Distributed Mobility Management                                  N. Tran
Internet-Draft                                                    Y. Kim
Intended status: Informational                       Soongsil University
Expires: 8 May 2025                                      4 November 2024


  Computing Aware Traffic Steering Consideration for Mobile User Plane
                              Architecture
                       draft-dcn-dmm-cats-mup-04

Abstract

   The document [I-D.draft-mhkk-dmm-mup-architecture] describes the
   Mobile User Plane (MUP) architecture for Distributed Mobility
   Management.  The proposed architecture converts the user mobility
   session information from the control plane entity to an IPv6
   dataplane routing information.  When there are multiple candidate
   instances located at different location to serve an user request, the
   MUP Provider Edge (PE) might prioritize the closest service location.
   However, the closest routing path might not be the optimal route.

   This document discusses how the mentioned MUP architecture can be
   leveraged to set up dataplane routing paths to the optimal service
   instance location with the assistance of computing-aware traffic
   steering capabilities.  For each session request, based on the up-to-
   date collected computing and network information, the MUP controller
   can convert the session information to the optimal route.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 May 2025.







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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology used in this draft  . . . . . . . . . . . . . . .   4
   3.  MUP enhancement requirements for supporting CATS  . . . . . .   4
   4.  MUP enhancement considerations for supporting CATS  . . . . .   5
     4.1.  CATS-MUP Centralized Deployment case  . . . . . . . . . .   5
       4.1.1.  MUP Route enhancements  . . . . . . . . . . . . . . .   5
       4.1.2.  Deployment architecture . . . . . . . . . . . . . . .   6
       4.1.3.  New UE request underlay routing setup procedure . . .   8
       4.1.4.  UE mobility handling procedure  . . . . . . . . . . .  10
     4.2.  CATS-MUP Distributed Deployment case  . . . . . . . . . .  12
       4.2.1.  MUP Route enhancements  . . . . . . . . . . . . . . .  12
       4.2.2.  Deployment architecture . . . . . . . . . . . . . . .  13
       4.2.3.  New UE request underlay routing setup procedure . . .  14
       4.2.4.  UE mobility handling procedure  . . . . . . . . . . .  15
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     5.1.  Informative References  . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The document [I-D.draft-mhkk-dmm-mup-architecture] describes the
   Mobile User Plane architecture for Distributed Mobility Management.
   This architecture is composed of a MUP controller and multiple MUP
   PEs.  When applying the MUP architecture in 5G network, the MUP PEs
   accomodate the N3 RAN network as Interwork Segment or the N6 DN
   network as Direct Segment.  The MUP PEs advertises the Interwork and
   Discovery Segment dataplane network reachability (e.g.  Segment
   Routing IPv6 segment identifier (SRv6 SID)) to the MUP network via
   the interwork and direct segment Discovery routes.  Meanwhile, the
   MUP controller transformed the received user mobility session
   information to the corresponding interwork and direct segment
   information.  Then, it advertises the transformed information to MUP



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   PEs via Session Transformed routes.  The MUP PEs use the matching
   Discovery routes to resolve the Session Transformed routes and
   forward the packet through the MUP SRv6 network.

   This document discusses the optimal route configuration problem when
   applying the mentioned MUP architecture in a network scenario where
   an user request can be served by multiple computing instances of the
   same service located at different locations.  The closest
   geographical service location to users might not be the optimal
   service instance's location as pointed out in the problem statement
   document of IETF Computing-Aware Traffic Steering (CATS) working
   group [I-D.draft-ietf-cats-usecases-requirements].  In this scenario,
   an optimal service instance location can be decided at the mobile
   control plane or data plane.

   In the control plane case, it is possible to use an Application
   Function (AF) to determine the optimal service instance and influence
   the 5G control plane to select the DN corresponding to the chosen
   instance.  The MUP-C only needs to transform the optimal DN
   information in the session information into the corresponding route.
   Meanwhile, in the data plane approach, the MUP-C should decide the
   optimal service instance location by itself and transform the
   unoptimal session information into the optimal route based on its
   decision.  The data plane approach can avoid additional signalling
   procedure at the control plane of the other approach.  It also
   supports IP Routing paradigm benefit of SRv6 mobile user plane as
   mentioned in the edge computing use case of the document
   [I-D.draft-ietf-dmm-srv6mob-arch].

