DMM Working Group U. Chunduri, Ed.
Internet-Draft R. Li
Intended status: Standards Track Huawei USA
Expires: January 16, 2019 J. Tantsura
Nuage Networks
July 15, 2018
Transport Network aware Mobility for 5G
draft-clt-dmm-tn-aware-mobility-00
Abstract
This document specifies a framework and a mapping function for 5G
mobile user plane with transport network slicing, integrated with
Mobile Radio Access and a Virtualized Core Network. The integrated
approach specified in a way to address all the mobility scenarios
defined in [TS23.501] and to be backward compatible with LTE
[TS23.401] network deployments.
It focuses on an optimized mobile user plane functionality with
various transport services needed for some of the 5G traffic needing
low and deterministic latency, real-time, mission-critical services.
This document describes, how this objective is achieved agnostic to
the transport underlay used (IPv4, IPv6, MPLS) in various deployments
and with a new transport network underlay routing, called Preferred
Path Routing (PPR).
Requirements Language
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 16, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . 3
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Solution Approach . . . . . . . . . . . . . . . . . . . . 4
2. Transport Network (TN) and Slice aware Mobility on N3/N9 . . 5
2.1. Discrete Approach . . . . . . . . . . . . . . . . . . . . 6
2.2. Integrated Approach . . . . . . . . . . . . . . . . . . . 7
3. Using PPR as TN Underlay . . . . . . . . . . . . . . . . . . 9
3.1. PPR with Transport Slicing aware Mobility on N3/N9 . . . 9
3.2. Path Steering Support to native IP user planes . . . . . 11
3.3. Service Level Guarantee in Underlay . . . . . . . . . . . 11
3.4. PPR with various 5G Mobility procedures . . . . . . . . . 11
3.4.1. SSC Mode1 . . . . . . . . . . . . . . . . . . . . . . 11
3.4.2. SSC Mode2 . . . . . . . . . . . . . . . . . . . . . . 12
3.4.3. SSC Mode3 . . . . . . . . . . . . . . . . . . . . . . 13
4. Other TE Technologies Applicability . . . . . . . . . . . . . 14
5. New Control Plane and User Planes . . . . . . . . . . . . . . 14
5.1. LISP and PPR . . . . . . . . . . . . . . . . . . . . . . 14
5.2. ILA and PPR . . . . . . . . . . . . . . . . . . . . . . . 15
6. Summary and Benefits with PPR . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction and Problem Statement
3GPP Release 15 for 5GC is defined in [TS.23.501-3GPP],
[TS.23.502-3GPP], [TS.23.503-3GPP]. A new user plane interface N9
[TS.23.501-3GPP] has been created between 2 User Plane
Functionalities (UPFs). While user plane for N9 interface being
finalized for REL16, both GTP-U based encapsulation or any other
compatible approach is being considered [CT4SID]. Concerning to this
document another relevant interface is N3, which is between gNB and
the UPF. N3 interface is similar to the user plane interface S1U in
LTE [TS 23.401]. This document:
o does not propose any change to existing N3 user plane
encapsulations to realize the benefits with the approach specified
here
o and can work with any encapsulation (including GTP-U) for the N9
interface.
[TS.23.501-3GPP] defines various Session and Service Continuity (SSC)
modes and mobility scenarios for 5G with slice awareness from Radio
and 5G Core (5GC) network. 5G System (5GS) as defined, allows
transport network between N3 and N9 interfaces work independently
with various IETF Traffic Engineering (TE) technologies.
However, lack of underlying Transport Network (TN) awareness can be
problematic for some of the 5GS procedures, for real-time, mission-
critical or for any deterministic latency services. These 5GS
procedures including but not limited to Service Request, PDU Session,
or User Equipment (UE) mobility need same service level
characteristics from the TN for the Protocols Data Unit (PDU)
session, similar to as provided in Radio and 5GC for various 5QI's
defined in [TS.23.501-3GPP] .
