; hence
it provides the possibility to place these logical interfaces in
distinct Layer 2 or Layer 3 service instances and implement
separation between slices via service instances. Since the 5G
interfaces are IP-based interfaces (the only exception could be the
F2 fronthaul-interface, where eCPRI with Ethernet encapsulation is
used), this VLAN is typically not transported across the provider
network. Typically, it has only local significance at a particular
SDP. For simplification it is recommended to rely on the same VLAN
identifier for all ACs, when possible. However, SDPs for a same
slice at different locations may also use different VLAN values.
Therefore, a VLAN to RFC 9543 Network Slice mapping table is
maintained for each AC, and the VLAN allocation is coordinated
between customer orchestration and provider orchestration. Thus,
while VLAN hand-off is simple for NFs, it adds complexity due to the
requirement of maintaining mapping tables for each SDP and requires a
configuration task of new VLANs and IP subnet for every slice on
every AC.
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VLANs representing slices VLANs representing slices
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ │
│ │ │ │
┌──────┐ ▼ ┌─┴───┐ Provider ┌─────┐ ▼ ┌─────┐ ▼ ┌──────┐
│ ●───────●■ │ │ ■●───────● ●───────● │
│ NF ●───────●■ PE │ │ PE ■●───────●L2/L3●───────● NF │
│ ●───────●■ │ │ ■●───────● ●───────● │
└──────┘ └─┬───┘ Network └─────┘ └─────┘ └──────┘
│
└ ─ ─ ─ ─ ─ ─ ─ ─ ─
└────────┘└────────────────────┘└────────┘ └───────────┘
Attachment Provider Network Attachment Customer Site
Circuit Segment Circuit Segment
● – Logical interface represented by a VLAN on a physical interface
■ - Service Demarcation Point
Figure 12: 5G Slice with VLAN Hand-off
4.2. IP Hand-off
In this option, an explicit mapping between source/destination IP
addresses and slice's specific S-NSSAI is used. The mapping can have
either local (e.g., pertaining to single NF attachment) or global TN
significance. The mapping can be realized in multiple ways,
including (but not limited to):
* S-NSSAI to a dedicated IP address for each NF
* S-NSSAI to a pool of IP addresses for global TN deployment
* S-NSSAI to a subset of bits of an IP address
* S-NSSAI to a DSCP value
* Use a deterministic algorithm to map S-NSAAI to an IP subnet,
prefix, or pools. For example, adaptations to the algorithm
defined in [RFC7422] may be considered.
Mapping S-NSSAI to IP addresses makes IP addresses an identifier for
eventual policy decisions in the Transport Network (e.g.,
Differentiated Services, traffic steering, bandwidth allocation,
security policies, or monitoring).
One example of the realization is the arrangement, where the slices
in the TN domain are instantiated using IP tunnels (for example,
IPsec or GTP-U tunnels) established between NFs, as depicted in
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Figure 13. The transport for a single 5G slice might be constructed
with multiple such tunnels, since a typical 5G slice contains many
NFs - especially DUs and CUs. If a shared NF (i.e., an NF that
serves multiple slices, for example a shared DU) is deployed,
multiple tunnels from shared NF are established, each tunnel
representing a single slice.
Tunnels representing slices
┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
│
┌──────┐ ┌──┴──┐ Provider ┌───┴─┐ ┌─────┐ ▼ ┌──────┐
│ ○════════════■════════════════■══════════════════════════○ │
│ NF ├───────┤ PE │ │ PE ├───────┤L2/L3├───────┤ NF │
│ ○════════════■════════════════■══════════════════════════○ │
└──────┘ └──┬──┘ Network └───┬─┘ └─────┘ └──────┘
└ ─ ─ ─ ─ ─ ─ ─ ─ ┘
└────────┘└────────────────────┘└────────┘ └───────────┘
Attachment Provider Network Attachment Customer Site
Circuit Segment Circuit Segment
○ – tunnel (IPsec, GTP-U, ...) termination point
■ - Service Demarcation Point
Figure 13: 5G Slice with IP Hand-off
As opposed to the VLAN hand-off case, there is no logical interface
representing a slice on the PE, hence all slices are handled within
single service instance. The IP and VLAN hand-offs are not mutually
exclusive, but instead could be used concurrently. Since the TN
doesn't recognize S-NSSAI, a mapping table similar to the VLAN Hand-
off solution should be utilized Section 4.1.
The mapping table can be simplified if, for example, IPv6 addressing
is used to address NFs. An IPv6 address is a 128-bit long field,
while the S-NSSAI is a 32-bit field: Slice/Service Type (SST): 8
bits, Slice Differentiator (SD): 24 bits. 32 bits, out of 128 bits of
the IPv6 address, may be used to encode the S-NSSAI, which makes an
IP to Slice mapping table unnecessary. Alternatively, instead of
using 2 full octets from the 8 octets in an IPv6 address, a provider
could build a mapping table that uses only one octet or parts of an
octet to represent utilized S-NSSAI. This mapping is a local
allocation method to allocate IPv6 addresses to NFs in order to be
representative of the S-NSSAI without redefining IPv6 semantic. IP
forwarding is not altered by this method and is still achieved
following BCP 198 [RFC7608].
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Different IPv6 address allocation schemes following this approach may
be used, with one example allocation shown in Figure 14.
Note that this addressing scheme is local to an ingress or egress
NF; intermediary TN nodes are not required to associate any
additional semantic with IPv6 address.
One benefit of embedding the S-NSSAI in the IPv6 address is that a
specific S-NSSAI can be identified as needed at any place in the TN
domain. This might be used, for example, to selectively enable per
S-NSSAI monitoring, traffic engineering, or any other per S-NSSAI
handling, if required.
However, operators using such mapping methods should be aware of the
implications of any change of S-NSSAI on the addressing plans. For
example, modifications of the S-NSSAIs in-use will require updating
the IP addresses used by NFs involved in the associated slices.
NF specific reserved
(not slice specific) for S-NSSAI
<───────────────────────────> <───────>
┌────┬────┬────┬────┬────┬────┬────┬────┐
│2001:0db8:xxxx:xxxx:xxxx:xxxx:ttdd:dddd│
└─────────┴─────────┴─────────┴─────────┘
tt - SST (8 bits)
dddddd - SD (24 bits)
Figure 14: An Example of S-NSSAI Embedded into IPv6
In the example shown in Figure 14, the most significant 96 bits of
the IPv6 address are unique to the NF, but do not carry any slice-
specific information. The S-NSSAI information is embedded in the
least significant 32 bits. The 96-bit part of the address may be
structured by the provider, for example, on the geographical location
or the DC identification.
Figure 15 uses the example from Figure 14 to demonstrate a slicing
deployment, where the entire S-NSSAI is embedded into IPv6 addresses
used by NFs. NF-A has a set of tunnel termination points, with
unique per-slice IP addresses allocated from the 2001:db8:a:0::/96
prefix, while NF-B uses a set of tunnel termination points with per-
slice IP addresses allocated from 2001:db8:b:0::/96. This example
shows two slices: customer A eMBB (SST=01, SD=00001) and customer B
MIoT (SST=03, SD=00003). Therefore, for customer A eMBB the tunnel
IP addresses are auto-derived (without the need for an explicit
mapping table) as the IP addresses {2001:db8:a::100:1,
2001:db8:b::100:1}, where {:0100:0001} is used as the last two
octets, and for customer B MIoT (SST=3, SD=00003) tunnel uses the IP
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addresses {2001:db8:a::300:3, 2001:db8:b::300:3} and simply adds
{:0300:0003} as the last two octets. Leading zeros are not
represented in the resulting IPv6 addresses as per [RFC5952].
2001:db8:a::/96 (NF-A) 2001:db8:b::/96 (NF-B)
2001:db8:a::100:1/128 2001:db8:b::100:1/128
│ │
│ │
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐ eMBB (SST=1) │
│ │ │
┌────▼─┐ ┌──┴──┐ Provider ┌───┴─┐ ▼ ┌─────┐ ┌─▼────┐
│ ○════════════■════════════════■══════════════════════════○ │
│ NF ├───────┤ PE │ │ PE ├───────┤L2/L3├───────┤ NF │
│ ○════════════■════════════════■══════════════════════════○ │
└────▲─┘ └──┬──┘ Network └───┬─┘ ▲ └─────┘ └─▲────┘
│ │ │
│ └ ─ ─ ─ ─ ─ ─ ─ ─ ┘ MIoT (SST=3) │
│ │
2001:db8:a::300:3/128 2001:db8:b::300:3/128
└────────┘└────────────────────┘└────────┘ └───────────┘
Attachment Provider Network Attachment Customer Site
Circuit Segment Circuit Segment
○ – tunnel (IPsec, GTP-U, ...) termination point
■ - Service Demarcation Point
Figure 15: Deployment Example with S-NSSAI Embedded into IPv6
Addresses
4.3. MPLS Label Hand-off
In this option, the service instances representing different slices
are created directly on the NF, or within the customer site hosting
the NF, and attached to the provider network. Therefore, the packet
is MPLS encapsulated outside the provider network with native MPLS
encapsulation, or MPLS-in-UDP encapsulation [RFC7510], depending on
the capability of the customer site, with the service label depicting
the slice.
There are three major methods (based upon Section 10 of [RFC4364])
for interconnecting MPLS services over multiple service domains:
Option A (Section 4.3.1): VRF-to-VRF connections.
Option B (Section 4.3.2): : redistribution of labeled VPN routes with
next-hop change at domain boundaries.
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Option C (Section 4.3.3): redistribution of labeled VPN routes
without next-hop change and redistribution of labeled transport
routes with next-hop change at domain boundaries.
4.3.1. Option A
This option is not based on MPLS label hand-off, but VLAN hand-off,
described in Section 4.1.
4.3.2. Option B
In this option, L3VPN service instances are instantiated outside the
provider network. These L3VPN service instances are instantiated in
the customer site, which could be for example either on the compute,
hosting mobile network functions (Figure 16, left hand side), or
within the DC/cloud infrastructure itself (e.g., on the top of the
rack or leaf switch within cloud IP fabric (Figure 16, right hand
side)). On the attachment circuit connected to PE, packets are
already MPLS encapsulated (or MPLS-in-UDP/MPLS-in-IP encapsulated, if
cloud or compute infrastructure don’t support native MPLS
encapsulation). Therefore, the PE uses neither a VLAN nor an IP
address for slice identification at the SDP, but instead uses the
MPLS label.
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<────── <────── <──────
BGP VPN BGP VPN BGP VPN
COM=1, L=A" COM=1, L=A' COM=1, L=A
COM=2, L=B" COM=2, L=B' COM=2, L=B
COM=3, L=C" COM=3, L=C' COM=3, L=C
<─────────────><────────────><─────────────>
nhs nhs nhs nhs
VLANs
service instances service instances representing
representing slices representing slices slices
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ │ │
│ Provider │ │ │
┌────▼─┐ ┌┴────┐ ┌─────┐ ┌─v──────┐ v ┌──────┐
│ ◙ │ │■ │ │ ■│ │ ◙………………●───────● │
│ NF ◙ ├───────┤■ PE │ │ PE ■├───────┤ ◙………………●───────● NF │
│ ◙ │ │■ │ │ ■│ │ ◙………………●───────● │
└──────┘ └┬────┘ └─────┘ └────────┘ └──────┘
Network │ L2/L3
└ ─ ─ ─ ─ ─ ─ ─ ─
└────────┘└───────────────────┘┘└────────┘ └───────────┘
Attachment Provider Network Attachment Customer Site
Circuit Segment Circuit Segment
● – Logical interface represented by VLAN on physical interface
◙ - Service instances (with unique MPLS labels)
■ - Service Demarcation Point
Figure 16: MPLS Hand-off: Option B
MPLS labels are allocated dynamically in Option B deployments, where
at the domain boundaries service prefixes are reflected with next-hop
self, and new label is dynamically allocated, as visible in Figure 16
(e.g., labels A, A', and A" for the first depicted slice).
Therefore, for any slice-specific per-hop behavior at the provider
network edge, the PE needs to determine which label represents which
slice. In the BGP control plane, when exchanging service prefixes
over attachment circuit, each slice might be represented by a unique
BGP community, so tracking label assignment to the slice is possible.
