DMM Working Group M. Kohno
Internet-Draft F. Clad
Intended status: Informational P. Camarillo
Expires: May 12, 2022 Z. Ali
Cisco Systems, Inc.
November 8, 2021
Architecture Discussion on SRv6 Mobile User plane
draft-kohno-dmm-srv6mob-arch-05
Abstract
SRv6 mobile user plane is standardized in IETF. It accomplishes the
mobile user-plane functions in a simple, flexible and scalable
manner, by utilizing the network programming nature of SRv6. It
leverages common native IPv6 data plane and creates interoperable
overlays with underlay optimization.
This document discusses the solution approach and its architectural
benefits of common data plane across domains and across overlay/
underlay.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Definition . . . . . . . . . . . . . . . . . . . . . 3
3. Common data plane across domains and across overlay/underlay 3
4. Control Plane Considerations . . . . . . . . . . . . . . . . 4
5. Incremental Deployability . . . . . . . . . . . . . . . . . . 4
6. SRv6 mobile user plane and the 5G use cases . . . . . . . . . 5
6.1. Network Slicing . . . . . . . . . . . . . . . . . . . . . 5
6.2. Edge Computing . . . . . . . . . . . . . . . . . . . . . 5
6.3. URLLC (Ultra-Reliable Low-Latency Communication) support 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Mobile architectures have evolved individually, and the user plane,
GTP-U, has been defined as an overlay tunnel that is agnostic to the
IP infrastructure.
However, the system requirements are changing as digitalization goes
into full swing. The continued use of GTP-U as a user plane protocol
will lock-in to the existing architectural structure and hinder the
innovation. GTP-U will not be able to meet the diverse SLA
requirements of the 5G era and beyond with efficiency and
scalability. Also it will not be able to meet the demands of new
mobile-first data intensive applications, which will be more
dynamically distributed.
SRv6 mobile user plane [I-D.ietf-dmm-srv6-mobile-uplane] is
standardized in IETF. It accomplishes the mobile user-plane
functions in a simple, flexible and scalable manner, by utilizing the
network programming nature of SRv6. It leverages common native IPv6
data plane and creates interoperable overlays with underlay
optimization.
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This document discusses the solution approach and its architectural
benefits of common data plane across domains (e.g., mobile domain, IP
infrastructure, data center, applications) and across overlay/
underlay.
2. Problem Definition
The current mobile user plane, GTP-U, defined as an overlay tunnel
that is agnostic to the IP infrastructure, has the following
limitations that prevent it from supporting new application demands.
o Non-optimal for any-to-any communication
o No control of the underlay path
o Non-optimal for edge/distributed computing
o Non-optimal for fixed and mobile path convergence
o Lack a way for application/service developers to manipulate and
interact
In addition, the centralized tunnel terminating gateway becomes a
scaling bottleneck and a single point of failure
For residential broadband IP and data center networking, tunnel
sessions could be eliminated (e.g. PPPoE -> IPoE, VXLAN/NSH ->
SRv6). This indicates that a tunnel session is not necessarily
absolute. But such a thing was unlikely to happen in the mobile
domain.
As for FMC, there is currently a coordinated standardization effort
between 3GPP WWC [TS.23316] and BBF [BBF407]. However, the idea is
to anchor even wireline traffic in the mobile packet core, which
compromises simplicity and scalability.
3. Common data plane across domains and across overlay/underlay
[I-D.ietf-dmm-srv6-mobile-uplane] defines SRv6 mobile user plane as
an alternative or co-existing solution to GTP-U.
Since SRv6 is a native IPv6 data plane, it can be a common data plane
regardless of the domain.
SRv6 Network Programming [RFC8986] enables the creation of overlays
with underlay optimization. In addition, SRv6 can be operated by
application developers because of its implementation in the computing
stack, e.g. VPP, Linux Kernel, smart NIC, and cloud native platform
such as Network Service Mesh.
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Data plane commonality offers significant advantage regarding
function, scaling, and cost. In particular, the benefits of the 5G
era are shown in Section 6.
Note that the interaction with underlay infrastructure is not a
mandatory in the data plane commonality. It just gives a design
choice to interact with the underlay and optimize it, and it is
totally fine to keep ovelray underlay-agnostic, which will allow the
coexistence of different capability of nodes.
4. Control Plane Considerations
This document focuses on the commonalization of data plane, and the
control plane is out of scope. The actual system characteristics
such as scaling and functionality depend heavily on the control
plane, though.
The potential of the SRv6 mobile user plane is huge, in the sense
that it can realize various functions of mobile management using SRv6
Network Programming. Protocols such as GTP-C, PMIPv6, BGP, LISP,
ILNP, hICN, or even others can be applied as a control plane to
control mobility.
For example, if hICN [I-D.auge-dmm-hicn-mobility] was used,
anchorless mobility can be realised.
5. Incremental Deployability
The mobile domain is a compound domain that includes Radio Access,
and it is difficult to implement a completely new architecture, and
incremental deployability is required.
