Internet DRAFT - draft-eubanks-mboned-transition-overview
draft-eubanks-mboned-transition-overview
Internet Engineering Task Force H. Asaeda
Internet-Draft Keio University
Intended status: Informational M. Eubanks
Expires: September 13, 2012 AmericaFree.TV
T. Tsou
Huawei Technologies (USA)
S. Venaas
Cisco Systems
March 12, 2012
Multicast Transition Overview
draft-eubanks-mboned-transition-overview-04
Abstract
IPTV providers must serve content to their customers during the
period of transition from IPv4 to IPv6. During this period, the
content provider may support only one version of IP while the
customer's receiver device supports only the other. Likewise, the
network between the provider and its customer may include segments
supporting only one version of IP or another.
This document provides an overview of the multicast transition
problem. It also provides an overview of the solution space. The
solution space is characterized by an adaptation function (AF) that
provides an interface between IPv4 and IPv6 multicast domains. This
document also discusses various multicast use cases which may occur
during IPv6 transitioning. These use cases motivate the solution
space discussion and the requirements that appear at the end.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 13, 2012.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. A Look At the Multicast Transition Problem Space . . . . . . . 3
2.1. Signaling Channels using Multicast Addresses . . . . . . . 4
2.2. Operator View of Use Cases . . . . . . . . . . . . . . . . 5
2.3. Requirements From The Use Cases . . . . . . . . . . . . . 8
3. A Look At the Solution Space For Multicast Transition . . . . 9
3.1. AF Forwarding Plane Operation . . . . . . . . . . . . . . 9
3.2. AF Control Plane Operation . . . . . . . . . . . . . . . . 10
3.3. Source Discovery . . . . . . . . . . . . . . . . . . . . . 10
3.4. Transitional Multicast Path Optimization . . . . . . . . . 10
4. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Informative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
IPTV providers must serve content to their customers during the
period of transition from IPv4 to IPv6. During this period, the
content provider may support only one version of IP while the
customer supports only the other. Likewise, the network between the
provider and its customer may include segments supporting only one
version of IP or another.
In current deployments, the IP multicast forwarding scheme is used by
many service providers to deliver services such as live TV
broadcasting. Multiple players intervene in the delivery of these
services, including content and service providers. Service providers
are responsible for carrying multicast flows from head-ends to
receivers. The content can be supplied by a service provider or by
other providers (e.g., case of externally paid channels).
Unlike the situation for unicast addresses, the IPv4 multicast
address space seems sufficient for most proposed uses. Hence the key
motivation for the work described here is to preserve the
efficiencies of multicast distribution of content (i.e., by reducing
total traffic on the network and minimizing the distance that
multicast streams must travel) when both IPv4 and IPv6 segments lie
on the path from source to receiver.
This document provides an overview of the multicast transition
problem. It also provides an overview of the solution space. The
solution space is characterized by an adaptation function (AF) that
provides an interface between IPv4 and IPv6 multicast segments. The
scope of this document is currently limited to IP transport, and
covers both single operator and inter-operator flows.
Section 2 describes the problem space in detail. This section
describes an environment that includes a content provider, a
customer, and an intervening network. Any component of that
environment may support only one version of IP or the other. At
points where IPv4-only devices lie on one side and IPv6-only devices
on the other, an adaptation function is required.
Section 3 proposes a framework for the solution. Section 4 defines
formal requirements for any proposed solution.
2. A Look At the Multicast Transition Problem Space
Historically, IPTV providers have served IPv4 content to receivers
over IPv4 multicast networks. CPE has thus until recently supported
IPv4 only. As the Internet transitions to IPv6, IPv6-capable
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equipment will be deployed by content providers and receivers, as
well as the networks that connect them to one another. So long as
all of the newly deployed gear supports both IPv4 and IPv6, the
transition to IPv6 may not require new IETF protocol specifications
in support of multicast deployment. In this case of dual-stack
environments, either IP address family can be used end to end for the
multicast traffic. However, if some of the newly deployed gear
supports IPv6 only, incompatibilities will be introduced. These
IPv6-only scenarios are being planned and deployed because the
exhaustion of IPv4 unicast address space. Instead of running large
NAT and IPv6 all together, some providers prefer to run a single
address family that is future proof, which is IPv6. This also brings
simpler management of the network. In this unicast case, IPv4
traffic can be either tunneled over IPv6 (e.g. softwire, dslite, 4rd)
or translated (NAT64). Therefore, some access networks are IPv6
only.