   Therefore, a solution to integrate CATS capabilities into the
   mentioned MUP architecture is presented in this document.  By
   considering service computing and network information of all
   candidate service instances, the MUP controller can convert the
   session information into the optimal dataplane route.

   This document is proposed to discuss a possible extension
   consideration of the original MUP architecture
   document[I-D.draft-mhkk-dmm-mup-architecture].  Regarding the
   Distributed Mobility Management requirements described in [RFC7333],
   the MUP architecture can partly address the "Non-optimal routes"
   problem and the "Multicast considerations" requirement by integrating
   CATS capabilties.  As described in [RFC4786], anycast is the practice
   of making a particular service address available in multiple
   locations.  Anycast support could be in the scope of multicast
   support for distributed mobility management.






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2.  Terminology used in this draft

   CATS-MUP-C: Computing-aware traffic steering MUP-C which integrates
   CATS path selection and MUP-C features.

   Besides, this document uses the following terminologies which has
   been defined in [I-D.draft-ldbc-cats-framework]

   CATS: Computing-Aware Traffic Steering takes into account the dynamic
   nature of computing resource metrics and network state metrics to
   steer service traffic to a service instance.

   Service: An offering that is made available by a provider by
   orchestrating a set of resources (networking, compute, storage,
   etc.).  The same service can be provided in many locations; each of
   them constitutes a service instance.

   Service instance: An instance of running resources according to a
   given service logic.

   Service contact instance: A client-facing service function instance
   that is responsible for receiving requests in the context of a given
   service.  A single service can be represented and accessed via
   several contact instances that run in different regions of a network.

   CATS Path Selector (C-PS): A functional entity that computes and
   selects paths towards service locations and instances and which
   accommodates the requirements of service requests.  Such a path
   computation engine takes into account the service and network status
   information.

   CATS Service Metric Agent (C-SMA): A functional entity that is
   responsible for collecting service capabilities and status, and for
   reporting them to a C-PS.

   CATS Network Metric Agent (C-NMA): functional entity that is
   responsible for collecting network capabilities and status, and for
   reporting them to a C-PS.


3.  MUP enhancement requirements for supporting CATS

   This section presents 3 enhancement points that need to be added in
   MUP for selecting an optimal service instance for serving an user
   request.






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   First, the MUP architecture should be capable of identifying the
   service and its candidate service instances.  These service
   identifiers are well defined in CATS framework document
   [I-D.draft-ldbc-cats-framework], CATS Service ID (CS-ID) is used to
   differentiate between different services.  CATS Instance Selector ID
   (CIS-ID) is used to differentiate between different service instances
   of the same service.

   Second, the MUP architecture should be capable of advertising service
   deployment information among its components.  The egress MUP PE
   attaching to the MUP direct segment should gather the corresponding
   service and servince instance information (CS-ID and CIS-ID) and
   avertise to the MUP environment.  Different methods can be considered
   for this requirement.

   Third, the MUP architecture should be capable of advertising the
   computing and network metrics (CATS metrics) related to the each
   service instance.  The egress MUP PE attaching to the MUP direct
   segment should gather the corresponding service CATS metrics and
   avertise to the MUP environment.  Different methods can be considered
   for this requirement.

   This document only discusses the requirements.  Different methods for
   service information and CATS metrics distribution to the network can
   be applied.  BGP extension is an example approach that can be
   referred from related IETF documents such as
   [I-D.draft-lin-idr-distribute-service-metric] or
   [I-D.draft-ietf-idr-5g-edge-service-metadata].

4.  MUP enhancement considerations for supporting CATS

4.1.  CATS-MUP Centralized Deployment case

4.1.1.  MUP Route enhancements

   Compared with the original route definition introduced in
   [I-D.draft-ldbc-cats-framework], the Direct Segment Discovery Route
   (DSD) and the Type 2 Session Transformed Route (T2ST) need
   modifications to support the centralized CATS-MUP deployment case.
   Another CATS Metrics Update Route (CMU) is also introduced.

