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Versions: (draft-kumar-bier-use-cases) 00 01 02 03 04 05 06 07 08 09 10

Network Working Group                                           N. Kumar
Internet-Draft                                                  R. Asati
Intended status: Informational                                     Cisco
Expires: February 5, 2020                                        M. Chen
                                                                   X. Xu
                                                                  Huawei
                                                             A. Dolganow
                                                                   Nokia
                                                           T. Przygienda
                                                        Juniper Networks
                                                                A. Gulko
                                                         Thomson Reuters
                                                             D. Robinson
                                                       id3as-company Ltd
                                                                 V. Arya
                                                             DirecTV Inc
                                                              C. Bestler
                                                                 Nexenta
                                                          August 4, 2019


                             BIER Use Cases
                    draft-ietf-bier-use-cases-10.txt

Abstract

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain any multicast related per-
   flow state.  BIER also does not require any explicit tree-building
   protocol for its operation.  A multicast data packet enters a BIER
   domain at a "Bit-Forwarding Ingress Router" (BFIR), and leaves the
   BIER domain at one or more "Bit-Forwarding Egress Routers" (BFERs).
   The BFIR router adds a BIER header to the packet.  The BIER header
   contains a bit-string in which each bit represents exactly one BFER
   to forward the packet to.  The set of BFERs to which the multicast
   packet needs to be forwarded is expressed by setting the bits that
   correspond to those routers in the BIER header.

   This document describes some of the use cases for BIER.

Status of This Memo

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

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



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   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on February 5, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   3
   3.  BIER Use Cases  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Multicast in L3VPN Networks . . . . . . . . . . . . . . .   3
     3.2.  BUM in EVPN . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  IPTV and OTT Services . . . . . . . . . . . . . . . . . .   5
     3.4.  Multi-Service, Converged L3VPN Network  . . . . . . . . .   6
     3.5.  Control-Plane Simplification and SDN-Controlled Networks    7
     3.6.  Data Center Virtualization/Overlay  . . . . . . . . . . .   7
     3.7.  Financial Services  . . . . . . . . . . . . . . . . . . .   8
     3.8.  4K Broadcast Video Services . . . . . . . . . . . . . . .   9
     3.9.  Distributed Storage Cluster . . . . . . . . . . . . . . .  10
     3.10. HTTP-Level Multicast  . . . . . . . . . . . . . . . . . .  11
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15



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1.  Introduction

   Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
   that provides optimal multicast forwarding through a "BIER domain"
   without requiring intermediate routers to maintain any multicast
   related per-flow state.  BIER also does not require any explicit
   tree-building protocol for its operation.  A multicast data packet
   enters a BIER domain at a "Bit-Forwarding Ingress Router" (BFIR), and
   leaves the BIER domain at one or more "Bit-Forwarding Egress Routers"
   (BFERs).  The BFIR router adds a BIER header to the packet.  The BIER
   header contains a bit-string in which each bit represents exactly one
   BFER to forward the packet to.  The set of BFERs to which the
   multicast packet needs to be forwarded is expressed by setting the
   bits that correspond to those routers in the BIER header.

   The obvious advantage of BIER is that there is no per flow multicast
   state in the core of the network and there is no tree building
   protocol that sets up tree on demand based on users joining a
   multicast flow.  In that sense, BIER is potentially applicable to
   many services where multicast is used and not limited to the examples
   described in this draft.  In this document we are describing a few
   use cases where BIER could provide benefit over using existing
   mechanisms.

