BGP AppMetaData for 5G Edge Computing Service
draft-dunbar-idr-5g-edge-compute-app-meta-data-08

Network Working Group                                   L. Dunbar
Internet Draft                                          Futurewei
Intended status: Standard                             K. Majumdar
Expires: January 11, 2023                              Microsoft
                                                          H. Wang
                                                           Huawei
                                                        G. Mishra
                                                          Verizon
                                                    July 11, 2022

           BGP AppMetaData for 5G Edge Computing Service
         draft-dunbar-idr-5g-edge-compute-app-meta-data-08

Abstract
   This draft describes a new AppMetaData subTLV carried by
   Tunnel Encap[RFC9012] Path Attribute for egress router to
   advertise the running status and environment for the directly
   attached 5G Edge Computing (EC) servers. The AppMetaData can
   be used by the ingress routers in the 5G Local Data Network to
   make path selection not only based on the routing distance but
   also the running environment of the destinations. The goal is
   to improve latency and performance for 5G EC services.

   The extension enables an EC server at one specific location to
   be more preferred than the others with the same IP address to
   receive data flows from a specific source (UE).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1. Introduction.............................................. 3
   2. Conventions used in this document......................... 3
   3. BGP Protocol Extension to advertise Load & Capacity....... 4
      3.1. Ingress Node BGP Path Selection Behavior............. 5
         3.1.1. AppMetaData Influenced BGP Path Selection....... 5
         3.1.2. Ingress Router Forwarding Behavior.............. 5
         3.1.3. Forwarding Behavior when UEs moving to new 5G
         Sites.................................................. 6
   4. The Sub-TLVs for AppMetaData.............................. 7
      4.1. Load Measurement sub-TLV format...................... 7
      4.2. Capacity Index sub-TLV format........................ 8
      4.3. The Site Preference Index sub-TLV format............. 9

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   5. AppMetaData Propagation Scope............................. 9
   6. Minimum Interval for Metrics Change Advertisement......... 9
   7. Manageability Considerations............................. 10
   8. Security Considerations.................................. 10
   9. IANA Considerations...................................... 10
   10. References.............................................. 10
      10.1. Normative References............................... 10
      10.2. Informative References............................. 11
   11. Acknowledgments......................................... 12

1. Introduction

   [5g-edge-Compute] describes the 5G Edge Computing background
   and how BGP can be used to advertise the running status and
   environment of the directly attached 5G edge computing (EC)
   servers. This document describes a new subTLV, AppMetaData,
   for egress routers to advertise the running status and
   environment for the directly attached Edge Computing (EC)
   servers. The AppMetaData can be used by the ingress routers in
   the 5G Local Data Network to make path selection not only
   based on the routing distance but also the running environment
   of the destinations. The goal is to improve latency and
   performance for 5G Edge Computing services.

2. Conventions used in this document

   A-ER:       Egress Router to an Application Server, [A-ER] is
               used to describe the last router that the
               Application Server is attached. For a 5G EC
               environment, the A-ER can be the gateway router to
               a (mini) Edge Computing Data Center.

   Application Server: An application server is a physical or
               virtual server that hosts the software system for
               the application.

   Application Server Location: Represent a cluster of servers at
               one location serving the same Application. One
               application may have a Layer 7 Load balancer,
               whose address(es) are reachable from an external
               IP network, in front of a set of application
               servers. From an IP network perspective, this
               whole group of servers is considered as the
               Application server at the location.

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   Edge Application Server: used interchangeably with Application
               Server throughout this document.

   EC:         Edge Computing

   Edge Hosting Environment: An environment providing the support
               required for Edge Application Server's execution.

               NOTE: The above terminologies are the same as
               those used in 3GPP TR 23.758

   Edge DC:    Edge Data Center, which provides the Edge
               Computing Hosting Environment. An Edge DC might
               host 5G core functions in addition to the
               frequently used application servers.

   gNB         next generation Node B

   L-DN:       Local Data Network

   PSA:        PDU Session Anchor (UPF)

   SSC:        Session and Service Continuity

   UE:         User Equipment

   UPF:        User Plane Function

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
   interpreted as described in BCP 14 [RFC2119] [RFC8174] when,
   and only when, they appear in all capitals, as shown here.

3. BGP Protocol Extension to advertise Load & Capacity

    The goal of the BGP extension is for egress routers to
    propagate the metrics about their running environment to
    ingress routers. Here are some examples of the metrics
    propagated by the egress routers:

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    - the Load Measurement Index for the attached EC Servers,

    - the Capacity Index, and

    - Site Preference Index.

    This section specifies the Load Index Sub-TLV, Capacity Sub-
    TLV, and the Site Preference Sub-TLV that can be carried by
    the Tunnel Encap Path Attribute associated with the routes.