1.1. Acronyms
5QI - 5G QoS Indicator
AMF - Access and Mobility Management Function (5G)
BP - Branch Point (5G)
CSR - Cell Site Router
DN - Data Network (5G)
FRR - Fast ReRoute
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gNB - 5G NodeB
GBR - Guaranteed Bit Rate (5G)
IGP - Interior Gateway Protocols (e.g. IS-IS, OSPFv2, OSPFv3)
MPLS - Multi Protocol Label Switching
QFI - QoS Flow ID (5G)
PPR - Preferred Path Routing
PDU - Protocol Data Unit (5G)
PW - Pseudo Wire
RQI - Reflective QoS Indicator (5G)
SBI - Service Based Interface (5G)
SID - Segment Identifier
SMF - Session Management Function (5G)
SSC - Session and Service Continuity (5G)
SST - Slice and Service Types (5G)
SR - Segment Routing
TE - Traffic Engineering
ULCL - Uplink Classifier (5G)
UPF - User Plane Function (5G)
1.2. Solution Approach
This document specifies a mechanism to fulfil the needs of 5GS to
transport user plane traffic from gNB to UPF for all service
continuity modes [TS.23.501-3GPP] in an optimized fashion. This is
done by, keeping mobility procedures aware of underlying transport
network along with slicing requirements. TN with mobility awareness
described here in a way, which does not erase performance and latency
gains made with 5G New Radio(5GNR) and virtualized cellular core
network features developed in [TS.23.501-3GPP].
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Section 2 describes two methods, with which Transport Network (TN)
aware mobility can be built irrespective of underlying TN technology
used. Using Preferred Path Routing (PPR) as TN Underlay is detailed
in Section 3. Section 3.4 further describes the applicability and
procedures of the same with 5G SSC modes on N3 and N9 interfaces.
Applicability of the TN aware mobility for other IETF Technologies
are specified in Section 4. At the end, Section 6 recapitulates the
benefits of specified approach in mobile networks.
2. Transport Network (TN) and Slice aware Mobility on N3/N9
Service Based Interfaces (SBI)
----+-----+-----+----+----+-----+----+--------+-----+----+------
| | | | | | | | | |
+---+---+ | +--+--+ | +--+---+ | +--+--+ +--+--+ | +-+--+
| NSSF | | | NRF | | | AUSF | | | UDM | | NEF | | | AF |
+-------+ | +-----+ | +------+ | +-----+ +-----+ | +----+
+---+----+ +--+--+ +---=++ +--------------+-+
| AMF | | PCF | | TNF | | SMF |
+---+--+-+ +-----+ +-+-+-+ +-+-----------+--+
N1 | | | | To |
to-UE+----+ N2 +----Ns---+ +-Nn-+ N4 +--Nn-+ N4
| | | | | |
+---+---+ +--++ +-+--+---+ +-+-----+ +----+
|gNB+======+CSR+------N3-----+ UPF +-N9--+ UPF +--N6--+ DN |
+---+ +---+ +-+------+ +-------+ +----+
| +----+
+-| DN |
N6 +----+
Figure 1: 5G Service Based Architecture
The above diagrams depicts one of the scenarios of the 5G network
specified in [TS.23.501-3GPP] and with a new and virtualized control
component Transport Network Function (TNF). A Cell Site Router (CSR)
is shown connecting to gNB. Though it is shown as a separate block
from gNB, in some cases both of these can be co-located. This
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document concerns with backhaul TN, from CSR to UPF on N3 interface
or from Staging UPF to Anchor UPF on N9 interface.
Currently specified Control Plane (CP) functions Access and Mobility
Management Function (AMF), Session Management Function (SMF) and User
plane (UP) components gNodeB (gNB), User Plane Function (UPF) with
N2, N3, N4, N6 and N9 are relevant to this document. Other
Virtualized 5G control plane components NRF, AUSF, PCF, AUSF, UDM,
NEF, and AF are not directly relevant for the discussion in this
document and one can see the functionalities of these in
[TS.23.501-3GPP].
