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Versions: 00 01 02

SPRING and DMM                                         P. Camarillo, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: July 19, 2019                                   H. Elmalky, Ed.
                                                              Individual
                                                           S. Matsushima
                                                                SoftBank
                                                                D. Voyer
                                                             Bell Canada
                                                                  A. Cui
                                                                    AT&T
                                                              B. Peirens
                                                                Proximus
                                                        January 15, 2019


                        SRv6 Mobility Use-Cases
         draft-camarilloelmalky-springdmm-srv6-mob-usecases-01

Abstract

   This document describes the SRv6 use-cases in the mobile network in
   association with different mobile generations (3G, 4G, and 5G).  It
   also highlights potential interworking with SR-MPLS in relevant use-
   cases.

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 RFC 2119 [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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 19, 2019.



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Copyright Notice

   Copyright (c) 2019 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/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Use-cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  SP Network Simplification use-cases . . . . . . . . . . .   5
       3.1.1.  Radio-core Handoff  . . . . . . . . . . . . . . . . .   5
         3.1.1.1.  Radio-transport programmability . . . . . . . . .   5
         3.1.1.2.  User-plane state transfer, offload, and mutation    6
         3.1.1.3.  Rip-n-replace of GTP with SRv6  . . . . . . . . .   8
       3.1.2.  End-to-end network slicing [N3, N9, N6 and transport]   9
       3.1.3.  GiLAN Service Programming [N6 and N9] . . . . . . . .   9
         3.1.3.1.  Service Programming on Gi-LAN for 3G/4G [SGi] . .  10
         3.1.3.2.  Service Programming for 5G [N6 and N9]  . . . . .  10
       3.1.4.  ID-Location Isolation at anchors  . . . . . . . . . .  10
     3.2.  New mobility use-cases  . . . . . . . . . . . . . . . . .  10
       3.2.1.  eMBB (Enhanced Mobile Broadband)  . . . . . . . . . .  10
         3.2.1.1.  Fixed/Mobile Convergence (HA, FWA & WA) . . . . .  10
         3.2.1.2.  Mobile Enforced SD-WAN  . . . . . . . . . . . . .  11
       3.2.2.  mMTC (massive Machine Type Communications)  . . . . .  11
         3.2.2.1.  Stationary IoT Devices (industrial applications)   11
       3.2.3.  URLLC (Ultra Reliable Low Latency Communications) . .  12
   4.  Work in progress  . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13








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1.  Introduction

   4G/LTE mobile networks are complex and the use cases that 5G has been
   architected to address, introduce new requirements and additional
   complexity to both the RAN and the mobile core.  The current
   architecture employs the GPRS tunneling protocol (GTP) as the primary
   vehicle for user plane interconnect in the RAN and 5GC.  GTP is
   currently used in two contexts, from the RAN to the first anchor
   point; the S-PGW/UPF (S1-U/N3 interface) and for inter S-PGW/UPF
   connectivity (S5-S8/N9 interface).  While the tunnels themselves do
   not impose significant state beyond that needed, they do have a
   significant control plane setup component and are a potential target
   for network delayering.

   Segment Routing [I-D.ietf-spring-segment-routing] is a network
   architecture that simplifies networks by removing state from the
   network infrastructure, creating a scalable SDN architecture for
   overlays (VPNs), underlay (SLA, Traffic Engineering, FRR) and service
   programming (GiLAN).  The IPv6 instantiation -also known as SRv6
   [I-D.filsfils-spring-srv6-network-programming]- takes this even
   further with the introduction of the Network Programming concept,
   allowing to bind segments to any kind of VNF anywhere in the network
   -from private DCs to public cloud services.

   Segment routing embodies a number of potentially useful properties
   for consideration in a 4G/5G mobile networking context:

   1.- Direct manipulation of path routing by the head-end

   SRv6 provides the ability to direct traffic through an arbitrary path
   without the imposition of path state in the network or requiring a
   separate signaling system.  It does this without signaling by
   encoding the path state in the packet header.  This means the path
   head-end can instantly fulfill changes to a path by simply changing
   the header encoded information.

   This capability has numerous applications as far as networking in
   general (traffic engineering, policy routing etc.), but has
   additional applicability to mobile networks:

   o  The ability of a path head-end to manipulate the intermediate hops
      in a path can be exploited for end system mobility, the
      penultimate hop simply becomes the "care of" address.

   o  The ability of path head-end to imply an asymmetric return path
      for a specific forwarding equivalence class (FEC).