2.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  BIER Use Cases

3.1.  Multicast in L3VPN Networks

   The Multicast L3VPN architecture [RFC6513] describes many different
   profiles in order to transport L3 multicast across a provider's
   network.  Each profile has its own different tradeoffs (see section
   2.1 [RFC6513]).  When using "Multidirectional Inclusive" "Provider
   Multicast Service Interface" (MI-PMSI) an efficient tree is built per
   VPN, but causes flooding of egress PE's that are part of the VPN, but
   have not joined a particular C-multicast flow.  This problem can be
   solved with the "Selective" PMSI (S-PMSI) by building a special tree
   for only those PEs that have joined the C-multicast flow for that
   specific VPN.  The more S-PMSI's, the less bandwidth is wasted due to
   flooding, but causes more state to be created in the provider's
   network.  This is a typical problem network operators are faced with
   by finding the right balance between the amount of state carried in
   the network and how much flooding (waste of bandwidth) is acceptable.



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   Some of the complexity with L3VPN's comes due to providing different
   profiles to accommodate these trade-offs.

   With BIER there is no trade-off between State and Flooding.  Since
   the receiver information is explicitly carried within the packet,
   there is no need to build S-PMSI's to deliver multicast to a sub-set
   of the VPN egress PE's.  Due to that behaviour, there is no need for
   S-PMSI's.

   MI-PMSI's and S-PMSI's are also used to provide the VPN context to
   the egress PE router that receives the multicast packet.  Also, in
   some MVPN profiles it is also required to know which Ingress PE
   forwarded the packet.  Based on the PMSI the packet is received from,
   the target VPN is determined.  This also means there is a requirement
   to have at least a PMSI per VPN or per VPN/ingress PE.  This means
   the amount of state created in the network is proportional to the VPN
   and ingress PEs.  Creating PMSI state per VPN can be prevented by
   applying the procedures as documented in [RFC5331].  This however has
   not been very much adopted/implemented due to the excessive flooding
   it would cause to egress PEs since *all* VPN multicast packets are
   forwarded to *all* PEs that have one or more VPNs attached to it.

   With BIER, the destination PEs are identified in the multicast
   packet, so there is no flooding concern when implementing [RFC5331].
   For that reason there is no need to create multiple BIER domains per
   VPN, the VPN context can be carry in the multicast packet using the
   procedures as defined in [RFC5331].  Also see [I-D.ietf-bier-mvpn]
   for more information.

   With BIER only a few MVPN profiles will remain relevant, simplifying
   the operational cost and making it easier to be interoperable among
   different vendors.

3.2.  BUM in EVPN

   The current widespread adoption of L2VPN services [RFC4664],
   especially the upcoming EVPN solution [RFC7432] which transgresses
   many limitations of VPLS, introduces the need for an efficient
   mechanism to replicate broadcast, unknown and multicast (BUM) traffic
   towards the PEs that participate in the same EVPN instances (EVIs).
   As simplest deployable mechanism, ingress replication is used but
   poses accordingly a high burden on the ingress node as well as
   saturating the underlying links with many copies of the same frame
   headed to different PEs.  Fortunately enough, EVPN signals internally
   PMSI attribute [RFC6513] to establish transport for BUM frames and
   with that allows to deploy a plethora of multicast replication
   services that the underlying network layer can provide.  It is
   therefore relatively simple to deploy BIER P-Tunnels for EVPN and



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   with that distribute BUM traffic without creating P-router states in
   the core that are required by PIM, mLDP or comparable solutions.

   Specifically, the same I-PMSI attribute suggested for mVPN can be
   used easily in EVPN, and given that EVPN can multiplex and
   disassociate BUM frames on p2mp and mp2mp trees using upstream
   assigned labels, BIER P-Tunnel will support BUM flooding for any
   number of EVIs over a single sub-domain for maximum scalability but
   allow at the other extreme of the spectrum to use a single BIER sub-
   domain per EVI if such a deployment is necessary.

   Multiplexing EVIs onto the same PMSI forces the PMSI to span more
   than the necessary number of PEs normally, i.e. the union of all PEs
   participating in the EVIs multiplexed on the PMSI.  Given the
   properties of BIER it is however possible to encode in the receiver
   bitmask only the PEs that participate in the EVI that the BUM frame
   targets.  In a sense, BIER is an inclusive as well as a selective
   tree and can allow delivering the frame to only the set of receivers
   interested in a frame even though many others participate in the same
   PMSI.

