Network Working Group                                         D. Trossen
Internet-Draft                                                    Huawei
Intended status: Informational                                 A. Rahman
Expires: August 7, 2020                                          C. Wang
                                        InterDigital Communications, LLC
                                                               T. Eckert
                                                        February 4, 2020

Applicability of BIER Multicast Overlay for Adaptive Streaming Services


   HTTP Level multicast, using BIER, is described as a use case in the
   BIER Use Cases document.  HTTP Level Multicast is used in today's
   video streaming and delivery services such as HLS, AR/VR etc.,
   generally realized over IP Multicast as well as other use cases such
   as software update delivery.  A realization of "HTTP Multicast" over
   "IP Multicast" is described for the video delivery use case.  IP
   multicast is commonly used for IPTV services.  DVB and BBF is also
   developing a reference architecture for IP Multicast service.  A few
   problems with IP Multicast, such as waste of transmission bandwidth,
   increase in signaling when there are few users are described.
   Realization over BIER, through a BIER Multicast Overlay Layer, is
   described as an alternative.  How BIER Multicast Overlay operation
   improves over IP Multicast, such as reduction in signaling, dynamic
   creation of multicast groups to reduce signaling and bandwidth
   wastage is described.  We conclude with few next steps.

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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   Drafts is at

   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 August 7, 2020.

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Copyright Notice

   Copyright (c) 2020 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Reference Deployment  . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   5
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  HTTP-based Steaming . . . . . . . . . . . . . . . . . . .   6
     3.2.  HTTP-based Software Updates . . . . . . . . . . . . . . .   7
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Realization over IP Multicast . . . . . . . . . . . . . . . .   8
     5.1.  Mapping to Requirements . . . . . . . . . . . . . . . . .   9
     5.2.  Problems  . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Realization over BIER . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Description of a "BIER Multicast Overlay" to support HTTP
           Multicast . . . . . . . . . . . . . . . . . . . . . . . .  10
       6.1.1.  BIER Multicast Overlay Components . . . . . . . . . .  11
       6.1.2.  BIER Multicast Overlay Operations . . . . . . . . . .  11
     6.2.  Achieving Multicast Responses . . . . . . . . . . . . . .  13
     6.3.  BIER Multicast Overlay Traffic Management . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The BIER Use Cases document [I-D.ietf-bier-use-cases] describes an
   "HTTP Level Multicast" scenario, where HTTP Responses are carried
   over a BIER multicast infrastructure to multiple clients.  Especially
   rate-adaptive HTTP solutions can benefit from the dynamic multicast
   group membership changes enabled by BIER.  For this, the server-side
   Network Attachment Point (NAP), creates a list of outstanding client-
   side NAP requesting for the same HTTP resource.  When the response is

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   available, the list of NAPs with outstanding client requests are
   converted into the BIER or BIER-TE bitstring and used to send the
   HTTP response.

   In this draft, we describe use cases for such HTTP response multicast
   capability.  Specifically for HTTP-based video streaming, we describe
   how this can be realized over IP Multicast and how the operation of
   the video delivery use case can be improved if realized over BIER.
   The realization over BIER is achieved through what is called "BIER
   Multicast overlay" layer, i.e., the methods by which the sending BIER
   router knows how to send other application packets.  The requirements
   for BIER Multicast overlay layer is described in this document.  It
   also describes the necessary functions that form the BIER multicast
   overlay and the operations that enable the desired "HTTP Level
   Multicast" behavior.  One such operation is generating the PATH ID
   (represents the path between BFIR and BFER) based on named service
   relationship and translating it to appropriate BIER header.  We
   describe a list of protocols needed for the realization of the
   individual operations.

1.1.  Reference Deployment

   Let us formulate the architecture of the BIER multicast overlay for
   the scenario outlined in [I-D.ietf-bier-use-cases].  This overlay is
   shown in Figure 1 below.

