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Versions: 00 01 02 03 04                                                
Network Working Group                                L. Dunbar
Internet Draft                                         H. Chen
Intended status: Standard                            Futurewei
Expires: June 18, 2021                              Aijun Wang
                                                 China Telecom

                                             December 18, 2020


          OSPF extension for 5G Edge Computing Service
          draft-dunbar-lsr-5g-edge-compute-ospf-ext-02

Abstract

   This draft describes an OSPF extension to distribute the 5G
   Edge Computing App running status and environment, so that
   other routers in the 5G Local Data Network can make
   intelligent decision to optimize forwarding of flows from
   UEs. The goal is to improve latency and performance for 5G
   Edge Computing services.

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
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   documents as Internet-Drafts.

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




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   The list of current Internet-Drafts can be accessed at
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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.......... 5
   2. Conventions used in this document...................... 6
   3. Solution Overview...................................... 7
      3.1. Flow Affinity to an ANYCAST server................ 8
      3.2. IP Layer Metrics to Gauge App Server Running Status
      ....................................................... 9
      3.3. To Equalize traffic among Multiple ANYCAST
      Locations............................................. 10
      3.4. Reason for using IGP Based Solution.............. 11
   4. Aggregated Cost Computed by Egress routers............ 11
      4.1. OSPFv3 LSA to carry the Aggregated Cost.......... 12
      4.2. OSPFv2 LSA to carry the Aggregated Cost.......... 12


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   5. IP Layer App-Metrics Advertisements................... 12
      5.1. OSPFv3 Extension to carry the App-Metrics........ 13
      5.2. OSPFv2 Extension to advertise the IP Layer App-
      Metrics............................................... 14
      5.3. IP Layer App-Metrics Sub-TLVs.................... 15
   6. Soft Anchoring of an ANYCAST Flow..................... 17
   7. Manageability Considerations.......................... 19
   8. Security Considerations............................... 19
   9. IANA Considerations................................... 19
   10. References........................................... 19
      10.1. Normative References............................ 19
      10.2. Informative References.......................... 20
   11. Acknowledgments...................................... 21

1. Introduction

   This document describes an OSPF extension to distribute the
   5G Edge Computing App running status and environment, so
   that other routers in the 5G Local Data Network can make
   intelligent decision to optimize 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 can be 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 to 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 decapsulates
   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 IP based LDN for 5G EC is




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   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 how UEs get the IP addresses for
   their Applications. 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, which can cause packets from one flow to be
   forwarded to different locations, resulting in service
   glitches.

 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 Servers should be hosted. When one App server is
   heavily utilized, other App servers of the same address
   close-by can be very under-utilized. 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
   must propagate the changes to 5G PSA or the PSA adjacent



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   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 Computing
   server, Application server, App 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.





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               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. Solution 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 packets to or from those applications on
   routers, especially on the routers adjacent to the 5G PSA
   and the routers to which the Application Servers are
   directly attached.





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   The proposed solution is for the routers, a.k.a.
   Application Egress Router (A-ER), to which the Application
   Servers are attached 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).

 3.1. Flow Affinity to an ANYCAST server

   When there are multiple Edge Computing Servers with the
   same ANYCAST address located in different mini Edge
   Computing Data Centers, each location is identified by its
   A-ER unicast address(es). To the routers in an LDN,
   achieving Flow Affinity is to send the packets of the same
   flow to the same A-ER's unicast address.  A-ER, e.g. R1 in
   Figure 1, should deliver the packets destined towards the
   ANYCAST address to its directly attached server even
   through the same address is also reachable from other
   routers, unless the directly attached server is no longer
   reachable due to Server or Link failure.

   Many commercial routers today support some forms of flow
   affinity to ensure packets belonging to one flow be
   forwarded along the same path. For servers with the same
   ANYCAST address attached to 3 different egress routers,
   routers supporting the flow affinity feature should forward
   the packets of one flow to the same egress router even if
   the cost towards the egress router changes.

   Editor's note: for IPv6 traffic, Flow Affinity can be
   supported by the routers of the Local Data Network (LDN)
   forwarding the packets with the same Flow Label in the
   packets' IPv6 Header along the same path towards the same
   egress router. For IPv4 traffic, 5 tuples in the IPv4
   header can be used to achieve the Flow Affinity















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 3.2. IP Layer Metrics to Gauge App Server Running Status

   Most application don't expose their internal logics to
   network. Their communications are generally encrypted. Most
   of them do not even respond to PING or ICMP messages
   initiated by routers or network gears.

   [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
       than others for flows from a specific UE.

   For ease of description, those metrics, more may be added
   later, are called IP Layer App-Metrics throughout the
   document.





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 3.3. To Equalize traffic among Multiple ANYCAST Locations

   The main benefit of using ANYCAST is to leverage the
   network layer information to balance the traffic among
   multiple Application Server locations.