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   o  Densification in the radio topology embodied in concepts like
      coordinated multipoint and multi-connectivity require the
      instantaneous redirection of traffic from the coordinating radio
      controller to any of several base stations.  This is critical to
      exploit ephemeral "rich paths" that 4G & 5G radio technologies
      depend upon to achieve high rates of information transfer.

   2.- Network programmability

   The ability to bind segments to network functions provides an
   increased level of abstraction in service delivery combined with a
   practical realization.  This would have applications in the GiLAN/N6,
   combined with the ability to specify a path from the head-end as
   applications in the GiLAN/N6.

   3.- Overall simplification of the control plane

   As noted previously SRv6 dispenses with a signaling system.  This has
   obvious benefits as a simplification to overall network operation,
   but may have additional benefits in the "signaling rich" environment
   of mobile networks.



   This memo serves to critically explore the applicability of SRv6 to
   4G/5G mobile networks.  It does that via an exploration of how SRv6
   can simplify current mobile network architecture to improve the
   status quo of eMBB operation, and then delves into the new use cases
   that 5G is targeted towards.


2.  Terminology

   This document focuses on the use-cases, and it's associated
   terminologies.  The full list of terminologies exists in
   [I-D.filsfils-spring-srv6-network-programming].

   In this document we focus on the 5G systems architecture, as
   specified in [TS.23501].  This document also refers to 3G and 4G
   networks as specified in [TS.23002].

   The uplink/upstream traffic is the traffic originated at the UE,
   while the downlink/downstream traffic is traffic destined towards the
   UE.







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3.  Use-cases

   Use-cases have been classified into multiple categories depending on
   their fit into the mobile-network domain (Radio, Transport, Core) or
   mobile network generation (3G/4G, or 5G).

3.1.  SP Network Simplification use-cases

3.1.1.  Radio-core Handoff

3.1.1.1.  Radio-transport programmability

   Advances in radio technology, the deployment of new spectrum for 5G
   and the quest for ever increasing spectral efficiency results in
   increasingly complex RAN and air interface topologies.  The result is
   that the RAN end of a GTP tunnel may appear as a single end point to
   the core network, but the actual realization is substantially more
   complex.

   Modern radio scheduling is increasingly focused on using techniques
   such as MIMO to multiply the instantaneous bandwidth available for
   information transfer for a given unit of spectrum.  A "rich path" can
   be very ephemeral so any latency between path measurement and
   initiating data transfer to a UE can be parasitic in the overall
   system efficiency.

3.1.1.1.1.  Multi-connectiveity and coordinated multi-point

   There are multiple scenarios where a UE can be associated with more
   than one antenna and the associated spectrum:

   Coordinated multipoint (CoMP) involves a UE associated with multiple
   geographically distributed antennas serving a common block of
   spectrum, and the radio controller selecting the best antenna at any
   given time.  The other antennas being quiescent in the sector
   occupied by the UE at the time of transmission to avoid overlap.
   This can be in the context of an RRC/RLC split (F1-U interface) or a
   Phy Hi/Phy Lo split (F2-U interface).

   Multi-connectivity can see a UE associated with multiple antennas
   each serving different spectral allocations.  Applications include
   offload from a macro cell to a small cell.  The possibility of
   simultaneous transfer from multiple antennas also exists.  And again
   this can be on the basis of an F1 or F2 split in the RAN.

   In both cases the radio controller is required to be able to
   instantly redirect traffic based on current radio measurements to any
   of a constellation of antennas serving a given UE.



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3.1.1.1.2.  Fronthaul

   Modern radio systems have been deconstructed in order to drive
   efficiency across a variety of metrics.  In essence various stages of
   waveform construction have been abstracted and exposed on interfaces
   as part of the 5G RAN architecture.  In the most simplest form it
   allows putting functionality where it is easy to service, such as the
   equipment at the bottom of the tower rather than the top.  In a rich
   radio connectivity context it permits co-location of radio scheduling
   and waveform generation which drives spectral efficiency, but where
   applied also results in significant multiples of bandwidth, and very
   tight jitter and delay requirements.  The current specification for
   the F2-U or e(CPRI) packet interface has a maximum latency of 75 usec
   and correspondingly tight jitter requirements.

3.1.1.2.  User-plane state transfer, offload, and mutation

   A proper session handoff between radio, transport, and mobile-core
   requires storing/recalling user-plane session state on multiple
   levels.  The use of SRv6 reduces the number of states needed in the
   network nodes by mapping the UE session state into IPv6 SID (Segment
   IDs) in SRH.  Furthermore, mutation of SID-lists shall enable SMF to
   program data-paths (handling-state) and policies (serving-state) on
   per-subscriber / per-application level.