   The Direct Segment Discovery route advertises the reachability
   information of the direct segment.  This route is advertised from the
   PEs attaching to the direct segments to the PEs attaching to the
   mobile network access side.  In CATS scenario, the direct segment is
   a specific instance of a service.  The service identifier CS-ID and
   service instance identifier CIS-ID information are required in this
   route.  The CS-ID can be used as the direct segment BGP extended



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   community attribute.  The list below shows the information that
   should be included in the BGP NLRI of the DSD route in CATS-MUP
   centralized deployment case:

   *  CS-ID

   *  CIS-ID

   *  Attached PE SID

   The Type 2 Session Transformed Route convert the session information
   into dataplane routing information.  This route is advertised from
   the CATS-MUP-C to the PEs attaching to the mobile network access
   side.  In CATS scenario, the direct segment is a specific instance of
   a service.  This route type includes the target service identifier
   CS-ID and the tunnel endpoint identifier on the mobile network core
   side information.  The optimal service instance identifier CIS-ID
   determined by the CATS-MUP-C is also required in this route
   information.  The list below shows the information that should be
   included in the BGP NLRI of the T2ST route in CATS-MUP centralized
   deployment case:

   *  CS-ID

   *  Optimal CIS-ID

   *  Tunnel Endpoint Identifier on the core side

   The CATS Metric Update route convert the session information into
   dataplane routing information.  This route is advertised from the PEs
   attaching to the direct segments to the CATS-MUP-C.  This route type
   update the CATS metrics related to the attaching service instance of
   each PE to the CATS-MUP-C.  The list below shows the information that
   should be included in the BGP NLRI of the CMU route in CATS-MUP
   centralized deployment case:

   *  CS-ID

   *  CIS-ID

   *  CATS metrics

4.1.2.  Deployment architecture








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                             +----------------+
                             |    Mobility    |
                             |   Management   |
                             |     System     |
                             +----------------+
                                      |
                        Session Information, CS-ID
                                      |
                     T2ST    +--------v-------+  CMU A
                     +-------|   CATS-MUP-C   |<-----+
                  +--|-------|    +------+    |------|--+
                  |  |       |    | C-PS |    |      |  |
                  |  |       +----------------+      |  |   +----------+
      UE-         |  v                 CMU B ^       |  |   |   C-SMA  |
         \+---+   +------+ DSD A             |   +------+   |----------|-Service1
      UE--|RAN|---|  PE  |<------------------|---|  PE  |---|  Service | Instance
          +---+   +------+<---------------\  \   +------+   |   Site A | (CS-ID S1)
      UE-/        |        DSD B           \  \         |   +----------+ (CIS-ID S1A)
                  |                         \  \        |
                  |                          \  \       |
                  |                           \  \      |
                  |     MUP network            \ +------+   +----------+
                  |      +-------+              \|  PE  |---|  Service |
                  |      | C-NMA |               +------+   |   Site B |-Service1
                  |      +-------+                      |   |----------| Instance
                  +-------------------------------------+   |   C-SMA  | (CS-ID S1)
                                                            +----------+ (CIS-ID S1B)




           Figure 1: CATS-MUP Centralized deployment option

   Figure 1 describes the CATS-MUP Centralized deployment architecture.
   The controller MUP-C in previous mentioned document is enhanced with
   CATS path selection capability and renamed to CATS-MUP-C.  The
   Centrailized deployment option has the following key features:

   *  The DSD routes advertise service and service instance identity
      information (CS-ID and CIS-ID) from the Service Site PEs to the
      RAN PEs.  This happens only one time when a service instance is
      deployed or removed at a service site

   *  The CMU routes periodically advertise CATS metrics corresponding
      to each service instance from the Service Site PEs to the CATS-
      MUP-C





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   *  The CATS-MUP-C decides the optimal service instance for each UE
      session based on the metrics from the CMU routes

   *  The T2ST routes convert the UE session information into the
      optimal underlay routing information and provide them to the RAN
      PEs.