   As another significant advantage, it is imaginable that the same BIER
   tunnel needed for BUM frames can optimize the delivery of the
   multicast frames though the signaling of group memberships for the
   PEs involved, but has not been specified as of date.

3.3.  IPTV and OTT Services

   IPTV is a service, well known for its characteristics of allowing
   both live and on-demand delivery of media traffic over an end-to-end
   managed IP network.

   Over The Top (OTT) is a similar service, well known for its
   characteristics of allowing live and on-demand delivery of media
   traffic between IP domains, where the source is often on an external
   network relative to the receivers.

   Content Delivery Networks (CDN) operators provide layer 4
   applications, and often some degree of managed layer 3 IP networks,
   that enable media to be securely and reliably delivered to many
   receivers.  In some models they may place applications within third
   party networks, or they may place those applications at the edges of
   their own managed network peerings and similar inter-domain
   connections.  CDNs provide capabilities to help publishers scale to
   meet large audience demand.  Their applications are not limited to
   audio and video delivery, but may include static and dynamic web
   content, or optimized delivery for Massive Multiplayer Gaming and
   similar.  Most publishers will use a CDN for public Internet



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   delivery, and some publishers will use a CDN internally within their
   IPTV networks to resolve layer 4 complexity.

   In a typical IPTV environment the egress routers connecting to the
   receivers will build the tree towards the ingress router connecting
   to the IPTV servers.  The egress routers would rely on IGMP/MLD
   (static or dynamic) to learn about the receiver's interest in one or
   more multicast groups/channels.  Interestingly, BIER could allow
   provisioning any new multicast group/channel by only modifying the
   channel mapping on ingress routers.  This is deemed beneficial for
   the linear IPTV video broadcasting in which all receivers behind all
   egress PE routers would receive the IPTV video traffic.

   With BIER in an IPTV environment, there is no need for tree building
   from egress to ingress.  Further, any addition of new channels or new
   egress routers can be directly controlled from the ingress router.
   When a new channel is included, the multicast group is mapped to a
   bit string that includes all egress routers.  Ingress router would
   start sending the new channel and deliver it to all egress routers.
   As it can be observed, there is no need for static IGMP provisioning
   in each egress router whenever a new group/channel is added.
   Instead, it can be controlled from ingress router itself by
   configuring the new group to bit mask mapping on ingress router.

   With BIER in OTT environment, the edge routers in CDN domain
   terminating the OTT user session connect to the ingress BIER routers
   connecting content provider domains or a local cache server and
   leverage the scalability benefit that BIER could provide.  This may
   rely on MBGP interoperation (or similar) between the egress of one
   domain and the ingress of the next domain, or some other SDN control
   plane may prove a more effective and simpler way to deploy BIER.  For
   a single CDN operator this could be well managed in the layer 4
   applications that they provide and it may be that the initial
   receiver in a remote domain is actually an application operated by
   the CDN which in turn acts as a source for the ingress BIER router in
   that remote domain, and by doing so keeps the BIER domains discrete.

3.4.  Multi-Service, Converged L3VPN Network

   Increasingly operators deploy single networks for multiple services.
   For example a single metro core network could be deployed to provide
   residential IPTV retail service, residential IPTV wholesale service,
   and business L3VPN service with multicast.  It may often be desired
   by an operator to use a single architecture to deliver multicast for
   all of those services.  In some cases, governing regulations may
   additionally require same service capabilities for both wholesale and
   retail multicast services.  To meet those requirements, some
   operators use the multicast architecture as defined in [RFC5331].



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   However, the need to support many L3VPNs, with some of those L3VPNs
   scaling to hundreds of egress PE's and thousands of C-multicast
   flows, make scaling/efficiency issues defined in earlier sections of
   this document even more prevalent.  Additionally support for tens of
   millions of BGP multicast A-D and join routes alone could be required
   in such networks with all of the consequences that such a scale
   brings.