For example, in Figure 16, for the slice identified with COM=1, the
PE advertises a dynamically allocated label A". Since, based on the
community, the label to slice association is known, the PE can use
this dynamically allocated label A" to identify incoming packets as
belonging to slice 1, and execute appropriate edge per-hop behavior.
It is worth noting that slice identification in the BGP control plane
might be with per-prefix granularity. In the extreme case, each
prefix can have different community representing a different slice.
Depending on the business requirements, each slice could be
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represented by a different service instance, as outlined in
Figure 16. In that case, the route target extended community might
be used as slice differentiator. In other deployments, all prefixes
(representing different slices) might be handled by a single 'mobile'
service instance, and some other BGP attribute (e.g., a standard
community) might be used for slice differentiation. There could be
also a deployment option that groups multiple slices together into a
single service instance, resulting in a handful of service instances.
In any case, fine-grained per-hop behavior at the edge of provider
network is possible.
4.3.3. Option C
Option B relies upon exchanging service prefixes between customer
sites and the provider network. This may lead to scaling challenges
in large scale 5G deployments as the PE node needs to carry all
service prefixes. To alleviate this scaling challenge, in Option C,
service prefixes are exchanged between customer sites only. In doing
so, the provider network is offloaded from carrying, propagating, and
programing appropriate forwarding entries for service prefixes.
Option C relies upon exchanging service prefixes via multi-hop BGP
sessions between customer sites, without changing the NEXT_HOP BGP
attribute. Additionally, IPv4/IPv6 labeled unicast (SAFI=4) host
routes, used as NEXT_HOP for service prefixes, are exchanged via
direct single-hop BGP sessions between adjacent nodes in a customer
site and a provider network, as depicted in Figure 17. As a result,
a node in a customer site performs hierarchical next-hop resolution.
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◁───────────────────────────────────────────
BGP VPN
COM=1, L=A, NEXT_HOP=CS2
COM=2, L=B, NEXT_HOP=CS2
COM=3, L=C, NEXT_HOP=CS2
◁──────────────────────────────────────────▷
◁────── ◁────── ◁──────
BGP LU BGP LU BGP LU
CS2, L=X" CS2, L=X' CS2, L=X
◁─────────────▷◁────────────▷◁─────────────▷
nhs nhs nhs nhs
VLANs
service instances service instances representing
representing slices representing slices slices
┌ ─ ─ ┬ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ┬ ─ ─ ─ ─ ─ ┬ ─ ─ ─ ─ ─
│ Provider │ │ │
│┌────▼─┤ ├─────┐ ┌─────┤ ├─▼──────┐ ▼ ┌──────┐
│ ◙ │ │■ │ │ ■│ │ ◙………………●───────● ││
││ NF ◙ ├───────┤■ PE │ │ PE ■├───────┤ ◙………………●───────● NF │
│ ◙ │ │■ │ │ ■│ │ ◙………………●───────● ││
│└──────┤ ├─────┘ └─────┤ ├────────┘ └──────┘
CS1 Network CS2 │
└ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└────────┘└───────────────────┘└────────┘ └───────────────────┘
Attachment Provider Network Attachment Customer Site
Circuit Segment Circuit Segment
● – logical interface represented by VLAN on physical interface
◙ - service instances (with unique MPLS label)
■ - Service Demarcation Point
Figure 17: MPLS Hand-off: Option C
This architecture requires an end-to-end Label Switched Path (LSP)
leading from a packet's ingress node inside one customer site to its
egress inside another customer site, through a provider network.
Hence, at the domain (customer site, provider network) boundaries
NEXT_HOP attribute for IPv4/IPv6 labeled unicast needs to be modified
to "next-hop self" (nhs), which results in new IPv4/IPv6 labeled
unicast label allocation. Appropriate label swap forwarding entries
for IPv4/IPv6 labeled unicast labels are programmed in the data
plane. On the attachment circuit there is no additional 'labeled
transport' protocol (i.e., no LDP, RSVP, SR, ...).
Packets are transmitted over the attachment circuit with the IPv4/
IPv6 labeled unicast as the top label, with service label deeper in
the label stack. In Option C, the service label is not used for
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forwarding lookup on the PE. This significantly lowers the scaling
pressure on PEs, as PEs need to program forwarding entries only for
IPv4/IPv6 labeled unicast host routes, used as NEXT_HOP for service
prefixes. Also, since one IPv4/IPv6 labeled unicast host route
represent one customer site, regardless of the number of slices in
the customer site, the number of forwarding entries on a PE is
considerably reduced.
For any slice-specific per-hop behavior at the provider network edge,
as described in details in Section 3.7, the PE need to determine
which label in the packet represents which slice. This can be
achieved, for example, by allocating non-overlapping service label
ranges for each slice, and use these ranges for slice identification
purposes on PE.
5. QoS Mapping Realization Models
5.1. QoS Layers
The resources are managed via various QoS policies deployed in the
network. QoS mapping models to support 5G slicing connectivity
implemented over packet switched provider network uses two layers of
QoS that are discussed in Section 5.1.
5.1.1. 5G QoS Layer
QoS treatment is indicated in the 5G QoS layer by the 5G QoS
Indicator (5QI), as defined in [TS-23.501]. A 5QI is an identifier
that is used as a reference to 5G QoS characteristics (e.g.,
scheduling weights, admission thresholds, queue management
thresholds, and link layer protocol configuration) in the RAN domain.
Given that 5QI applies to the RAN domain, it is not visible to the
provider network. Therefore, if 5QI-aware treatment is desired in
the provider network as well, 5G network functions might set DSCP
with a value representing 5QI so that differentiated treatment can
implemented in the provider network as well. Based on these DSCP
values, at SDP of each provider network segment used to construct
transport for given 5G slice, very granular QoS enforcement might be
implemented.
The exact mapping between 5QI and DSCP is out of scope for this
document. Mapping recommendations are documented, e.g., in
[I-D.henry-tsvwg-diffserv-to-qci].
Each slice service might have flows with multiple 5QIs. 5QIs (or,
more precisely, corresponding DSCP values) are visible to the
provider network at SDPs (i.e., at the edge of the provider network).
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In this document, this layer of QoS is referred to as '5G QoS Class'
('5G QoS' in short) or '5G DSCP'.
5.1.2. TN QoS Layer
Control of the TN resources on provider network transit links, as
well as traffic scheduling/prioritization on provider network transit
links, is based on a flat (non-hierarchical) QoS model in this
Network Slice realization. That is, RFC 9543 Network Slices are
assigned dedicated resources (e.g., QoS queues) at the edge of the
provider network (at SDPs), while all RFC 9543 Network Slices are
sharing resources (sharing QoS queues) on the transit links of the
provider network. Typical router hardware can support up to 8
traffic queues per port, therefore the document assumes 8 traffic
queues per port support in general.
At this layer, QoS treatment is indicated by a QoS indicator specific
to the encapsulation used in the provider network. Such an indicator
may be DSCP or MPLS Traffic Class (TC). This layer of QoS is
referred to as 'TN QoS Class', or 'TN QoS' for short, in this
document.
5.2. QoS Realization Models
While 5QI might be exposed to the provider network via the DSCP value
(corresponding to specific 5QI value) set in the IP packet generated
by NFs, some 5G deployments might use 5QI in the RAN domain only,
without requesting per-5QI differentiated treatment from the provider
network. This might be due to a NF limitation (e.g., no capability
to set DSCP), or it might simply depend on the overall slicing
deployment model. The O-RAN Alliance, for example, defines a phased
approach to the slicing, with initial phases utilizing only per-
slice, but not per-5QI, differentiated treatment in the TN domain
(Annex F of [O-RAN.WG9.XPSAAS]).
Therefore, from a QoS perspective, the 5G slicing connectivity
realization defines two high-level realization models for slicing in
the TN domain: a 5QI-unaware model and a 5QI- aware model. Both
slicing models in the TN domain could be used concurrently within the
same 5G slice. For example, the TN segment for 5G midhaul (F1-U
interface) might be 5QI-aware, while at the same time the TN segment
for 5G backhaul (N3 interface) might follow the 5QI-unaware model.
These models are further elaborated in the following two subsections.
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5.2.1. 5QI-unaware Model
In 5QI-unaware mode, the DSCP values in the packets received from NF
at SDP are ignored. In the provider network, there is no QoS
differentiation at the 5G QoS Class level. The entire RFC 9543
Network Slice is mapped to a single TN QoS Class, and, therefore, to
a single QoS queue on the routers in the provider network. With a
small number of deployed 5G slices (for example, only two 5G slices:
eMBB and MIoT), it is possible to dedicate a separate QoS queue for
each slice on transit routers in the provider network. However, with
the introduction of private/enterprises slices, as the number of 5G
slices (and thus corresponding RFC 9543 Network Slices) increases, a
single QoS queue on transit links in the provider network serves
multiple slices with similar characteristics. QoS enforcement on
transit links is fully coarse-grained (single NRP, sharing resources
among all RFC 9543 Network Slices), as displayed in Figure 18.
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┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ PE │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃
┃ SDP ┃ ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
┃│ ┌──────────┐ │┃ ┃ Transit link ┃
┃ │ NS 1 ├────────────┐ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ ├─────> TN QoS Class 1 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 2 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │ NS 2 ├────────┐ │ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ │ │ ┃│ TN QoS Class 3 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ └─────────> TN QoS Class 4 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │ NS 3 ├────────────┘ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ ┌─────────> TN QoS Class 5 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 6 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │ NS 4 ├────────┤ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ │ ┃│ TN QoS Class 7 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 8 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │ NS 5 ├────────┘ ┃ Max 8 TN Classes ┃
┃│ └──────────┘ │┃ ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │
┣━━━━━━━━━━━━━━━━━┛
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Fine-grained QoS enforcement Coarse-grained QoS enforcement
(dedicated resources per (resources shared by multiple
RFC XXXX Network Slice) RFC XXXX Network Slices)
Figure 18: Slice to TN QoS Mapping (5QI-unaware Model)
When the IP traffic is handed over at the SDP from the attachment
circuit to the provider network, the PE encapsulates the traffic into
MPLS (if MPLS transport is used in the provider network), or IPv6 -
optionally with some additional headers (if SRv6 transport is used in
the provider network), and sends out the packets on the provider
network transit link.
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The original IP header retains the DCSP marking (which is ignored in
5QI-unaware model), while the new header (MPLS or IPv6) carries QoS
marking (MPLS Traffic Class bits for MPLS encapsulation, or DSCP for
SRv6/IPv6 encapsulation) related to TN CoS. Based on TN CoS marking,
per-hop behavior for all RFC 9543 Network Slices is executed on
provider network transit links. Provider network transit routers do
not evaluate the original IP header for QoS-related decisions. This
model is outlined in Figure 19 for MPLS encapsulation, and in
Figure 20 for SRv6 encapsulation.
┌──────────────┐
│ MPLS Header │
├─────┬─────┐ │
│Label│TN TC│ │
┌──────────────┐ ─ ─ ─ ─ ─ ─ ─ ─ ├─────┴─────┴──┤
│ IP Header │ │╲ │ IP Header │
│ ┌───────┤ │ ╲ │ ┌───────┤
│ │5G DSCP│ ────────┘ ╲ │ │5G DSCP│
├──────┴───────┤ ╲ ├──────┴───────┤
│ │ ╲ │ │
│ │ ╲ │ │
│ │ ▏│ │
│ Payload │ ╱ │ Payload │
│(GTP-U/IPsec) │ ╱ │(GTP-U/IPsec) │
│ │ ╱ │ │
│ │ ────────┐ ╱ │ │
│ │ │ ╱ │ │
│ │ │╱ │ │
└──────────────┘ ─ ─ ─ ─ ─ ─ ─ ─ └──────────────┘
Figure 19: QoS with MPLS Encapsulation
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┌──────────────┐
│ IPv6 Header │
│ ┌───────┤
│ │TN DSCP│
├──────┴───────┤
optional
│ IPv6 │
headers
┌──────────────┐ ─ ─ ─ ─ ─ ─ ─ ─ ├──────────────┤
│ IP Header │ │╲ │ IP Header │
│ ┌───────┤ │ ╲ │ ┌───────┤
│ │5G DSCP│ ────────┘ ╲ │ │5G DSCP│
├──────┴───────┤ ╲ ├──────┴───────┤
│ │ ╲ │ │
│ │ ╲ │ │
│ │ ││ │
│ Payload │ ╱ │ Payload │
│(GTP-U/IPsec) │ ╱ │(GTP-U/IPsec) │
│ │ ╱ │ │
│ │ ────────┐ ╱ │ │
│ │ │ ╱ │ │
│ │ │╱ │ │
└──────────────┘ ─ ─ ─ ─ ─ ─ ─ ─ └──────────────┘
Figure 20: QoS with IPv6 Encapsulation
From a QoS perspective, both options are similar. However, there is
one difference between the two options. The MPLS TC is only 3 bits
(8 possible combinations), while DSCP is 6 bits (64 possible
combinations). Hence, SRv6 provides more flexibility for TN CoS
design, especially in combination with soft policing with in-profile/
out-profile traffic, as discussed in Section 5.2.1.1.