4.1.3.  New UE request underlay routing setup procedure











































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   +----+  +----+  +-----+  +-----+  +-----+
   | UE |  |RAN1|  |CATS |  |SiteA|  |SiteB|
   |    |  | PE |  |MUP-C|  | PE  |  | PE  |
   +----+  +----+  +-----+  +-----+  +-----+
     |       |       |        |        |
     |       0.DSD
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID)
     |       |<---------------|        |
     |       |<------------------------|
     |       |       |        |        |
     |       1.CMU - periodically advertised
     |       (CS-ID S1, CIS-ID S1A, CATS metrics)
     |       (CS-ID S1, CIS-ID S1B, CATS metrics)
     |       |       |<-------|        |
     |       |       |<----------------|
     2. UE request session establishment
     CATS-MUP-C recieves UE session information
     |       |       |        |        |
     |      3.CATS-MUP-C determines
     |      optimal service instance S1A
     |       |       |        |        |
     |      4.TS2T
     |      (CS-ID S1, CIS-ID S1A, TEID)
     |       |<------|        |        |
     |       |       |        |        |
     5. RAN1 PE use DSD route from SiteA (CIS-ID S1A)
     to route UE traffic to SiteA
     |------>|--------------->|        |
     |       |       |        |        |
     6. In case of optimal service instance change
     to SiteB based on current metrics
     |       |       |        |        |
     |      7.CATS-MUP-C determines
     |      optimal service instance S1B
     |       |       |        |        |
     |      8.TS2T
     |      (CS-ID S1, CIS-ID S1B, TEID)
     |       |<------|        |        |
     |       |       |        |        |
     9. RAN1 PE use DSD route from SiteB (CIS-ID S1B)
     to route UE traffic to SiteB
     |------>|------------------------>|



         Figure 2: New UE request underlay routing setup procedure




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   Figure 3 describes the sequence of how the CATS-MUP Centralized
   deployment approach setup the underlay routing path for an UE
   request.

   *  First, when a service instance is available at a service site, a
      DSD route is advertised from the corresponding PE of that site.
      In the example in Figure 3, DSD routes are advertised from SiteA
      and SiteB PEs to all of the RAN PEs.  These routes announce the
      service and service instance identities (CS-ID, CIS-ID) running at
      each service site and the corresponding PE SRv6 SID

   *  Then, the CATS metrics corresponding to each service instance is
      periodically updated from the Site PEs to the CATS-MUP-C via the
      CMU routes

   *  When a UE request session establishment to the mobile management
      system, the CATS-MUP-C recieves the session information which
      includes the requested service CS-ID and the TEID of the session.
      The CATS-MUP-C determines the optimal service instance for the
      session based on current CATS metrics.

   *  Then, the CATS-MUP-C maps the session information TEID with the
      optimal service instance CIS-ID and advertises this information to
      the RAN PE via the T2ST route.

   *  Upon recieving the T2ST route, the RAN PE selects the DSD route
      that has the same CIS-ID information with the recieved T2ST route
      (CIS-ID S1A in this example).  The RAN PE uses this D2D route for
      steering the UE traffic to the optimal service site.

   *  In case of the optimal service instance change to another site
      (SiteB in this example) due to current CATS metrics update, the
      CATS-MUP-C advertises a new T2ST route to the RAN PE, which maps
      the session information TEID with the new optimal service instance
      CIS-ID (S1B in this example).  The RAN PE resolves the new T2ST
      route with the corresponding DSD route of the new CIS-ID.

4.1.4.  UE mobility handling procedure













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   +----+  +----+ +----+ +-----+  +-----+  +-----+
   | UE |  |RAN1| |RAN2| |CATS |  |SiteA|  |SiteB|
   |    |  | PE | | PE | |MUP-C|  | PE  |  | PE  |
   +----+  +----+ +----+ +-----+  +-----+  +-----+
     |       |       |      |        |        |
     |       0.DSD
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID)
     |       |<----------------------|        |
     |       |<-------------------------------|
     |       0.DSD
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID)
     |       |       |<--------------|        |
     |       |       |<-----------------------|
     |       |       |      |        |        |
     |       1.CMU - periodically advertised
     |       (CS-ID S1, CIS-ID S1A, CATS metrics)
     |       (CS-ID S1, CIS-ID S1B, CATS metrics)
     |       |       |      |<-------|        |
     |       |       |      |<----------------|
        UE traffic is currently routed
             from RAN1 to SiteA
     |------>|---------------------->|        |
     |       |       |      |        |        |
     2.UE moves to RAN2
     CATS-MUP-C recieves modified UE session information
     |       |       |      |        |        |
     |       |       |      |        |        |
     |      3.CATS-MUP-C determines
     |      optimal service instance S1B
     |       |       |      |        |        |
     |      4.TS2T
     |      (CS-ID S1, CIS-ID S1B, TEID)
     |       |       |      |        |        |
     |       |       |<-----|        |        |
     9. RAN2 PE use DSD route from SiteB (CIS-ID S1B)
     to route UE traffic to SiteB
     |-------------->|----------------------->|



                  Figure 3: UE mobility handling procedure

   Figure 4 describes the sequence of how the CATS-MUP Centralized
   deployment approach setup the underlay routing path when UE moves to
   a new RAN.