   That session state can be broken down into two categories:

   1.- Handling state: Who is the session handler?

   o  A 1-to-1 mapping between GTP tunnel (TEID) and S-PGW/UPF

   o  Usually stored at load-balancers deployed ahead of S-PGW/UPF
      instances or embedded inside the S-PGW/UPF system.

   2.- Serving state: What is the serving-policy associated with this
   session?

   o  A 1-to-1 mapping between the UE and a specific policy to be
      enforced on the subscriber traffic.

   o  The policy may include (but not limited to) the authorization &
      accounting profile, one or multiple QoS profiles, one or multiple
      service-chaining/programming profiles.

   o  A 1-to-1 mapping between a UE session and it's stats-registers at
      the S-PGW/UPF.





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   o  It is typical that S-PGW/UPF may break down the service-state into
      sub-states reflecting groups of 5-tuple flows, or employ other
      techniques (ex.  DPI, deep packet inspection) to break down the
      serving-state even further within the same 5-tuple flow.

   The ability to transfer, offload, or mutate the user-plane state with
   no/minimum disruption to end-users is one of the most significant
   challenges facing the mobile network's scalability towards mMTC use-
   cases (The current GTP-U mandates a per-session tunnel creation &
   handling).  Moreover, the direct 1-to-1 binding between UE session ID
   and Location affects the optimal-path selection, which is one of the
   most significant challenges facing URLLC use-cases in 5G.

   The use of SRv6 shall simplify the state storage dramatically where a
   single SID-list embedded in the UE session packet can store the
   handling-state and the majority of the serving-state.  SRv6
   programmability and traffic-engineering shall allow an easy way to
   transfer, offload, or mutate that state.

3.1.1.2.1.  State-offload:

   Upstream state-offload:
   the use of SRv6 shall allow the S-PGW/UPF anchor(s) to offload the
   load-balancing function from a dedicated load-balancer in mobile-core
   to be a standard function in packet-forwarding in transport network
   where any SR-aware node on the path between eNB and S-PGW/UPF can
   forward the UE session to the proper S-PGW/UPF handling instant by
   relying on the handling-state stored in the SID-list in each packet.

   Downstream state-offload:
   The L3 anchor (PGW/UPF) is the first node that handles the subscriber
   traffic in the downstream direction, depending on the policy
   associated with the subscriber traffic.  The PGW/UPF may decide to
   hairpin the traffic through multiple application (service chain)
   before sending it towards the radio-network.  This implies double
   packet-processing on PGW/UPF instant (50% penalty on the VNF useful
   throughput).

   The use of SRv6 shall allow the PGW/UPF to impose a specific data-
   path on a group of 5-tuple flows without the need for hairpins all
   the traffic through PGW/UPF.  Which means the PGW/UPF can offload the
   first packet processing towards another none-SR- node earlier in the
   downstream path (ex.  Service-proxy, or packet inspector) as per
   specific service-pipeline policy.

   Moreover, that offload-service can be programmed once the S-PGW/UPF
   terminate the subs-session on the upstream direction.  Alternatively,




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   the offload-service can be programmed on-demand after the first few
   packets been hair-pinned through the PGW/UPF on the downstream path.

3.1.1.2.2.  State-transfer:

   Handling-state:
   SRv6 shall enable the handling-state to be embedded in the data-flow
   as metadata (in a form of SID-list).  This means that all load-
   balancing operations can be performed by any of the SR-aware
   intermediate nodes in a stateless fashion with a zero-state transfer
   at failure scenarios.

   Serving-state:
   Depending on the applied policy, a significant portion of the
   serving-state can be embedded in the data-flow as metadata (in a form
   of SID-list).  This means that serving nodes (S-PGW/UPF) have a
   smaller amount of data to store/recall to serve the UE session.

3.1.1.2.3.  State-mutation:

   SRv6 provides a more natural way to mutate the handling-state and
   serving-state to follow the optimal data path or fulfill traffic-
   engineering constrain(s).

   In contrast to the current limitation of mutating the state only at
   SGW (session L2-anchor point) or PGW (session L3-anchor point).  SRv6
   shall allow the state mutation on any authorized SR-aware node
   between radio and mobile core.

