Internet Engineering Task Force                                  T. Tsou
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Informational                               A. Clauberg
Expires: January 11, 2013                               Deutsche Telekom
                                                            M. Boucadair
                                                          France Telecom
                                                               S. Venaas
                                                           Cisco Systems
                                                                  Q. Sun
                                                           China Telecom
                                                           July 10, 2012

   Address Acquisition For Multicast Content When Source and Receiver
                     Support Differing IP Versions


   Each IPTV operator has their own arrangements for pre-provisioning
   program information including addresses of the multicast groups
   corresponding to broadcast programs on the subscriber receiver.
   During the transition from IPv4 to IPv6, scenarios can occur where
   the IP version supported by the receiver differs from that supported
   by the source.  This memo examines what has to be done to allow the
   receiver to acquire multicast address information in the version it
   supports in such scenarios.

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
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   This Internet-Draft will expire on January 11, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the

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   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Which Problem Are We Solving? . . . . . . . . . . . . . . . . . 3
   3.  Possible Solutions  . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  The Reactive Strategy . . . . . . . . . . . . . . . . . . . 4
     3.2.  Dynamic Modification  . . . . . . . . . . . . . . . . . . . 5
     3.3.  Administrative Preparation  . . . . . . . . . . . . . . . . 5
   4.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  Informative References  . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Some Background On Program Guides  . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   Discussion of the multicast transition problem has focussed on the
   case of broadcast delivery of program content.  Within this scenario,
   the operation of viewing a program follows a well-defined sequence.
   For the sake of reducing channel switching delay, the list of
   multicast addresses is generally pre-provisioned to the receiver as
   part of the program guide.  Each operator has their own solution for
   achieving this delivery, despite the attempts at standardization
   recounted in Appendix A.

   At some later time, after the program guide is delivered, the user
   chooses to view a program, possibly by selecting it from a displayed
   program listing, or simply by selecting a channel.  The receiver uses
   its pre-acquired information to signal to the network to receive the
   desired content.  In particular, the receiver initiates reception of
   multicast content using the multicast group address and possibly a
   unicast source address supplied within the program guide.

   If the network, the source of the multicast content, and the
   receivers all use IPv4, it is evident that the program information
   will only include IPv4 addresses.  Suppose now, as can occur in some
   transition scenarios, that the program guide contains only IPv4
   addresses and the receiver supports IPv6 only, or vice versa.  Then
   there will be a mismatch: the receivers will be unable to use the
   addresses that are provided in the program guide.  This memo examines
   the possible strategies for remedying this mismatch, evaluating them
   in terms of their impact on receiver implementation and network

   Note that the simplest solution might be to avoid mismatches by
   making sure that new receivers are dual stack rather than IPv6- only.

   The remarks in Section 4.1 of [ID.mboned-v4v6-mcast-ps] are relevant
   to the problem considered here, but are more restricted in scope.

2.  Which Problem Are We Solving?

   In some transition scenarios, the source supports one IP version
   while the receiver and the provider network support the other (e.g.,
   the source supports IPv4, the receiver and the network to which it is
   attached support IPv6).  In this case, the problem stated above can
   be expressed as follows: how does the receiver acquire addresses of
   the IP version it supports, possibly with the help of the provider

   In other transition scenarios, the source and provider network may

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   support one IP version while the receiver supports another.  In this
   case there are actually two problems: how the receiver acquires
   addresses that it supports (as already stated), and how to make those
   addresses usable in a network supporting a different version?  This
   second problem is the subject of a different memo and out of scope of
   the present one.

   There is also a third class of scenarios, where the source and
   receiver support the same IP version but the intervening network
   supports a different one (e.g., the 4-6-4 scenario, Section 3.1 of
   [ID.mboned-v4v6-mcast-ps]).  In those scenarios, delivering addresses
   of the right IP version to the receiver within the program guide is
   notionally a non-problem.  The problem still can arise, if the
   intervening network intercepts and modifies the program guide to be
   consistent with the IP version it supports.  In this case, the
   problem can be re-stated as: how can such modification be avoided
   when it is not needed?

3.  Possible Solutions

   This section explores three classes of solutions to the problem just

   o  reactive: the receiver recognizes that addresses it has received
      are in the wrong version and converts them through a request to a
      mapping function or using an in-built algorithm and accompanying

   o  dynamic modification: the network intercepts the access
      information and modifies it as necessary to meet the requirements
      of the receiver;

   o  administrative: the electronic program guide is modified in
      advance of its acquisition by the receiver to provide alternative
      address versions.  Two variations on this strategy are identified.