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   *  DSD routes are advertised from service site PEs to all RAN PEs.
      CMU routes are periodically advertised from the site PEs to the
      CATS-MUP-C

   *  When UE moves to a different RAN, the CATS-MUP-C recieves modified
      UE session information from the mobility management system

   *  The CATS-MUP-C select the new optimal service instance based on
      the current CATS metrics and send a corresponding T2ST route to
      the new RAN PE that maps the session information with the new
      optimal service instance CIS-ID (CIS-ID S1B in this example).  In
      case of connection to the previous service instance is required,
      the CATS-MUP-C should send a T2ST route that maps the session
      information with the previous service instance CIS-ID first before
      updating with a new T2ST route later.

   *  Upon recieving the T2ST route, the RAN PE selects the DSD route
      that has the same CIS-ID information with the recieved T2ST route
      (CIS-ID S1B in this example).  The RAN PE uses this D2D route for
      steering the UE traffic to the optimal service site.

4.2.  CATS-MUP Distributed Deployment case

4.2.1.  MUP Route enhancements

   Compared with the original route definition introduced in
   [I-D.draft-ldbc-cats-framework], the Direct Segment Discovery Route
   (DSD) and the Type 2 Session Transformed Route (T2ST) need
   modifications to support the distributed CATS-MUP deployment case.

   The Direct Segment Discovery route advertises the reachability
   information of the direct segment.  This route is advertised from the
   PEs attaching to the direct segments to the PEs attaching to the
   mobile network access side.  For the distributed CATS-MUP deployment
   case, in addition to the CS-ID and the CIS-ID, the CATS metrics of
   the corresponding service instance of the PE is also included.  The
   CS-ID can be used as the direct segment extended community ID.  The
   list below shows the information that should be included in the BGP
   NLRI of the DSD route in CATS-MUP centralized deployment case:

   *  CS-ID

   *  CIS-ID

   *  CATS metrics

   *  Attached PE SID




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   The Type 2 Session Transformed Route convert the session information
   into dataplane routing information.  This route is advertised from
   the CATS-MUP-C to the PEs attaching to the mobile network access
   side.  For the distributed CATS-MUP deployment case, this route type
   only includes the target service identifier CS-ID and the tunnel
   endpoint identifier on the mobile network core side information.  The
   list below shows the information that should be included in the BGP
   NLRI of the T2ST route in CATS-MUP centralized deployment case:

   *  CS-ID

   *  Tunnel Endpoint Identifier on the core side

4.2.2.  Deployment architecture

                             +----------------+
                             |    Mobility    |
                             |   Management   |
                             |     System     |
                             +----------------+
                                      |
                        Session Information, CS-ID
                                      |
                     T2ST    +--------v-------+
                     +-------|                |
                  +--|-------|      MUP-C     |---------+
                  |  |       |                |         |
                  |  |       +----------------+         |   +----------+
      UE-         |  v                                  |   |   C-SMA  |
         \+---+   +------+ DSD A                 +------+   |----------|-Service1
      UE--|RAN|---|  PE  |<----------------------|  PE  |---|  Service | Instance
          +---+   +------+<---------------\      +------+   |   Site A | (CS-ID S1)
      UE-/        | C-PS | DSD B           \            |   +----------+ (CIS-ID S1A)
                  +------+                  \           |
                  |                          \          |
                  |                           \         |
                  |     MUP network            \ +------+   +----------+
                  |      +-------+              \|  PE  |---|  Service |
                  |      | C-NMA |               +------+   |   Site B |-Service1
                  |      +-------+                      |   |----------| Instance
                  +-------------------------------------+   |   C-SMA  | (CS-ID S1)
                                                            +----------+ (CIS-ID S1B)




           Figure 4: CATS-MUP Distributed deployment option




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   Figure 5 describes the CATS-MUP Distributed deployment architecture.
   This option has the following key features:

   *  The DSD routes periodically advertise service, service instance
      identity information (CS-ID and CIS-ID) and CATS metrics from the
      Service Site PEs to the RAN PEs.

   *  The T2ST routes provides the UE session information and requested
      service CS-ID to the RAN-PE.

   *  The C-PS at the RAN-PE selects the optimal service instance based
      on current CATS metrics provided from the DSD routes.