An incompatibility occurs at a device lying along the path between
the source and the receiver when the next device on the path on one
side of it supports a different version of IP from the next device on
the path on the other side of it (i.e., one device supports IPv4 only
and the other supports IPv6 only). For the purposes of this
document, we will call these points of incompatibility "IP version
transition points". The communication path between source and
receiver (which includes both endpoints) can include zero or more IP
version transition points.
IP version transition points may be introduced at any point along the
path. These IP version transition points may reside in the
subscriber premises, at the CPE, in the intervening network etc. In
addition, the Set Top Box (STB) and Electronic Program Guides (EPG)
may have different IP versions.
In order to maintain multicast connectivity, one or more adaptation
functions (AF) are required. The AF operates in both the forwarding
and control planes. Because it provides an interface between the
IPv4 and IPv6 domain, it must be both IPv4-capable and IPv6-capable.
In most cases, the adaptation function will mediate between IPv4 and
IPv6 on both the control and forwarding planes. However, in
scenarios where the path between source and receiver contains
multiple IP version transition points, adaptation function instances
may tunnel traffic between one another.
2.1. Signaling Channels using Multicast Addresses
The receiver is provided the necessary multicast addresses for
channel reception by some means such as an Electronic Program Guide
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(EPG). If the source uses the same address family as the receiver,
the receiver will subscribe to a multicast address of the appropriate
address family. However, If the source uses the other address
family, then the signaling must be translated in the path (or at the
program guide).
An early assessment of the market seems to suggest that most
signaling is done with proprietary protocols, and that most EPG are
also proprietary. It remains to be seen if a standardized solution
for this issue a need or even a possibility, given these market
realities.
2.2. Operator View of Use Cases
Discussion with operators has indicated in the first place that the
distribution of Electronic Program Guide material is done by
proprietary means, and they have no interest in a standardized
solution. SSM (Specific Source Multicast) is the technically
preferable mode of operation. However, some operators may have to
use ASM (Any Source Multicast) because of the limitations of existing
receivers (i.e., limitations on the support of IGMP v3 or MLD v2).
In what follows, this document uses the following numeric convention
to specify a particular scenario: <receiver version>-<network
version(s)>-<source version> (e.g., 6-4-6-4 for the second scenario
described below).
For a number of operators, the expected evolution path is to first
upgrade the network to IPv6, then upgrade the receivers to IPv6
through a gradual process of replacement, and then add IPv6 sources
when a critical mass of IPv6 receivers is reached. This sequence
implies that the immediate priority is to support the 4-6-4 scenario
shown in Figure 1. One can immediately see that two instances of the
AF are needed, one at each side of the IPv6 network. The receiver
signals using IGMP. The AF translates the IGMP either to MLD
[RFC3810] or to PIM [RFC4601] running on IPv6. At the other side,
the AF most likely interworks between PIM with IPv6 and PIM with
IPv4. In the reverse direction, multicast data packets can either be
translated or tunneled between the AF instances, as noted above.
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+------+ +-----+ +----+ +------+ +-----+
| Host | | DS | | | | MR | | |
| Rcvr |------| AF | | MR | . . . | |------| Src |
| | IPv4 | | | | IPv4 | (DR) | IPv4 | |
+------+ +-----+ +----+ +------+ +-----+
/ \
/ IPv6 \ IPv4
/ \
+----+ +----+ +------+
| | | | | DS |
| MR |------| MR | . . . | AF |
| | IPv6 | | IPv6 | |
+----+ +----+ +------+
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast router
DR : Designated Router
Src : Multicast source
Figure 1: An Initial Scenario: IPv4 Source and Receiver Via an IPv6
Network
An alternative view of network evolution contemplates a more
immediate rollout of IPv6 receivers, but a slow evolution of sources
from IPv4 to IPv6. The backbone network will be IPv6 in all cases,
but the metro network may be either IPv4 or IPv6. The first case
(6-4-6-4), with an IPv4 metro network, is shown in Figure 2. Three
AF instances are needed, at the IP version transition points between
the source and backbone network, between the backbone and metro
network, and between the metro network and the receiver.