N3 interface is similar to S1U in 4G/LTE [TS23.401] network and uses
GTP-U [TS.29.281-3GPP] encapsulation to transport any UE PDUs (IPv4,
IPv6, IPv4v6, Ethernet or Unstructured). N9 interface is a new
interface to connect UPFs in SSC Mode3 Section 3.4.3 and right user
plane protocol/encapsulation is being studied through 3GPP CT4 WG
approved study item [CT4SID] for REL-16.
TN Aware Mobility with optimized transport network functionality
is explained in the below section. How PPR fits in this framework
in detail along with other various TE technologies briefly are
in Section 3 and Section 4 respectively.
2.1. Discrete Approach
In this approach transport network functionality from gNB to UPF is
discrete and 5GS is not aware of the underlying transport network and
the resources available. Deployment specific mapping function is
used to map the GTP-U encapsulated traffic at gNB at UL and UPF in DL
direction to the appropriate transport slice or transport Traffic
Engineered (TE) paths. These TE paths can be established using RSVP-
TE [RFC3209] for MPLS underlay, SR [I-D.ietf-spring-segment-routing]
for both MPLS and IPv6 underlay or PPR
[I-D.chunduri-lsr-isis-preferred-path-routing] with MPLS, IPv6 with
SRH, native IPv6 and native IPv4 underlays.
In this case, the encapsulation provided by GTP-U helps carry
different PDU session types (IPv4, IPv6, IPv4IPv6, Ethernet and
Unstructured) independent of the underlying transport or user plane
(IPv4, IPv6 or MPLS) network. Mapping of the PDU sessions to TE
paths can be done based on the source UDP port ranges (if these are
assigned based on the PDU session QCIs, as done in some deployments
with 4G/LT) of the GTP-U encapsulated packet or based on the 5QI or
RQI values in the GTP-U header. Here, TNF as shown in Figure 1 need
not be part of the 5G Service Based Interface (SBI). Only management
plane functionality is needed to create, monitor, manage and delete
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(life cycle management) the transport TE paths/transport slices from
gNB to UPF (on N3/N9 interfaces). This approach provide partial
inetgration of the transport network into 5GS with some benefits.
One of the limitations of this approach is the inability of 5GS
procedures to know, if underlying transport resources are available
for the traffic type being carried in PDU session before making
certain decisions in the 5G CP. One example scenario/decision could
be, a target gNB selection in Xn mobility in SSC Mode1, without
knowing if the target gNB is having a underlay transport slice
resource for the 5QI of the PDU session. The below approach can
mitigate this.
2.2. Integrated Approach
Network Slice Selection Function (NSSF) as defined in
[TS.23.501-3GPP] concerns with multiple aspects related to creation,
selection, mobility, roaming and co-ordination among other CP
functions in 5GS. However, the scope is only in 5GC (both control
and user plane) and NG Radio Access network including N3IWF for non-
3GPP access. Slice functionality is per PDU session granularity.
While this fully covers needed functionality and resources from UE
registration, Tracking Area (TA) updates, mobility and roaming,
resources and functionalities needed from transport network is not
specified. This is seen as independent functionality though part of
5GS. If transport network is not factored in an integrated fashion
w.r.t available resources (with network characteristics from desired
bandwidth, latency, burst size handling and optionally jitter) some
of the gains made with optimizations through 5GNR and 5GC can be
degraded.
To assuage the above situation, TNF is described (Figure 1) as part
of control plane. This has the view of the underlying transport
network with all links and nodes as well as various possible underlay
paths with different characteristics. TNF can be seen as supporting
PCE functionality [RFC5440] and optionally BGP-LS [RFC7752] to get
the TE and topology information of the underlying IGP network.