 3.1. Ingress Node BGP Path Selection Behavior

 3.1.1. AppMetaData Influenced BGP Path Selection

   When an ingress router receives BGP updates for the same IP
   address from multiple egress routers, all those egress routers
   are considered as the next hops for the IP address. For the
   selected EC services, the ingress router's BGP engine would
   call a Plugin function that can select paths based on the
   AppMetaData received. The Plugin function is called Load
   Compute Engine throughout this document.

   Suppose a destination address for 5G (S1:aa08::4450) can be
   reached by three next hops (R1, R2, R3). Further, suppose the
   local BGP's Compute Engine Identifies the R1 as the optimal
   next hop for flows to be sent to this destination
   (S1:aa08::4450). The Load Compute Engine can insert a higher
   weight for the tunnel associated with R1 for the prefix via
   the tunnel.

 3.1.2. Ingress Router Forwarding Behavior

   When the ingress router receives a packet and lookup the route
   in the FIB, it gets the destination prefix's whole path. It
   encapsulates the packet destined towards the optimal egress
   node.

   For subsequent packets belonging to the same flow, the ingress
   router needs to forward them to the same egress router unless
   the selected egress router is no longer reachable. Keeping
   packets from one flow to the same egress router, a.k.a. Flow
   Affinity, is supported by many commercial routers. Most
   registered EC services have relatively short flows.

   How Flow Affinity is implemented is out of the scope for this
   document. Here is one example to illustrate how Flow Affinity
   can be achieved. This illustration is not to be standardized.

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     For the registered EC services, the ingress node keeps a
     table of
     -   Service ID (i.e., IP address)
     -   Flow-ID
     -   Sticky Egress ID (egress router loopback address)
     -   A timer

     The Flow-ID in this table is to identify a flow, initialized
     to NULL. How Flow-ID is constructed is out of the scope for
     this document. Here is one example of constructing the Flow-
     ID:
       - For IPv6, the Flow-ID can be the Flow-ID extracted from
          the IPv6 packet header with or without the source
          address.
       - For IPv4, the Flow-ID can be the combination of the
          Source Address with or without the TCP/UDP Port number.

     The Sticky Egress ID is the egress node address for the same
     flow. [5G-Sticky-Service] describes several methods to
     derive the Sticky Egress ID.

     The Timer is always refreshed when a packet with the
     matching EC Service ID (IP address) is received by the node.

     If there is no Stick Egress ID present in the table for the
     EC Service ID, the forwarding plane can select a NextHop
     influenced by the Load Compute Engine. The forwarding plane
     encapsulates the packet with a tunnel to the chosen NextHop.
     The chosen NextHop and the Flow ID are recorded in the EC
     Service table entry.

   When the selected optimal NextHop (egress router) is no longer
   reachable, refer to Section 6 Soft Anchoring on how another
   path is selected.

 3.1.3. Forwarding Behavior when UEs moving to new 5G Sites

   When a UE moves to a new 5G eNB which is anchored to the same
   UPF, the packets from the UE traverse to the same ingress
   router. Path selection and forwarding behavior are same as
   before.

   If the UE maintains the same IP address when anchored to a new
   UPF, the directly connected ingress router might use the
   information passed from a neighboring router to derive the
   optimal Next Hop for this route. [5G-Edge-Sticky] describes

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   some methods for the ingress router connected to the UPF in
   the new site to consider the information passed from other
   ingress routers in selecting the optimal paths. The detailed
   algorithm is out of the scope of this document.

4. The Sub-TLVs for AppMetaData

   The AppMetaData attribute is encoded in an optional subTLV
   within the Tunnel Encap [RFC9012] Path Attribute.

   All values in the Sub-TLVs are unsigned 32 bits integers.

4.1. Load Measurement sub-TLV format

   Two types of Load Measurement Sub-TLVs are specified. One is
   to carry the aggregated cost Index based on a weighted
   combination of the collected measurements; another one is to
   carry the raw measurements of packets/bytes to/from the App
   Server address. The raw measurement is useful when ingress
   routers have embedded analytics relying on the raw
   measurements.

     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type (TBD1)           |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 2: Aggregated Load Index Sub-TLV

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   Raw Load Measurement sub-TLV has the following format:

     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Type (TBD2)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of packets to the AppServer            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of packets from the AppServer          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of bytes to the AppServer              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of bytes from the AppServer            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 3: Raw Load Measurement Sub-TLV

     Type =TBD1: Aggregated Load Measurement Index derived from
     the Weighted combination of bytes/packets sent to/received
     from the App server:

     Index=w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes

     Where wi is a value between 0 and 1; w1+ w2+ w3+ w4 = 1.

     Type= TBD2: Raw measurements of packets/bytes to/from the
     App Server address.