Provider network edge resources are controlled in a granular, fine-
grained manner, with dedicated resource allocation for each RFC 9543
Network Slice. The resource control/enforcement happens at each SDP
in two directions: inbound and outbound.
5.2.1.1. Inbound Edge Resource Control
The main aspect of inbound provider network edge resource control is
per-slice traffic volume enforcement. This kind of enforcement is
often called 'admission control' or 'traffic conditioning'. The goal
of this inbound enforcement is to ensure that the traffic above the
contracted rate is dropped or deprioritized, depending on the
business rules, right at the edge of provider network. This,
combined with appropriate network capacity planning/management
(Section 7) is required to ensure proper isolation between slices in
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a scalable manner. As a result, traffic of one slice has no
influence on the traffic of other slices, even if the slice is
misbehaving (e.g., Distributed Denial-of-Service (DDoS) attacks or
node/link failures) and generates traffic volumes above the
contracted rates.
The slice rates can be characterized with following parameters
[I-D.ietf-teas-ietf-network-slice-nbi-yang]:
* CIR: Committed Information Rate (i.e., guaranteed bandwidth)
* PIR: Peak Information Rate (i.e., maximum bandwidth)
These parameters define the traffic characteristics of the slice and
are part of SLO parameter set provided by the 5G NSO to RFC 9543 NSC.
Based on these parameters the provider network inbound policy can be
implemented using one of following options:
* 1r2c (single-rate two-color) rate limiter
This is the most basic rate limiter, described in Section 2.3 of
[RFC2475]. It meters at the SDP a traffic stream of given slice
and marks its packets as in-profile (below CIR being enforced) or
out-of-profile (above CIR being enforced). In-profile packets are
accepted and forwarded. Out-of profile packets are either dropped
right at the SDP (hard rate limiting), or remarked (with different
MPLS TC or DSCP TN markings) to signify 'this packet should be
dropped in the first place, if there is a congestion' (soft rate
limiting), depending on the business policy of the provider
network. In the second case, while packets above CIR are
forwarded at the SDP, they are subject to being dropped during any
congestion event at any place in the provider network.
* 2r3c (two-rate three-color) rate limiter
This was initially defined in [RFC2698], and its improved version
in [RFC4115]. In essence, the traffic is assigned to one of the
these three categories:
- Green, for traffic under CIR
- Yellow, for traffic between CIR and PIR
- Red, for traffic above PIR
An inbound 2r3c meter implemented with [RFC4115], compared to
[RFC2698], is more 'customer friendly' as it doesn't impose
outbound peak-rate shaping requirements on customer edge (CE)
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devices. 2r3c meters in general give greater flexibility for
provider network edge enforcement regarding accepting the traffic
(green), de- prioritizing and potentially dropping the traffic on
transit during congestion (yellow), or hard dropping the traffic
(red).
Inbound provider network edge enforcement model for 5QI-unaware
model, where all packets belonging to the slice are treated the same
way in the provider network (no 5Q QoS Class differentiation in the
provider) is outlined in Figure 21.
Slice
policer ┌─────────┐
║ ┌───┴──┐ │
║ │ │ │
║ │ S │ │
║ │ l │ │
v │ i │ │
──────────────◇────┼──> c │ │
│ e │ A │
│ │ t │
│ 1 │ t │
│ │ a │
├──────┤ c │
│ │ h │
│ S │ m │
│ l │ e │
│ i │ n │
──────────────◇────┼──> c │ t │
│ e │ │
│ │ C │
│ 2 │ i │
│ │ r │
├──────┤ c │
│ │ u │
│ S │ i │
│ l │ t │
│ i │ │
──────────────◇────┼──> c │ │
│ e │ │
│ │ │
│ 3 │ │
│ │ │
└───┬──┘ │
└─────────┘
Figure 21: Ingress Slice Admission Control (5QI-unware Model)
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5.2.1.2. Outbound Edge Resource Control
While inbound slice admission control at the provider network edge is
mandatory in the architecture described in this document, outbound
provider network edge resource control might not be required in all
use cases. Use cases that specifically call for outbound provider
network edge resource control are:
* Slices use both CIR and PIR parameters, and provider network edge
links (attachment circuits) are dimensioned to fulfil the
aggregate of slice CIRs. If at any given time, some slices send
the traffic above CIR, congestion in outbound direction on the
provider network edge link (attachment circuit) might happen.
Therefore, fine-grained resource control to guarantee at least CIR
for each slice is required.
* Any-to-Any (A2A) connectivity constructs are deployed, again
resulting in potential congestion in outbound direction on the
provider network edge links, even if only slice CIR parameters are
used. This again requires fine-grained resource control per slice
in outbound direction at the provider network edge links.
As opposed to inbound provider network edge resource control,
typically implemented with rate-limiters/policers, outbound resource
control is typically implemented with a weighted/priority queuing,
potentially combined with optional shapers (per slice). A detailed
analysis of different queuing mechanisms is out of scope for this
document, but is provided in [RFC7806].
Figure 22 outlines the outbound provider network edge resource
control model for 5QI-unaware slices. Each slice is assigned a
single egress queue. The sum of slice CIRs, used as the weight in
weighted queueing model, should not exceed the physical capacity of
the attachment circuit. Slice requests above this limit should be
rejected by the RFC 9543 NSC, unless an already established slice
with lower priority, if such exists, is preempted.
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┌─────────┐ QoS output queues
│ ┌───┴──┐─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │ S │ ╲│╱
│ │ l │ │
│ │ i │ │
│ A │ c │ │ weight=Slice-1-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-1-PIR
───┼──t──┼────> │ │
│ a │ 1 └─┬──────────────────────────┘ ╱│╲
│ c ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ h │ S │ ╲│╱
│ m │ l │ │
│ e │ i │ │
│ n │ c │ │ weight=Slice-2-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-2-PIR
───┼─────┼────> │ │
│ C │ 2 └─┬──────────────────────────┘ ╱│╲
│ i ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ r │ S │ ╲│╱
│ c │ l │ │
│ u │ i │ │
│ i │ c │ │ weight=Slice-3-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-3-PIR
───┼─────┼────> │ │
│ │ 3 └─┬──────────────────────────┘ ╱│╲
│ └───┬──┘─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└─────────┘
Figure 22: Ingress Slice Admission control (5QI-unaware Model)
5.2.2. 5QI-aware Model
In the 5QI-aware model, potentially a large number of 5G QoS Classes,
represented via the DSCP set by NFs (the architecture scales to
thousands of 5G slices) is mapped (multiplexed) to up to 8 TN QoS
Classes used in a provider network transit equipment, as outlined in
Figure 23.
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┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ PE │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃
R ┃ SDP ┃ ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
F ┃│ ┌──────────┐ │┃ ┃ Transit link ┃
C ┃ │5G DSCP A ├───────────────┐ ┃┌────────────────────────┐ ┃
X ┃│ └──────────┘ │┃ ├──> TN QoS Class 1 │ ┃
X ┃ ┌──────────┐ ┃ │ ┃└────────────────────────┘ ┃
X ┃│ │5G DSCP B ├───────────┐ │ ┃┌────────────────────────┐ ┃
X ┃ └──────────┘ ┃ │ │ ┃│ TN QoS Class 2 │ ┃
┃│ ┌──────────┐ │┃ │ │ ┃└────────────────────────┘ ┃
N ┃ │5G DSCP C ├──╋─────┐ │ │ ┃┌────────────────────────┐ ┃
S ┃│ └──────────┘ │┃ │ │ │ ┃│ TN QoS Class 3 │ ┃
┃ ┌──────────┐ ┃ │ │ │ ┃└────────────────────────┘ ┃
1 ┃│ │5G DSCP D ├─────┐ │ │ │ ┃┌────────────────────────┐ ┃
┃ └──────────┘ ┃ │ │ ├──────> TN QoS Class 4 │ ┃
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │ │ │ │ ┃└────────────────────────┘ ┃
R ┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │ │ ┃┌────────────────────────┐ ┃
F ┃ ┌──────────┐ ┃ │ ├─────────> TN QoS Class 5 │ ┃
C ┃│ │5G DSCP A ├─────│──│──│───┘ ┃└────────────────────────┘ ┃
X ┃ └──────────┘ ┃ │ │ │ ┃┌────────────────────────┐ ┃
X ┃│ ┌──────────┐ │┃ │ │ │ ┃│ TN QoS Class 6 │ ┃
X ┃ │5G DSCP E ├─────│──│──┘ ┃└────────────────────────┘ ┃
X ┃│ └──────────┘ │┃ │ │ ┃┌────────────────────────┐ ┃
┃ ┌──────────┐ ┃ │ │ ┃│ TN QoS Class 7 │ ┃
N ┃│ │5G DSCP F ├─────│──┘ ┃└────────────────────────┘ ┃
S ┃ └──────────┘ ┃ │ ┃┌────────────────────────┐ ┃
┃│ ┌──────────┐ │┃ ├────────────> TN QoS Class 8 │ ┃
2 ┃ │5G DSCP G ├─────┘ ┃└────────────────────────┘ ┃
┃│ └──────────┘ │┃ ┃ Max 8 TN Classes ┃
┃ SDP ┃ ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │
┣━━━━━━━━━━━━━━━━━┛
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Fine-grained QoS enforcement Coarse-grained QoS enforcement
(dedicated resources per (resources shared by multiple
RFC XXXX Network Slice) RFC XXXX Network Slices)
Figure 23: Slice 5Q QoS to TN QoS Mapping (5QI-aware Model)
Given that in deployments with a large number of 5G slices, the
number of potential 5G QoS Classes is much higher than the number of
TN QoS Classes, multiple 5G QoS Classes with similar characteristics
- potentially from different slices - would be grouped with common
operator-defined TN logic and mapped to a same TN QoS Class when
transported in the provider network. That is, common Per-hop
Behavior (PHB) [RFC2474] is executed on transit provider network
routers for all packets grouped together. An example of this
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approach is outlined in Figure 24. A provider may decide to
implement Diffserv-Intercon PHBs at the boundaries of its network
domain [RFC8100].
Note: The numbers indicated in Figure 24 (S-NSSAI, 5QI, DSCP, queue,
etc.) are provided for illustration purposes only and should not
be considered as deployment guidance.