A south bound interface Ns is shown which interacts with the gNB/CSR.
'Ns' can use one or more mechanism available today (PCEP [RFC5440],
NETCONF [RFC6241], RESTCONF [RFC8040] or gNMI) to provision the L2/L3
VPNs along with TE underlay paths from gNB to UPF.
These VPNs and/or underlay TE paths MUST be similar on all gNB/CSRs
and UPFs concerned to allow mobility of UEs while associated with one
of the Slice/Service Types (SSTs)as defined in [TS.23.501-3GPP]. A
north bound interface 'Nn' is shown from one or more of the transport
network nodes (or ULCL/BP UPF, Anchor Point UPF) to TNF as shown in
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Figure 1. It would enable learning the TE characteristics of all
links and nodes of the network continuously (through BGP-LS [RFC7752]
or through a passive IGP adjacency and PCEP [RFC5440]).
With the TNF in 5GS Service Based Interface, the following additional
functionalities are required for end-2-end slice management including
the transport network:
o In the Network Slice Selection Assistance Information (NSSAI) PDU
session's assigned transport VPN and the TE path information is
needed.
o For transport slice assignment for various SSTs (eMBB, URLLC,
MIoT) corresponding underlay paths need to be created and
monitored from each transport end point (gNB/CSR and UPF).
o During PDU session creation, apart from radio and 5GC resources,
transport network resources needed to be verified matching the
characteristics of the PDU session traffic type.
o Mapping of PDU session parameters to underlay SST paths need to be
done. One way to do this is through 5QI/QFI information in the
GTP-U header and map the same to the underlying transport path
(including VPN or PW). This works for uplink (UL) direction.
o For downlink direction RQI need to be considered to map the DL
packet to one of the underlay paths at the UPF.
o If any other form of encapsulation (other than GTP-U) either on N3
or N9 corresponding 5QI/QFI or RQI information MUST be there in
the encapsulation header.
o If SSC Mode3 Section 3.4.3 is used, segmented path (gNB to
staging/ULCL/BP-UPF to anchor-point-UPF) with corresponding path
characteristics MUST be used. This includes a path from gNB/CSR
to UL-CL/BP UPF [TS.23.501-3GPP] and UL-CL/BP UPF to eventual UPF
access to DN.
o Continuous monitoring of transport path characteristics and
reassignment at the endpoints MUST be performed. For all the
effected PDU sessions, degraded transport paths need to be updated
dynamically with similar alternate paths.
o During UE mobility event similar to 4G/LTE i.e., gNB mobility (Xn
based or N2 based), for target gNB selection, apart from radio
resources, transport resources MUST be factored. This enables
handling of all PDU sessions from the UE to target gNB and this
require co-ordination of AMF, SMF with the TNF module.
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Changes to detailed signaling to integrate the above for various 5GS
procedures as defined in [TS.23.502-3GPP] is beyond the scope of this
document.
3. Using PPR as TN Underlay
In a network implementing source routing, packets may be transported
through the use of Segment Identifiers (SIDs), where a SID uniquely
identifies a segment as defined in [I-D.ietf-spring-segment-routing].
Section 5.3 [I-D.bogineni-dmm-optimized-mobile-user-plane] lays out
all SRv6 features along with a few concerns in Section 5.3.7 of the
same document. Those concerns are addressed by a new backhaul
routing mechanism called Preferred Path Routing (PPR), of which this
Section provides an overview.
Like SR, PPR uses the concept of identifiers that can be computed by
a controller to create an end to end path. However, unlike SR, the
labels refer not to Segment Identifiers of segments of which the path
is composed, but to the identifier of a path that is deployed on
network nodes. The fact that paths and path identifiers can be
computed and controlled by a controller, not a routing protocol,
allows the deployment of any path that network operators prefer, not
just shortest paths. As packets refer to a path towards a given
destination and nodes make their forwarding decision based on the
identifier of a path, not the identifier of a next segment node, it
is no longer necessary to carry a sequence of labels. This results
in multiple benefits including significant reduction in network layer
overhead, increased performance and hardware compatibility for
carrying both path and services along the path.