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    +---------+   +------------+
    |         |   |            |/
    +IP only  +---+  SH + BFER +-----|
    |receiver |   |  (CNAP)    |\    |
    |UE       |   +----/\------+     |
    +---------+        ||            |
                       ||       +----------+   +---------+
                       ||       |          |   |         |
                |--------       |  BFR     |---|  BFR    |------|
                |               |          |   |         |      |
                |               +----------+   +---------+      |
            +---------+                                     +-------+
            |         |------------------------------------>| BFIR  |
            + BIER TE +                                     |  +    |
            |  PCE    |         +---------+    +-------+    |  SH   |
            |         |--||     |         |----| BFR   |----|(SNAP) |
            +---------+  ||     |   BFR   |    +-------+    |       |
                         ||     |         |                 +-------+
                         ||     +---------+                    /|\
    +---------+   +------\/----+      |                         |
    |         |   |            |/     |                         |
    +IP only  +---+  SH + BFER +------|                   +----------+
    |receiver |   |   (CNAP)   |\                         | IP only  |
    +---------+   +------------+                          | Sender   |
                                                          |(Server)  |

    [SH : Service Handler, CNAP : Client Network Attachment Point]
    [SNAP : Server Network Attachment Point]
    [PCE : Path Computation Element]

                      Figure 1: Deployment over BIER

   The multicast overlay is formed by the BFIR and BFER of the BIER
   layer and the additional Service Handler (SH) and Path Computation
   Element (PCE) elements shown in the figure.  When interconnecting
   with a non-BIER enabled IP routed peering network, a special SH, such
   as Border Gateway may be used.

   The Service Handler and BFER can be assumed to be collocated and can
   be viewed as Client Network Attachment Point (CNAP).  Clients sends
   and receives HTTP transactions through CNAP.

   On the server side, the Service handling function can be part of the
   Server Network Attachment Point (SNAP).  It includes the BFIR
   function and SH.  SNAP is responsible for aggregating the relevant

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   HTTP Requests and sending one or more BIER Multicast HTTP response to
   multiple clients who requested the same content.

   The SH function is assumed to be collocated with BFIR / BFER.  The
   BFIR and BFER is assumed to be normal router boxes in the network.
   If the additional function of SH cannot be added to normal routers,
   then SH can be deployed as a separate function outside the routers.
   In such scenario an interface between SH and BFIR or BFER needs to be

   As part of the POINT/RIFE/FLAME EU Horizon 2020 projects, HTTP Level
   Multicast use case has been executed on SDN based and ICN based
   underlay network, as described in the

   "HTTP multicast" demonstrated benefits in HTTP-level streaming video
   delivery, when deployed on a POINT test bed with 80+ nodes.  This
   draft [I-D.irtf-icnrg-deployment-guidelines] also describes protocol
   requirements to enable HTTP multicast to work on ICN underlay.

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Use Cases

   With the extensive use of "web technology", "distributed services"
   and availability of heterogeneous network, HTTP has effectively
   transitioned into the common transport or session layer for E2E and
   multi-hop communication across the web that is also called Service
   signaling.  Multi-hop when using a sequence of HTTP instance such as
   HTTP caches.  The draft "On the use of HTTP as a Substrate"
   [I-D.ietf-httpbis-bcp56bis], describes how HTTP is commonly used
   among service instances to communicate with each other, thus
   abstracting the lower layer details to application developers.

   For example, HTTP provides a common transport to support application
   layer streaming (Section 3.1) for not only conventional TV
   broadcasting, but also emerging Virtual Reality (VR) applications
   like VR-based tourist guide.  HTTP can also be leveraged to support
   wide-area large-scale software updates (Section 3.2) such as for
   Vehicle-to-Everything (V2X) or Internet of vehicles use case.  In the
   following, we present how such HTTP transport capability can be
   extended with multicast delivery for HTTP responses in certain use

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3.1.  HTTP-based Steaming

   Referring to the BIER Use Cases [I-D.ietf-bier-use-cases], multicast
   is used to scale out HTTP Live Streaming (HLS) to a large number of
   receivers that use HTTP.  This is used today in solutions like DOCSIS
   hybrid streaming [TR_IPMC_ABR].  Multicast can speed up both live and
   high-demand VoD streaming.  Adaptive Bit Rate IPMC [TR_IPMC_ABR]
   describes use of IP multicast towards the CMTS or a box beside it,
   where the content is converted to HTTP/TCP to stream to the receivers
   (e.g., homes).  A server hosting the HLS content is shown as "NAP
   Server".  The gateways acting as receivers for the multicast from the
   server are shown as "Client-NAP" (CNAP).  Each CNAP can serve
   multiple clients.

