Considerations for defining a Transport Slice NBI
draft-contreras-teas-slice-nbi-02
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| Authors | Luis M. Contreras , Shunsuke Homma , Jose A. Ordonez-Lucena | ||
| Last updated | 2020-07-13 | ||
| Replaced by | draft-ietf-teas-ietf-network-slice-use-cases | ||
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draft-contreras-teas-slice-nbi-02
TEAS Working Group LM. Contreras
Internet-Draft Telefonica
Intended status: Informational S. Homma
Expires: January 14, 2021 NTT
J. Ordonez-Lucena
Telefonica
July 13, 2020
Considerations for defining a Transport Slice NBI
draft-contreras-teas-slice-nbi-02
Abstract
The transport network is an essential component in the end-to-end
delivery of services and, consequently, with the advent of network
slicing it is necessary to understand what could be the way in which
the transport network is consumed as a slice. This document analyses
the needs of potential transport slice customers (i.e., use cases) in
order to identify the functionality required on the North Bound
Interface (NBI) of a transport slice controller for satisfying such
transport slice requests.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Northbound interface for transport slices . . . . . . . . . . 3
4. Transport slice use cases . . . . . . . . . . . . . . . . . . 4
4.1. 5G Services . . . . . . . . . . . . . . . . . . . . . . . 4
4.1.1. Generic network Slice Template . . . . . . . . . . . 5
4.1.2. Categorization of GST attributes . . . . . . . . . . 6
4.1.2.1. Attributes with direct impact on the transport
slice definition . . . . . . . . . . . . . . . . 7
4.1.2.2. Attributes with indirect impact on the transport
slice definition . . . . . . . . . . . . . . . . 7
4.1.2.3. Attributes with no impact on the transport slice
definition . . . . . . . . . . . . . . . . . . . 8
4.1.3. Provisioning procedures . . . . . . . . . . . . . . . 9
4.2. NFV-based services . . . . . . . . . . . . . . . . . . . 9
4.2.1. Connectivity attributes . . . . . . . . . . . . . . . 10
4.2.2. Provisioning procedures . . . . . . . . . . . . . . . 10
4.3. Network sharing . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
A number of new technologies, such as 5G, NFV and SDN are not only
evolving the network from a pure technological perspective but also
are changing the concept in which new services are offered to the
customers [I-D.homma-slice-provision-models] by introducing the
concept of network slicing.
The transport network is an essential component in the end-to-end
delivery of services and, consequently, it is necessary to understand
what could be the way in which the transport network is consumed as a
slice. For a definition of transport slice refer to
[I-D.nsdt-teas-transport-slice-definition].
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In this document it is assumed that there exists a (logically)
centralized component in the transport network, namely Transport
Slice Controller (TSC) with the responsibilities on the control and
management of the transport slices invoked for a given service, as
requested by Transport Slice customers.
This document analyses different use cases deriving the needs of
potential transport slice customers in order to identify the
functionality required on the North Bound Interface (NBI) of the TSC
to be exposed towards such transport slice customers. Solutions to
construct the requested transport slices are out of scope of this
document.
This document addresses some of the discussions of the TEAS Slice
Design Team. However, it is not at this stage an official outcome of
the Design Team.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
3. Northbound interface for transport slices
In a general manner, the transport network supports different kinds
of services. These services consume capabilities provided by the
transport network for deploying end-to-end services, interconnecting
network functions or applications spread across the network and
providing connectivity toward the final users of these services.
Under the slicing approach, a transport slice customer requests to a
transport slice controller a slice with certain characteristics and
parametrization. Such request it is assumed here to be done through
a NBI exposed by the TSC to the customer, as reflected in Fig. 1.
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+--------------------+
| |
| Transport |
| Slice Customer |
| |
+--------------------+
A
|
| Transport
| Slice
| NBI
|
V
+--------------------+
| |
| Transport |
| Slice Controller |
| |
+--------------------+
Figure 1: Transport slice NBI concept
The functionality supported by the NBI depends on the requirements
that the slice customer has to satisfy. It is then important to
understand the needs of the slice customers as well as the way of
expressing them.
4. Transport slice use cases
Different use cases for slice customers can be identified, as
described in the following sections.
4.1. 5G Services
5G services natively rely on the concept of network slicing. 5G is
expected to allow vertical customers to request slices in such a
manner that the allocated resources and capabilities in the network
appear as dedicated for them.
In network slicing scenarios, a vertical customer requests a network
operator to allocate a network slice instance (NSI) satisfying a
particular set of service requirements. The content/format of these
requirements are highly dependent on the networking expertise and use
cases of the customer under consideration. To deal with this
heterogeneity, it is fundamental for the network operator to define a
a unified ability to interpret service requirements from different
vertical customers, and to represent them in a common language, with
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the purposes of facilitating their translation/mapping into specific
slicing-aware network configuration actions. In this regard, model-
based network slice descriptors built on the principles of
reproducibility, reusability and customizability can be defined for
this end.
As a starting point for such a definition, GSMA developed the idea of
having a universal blueprint that, being offered by network
operators, can be used by any vertical customer to order the
deployment of an NSI based on a specific set of service requirements.