┌───────────── PE ─────────────────┐
┌────── NF-A ──────┐ │ │
│ │ │ ┌ ─ ─ ─ ─ ┐ │
│ 3GPP S-NSSAI 100 │ │ SDP │
│┌──────┐ ┌───────┐│ │ │┌───────┐│ │
││5QI=1 ├─>DSCP=46├──────>DSCP=46├───┐ │
│└──────┘ └───────┘│ │ │└───────┘│ │ │
│┌──────┐ ┌───────┐│ │ ┌───────┐ │ │
││5QI=65├─>DSCP=46├──────>DSCP=46├┼──┤ │
│└──────┘ └───────┘│ │ └───────┘ │ │
│┌──────┐ ┌───────┐│ │ │┌───────┐│ │ │
││5QI=7 ├─>DSCP=10├──────>DSCP=10──────┐ ┌──────────────┐ │
│└──────┘ └───────┘│ │ │└───────┘│ │ │ │TN QoS Class 5│ │
└──────────────────┘ │ ─ ─ ─ ─ ─ ├─│──> Queue 5 │ │
│ │ │ └──────────────┘ │
┌────── NF-B ──────┐ │ │ │ │
│ │ │ ┌ ─ ─ ─ ─ ┐ │ │ │
│ 3GPP S-NSSAI 200 │ │ SDP │ │ │
│┌──────┐ ┌───────┐│ │ │┌───────┐│ │ │ │
││5QI=1 ├─>DSCP=46├──────>DSCP=46├───┤ │ ┌──────────────┐ │
│└──────┘ └───────┘│ │ │└───────┘│ │ │ │TN QoS Class 1│ │
│┌──────┐ ┌───────┐│ │ ┌───────┐ │ ├──> Queue 1 │ │
││5QI=65├─>DSCP=46├──────>DSCP=46├┼──┘ │ └──────────────┘ │
│└──────┘ └───────┘│ │ └───────┘ │ │
│┌──────┐ ┌───────┐│ │ │┌───────┐│ │ │
││5QI=7 ├─>DSCP=10├──────>DSCP=10├─────┘ │
│└──────┘ └───────┘│ │ │└───────┘│ │
└──────────────────┘ │ ─ ─ ─ ─ ─ │
└────────────────────────────────────┘
Figure 24: Example of 3GPP QoS Mapped to TN QoS
In current SDO progress of 3GPP (Release 17) and O-RAN, the mapping
of 5QI to DSCP is not expected to be in a per-slice fashion, where
5QI to DSCP mapping may vary from 3GPP slice to 3GPP slice, hence the
mapping of 5G QoS DSCP values to TN QoS Classes may be rather common.
Like in the 5QI-unaware model, the original IP header retains the
DCSP marking corresponding to 5QI (5G QoS Class), while the new
header (MPLS or IPv6) carries QoS marking related to TN QoS Class.
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Based on TN QoS Class marking, per-hop behavior for all aggregated 5G
QoS Classes from all RFC 9543 Network Slices is executed on the
provider network transit links. Provider network transit routers do
not evaluate the original IP header for QoS related decisions. The
original DSCP marking retained in the original IP header is used at
the PE for fine-grained per slice and per 5G QoS Class inbound/
outbound enforcement on the AC.
In the 5QI-aware model, compared to the 5QI-unware model, provider
network edge resources are controlled in an even more granular, fine-
grained manner, with dedicated resource allocation for each RFC 9543
Network Slice and dedicated resource allocation for number of traffic
classes (most commonly up 4 or 8 traffic classes, depending on the HW
capability of the equipment) within each RFC 9543 Network Slice.
5.2.2.1. Inbound Edge Resource Control
Compared to the 5QI-unware model, admission control (traffic
conditioning) in the 5QI-aware model is more granular, as it enforces
not only per slice capacity constraints, but may as well enforce the
constraints per 5G QoS Class within each slice.
A 5G slice using multiple 5QIs can potentially specify rates in one
of the following ways:
* Rates per traffic class (CIR or CIR+PIR), no rate per slice (sum
of rates per class gives the rate per slice).
* Rate per slice (CIR or CIR+PIR), and rates per prioritized
(premium) traffic classes (CIR only). Best effort traffic class
uses the bandwidth (within slice CIR/PIR) not consumed by
prioritized classes.
In the first option, the slice admission control is executed with
traffic class granularity, as outlined in Figure 25. In this model,
if a premium class doesn't consume all available class capacity, it
cannot be reused by non-premium (i.e., Best Effort) class.
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Class ┌─────────┐
policer ┌──┴───┐ │
│ │ │
5Q-QoS-A: CIR-1A ──────◇────────────┼──> S │ │
5Q-QoS-B: CIR-1B ──────◇────────────┼──> l │ │
5Q-QoS-C: CIR-1C ──────◇────────────┼──> i │ │
│ c │ │
│ e │ │
BE CIR/PIR-1D ──────◇────────────┼──> │ A │
│ 1 │ t │
│ │ t │
├──────┤ a │
│ │ c │
5Q-QoS-A: CIR-2A ──────◇────────────┼─> S │ h │
5Q-QoS-B: CIR-2B ──────◇────────────┼─> l │ m │
5Q-QoS-C: CIR-2C ──────◇────────────┼─> i │ e │
│ c │ n │
│ e │ t │
BE CIR/PIR-2D ──────◇────────────┼─> │ │
│ 2 │ C │
│ │ i │
├──────┤ r │
│ │ c │
5Q-QoS-A: CIR-3A ──────◇────────────┼─> S │ u │
5Q-QoS-B: CIR-3B ──────◇────────────┼─> l │ i │
5Q-QoS-C: CIR-3C ──────◇────────────┼─> i │ t │
│ c │ │
│ e │ │
BE CIR/PIR-3D───────◇────────────┼─> │ │
│ 3 │ │
│ │ │
└──┬───┘ │
└─────────┘
Figure 25: Ingress Slice Admission Control (5QI-aware Model)
The second model combines the advantages of 5QI-unaware model (per
slice admission control) with the per traffic class admission
control, as outlined in Figure 25. Ingress admission control is at
class granularity for premium classes (CIR only). Non-premium class
(i.e., Best Effort) has no separate class admission control policy,
but it is allowed to use the entire slice capacity, which is
available at any given moment. I.e., slice capacity, which is not
consumed by premium classes. It is a hierarchical model, as depicted
in Figure 26.
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Slice
policer ┌─────────┐
Class . ┌──┴───┐ │
policer ; : │ │ │
5Q-QoS-A: CIR-1A ────◇─────────┤─┼──┼──> S │ │
5Q-QoS-B: CIR-1B ────◇─────────┤─┼──┼──> l │ │
5Q-QoS-C: CIR-1C ────◇─────────┤─┼──┼──> i │ │
│ │ │ c │ │
│ │ │ e │ │
BE CIR/PIR-1D ──────────────┤─┼──┼──> │ A │
│ │ │ 1 │ t │
: ; │ │ t │
. ├──────┤ a │
; : │ │ c │
5Q-QoS-A: CIR-2A ────◇─────────┤─┼──┼──> S │ h │
5Q-QoS-B: CIR-2B ────◇─────────┤─┼──┼──> l │ m │
5Q-QoS-C: CIR-2C ────◇─────────┤─┼──┼──> i │ e │
│ │ │ c │ n │
│ │ │ e │ t │
BE CIR/PIR-2D ──────────────┤─┼──┼──> │ │
│ │ │ 2 │ C │
: ; │ │ i │
. ├──────┤ r │
; : │ │ c │
5Q-QoS-A: CIR-3A ────◇─────────┤─┼──┼──> S │ u │
5Q-QoS-B: CIR-3B ────◇─────────┤─┼──┼──> l │ i │
5Q-QoS-C: CIR-3C ────◇───── ───┤─┼──┼──> i │ t │
│ │ │ c │ │
│ │ │ e │ │
BE CIR/PIR-3D ──────────────┤─┼──┼──> │ │
│ │ │ 3 │ │
: ; │ │ │
' └──┬───┘ │
└─────────┘
Figure 26: Ingress Slice Admission Control (5QI-aware) - Hierarchical
5.2.2.2. Outbound Edge Resource Control
Figure 27 outlines the outbound edge resource control model at the
transport network layer for 5QI-aware slices. Each slice is assigned
multiple egress queues. The sum of queue weights, which are 5Q QoS
queue CIRs within the slice, should not exceed the CIR of the slice
itself. And, similarly to the 5QI-aware model, the sum of slice CIRs
should not exceed the physical capacity of the attachment circuit.
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┌─────────┐ QoS output queues
│ ┌───┴──┐─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │ ┌─┴──────────────────────────┐ ╲│╱
───┼─────┼────> 5Q-QoS-A: w=5Q-QoS-A-CIR │ │
│ │ S └─┬──────────────────────────┘ │
│ │ l ┌─┴──────────────────────────┐ │
───┼─────┼─i──> 5Q-QoS-B: w=5Q-QoS-B-CIR │ │
│ │ c └─┬──────────────────────────┘ │ weight=Slice-1-CIR
│ │ e ┌─┴──────────────────────────┐ │ shaping=Slice-1-PIR
───┼─────┼────> 5Q-QoS-C: w=5Q-QoS-C-CIR │ │
│ │ 1 └─┬──────────────────────────┘ │
│ │ ┌─┴──────────────────────────┐ │
───┼─────┼────> Best Effort (remainder) │ │
│ │ └─┬──────────────────────────┘ ╱│╲
│ A ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ t │ ┌─┴──────────────────────────┐ ╲│╱
│ t │ │ │ │
│ a │ └─┬──────────────────────────┘ │
│ c │ S ┌─┴──────────────────────────┐ │
│ h │ l │ │ │
│ m │ i └─┬──────────────────────────┘ │ weight=Slice-2-CIR
│ e │ c ┌─┴──────────────────────────┐ │ shaping=Slice-2-PIR
│ n │ e │ │ │
│ t │ └─┬──────────────────────────┘ │
│ │ 2 ┌─┴──────────────────────────┐ │
│ C │ │ │ │
│ i │ └─┬──────────────────────────┘ ╱│╲
│ r ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ c │ ┌─┴──────────────────────────┐ ╲│╱
│ u │ │ │ │
│ i │ S └─┬──────────────────────────┘ │
│ t │ l ┌─┴──────────────────────────┐ │
│ │ i │ │ │
│ │ c └─┬──────────────────────────┘ │ weight=Slice-3-CIR
│ │ e ┌─┴──────────────────────────┐ │ shaping=Slice-3-PIR
│ │ │ │ │
│ │ 3 └─┬──────────────────────────┘ │
│ │ ┌─┴──────────────────────────┐ │
│ │ │ │ │
│ │ └─┬──────────────────────────┘ ╱│╲
│ └───┬──┘─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└─────────┘
Figure 27: Egress Slice Admission Control (5QI-aware)
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5.3. Transit Resource Control
Transit resource control is much simpler than Edge resource control
in the provider network. As outlined in Figure 23, at the provider
network edge, 5Q QoS Class marking (represented by DSCP related to
5QI set by mobile network functions in the packets handed off to the
TN) is mapped to the TN QoS Class. Based on TN QoS Class, when the
packet is encapsulated with outer header (MPLS or IPv6), TN QoS Class
marking (MPLS TC or IPv6 DSCP in outer header, as depicted in
Figure 19 and Figure 20) is set in the outer header. PHB in provider
network transit routers is based exclusively on that TN QoS Class
marking, i.e., original 5G QoS Class DSCP is not taken into
consideration on transit.
Provider network transit resource control does not use any inbound
interface policy, but only outbound interface policy, which is based
on priority queue combined with weighted or deficit queuing model,
without any shaper. The main purpose of transit resource control is
to ensure that during network congestion events, for example caused
by network failures and temporary rerouting, premium classes are
prioritized, and any drops only occur in traffic that was de-
prioritized by ingress admission control Section 5.2.1.1 or in non-
premium (best-effort) classes. Capacity planning and management, as
described in Section 7, ensures that enough capacity is available to
fulfill all approved slice requests.
6. Transport Planes Mapping Models
A network operator can define multiple transport planes. A transport
plane may be realized in multiple ways such as (but not limited to):
* A mesh of RSVP-TE [RFC3209] or SR-TE [RFC9256] tunnels created
with specific optimization criteria and constraints. For example,
mesh "A" might represent tunnels optimized for latency, and mesh
"B" might represent tunnels optimized for high capacity.
* A flex-algo [RFC9350] with a particular metric-type (e.g.,
latency), or one that only uses links with particular properties
(e.g., MACsec link [IEEE802.1AE]), or excludes links that are
within a particular geography.
* An NRP [I-D.ietf-teas-ns-ip-mpls]
* Any combination thereof.
Detailed realization of transport planes is out of the scope of this
document.