     Measure Period: BGP Update period or user-specified period.

  4.2. Capacity Index sub-TLV format

   The Capacity Index sub-TLV has the following format:

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Type (TBD3)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Capacity Index                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 4: Capacity Index Sub-TLV

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   Note: "Capacity Index" can be more stable for each site. If
   those values are configured to nodes, they might not need to
   be included in every BGP UPDATE.

  4.3. The Site Preference Index sub-TLV format

   The site Preference Index is used to achieve Soft Anchoring
   [Section 5] an application flow from a UE to a specific
   location when the UE moves from one 5G site to another.

   The Preference Index sub-TLV has the following format:

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Type (TBD4)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Preference Index                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 5: Preference Index Sub-TLV

   Note: "Site Preference Index" can be more stable for each
   site. If those values are configured to nodes, they might not
   need to be included in every BGP UPDATE.

5. AppMetaData Propagation Scope

   AppMetaData is only to be distributed to the relevant ingress
   nodes of the 5G EC local data networks. Only the ingress
   routers that are configured with the 5G EC services need to
   receive the AppMetaData for specific Service IDs.

   For each registered EC service, a corresponding filter group
   can be formed on RR to represent the interested ingress
   routers that are interested in receiving the corresponding
   AppMetaData information.

6. Minimum Interval for Metrics Change Advertisement

   As the metrics change can impact the path selection, the
   Minimum Interval for Metrics Change Advertisement is
   configured to control the update frequency to avoid route
   oscillations. Default is 30s.

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   Significant load changes at EC data centers can be triggered
   by short-term gatherings of UEs, like conventions, lasting a
   few hours or days, which are too short to justify adjusting EC
   server capacities among DCs. Therefore, the load metrics
   change rate can be in the magnitude of hours or days.

7. Manageability Considerations

     To be added.

8. Security Considerations

   To be added.

9. IANA Considerations

   Here are new Sub-TLV types requiring IANA registration:

   Type = TBD1: Aggregated Load Measurement Index derived from
   the Weighted combination of bytes/packets sent to/received
   from the App server.

   Type = TBD2: Raw measurements of packets/bytes to/from the
   App Server address.

   Type = TBD3: Capacity value sub-TLV

   Type = TBD4: Site preference value sub-TLV

10. References

  10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
             networks (VPNs)", Feb 2006.

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   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
             RFC 2119 Key Words", BCP 14, RFC 8174, DOI
             10.17487/RFC8174, May 2017, <https://www.rfc-
             editor.org/info/rfc8174>.

   [RFC8200] s. Deering R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", July 2017

  10.2. Informative References

   [3GPP-EdgeComputing] 3GPP TR 23.748, "3rd Generation
             Partnership Project; Technical Specification Group
             Services and System Aspects; Study on enhancement of
             support for Edge Computing in 5G Core network
             (5GC)", Release 17 work in progress, Aug 2020.

   [5G-EC-Metrics] L. Dunbar, H. Song, J. Kaippallimalil, "IP
             Layer Metrics for 5G Edge Computing Service", draft-
             dunbar-ippm-5g-edge-compute-ip-layer-metrics-00,
             work-in-progress, Oct 2020.

   [5g-edge-Compute] L. Dunbar, K. Majumdar, H. Wang, and G.
             Mishra, "BGP Usage for 5G Edge Computing service
             Metadata", draft-dunbar-idr-5g-edge-compute-bgp-
             usage-00, work-in-progress, July 2022.

   [5G-Edge-Sticky] L. Dunbar, J. Kaippallimalil, "IPv6 Solution
             for 5G Edge Computing Sticky Service", draft-dunbar-
             6man-5g-ec-sticky-service-00, work-in-progress, Oct
             2020.

   [RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation
             Subsequent Address Family Identifier (SAFI) and the
             BGP Tunnel Encapsulation Attribute", April 2009.

   [BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension
             for SDWAN Overlay Networks", draft-dunbar-idr-bgp-
             sdwan-overlay-ext-03, work-in-progress, Nov 2018.

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   [SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
             Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
             draft-dunbar-idr-sdwan-edge-discovery-00, work-in-
             progress, July 2020.

   [Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation
             Attribute", draft-ietf-idr-tunnel-encaps-10, Aug
             2018.

11. Acknowledgments

   Acknowledgements to Sue Hares, Donald Eastlake for their
   review and contributions.

   This document was prepared using 2-Word-v2.0.template.dot.

Authors' Addresses

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Kausik Majumdar
   Microsoft
   Email: kmajumdar@microsoft.com

   Haibo Wang
   Huawei
   Email: rainsword.wang@huawei.com

   Gyan Mishra
   Verizon
   Email: gyan.s.mishra@verizon.com

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