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Versions: 00 01 02                                                      
Network Working Group                                   L. Dunbar
Internet Draft                                          Futurewei
Intended status: Standard                             K. Majumdar
Expires: May 2, 2021
CommScope
                                                          H. Wang
                                                           Huawei

                                                 November 2, 2020

        BGP NLRI App Meta Data for 5G Edge Computing Service
         draft-dunbar-idr-5g-edge-compute-app-meta-data-01

Abstract

   This draft describes a new BGP Network Layer Reachability
   Information (BGP NLRI) Path Attribute, AppMetaData, that can
   distribute the 5G Edge Computing App running status and
   environment, so that other routers in the 5G Local Data
   Network can make intelligent decision on optimized forwarding
   of flows from UEs. The goal is to improve latency and
   performance for 5G Edge Computing services.

   The extension enables a feature, called soft anchoring, which
   makes one Edge Computing Server at one specific location to be
   more preferred than others for the same application to receive
   packets 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.

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79. This document may not be
   modified, and derivative works of it may not be created,
   except to publish it as an RFC and to translate it into
   languages other than English.

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working
   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.



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   Internet-Drafts are draft documents valid for a maximum of six
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Table of Contents


   1. Introduction.............................................. 3
      1.1. 5G Edge Computing Background......................... 3
      1.2. Problem#1: ANYCAST in 5G EC Environment.............. 5
      1.3. Problem #2: Unbalanced Anycast Distribution due to UE
      Mobility.................................................. 6


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      1.4. Problem 3: Application Server Relocation............. 6
   2. Conventions used in this document......................... 7
   3. Usage of App Meta Data for 5G Edge Computing.............. 8
      3.1. Overview............................................. 8
      3.2. IP Layer Metrics to Gauge Application Behavior....... 9
      3.3. To Equalize among Multiple ANYCAST Locations........ 10
      3.4. BGP Protocol Extension to advertise Load & Capacity. 10
   4. The NLRI Path Attribute for App Meta Data................ 11
      4.1. Load Measurement sub-TLV format..................... 13
      4.2. Capacity Index sub-TLV format....................... 14
      4.3. The Site Preference Index sub-TLV format............ 14
   5. Soft Anchoring of an ANYCAST Flow........................ 15
   6. Manageability Considerations............................. 17
   7. Security Considerations.................................. 17
   8. IANA Considerations...................................... 17
   9. References............................................... 17
      9.1. Normative References................................ 17
      9.2. Informative References.............................. 17
   10. Acknowledgments......................................... 18

1. Introduction

   This document describes a new BGP Network Layer Reachability
   Information (BGP NLRI) Path Attribute, AppMetaData, that can
   distribute the 5G Edge Computing App running status and
   environment, so that other routers in the 5G Local Data
   Network can make intelligent decision on optimized forwarding
   of flows from UEs. The goal is to improve latency and
   performance for 5G Edge Computing services.



  1.1. 5G Edge Computing Background

   As described in [5G-EC-Metrics], one Application can have
   multiple Application Servers hosted in different Edge
   Computing data centers that are close in proximity. Those Edge
   Computing (mini) data centers are usually very close to, or
   co-located with, 5G base stations, with the goal to minimize
   latency and optimize the user experience.

   When a UE (User Equipment) initiates application packets using
   the destination address from a DNS reply or from its own
   cache, the packets from the UE are carried in a PDU session
   through 5G Core [5GC] to the 5G UPF-PSA (User Plan Function -


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   PDU Session Anchor). The UPF-PSA decapsulate the 5G GTP outer
   header and forwards the packets from the UEs to the Ingress
   router of the Edge Computing (EC) Local Data Network (LDN).
   The LDN for 5G EC, which is the IP Networks from 5GC
   perspective, is responsible for forwarding the packets to the
   intended destinations.

   When the UE moves out of coverage of its current gNB (next
   generation Node B) (gNB1), handover procedures are initiated
   and the 5G SMF (Session Management Function) also selects a
   new UPF-PSA. The standard handover procedures described in
   3GPP TS 23.501 and TS 23.502 are followed. When the handover
   process is complete, the UE has a new IP address and the IP
   point of attachment is to the new UPF-PSA. 5GC may maintain a
   path from the old UPF to new the UPF for a short period of
   time for SSC [Session and Service Continuity] mode 3 to make
   the handover process more seamless.