   With BIER, again there is no need of tree building from egress to
   ingress for each L3VPN or individual or group of c-multicast flows.
   As described earlier, any addition of a new IPTV channel or new
   egress router can be directly controlled from ingress router and
   there is no flooding concern when implementing [RFC5331].

3.5.  Control-Plane Simplification and SDN-Controlled Networks

   With the advent of Software Defined Networking, some operators are
   looking at various ways to reduce the overall cost of providing
   networking services including multicast delivery.  Some of the
   alternatives being considered include minimizing capex cost through
   deployment of network elements with a simplified control plane
   function, minimizing operational cost by reducing control protocols
   required to achieve a particular service, etc.  Segment routing as
   described in [RFC8402] provides a solution that could be used to
   provide simplified control plane architecture for unicast traffic.
   With Segment routing deployed for unicast, a solution that simplifies
   control plane for multicast would thus also be required, or
   operational and capex cost reductions will not be achieved to their
   full potential.

   With BIER, there is no longer a need to run control protocols
   required to build a distribution tree.  If L3VPN with multicast, for
   example, is deployed using [RFC5331] with MPLS in P-instance, the
   MPLS control plane would no longer be required.  BIER also allows
   migration of C-multicast flows from non-BIER to BIER-based
   architecture, which simplifies the operation of transitioning the
   control plane.  Finally, for operators, who desire a centralized,
   offloaded control plane, multicast overlay as well as BIER forwarding
   could be used with controller-based programming.

3.6.  Data Center Virtualization/Overlay

   Virtual eXtensible Local Area Network (VXLAN) [RFC7348] is a kind of
   network virtualization overlay technology which is intended for
   multi-tenancy data center networks.  To emulate a layer 2 flooding
   domain across the layer 3 underlay, it requires a 1:1 or n:1 mapping
   between the VXLAN Virtual Network Instance (VNI) and the
   corresponding IP multicast group.  In other words, it requires



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   enabling the multicast capability in the underlay.  For instance, it
   requires enabling PIM-SM [RFC4601] or PIM-BIDIR [RFC5015] multicast
   routing protocol in the underlay.  VXLAN is designed to support 16M
   VNIs at maximum.  In the mapping ratio of 1:1, it would require 16M
   multicast groups in the underlay which would become a significant
   challenge to both the control plane and the data plane of the data
   center switches.  In the mapping ratio of n:1, it would result in
   inefficiency bandwidth utilization which is not optimal in data
   center networks.  More importantly, it is recognized by many data
   center operators as an undesireable burden to run multicast in data
   center networks from the perspective of network operation and
   maintenance.  As a result, many VXLAN implementations claim to
   support the ingress replication capability since ingress replication
   eliminates the burden of running multicast in the underlay.  Ingress
   replication is an acceptable choice in small-sized networks where the
   average number of receivers per multicast flow is not too large.
   However, in multi-tenant data center networks, especially those in
   which the NVE functionality is enabled on a large number of physical
   servers, the average number of NVEs per VN instance would be very
   large.  As a result, the ingress replication scheme would result in a
   serious bandwidth waste in the underlay and a significant replication
   burden on ingress NVEs.

   With BIER, there is no need for maintaining that huge amount of
   multicast state in the underlay anymore while the delivery efficiency
   of overlay BUM traffic is the same as if any kind of stateful
   multicast protocols such as PIM-SM or PIM-BIDIR is enabled in the
   underlay.

3.7.  Financial Services

   Financial services extensively rely on IP multicast to deliver stock
   market data and its derivatives, and critically require optimal
   latency path (from publisher to subscribers), deterministic
   convergence (so as to deliver market data derivatives fairly to each
   client) and secured delivery.