   Dynamic Adaptive Streaming (DASH) [ISO_DASH] over HTTP is another
   HTTP-based streaming approach.  In DASH, each media is described by a
   Media Presentation Description (MPD) file, through which a DASH
   client (e.g. a media player) is instructed how to download, interpret
   and play the media.  The media content is encoded into fragments or
   chunks at different bit rates.  Both the MPD and media fragments are
   stored at a server.  The DASH client first needs to retrieve the MPD
   file from the server; then it can start to retrieve media fragments
   encoded at different bits rates from the server.  DASH players may
   use rate adaptation, i.e., switching the retrieval from one rate
   chunks to another rate.  Usually this rate adaptation is utilizing
   delay measurements, resulting in TCP like behavior in terms of
   backoff in case of increasing delay.  DASH has been designed to reuse
   most of existing Internet infrastructure and protocols and can run
   over different underlying transports including HTTP.  For example,
   two major media service providers Netflix and Youtube use DASH over
   HTTP as their streaming technology.

   HTTP request and response used in media streaming services like HLS
   and DASH over HTTP, use HTTP responses for delivery of content, i.e.,
   each chunk is returned as an HTTP response to the requesting client.
   In such scenarios, where semi-synchronous access to the same resource
   occurs (such as watching prominent videos over Netflix or similar
   platforms or live TV over HTTP), traffic grows linearly with the
   number of viewers since the HTTP-based server will provide an HTTP
   response to each individual viewer.  This poses a significant burden
   on operators in terms of costs and on users in terms of likely
   degradation of quality.

   The use of HTTP-based streaming of video content is not limited to
   traditional TV broadcasting.  Consider a virtual reality use case
   where several users are joining a VR session at the same time, e.g.,
   centered around a joint event.  Hence, due to the temporal
   correlation of the VR sessions, we can assume that multiple requests

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   are sent for the same content at any point, particularly when viewing
   angles of VR clients are similar or the same.  Due to availability of
   virtual functions and cloud technology, the actual end point from
   where content is delivered may change.

3.2.  HTTP-based Software Updates

   Various new types of devices such as vehicles and robots are being
   connected to Internet.  They could be physically located at or moving
   between different places and connect to Internet via different
   telecom operators.  Software updates for these devices become
   important and introduce point-to-multipoint traffic from a software
   server to devices.  Using V2X as an example, the software server
   could be a part of telecom operators or maintained by car
   manufacturers.  In either case, the software server keeps vehicle
   software or firmware images, which will be transmitted to many
   vehicles across the global Internet, based on a pull or push model.
   HTTP is commonly used for those software updates to provide an E2E
   transport between the software server and each vehicle requesting
   software updates.  As a result, the traffic from the software server
   to vehicles increases linearly with the number of connected vehicles
   since each vehicle will establish a HTTP connection with the software

4.  Requirements

   A realization for the "HTTP multicast" use case may have the
   following requirements:

   o  MUST support multiple FQDN-based service endpoints to exist in the
      overlay to allow for utilizing several service endpoints for
      delivery and would therefore enable localization of content

   o  MUST send FQDN-based service requests at the network level to a
      suitable FQDN-based service endpoint via policy-based selection of
      appropriate path information.

   o  MUST allow for multicast delivery of HTTP response to same HTTP
      request URI.

   o  MUST provide direct path mobility, where the path between the
      egress and ingress Service Routers(SR) can be determined as being
      optimal (e.g., shortest path or direct path to a selected
      instance), is needed to avoid the use of anchor points and further
      reduce service-level latency.