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Figure 28 depicts an example of a simple network with two transport
planes, each using a mesh of TE tunnels with or without Path
Computation Element (PCE) [RFC5440], and with or without bandwidth
reservations. Section 7 discusses in detail different bandwidth
models that can be deployed in the provider network. However,
discussion about how to realize or orchestrate transport planes is
out of scope for this document.
┌───────────────┐ ┌──────┐
│ Ingress PE │ ╔═══════════════════════════════>│ PE-A │
│ │ ║ ╔═══════════════════════════▷│ │
│ ┌ ─ ─ ─ ─ ┐ │ ║ ╚═════════════════════╗ └──────┘
│ ●══════╝ ╔═════════════════════╝
│ │Transport●════════════════════════════════╗ ┌──────┐
│ Plane A ●═════════════╗ ╚═════>│ PE-B │
│ │ ●═══════╗ ║ ║ ╔═══╗ ╔═══╗ ╔═════▷│ │
│ ─ ─ ─ ─ ─ │ ║ ║ ║ ║ ║ ║ ║ ║ └──────┘
│ │ ║ ║ ║ ║ ╚═══╝ ╚═══╝
│ ┌ ─ ─ ─ ─ ┐ │ ║ ║ ║ ║ ┌──────┐
│ ○═══════║══╝ ╚════════════════════════>│ PE-C │
│ │Transport○═══════║════════╝ ╔═════▷│ │
│ Plane B ○═══════║═════════════════╗ ║ └──────┘
│ │ ○═════╗ ╚═══════════════╗ ║ ║
│ ─ ─ ─ ─ ─ │ ║ ╔═╗ ╔═╗ ╔═╗ ╔═╗ ║ ╚══════╝ ┌──────┐
│ │ ║ ║ ║ ║ ║ ║ ║ ║ ║ ╚══════════════>│ PE-D │
└───────────────┘ ╚═╝ ╚═╝ ╚═╝ ╚═╝ ╚════════════════▷│ │
└──────┘
●════════▶ Tunnels of Transport Plane A
○════════▷ Tunnels of Transport Plane B
Figure 28: Transport Planes example based on TE tunnels
Note that there might be multiple tunnels within a single transport
plane between any pair of PEs. Figure 28 shows only single tunnel
per transport plane for (ingress PE, egress PE) pair.
Similar to the QoS mapping models discussed in Section 5, for mapping
to transport planes at the ingress PE, both 5QI-unaware and 5QI-aware
models are defined. Essentially, entire slices can be mapped to
transport planes without 5G QoS consideration (5QI-unaware model).
For example, flows with different 5G QoS Classes, even from same
slice, can be mapped to different transport planes (5QI-aware model).
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6.1. 5QI-unaware Model
As discussed in Section 5.2.1, in the 5QI-unware model, the provider
network doesn't take into account 5G QoS during execution of per-hop
behavior. The entire slice is mapped to single TN QoS Class,
therefore the entire slice is subject to the same per-hop behavior.
Similarly, in 5QI-unaware transport plane mapping model, the entire
slice is mapped to a single transport plane, as depicted in
Figure 29.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ │
┃ Attach. Circuit ┃ PE router
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │
┃ SDP ┃
┃│ ┌──────────┐ │┃ │
┃ │ NS 1 ├──────────┐
┃│ └──────────┘ │┃ │ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┌─────────┐ │
┃ SDP ┃ │ │ │
┃│ ┌──────────┐ │┃ │ │Transport│ │
┃ │ NS 2 ├──────┐ ├───> Plane │
┃│ └──────────┘ │┃ │ │ │ A │ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ │ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ └─────────┘ │
┃ SDP ┃ │ │
┃│ ┌──────────┐ │┃ │ │ │
┃ │ NS 3 ├──────┤ │
┃│ └──────────┘ │┃ │ │ ┌─────────┐ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ │ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │Transport│ │
┃ SDP ┃ ├───│───> Plane │
┃│ ┌──────────┐ │┃ │ │ │ B │ │
┃ │ NS 4 ├──────┘ │ │ │
┃│ └──────────┘ │┃ │ └─────────┘ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │
┃ SDP ┃ │
┃│ ┌──────────┐ │┃ │ │
┃ │ NS 5 ├──────────┘
┃│ └──────────┘ │┃ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃
┗━━━━━━━━━━━━━━━━━┛ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 29: Slice to Transport Plane Mapping (5QI-unaware Model)
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It is worth noting that TN QoS Classes and Transport Planes are
orthogonal. The TN domain can be operated with e.g., 8 TN QoS
Classes (representing 8 hardware queues in the routers), and 2
Transport Planes (e.g., latency optimized transport plane using link
latency metrics for path calculation, and transport plane following
Interior Gateway Protocol (IGP) metrics). TN QoS Class determines
the per-hop behavior when the packets are transiting through the
provider network, while transport plane determines the paths for
packets through provider network based on operator's business model
(operator's requirement). This path can be optimised or constrained.
6.2. 5QI-aware Model
In 5QI-aware model, the traffic can be mapped to transport planes at
the granularity of 5G QoS Class. Given that the potential number of
transport planes is limited, packets from multiple 5G QoS Classes
with similar characteristics are mapped to a common transport plane,
as depicted in Figure 30.
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┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┏━━━━━━━━━━━━━━━━━┓
┃ Attach. Circuit ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ PE router
R ┃ SDP ┃ │
F ┃│ ┌──────────┐ │┃
C ┃ │ 5G QoS A ├──────┐ │
X ┃│ └──────────┘ │┃ │
X ┃ ┌──────────┐ ┃ │ │
X ┃│ │ 5G QoS B ├──────┤
X ┃ └──────────┘ ┃ │ ┌─────────┐ │
┃│ ┌──────────┐ │┃ │ │ │
N ┃ │ 5G QoS C ├───────────┐ │Transport│ │
S ┃│ └──────────┘ │┃ ├────│────> Plane │
┃ ┌──────────┐ ┃ │ │ │ A │ │
1 ┃│ │ 5G QoS D ├───────────┤ │ │
┃ └──────────┘ ┃ │ │ └─────────┘ │
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │ │
R ┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │
F ┃ ┌──────────┐ ┃ │ │
C ┃│ │ 5G QoS A ├──────┤ │ ┌─────────┐ │
X ┃ └──────────┘ ┃ │ │ │ │
X ┃│ ┌──────────┐ │┃ │ │ │Transport│ │
X ┃ │ 5G QoS E ├──────┘ ├────> Plane │
X ┃│ └──────────┘ │┃ │ │ B │ │
┃ ┌──────────┐ ┃ │ │ │
N ┃│ │ 5G QoS F ├───────────┤ └─────────┘ │
S ┃ └──────────┘ ┃ │
┃│ ┌──────────┐ │┃ │ │
2 ┃ │ 5G QoS G ├───────────┘
┃│ └──────────┘ │┃ │
┃ SDP ┃
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │
┗━━━━━━━━━━━━━━━━━┛
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 30: Slice to Transport Plane mapping (5QI-aware Model)
7. Capacity Planning/Management
7.1. Bandwidth Requirements
This section describes the information conveyed by the 5G NSO to the
RFCXXXX NSC with respect to slice bandwidth requirements.
Figure 31 shows three DCs that contain instances of network
functions. Also shown are PEs that have links to the DCs. The PEs
belong to the provider network. Other details of the provider
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network, such as P-routers and transit links are not shown. Also
details of the DC infrastructure in customer sites, such as switches
and routers, are not shown.
The 5G NSO is aware of the existence of the network functions and
their locations. However, it is not aware of the details of the
provider network. The RFCXXXX NSC has the opposite view - it is
aware of the provider network infrastructure and the links between
the PEs and the DCs, but is not aware of the individual network
functions at customer sites.
┌ ─ ─ ─ ─ DC 1─ ─ ─ ─ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ DC 2─ ─ ─ ─
┌──────┐ │ ┌────┐ ┌────┐ ┌──────┐ │
│ │ NF1A │ ───■PE1A│ │PE2A■──┤ │ NF2A │
└──────┘ │ └────┘ └────┘ └──────┘ │
│ ┌──────┐ │ │ │ ┌──────┐
│ NF1B │ │ │ NF2B │ │
│ └──────┘ │ │ │ └──────┘
┌──────┐ │ ┌────┐ ┌────┐ ┌──────┐ │
│ │ NF1C │ ───■PE1B│ │PE2B■──┤ │ NF2C │
└──────┘ │ └────┘ └────┘ └──────┘ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ Provider │ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ Network │ ┌ ─ ─ ─ ─ DC 3─ ─ ─ ─
┌────┐ ┌──────┐ │
│ │PE3A■──┤ │ NF3A │
└────┘ └──────┘ │
│ │ │ ┌──────┐
│ NF3B │ │
│ │ │ └──────┘
┌────┐ ┌──────┐ │
│ │PE3B■──┤ │ NF3C │
└────┘ └──────┘ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
■ - SDP, with fine-grained QoS (dedicated resources per RFC XXXX NS)
Figure 31: An Example of Multi-DC Architecture
Let us consider 5G slice "X" that uses some of the network functions
in the three DCs. If this slice has latency requirements, the 5G NSO
will have taken those into account when deciding which NF instances
in which DC are to be invoked for this slice. As a result of such a
placement decision, the three DCs shown are involved in 5G slice "X",
rather than other DCs. For its decision-making, the 5G NSO needs
information from the NSC about the observed latency between DCs.
Preferably, the NSC would present the topology in an abstracted form,
consisting of point-to-point abstracted links between pairs of DCs
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and associated latency and, optionally, delay variation and link loss
values. It would be valuable to have a mechanism for the 5G NSO to
inform the NSC which DC-pairs are of interest for these metrics -
there may be of order thousands of DCs, but the 5G NSO will only be
interested in these metrics for a small fraction of all the possible
DC-pairs, i.e. those in the same region of the provider network. The
mechanism for conveying the information is out of scope for this
document.
Figure 32 shows the matrix of bandwidth demands for 5G slice "X".
Within the slice, multiple network function instances might be
sending traffic from DCi to DCj. However, the 5G NSO sums the
associated demands into one value. For example, NF1A and NF1B in DC1
might be sending traffic to multiple NFs in DC2, but this is
expressed as one value in the traffic matrix: the total bandwidth
required for 5G slice X from DC1 to DC2 (8 units). Each row in the
right-most column in the traffic matrix shows the total amount of
traffic going from a given DC into the transport network, regardless
of the destination DC. Note that this number can be less than the
sum of DC-to-DC demands in the same row, on the basis that not all
the network functions are likely to be sending at their maximum rate
simultaneously. For example, the total traffic from DC1 for Slice X
is 11 units, which is less than the sum of the DC-to-DC demands in
the same row (13 units). Note, as described in Section 5, a slice
may have per-QoS class bandwidth requirements, and may have CIR and
PIR limits. This is not included in the example, but the same
principles apply in such cases.
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To┌──────┬──────┬──────┬──────────────┐
From │ DC 1 │ DC 2 │ DC 3 │Total from DC │
┌──────┼──────┼──────┼──────┼──────────────┤
│ DC 1 │ n/a │ 8 │ 5 │ 11.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 2 │ 1 │ n/a │ 2 │ 2.5 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 3 │ 4 │ 7 │ n/a │ 10.0 │
└──────┴──────┴──────┴──────┴──────────────┘
Slice X
To┌──────┬──────┬──────┬──────────────┐
From │ DC 1 │ DC 2 │ DC 3 │Total from DC │
┌──────┼──────┼──────┼──────┼──────────────┤
│ DC 1 │ n/a │ 4 │ 2.5 │ 6.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 2 │ 0.5 │ n/a │ 0.8 │ 1.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 3 │ 2.6 │ 3 │ n/a │ 5.1 │
└──────┴──────┴──────┴──────┴──────────────┘
Slice Y
Figure 32: Inter-DC Traffic Demand Matrix
[I-D.ietf-teas-ietf-network-slice-nbi-yang] can be used to convey all
of the information in the traffic matrix to the RFC 9543 NSC. The
RFC 9543 NSC applies policers corresponding to the last column in the
traffic matrix to the appropriate PE routers, in order to enforce the
bandwidth contract. For example, it applies a policer of 11 units to
PE1A and PE1B that face DC1, as this is the total bandwidth that DC1
sends into the provider network corresponding to Slice X. Also, the
controller may apply shapers in the direction from the TN to the DC,
if otherwise there is the possibility of a link in the DC being
oversubscribed. Note that a peer NF endpoint of an AC can be
identified using 'peer-sap-id' as defined in [RFC9408].