   Current multicast solutions, e.g.  PIM, mLDP, etc., however, don't
   sufficiently address the above requirements.  The reason is that the
   current solutions are primarily subscriber driven, i.e. multicast
   tree is setup using reverse path forwarding techniques, and as a
   result, the chosen path for market data may not be latency optimal
   from publisher to the (market data) subscribers.

   As the number of multicast flows grows, the convergence time might
   increase and make it somewhat nondeterministic from the first to the
   last flow depending on platforms/implementations.  Also, by having
   more protocols in the network, the variability to ensure secured



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   delivery of multicast data increases, thereby undermining the overall
   security aspect.

   BIER enables setting up the most optimal path from publisher to
   subscribers by leveraging unicast routing relevant for the
   subscribers.  With BIER, the multicast convergence is as fast as
   unicast, uniform and deterministic regardless of number of multicast
   flows.  This makes BIER a perfect multicast technology to achieve
   fairness for market derivatives per each subscriber.

3.8.  4K Broadcast Video Services

   In a broadcast network environment, the media content is sourced from
   various content providers across different locations.  The 4k
   broadcast video is an evolving service placing enormous demand on
   network infrastructure in terms of low latency, faster convergence,
   high throughput, and high bandwidth.

   In a typical broadcast satellite network environment, the receivers
   are the satellite terminal nodes which will receive the content from
   various sources and feed the data to the satellite.  Typically a
   multicast group address is assigned for each source.  Currently the
   receivers can join the sources using either PIM-SM [RFC4601] or PIM-
   SSM [RFC4607].

   In such network scenarios, normally PIM will be the multicast routing
   protocol used to establish the tree between ingress connecting the
   content media sources to egress routers connecting the receivers.  In
   PIM-SM mode, the receivers relies on shared tree to learn the source
   address and build source tree while in PIM-SSM mode, IGMPv3 is used
   by receiver to signal the source address to the egress router.  In
   either case, as the number of sources increases, the number of
   multicast trees in the core also increases resulting in more
   multicast state entries in the core and increasing the convergence
   time.

   With BIER in 4k broadcast satellite network environment, there is no
   need to run PIM in the core and no need to maintain any multicast
   state.  The obvious advantage with BIER is the low multicast state
   maintained in the core and the faster convergence (which is typically
   at par with the unicast convergence).  The edge router at the content
   source facility can act as BIFR router and the edge router at the
   receiver facility can act as BFER routers.  Any addition of a new
   content source or new satellite Terminal nodes can be added
   seamlessly in to the BEIR domain.  The group membership from the
   receivers to the sources can be provisioned either by BGP or an SDN
   controller.




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3.9.  Distributed Storage Cluster

   Distributed Storage Clusters can benefit from dynamically targeted
   multicast messaging both for dynamic load-balancing negotiations and
   efficient concurrent replication of content to multiple targets.

   For example, in the NexentaEdge storage cluster (by Nexenta Systems)
   a Chunk Put transaction is accomplished with the following steps:

   o  The Client multicasts a Chunk Put Request to a multicast group
      known as a Negotiating Group.  This group holds a small number of
      storage targets that are collectively responsible for providing
      storage for a stable subset of the chunks to be stored.  In
      NexentaEdge this is based upon a cryptographic hash of the Object
      Name or the Chunk payload.

   o  Each recipient of the Chunk Put Request unicasts a Chunk Put
      Response to the Client indicating when it could accept a transfer
      of the Chunk.

   o  The Client selects a different multicast group (a Rendezvous
      Group) which will target the set storage targets selected to hold
      the Chunk.  This is a subset of the Negotiation Group, presumably
      selected so as to complete the transfer as early as possible.

   o  >The Client multicasts a Chunk Put Accept message to inform the
      Negotiation Group of what storage targets have been selected, when
      the transfer will occur and over what multicast group.

   o  The client performs the multicast transfer over the Rendezvous
      Group at the agreed upon time.

   o  Each recipient sends a Chunk Put Ack to positively or negatively
      acknowledge the chunk transfer.

   o  The client will retry the entire transaction as needed if there
      are not yet sufficient replicas of the Chunk.

