Download Issue - IETF

Issues In Multicast Transition
For presentation to the Multrans BOF
Tom Taylor <[email protected]>
Cathy Zhou <[email protected]>
2011-06-27
Issues In Multicast Transition
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Contents
Chart 3: Management Issues
Chart 4: Technical Issues
Chart 5: Address Acquisition
Chart 6: Multicast Signalling
Chart 7: Transition Techniques
Chart 8: Translation
Chart 9: Encapsulation
Chart 10: Dual Stack
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Management Issues
Issue: no obvious home for the Problem Statement
draft (draft-jaclee-behave-v4v6-mcast-ps)
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Mboned WG seems to have related milestones, though far
out of date.
Issue: work needs to be coordinated across a number
of Working Groups in different Areas
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Behave, Softwires, PIM, Mboned, possibly AVTCore
Need to ensure necessary expertise is available for each
work item
If work items are distributed amongst WGs, need to ensure
they get adequate priority
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Techical Issues
Multicast distribution of a given stream is enabled in
three stages:
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Address acquisition by the receiver
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–
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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)
Multicast signalling from the receiver toward the source to
set up the multicast tree
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
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Address acquisition can be done in a number of ways:
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configuration, session signalling (SIP, HTML),
announcements (SAP)
Issue: if the receiver just supports one IP version, it
has to receive the addresses in that version
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Implies either off-line translation or translation along the
session signalling path if the addresses in their original form
are in the other IP version
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Multicast Signalling
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Multicast signalling uses three protocols -- IGMP
(IPv4), MLD (IPv6), and PIM (IPv4 and IPv6) – to
establish paths between sources, multicast routers,
and receivers
●
●
Objective is to minimize total bandwidth required to distribute
multicast content
Outcome is tree structures set up with multicast routers as
the intermediate nodes
Issue: IPv6 transition creates new protocol
interworking combinations
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IGMP ó PIM v6, MLD ó PIM v4, PIM v4 ó PIM v6,
IGMP ó MLD
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Transition Techniques
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Three basic transition techniques:
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Translation
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Encapsulation
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Dual stack
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Translation
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Depending on the scenario, stateless translation may
be an option. Stateful translation is the alternative.
Issue: need the multicast equivalent of RFC 6052 for
stateless translation.
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draft-boucadair-behave-64-multicast-address-format is a
candidate.
Issue: translation of a given address tends to happen
at multiple nodes, and at different stages within the
same node.
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Need the same mapping or its inverse, as applicable, to be
used each time a given address is translated. Implies internodal coordination in some form.
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Encapsulation
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Unicast encapsulation solutions such as 6rd or DS-lite do not
apply to multicast.
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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
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Possible to use encapsulation in the form of a softwire mesh
between multicast routers.
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For IP-in-IP encapsulation the multicast routers can route based
on the outer header.
For non-IP encapsulation, multicast routing must use the inner
header, which may need translation to make it usable.
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Dual Stack
Issue: need to avoid carrying the same content in
parallel IPv4 and IPv6 streams through the network.
●
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Hence operating source in dual stack mode is undesirable.
For dual stack network, have two basic strategies:
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Translate all streams to common IP version upon entry.
–
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Results in double translation when source and receiver
support one version and the network supports the other.
Carry each stream as far as possible in its original version.
Issue: multicast signalling to set up the path has to be for the
source IP version. This implies that the translating node at the
receiver end is aware of the source IP version in the multicast
signalling stage.
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Questions for clarification?
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