Depending on the bandwidth model used in the provider network
(Section 7.2), the other values in the matrix, i.e., the DC-to-DC
demands, may not be directly applied to the provider network. Even
so, the information may be useful to the RFC 9543 NSC for capacity
planning and failure simulation purposes. If, on the other hand, the
DC-to-DC demand information is not used by the RFC 9543 NSC, the IETF
YANG Data Model for L3VPN Service Delivery [RFC8299] or the IETF YANG
Data Model for L2VPN Service Delivery [RFC8466] could be used instead
of [I-D.ietf-teas-ietf-network-slice-nbi-yang], as they support
conveying the bandwidth information in the right-most column of the
traffic matrix.
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The provider network may be implemented in such a way that it has
various types of paths, for example low-latency traffic might be
mapped onto a different transport path to other traffic (for example
a particular flex-algo, a particular set of TE LSPs, or a specific
queue [RFC9330]), as discussed in Section 5. The 5G NSO can use
[I-D.ietf-teas-ietf-network-slice-nbi-yang] to request low-latency
transport for a given slice if required. However, [RFC8299] or
[RFC8466] do not support requesting a particular transport-type,
e.g., low-latency. One option is to augment these models to convey
this information. This can be achieved by reusing the 'underlay-
transport' construct defined in [RFC9182] and [RFC9291].
7.2. Bandwidth Models
This section describes three bandwidth management schemes that could
be employed in the provider network. Many variations are possible,
but each example describes the salient points of the corresponding
scheme. Schemes 2 and 3 use TE; other variations on TE are possible
as described in [RFC9522].
7.2.1. Scheme 1: Shortest Path Forwarding (SPF)
Shortest path forwarding is used according to the IGP metric. Given
that some slices are likely to have latency SLOs, the IGP metric on
each link can be set to be in proportion to the latency of the link.
In this way, all traffic follows the minimum latency path between
endpoints.
In Scheme 1, although the operator provides bandwidth guarantees to
the slice customers, there is no explicit end-to-end underpinning of
the bandwidth SLO, in the form of bandwidth reservations across the
provider network. Rather, the expected performance is achieved via
capacity planning, based on traffic growth trends and anticipated
future demands, in order to ensure that network links are not over-
subscribed. This scheme is analogous to that used in many existing
business VPN deployments, in that bandwidth guarantees are provided
to the customers but are not explicitly underpinned end to end across
the provider network.
A variation on the scheme is that Flex-Algo [RFC9350] is used. For
example one Flex-Algo could use latency-based metrics and another
Flex-Algo could use the IGP metric. There would be a many-to-one
mapping of Network Slices to Flex- Algos.
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While Scheme 1 is technically feasible, it is vulnerable to
unexpected changes in traffic patterns and/or network element
failures resulting in congestion. This is because, unlike Schemes 2
and 3 that employ TE, traffic cannot be diverted from the shortest
path.
7.2.2. Scheme 2: TE LSPs with Fixed Bandwidth Reservations
Scheme 2 uses RSVP-TE [RFC3209] or SR-TE LSPs [RFC9256] with fixed
bandwidth reservations. By "fixed", we mean a value that stays
constant over time, unless the 5G NSO communicates a change in slice
bandwidth requirements, due to the creation or modification of a
slice. Note that the "reservations" would be in the mind of the
transport controller - it is not necessary (or indeed possible for
SR-TE) to reserve bandwidth at the network layer. The bandwidth
requirement acts as a constraint whenever the controller (re)computes
the path of an LSP. There could be a single mesh of LSPs between
endpoints that carry all of the traffic types, or there could be a
small handful of meshes, for example one mesh for low-latency traffic
that follows the minimum latency path and another mesh for the other
traffic that follows the minimum IGP metric path, as described in
Section 5. There would be a many-to-one mapping of slices to LSPs.
The bandwidth requirement from DCi to DCj is the sum of the DCi-DCj
demands of the individual slices. For example, if only Slice X and
Slice Y are present, then the bandwidth requirement from DC1 to DC2
is 12 units (8 units for Slice X and 4 units for Slice Y). When the
5G NSO requests a new slice, the RFCXXXX NSC, in its mind, increments
the bandwidth requirement according to the requirements of the new
slice. For example, in Figure 31, suppose a new slice is
instantiated that needs 0.8 Gbps from DC1 to DC2. The transport
controller would increase its notion of the bandwidth requirement
from DC1 to DC2 from 12 Gbps to 12.8 Gbps to accommodate the
additional expected traffic.
In the example, each DC has two PEs facing it for reasons of
resilience. The RFCXXXX NSC needs to determine how to map the DC1 to
DC2 bandwidth requirement to bandwidth reservations of TE LSPs from
DC1 to DC2. For example, if the routing configuration is arranged
such that in the absence of any network failure, traffic from DC1 to
DC2 always enters PE1A and goes to PE2A, the controller reserves 12.8
Gbps of bandwidth on the LSP from PE1A to PE2A. If, on the other
hand, the routing configuration is arranged such that in the absence
of any network failure, traffic from DC1 to DC2 always enters PE1A
and is load-balanced across PE2A and PE2B, the controller reserves
6.4 Gbps of bandwidth on the LSP from PE1A to PE2A and 6.4 Gbps of
bandwidth on the LSP from PE1A to PE2B. It might be tricky for the
RFCXXXX NSC to be aware of all conditions that change the way traffic
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lands on the various PEs, and therefore know that it needs to change
bandwidth reservations of LSPs accordingly. For example, there might
be an internal failure within DC1 that causes traffic from DC1 to
land on PE1B, rather than PE1A. The RFCXXXX NSC may not be aware of
the failure and therefore may not know that it now needs to apply
bandwidth reservations to LSPs from PE1B to PE2A/PE2B.
7.2.3. Scheme 3: TE LSPs without Bandwidth Reservation
Like Scheme 2, Scheme 3 uses RSVP-TE or SR-TE LSPs. There could be a
single mesh of LSPs between endpoints that carry all of the traffic
types, or there could be a small handful of meshes, for example one
mesh for low-latency traffic that follows the minimum latency path
and another mesh for the other traffic that follows the minimum IGP
metric path, as described in Section 5. There would be a many-to-one
mapping of slices to LSPs.
The difference between Scheme 2 and Scheme 3 is that Scheme 3 does
not have fixed bandwidth reservations for the LSPs. Instead, actual
measured data-plane traffic volumes are used to influence the
placement of TE LSPs. One way of achieving this is to use
distributed RSVP-TE with auto-bandwidth. Alternatively, the RFCXXXX
NSC can use telemetry-driven automatic congestion avoidance. In this
approach, when the actual traffic volume in the data plane on given
link exceeds a threshold, the controller, knowing how much actual
data plane traffic is currently travelling along each RSVP or SR-TE
LSP, can tune the paths of one or more LSPs using the link such that
they avoid that link.
It would be undesirable to move a minimum-latency LSP rather than
another type of LSP in order to ease the congestion, as the new path
will typically have a higher latency, if the minimum-latency LSP is
currently following the minimum-latency path. This can be avoided by
designing the algorithms described in the previous paragraph such
that they avoid moving minimum-latency LSPs unless there is no
alternative.
8. Network Slicing OAM
The deployment and maintenance of slices within a network imply that
a set of OAM functions ([RFC6291]) need to be deployed by the
providers, e.g.:
* Providers should be able to execute OAM tasks on a per Network
Slice basis. These tasks can cover the "full" slice within a
domain or a portion of that slice (for troubleshooting purposes,
for example).
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For example, per-slice OAM tasks can consist of (but not limited
to):
- tracing resources that are bound to a given Network Slice,
- tracing resources that are invoked when forwarding a given flow
bound to a given Network Slice,
- assessing whether flow isolation characteristics are in
conformance with the Network Slice Service requirements, or
- assessing the compliance of the allocated Network Slice
resources against flow/ customer service requirements.
[RFC7276] provides an overview of available OAM tools. These
technology-specific tools can be reused in the context of network
slicing. Providers that deploy network slicing capabilities
should be able to select whatever OAM technology or specific
feature that would address their needs.
SFC OAM [RFC9451] should also be supported for slices that make
uses of service function chaining [RFC7665]. An example of SFC
OAM technique to Continuity Check, Connectivity Verification, or
tracing service functions is specified in [RFC9516].
* Providers may want to enable differentiated failure detect and
repair features for a subset of network slices. For example, a
given Network Slice may require fast detect and repair mechanisms,
while others may not be engineered with such means. The provider
can use techniques such as [RFC5286], [RFC5714], or [RFC8355].
* Providers may deploy means to dynamically discover the set of
Network Slices that are enabled within its network. Such dynamic
discovery capability facilitates the detection of any mismatch
between the view maintained by the control/management plane and
the actual network configuration. When mismatches are detected,
corrective actions should be undertaken accordingly. For example,
a provider may rely upon the L3NM [RFC9182] or the L2NM [RFC9291]
to maintain the full set of L3VPN/L2VPNs that are used to deliver
Network Slice Services. The correlation between an LxVPN instance
and a Network Slice Service is maintained using "parent-service-
id" attribute (Section 7.3 of [RFC9182]).
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* Means to report a set of network performance metrics to assess
whether the agreed slice service objectives are honored. These
means are used for SLO monitoring and violation detect purposes.
For example, [RFC9375] can be used to report links' one-way delay,
one-way delay variation, etc. Both conventional active/passive
measurement methods [RFC7799] and more recent telemetry methods
(e.g., YANG Push [RFC8641]) can be used.
* Means to report and expose observed performance metrics and other
OAM state to customer. For example,
[I-D.ietf-teas-ietf-network-slice-nbi-yang] exposes a set of
statistics per SDP, connectivity construct, and connection group.
9. IANA Considerations
This document does not make any IANA request.
10. Security Considerations
Section 10 of [RFC9543] discusses generic security considerations
that are applicable to network slicing, with a focus on the following
considerations:
* Conformance to security constraints:
Specific security requests, such as not routing traffic through a
particular geographical region can be met by mapping the traffic
to a transport plane that avoids that region.
* IETF NSC authentication:
This is out of the scope for this document. It should be
addressed in documents that describe IETF NSC realization (e.g.,
[I-D.ietf-teas-ns-controller-models]).
* Specific isolation criteria:
Adequate admission control policies, for example policers as
described in Section 5.2.1.1, should be configured in the edge of
the provider network to control access to specific slice
resources. This prevents the possibility of one slice consuming
resources at the expense of other slices. Likewise, access to
classification and mapping tables have to be controlled to prevent
misbehaviors (an unauthorized entity may modify the table to bind
traffic to a random slice, redirect the traffic, etc.). Network
devices have to check that a required access privilege is provided
before granting access to specific data or performing specific
actions.
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* Data Confidentiality and Integrity of an IETF Network Slice:
As described in Section 5.1.2.1 of [RFC9543], the customer might
request an SLE that mandates encryption. As described in
Section 6, this can be achieved, e.g., by mapping the traffic to a
transport plane that uses only MACsec-encrypted links.
Many of the YANG modules cited in this document define schema for
data that is designed to be accessed via network management protocols
such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF
layer is the secure transport layer, and the mandatory-to-implement
secure transport is Secure Shell (SSH) [RFC6242]. The lowest
RESTCONF layer is HTTPS, and the mandatory-to-implement secure
transport is TLS [RFC8446].
The NETCONF access control model [RFC8341] provides the means to
restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
In order to avoid the need for a mapping table to associate source/
destination IP addresses and slices’ specific S-NSSAIs, Section 4.2
describes an approach where some or all S-NSSAI bits are embedded in
an IPv6 address using an algorithm approach. An attacker from within
the transport network who has access to the mapping configuration may
infer the slices to which belong a packet. It may also alter these
bits which may lead to steering the packet via a distinct network
slice, and thus lead to service disruption. Note that such an on-
path attacker may make more damage (e.g., randomly drop packets).