Details of the IGP extensions for PPR are provided here:
o IS-IS - [I-D.chunduri-lsr-isis-preferred-path-routing]
o OSPF - [I-D.chunduri-lsr-ospf-preferred-path-routing]
3.1. PPR with Transport Slicing aware Mobility on N3/N9
PPR does not remove GTP-U, unlike some other proposals laid out in
[I-D.bogineni-dmm-optimized-mobile-user-plane]. Instead, PPR works
with the existing cellular user plane (GTP-U) for both N3 and any
approach selected for N9 (encap or no-encap). In this scenario, PPR
will only help providing TE benefits needed for 5G slices from
transport domain perspective. It does so without adding any
additional overhead to the user plane, unlike SR-MPLS or SRv6. This
is achieved by:
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o For 3 different SSTs, 3 PPR-IDs can signaled from any node in the
transport network. For Uplink traffic, gNB will choose the right
PPR-ID of the UPF based on the 5QI value in the encapsulation
header of the PDU session. Similarly in the Downlink direction
matching PPR-ID of the gNB is chosen for the RQI value in the
encapsulated SL payload. The table below shows a typical mapping:
+--------------------------------------------------------------+
| 5QI (Ranges)/ SST Transport Path Transport Path |
| RQI (Ranges) Info Characteristics |
+--------------------------------------------------------------+
| Range Xx - Xy |
| X1, X2 (discrete MIOT PW ID/VPN info, GBR (Guaranteed |
| values) PPR-ID-A Bit Rate) |
| Bandwidth: Bx |
| Delay: Dx |
| Jitter: Jx |
+--------------------------------------------------------------+
| Range Yx - Yy |
| Y1, Y2 (discrete URLLC PW ID/VPN info, GBR with Delay |
| values) PPR-ID-B Req. |
| Bandwidth: By |
| Delay: Dy |
| Jitter: Jy |
+--------------------------------------------------------------+
| Range Zx - Zy |
| Z1, Z2 (discrete EMBB PW ID/VPN info, Non-GBR |
| values) PPR-ID-C Bandwidth: Bx |
+--------------------------------------------------------------+
Figure 2: 5QI/RQI Mapping with PPR-IDs on N3/N9
o It is possible to have a single PPR-ID for multiple input points
through a PPR tree structure separate in UL and DL direction.
o Same set of PPRs are created uniformly across all needed gNBs and
UPFs to allow various mobility scenarios.
o Any modification of TE parameters of the path, replacement path
and deleted path needed to be updated from TNF to the relevant
ingress points. Same information can be pushed to the NSSF, AMF
and SMF as needed.
o PPR can be supported with any native IPv4 and IPv6 data/user
planes (Section 3.2 with optional TE features Section 3.3 . As
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this is an underlay mechanism it can work with any overlay
encapsulation approach including GTP-U as defined currently for N3
interface.
3.2. Path Steering Support to native IP user planes
PPR works in fully compatible way with SR defined user planes (SR-
MPLS and SRv6) by reducing the path overhead and other challenges as
listed in [I-D.chunduri-lsr-isis-preferred-path-routing] or
Section 5.3.7 of [I-D.bogineni-dmm-optimized-mobile-user-plane]. PPR
also expands the source routing to user planes beyond SR-MPLS and
SRv6 i.e., native IPv6 and IPv4 user planes. This helps legacy
transport networks to get the immediate path steering benefits and
helps in overall migration strategy of the network to the desired
user plane. It is important to note, these benefits can be realized
with no hardware upgrade except control plane software for native
IPv6 and IPv4 user planes.