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5.  Realization over IP Multicast

   We now discuss the realization of chunk-based delivery over IP
   multicast delivery methods.  We focus our presentation here on the
   video streaming use case in Section 3.1.

   IPTV or Internet video distribution in CDNs, uses HTTP Level
   Multicast and realized over IP Multicast (IPMC).  Many features of
   the IPTV service uses IPMC Group dependent state.  Besides popular
   features like PIM, Mldp, in a variable bit rate encoded content
   source, content consumption also depends on group state.

   DVB released reference architecture [DVB_REF_ARCH] for an end-to-end
   system to deliver linear content over IP networks in a scalable and
   standards-compliant manner.  It focuses on delivering Adaptive Bit
   Rate unicast content over a IP multicast network.

   A Multicast gateway is deployed in a CPE, Upstream Network Edge
   device or Terminal and provides multicast to unicast conversion
   facilities for several homes.  All in-scope traffic on the access
   network between the Multicast Gateway (e.g. network edge device) and
   the Terminal or home gateway device is unicast.  The individual media
   files are encapsulated into other protocols, so that they can be
   recovered as discrete files, when they exit the multicast pipe, which
   is terminated at Multicast Gateway.  Interface "L" between Multicast
   server and Content playback supports fetching of all specified types
   of Content, Conditional request, Range request, Caching etc.  BBF
   also started similar work in October 2016, called WT-399.  This work
   is now coordinated with DVB.  BBF focuses on developing the device
   management model.

   Assume clients that are consuming the same content (such as a TV
   program) and that this content has for each block (typically segments
   worth 2 seconds of content) a set of outstanding requests from its
   clients.  When IP Multicast is used in the domain, such as in
   aforementioned pre-existing solutions like in Cablelabs/DOCSIS
   [TR_IPMC_ABR], all possible blocks of the content have to be mapped
   to some IP multicast group, and the CNAP will need to know the
   mapping of block to groups.  For example, a live stream may have 11
   different bitrates available.  In the most simple Block to IP
   multicast group mapping scheme, there could be 11 multicast groups,
   one for all the blocks of one bitrate (note that this is not
   necessarily done in deployments of this solution, but we consider it
   here for the purpose of explanation).

   If the multicast domain and especially the links into the CNAP has
   enough bandwidth, this solution work well with IP multicast.  As soon
   as there is at least one Client connected to a CNAP for one

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   particular content, the CNAP would join all 11 multicast groups for
   this content.

5.1.  Mapping to Requirements

   To realize "HTTP Level Multicast" over "IP Multicast", some
   additional functions needs to be supported in an intermediate
   (overlay) layer.

   Support of mapping between FQDN based end points, Multicast Address.
   Creating multicast group from FQDN based end points.

   Control mechanism related to time when to start sending response as
   the multicast group is created.  It is required that the source
   should not send response immediately to the Multicast address.  Wait
   for some time to build the group sufficiently and then send response.

   Support of IGMP signaling between User device, NAPs and Multicast

5.2.  Problems

   If the number of clients on a CNAP for a particular program is large,
   the approach will work fairly well, because the likelihood that each
   of the 11 bitrates of a content is necessary for at least one Client
   is then fairly high.

   When the number of receivers is not very large, IP multicast runs
   into two issues.  If all the bitrates for the content are sent across
   the same group, then many of the bitrates may not be required and
   would have to be received unnecessarily and dropped by the CNAP.  If
   each bitrate was sent on a different IP multicast group, the CNAP
   could dynamically join/leave each multicast group based on the known
   receivers, but that would create an extremely high and undesirable
   amount of IP multicast signaling protocol activity (PIM/IGMP) that is
   easily overloading the network

   For efficiency reasons, the CNAP would need to dynamically join to
   only those bitrate steams where it does have outstanding requests,
   therefore achieving the best efficiency.  This would mean in the
   worst case that a CNAP would need to send for each new block, aka.:
   every two second for every client one IGMP/PIM leave and one IGMP/PIM
   join towards the upstream router to get a block for an appropriate
   bitrate (or changed content) whenever bitrate or content on a client
   have changed.  This high rate of control-plane signaling between CNAP
   and routers, and even between routers inside the multicast Domain is
   a major pain point and may easily prohibit deployment of these
   solutions because in many network devices, the performance of PIM/

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   IGMP is not scaled for continuous change in forwarding.  Even worse,
   the limit may not simply be the CPU performance of the routers
   control plane, but a limitation in the number of changes in
   forwarding that the forwarding plane units (NPU/ASICs) can support.