Security considerations specific to each of the technologies and
protocols listed in the document are discussed in the specification
documents of each of these protocols.
11. References
11.1. Normative References
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/rfc/rfc4364>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/rfc/rfc6241>.
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[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/rfc/rfc6242>.
[RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
Length Recommendation for Forwarding", BCP 198, RFC 7608,
DOI 10.17487/RFC7608, July 2015,
<https://www.rfc-editor.org/rfc/rfc7608>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/rfc/rfc8040>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/rfc/rfc8341>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9543] Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L., and J. Tantsura, "A
Framework for Network Slices in Networks Built from IETF
Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
<https://www.rfc-editor.org/rfc/rfc9543>.
11.2. Informative References
[I-D.henry-tsvwg-diffserv-to-qci]
Henry, J., Szigeti, T., and L. M. Contreras, "Diffserv to
QCI Mapping", Work in Progress, Internet-Draft, draft-
henry-tsvwg-diffserv-to-qci-04, 13 April 2020,
<https://datatracker.ietf.org/doc/html/draft-henry-tsvwg-
diffserv-to-qci-04>.
[I-D.ietf-opsawg-ntw-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "A Network YANG Data Model for Attachment
Circuits", Work in Progress, Internet-Draft, draft-ietf-
opsawg-ntw-attachment-circuit-05, 9 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ntw-attachment-circuit-05>.
[I-D.ietf-opsawg-teas-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "YANG Data Models for Bearers and 'Attachment
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Circuits'-as-a-Service (ACaaS)", Work in Progress,
Internet-Draft, draft-ietf-opsawg-teas-attachment-circuit-
08, 16 March 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-opsawg-teas-attachment-circuit-08>.
[I-D.ietf-teas-5g-network-slice-application]
Geng, X., Contreras, L. M., Rokui, R., Dong, J., and I.
Bykov, "IETF Network Slice Application in 3GPP 5G End-to-
End Network Slice", Work in Progress, Internet-Draft,
draft-ietf-teas-5g-network-slice-application-02, 23
October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-teas-5g-network-slice-application-02>.
[I-D.ietf-teas-ietf-network-slice-nbi-yang]
Wu, B., Dhody, D., Rokui, R., Saad, T., and J. Mullooly,
"A YANG Data Model for the RFC 9543 Network Slice
Service", Work in Progress, Internet-Draft, draft-ietf-
teas-ietf-network-slice-nbi-yang-10, 16 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-nbi-yang-10>.
[I-D.ietf-teas-ns-controller-models]
Contreras, L. M., Rokui, R., Tantsura, J., Wu, B., Liu,
X., Dhody, D., and S. Belotti, "IETF Network Slice
Controller and its associated data models", Work in
Progress, Internet-Draft, draft-ietf-teas-ns-controller-
models-01, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-ns-
controller-models-01>.
[I-D.ietf-teas-ns-ip-mpls]
Saad, T., Beeram, V. P., Dong, J., Wen, B., Ceccarelli,
D., Halpern, J. M., Peng, S., Chen, R., Liu, X.,
Contreras, L. M., Rokui, R., and L. Jalil, "Realizing
Network Slices in IP/MPLS Networks", Work in Progress,
Internet-Draft, draft-ietf-teas-ns-ip-mpls-03, 26 November
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
teas-ns-ip-mpls-03>.
[IEEE802.1AE]
IEEE, "802.1AE: MAC Security (MACsec)", n.d.,
<https://1.ieee802.org/security/802-1ae/>.
[NG.113] GSMA, "NG.113: 5GS Roaming Guidelines Version 4.0", May
2021, <https://www.gsma.com/newsroom/wp-content/
uploads//NG.113-v4.0.pdf>.
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[O-RAN.WG9.XPSAAS]
O-RAN Alliance, "O-RAN.WG9.XPSAAS: O-RAN WG9 Xhaul Packet
Switched Architectures and Solutions Version 04.00", March
2023, <https://www.o-ran.org/specifications>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/rfc/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/rfc/rfc2475>.
[RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
Marker", RFC 2698, DOI 10.17487/RFC2698, September 1999,
<https://www.rfc-editor.org/rfc/rfc2698>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/rfc/rfc3209>.
[RFC4115] Aboul-Magd, O. and S. Rabie, "A Differentiated Service
Two-Rate, Three-Color Marker with Efficient Handling of
in-Profile Traffic", RFC 4115, DOI 10.17487/RFC4115, July
2005, <https://www.rfc-editor.org/rfc/rfc4115>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/rfc/rfc4664>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/rfc/rfc5286>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/rfc/rfc5440>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/rfc/rfc5714>.
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[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/rfc/rfc5952>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/rfc/rfc6291>.
[RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, DOI 10.17487/RFC6459, January 2012,
<https://www.rfc-editor.org/rfc/rfc6459>.
[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<https://www.rfc-editor.org/rfc/rfc7276>.
[RFC7422] Donley, C., Grundemann, C., Sarawat, V., Sundaresan, K.,
and O. Vautrin, "Deterministic Address Mapping to Reduce
Logging in Carrier-Grade NAT Deployments", RFC 7422,
DOI 10.17487/RFC7422, December 2014,
<https://www.rfc-editor.org/rfc/rfc7422>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/rfc/rfc7510>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/rfc/rfc7665>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/rfc/rfc7799>.
[RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
RFC 7806, DOI 10.17487/RFC7806, April 2016,
<https://www.rfc-editor.org/rfc/rfc7806>.
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[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <https://www.rfc-editor.org/rfc/rfc8100>.
[RFC8299] Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
"YANG Data Model for L3VPN Service Delivery", RFC 8299,
DOI 10.17487/RFC8299, January 2018,
<https://www.rfc-editor.org/rfc/rfc8299>.
[RFC8355] Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R.
Shakir, "Resiliency Use Cases in Source Packet Routing in
Networking (SPRING) Networks", RFC 8355,
DOI 10.17487/RFC8355, March 2018,
<https://www.rfc-editor.org/rfc/rfc8355>.
[RFC8466] Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
Data Model for Layer 2 Virtual Private Network (L2VPN)
Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
2018, <https://www.rfc-editor.org/rfc/rfc8466>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/rfc/rfc8641>.
[RFC8969] Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and
L. Geng, "A Framework for Automating Service and Network
Management with YANG", RFC 8969, DOI 10.17487/RFC8969,
January 2021, <https://www.rfc-editor.org/rfc/rfc8969>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/rfc/rfc8986>.
[RFC9182] Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model
for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182,
February 2022, <https://www.rfc-editor.org/rfc/rfc9182>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/rfc/rfc9256>.
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[RFC9291] Boucadair, M., Ed., Gonzalez de Dios, O., Ed., Barguil,
S., and L. Munoz, "A YANG Network Data Model for Layer 2
VPNs", RFC 9291, DOI 10.17487/RFC9291, September 2022,
<https://www.rfc-editor.org/rfc/rfc9291>.
[RFC9330] Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G.
White, "Low Latency, Low Loss, and Scalable Throughput
(L4S) Internet Service: Architecture", RFC 9330,
DOI 10.17487/RFC9330, January 2023,
<https://www.rfc-editor.org/rfc/rfc9330>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/rfc/rfc9350>.
[RFC9375] Wu, B., Ed., Wu, Q., Ed., Boucadair, M., Ed., Gonzalez de
Dios, O., and B. Wen, "A YANG Data Model for Network and
VPN Service Performance Monitoring", RFC 9375,
DOI 10.17487/RFC9375, April 2023,
<https://www.rfc-editor.org/rfc/rfc9375>.
[RFC9408] Boucadair, M., Ed., Gonzalez de Dios, O., Barguil, S., Wu,
Q., and V. Lopez, "A YANG Network Data Model for Service
Attachment Points (SAPs)", RFC 9408, DOI 10.17487/RFC9408,
June 2023, <https://www.rfc-editor.org/rfc/rfc9408>.
[RFC9451] Boucadair, M., "Operations, Administration, and
Maintenance (OAM) Packet and Behavior in the Network
Service Header (NSH)", RFC 9451, DOI 10.17487/RFC9451,
August 2023, <https://www.rfc-editor.org/rfc/rfc9451>.
[RFC9516] Mirsky, G., Meng, W., Ao, T., Khasnabish, B., Leung, K.,
and G. Mishra, "Active Operations, Administration, and
Maintenance (OAM) for Service Function Chaining (SFC)",
RFC 9516, DOI 10.17487/RFC9516, November 2023,
<https://www.rfc-editor.org/rfc/rfc9516>.
[RFC9522] Farrel, A., Ed., "Overview and Principles of Internet
Traffic Engineering", RFC 9522, DOI 10.17487/RFC9522,
January 2024, <https://www.rfc-editor.org/rfc/rfc9522>.
[TR-GSTR-TN5G]
ITU-T, "Technical Report GSTR-TN5G", February 2018,
<https://www.itu.int/dms_pub/itu-t/opb/tut/T-TUT-HOME-
2018-PDF-E.pdf>.
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[TS-23.501]
3GPP, "TS 23.501: System architecture for the 5G System
(5GS)", 2021,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS-28.530]
3GPP, "TS 23.530: Management and orchestration; Concepts,
use cases and requirements)", 2023,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
[_5G-Book] Peterson, L., Sunay, O., and B. Davie, "5G Mobile
Networks: A Systems Approach", 2022,
<https://5g.systemsapproach.org/>.
Appendix A. Acronyms and Abbreviations
3GPP: 3rd Generation Partnership Project
5GC: 5G Core
5QI: 5G QoS Indicator
A2A: Any-to-Any
AC: Attachment Circuit
AMF: Access and Mobility Management Function
AUSF: Authentication Server Function
BBU: Baseband Unit
BH: Backhaul
BS: Base Station
CE: Customer Edge
CIR: Committed Information Rate
CN: Core Network
CoS: Class of Service
CP: Control Plane
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CSP: Communication Service Provider
CU: Centralized Unit
CU-CP: Centralized Unit Control Plane
CU-UP: Centralized Unit User Plane
DC: Data Center
DDoS: Distributed Denial of Services
DN: Data Network
DSCP: Differentiated Services Code Point
DU: Distributed Unit
eCPRI: enhanced Common Public Radio Interface
FH: Fronthaul
FIB: Forwarding Information Base
GPRS: Generic Packet Radio Service
gNB: gNodeB
GTP: GPRS Tunneling Protocol
GTP-U: GPRS Tunneling Protocol User plane
HW: Hardware
ID: Identifier
IGP: Interior Gateway Protocol
L2VPN: Layer 2 Virtual Private Network
L3VPN: Layer 3 Virtual Private Network
LSP: Label Switched Path
MH: Midhaul
MIoT: Massive Internet of Things
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MPLS: Multiprotocol Label Switching
NF: Network Function
NR: New Radio
NRF: Network Function Repository
NRP: Network Resource Partition
NSC: Network Slice Controller
PE: Provider Edge
PIR: Peak Information Rate
PLMN: Public Land Mobile Network
PSTN: Public Switched Telephony Network
QoS: Quality of Service
RAN: Radio Access Network
RF: Radio Frequency
RIB: Routing Information Base
RSVP: Resource Reservation Protocol
RU: Radio Unit
SD: Slice Differentiator
SDP: Service Demarcation Point
SLA: Service Level Agreement
SLO: Service Level Objective
SMF: Session Management Function
S-NSSAI: Single Network Slice Selection Assistance Information
SST: Slice/Service Type
SR: Segment Routing
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SRv6: Segment Routing version 6
TC: Traffic Class
TE: Traffic Engineering
TN: Transport Network
TS: Technical Specification
UDM: Unified Data Management
UE: User Equipment
UP: User Plane
UPF: User Plane Function
URLLC: Ultra Reliable Low Latency Communication
VLAN: Virtual Local Area Network
VNF: Virtual Network Function
VPN: Virtual Private Network
VRF: Virtual Routing and Forwarding
VXLAN: Virtual Extensible Local Area Network
Appendix B. An Overview of 5G Networking
This section provides a brief introduction to 5G mobile networking
with a perspective on the Transport Network. This section does not
intend to replace or define 3GPP architecture, instead its objective
is to provide an overview for readers that do not have a mobile
background. For more comprehensive information, refer to
[TS-23.501].