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+------+ +-----+ +----+ +------+
| Host | | DS | | | | DS |
| Rcvr |------| AF |------| MR | . . .| AF |
| | IPv6 | | IPv4 | | IPv4 | |
+------+ +-----+ +----+ +------+
/
----------------------------
/ IPv6
+----+ +----+ +------+
| | | | | DS |
| MR |------| MR | . . . | AF |
| | IPv6 | | IPv6 | |
+----+ +----+ +------+
/
-------------------------
/ IPv4
+----+ +------+ +-----+
| | | MR | | |
| MR | . . . . | |------| Src |
| | IPv4 | (DR) | IPv4 | |
+----+ +------+ +-----+
Rcvr: Multicast receiver
Src : Multicast source
DS : Dual Stack
AF : Adaptation function
MR : Multicast Router
DR : Designated Router
Figure 2: Initial Scenario With IPv6 Host, IPv4 Source, and Both IPv4
and IPv6 Intervening Networks
The case where the metro network has evolved to IPv6 (6-6-4) is shown
in Figure 3. Here, only one AF instance is needed. It translates
between IPv6 PIM in the receiver network and IPv4 PIM in the content
provider network.
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+------+ +-----+ +----+ +------+
| Host | | MR | | | | DS |
| Rcvr |------| |------| MR | . . .| AF |
| | IPv6 |(DR) | IPv6 | | IPv6 | |
+------+ +-----+ +----+ +------+
/
-------------------------
/ IPv4
+----+ +------+ +-----+
| | | MR | | |
| MR | . . . . | |------| Src |
| | IPv4 | (DR) | IPv4 | |
+----+ +------+ +-----+
Rcvr: Multicast receiver
Src : Multicast source
DS : Dual Stack
AF : Adaptation function
MR : Multicast Router
DR : Designated Router
Figure 3: Initial Scenario With IPv6 Host, IPv4 Source, and IPv6
Intervening Network
2.3. Requirements From The Use Cases
All three of the immediately relevant scenarios just described
feature IPv4 sources. This means that no solution is required in the
short term for translation from general IPv6 addresses to IPv4
addresses. In the longer run operators may have the situation of
IPv6 sources serving receivers that have remained at IPv4. That
presents a more difficult translation problem, but the scenario has
low priority.
The three cases illustrate a number of protocol interworking
combinations. As indicated below, some combinations can act as a
part of others, reducing the total development effort.
In summary, the use cases expose the following gaps for which there
are no existing IETF standards:
o Translating from IPv4 to IPv6 multicast addresses and back again.
o Translating from IGMP downstream to MLD upstream (4-6-4 case) and
from MLD downstream to IGMP upstream (6-4-6-4 case).
o Interworking between IGMP and PIM with IPv6 (4-6-4 case). This
could be synthesized by translating the IGMP to MLD and having MLD
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interwork with PIM as usual.
o Interworking between MLD and PIM with IPv4 (6-4-6-4 case). Again,
this could be synthesized, by translating MLD to IGMP and
interworking the latter to PIM as usual.
o Operating PIM with IPv4 downstream and IPv6 upstream (6-4-6-4
case) and with IPv6 downstream and IPv4 upstream (4-6-4 and 6-6-4
cases).
3. A Look At the Solution Space For Multicast Transition
The AF operates on both the forwarding and control planes. On the
forwarding plane, the AF inserts itself into the forwarding path
translating multicast packets from one IP version to the other. On
the control plane, the AF receives routing and signaling messages of
one protocol and sends out routing and signaling messages of another
protocol.[Forward reference to future high-level description of the
AF.]
3.1. AF Forwarding Plane Operation
The AF accepts packets from one IP version, removes the IP header,
and replaces it with an IP Header of the other version. A
significant portion of that task is address translation. Ideally the
address translation strategy used by an AF should be algorithmic,
stateless and reversible. This should be simple when addresses from
one IP version can simply be embedded into another (IPv4 into IPv6),
but this may not be possible in the opposite direction. That the
translation is reversible means that there is a stateless algorithm
for translating back into the original address.
[RFC6052] provides an algorithm for translating unicast addresses
between IPv4 and IPv6. Likewise [I-D.mboned-64-mcast-addr-fmt]
provides an algorithm for multicast address conversion between IPv4
and IPv6. Note that using this algorithm, different translators
could choose different IPv6 prefixes for embedding the IPv4
addresses. But the format allows for stateless translation back to
the original IPv4 addresses.
