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Versions: 00 01 02                                                      
Network Working Group                                     L. Dunbar
Internet Draft                                            Futurewei
Intended status: Standard                               K. Majumdar
Expires: April 31, 2021                                  CommScope

                                                   October 31, 2020



         BGP NLRI App Meta Data for 5G Edge Computing Service
          draft-dunbar-idr-5g-edge-compute-app-meta-data-00

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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   This Internet-Draft will expire on April 7, 2021.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
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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.................................................... 5
      1.4. Problem 3: Application Server Relocation............... 6
   2. Conventions used in this document........................... 6
   3. Usage of App Meta Data for 5G Edge Computing................ 7
      3.1. Overview............................................... 7


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      3.2. IP Layer Metrics to Gauge Application Behavior......... 8
      3.3. To Equalize among Multiple ANYCAST Locations........... 9
      3.4. BGP Protocol Extension to advertise Load & Capacity... 10
      3.5. Reason for using BGP Based Solution:.................. 10
   4. The NLRI Path Attribute for App Meta Data.................. 10
      4.1. Load Measurement sub-TLV format....................... 12
      4.2. Capacity Index sub-TLV format......................... 13
      4.3. The Site Preference Index sub-TLV format.............. 13
   5. Soft Anchoring of an ANYCAST Flow.......................... 14
   6. Manageability Considerations............................... 16
   7. Security Considerations.................................... 16
   8. IANA Considerations........................................ 16
   9. References................................................. 16
      9.1. Normative References.................................. 16
      9.2. Informative References................................ 16
   10. Acknowledgments........................................... 17

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 - 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,


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   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.
   +--+
   |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



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  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 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.


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  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.







   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.



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   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

   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


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   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).



  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.




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   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.


  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:

         alpha*(LoadIndex-i*Beta-i)   (1-alpha)*(Delay-i*gamma-i)
Cost=min(--------------- ----------  + -----------------------------)
          (LoadIndex-j * Beta-j)          ( Delay-j *gamm-j)




      LoadIndex-i: weighted combination of the total bytes (or/and
      packets) sent to/received from the Application Server at
      Site-i during a fixed time period.

      Beta-i (larger value means higher capacity): capacity index
      at the site i.

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

      gamma (larger value means higher preference): Network
      Preference index for the site-I.



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      alpha (a value between 0 and 1: Weight for load & site Index.
      If smaller than 0.5, Network latency has more influence;
      otherwise, Server load has more influence).



   3.4. BGP Protocol Extension to advertise Load & Capacity

   Goal of the protocol extension:
   - 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.



   3.5. Reason for using BGP Based Solution:

   To Be Added


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:











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      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.

   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.



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     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.



4.1. Load Measurement sub-TLV format

   Two types of Load Measurement Sub-TLVs are specified. One is to
   carry the measurements of packets/bytes to/from the App Server
   address, another one is to carry the aggregated cost Index based
   on weighted combination of the collected measurements.


   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 4: Load Measurement Sub-TLV



     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                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 5: Aggregated Load Index Sub-TLV

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





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     Type =TBD3: 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;

     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                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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   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. 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,





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           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.
           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




































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