[I-D.ietf-dmm-srv6-mobile-uplane] defines the conversion between
GTP-U and SRv6, so that it can co-exist with the current mobile
architecture as needed. Since the conversion is done statelessly
(i.e., all necessary information is retained in the packet), there
will not be a scaling bottleneck or a single point of failure.
Further, [I-D.mhkk-dmm-srv6mup-architecture] defines the SRv6 MUP
architecture for Distributed Mobility Management, which can be
plugged to the existing mobile service architecture.
In this way, SRv6 Network Programmability allows for proper
deployability.
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6. SRv6 mobile user plane and the 5G use cases
This section describes the advantages of the common data plane and of
applying SRv6 mobile user plane for 5G use cases.
6.1. Network Slicing
Network slicing enables network segmentation, isolation, and SLA
differentiation in terms of latency and availability. End-to-end
slicing will be achieved by mapping and coordinating IP network
slicing, RAN and mobile packet core slicing.
However, as pointed out in [I-D.clt-dmm-tn-aware-mobility], the 5G
System as defined, does not have underlying IP network awareness,
which could lead to the inability in meeting SLAs.
Segment Routing has a comprehensive set of slice engineering
technologies. How to build network slicing using the Segment Routing
based technology is described in
[I-D.ali-spring-network-slicing-building-blocks].
In the typical GTP-U over IP/MPLS/SR configuration, 3GPP data plane
entity such as UPF is a CE to the transport networks PE. But if 3GPP
they support SRv6 mobile user plane, they can directly participate in
network slicing, and solves the following issues.
o A certain Extra ID such as VLAN-ID is needed for segregating
traffic and mapping it onto a designated slice.
o PE and the PE-CE connection is a single point of failure, so some
form of PE redundancy (using routing protocols, MC-LAG, etc.) is
required.
Moreover, the stateless slice identifier encoding
[I-D.filsfils-spring-srv6-stateless-slice-id] can be applicable to
enable per-slice forwarding policy using the IPv6 header.
6.2. Edge Computing
Edge computing, where the computing workloads and datastores are
placed closer to users, is recognized as one of the key pillars to
meet 5G's demanding requirements, with regard to low latency,
bandwidth efficiency, and data privacy. The computing workload
includes network services, security, data analytics, content cache
and various applications. (UPF itself can also be viewed as a
distributed network service function.)
Edge computing is more important than ever. This is because no
matter how much 5G improves access speeds, it won't improve end-to-
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end throughput because it's largely bound to round trip delay. It is
also important from the viewpoint of "local production for local
consumption" and privacy protection.
However, the current MEC discussion [ETSI-MEC] focuses on how to
properly select the UPF of adequate proximity, and not on how to
interact with applications.
SRv6 has an advantage in enabling edge computing for the following
reasons.
o Programmable and Flexible Traffic Steering : SRv6's flexible
traffic steering capabilities and the network programming concept
is suitable for flexible placement of computing workload.
o Common data plane across domains : SRv6/IPv6 can be a common data
plane regardless of the domains such as mobile including UE, IP
transport, data center, applications.
o Stateless Service Chaining : It does not require any per-flow
state in network fabric.
o Interaction with Applications : SRv6 can be implemented in the
compute stack and can be manipulated by applications using socket
API. Also, SRv6 can carry meta data, which can be used for
interacting with applications.
o Functionality without performance degradation : Various
information can be exposed in IP header, but it does not degrade
performance thanks to the longest match mechanism in the IP
routing. Only who needs the information for granular processing
are to lookup.
It is even more beneficial if service functions/applications directly
support SRv6.
6.3. URLLC (Ultra-Reliable Low-Latency Communication) support
3GPP [TR.23725] investigates the key issues for meeting the URLLC
requirements on latency, jitter and reliability in the 5G System.
The solutions provided in the document are focused at improving the
overlay protocol (GTP-U) and limits to provide a few hints into how
to map such tight-SLA into the transport network. These hints are
based on static configuration or static mapping for steering the
overlay packet into the right transport SLA. Such solutions do not
scale and hinder network economics.
Some of the issues can be solved more simply without GTP-U tunnel.
SRv6 mobile user plane can exposes session and QoS flow information
in IP header as discussed in the previous section. This would make
routing and forwarding path optimized for URLLC, much simpler than
the case with GTP-U tunnel.
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Another issue that deserves special mention is the ultra-reliability
issue. In 3GPP, in order to support ultra-reliability, redundant
user planes paths based on dual connectivity has been proposed. The
proposal has two main options.
o Dual Connectivity based end-to-end Redundant User Plane Paths
o Support of redundant transmission on N3/N9 interfaces
In the case of the former, UE and hosts have RHF(Redundancy Handling
Function). In sending, RFH is to replicate the traffic onto two
GTP-U tunnels, and in receiving, RHF is to merge the traffic.
In the case of the latter, the 3GPP data plane entities are to
replicate and merge the packets with the same sequence for specific
QoS flow, which requires further enhancements.
And in either cases, the bigger problem is the lack of a reliable way
for the redundant sessions to get through the disjoint path: even
with the redundant sessions, if it ends up using the same
infrastructure at some points, the redundancy is meaningless.
