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SAM Research Group                                          M. Waehlisch
Internet-Draft                                      link-lab & FU Berlin
Intended status: Informational                              T C. Schmidt
Expires: April 29, 2010                                      HAW Hamburg
                                                               S. Venaas
                                                           cisco Systems
                                                        October 26, 2009

             A Common API for Transparent Hybrid Multicast

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 29, 2010.

Copyright Notice

   Copyright (c) 2009 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
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   Please review these documents carefully, as they describe your rights
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   Group communication services are most efficiently implemented on the
   lowest layer available.  However, as the deployment status of
   multicast distribution largely varies throughout the Intenet,
   globally operational group solutions are frequently restricted to
   using a stable, upper layer protocol controlled by the application
   itself.  This document describes a common multicast API that serves
   the requirements of data distribution and maintenance for multicast
   and broadcast on a middleware abstraction layer, suitable for
   transparent underlay and overlay communication.  It proposes and
   discusses mapping mechanisms between different namespaces and
   forwarding technologies.  Additionally, it describes the application
   of this API at gateways operating between current multicast instances
   throughout the Internet.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Objectives and Reference Scenarios . . . . . . . . . . . . . .  4
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Hybrid Multicast API . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Abstract Data Types  . . . . . . . . . . . . . . . . . . .  7
     5.2.  Send/Receive Calls . . . . . . . . . . . . . . . . . . . .  7
     5.3.  Service Calls  . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Deployment Use Cases . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  DVMRP  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.2.  PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.3.  PIM-SSM  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.4.  BIDIR-PIM  . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. Informative References . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   Group communication is implemented on different layers (e.g., IP vs.
   application layer multicast) as well as based on different
   technologies on the same tier (e.g.  IPv4 vs. IPv6).  To allow for a
   reliable deployment of applications and group services, a common API
   is required that offers calls to transmit and receive multicast data
   independent of the underlying technology, and also provides a
   consistent view on multicast states.  This document describes an
   abstract group communication API and core functions required for
   transparent operations.  Specific implementation guidelines with
   respect to operating systems or programming languages are out-of-
   scope of this document.

   The aim of this common API is twofold:

   o  Enable any application programmer to implement group-oriented data
      communication independent of the underlying delivery mechanisms.
      In particular, make applications efficient, but robust with
      respect to deployment aspects.

   o  Allow for a flexible namespace support in group addressing, and
      thereby separate addressing and routing schemes from application
      design.  This abstraction not only reduces the dependency on
      specific apects of underlying protocols, but may open application
      design to extend to specifically flavored group services.

   Multicast technologies may be various P2P-based, IPv4 or IPv6 network
   layer multicast, or implemented by some other application service.
   Corresponding namespaces may be IP addresses, overlay hashes, other
   application layer group identifiers, e.g., <sip:*@peanuts.org>, or
   names defined by the applications.

   This document also proposes and discusses mapping mechanisms between
   different namespaces and forwarding technologies.  Additionally, the
   multicast API provides internal interfaces to access current
   multicast states at the host.  Multiple multicast protocols may run
   in parallel on a single host.  These protocols may interact to
   provide a gateway function that bridges data between different
   domains.  The application of this API at gateways operating between
   current multicast instances throughout the Internet is described, as

2.  Terminology

   This document uses the terminology as defined for the multicast
   protocols [RFC2710],[RFC3376],[RFC3810],[RFC4601],[RFC4604].  In

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   addition, the following terms will be used.

   Multicast Namespace:  A Multicast Namespace is a collection of
      designators for groups that share a common syntax.  Typical
      instances of namespaces are IPv4 or IPv6 multicast addresses,
      overlay group ids, group names defined on the application layer,
      or some human readable

   Multicast Context:  A Multicast Context is a domain that accommodates
      nodes and routers of a common, single mutlicast forwarding
      technology and is bound to a single namespace.