4.2.3.  New UE request underlay routing setup procedure

   +----+  +----+  +-----+  +-----+  +-----+
   | UE |  |RAN1|  |     |  |SiteA|  |SiteB|
   |    |  | PE |  |MUP-C|  | PE  |  | PE  |
   +----+  +----+  +-----+  +-----+  +-----+
     |       |       |        |        |
     |       0.DSD (periodically advertised)
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID, CATS metrics)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID, CATS metrics)
     |       |<---------------|        |
     |       |<------------------------|
     |       |       |        |        |
     1. UE request session establishment
     MUP-C recieves UE session information
     |       |       |        |        |
     |      2.TS2T
     |      (CS-ID S1, TEID)
     |       |<------|        |        |
     |       |       |        |        |
     3. C-PS at RAN1 PE determines service instance CIS-ID S1A
     as the optimal one, use the DSD route that has CIS-ID S1A
     to route UE request
     |------>|--------------->|        |
     |       |       |        |        |
     4. In case of optimal service instance change
     to SiteB based on current metrics
     |       |       |        |        |
     5. C-PS at RAN1 PE determines service instance CIS-ID S1B
     as the optimal one, use the DSD route that has CIS-ID S1B
     to route UE request
     |------>|------------------------>|






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         Figure 5: New UE request underlay routing setup procedure

   Figure 6 describes the sequence of how the CATS-MUP Distributed
   deployment approach setup the underlay routing path for an UE
   request.

   *  DSD routes are advertised from the PEs of the service sites that
      hosts the service instances to all of the RAN PEs.  Because CATS
      metrics are periodically updated, these routes are also
      periodically advertises to the RAN PEs with the latest CATS
      metrics alongside the service, service instance identities (CS-ID,
      CIS-ID) and the PE SRv6 SID.

   *  When a UE request session establishment to the mobile management
      system, the MUP-C recieves the session information which includes
      the requested service CS-ID and the TEID of the session.  The
      MUP-C provides this information to the RAN PEs via the T2ST
      routes.

   *  Upon recieving the T2ST route, the C-PS at the RAN PE selects
      optimal service instance for the requested service (identified by
      the CS-ID) based on the current CATS metrics of the service
      advertised from the DSD routes.  The RAN PE uses the D2D route
      that has the optimal service instance CIS-ID for steering the UE
      traffic to the optimal service site.

   *  In case of the optimal service instance change to another site
      (SiteB in this example) due to current CATS metrics update, the
      C-PS at the RAN-PE selects a new optimal service instance based on
      current CATS metrics.  Then, the RAN PE uses the corresponding DSD
      route of the new optimal service instance to route the UE request.

4.2.4.  UE mobility handling procedure


















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   +----+  +----+ +----+ +-----+  +-----+  +-----+
   | UE |  |RAN1| |RAN2| |CATS |  |SiteA|  |SiteB|
   |    |  | PE | | PE | |MUP-C|  | PE  |  | PE  |
   +----+  +----+ +----+ +-----+  +-----+  +-----+
     |       |       |      |        |        |
     |       0.DSD (periodically advertised)
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID, CATS metrics)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID, CATS metrics)
     |       |<----------------------|        |
     |       |<-------------------------------|
     |       0.DSD (periodically advertised)
     |       (CS-ID S1, CIS-ID S1A, SiteA PE SID, CATS metrics)
     |       (CS-ID S1, CIS-ID S1B, SiteB PE SID, CATS metrics)
     |       |       |<--------------|        |
     |       |       |<-----------------------|
     |       |       |      |        |        |
        UE traffic is currently routed
             from RAN1 to SiteA
     |------>|---------------------->|        |
     |       |       |      |        |        |
     2.UE moves to RAN2
     MUP-C recieves modified UE session information
     |       |       |      |        |        |
     |      3.TS2T
     |      (CS-ID S1, TEID)
     |       |       |      |        |        |
     |       |       |<-----|        |        |
     4. C-PS at RAN2 PE determines service instance CIS-ID S1B
     as the optimal one, use the DSD route that has CIS-ID S1B
     to route UE request
     |-------------->|----------------------->|



                  Figure 6: UE mobility handling procedure

   Figure 7 describes the sequence of how the CATS-MUP Distributed
   deployment approach setup the underlay routing path when UE moves to
   a new RAN.