B.1. Key Building Blocks
[TS-23.501] defines the Network Functions (UPF, AMF, etc.) that
compose the 5G System (5GS) Architecture together with related
interfaces (e.g., N1, N2). This architecture has native Control and
User Plane separation, and the Control Plane leverages a service-
based architecture. Figure 33 outlines an example 5GS architecture
with a subset of possible network functions and network interfaces.
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┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐
│NSSF │ │ NEF │ │ NRF │ │ PCF │ │ UDM │ │ AF │
└──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘
Nnssf│ Nnef│ Nnrf│ Npcf│ Nudm│ │Naf
───┴────────┴──┬─────┴──┬───────┴───┬────┴────────┴────
Nausf│ Namf│ Nsmf│
┌──┴──┐ ┌──┴──┐ ┌──┴──────┐
│AUSR │ │ AMF │ │ SMF │
└─────┘ └──┬──┘ └──┬──────┘
╱ │ │ ╲
Control Plane N1 ╱ │N2 │N4 ╲N4
════════════════════════════════════════════════════════════
User Plane ╱ │ │ ╲
┌───┐ ┌──┴──┐ N3 ┌──┴──┐ N9 ┌─────┐ N6 .───.
│UE ├──┤(R)AN├─────┤ UPF ├────┤ UPF ├────( DN )
└───┘ └─────┘ └─────┘ └─────┘ `───'
Figure 33: 5GS Architecture and Service-based Interfaces
Similar to previous versions of 3GPP mobile networks [RFC6459], a 5G
mobile network is split into the following four major domains
(Figure 34):
* UE, MS, MN, and Mobile:
The terms UE (User Equipment), MS (Mobile Station), MN (Mobile
Node), and mobile refer to the devices that are hosts with the
ability to obtain Internet connectivity via a 3GPP network. An MS
is comprised of the Terminal Equipment (TE) and a Mobile Terminal
(MT). The terms UE, MS, MN, and mobile are used interchangeably
within this document.
* Radio Access Network (RAN):
Provides wireless connectivity to the UE devices via radio. It is
made up of the Antenna that transmits and receives signals to the
UE and the Base Station that digitizes the signal and converts the
RF data stream to IP packets.
* Core Network (CN):
Controls the CP of the RAN and provides connectivity to the Data
Network (e.g., the Internet or a private VPN). The Core Network
hosts dozens of services such as authentication, phone registry,
charging, access to PSTN and handover.
* Transport Network (TN):
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Provides connectivity between 5G Network Functions. The TN may
provide connectivity from the RAN to the Core Network, as well as
within the RAN or within the CN. The traffic generated by NFs is
- mostly - based on IP or Ethernet.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
│ ┌────────────┐ ┌────────────┐
│ │ │ │ │
│ ┌────┐ │ │ │ │ .───────.
│ UE ├──────┤ RAN │ │ CN ├────( DN )
│ └────┘ │ │ │ │ `───────'
│ │ │ │ │
│ └──────┬─────┘ └──────┬─────┘
│ │ │
│ │ │
│ │ │
│ ┌─────┴─────────────────┴────┐
│ │ │
│ │ │
│ Transport Network │ │
│ │ │
│ │ │
│ └────────────────────────────┘
│
│ 5G System
│
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 34: Building Blocks of 5G Architecture (A High-Level
Representation)
B.2. Core Network (CN)
The 5G Core Network (5GC) is made up of a set of NFs which fall into
two main categories (Figure 35):
* 5GC User Plane:
The User Plane Function (UPF) is the interconnect point between
the mobile infrastructure and the Data Network (DN). It
interfaces with the RAN via the N3 interface by encapsulating/
decapsulating the User Plane Traffic in GTP Tunnels (aka GTP-U or
Mobile User Plane).
* 5GC Control Plane:
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The 5G Control Plane is made up of a comprehensive set of Network
Functions. An exhaustive list and description of these entities
is out of the scope of this document. The following NFs and
interfaces are worth mentioning, since their connectivity may rely
on the Transport Network:
- the AMF (Access and Mobility Function) connects with the RAN
control plane over the N2 interface
- the SMF controls the 5GC UPF via the N4 interface
┌ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
RAN 5G Core (5GC)
│ │ │ │
│ │ │ [AUSF] [NRF] [UDM] etc. │
│ │ │ (Service Based) │
( Architecture)
│ │ │ │
N2 ┌─────┐ N11 ┌─────┐
│ CP ───────────┤ AMF ├─────┤ SMF │ │
└─────┘ └──┬──┘
│ │ │ │ │
│ Control Plane
═══════════════════════════════════════════════════════════
│ User Plane
│ │ │ │ N4 │
N3 ┌──┴──┐ N6 .───────.
│ UP ───────────────────────┤ UPF ├───────>( DN )
└─────┘ `───────'
│ │ │ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 35: 5G Core Network (CN)
B.3. Radio Access Network (RAN)
The RAN connects cellular wireless devices to a mobile Core Network.
The RAN is made up of three components, which form the Radio Base
Station:
* The Baseband Unit (BBU) provides the interface between the Core
Network and the Radio Network. It connects to the Radio Unit and
is responsible for the baseband signal processing to packet.
* The Radio Unit (RU) is located close to the Antenna and controlled
by the BBU. It converts the Baseband signal received from the BBU
to a Radio frequency signal.
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* The Antenna converts the electric signal received from the RU to
radio waves
The 5G RAN Base Station is called a gNodeB (gNB). It connects to the
Core Network via the N3 (User Plane) and N2 (Control Plane)
interfaces.
The 5G RAN architecture supports RAN disaggregation in various ways.
Notably, the BBU can be split into a DU (Distributed Unit) for
digital signal processing and a CU (Centralized Unit) for RAN Layer 3
processing. Furthermore, the CU can be itself split into Control
Plane (CU-CP) and User Plane (CU-UP).
Figure 36 depicts a disaggregated RAN with NFs and interfaces.
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┌─────────────────────────────────┐ ┌ ─ ─ ─ ─ ─ ┐
│ │ N3
┌────┐ NR │ ├────┤ 5G Core │
│ UE ├──────┤ gNodeB │
└────┘ │ ├────┤ (5GC) │
│ │ N2
└─────────────────────────────────┘ └ ─ ─ ─ ─ ─ ┘
│ │
│ │
│ │
─┘ └─
╲ ╱
╲ ╱
V
┌─────────────────────────────────┐ ┌ ─ ─ ─ ─ ─ ┐
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
│ │ │ │
┌────┐ NR │ ┌────┐ F2 │┌────┐ F1-U ┌─────┐│ │ N3 ┌─────┐
│ UE ├────────┤ RU ├─────┤ DU ├──────┤CU-UP├──────────┤ UPF │ │
└────┘ │ └────┘ │└────┘ └──┬──┘│ │ └─────┘
│ ╲ │ │ │ │
│ │ ╲ │ │ │
│ ╲ │ │ │ │
│ │ ╲ │E1 │ │
│ F1-C ╲ │ │ │ │
│ │ ╲ │ │ │
│ ╲ │ │ │ │
│ │ ╲ │ │ │
│ ┌──┴──┐ │ N2 │ ┌─────┐ │
│ │ │CU-CP├──────────┤ AMF │
│ └─────┘ │ │ └─────┘ │
│ │ │ │
│ BBU split │ │ 5G Core │
│ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ │
│ │ │ (5GC) │
│ disaggregated gNodeB │
└─────────────────────────────────┘ └ ─ ─ ─ ─ ─ ┘
Figure 36: RAN Disaggregation
B.4. Transport Network (TN)
The 5G transport architecture defines three main segments for the
Transport Network, which are commonly referred to as Fronthaul (FH),
Midhaul (MH), and Backhaul (BH) [TR-GSTR-TN5G]:
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* Fronthaul happens before the BBU processing. In 5G, this
interface is based on eCPRI (Enhanced CPRI) with native Ethernet
or IP encapsulation.
* Midhaul is optional: this segment is introduced in the BBU split
presented in Appendix B.3, where Midhaul network refers to the DU-
CU interconnection (i.e., F1 interface). At this level, all
traffic is encapsulated in IP (signaling and user plane).
* Backhaul happens after BBU processing. Therefore, it maps to the
interconnection between the RAN and the Core Network. All traffic
is also encapsulated in IP.
Figure 37 illustrates the different segments of the Transport Network
with the relevant Network Functions.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
│ Transport Network │
│ │
TN Segment 1 TN Segment 2 TN Segment 3
│ (Fronthaul) (Midhaul) (Backhaul) │
┌───────────┐ ┌────────────┐ ┌───────────┐
│ │ │ │ │ │ │ │
─ ┼ ─ ─ ─ ─ ─ ┼ ┼ ─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─
┌─┴──┐ ┌─┴─┴┐ ┌─┴─┴┐ ┌──┴──┐ .───.
│ RU │ │ DU │ │ CU │ │ UPF ├────( DN )
└────┘ └────┘ └────┘ └─────┘ `───'
Figure 37: 5G Transport Segments
It is worth mentioning that a given part of the transport network can
carry several 5G transport segments concurrently, as outlined in
Figure 38. This is because different types of 5G network functions
might be placed in the same location (e.g., the UPF from one slice
might be placed in the same location as the CU-UP from another
slice).
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┌ ─ ─ ─ ─ ┐
┌────┐ Colocated
││RU-1│ │ RU/DU
└─┬──┘
│ │ FH-1 │
┌─┴──┐
││DU-1│ │ ┌────┐ ┌─────┐ .───.
└─┬──┘ │CU-1│ │UPF-1├────────( DN )
└ ─│─ ─ ─ ┘ └─┬─┬┘ └─┬───┘ `───'
┌ ─│─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ MH-1 │ │ BH-1 │ Transport Network │
│ └───────────┘ └────────────┘
┌───────────┐ ┌────────────┐ ┌───────────┐ │
│ │ FH-2 │ │ MH-2 │ │ BH-2 │
─ ┼ ─ ─ ─ ─ ─ ┼ ┼ ─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ┘
┌─┴──┐ ┌─┴─┴┐ ┌─┴─┴┐ ┌─┴───┐ .───.
│RU-2│ │DU-2│ │CU-2│ │UPF-2├────( DN )
└────┘ └────┘ └────┘ └─────┘ `───'
Figure 38: Concurrent 5G Transport Segments
Acknowledgments
The authors would like to thank Adrian Farrel, Joel Halpern, Tarek
Saad, Jie Dong, Greg Mirsky, Rüdiger Geib, Nicklous D. Morris,
Daniele Ceccarelli, and Bo Wu for their review of this document and
for providing valuable comments.
Thanks to Alvaro Retana for the rtg-dir review, Yoshifumi Nishida for
the tsv-art review, and Timothy Winters for the int-dir review.
Contributors
John Drake
Juniper Networks
Sunnyvale,
United States of America
Email: jdrake@juniper.net
Ivan Bykov
Ribbon Communications
Tel Aviv
Israel
Email: ivan.bykov@rbbn.com
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Reza Rokui
Ciena
Ottawa
Canada
Email: rrokui@ciena.com
Luay Jalil
Verizon
Dallas, TX,
United States of America
Email: luay.jalil@verizon.com
Beny Dwi Setyawan
XL Axiata
Jakarta
Indonesia
Email: benyds@xl.co.id
Amit Dhamija
Rakuten
Bangalore
India
Email: amit.dhamija@rakuten.com
Mojdeh Amani
British Telecom
London
United Kingdom
Email: mojdeh.amani@bt.com
Authors' Addresses
Krzysztof G. Szarkowicz (editor)
Juniper Networks
Wien
Austria
Email: kszarkowicz@juniper.net
Richard Roberts (editor)
Juniper Networks
Rennes
France
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Email: rroberts@juniper.net
Julian Lucek
Juniper Networks
London
United Kingdom
Email: jlucek@juniper.net
Mohamed Boucadair (editor)
Orange
France
Email: mohamed.boucadair@orange.com
Luis M. Contreras
Telefonica
Ronda de la Comunicacion, s/n
Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com/
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