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Issues In Multicast Transition
For presentation to the Multrans BOF
Tom Taylor <[email protected]>
Cathy Zhou <[email protected]>
Contents
3.Technical Issues
4.Address Acquisition
5.Multicast Signalling
6.Transition Techniques
7.Translation
8.Encapsulation
9.Dual Stack Source Operation
10.Dual Stack Network Operation
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Technical Issues
Multicast distribution of a given stream enabled in three
stages:
1) Address acquisition by the receiver

Multicast group address and, for SSM, unicast source address
for the desired multicast stream

Could be other unicast addresses involved (e.g., RTCP
feedback target)
2) Multicast signalling from the receiver toward the source to
set up the multicast tree
3) Transporting multicast content from a source to the receivers
through the tree that has been set up
Multicast transition presents issues at each stage.
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Address Acquisition

Various ways to do address acquisition:

Configuration, session signalling (SIP), announcements
(SAP), proprietary program guide (HTML), ...
Issue: if the receiver just supports one IP version, it has
to receive the addresses in that version

May need translation, either off-line or in some node along
the acquisition stage messaging path.
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Multicast Signalling

Three protocols -- IGMP (IPv4, three versions), MLD
(IPv6, two versions), and PIM-SM (IPv4 and IPv6)



Establish paths between sources, multicast routers, and
receivers
Objective: minimize total bandwidth required to distribute
multicast content
Outcome: tree structures set up with multicast routers as the
intermediate nodes
Issue: IPv6 transition creates new protocol interworking
combinations

IGMP  PIM v6, MLD  PIM v4, PIM v4  PIM v6,
IGMP  MLD
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Transition Techniques

Three basic transition techniques:

Translation

Encapsulation

Dual stack
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Translation

Stateless translation may be an option (true in higherpriority scenarios).
Issue: need the multicast equivalent of RFC 6052 for stateless
translation.


draft-boucadair-behave-64-multicast-address-format is a
candidate.
Translation of a given address happens at multiple
nodes, different stages within the same node.
Issue: for stateful mapping, need coordination to ensure the
same mapping or its inverse, as applicable, is used each
time a given address is translated.
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Encapsulation

Unicast encapsulation solutions such as 6rd or DS-lite do not
apply to multicast.

Unicast solutions carry packets from edge to edge. Multicast
signalling and content distribution has to pass from one multicast
router to the next within the network interior.
Issue: at the architectural level, interaction with unicast solutions in
terms of potential collocation/reuse of functions

May use tunneling between multicast routers for content
distribution.


IP-in-IP encapsulation: multicast routers can route based on the
outer header.
IP-in-non-IP encapsulation: multicast routing may use the inner
header, which then may need translation to make it usable.
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Dual Stack Source Operation
Issue: need to avoid carrying the same content in
parallel IPv4 and IPv6 streams through the network.

Hence operating source in dual stack mode is undesirable.

Translate at receiver end instead.
S
IPv6
S
IPv4
IPv4
MR
MR
IPv6
IPv4
IPv4
MR
IPv6
IPv4
IPv4
MR
IPv4
IPv4
T
IPv6
R
R
R
R
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R
R
9
Dual Stack Network Operation
Two basic strategies (applicable both to ASM and SSM):
Common Core
S
Pv6
S
S
IPv4
T
Source version through network
IPv6
IPv4
Dual stack network
operating as (e.g.)
IPv4 network
for multicast
Dual stack • Source-IPv6: PIMv6 to set up
network
multicast tree, some v4
T
IPv4
S
T
T
R
R
receivers can receive the
content by v6->v4 translation
• Source-IPv4: PIMv4 to set up
multicast tree, some v6
receivers can receive the
content by v4->v6 translation
IPv6
R
R
Double translation
for some streams
IPv4
IPv6
Operational complexity
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Acknowledgement
The authors would like to thank Joel M. Halpern, Dan
Wing, Jacni Qin and Yiu Lee for their valuable
comments.
Questions for clarification?
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