Internet DRAFT - draft-tsou-mboned-multrans-addr-acquisition
draft-tsou-mboned-multrans-addr-acquisition
Internet Engineering Task Force T. Tsou
Internet-Draft Huawei Technologies (USA)
Intended status: Informational A. Clauberg
Expires: September 13, 2012 Deutsche Telekom
M. Boucadair
France Telecom
S. Venaas
Cisco Systems
Q. Sun
China Telecom
March 12, 2012
Address Acquisition For Multicast Content When Source and Receiver
Support Differing IP Versions
draft-tsou-mboned-multrans-addr-acquisition-01
Abstract
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 and evaluates alternative
strategies for allowing the receiver to acquire multicast address
information in the version it supports in such scenarios. Operators
may find this review useful when planning their own transition
strategy.
Status of this Memo
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This Internet-Draft will expire on September 13, 2012.
Copyright Notice
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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
operation.
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.jaclee-behave-v4v6-multicast-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
network?
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In other transition scenarios, the source and provider network may
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.jaclee-behave-v4v6-multicast-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
described:
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
configuration;
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
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does the receiver need to recognize that addresses are the wrong
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.qin-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
approaches:
o separate alternative versions of the access information are
prepared. The correct version is served up to the receiver when
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it requests it. Like the dynamic modification strategy, this
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
TBD
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
To come.
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8. Informative References
[ID.boucadair-altc]
Boucadair, M., Kaplan, H., Gilman, R., and S.
Veikkolainen, "Session Description Protocol (SDP)
Alternate Connectivity (ALTC) Attribute (Work in
Progress)", November 2011.
[ID.jaclee-behave-v4v6-multicast-ps]
Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., and T.
Tsou, "IPv4-IPv6 Multicast: Problem Statement and Use
Cases (Work in Progress)", November 2011.
[ID.mboned-64-multicast-address-format]
Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
M. Xu, "IPv4-Embedded IPv6 Multicast Address Format (Work
in Progress)", February 2012.
[ID.qin-softwire-multicast-prefix-option]
Qin, J., Boucadair, M., and T. Tsou, "DHCPv6 Options for
IPv6 DS-Lite Multicast Prefix (Work in Progress)",
October 2011.
[MPEG-7_DDL]
ISO/IEC, "ISO/IEC 15938-2 (2002): "Information technology
- Multimedia content description interface - Part 2:
Description definition language".", 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 (http://www.tv-anytime.org/) 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
unspecified.
The Open IPTV Forum (http://www.oipf.tv) 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,
http://www.openmobilealliance.org/) 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
modification.
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
USA
Phone: +1 408 330 4424
Email: Tina.Tsou.Zouting@huawei.com
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Axel Clauberg
Deutsche Telekom
Deutsche Telekom AG, GTN-FM4
Landgrabenweg 151
Bonn, 53227
Germany
Phone: +4922893618546
Email: axel.clauberg@telekom.de
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Phone:
Email: mohamed.boucadair@orange.com
Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Phone:
Email: stig@cisco.com
Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing, 100035
P.R.China
Phone: +86-10-58552936
Email: sunqiong@ctbri.com.cn
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