   Chunks are retrieved by multicasting a Chunk Get Request to the same
   Negotiating Group, collecting Chunk Get Responses, picking one source
   from those responses, sending a Chunk Get Accept message to identify
   the selected source and having the selected storage server unicast
   the chunk to the source.

   Chunks are found by the Object Name or by having the payload
   cryptographic hash of payload chunks be recorded in a "chunk
   reference" in a metadata chunk.  The metadata chunks are found using
   the Object Name.



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   The general pattern in use here, which should apply to other cluster
   applications, is that multicast messages are sent amongst a
   dynamically selected subset of the entire cluster, which may result
   in exchanging further messages over a smaller subset even more
   dynamically selected.

   Currently the distributed storage application discussed use of MLD
   managed IPV6 multicast groups.  This in turn requires either a push-
   based mechanism for dynamically configuring Rendezvous Groups or pre-
   provisioning a very large number of potential Rendezvous Groups and
   dynamically selecting the multicast group that will deliver to the
   selected set of storage targets.

   BIER would eliminate the need for a vast number of multicast groups.
   The entire cluster can be represented as a single BIER domain using
   only the default sub-domain.  Each Negotiating Group is simply a
   subset of the whole that is deterministically selected by the
   Cryptographic Hash of the Object Name or Chunk Payload.  Each
   Rendezvous Group is a further subset of the Negotiating Group.

   In a simple mapping of the MLD managed multicast groups, each
   Negotiating Group could be represented by a short bit string selected
   by a Set Identifier.  The Set Identier effectively becomes the
   Negotiating Group.  To address the entire Negotiating Group the bit
   string is set to all ones.  To later address a subset of the group a
   subset bit string is used.

   This allows a short fixed size BIER header to multicast to a very
   large storage cluster.

3.10.  HTTP-Level Multicast

   Scenarios where a number of HTTP-level clients are quasi-
   synchronously accessing the same HTTP-level resource can benefit from
   the dynamic multicast group formation enabled by BIER.

   For example, in the FLIPS (Flexible IP Services) solution by
   InterDigital, network attachment points (NAPs) provide a protocol
   mapping from HTTP to an efficient BIER-compliant transfer along a
   bit-indexed path between an ingress (here the NAP to which the
   clients connect) and an egress (here the NAP to which the HTTP-level
   server connects).  This is accomplished with the following steps:

   o  at the client NAP, the HTTP request is terminated at the HTTP
      level at a local HTTP proxy.

   o  the HTTP request is published by the client NAP towards the FQDN
      of the server defined in the HTTP request



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      *  if no local BIER forwarding information exists to the server
         (NAP), a path computation entity (PCE) is consulted, which
         calculates a unicast path to the egress NAP (here the server
         NAP).  The PCE provides the forwarding information to the
         client NAP, which in turn caches the result.

         +  if the local BIER forwarding information exists in the NAP-
            local cache, it is used instead.

   o  Upon arrival of a client NAP request at the server NAP, the server
      NAP proxy forwards the HTTP request as a well-formed HTTP request
      locally to the server.

      *  If no client NAP forwarding information exists for the reverse
         direction, this information is requested from the PCE.  Upon
         arrival of such reverse direction forwarding information, it is
         stored in a local table for future use.

   o  Upon arrival of any further client NAP request at the server NAP
      to an HTTP request whose response is still outstanding, the client
      NAP is added to an internal request table and the request is
      suppressed from being sent to the server.