6.  Realization over BIER

6.1.  Description of a "BIER Multicast Overlay" to support HTTP

   The Service Handler (as in Figure 1) in BIER Multicast Overlay,
   process the FQDN in the service request.  At the service level, e.g.
   HTTP service, the fixed relationship among consumer and providers may
   be abstracted using "Service Names", and the changing relationship at
   the Service execution endpoints can be managed at the "multicast
   overlay" level, handing out the exact locations where service request
   or response needs to be sent to BIER layer.

          +-------------+        +-----------+       +-----------+
          |             |        |           |       | PATH ID   |
          | Service name|        | Multicast |       | translates|
          | [producer,  |------->| Overlay   |------>| to BIER   |
          |  consumer]  |        | Layer     |       | header    |
          |             |        |           |       |           |
          +-------------+        +-----------+       +-----------+

               Figure 2: Service Name to Path ID Translation

   We illustrate this using HTTP URI as service names.  It should be
   noted, other identifiers can also be used as service name, such as an
   IP address.  In the example illustration, other layers such as TCP,
   IP has been terminated at the egress point.  Outside BIER domain we
   terminate TCP/IP session to extract the URI.  The URI is processed by
   the "multicast overlay" layer to generate PATH IDENTIFIER , which is
   used as BIER header.

   Path Identifier or PATH ID, is used in path-based approach, which
   utilizes path information provided by the source of the packet for
   forwarding said packet in the network.  This is similar to segment
   routing albeit differing in the type of information provided for such
   source-based forwarding.

   Once the BIER header is determined and added at the BFIR, the rest of
   the transport layers is assumed to be any underlay technology as
   supported by BIER.  We assume TCP friendly transport, which can
   assure reliable delivery.

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6.1.1.  BIER Multicast Overlay Components

   With reference to Figure 1, the following components are part of BIER
   Multicast Overlay Layer.

   o  Service Handler (SH): The Service handler terminates transport
      level protocols, such as TCP, and extracts the URI.  It processes
      the URI in order to determine the PATH ID by contacting the PCE
      for a suitable path resolution, which in turn is used to send the
      HTTP Request.

   o  Optional PCE : Path Computation Element keeps track of all service
      execution end points through a registration process.  SH interacts
      with the PCE to obtain PATH information by resolving the FQDN from
      the incoming URI at the ingress SH to a suitable PATH ID.

   o  Interface functions to BFIR where the PATH ID is mapped to BIER
      header.  An Interface to the BFER is likely not required because
      the BFER will only receive the traffic that they need and should
      be able to derive from the BIER payload which subset of its
      receivers need to get an HTTP encapsulated version of a particular

6.1.2.  BIER Multicast Overlay Operations

   As shown in Figure 3, the "Multicast overlay function" includes a
   function called PCE (Path Computation Element function), which is
   responsible for selecting the correct multicast end point and
   possibly realizing path policy enforcement.  The result of the
   selection is a BIER path identifier, which is delivered to the SH
   upon initial path computation request (or provided to the ingress
   router BFIR to be added as BIER header ) (i.e., when sending a
   request to or response for a specific URL for the first time).  The
   path identifier is utilized for any future request for a given URL-
   based request.

   All service end points indicate availability to the PCE through a
   registration procedure, the PCE will instruct all SHs to invalidate
   previous path identifiers to the specific URL that might exist.  This
   may result in an a renewed path computation request at the next
   service request forwarding.  Through this, the newly registered
   service endpoint might be utilized if the policy-governed path
   computation selects said service instance.  Otherwise, a previously
   resolved PATH ID for the URI determined at the ingress SH is being
   used instead, removing any resolution latency to an SH-local lookup
   of the PATH ID.