The result of this work has been the definition of a baseline network
slice descriptor called Generic network Slice Template (GST). The
GST contains multiple attributes that can be used to characterize a
network slice. A Network Slice Type (NEST) describes the
characteristics of a network slice by means of filling GST attributes
with values based on specific service requirements. Basically, a
NEST is a filled-in version of a GST. Different NESTs allow
describing different types of network slices. For slices based on
standardized service types, e.g. eMBB, uRLLC and mIoT, the network
operator may have a set of readymade, standardized NESTs (S-NESTs).
For slices based on specific industry use cases, the network operator
can define additional NESTs.
Service requirements from a given vertical customer are mapped to a
NEST, which provides a self-contained description of the network
slice to be provisioned for that vertical customer. According to
this reasoning, the NEST can be used by the network operator as input
to the NSI preparation phase, which is defined in [TS28.530]. 3GPP is
working on the translation of the GST/NEST attributes into NSI
related requirements, which are defined in the "ServiceProfile" data
type from the Network Slice Information Object Class (IOC) in
[TS28.541]. These requirements are used by the 3GPP Management
System to allocate the NSI across all network domains, including
transport network. The transport slice defines the part of that NSI
that is deployed across the transport network.
Despite the translation is an on-going work in 3GPP it seems
convenient to start looking at the GST attributes to understand what
kind of parameters could be required for the transport slice NBI.
4.1.1. Generic network Slice Template
The structure of the GST is defined in [GSMA]. The template defines
a total of 35 attributes. For each of them, the following
information is provided:
o Attribute definition, which provides a formal definition of what
the attribute represents.
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o Attribute parameters, including:
* Value, e.g. integer, float.
* Measurement unit, e.g. milliseconds, Gbps
* Example, which provides examples of values the parameter can
take in different use cases.
* Tag, which allow describing the type of parameter, according to
its semantics. An attribute can be tagged as a
characterization attribute or a scalability attribute. If it
is characterization attribute, it can be further tagged as a
performance-related attribute, a functionality-related
attribute or an operation-related attribute.
* Exposure, which allow describing how this attribute interact
with the slice customer, either as an API or a KPI.
o Attribute presence, either mandatory, conditional or optional.
Attributes from GST can be used by the network operator (slice
controller) and a vertical customer (slice customer) to agree SLA.
GST attributes are generic in the sense that they can be used to
characterize different types of network slices. Once those
attributes become filled with specific values, it becomes a NEST
which can be ordered by slice customers.
4.1.2. Categorization of GST attributes
Not all the GST attributes as defined in [GSMA] have impact in the
transport network since some of them are specific to either the radio
or the mobile core part.
In the analysis performed in this document, the attributes have been
categorized as:
o Directly impactive attributes, which are those that have direct
impact on the definition of the transport slice, i.e., attributes
that can be directly translated into requirements required to be
satisfied by a transport slice.
o Indirectly impactive attributes, which are thise that impact in an
indirect manner on the definition of the transport slice, i.e.,
attributes that indirectly impose some requirements to a transport
slice.
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o Non-impactive attributes, that are those which do not have impact
on the transport slice at all.
The following sections describe the attributes falling into the three
categories.
4.1.2.1. Attributes with direct impact on the transport slice
definition
The following attributes impose requirements in the transport slice
o Availability
o Deterministic communication
o Downlink throughput per network slice
o Energy efficiency
o Group communication support
o Isolation level
o Maximum supported packet size
o Mission critical support
o Performance monitoring
o Slice quality of service parameters
o Support for non-IP traffic
o Uplink throughput per network slice
o User data access (i.e., tunneling mechanisms)
4.1.2.2. Attributes with indirect impact on the transport slice
definition
The following attributes indirectly impose requirements in the
transport slice to support the end-to-end service.
o Area of service (i.e., the area where terminals can access a
particular network slice)
o Delay tolerance (i.e., if the service can be delivered when the
system has sufficient resources)
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o Downlink (maximum) throughput per UE
o Network functions owned by Network Slice Customer
o Maximum number of (concurrent) PDU sessions
o Performance prediction (i.e., capability to predict the network
and service status)
o Root cause investigation
o Session and Service Continuity support
o Simultaneous use of the network slice
o Supported device velocity
o UE density
o Uplink (maximum) throughput per UE
o User management openness (i.e., capability to manage users'
network services and corresponding requirements)
o Latency from (last) UPF to Application Server
4.1.2.3. Attributes with no impact on the transport slice definition
The following attributes do not impact the transport slice.
o Location based message delivery (not related to the geographical
spread of the network slice itself but with the localized
distribution of information)
o MMTel support, i.e. support of and Multimedia Telephony Service
(MMTel)as well as IP Multimedia Subsystem (IMS) support.
o NB-IoT Support, i.e., support of NB-IoT in the RAN in the network
slice.
o Maximum number of (simultaneous) UEs
o Positioning support
o Radio spectrum
o Synchronicity (among devices)
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o V2X communication mode
o Network Slice Specific Authentication and Authorization (NSSAA)
4.1.3. Provisioning procedures
3GPP identifies in [TS28.531] a number of procedures for the
provisioning of a network slice in general. It can be assumed that
similar procedures may also apply to a transport slice, facilitating
a consistent management and control of end-to-end slices.
