multicast routing. unicast: one source to one destination multicast: one source to many destinations...
TRANSCRIPT
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Multicast Routing
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Multicast Routing
• Unicast: one source to one destination• Multicast: one source to many destinations• Two main functions:
– Efficient data distribution – Logical naming of a group
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Unicast
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Unicast
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Unicast
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Unicast
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Unicast
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Unicast
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Multicast
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Multicast
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Multicast
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Multicast
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Multicast
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Multicast
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Multicast state
• Router:– learn of the existence of multicast groups
(advertisement)– identify links with group members– establish state to route packets
• replicate packets on appropriate interfaces
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Logical naming
• Application level multicast: mailing lists• Single address maps to logically related set of
destinations• Convenience• Scaling: single name/address as group grows,
changes
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Multicast groups
• Members are the intended receivers• Senders may or may not be members• Destination address is class D IP address
– globally known portion of address space• Hosts may belong to many groups• Hosts may send to many groups• Support dynamic creation of groups, dynamic
membership, dynamic sources
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Example applications
• Broadcast audio/video• Push-based systems• Software distribution• Web-cache updates • Teleconferencing (audio, video, shared
whiteboard, text editor)• Multi-player games
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Other parts of the architecture
• Multicast address allocation (later)• Assume address is advertised • Avoid collisions as much as possible
– Mcast address must be unique in space and time
• Use randomization• Can’t have highly used address space• Multiple multicast groups per conference…different
app streams, different layers…more later
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Some concepts
• Application level multicast• Network level multicast• Aside: active networks
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Application-level multicast (another way)
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..application-level multicast
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Components of theIP Multicast Architecture
hosts
routers
service model
host-to-router protocol(IGMP)
multicast routing protocols(various)
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IP Multicast Service Model(RFC-1112)
• each group identified by a single IP address
• groups may be of any size• members of groups may be located
anywhere in the Internet• members of groups can join and leave at
will• senders need not be members
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Service model
• Group membership not known explicitly • Analogy:
– each multicast address is like a radio frequency, on which anyone can transmit, and to which anyone can tune-in.
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IP Multicast Addresses
Class D IP addresses:
in “dotted decimal” notation: 224.0.0.0 —
239.255.255.255
two administrative categories:– “well-known” multicast addresses, assigned by IANA– “transient” multicast addresses, assigned and
reclaimed dynamically, e.g., by “sdr” program
1 1 1 0 group ID
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IP Multicast Service — Sending• uses normal IP-Send operation, with an IP
multicast address specified as the destination• must provide sending application a way to:
– specify outgoing network interface, if >1 available
– specify IP time-to-live (TTL) on outgoing packet– enable/disable loopback if the sending host is a
member of the destination group on the outgoing interface
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IP Multicast Service — Receiving
• two new operations:Join-IP-Multicast-Group ( group-address,
interface )Leave-IP-Multicast-Group ( group-address,
interface )
• receive multicast packets for joined groups via normal IP-Receive operation