3.1.1.3.  Rip-n-replace of GTP with SRv6

   A possible mechanism to do an early-deployment of SRv6 is to keep the
   tunnel-nature of GTP but do a simple data-plane replacement of
   IP/UDP/GTP-U with SRv6 for specific PDU sessions.  In this case,
   there is no session aggregation, and the SRv6 segment corresponding
   to the overlay creation now carries the TEID, QFI and RQI as part of
   the SID arguments.

   In this use-case there is no subscriber-traffic integration with the
   underlay or service programming.  There could be some integration but
   it is based on static policies and not configured via the currently
   existing mobility management.

   This is an interworking mechanism that shall used for an early stage
   implementation with no changes to the N4 interface.






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3.1.2.  End-to-end network slicing [N3, N9, N6 and transport]

   One of operator's main challenges is providing end-to-end network
   slicing, taking into consideration the RAN, the S-PGW/UPF and the
   VNFs in the GiLAN; but more importantly taking also into
   consideration the transport network.

   SRv6 can help bridging the gap in between all of these since it
   integrates the overlay, underlay and service programming into a
   single protocol.  End-to-end SR policies can be defined that span
   across the RAN, S-PGW/UPF and transport network, without requiring
   any stitching configuration at the domain boundaries.  From an
   overlay perspective, it is clear that SRv6 can provide -if desired-
   isolation among different RAN or S-PGW/UPF nodes.

   In the transport network, the SRv6 overlay can integrate with an
   existing SRv6 or SR-MPLS transport network to provide traffic
   engineering in the underlay network infrastructure.  SR provides
   operators with a stateless mechanism to build network slices with
   different optimization objectives or constrains i.e. low-latency
   (uRLLC), resource isolation (disjointness), etc...

   Also, SR provides mechanisms for in-band performance monitoring.
   This implies that the end-to-end network slice can react upon
   topology changes -that for example might change the low-latency
   path-.

3.1.3.  GiLAN Service Programming [N6 and N9]

   Service Programming, in coordination with SRv6 can be used for
   optimal placement of VNFs in the Gi-LAN of mobile operators for
   flawless VNF management and placement -DC resource utilization-.

   SRv6 transparently integrates VNFs
   [I-D.xuclad-spring-sr-service-programming], in the same SR policy
   used for overlay creation and underlay control.  The VNFs are cloud-
   infrastructure agnostic -can be hosted on a private DC or public
   cloud-, and there is no state per-flow or per-chain in the network
   infrastructure.  This implies a huge flexibility for mobile
   operators.  Note that VMs can be distributed in different tenants, or
   can be migrated while there is live traffic without any major
   manageability complexity, state to update in the network
   infrastructure or packet loss.  Note also that in the case of network
   slicing, the VNFs can be shared across multiple slices or can be
   restricted to only a particular slice.  This can be chosen on a per-
   VNF granularity.





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   In addition, SRv6 offers mechanisms to do VNF load-balancing and to
   convey additional flow information to stateless VNFs using the SRv6
   SID arguments, by leveraging the network programming concept.

3.1.3.1.  Service Programming on Gi-LAN for 3G/4G [SGi]

   SRv6-based NFV provides an approach to optimally steer traffic
   through Gi-LAN network functions in 3G/4G networks.

   The PGW can steer uplink traffic into a specific SR policy that
   contains as many segments as VNFs that the packet must traverse.  The
   packet follows the path specified in the SR policy, traversing the
   set of VNFs before getting delivered to the external PDN -i.e.
   internet-.

3.1.3.2.  Service Programming for 5G [N6 and N9]

   In 5G networks SRv6 can offer NFV control, as done in the Gi-LAN for
   3G-4G networks (N6 interface), but can also integrate the VNFs within
   the N9 interface.  This means that we can have more flexibility
   regarding the distribution and association of the functions/VNFs/
   micro-services, and bring applications closer to the user, where they
   might be better located for the operator and improve the overall
   customer experience.

3.1.4.  ID-Location Isolation at anchors

   TBD

3.2.  New mobility use-cases

3.2.1.  eMBB (Enhanced Mobile Broadband)

3.2.1.1.  Fixed/Mobile Convergence (HA, FWA & WA)

   The end users of different access networks under control of the same
   service provider would obtain significant benefit if there is a tight
   integration for service delivery in between the mobile access network
   and the fixed network.

   This is the example of a residential user that is accessing content
   from his mobile phone, and once he arrives home his phone
   automatically connects to his home wireless network provided whose
   connectivity is provided by the same operator.  As per today, these
   networks have different architectures, with different control-planes
   and data-planes, and with different policy control and service
   management.




