Multicast Routing

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Oct 29, 2013 (3 years and 9 months ago)

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©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

1

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Chapter 14

Multicasting And Multicast

Routing Protocols



INTRODUCTION



MULTICAST ROUTING



MULTICAST TREES



MULTICAST ROUTING PROTOCOLS



DVMRP



MOSPF



CBT



PIM



MBONE

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
1

In unicast routing, the router forwards

the received packet through

only one of its interfaces.

14.1 Introduction: Unicasting


©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Multicasting

In multicast routing,

the router may forward the

received packet

through several of its

interfaces.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
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Multicasting versus multiple unicasting

Emulation of multicasting through

multiple unicasting is not

efficient and may

create long delays,

particularly with a large group.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Application of Multicasting


Access to Distributed Databases


Information Dissemination: e.g. multicast software updates to
customers


News Delivery


Teleconferencing, Web Seminars


Distant Learning

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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14.3 Multicast Routing

Objectives


Every member receives EXACTLY ONE copy of the packet


Non
-
members receive nothing


No loops in route


Optimal path from source to each destination.


Terminology


Spanning Tree
: Source is the
root
, group members are the
leaves
.


Shortest Path Spanning Tree
: Each path from root to a leaf is the
shortest according to some metric

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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14.3 Multicast Trees


Source
-
Based Tree:


For each combination of (source , group), there is a shortest path
spanning tree.


Approach 1: DVMRP; an extension of unicast distance vector
routing (e.g. RIP)


Approach 2: MOSPF; an extension of unicast link state routing
(e.g. OSPF)


Group
-
Share Tree


One tree for the entire group


Rendezvous
-
Point Tree: one router is the center of the group and
therefore the root of the tree.


CBT and PIM
-
SP protocols.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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14.4 Multicast routing protocols

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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14.5 Distance Vector Multicast Routing Protocol
-

DVMRP


No pre
-
defined route from source to destination. Tree is gradually
created by successive routers along the path.


Uses shortest path (fewest hops)


Prevent loops: apply Reverse Path Forwarding (RFP)


Prevent Duplication: apply Reverse Path Broadcasting (RPB)


Multicast with dynamic membership: apply Reverse Path
Multicasting (RPM) with pruning, grafting, and lifetime.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Reverse Path Forwarding

In reverse path forwarding (RPF),

the router forwards only

the packets that have traveled the

shortest path from the source

to the router; all other

copies are discarded. No Loops

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Reverse Path Broadcasting

Prevent Duplication in RPF

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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RPF versus RPB


The router with the shortest path to the source becomes the
designated parent of a network


A Router forwards packets only to its designated child networks

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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RPB creates a shortest path

broadcast tree from the source

to each destination.

It guarantees that each destination

receives one and only

one copy of the packet.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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RPF, RPB, and RPM

RPM adds pruning and grafting to RPB

to create a multicast shortest

path tree that supports

dynamic membership changes.

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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MOSPF

14.6

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The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Unicast tree and multicast tree

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Core
-
Based Tree

CBT

14.7

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Shared
-
group tree with rendezvous router

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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Figure 14
-
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Sending a multicast packet to

the rendezvous router

©
The McGraw
-
Hill Companies, Inc., 2000

© Adapted for use at JMU by
Mohamed Aboutabl
, 2003

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In CBT, the source sends the

multicast packet (encapsulated in a

unicast packet) to the core router.

The core router decapsulates the

packet and forwards it

to all interested hosts.