   *  DSD routes are periodically advertised from service site PEs to
      all RAN PEs with the corresponding CATS metrics

   *  When UE moves to a different RAN, the MUP-C recieves modified UE
      session information from the mobility management system, and
      provided the session information TEID and the requested service
      CS-ID to the new RAN PE via the T2ST route.




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   *  The C-PS at the new RAN PE selects new optimal service instance
      based on current CATS metrics provided by the DSD routes.  Then it
      uses the DSD route that has the optimal service instance CIS-ID to
      route the UE request.

   *  In case of connection to the previous service instance is
      required, the MUP-C should provide this information in the T2ST
      route NLRI.  Then the RAN-PE uses the DSD route that has the
      previous service instance CIS-ID to route the traffic for the
      required duration before selecting the new optimal service
      instance and change the chosen DSD route for routing.

5.  References

5.1.  Informative References

   [I-D.draft-ietf-cats-usecases-requirements]
              Yao, K., Trossen, D., Boucadair, M., Contreras, LM., Shi,
              H., Li, Y., Zhang, S., and Q. An, "Mobile User Plane
              Architecture using Segment Routing for Distributed
              Mobility Management", 2 January 2024,
              <https://datatracker.ietf.org/doc/draft-ietf-cats-
              usecases-requirements/>.

   [I-D.draft-ietf-dmm-srv6mob-arch]
              Kohno, M., Clad, F., Camarillo, P., Ali, Z., and L. Jalil,
              "Architecture Discussion on SRv6 Mobile User plane", 15
              February 2024, <https://datatracker.ietf.org/doc/draft-
              ietf-dmm-srv6mob-arch/>.

   [I-D.draft-ietf-idr-5g-edge-service-metadata]
              Dunbar, L., Majumdar, K., Li, C., Mishra, G., and Z. Du,
              "Distribute Service Metric By BGP", 22 July 2024,
              <https://datatracker.ietf.org/doc/draft-ietf-idr-5g-edge-
              service-metadata/>.

   [I-D.draft-ldbc-cats-framework]
              Li, C., Du, Z., Boucadair, M., Contreras, L. M., Drake,
              J., Huang, D., and G. S. Mishra, "A Framework for
              Computing-Aware Traffic Steering (CATS)", Work in
              Progress, Internet-Draft, draft-ldbc-cats-framework-03, 22
              June 2023, <https://datatracker.ietf.org/doc/html/draft-
              ldbc-cats-framework-03>.

   [I-D.draft-lin-idr-distribute-service-metric]
              Lin, C. and H. Yao, "Distribute Service Metric By BGP", 6
              June 2024, <https://datatracker.ietf.org/doc/draft-lin-
              idr-distribute-service-metric/>.



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   [I-D.draft-mhkk-dmm-mup-architecture]
              Matsushima, S., Horiba, K., Khan, A., Kawakami, Y.,
              Murakami, T., Patel, K., Kohno, M., Kamata, T., Camarillo,
              P., Horn, J., Voyer, D., Zadok, S., Meilik, I., Agrawal,
              A., and K. Perumal, "Mobile User Plane Architecture using
              Segment Routing for Distributed Mobility Management", Work
              in Progress, Internet-Draft, mhkk-dmm-mup-architecture, 3
              March 2024, <https://datatracker.ietf.org/doc/draft-mhkk-
              dmm-mup-architecture/>.

   [ieee-access-cats-mup]
              Tran, M-N., Duong, V-B., and Y. Kim, "Design of Computing-
              Aware Traffic Steering Architecture for 5G Mobile User
              Plane", 24 June 2024,
              <https://doi.org/10.1109/ACCESS.2024.3418960>.

   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", December 2006,
              <https://datatracker.ietf.org/doc/rfc4786/>.

   [RFC7333]  Chan, H., Liu, D., Seite, P., Yokota, H., and J. Korhonen,
              "Requirements for Distributed Mobility Management", August
              2014, <https://datatracker.ietf.org/doc/rfc7333/>.

Authors' Addresses

   Minh-Ngoc Tran
   Soongsil University
   369, Sangdo-ro, Dongjak-gu
   Seoul
   06978
   Republic of Korea
   Email: mipearlska1307@dcn.ssu.ac.kr


   Younghan Kim
   Soongsil University
   369, Sangdo-ro, Dongjak-gu
   Seoul
   06978
   Republic of Korea
   Phone: +82 10 2691 0904
   Email: younghak@ssu.ac.kr








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