SRv6 mobile user plane has some advantages for URLLC traffic. First,
with SRv6, Traffic can be mapped to a disjoint path or low latency
path as needed, by means of the scalable Traffic Engineering.
Additionally, SRv6 provides an automated reliability protection
mechanism known as TI-LFA, which is a sub-50ms FRR mechanism that
provides protection regardless of the topology through the optimal
backup path. It can be provisioned slice-aware.
With the case that dual live-live path is required, the problem is
not only the complexity but that the replication point and the
merging point would be the single point of failure. The SRv6 mobile
user plane also has an advantage in this respect, because any
endpoints or 3GPP data plane nodes themselves can be the replication/
merging point when they are SRv6 aware.
Furthermore, SRv6 supports inband telemetry/time stamping for latency
monitoring and control.
7. Security Considerations
TBD
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8. IANA Considerations
NA
9. Acknowledgements
Authors would like to thank Satoru Matsushima, Shunsuke Homma,Yuji
Tochio and Jeffrey Zhang, for their insights and comments.
10. References
10.1. Normative References
[I-D.hegdeppsenak-isis-sr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., and A. Gulko, "ISIS
Segment Routing Flexible Algorithm", draft-hegdeppsenak-
isis-sr-flex-algo-02 (work in progress), February 2018.
[I-D.ietf-dmm-srv6-mobile-uplane]
Matsushima, S., Filsfils, C., Kohno, M., Garvia, P. C.,
Voyer, D., and C. E. Perkins, "Segment Routing IPv6 for
Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-17
(work in progress), October 2021.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[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/info/rfc8986>.
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10.2. Informative References
[BBF407] BBF, "5G Wireless Wireline Convergence Architecture", BBF
TR-407 Issue:1, August 2020.
[ETSI-MEC]
ETSI, "MEC in 5G Networks", ETSI White Paper No.28, June
2018.
[I-D.ali-spring-network-slicing-building-blocks]
Ali, Z., Filsfils, C., Camarillo, P., and D. Voyer,
"Building blocks for Slicing in Segment Routing Network",
draft-ali-spring-network-slicing-building-blocks-04 (work
in progress), February 2021.
[I-D.auge-dmm-hicn-mobility]
Auge, J., Carofiglio, G., Muscariello, L., and M.
Papalini, "Anchorless mobility through hICN", draft-auge-
dmm-hicn-mobility-04 (work in progress), July 2020.
[I-D.auge-dmm-hicn-mobility-deployment-options]
Auge, J., Carofiglio, G., Muscariello, L., and M.
Papalini, "Anchorless mobility management through hICN
(hICN-AMM): Deployment options", draft-auge-dmm-hicn-
mobility-deployment-options-04 (work in progress), July
2020.
[I-D.clt-dmm-tn-aware-mobility]
Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J.,
Tantsura, J., Contreras, L. M., and P. Muley, "Transport
Network aware Mobility for 5G", draft-clt-dmm-tn-aware-
mobility-09 (work in progress), February 2021.
[I-D.filsfils-spring-srv6-stateless-slice-id]
Filsfils, C., Clad, F., Camarillo, P., Raza, K., Voyer,
D., and R. Rokui, "Stateless and Scalable Network Slice
Identification for SRv6", draft-filsfils-spring-srv6-
stateless-slice-id-04 (work in progress), July 2021.
[I-D.mhkk-dmm-srv6mup-architecture]
Matsushima, S., Horiba, K., Khan, A., Kawakami, Y.,
Murakami, T., Patel, K., Kohno, M., Kamata, T., and P.
Camarillo, "Segment Routing IPv6 Mobile User Plane
Architecture for Distributed Mobility Management", draft-
mhkk-dmm-srv6mup-architecture-00 (work in progress),
October 2021.
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[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
RFC 5213, DOI 10.17487/RFC5213, August 2008,
<https://www.rfc-editor.org/info/rfc5213>.
[TR.23725]
3GPP, "Study on enhancement of Ultra-Reliable Low-Latency
Communication (URLLC) support in the 5G Core network
(5GC)", 3GPP TR 23.725 16.2.0, June 2019.
[TR.29892]
3GPP, "Study on User Plane Protocol in 5GC", 3GPP TR
29.892 16.1.0, April 2019.
[TS.23316]
3GPP, "Wireless and wireline convergence access support
for the 5G System (5GS)", 3GPP TS 23.316 16.7.0, September
2021.
[TS.23501]
3GPP, "System Architecture for the 5G System", 3GPP TS
23.501 15.0.0, November 2017.
[TS.29244]
3GPP, "Interface between the Control Plane and the User
Plane Nodes", 3GPP TS 29.244 15.0.0, December 2017.
[TS.29281]
3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 15.1.0,
December 2017.
Authors' Addresses
Miya Kohno
Cisco Systems, Inc.
Japan
Email: mkohno@cisco.com
Francois Clad
Cisco Systems, Inc.
France
Email: fclad@cisco.com
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Pablo Camarillo Garvia
Cisco Systems, Inc.
Spain
Email: pcamaril@cisco.com
Zafar Ali
Cisco Systems, Inc.
Canada
Email: zali@cisco.com
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