   Inter-domain Multicast Gateway:  An Inter-domain Multicast Gateway
      (IMG) is an entity that interconnects domains of different
      mutlicast contexts.  Its objective is to transparently forward
      data between contexts, e.g., between IP layer and overlay

3.  Objectives and Reference Scenarios

   The default use case addressed in this memo targets at applications
   that jointly communicate in a group by using a common identifier
   taken from some common namespace.  Programmers shall be entitled to
   transparently use this identifier in their program without the need
   to consider a deployment status in target domains.  Aided by gateways
   and, where available, by a node-specific multicast middleware,
   applications shall be enabled to establish group communication, even
   if resident in domains that are not connected by a common multicast
   service technology.

   This draft covers the following two general scenarios:

   1.  Multicast domains running the same multicast technology but
       remaining isolated, possibly only connected by network layer

   2.  Multicast domains running different multicast technologies, but
       hosting nodes that are members of the same multicast group.

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                                        +-------+         +-------+
                                        | Member|         | Member|
                                        |  Foo  |         |   G   |
                                        +-------+         +-------+
                                              \            /
                                            ***  ***  ***  ***
                                           *   **   **   **   *
                                          *                    *
                                           *   MCast Tec A    *
                                          *                    *
                                           *   **   **   **   *
                                            ***  ***  ***  ***
   +-------+          +-------+                      |
   | Member|          | Member|                  +-------+
   |   G   |          |  Foo  |                  |  IMG  |
   +-------+          +-------+                  +-------+
       |                |                            |
       ***  ***  ***  ***                  ***  ***  ***  ***
      *   **   **   **   *                *   **   **   **   *
     *                    *  +-------+   *                    *
      *   MCast Tec A    * --|  IMG  |--  *   MCast Tec B    *    +-------+
     *                    *  +-------+   *                    * - | Member|
      *   **   **   **   *                *   **   **   **   *    |   G   |
       ***  ***  ***  ***                  ***  ***  ***  ***     +-------+

   Reference scenarios for hybrid multicast, interconnecting group
   members from isolated homogeneous and heterogeneous domains.

   It is assumed throughout the document that the domain composition, as
   well as the node attachement to a specific technology remain
   unchanged during a multicast session.

4.  Overview

   The extended multicast functions should be implemented by a
   middleware.  This middleware exhibits two tasks, it

   o  provides an extended API that supports a common multicast
      interface with namespace support

   o  bridges data between different multicast technologies.

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   *-------*     *-------*
   | App 1 |     | App 2 |
   *-------*     *-------*
       |             |
   |   Middleware        |
        |          |
   *---------*     |
   | Overlay |     |
   *---------*     |
        |          |
        |          |
   |   Underlay          |

       Figure 1: The middleware covers underlay and overlay for the

   The general procedure to initiate multicast communication is the

   1.  An Application subscribes/leaves/sends to a logical group

   2.  A middleware maps the logical group ID to a technical group ID.

   3.  The technical group ID is allocated or revised if already in use.

   The application communicates via the logical ID and data distribution
   is based on the technical ID.  A mapping is required between the IDs,
   especially if both identifiers belong to different namespaces.  This
   mapping can be realized by embedding smaller in larger namespaces or
   selecting an arbitrary, unused ID in the target space.  The relation
   between logical and technical ID is stored based on a mapping service
   (e.g.  DHT).  The middleware, thus queries the mapping service first,
   and creates an new technical group ID only if there is no identifier
   available for the namespace in use.  Depending on the scope of the
   mapping service, it ensures a consistent use of the technical ID in a
   local or global domain.

   Hosts may support several multicast protocols.  In this case, they
   will be enabled to forward data between the different technologies
   using the service calls of the API.  Such a proxy function can be
   implemented on each host or on dedicated gateways.  These gateways
   also assist multicast members that have no middleware support to be
   integrated in additional namespaces.

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5.  Hybrid Multicast API

5.1.  Abstract Data Types

   Namespace  describes the domain-specific context in which the
      applications operate.

   Address  is any kind of address in underlay (e.g.  IPv4, IPv6) or
      overlay (e.g.  SIP, hash-based ID).

   Mode  denotes the layer on which the corresponding call will be
      effective.  This may be unspecified to leave the decicision at the
      group communication stack.