   For 5G Edge Computing environment, the routers in the LDN
   need to be notified of various measurement 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 in LDN to compare the cost to reach the App
   Servers between the Site-i or Site-j:

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

      Network Delay-i: Network latency measurement (RTT) to
      the A-ER that has the Application Server attached at the
      site-i.
      Noted: Ingress nodes can easily measure RTT to all the
      egress nodes by existing IPPM metrics. But it is not so
      easy for ingress nodes to measure RTT to all the App
      Servers. Therefore, "Network-Delay-i", a.k.a. Network
      latency measurement (RTT), is between the Ingress nodes
      and egress nodes. The link cost between the egress nodes
      to their attached servers are embedded in the "capacity
      index".

      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;



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      otherwise, Server load and its capacity have more
      influence.

 3.4. Reason for using IGP Based Solution

    Goal of the proposed OSPF extension is to propagate the IP
    Layer App-Metrics to other routers in the LDN.
    Here are some of the benefits in using IGP to propagate
    the IP Layer App-Metrics:
    - Intermediate routers can derive the aggregated cost to
      reach the Application Servers attached to different
      egress nodes, especially:
        - the path to the optimal egress node can be more
           accurate or shorter
        - convergence is shorter when there is any failure
           along the way towards the optimal ANYCAST server.
        - When there is any failure at the intended ANYCAST
           server, all the transient packets can be optimally
           forwarded to another App Server with the same
           ANYCAST address attached to a different egress
           router.
    - Doesn't need ingress node to establish tunnels with
      egress nodes.

    Of course, there are limitation of using IGP too, such as:

    - The IGP approach might not suit well to 5G EC LDN
      operated by multiple ISPs networks.
      For LDN operated by multiple IPSs, BGP should be used.
      AppMetaData NLRI Path Attribute [5G-AppMetaData]
      describes the BGP UPDATE message to propagate IP Layer
      App-Metrics crossing multiple ISPs.



4. Aggregated Cost Computed by Egress routers

   If all egress routers to which the App Servers are attached
   can be configured with a consistent algorithm to compute an
   aggregated cost that take into consideration of Load
   Measurement, Capacity value and Preference value. Then this
   aggregated cost can be considered as the Metric of the link
   to the App Server.




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   In this scenario, there is no protocol extension needed,
   but requires all egress routers to agree upon a consistent
   algorithm to compute the cost to the attached App servers.

 4.1. OSPFv3 LSA to carry the Aggregated Cost

   If the App Servers use IPv6 ANYCAST address, the aggregated
   cost computed by the egress routers can be encoded in the
   Metric field [the interface cost] of Intra-Area-Prefix-LSA
   specified by the Section 3.7 of the [ RFC5340].

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     6 (Intra-Area Prefix)     |         TLV Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          0    | Aggregated Cost to the App Server             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | PrefixLength  | PrefixOptions |             0                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Address Prefix                      |
     |                               ...                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 2: Aggregated Cost to App Server


 4.2. OSPFv2 LSA to carry the Aggregated Cost

   For App Servers in IPv4 address, the Aggregated Cost can be
   encoded in the "Metric" field of the Stub Link LSA [Link
   type =3] specified by the Section 12.4 of the [RFC2328].



5. IP Layer App-Metrics Advertisements

   This section describes the approaches to advertise the IP
   Layer App-Metrics to other nodes. Those approaches are
   needed for a scenario when it is not possible for all the
   egress routers to have a consistent algorithm to compute
   the aggregated cost, or the ingress routers need all the
   detailed IP Layer metrics for the App Servers for other
   purposes.

   Under this scenario, the IP Layer Metrics to Gauge App
   Server running status are encoded in the sub-TLVs, which
   are specified in Section 5.3.




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   Since only a subset of routers within an IGP domain need to
   know those detailed metrics, it makes sense to use the
   OSPFv2 Extended Prefix Opaque LSA for IPv4 and OSPFv3
   Extended LSA with Intra-Area-Prefix TLV to carry the
   detailed sub-TLVs.  For routers that don't care about those
   metrics, they can ignore them very easily.

   It worth noting that not all hosts (prefix) attached to an
   A-ER are ANYCAST servers that need network optimization
   among multiple locations. An A-ER only needs to advertise
   the App-Metrics for the ANYCAST servers that need the
   network to optimize the forwarding. Therefore, A-ER do not
   need to include App-Metrics for all attached prefixes.

   Draft [draft-wang-lsr-passive-interface-attribute]
   introduces the Stub-Link TLV for OSPFv2/v3 and ISIS
   protocol respectively. Considering the interfaces on an
   edge router that connects to the App servers are normally
   configured as passive interfaces, these IP-layer App-
   metrics can also be advertised as the attributes of the
   passive/stub link. The associated prefixes can then be
   advertised in the "Stub-Link Prefix Sub-TLV" that defined
   in [draft-wang-lsr-passive-interface-attribute]. All the
   associated prefixes share the same characteristic of the
   link. Other link related sub-TLVs that defined in
   [RFC8920] can also be attached and applied to the
   calculation of path to the associated prefixes.