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   +-------+    +------+----+   +--------+                  +----+-----+
   |Apps   |    |Apps---->  |   | PCE    |                  |    | APP |
   |layer  |--->|layer | SH |   +---/\---+                  | SH-->    |
   |prot   |    |prot  |    |       ||                      |    | LYR |
   +-------+    +------+----+   +---------+   +---------+   +----+-----+
   |   L2  |    |      L2   |-->|Forwarder|-->|Forwarder|-->|    L2    |
   +-------+    +------+----+   +---------+   +---------+   +----------+
                              |--------BIER DOMAIN -------|

              Figure 3: Protocol for Multicast Overlay Layer

   In the diagram shown above, an HTTP request is sent by an IP-based
   device towards the FQDN of the server defined in the HTTP request.

   At the client facing SH, the HTTP request is terminated at the TCP
   level at a local HTTP proxy.  The server side SH at the egress
   terminates any transport protocol on the outgoing (server) side.
   These terminating functions are assumed to be part of the client/
   server SH.  As a consequence, the SH obtains the destination "Service
   Name" from the received HTTP request.

   If no local BIER forwarding information exists at the client side SH,
   the path computation entity (PCE) is consulted, which calculates a
   unicast path from the BFIR to which the client SH is connected to the
   BFER to which the server SH is connected.  The PCE provides the
   forwarding information (Path ID) to the client SH, which in turn
   caches the result.  The Client SH may forward the Path ID to BFIR,
   which creates the BIER header.

                       |             |              |
                       | BIER HEADER | HTTP REQUEST |
                       |             | [ENCODED IN  |
                       |             | TEXT]        |
                       |             |              |

                Figure 4: Encapsulation of Service Request

   Ultimately, the "HTTP Request" encapsulated by BIER header, as shown
   in above diagram, is forwarded by the client SH towards the server-
   facing SH via the local BFIR.  We assume a (TCP-friendly) transport
   protocol being used for the transmission between client and server
   SH.  The possibility of sending one HTTP response to several CNAPs
   makes this a reliable multicast transport protocol.  The exact nature

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   of this transport protocol is left for further studies.  A suitable
   transport or Layer 2 encapsulation, as supported by BIER layer, is
   added to the above payload.

                |             |             |              |
                | Transport L2| BIER HEADER | HTTP REQUEST |
                |   HEADER    |             | [ENCODED IN  |
                |             |             | TEXT]        |
                |             |             |              |

             Figure 5: Transport Encapsulation of BIER payload

   Upon arrival of an HTTP request at the server SH, it forwards the
   HTTP request as a well-formed HTTP request locally to the server,
   awaiting an HTTP response for the reverse direction.

   If no BIER forwarding information exists for the reverse direction
   towards the requesting client SH, this information is requested from
   the PCE, similar to the operation in forward direction.

6.2.  Achieving Multicast Responses

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

   Upon arrival of an HTTP response at the server SH, the server SH
   consults its internal request table for any outstanding HTTP requests
   to the same request.  The server SH retrieves the stored BIER
   forwarding information for the reverse direction for all outstanding
   HTTP requests and determines the path information to all client SHs
   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.

   BIER makes the solution scalable.  Instead of IP multicast with IGMP/
   PIM, BIER is being used between Server NAP (SNAP) and CNAP, the SNAP
   simply coalesces the forwarded HTTP requests from the CNAP, and
   determines for every requested block the set of CNAPs requesting it.
   A set of CNAPs corresponds to a set of bits in the BIER-bitstring,
   one bit per CNAP.  The SNAP then sends the block into BIER with the
   appropriate bitstring set.

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   This completely eliminates any dynamic multicast signaling between
   CNAP and SNAP.  It also avoids sending of any unnecessary data block,
   which in the IP multicast solution is pretty much unavoidable.

   Furthermore, using the approach with BIER, the SNAP can also easily
   control how long to delay sending of blocks.  For example, it may
   wait for some percentage of the time of a block (e.g, 50% = 1
   second), therefore ensuring that it is coalescing as many requests
   into one BIER multicast answer as possible.