      *  If no client NAP forwarding information exists for the reverse
         direction, this information is requested from the PCE.  Upon
         arrival of such reverse direction forwarding information, it is
         stored in a local table for future use.

   o  Upon arrival of an HTTP response at the server NAP, the server NAP
      consults its internal request table for any outstanding HTTP
      requests to the same request

         the server NAP retrieves the stored BIER forwarding information
         for the reverse direction for all outstanding HTTP requests
         found above and determines the path information to all client
         NAPs through a binary OR over all BIER forwarding identifiers
         with the same SI field.  This newly formed joint BIER multicast
         response identifier is used to send the HTTP response across
         the network, while the procedure is executed until all requests
         have been served.

   o  Upon arrival of the HTTP response at a client NAP, it will be sent
      by the client NAP proxy to the locally connected client.

   A number of solutions exist to manage necessary updates in locally
   stored BIER forwarding information for cases of client/server
   mobility as well as for resilience purposes.




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   Applications for HTTP-level multicast are manifold.  Examples are
   HTTP-level streaming (HLS) services, provided as an OTT offering,
   either at the level of end user clients (connected to BIER-enabled
   NAPs) or site-level clients.  Others are corporate intranet storage
   cluster solutions that utilize HTTP- level synchronization.  In
   multi-tenant data centre scenarios such as outlined in Section 3.6.,
   the aforementioned solution can satisfy HTTP-level requests to
   popular services and content in a multicast delivery manner.

   BIER enables such solution through the bitfield representation of
   forwarding information, which is in turn used for ad-hoc multicast
   group formation at the HTTP request level.  While such solution works
   well in SDN-enabled intra- domain scenarios, BIER would enable the
   realization of such scenarios in multi-domain scenarios over legacy
   transport networks without relying on SDN-controlled infrastructure.

4.  Security Considerations

   There are no security issues introduced by this draft.

5.  IANA Considerations

   There are no IANA consideration introduced by this draft.

6.  Acknowledgments

   The authors would like to thank IJsbrand Wijnands, Greg Shepherd and
   Christian Martin for their contribution.

   The authors would also like to thank Anoop Ghanwani for his thorough
   review and comments.

7.  Contributing Authors

   Dirk Trossen
   InterDigital Inc
   Email: dirk.trossen@interdigital.com

8.  References

8.1.  Normative References

   [I-D.ietf-bier-mvpn]
              Rosen, E., Sivakumar, M., Wijnands, I., Aldrin, S.,
              Dolganow, A., and T. Przygienda, "Multicast VPN Using
              BIER", draft-ietf-bier-mvpn-01 (work in progress), July
              2015.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

8.2.  Informative References

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601,
              DOI 10.17487/RFC4601, August 2006,
              <https://www.rfc-editor.org/info/rfc4601>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/info/rfc4607>.

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,
              <https://www.rfc-editor.org/info/rfc4664>.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
              <https://www.rfc-editor.org/info/rfc5015>.

   [RFC5331]  Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
              Label Assignment and Context-Specific Label Space",
              RFC 5331, DOI 10.17487/RFC5331, August 2008,
              <https://www.rfc-editor.org/info/rfc5331>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.



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   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Authors' Addresses

   Nagendra Kumar
   Cisco
   7200 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: naikumar@cisco.com


   Rajiv Asati
   Cisco
   7200 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: rajiva@cisco.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com


   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com











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   Andrew Dolganow
   Nokia
   750D Chai Chee Rd
   06-06 Viva Business Park  469004
   Singapore

   Email: andrew.dolganow@nokia.com


   Tony Przygienda
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  95089
   USA

   Email: prz@juniper.net


   Arkadiy Gulko
   Thomson Reuters
   195 Broadway
   New York  NY 10007
   USA

   Email: arkadiy.gulko@thomsonreuters.com


   Dom Robinson
   id3as-company Ltd
   UK

   Email: Dom@id3as.co.uk


   Vishal Arya
   DirecTV Inc
   2230 E Imperial Hwy
   CA  90245
   USA

   Email: varya@directv.com










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   Caitlin Bestler
   Nexenta Systems
   451 El Camino Real
   Santa Clara, CA
   US

   Email: caitlin.bestler@nexenta.com












































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