3.3. Service Level Guarantee in Underlay
PPR also optionally allows to allocate resources that are to be
reserved along the preferred path. These resources are required in
some cases (for some 5G SSTs with stringent GBR and latency
requirements) not only for providing committed bandwidth or
deterministic latency, but also for assuring overall service level
guarantee in the network. This approach does not require per-hop
provisioning and reduces the OPEX by minimizing the number of
protocols needed and allows dynamism with Fast-ReRoute (FRR)
capabilities.
3.4. PPR with various 5G Mobility procedures
PPR fulfills the needs of 5GS to transport the user plane traffic
from gNB to UPF in all 3 SSC modes defined [TS.23.501-3GPP]. This is
done in keeping the backhaul network at par with 5G slicing
requirements that are applicable to Radio and virtualized core
network to create a truly end-to-end slice path for 5G traffic. When
UE moves from one gNB to another gNB, there is no transport network
reconfiguration require with the approach above.
SSC mode would be specified/defaulted by SMF. No change in the mode
once connection is initiated and this property is not altered here.
3.4.1. SSC Mode1
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+---+----+ +-----+ +----------------+
| AMF | | TNF | | SMF |
+---+--+-+ +-+-+-+ +-+--------------+
N1 | | | |
+--------+ N2 +----Ns---+ +-Nn-+ N4
| | | | |
+ +---+---+ +--++ +-+--+---+ +----+
UE1 |gNB+======+CSR+------N3-----+ UPF +-N6--+ DN |
== +---+ +---+ +--------+ +----+
Figure 3: SSC Mode1 with integrated Transport Slice Function
After UE1 moved to another gNB in the same UPF serving area
+---+----+ +-----+ +----------------+
| AMF | | TNF | | SMF |
+---_--+-+ +-+-+-+ +-+--------------+
| | | |
N2 +----Ns---+ +-Nn-+ N4
| | | |
+----+--+ +-+-+ ++--+----+ +----+
|gNB1+======+CSR+------N3-----+ UPF +-N6--+ DN |
+----+ +---+ +---+----+ +----+
|
|
|
|
+----+ +--++ |
UE1 |gNB2+======+CSR+------N3--------+
== +----+ +---+
Figure 4: SSC Mode1 with integrated Transport Slice Function
In this mode, IP address at the UE is preserved during mobility
events. This is similar to 4G/LTE mechanism and for respective
slices, corresponding PPR-ID (TE Path) has to be assigned to the
packet at UL and DL direction. During Xn mobility as shown above,
AMF has to additionally ensure transport path's resources from TNF
are available at the target gNB apart from radio resources check (at
decision and request phase of Xn/N2 mobility scenario).
3.4.2. SSC Mode2
In this case, if IP Address is changed during mobility (different UPF
area), then corresponding PDU session is released. No session
continuity from the network is provided and this is designed as an
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application offload and application manages the session continuity,
if needed. For PDU Session, Service Request and Mobility cases
mechanism to select the transport resource and the PPR-ID (TE Path)
is similar to SSC Mode1.
3.4.3. SSC Mode3
In this mode, new IP address may be assigned because of UE moved to
another UPF coverage area. Network ensures UE suffers no loss of
'connectivity'. A connection through new PDU session anchor point is
established before the connection is terminated for better service
continuity.
+---+----+ +-----+ +----------------+
| AMF | | TNF | | SMF |
+---+--+-+ +-+-+-+ +-+-----------+--+
N1 | | | | |
to-UE+----+ N2 +-------Ns---+ +-Nn-+ N4 N4|
| | | | |
+-------+--+ +--+-------+--+ +-----+-+
|gNB/CSR +---N3---+ BP/ULCL UPF +-N9--+ UPF +-N6--
+----------+ +----------+--+ +-------+ to DN
| +----+
+-| DN |
N6 +----+
Figure 5: SSC Mode3 and Service Continuity
In the uplink direction for the traffic offloading from UL/CL case,
packet has to reach to the right exit UPF. In this case packet gets
re-encapsulated with ULCL marker (with either GTP-U or the chosen
encapsulation) after bit rate enforcement and LI to the anchor UPF.