3.1.  The Reactive Strategy

   According to this strategy, a receiver recognizes that it has
   received multicast group addresses, even when they are the wrong
   version.  As one possibility, it invokes an external mapping function
   to convert them to the version it supports.  The mapping function
   could be located in another node at the user site or at a node in the
   provider network.

   This approach involves a fair amount of work to implement.  Not only
   does the receiver need to recognize that addresses are the wrong

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   version; it also has to implement a new protocol to the mapping
   function.  It also has to discover that function.

   As an alternative, the receiver can implement an algorithm to perform
   the mapping itself, for example, synthesizing an IPv6 address given
   the IPv4 address of the source using the approach described by
   [ID.mboned-64-multicast-address-format] for multicast group addresses
   or [RFC6052] for unicast source addresses.  In this case, the
   receiver must be configured with the IPv6 prefixes allocated for that
   purpose in the network to which the receiver is attached (e.g., using
   [ID.softwire-multicast-prefix-option]).  When applicable, this
   approach clearly has advantages over an approach using an external
   mapping function.  It still requires implementation effort in the
   receiver, but at a more limited level.

3.2.  Dynamic Modification

   This strategy puts the entire burden of address adaptation on the
   provider network.  It requires that an element in that network must
   intercept program guide information destined to the receiver, locate
   the access information, and map IP addresses to an alternate version
   as necessary to suit the receiver.  If the problem identified in the
   last paragraph of Section 2 is to be avoided, the intercepting
   element has to be aware of the version supported by each receiver.

   As noted in the description of the OMA architecture in Appendix A, it
   is possible that such an adaptive function is present, but not clear
   that its scope would extend to IP version changes.  The need to
   include IP version along with other receiver- related information
   might or might not prove to be administratively demanding.  With the
   dynamic modification strategy the workload on the adaptation function
   might be large enough to make it a bottleneck in the process of
   program acquisition.  The mitigating factor is that program metadata
   will typically be retrieved rather less often than program content.

   This strategy has the clear advantage that it requires no changes in
   the receiver.

3.3.  Administrative Preparation

   The basic idea with this strategy is that the access information in
   the program metadata is set up to provide the right address version
   in advance of acquisition by any receiver.  There are two basic

   o  separate alternative versions of the access information are
      prepared.  The correct version is served up to the receiver when
      it requests it.  Like the dynamic modification strategy, this

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      approach assumes that it is administratively feasible for the
      program guide server to know the IP version of the requesting
      receiver.  That may or may not be true in a given operator's
      context.  Also as with the dynamic modification approach, no
      change is required in the receiver.  The big advantage over
      dynamic modification is that there is no need for the
      complications of an intercepting adapting element.

   o  The same access information instance contains alternative IP
      address versions.  Where SDP is used, we can think of ICE or ICE-
      lite [RFC5245] or the proposed 'altc' mechanism
      [ID.boucadair-altc].  This requires receiver modification to
      recognize the alternative syntax and (in the case of ICE and
      potentially in the case of ICE-Lite) to take part in STUN
      exchanges.  However, it means that the same access information can
      be served up to all receivers in a backward-compatible manner.

   The administrative strategy requires that the network provider have
   control over the translations used in the preparation of the
   alternative versions of the access information.  The network has to
   be aware of the translations used, so it can reuse them at other
   stages of the multicast acquisition process.  Note networks owned by
   different operators are likely to have different mappings between
   IPv4 and IPv6 addresses, so if multiple receiving networks are
   downstream of the same source network, each of them may have to
   prepare and make available its own IPv6 version of the electronic
   program guide.

4.  Conclusions

   To come.

5.  Acknowledgements


6.  IANA Considerations

   This memo includes no request to IANA.

7.  Security Considerations

   To come.

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8.  Informative References

              Boucadair, M., Kaplan, H., Gilman, R., and S.
              Veikkolainen, "Session Description Protocol (SDP)
              Alternate Connectivity (ALTC) Attribute (Work in
              Progress)", April 2012.

              Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
              M. Xu, "IPv4-Embedded IPv6 Multicast Address Format (Work
              in Progress)", May 2012.

              Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., Tsou, T.,
              and Q. Sun, "IPv4-IPv6 Multicast: Problem Statement and
              Use Cases (Work in Progress)", May 2012.

              Qin, J., Boucadair, M., Tsou, T., and X. Deng, "DHCPv6
              Options for IPv6 DS-Lite Multicast Prefix (Work in
              Progress)", March 2012.

              "Information technology - Multimedia content description
              interface - Part 2: Description definition language", ISI/
              IEC 15938-2 (2002), 2002.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC4078]  Earnshaw, N., Aoki, S., Ashley, A., and W. Kameyama, "The
              TV-Anytime Content Reference Identifier (CRID)", RFC 4078,
              May 2005.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

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Appendix A.  Some Background On Program Guides

   Numerous organizations have been involved in the development of
   specifications for IPTV.  Those specifications and the requirements
   of individual providers have influenced the development of existing
   receivers.  Any solution to the multicast transition problem
   described in Section 1 has to take account of the effort involved not
   only in the direct development of a new generation of receivers, but
   also in evolving the specifications on which those receivers are
   based.  It is thus worthwhile to review the current situation as it
   affects multicast transition.

   The TV-Anytime forum ( did early work in
   the area, formally terminating in 2005.  Their work focussed on the
   description of program content, to facilitate the creation of such
   descriptions and their navigation by the user.  The results are
   documented in the ETSI TS 102 822 series of technical specifications.

   The content reference identifier (CRID) is a fundamental concept in
   the TV-Anytime data model.  It refers to a specific piece of content
   or to other CRIDs, the latter thereby providing a method for grouping
   related pieces of content.  TV-Anytime registered the CRID: URL
   schema in [RFC4078].  Quoting from the abstract of that document:

      The Uniform Resource Locator (URL) scheme "CRID:" has been devised
      to allow references to current or future scheduled publications of
      broadcast media content over television distribution platforms and
      the Internet.

      The initial intended application is as an embedded link within
      scheduled programme description metadata that can be used by the
      home user or agent to associate a programme selection with the
      corresponding programme location information for subsequent
      automatic acquisition.

   The process of location resolution for the CRID: URL for an
   individual piece of content locates the content itself so that the
   user can access it.  TV-Anywhere left the details of that process

   The Open IPTV Forum ( has focussed on defining the
   user-to-network interface, particularly for fixed broadband access.
   The architecture is based on the ETSI NGN (Next Generation Networks)
   model.  The receiver obtains the actual access information for a
   given program, including the multicast group address and possibly a
   unicast source address, from XML-encoded program information
   following the Open IPTV Forum schema.  The receiver uses SIP (Session
   Initiation Protocol [RFC3261]) signalling to obtain authorization and

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   resources for a session, before signalling at the multicast level to
   acquire the program.  The SIP signalling conveys the multicast group
   address and the unicast source address, if available, in the form of
   an SDP (Session Description Protocol [RFC4566]) session description.

   Finally, the Open Mobile Alliance (OMA, has defined a series of
   specifications relating to broadcast services over wireless networks.
   The source and multicast group addresses used to acquire a given
   program instance are provided in SDP fragments either directly
   embedded in the primary electronic program guide or pointed to by it.
   The OMA architecture provides functionality to adapt access
   information within the program guide to the requirements of the
   transport network to which the user is attached, but this
   functionality appears to be primarily directed toward overcoming
   differences in technology rather than a general capability for

   In conclusion, it appears that there are at least two extant sources
   of specifications for the receiver interface, each providing its own
   data model, XML data schema, and detailed architecture.  In the OMA
   case, the access information including the source and multicast group
   addresses is embedded as an SDP fragment within a larger set of XML-
   encoded program metadata.  The OMA metadata can be supplied to the
   receiver in multiple segments, through multiple channels.  This
   complicates the task of intercepting that metadata and modifying it
   in a particular transport network.

Authors' Addresses

   Tina Tsou
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara, CA  95050

   Phone: +1 408 330 4424

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   Axel Clauberg
   Deutsche Telekom
   Deutsche Telekom AG, GTN-FM4
   Landgrabenweg 151
   Bonn  53227

   Phone: +4922893618546

   Mohamed Boucadair
   France Telecom
   Rennes  35000


   Stig Venaas
   Cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Qiong Sun
   China Telecom
   Room 708
   No.118, Xizhimennei Street
   Beijing,   100035

   Phone: +86-10-58552936

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