5.2.  Send/Receive Calls

   init(in Namespace n)  This call is implemented

   join(in Address a, in Mode m)  This operation initiates a group
      subscription.  Depending on the mode, this may result in an IGMP/
      MLD report.

   leave(in Address a, in Mode m)  This operation results in an
      unsubscription for the given address.

   send(in Address a, in Mode m, out Message msg)

   receive(in Address a, in Mode m, out Message msg)

5.3.  Service Calls

   groupSet(out Address[] g, in Mode m)  This operation returns all
      registered multicast groups.  The information can be provided by
      group management or routing protocols.  The return values
      distinguish between sender and listener states.

   neighborSet(out Address[] a, in Mode m)  This function can be invoked
      to get the set of multicast routing neighbors.

   designatedHost(out Bool b, in Address a)  This function returns true,
      if the host has the role of a designated forwarder or querier.
      Such an information is provided by almost all multicast protocols
      to handle packet duplication, if multiple multicast instances
      serve on the same subnet.

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   updateListener(out Address g, in Mode m)  This upcall is invoked to
      inform a group service about a change of listener states for a
      group.  This is the result of receiver new subscriptions or
      leaves.  The group service may call groupSet to get updated

   updateSender(out Address g, in Mode m)  This upcall should be
      implemented to inform the application about source state changes.
      Analog to the updateListener case, the group service may call
      thereupon groupSet.

6.  Deployment Use Cases

   This section describes the application of the defined API to
   implement an IMG.

6.1.  DVMRP

   The following procedure describes a transparent mapping of a DVMRP-
   based any source multicast service to another many-to-many multicast

   An arbitrary DVMRP [RFC1075] router will not be informed about new
   receivers, but will learn about new sources immediately.  The concept
   of DVMRP does not provide any central multicast instance.  Thus, the
   IMG can be placed anywhere inside the multicast region, but requires
   a DVMRP neighbor connectivity.  The group communication stack used by
   the IMG is enhanced by a DVMRP implementation.  New sources in the
   underlay will be advertised based on the DVMRP flooding mechanism and
   received by the IMG.  Based on this the updateSender() call is
   triggered.  The relay agent initiates a corresponding join in the
   native network and forwards the received source data towards the
   overlay routing protocol.  Depending on the group states, the data
   will be distributed to overlay peers.

   DVMRP establishes source specific multicast trees.  Therefore, a
   graft message is only visible for DVMRP routers on the path from the
   new receiver subnet to the source, but in general not for an IMG.  To
   overcome this problem, data of multicast senders will be flooded in
   the overlay as well as in the underlay.  Hence, an IMG has to
   initiate an all-group join to the overlay using the namespace
   extension of the API.  Each IMG is initially required to forward the
   received overlay data to the underlay, independent of native
   multicast receivers.  Subsequent prunes may limit unwanted data
   distribution thereafter.

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6.2.  PIM-SM

   The following procedure describes a transparent mapping of a PIM-SM-
   based any source multicast service to another many-to-many multicast

   The Protocol Independent Multicast Sparse Mode (PIM-SM) [RFC4601]
   establishes rendezvous points (RP).  These entities receive listener
   and source subscriptions of a domain.  To be continuously updated, an
   IMG has to be co-located with a RP.  Whenever PIM register messages
   are received, the IMG must signal internally a new multicast source
   using updateSender().  Subsequently, the IMG joins the group and a
   shared tree between the RP and the sources will be established, which
   may change to a source specific tree after a sufficient number of
   data has been delivered.  Source traffic will be forwarded to the RP
   based on the IMG join, even if there are no further receivers in the
   native multicast domain.  Designated routers of a PIM-domain send
   receiver subscriptions towards the PIM-SM RP.  The reception of such
   messages invokes the updateListener() call at the IMG, which
   initiates a join towards the overlay routing protocol.  Overlay
   multicast data arriving at the IMG will then transparently be
   forwarded in the underlay network and distributed through the RP

6.3.  PIM-SSM

   The following procedure describes a transparent mapping of a PIM-SSM-
   based source specific multicast service to another one-to-many
   multicast technology.

