IP: Addresses and Forwarding

114 Pages·2002·0.92 MB·English

by  Shivkumar Kalyanaraman

Multicast
Shivkumar Kalyanaraman
[email protected]
http://www.ecse.rpi.edu/Homepages/shivkuma
Adapted in part from Srini Seshan’s (CMU) and Ion Stoica (UCB)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
1
Overview
Why multicast ? Multicast apps ...
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Concepts: groups, scopes, trees
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Multicast addresses, LAN multicast
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Group management: IGMP
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Multicast routing and forwarding: MBONE, PIM
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Reliable Multicast Transport Protocols
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Multicast Congestion Control
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Deployment issues, Source-Specific Multicast (SSM),
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Application-level Multicast
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Multicast = Efficient Data Distribution
Src Src
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Why Multicast ?
Need for efficient one-to-many delivery of same data
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Applications:
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News/sports/stock/weather updates
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Distance learning
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Configuration, routing updates, service location
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Pointcast-type “push” apps
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Teleconferencing (audio, video, shared whiteboard,
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text editor)
Distributed interactive gaming or simulations
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Email distribution lists
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Content distribution; Software distribution
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Web-cache updates
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Database replication
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Why Not Broadcast or Unicast?
Broadcast:
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Send a copy to every machine on the net
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Simple, but inefficient
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All nodes must process packet even if they don’t care
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Wastes more CPU cycles of slower machines
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(“broadcast radiation”)
Network loops lead to “broadcast storms”
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Replicated Unicast:
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Sender sends a copy to each receiver in turn
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Receivers need to register or sender must be pre-
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configured
Sender is focal point of all control traffic
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Reliability => per-receiver state, separate
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sessions/processes at sender
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Why IP multicast ?
Application-layer relays:
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A “relay” node or set of nodes does the replicated
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unicast function instead of the source
Multiple relays can handle “groups” of receivers
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and reduce number of packets per multicast =>
efficiency
Manager has to manually configure names of
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receivers in relays etc
App-level topology may be sub-optimal
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But bandwidth is becoming cheaper
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Becoming more popular in content distribution
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IP Multicast: replication/multicast engine at the
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network layer
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Multicast Apps Characteristics
Number of (simultaneous) senders to the group
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The size of the groups
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Number of members (receivers)
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Geographic extent or scope
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Diameter of the group measured in router hops
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The longevity of the group
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Number of aggregate packets/second
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The peak/average used by source
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Level of human interactivity
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Lecture mode vs interactive
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Data-only (eg database replication) vs multimedia
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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IP Multicast Architecture
SSeerrvviiccee mmooddeell
Hosts
Host-to-router protocol
(IGMP)
Routers
Multicast routing protocols
(various)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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IP Multicast model: RFC 1112
Message sent to multicast “group” (of receivers)
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Senders need not be group members
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A group identified by a single “group address”
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Use “group address” instead of destination
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address in IP packet sent to group
Groups can have any size;
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Group members can be located anywhere on
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the Internet
Group membership is not explicitly known
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Receivers can join/leave at will
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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IP Multicast Concepts (Continued)
Packets are not duplicated or delivered to
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destinations outside the group
Distribution tree constructed for delivery of
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packets
Packets forwarded “away” from the source
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No more than one copy of packet appears on
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any subnet
Packets delivered only to “interested” receivers
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=> multicast delivery tree changes dynamically
Network has to actively discover paths between
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senders and receivers
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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