Other issues associated with IP version translation may arise (e.g.,
fragmentation and checksums and will be resolved as appropriate in
conjunction with appropriate IETF working groups.
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3.2. AF Control Plane Operation
On the control plane, the AF mediates between:
o IGMPv3 [RFC3376] and MLDv2 [RFC3810];
o PIM(v4) [RFC4601] and PIM(v6);
o IGMPv3 and PIM(v6);
o MLD and PIM(v4);
The IGMP-to-MLD translation may be configured to use only IGMPv2
features. It is defined in [draft to come].
[I-D.perreault-mboned-igmp-mld-translation] is a candidate for this
specification.
The PIM-to-PIM mediation operates between PIM protocol operations of
one IP version with operations of the other version.
[I-D.taylor-pim-v4v6-translation] is a candidate for this
specification.
3.3. Source Discovery
Source discovery is out of scope and is left for further study.
[I-D.tsou-mboned-multrans-addr-acquisition] provides an informative
discussion of the options open to operators.
3.4. Transitional Multicast Path Optimization
A mechanism to optimize the path to the multicast source for a
combination of IPv4 and IPv6 networks is not immediately required,
but is a topic for future work.
[I-D.zhou-mboned-multrans-path-optimization] is a candidate for this
specification.
4. Contributors
Some of the introductory text of this document was drawn from
[I-D.jaclee-behave-v4v6-mcast-ps]. Figures from Section 3 of that
document were the starting point for the figures in Section 2.1 of
this document. The strong participation of the authors of
[I-D.jaclee-behave-v4v6-mcast-ps] in the work on multicast transition
leading up to the creation of this document must be acknowledged.
These authors include two co-authors of the present document, plus
Mohamed Boucadair, Yiu Lee, Hitoshi Asaeda, and Jacni Qin, who should
be considered honorary co-authors.
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5. Acknowledgements
Ron Bonica inspired the writing of this memo and shaped its content.
Michael McBride and Marc Blanchet provided useful comments on
intermediate versions of this document.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
To come.
8. Informative References
[I-D.jaclee-behave-v4v6-mcast-ps]
Jacquenet, C., Boucadair, M., Lee, Y., Qin, J., and T.
Tsou, "IPv4-IPv6 Multicast: Problem Statement and Use
Cases", draft-jaclee-behave-v4v6-mcast-ps-03 (work in
progress), October 2011.
[I-D.mboned-64-mcast-addr-fmt]
Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
M. Xu, "IPv4-Embedded IPv6 Multicast Address Format (Work
in Progress)", March 2012.
[I-D.perreault-mboned-igmp-mld-translation]
Perreault, S. and T. Tsou, "Internet Group Management
Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based
Multicast Translation ("IGMP/MLD Translation")",
draft-perreault-mboned-igmp-mld-translation-00 (work in
progress), February 2012.
[I-D.taylor-pim-v4v6-translation]
Taylor, T. and C. Zhou, "A Translator For Protocol
Independent Multicast (PIM) Interworking Between IPv4 and
IPv6", draft-taylor-pim-v4v6-translation-00 (work in
progress), March 2012.
[I-D.tsou-mboned-multrans-addr-acquisition]
Clauberg, A., Boucadair, M., Sun, Q., Venaas, S., and T.
Tsou, "Address Acquisition For Multicast Content When
Source and Receiver Support Differing IP Versions",
draft-tsou-mboned-multrans-addr-acquisition-00 (work in
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progress), February 2012.
[I-D.zhou-mboned-multrans-path-optimization]
Sun, Q. and C. Zhou, "Multicast transition path
optimization in IPv4 and IPv6 networks",
draft-zhou-mboned-multrans-path-optimization-01 (work in
progress), March 2012.
[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.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
Authors' Addresses
Hitoshi Asaeda
Keio University
Graduate School of Media and Governance
5322 Endo
Fujisawa, Kanagawa 252-0882
Japan
Email: asaeda@wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/
Marshall Eubanks
AmericaFree.TV
P.O. Box 141
Clifton, VA 20124
USA
Phone:
Email: marshall.eubanks@gmail.com
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Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 408 330 4424
Email: Tina.Tsou.Zouting@huawei.com
Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Phone:
Email: stig@cisco.com
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