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   +--+
   |UE|---\+---------+                 +------------------+
   +--+    |  5G     |    +---------+  |   S1: aa08::4450 |
   +--+    | Site +--++---+         +----+                |
   |UE|----|  A   |PSA| Ra|         | R1 | S2: aa08::4460 |
   +--+    |      +---+---+         +----+                |
  +---+    |         |  |           |  |   S3: aa08::4470 |
  |UE1|---/+---------+  |           |  +------------------+
  +---+                 |IP Network |       L-DN1
                        |(3GPP N6)  |
     |                  |           |  +------------------+
     | UE1              |           |  |  S1: aa08::4450  |
     | moves to         |          +----+                 |
     | Site B           |          | R3 | S2: aa08::4460  |
     v                  |          +----+                 |
                        |           |  |  S3: aa08::4470  |
                        |           |  +------------------+
                        |           |      L-DN3
   +--+                 |           |
   |UE|---\+---------+  |           |  +------------------+
   +--+    |  5G     |  |           |  |  S1: aa08::4450  |
   +--+    | Site +--++-+--+        +----+                |
   |UE|----|  B   |PSA| Rb |        | R2 | S2: aa08::4460 |
   +--+    |      +--++----+        +----+                |
   +--+    |         |  +-----------+  |  S3: aa08::4470  |
   |UE|---/+---------+                 +------------------+
   +--+                                     L-DN2
            Figure 1: App Servers in different edge DCs



  1.2. Problem#1: ANYCAST in 5G EC Environment

   Increasingly, Anycast is used extensively by various
   application providers and CDNs because ANYCAST makes it
   possible to dynamically load balance across server locations
   based on network conditions.

   Application Server location selection using Anycast address
   leverages the proximity information present in the network
   (routing) layer and eliminates the single point of failure and
   bottleneck at the DNS resolvers and application layer load
   balancers. Another benefit of using ANYCAST address is


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   removing the dependency on UEs. Some UEs (or clients) might
   use their cached IP addresses instead of querying DNS for
   extended period.

   But, having multiple locations of the same ANYCAST address in
   5G Edge Computing environment can be problematic because all
   those edge computing Data Centers can be close in proximity.
   There might be very little difference in the routing cost to
   reach the Application Servers in different Edge DCs.

   BGP is an integral part in the way IP Anycast usually
   functions. Within BGP routing there are multiple routes for
   the same IP address which are pointing to different locations.

   This draft describes the BGP UPDATE extension to allow the App
   Servers Running status and environment to be included in the
   BGP UPDATE messages, so that other routers can select more
   optimal ANYCAST location based on the combination of network
   delay, the App Server load index, the location capacity index
   and the location preference.



  1.3. Problem #2: Unbalanced Anycast Distribution due to UE
    Mobility

   Another problem of using ANYCAST address for multiple
   Application Servers of the same application in 5G environment
   is that UEs' frequent moving from one 5G site to another,
   which can make it difficult to plan where the App Server
   should be hosted. When one App server is heavily utilized,
   other App servers of the same address close-by can be very
   underutilized. Since the condition can be short lived, it is
   difficult for the application controller to anticipate the
   move and adjust.



  1.4. Problem 3: Application Server Relocation

   When an Application Server is added to, moved, or deleted from
   a 5G Edge Computing Data Center, the routing protocol needs to
   propagate the changes to 5G PSA or the PSA adjacent routers.
   After the change, the cost associated with the site [5G-EC-
   Metrics] might change as well.




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   Note: for the ease of description, the Edge Application Server
   and Application Server are used interchangeably throughout
   this document.



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 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 host 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 external IP
               network, in front of a set of application servers.
               From IP network perspective, this whole group of
               servers are considered as the Application server
               at the location.

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

   EC:         Edge Computing

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

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


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   Edge DC:    Edge Data Center, which provides the Edge
               Computing Hosting Environment. It might be co-
               located with 5G Base Station and not only host 5G
               core functions, but also host frequently used Edge
               server instances.

   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. Usage of App Meta Data for 5G Edge Computing

  3.1. Overview

   From IP Layer, the Application Servers are identified by their
   IP (ANYCAST) addresses. The 5G Edge Computing controller or
   management system is aware of the ANYCAST addresses of the
   Applications that need optimized forwarding in 5G EC
   environment. The 5G Edge Computing controller or management
   system can configure the ACLs to filter out those applications
   on the routers adjacent to the 5G PSA and the routers to which
   the Application Servers are directly attached.

   The proposed solution is for the routers, i.e. A-ER, that have
   direct links to the Application Servers to collect various
   measurements about the Servers' running status [5G-EC-Metrics]
   and advertise the metrics to other routers in 5G EC LDN (Local
   Data Network).