   PIM Source Specific Multicast (PIM-SSM) is defined as part of PIM-SM
   and admits source specific joins (S,G) according to the source
   specific host group model [RFC4604].  A multicast distribution tree
   can be established without the assistance of a rendezvous point.

   Sources are not advertised within a PIM-SSM domain.  Consequently, an
   IMG cannot anticipate the local join inside a sender domain and
   deliver a priori the multicast data to the overlay instance.  If an
   IMG of a receiver domain initiates a group subscription via the
   overlay routing protocol, relaying multicast data fails, as data are
   not available at the overlay instance.  The IMG instance of the
   receiver domain, thus, has to locate the IMG instance of the source
   domain to trigger the corresponding join.  In the sense of PIM-SSM,
   the signaling should not be flooded in underlay and overlay.

   One solution could be to intercept the subscription at both, source
   and receiver sites: To monitor multicast receiver subscriptions
   (updateListener()) in the underlay, the IMG is placed on path towards

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   the source, e.g., at a domain border router.  This router intercepts
   join messages and extracts the unicast source address S, initializing
   an IMG specific join to S via regular unicast.  Multicast data
   arriving at the IMG of the sender domain can be distributed via the
   overlay.  Discovering the IMG of a multicast sender domain may be
   implemented analogously to AMT [I-D.ietf-mboned-auto-multicast] by
   anycast.  Consequently, the source address S of the group (S,G)
   should be built based on an anycast prefix.  The corresponding IMG
   anycast address for a source domain is then derived from the prefix
   of S.


   The following procedure describes a transparent mapping of a BIDIR-
   PIM-based any source multicast service to another many-to-many
   multicast technology.

   Bidirectional PIM [RFC5015] is a variant of PIM-SM.  In contrast to
   PIM-SM, the protocol pre-establishes bidirectional shared trees per
   group, connecting multicast sources and receivers.  The rendezvous
   points are virtualized in BIDIR-PIM as an address to identify on-tree
   directions (up and down).  However, routers with the best link
   towards the (virtualized) rendezvous point address are selected as
   designated forwarders for a link-local domain and represent the
   actual distribution tree.  The IMG is to be placed at the RP-link,
   where the rendezvous point address is located.  As source data in
   either cases will be transmitted to the rendezvous point address, the
   BIDIR-PIM instance of the IMG receives the data and can internally
   signal new senders towards the stack via updateSender().  The first
   receiver subscription for a new group within a BIDIR-PIM domain needs
   to be transmitted to the RP to establish the first branching point.
   Using the updateListener() invocation, an IMG will thereby be
   informed about group requests from its domain, which are then
   delegated to the overlay.

7.  IANA Considerations

   This document makes no request of IANA.

8.  Security Considerations

   This draft does neither introduce additional messages nor novel
   protocol operations.  TODO

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9.  Acknowledgements


10.  Informative References

              Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
              Pusateri, "Automatic IP Multicast Without Explicit Tunnels
              (AMT)", draft-ietf-mboned-auto-multicast-09 (work in
              progress), June 2008.

   [RFC1075]  Waitzman, D., Partridge, C., and S. Deering, "Distance
              Vector Multicast Routing Protocol", RFC 1075,
              November 1988.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              October 1999.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.

   [RFC4604]  Holbrook, H., Cain, B., and B. Haberman, "Using Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Protocol Version 2 (MLDv2) for Source-
              Specific Multicast", RFC 4604, August 2006.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, October 2007.

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Authors' Addresses

   Matthias Waehlisch
   link-lab & FU Berlin
   Hoenower Str. 35
   Berlin  10318

   Email: mw@link-lab.net
   URI:   http://www.inf.fu-berlin.de/~waehl

   Thomas C. Schmidt
   HAW Hamburg
   Berliner Tor 7
   Hamburg  20099

   Email: schmidt@informatik.haw-hamburg.de
   URI:   http://inet.cpt.haw-hamburg.de/members/schmidt

   Stig Venaas
   cisco Systems
   Tasman Drive
   San Jose, CA  95134

   Email: stig@cisco.com

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