The envisioned procedures are the following:
o Slice instance allocation: this procedure permits to create a new
slice instance (or reuse an existing one).
o Slice instance de-allocation: this procedure decommissions a
previously instantiated slice.
o Slice instance modification: this procedure permits the change in
the characteristics of an existing slice instance.
o Get slice instance status: this procedure helps to retrieve run-
time information on the status of a deployed slice instance.
o Retrieval of slice capabilities: this procedure assists on getting
information about the capabilities (e.g. maximum latency
supported).
All these procedures fit in the operation of transport network
slices.
4.2. NFV-based services
NFV technology allows the flexible and dynamic instantiation of
virtualized network functions (and their composition into network
services) on top of a distributed, cloud-enabled compute
infrastructure. This infrastructure can span across different points
of presence in a carrier network. By leveraging on transport network
slicing, connectivity services established across geographically
remote points of presence can be enriched by providing additional QoS
guarantees with respect present state-of-the-art mechanisms, as
conventional L2/L3 VPNs.
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4.2.1. Connectivity attributes
The connectivity services are expressed through a number of
attributes as listed:
o Incoming and outgoing bandwidth: bandwidth required for the
connectivity services (in Mbps).
o Qos metrics: set of metrics (e.g., cost, latency and delay
variation) applicable to a specific connectivity service
o Directionality: indication if the traffic is unidirectional or
bidirectional.
o MTU: value of the largest PDU to be transmitted in the
connectivity service.
o Protection scheme: indication of the kind of protection to be
performed (e.g., 1;1, 1+1, etc.)
o Connectivity mode: indication of the service is point-to-point of
point-to-multipoint
All those attributes will assist on the characterization of the
connectivity slice to be deployed, and thus, are relevant for the
definition of a transport slice supporting such connectivity.
4.2.2. Provisioning procedures
ETSI NFV defines the role of WAN Infrastructure Manager (WIM) as the
component in charge of managing and controlling the connectivity
external to the PoPs. In [IFA032] a number of interfaces are
identified to be exposed by the WIM for supporting the multi-site
connectivity, thus representing the capabilities expected for a
transport network slice, as well, in case of satisfying such
connectivity needs by means of the slice concept.
The interfaces considered are the following:
o Multi-Site Connectivity Service (MSCS) Management: this interface
permits the creation, termination, update and query of MSCSs,
including reservation. It also enables subscription for
notifications and information retrieval associated to the
connectivity service.
o Capacity Management: this interface allows querying about the
capacity (e.g. bandwidth), topology, and network edge points of
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the connectivity service, as well as about information of consumed
and available capacity on the underlying network resources.
o Fault Management: this interface serves for the provision of
alarms related to the MSCSs.
o Performance Management: this interface assists on the retrieval of
performance information (measurement results collection and
notifications) related to MSCSs.
4.3. Network sharing
To be done.
5. Security Considerations
This draft does not include any security considerations.
6. IANA Considerations
This draft does not include any IANA considerations
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[GSMA] "Generic Network Slice Template, version 3.0", NG.116 ,
May 2020.
[I-D.homma-slice-provision-models]
Homma, S., Nishihara, H., Miyasaka, T., Galis, A., OV, V.,
Lopez, D., Contreras, L., Ordonez-Lucena, J., Martinez-
Julia, P., Qiang, L., Rokui, R., Ciavaglia, L., and X.
Foy, "Network Slice Provision Models", draft-homma-slice-
provision-models-02 (work in progress), November 2019.
[I-D.nsdt-teas-transport-slice-definition]
Rokui, R., Homma, S., Makhijani, K., Contreras, L., and J.
Tantsura, "IETF Definition of Transport Slice", draft-
nsdt-teas-transport-slice-definition-03 (work in
progress), July 2020.
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[IFA032] "IFA032 Interface and Information Model Specification for
Multi-Site Connectivity Services V3.2.1.", ETSI GS NFV-IFA
032 V3.2.1 , April 2019.
[TS28.530]
"TS 28.530 Management and orchestration; Concepts, use
cases and requirements (Release 16) V16.0.0.", 3GPP TS
28.530 V16.0.0 , September 2019.
[TS28.541]
"TS 28.541 Management and orchestration; 5G Network
Resource Model (NRM); Stage 2 and stage 3 (Release 16)
V16.2.0.", 3GPP TS 28.541 V16.2.0 , September 2019.
Authors' Addresses
Luis M. Contreras
Telefonica
Ronda de la Comunicacion, s/n
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com/
Shunsuke Homma
NTT
Japan
Email: shunsuke.homma.fp@hco.ntt.co.jp
Jose A. Ordonez-Lucena
Telefonica
Ronda de la Comunicacion, s/n
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: joseantonio.ordonezlucena@telefonica.com
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