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  3.2.  IP Layer Metrics to Gauge Application Behavior

   [5G-EC-Metrics] describes the IP Layer Metrics that can gauge
   the application servers running status and environment:

   - IP-Layer Metric for App Server Load Measurement:
     The Load Measurement to an App Server is a weighted
     combination of the number of packets/bites to the App Server
     and the number of packets/bytes from the App Server which
     are collected by the A-ER to which the App Server is
     directly attached.
     The A-ER is configured with an ACL that can filter out the
     packets for the Application Server.
   - Capacity Index
     Capacity Index is used to differentiate the running
     environment of the application server. Some data centers can
     have hundreds, or thousands, of servers behind an
     Application Server's App Layer Load Balancer that is
     reachable from external world. Other data centers can have
     very small number of servers for the application server.
     "Capacity Index", which is a numeric number, is used to
     represent the capacity of the application server in a
     specific location.
   - Site preference index:
     [IPv6-StickyService] describes a scenario that some sites
     are more preferred for handling an application server than
     others for flows from a specific UE.


   In this document, the term "Application Server Egress Router"
   [A-ER] is used to describe the last router that an Application
   Server is attached. For 5G EC environment, the A-ER can be the
   gateway router to the EC DC where multiple Application
   servers' instance are hosted.

   From IP Layer, an Application Server is identified by its IP
   (ANYCAST) Address. Those IP addresses are called the
   Application Server IDs throughout this document.




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  3.3. To Equalize among Multiple ANYCAST Locations

   The main benefit of using ANYCAST is to leverage the network
   layer information to equalize the traffic among multiple
   Application Server locations of the same Application, which is
   identified by its ANYCAST addresses.

   For 5G Edge Computing environment, the ingress routers to the
   LDN needs to be notified of the Load Index and Capacity Index
   of the App Servers at different EC data centers to make the
   intelligent decision on where to forward the traffic for the
   application from UEs.

   [5G-EC-Metrics] describes the algorithms that can be used by
   the routers directly attached to the 5G PSA to compare the
   cost to reach the App Servers between the Site-i or Site-j:

               Load-i * CP-j               Pref-j * Delay-i
Cost-i=min(w *(----------------) + (1-w) *(------------------))
              Load-j * CP-i               Pref-i * Delay-j


      Load-i: Load Index at Site-i, it is the weighted
      combination of the total packets or/and bytes sent to and
      received from the Application Server at Site-i during a
      fixed time period.

      CP-i: capacity index at the site I, higher value means
      higher capacity.

      Delay-i: Network latency measurement (RTT) to the A-ER that
      has the Application Server attached at the site-i.

      Pref-i: Preference index for the site-i, higher value means
      higher preference.

      w: Weight for load and site information, which is a value
      between 0 and 1. If smaller than 0.5, Network latency and
      the site Preference have more influence; otherwise, Server
      load and its capacity have more influence.



   3.4. BGP Protocol Extension to advertise Load & Capacity

   Goal of the protocol extension:



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   - Propagate the Load Measurement Index for the attached App
     Servers to other routers in the LDN.

   - Propagate the Capacity Index &

   - Propagate Site Preference Index.

   The BGP extension is to add the Load Index Sub-TLV, Capacity
   Sub-TLV, and the Site Preference Sub-TLV in the NLRI
   associated with the routes.




4. The NLRI Path Attribute for App Meta Data

   The App Meta Data attribute is an optional transitive BGP Path
   attribute to carry application specific data, such as running
   status, capacity and site preference.  Will need IANA to
   assign a value as the type code of the attribute.  The
   attribute is composed of a set of Type-Length-Value (TLV)
   encodings.  Each TLV contains information corresponding to
   metrics to a specific Application Server.  An App Meta Data
   TLV, is structured as shown in Figure 1:

      0                   1                   2                   3
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | AppMetaData Type (2 Octets)   |        Length (2 Octets)      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                             Value                             |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 2: App Meta Data TLV Value Field


   AppMetaData Type (2 octets): identifies a type of Application
   related metadata.  The field contains values from the IANA
   Registry "BGP AppMetaData Types". To be added.

      o  Length (2 octets): the total number of octets of the
   value field.

      o  Value (variable): comprised of multiple sub-TLVs.




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   Each sub-TLV consists of three fields: a 1-octet type, a 1-
   octet or 2-octet length field (depending on the type), and
   zero or more octets of value.  A sub-TLV is structured as
   shown in Figure 2:

                       +--------------------------------+
                       | Sub-TLV Type (1 Octet)         |
                       +--------------------------------+
                       | Sub-TLV Length (1 or 2 Octets) |
                       +--------------------------------+
                       | Sub-TLV Value (Variable)       |
                       +--------------------------------+

                Figure 3: App Metadata Sub-TLV Value Field


     o  Sub-TLV Type (1 octet): each sub-TLV type defines a
     certain property about the AppMetaData TLV that contains
     this sub-TLV.  The field contains values from the IANA
     Registry "BGP AppMetaData Attribute Sub-TLVs".

     o  Sub-TLV Length (1 or 2 octets): the total number of
     octets of the sub-TLV value field.  The Sub-TLV Length field
     contains 1 octet if the Sub-TLV Type field contains a value
     in the range from 0-127. The Sub-TLV Length field contains
     two octets if the Sub-TLV Type field contains a value in the
     range from 128-255.

     o  Sub-TLV Value (variable): encodings of the value field
     depend on the sub-TLV type as enumerated above. The
     following sub-sections define the encoding in detail.



















