Post on 03-Jun-2018
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Multicast Routing on the Internet
Jason Chu
Svetlana Kotchenova
Can Le
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
What is multicast?
Individual hosts are configured as members of different
multicast groups
Point-to-multipoint transmission
Multicasting is not connection oriented
An IP multicast group is identified by a Class D address
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Multicast IP Delivery Service
The Internet Management Protocol runs between host and their
immediately neighboring multicast routers
A Multicast Routing Protocol is responsible for the construction ofmulticast delivery trees and forwarding of multicast datagramsacross an internetwork
Group MembershipProtocol
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Internet Group Management Protocol (IGMP)
A multicast router periodically transmits Host Membership Querymessages
When a host wants to join a group, it immediately transmits a HostMembership Report for the group
Election of the querier (The router with the lowest IP address)
A Group-Specific Query Message
A Leave Group message
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Multicast forwarding algorithms
Flooding
Spanning Trees
Reverse Path Broadcasting
Truncated Reverse Path Broadcasting Reverse Path Multicasting
Core-Based Trees
Multicast Routing Protocols Distance Vector Multicast Routing protocol
Multicast OSPF
Protocol Independent Multicast (Dense and Sparse modes)
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Reverse Path Multicasting
Every time a router receives a packet
on one of its links, it checks whether
this link belongs to the shortest path
towards the source
yes no
Forward the
packet to all
downstream
neighbors
Discard the
packet
Poison reversethe route
The parent link the interface over
which a router expects to receive multicastpackets from a particular source
The child links the outgoing links over
which a router forwards multicast packets
S
A
B
D
C
E
1
4
3
2
5
8
(RPB)
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Reverse Path Multicasting
Multicast Group
Membership should be
taken into account ->
use of the IGMP (TRPB)
A router can transmit a
prune message on its
parent link (RPM)
Prune messages aresent only one hop back
toward the source
Result: a source-rooted, shortest-path tree for each (source-group) pair
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Drawbacks of RPM
1. The prune information in routers must be removedperiodically and the next packet for a (source, group) isforwarded to all leaf routers
2. Relatively big memory space is required for maintainingstate information for all (source, group) pairs -> it makesthe algorithm not scalable
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Project goals
Simulation of unicast forwarding since in real life bothunicast and multicast communication pattern areused in the same network
Simulation of Reverse Path Multicasting using aspecial data structure to store the information
Evaluation of the algorithm efficiency in the case of
the large internetworks (up to 10000 nodes)
Comparison with another multicast forwardingalgorithm, Core-Based Trees, which was preliminary
created to overcome the limitations of Reverse Path
Multicasting
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Core-Based Trees
A single router or a set of routers acts as the core
A host that wishes to receive traffic for a multicast group isrequired to send a join message to one of the groups corerouters.
Result: a single delivery tree that is shared by all members of a group
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Core-Based Trees
Benefits
Efficient use of router
resources (maintenance of
information for each group,not for each (source, group)
pair)
Conserves network
bandwidth
Limitations
Traffic concentration near
core routers
Possible delays
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Where can multicast be used?
Sharing audio and video (multiparty video-conferencing)
Web caching (the temporary storage of web objects for
later retrieval)
Web clustering
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SC546 Computer Communications and Networks, Boston University, Spring, 2001
Thank you!
Any questions?..