At this point packet has to be on the appropriate VPN/PW to the
anchor UPF. This mapping is done based on the 5QI to the PPR-ID of
the exit node by selecting the respective TE PPR-ID (PPR path) of the
UPF. If it's a non-MPLS underlay, destination IP address of the
encapsulation header would be the mapped PPR-ID (TE path).
In the downlink direction for the incoming packet, UPF has to
encapsulate the packet (with either GTP-U or the chosen
encapsulation) to reach the BP/ULCL UPF. Here mapping is done for
RQI parameter in the encapsulation header to PPR-ID (TE Path) of the
BP/ULCL UPF. If it's a non-MPLS underlay, destination IP address of
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the encapsulation header would be the mapped PPR-ID (TE path). In
summary:
o Respective PPR-ID on N3 and N9 has to be selected with correct
transport characteristics from TNF.
o For N2 based mobility AMF/SMF has to ensure transport resources
are available for N3 Interface to new ULCL and from there the
original anchor point UPF.
o For Service continuity with multi-homed PDU session same transport
network characteristics of the original PDU session (both on N3
and N9) need to be observed for the newly created PDU session.
4. Other TE Technologies Applicability
RSVP-TE [RFC3209] provides a lean transport overhead for the TE path
for MPLS user plane. However, it is perceived as less dynamic in
some cases and has some provisioning overhead across all the nodes in
N3 and N9 interface nodes. Also it has another drawback with
excessive state refresh overhead across adjacent nodes and this can
be mitigated with [RFC8370].
SR-TE [I-D.ietf-spring-segment-routing] does not explicitly signal
neither bandwidth reservation nor mechanism to guarantee latency on
the nodes/links on SR path. But, SR allows path steering for any
flow at the ingress and particular path for a flow can be chosen.
Some of the issues around path overhead/tax, MTU issues are
documented at Section 5.3 of
[I-D.bogineni-dmm-optimized-mobile-user-plane]. Also SR allows
reduction of the control protocols to one IGP (with out needing for
LDP and RSVP).
However, as specified above with PPR (Section 3), in the integrated
transport network function (TNF) a particular RSVP-TE path for MPLS
or SR path for MPLS and IPv6 with SRH user plane, can be supplied to
NSSF/AMF/SMF for mapping a particular PDU session to the transport
path.
5. New Control Plane and User Planes
5.1. LISP and PPR
PPR can also be used with LISP control plane for 3GPP as described in
[I-D.farinacci-lisp-mobile-network]. This can be achieved by mapping
the UE IP address (EID) to PPR-ID, which acts as Routing Locator
(RLOC). Any encapsulation supported by LISP can work well with PPR.
If the RLOC refers to an IPv4 or IPv6 destination address in the LISP
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encapsulated header, packets are transported on the preferred path in
the network as opposed to traditional shortest path routing with no
additional user plane overhead related to TE path in the network
layer.
Some of the distinct advantages of the LISP approach is, its
scalability, support for service continuity in SSC Mode3 as well as
native support for session continuity (session survivable mobility).
Various other advantages are documented at
[I-D.farinacci-lisp-mobile-network].
5.2. ILA and PPR
If an ILA-prefix is allowed to refer to a PPR-ID, ILA can be
leveraged with all the benefits (including mobility) that it
provides. This works fine in the DL direction as packet is destined
to UE IP address at UPF. However, in the UL direction, packet is
destined to an external internet address (SIR Prefix to ILA Prefix
transformation happens on the Source address of the original UE
packet). One way to route the packet with out bringing the complete
DFZ BGP routing table is by doing a default route to the UPF (ILA-R).
In this case, how TE can be achieved is TBD (to be expanded further
with details).
6. Summary and Benefits with PPR
This document specifies an approach to transport and slice aware
mobility with a simple mapping function from PDU Session to transport
path applicable to any TE underlay.