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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 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 the egress
   routers cannot be configured with a consistent algorithm to
   compute the aggregated load index and the raw measurements are
   needed by a central analytic system.

     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                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 4: Aggregated Load Index Sub-TLV



   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 (TBD3)         |               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 5: Raw Load Measurement Sub-TLV


     Type =TBD2: 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 w1+ w2+ w3+ w4 = 1 and  0< wi <1;


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     Type= TBD3: 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 (TBD4)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Capacity Index                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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 (TBD5)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Preference Index                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   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.






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5. Soft Anchoring of an ANYCAST Flow
   "Sticky Service" in the 3GPP Edge Computing specification
   (3GPP TR 23.748) requires a UE to a specific ANYCAST location
   when the UE moves from one 5G Site to another.

   "Soft Anchoring" is referring to forwarding the Application
   flow from the UE to the a preferred location for the ANYCAST
   address, when the preferred location is in good condition.
   But if there is any failure at the preferred location, the
   Application flow from the UE need to be forwarded to another
   location that host the same application.

   This section describes a solution that can softly anchor an
   application flow from a UE to a preferred location.

   Lets' assume one application "App.net" is instantiated on
   four servers that are attached to four different routers R1,
   R2, R3, and R4 respectively. It is desired for packets to the
   "App.net" from UE-1 to stick with one server, say the App
   Server attached to R1, even when the UE moves from one 5G
   site to another. When there is failure at R1 or the
   Application Server attached to R1, the packets of the flow
   "App.net" from UE-1 need to be forwarded to the Application
   Server attached to R2, R3, or R4.

   We call this kind of sticky service "Soft Anchoring", meaning
   that anchoring to the site of R1 is preferred, but other
   sites can be chosen when the preferred site encounters
   failure.

   Here is details of this solution:

      - Assign a group of ANYCAST addresses to one application.
        For example, "App.net" is assigned with 4 ANYCAST
        addresses, L1, L2, L3, and L4. L1/L2/L3/L4 represents
        the location preferred ANYCAST addresses.
      - For the App.net Server attached to a router, the router
        has four Stub links to the same Server, L1, L2, L3, and
        L4 respectively. The cost to L1, L2, L3 and L4 is
        assigned differently for different routers. For example,
           o When attached to R1, the L1 has the lowest cost,
             say 10, when attached to R2, R3, and R4, the L1 can
             have higher cost, say 30.




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           o ANYCAST L2 has the lowest cost when attached to R2,
             higher cost when attached to R1, R3, R4
             respectively.
           o ANYCAST L3 has the lowest cost when attached to R3,
             higher cost when attached to R1, R2, R4
             respectively, and
           o ANYCAST L4 has the lowest cost when attached to R4,
             higher cost when attached to R1, R2, R3
             respectively
      - When a UE queries for the "App.net" for the first time,
        the DNS replies the location preferred ANYCAST address,
        say L1, based on where the query is initiated.
      - When the UE moves from one 5G site-A to Site-B, UE
        continues sending packets of the "App.net" to ANYCAST
        address L1. The routers will continue sending packets to
        R1 because the total cost for the App.net instance for
        ANYCAST L1 is lowest at R1. If any failure occurs making
        R1 not reachable, the packets of the "App.net" from UE-1
        will be sent to R2, R3, or R4 (depending on the total
        cost to reach each of them).


   If the Application Server supports the HTTP redirect, more
   optimal forwarding can be achieved.

      - When a UE queries for the "App.net" for the first time,
        the global DNS replies the ANYCAST address G1, which has
        the same cost regardless where the Application Servers
        are attached.
      - When the UE initiates the communication to G1, the
        packets from the UE will be sent to the Application
        Server that has the lowest cost, say the Server attached
        to R1. The Application server is instructed with HTTPs
        Redirect to respond back a location specific URL, say
        App.net-Loc1. The client on the UE will query the DNS
        for App.net-Loc1 and get the response of ANYCAST L1. The
        subsequent packets from the UE-1 for App.net are sent to
        L1.




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6. Manageability Considerations

     To be added.

7. Security Considerations


   To be added.

8. IANA Considerations

       To be added.

9. References


 9.1. 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.

   [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


 9.2. 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.





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   [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-StickyService] 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.

   [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.



10. Acknowledgments

   Acknowledgements to Donald Eastlake for their review and
   contributions.

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










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Authors' Addresses

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Kausik Majumdar
   CommScope
   350 W Java Drive, Sunnyvale, CA 94089
   Email:  kausik.majumdar@commscope.com

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
































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