6.3.  BIER Multicast Overlay Traffic Management

   BIER-TE (BIER Traffic Engineering [I-D.ietf-bier-te-arch]) forwards
   and replicates packets like BIER based on a BitString in the packet
   header.  Where BIER forwards and replicates its packets on shortest
   paths towards BFER, BIER-TE allows (and requires) to also use bits in
   the bitstring to indicate the paths in the BIER domain across which
   the BIER-TE packets are to be sent.  This is done to support Traffic
   Engineering for BIER packets via explicit hop-by-hop and/or loose hop
   forwarding of BIER-TE packets.  A BIER-TE controller calculates
   explicit paths for this packet forwarding.

   The Multicast Flow Overlay operates as in BIER.  Instead of
   interacting with the BIER layer, it interacts with the BIER-TE

   In this draft, "Name-based" service forwarding over BIER, is
   described to handle changes in service execution end points and
   manage adhoc relationship in a multicast group.  BIER-TE is another
   way of doing this, while integrated with BIER architecture.  The PCE
   function described earlier in the BIER Multicast Overlay, may become
   part of BIER-TE Controller.  The SH function in the CNAP and SNAP
   communicates with BIER TE controller.  SH sends the service name to
   the controller, which process the request using the PCE function and
   returns the "bitstring" to be used as BIER header for delivery of the
   HTTP response to multiple clients.

7.  IANA Considerations

   This document requests no IANA actions.

8.  Security Considerations

   The operations in Section 6 consider the forwarding of HTTP packets
   between ingress and egress points based on information derived from
   the HTTP request.  The support for HTTPS is foreseen to ensure
   suitable encryption capability of such exchanges.  For this to
   happen, we expect certificate sharing agreements to exist between the

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   content provider and the BIER overlay provider, ensuring the
   extraction of the suitable request parameters while allowing for the
   re-encryption of the content for an encrypted delivery over the BIER
   network.  Since we liken the relationship between content and BIER
   overlay provider to that between content and CDN provider, the
   existence of certificate sharing agreements is similar to the
   practice used for CDNs.

9.  Informative References

              DVB, "Adaptive media streaming over IP multicast", DVB
              Document A176, March 2018,

              Eckert, T., Cauchie, G., Braun, W., and M. Menth, "Traffic
              Engineering for Bit Index Explicit Replication (BIER-TE)",
              draft-ietf-bier-te-arch-00 (work in progress), January

              Kumar, N., Asati, R., Chen, M., Xu, X., Dolganow, A.,
              Przygienda, T., Gulko, A., Robinson, D., Arya, V., and C.
              Bestler, "BIER Use Cases", draft-ietf-bier-use-cases-10
              (work in progress), August 2019.

              Nottingham, M., "On the use of HTTP as a Substrate",
              draft-ietf-httpbis-bcp56bis-05 (work in progress), May

              Rahman, A., Trossen, D., Kutscher, D., and R. Ravindran,
              "Deployment Considerations for Information-Centric
              Networking (ICN)", draft-irtf-icnrg-deployment-
              guidelines-07 (work in progress), September 2019.

              ISO, "Information technology -- Dynamic adaptive streaming
              over HTTP (DASH) -- Part 1: Media presentation description
              and segment formats", ISO/IEC 23009-1:2014, May 2014,

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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,

              CableLabs, "IP Multicast Adaptive Bit Rate Architecture
              Technical Report", OC-TR-IP-MULTI-ARCH-V01-141112 C01,
              October 2016,

Authors' Addresses

   Dirk Trossen
   Huawei Technologies Duesseldorf GmbH
   205 Hansallee
   Duesseldorf  40549


   Akbar Rahman
   InterDigital Communications, LLC
   1000 Sherbrooke Street West
   Montreal  H3A 3G4


   Chonggang Wang
   InterDigital Communications, LLC
   1001 E Hector St
   Conshohocken  19428


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   Toerless Eckert
   Futurewei Technologies Inc.
   2330 Central Expy
   Santa Clara  95050


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