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   SRv6 helps uniting the gap in between different access networks by
   optimizing the data path in between hierarchical networks and
   directly adding an SR policy that spans from the mobile packet core
   up to the broadband network BNG.  Such capability will simplify the
   delivery of fixed-services on top of wireless infrastructure. it will
   also enable the simultaneous use of wireless and fixed connections
   towards end-user.

3.2.1.2.  Mobile Enforced SD-WAN

   TBD

3.2.2.  mMTC (massive Machine Type Communications)

3.2.2.1.  Stationary IoT Devices (industrial applications)

   There are many types of IoT devices, ranging from connected cars to
   massive machine type devices like meter readers, which are
   stationary.  One of these examples is electricity meters.  These
   devices are static and might only attach to other gNBs due to
   changing RF conditions.

   Massive machine type devices is projected to grow to 10's of billions
   in operator networks in the next few years.  However, the traditional
   3GPP GTP tunnel/bearer based connection-oriented architecture does
   not scale for billions of IoT devices due to the amount of signaling
   overhead associated with GTP tunnel setup/tear- down and the UE
   context information maintained at various parts of the mobile
   network.

   Unlike smart devices, electric meters never move and each generates
   low RPU for carriers.  For this reason, to efficiently support the
   massive machine type of stationary IoT devices, a simpler and more
   scalable control and user plane architecture is needed that can
   reduce the amount of signaling overhead and the UE context
   information kept in the network.  This new architecture will need to
   work across all types of access technologies to improve adaptability
   to future RAT networks.

   SRv6 can help improve scalability in the RAN, transport, and packet
   core networks significantly by removing GTP tunnels for each
   individual stationary IoT device, and replacing by the aggregated
   SRv6 route information for all the similar stationary IoT devices.
   For instance, at the eNB/gNB, only the first electric meter device
   for an electric company needs the SRv6 route set up procedure, which
   has one SRv6 look up table entry associated with it.  No subsequent
   SRv6 route set up procedures and no additional SRv6 table entries for
   the succeeding electric meters are needed at the same eNB/gNB.  This



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   effectively reduces the signaling overhead and UE context overhead by
   (1-1/N)% (where N is the number of the electric company meter readers
   in the same eNB/gNB).  In the case of RAN virtualization with an
   aggregated vBBU for many cell sites, the reduction of the signaling
   and UE context overhead will be greater since N is a much bigger
   number.

   The significant reduction of the signalling overhead and UE context
   overhead can be translated to the cost reduction of running
   operators' wireless network.  In addition, this new architecture
   using SRv6 allows flexible service edge treatment, service chaining,
   such as billing, TE or other capabilities.

3.2.3.  URLLC (Ultra Reliable Low Latency Communications)

   TBD

4.  Work in progress

   o  Use of SRv6 in optimizing interface (reference N4 as defined by
      3GPP xxx r16) between control-plane and user-plane.

   o  Security implications & benefits of SRv6 in mobile networks.

5.  Acknowledgements

   We would like to thank Francois Clad, Darren Dukes, Zafar Ali, Peter
   Bosch, Simon Spraggs and Tom Anschutz for their help.

6.  References

6.1.  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>.

   [TS.23501]
              3GPP, "System Architecture for the 5G System", 3GPP TS
              23.501 15.2.0, June 2018.

6.2.  Informative References








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   [I-D.filsfils-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-filsfils-spring-srv6-network-
              programming-06 (work in progress), October 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.

   [I-D.xuclad-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-xuclad-spring-sr-service-
              programming-01 (work in progress), October 2018.

   [TS.23002]
              3GPP, "Network Architecture", 3GPP TS 23.23002 15.0.0,
              March 2018.

Authors' Addresses

   Pablo Camarillo Garvia (editor)
   Cisco Systems, Inc.
   Spain

   Email: pcamaril@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium

   Email: cf@cisco.com


   Hani Elmalky (editor)
   Individual
   United States of America

   Email: hani.elmalky@gmail.com







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Internet-Draft           SRv6 Mobility Use-Cases            January 2019


   Satoru Matsushima
   SoftBank
   1-9-1,Higashi-Shimbashi,Minato-Ku
   Tokyo  105-7322
   Japan

   Email: satoru.matsushima@g.softbank.co.jp


   Daniel Voyer
   Bell Canada
   Canada

   Email: daniel.voyer@bell.ca


   Anna Cui
   AT&T
   United States of America

   Email: zc1294@att.com


   Bart Peirens
   Proximus
   Belgium

   Email: bart.peirens@proximus.com























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