This also describes PPR
[I-D.chunduri-lsr-isis-preferred-path-routing], a transport underlay
routing mechanism, which helps with goal of optimized user plane for
N9 interface. PPR provides a method for N3 and N9 interfaces to
support transport slicing in a way which does not erase the gains
made with 5GNR and virtualized cellular core network features for
various types of 5G traffic (e.g. needing low and deterministic
latency, real-time, mission-critical or AR/VR traffic). PPR provides
path steering, optionally guaranteed services with TE, unique Fast-
ReRoute (FRR) mechanism beyond shortest path backups in the backhaul
network with any underlay being used in the operator's network (IPv4,
IPv6 or MPLS) in an optimized fashion.
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7. Acknowledgements
TBD.
8. IANA Considerations
This document has no requests for any IANA code point allocations.
9. Security Considerations
This document does not introduce any new security issues.
10. References
10.1. 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>.
10.2. Informative References
[I-D.bogineni-dmm-optimized-mobile-user-plane]
Bogineni, K., Akhavain, A., Herbert, T., Farinacci, D.,
Rodriguez-Natal, A., Carofiglio, G., Auge, J.,
Muscariello, L., Camarillo, P., and S. Homma, "Optimized
Mobile User Plane Solutions for 5G", draft-bogineni-dmm-
optimized-mobile-user-plane-01 (work in progress), June
2018.
[I-D.chunduri-lsr-isis-preferred-path-routing]
Chunduri, U., Li, R., White, R., Tantsura, J., Contreras,
L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
draft-chunduri-lsr-isis-preferred-path-routing-01 (work in
progress), July 2018.
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[I-D.chunduri-lsr-ospf-preferred-path-routing]
Chunduri, U., Qu, Y., White, R., Tantsura, J., and L.
Contreras, "Preferred Path Routing (PPR) in OSPF", draft-
chunduri-lsr-ospf-preferred-path-routing-01 (work in
progress), July 2018.
[I-D.farinacci-lisp-mobile-network]
Farinacci, D., Pillay-Esnault, P., and U. Chunduri, "LISP
for the Mobile Network", draft-farinacci-lisp-mobile-
network-03 (work in progress), March 2018.
[I-D.ietf-dmm-srv6-mobile-uplane]
Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,
daniel.voyer@bell.ca, d., and C. Perkins, "Segment Routing
IPv6 for Mobile User Plane", draft-ietf-dmm-srv6-mobile-
uplane-02 (work in progress), July 2018.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[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/info/rfc3209>.
[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/info/rfc5440>.
[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/info/rfc6241>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8370] Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and
T. Saad, "Techniques to Improve the Scalability of RSVP-TE
Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018,
<https://www.rfc-editor.org/info/rfc8370>.
[TS.23.501-3GPP]
3rd Generation Partnership Project (3GPP), "System
Architecture for 5G System; Stage 2, 3GPP TS 23.501
v2.0.1", December 2017.
[TS.23.502-3GPP]
3rd Generation Partnership Project (3GPP), "Procedures for
5G System; Stage 2, 3GPP TS 23.502, v2.0.0", December
2017.
[TS.23.503-3GPP]
3rd Generation Partnership Project (3GPP), "Policy and
Charging Control System for 5G Framework; Stage 2, 3GPP TS
23.503 v1.0.0", December 2017.
[TS.29.281-3GPP]
3rd Generation Partnership Project (3GPP), "GPRS Tunneling
Protocol User Plane (GTPv1-U), 3GPP TS 29.281 v15.1.0",
December 2017.
Authors' Addresses
Uma Chunduri (editor)
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: uma.chunduri@huawei.com
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Richard Li
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: renwei.li@huawei.com
Jeff Tantsura
Nuage Networks
755 Ravendale Drive
Mountain View, CA 94043
USA
Email: jefftant.ietf@gmail.com