 5.1. OSPFv3 Extension to carry the App-Metrics

   For App Servers using IPv6, the OSPFv3 Extended LSA with
   the Intra-Area-Prefix Address TLV specified by the Section
   3.7 of RFC8362 can be used to carry the App-Metrics for the
   attached App Servers.












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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |7 (IPv6 Local-Local Address)   |               Length          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            IPv6 AppServer (ANYCAST) address                   |
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Load measurement sub-TLV                           |
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Capability sub-TLV                                 |
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Preference sub-TLV                                |
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 3: IPv6 App Server App-Metrics Encoding



 5.2. OSPFv2 Extension to advertise the IP Layer App-Metrics

   For App Servers using IPv4 addresses, the OSPFv2 Extended
   Prefix Opaque LSA with the extended Prefix TLV can be used
   to carry the App Metrics sub-TLVs, as specified by the
   Section 2.1 [RFC7684].


   Here is the proposed encoding:

      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                          | Length                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Route Type    | Prefix Length | AF            | Flags         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Address Prefix (variable)                                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Load Measurement Sub-TLV                                      |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | capacity Index Sub-TLV                                        |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Site Preference Sub-TLV                                       |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   Figure 4: App-Metrix Sub-TLVs in OSPFv2 Extended Prefix TLV


 5.3. IP Layer App-Metrics Sub-TLVs

   Two types of Load Measurement Sub-TLVs are specified:

   a) The Aggregated Load Index based on weighted combination
     of the collected measurements;
   b) 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 or the
     raw measurements are needed by a central analytic
     system.


   The Aggregated Load 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 (TBD2)           |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 5: Aggregated Load Index Sub-TLV

     Type=TBD2 (to be assigned by IANA) indicates that the
     sub-TLV carries the 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.












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   The 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 (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 6: Raw Load Measurement Sub-TLV



     Type= TBD3 (to be assigned by IANA) indicates that the
     sub-TLV carries the Raw measurements of packets/bytes
     to/from the App Server ANYCAST address.

     Measurement Period: A user specified period in seconds,
     default is 3600 seconds.



   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 7: Capacity Index Sub-TLV









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   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 8: Preference Index Sub-TLV


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




6. Soft Anchoring of an ANYCAST Flow
   This section describes a solution that can anchor an
   application flow from a UE to a specific ANYCAST Server
   location even when the UE moves from one 5G Site to
   another. This is called "Sticky Service" in the 3GPP Edge
   Computing specification.

   Lets' assume one application "App.net" is instantiated on
   four servers that are attached to four different A-ERs:
   R1, R2, R3, and R4 respectively. The "App.net" needs to be
   Sticky means that the packets to the "App.net" from UE-1
   needs to stick with one server, say the "App.net" 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 are the steps to achieving "Soft Anchoring":

      - Assign a group of ANYCAST addresses to one
        application. For example, "App.net" is assigned with


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        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.
           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,



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        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.

7. Manageability Considerations

     To be added.

8. Security Considerations


   To be added.

9. IANA Considerations

       The following Sub-TLV types need to be added by IANA
       to OSPFv4 Extended-LSA Sub-TLVs and OSPFv2 Extended
       Link Opaque LSA TLVs Registry.

          - Aggregated Load Index Sub-TLV type
          - Raw Load Measurement Sub-TLV type
          - Capacity Index Sub-TLV type
          - Preference Index Sub-TLV type



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.



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   [RFC2328] J. Moy, "OSPF Version 2", RFC 2328, April 1998.

   [RFC7684] P. Psenak, et al, "OSPFv2 Prefix/Link Attribute
             Advertisement", RFC 7684, Nov. 2015.

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

   [RFC8326] A. Lindem, et al, "OSPFv3 Link State
             advertisement (LSA0 Extensibility", RFC 8362,
             April 2018.


 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-AppMetaData] L. Dunbar, K. Majumdar, H. Wang, "BGP NLRI
             App Meta Data for 5G Edge Computing Service",
             draft-dunbar-idr-5g-edge-compute-app-meta-data-
             01, work-in-progress, Nov 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-01, work-in-progress, Nov 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.



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   [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.



11. Acknowledgments

   Acknowledgements to Acee Lindem, Jeff Tantsura, and Donald
   Eastlake for their review and suggestions.

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



Authors' Addresses

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Huaimo Chen
   Futurewei
   Email: huaimo.chen@futurewei.com

   Aijun Wang
   China Telecom
   Email: wangaj3@chinatelecom.cn






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