Introduction to Multicast

8/12/2019 Introduction to Multicast

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Multicast

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Spencer Tsai

Mobile Communication & Broadband Network Lab

CSIE

Fu-Jen Catholic University

Introduction to Multicast


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Outline

Overview

IGMP

Multicast Routing on the Internet

Multicast Routing between Domains

Reference


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Overview

Unicast

Multicast

Multicast Characteristic

IP Multicast Address

Examples of permanent groups Architecture of Multicast


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Unicast

Host

Router

Point to point

N receivers, send n times

Not suitable for group communication

Receiver


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Multicast

Host

Router

1 sender and n receivers

N receivers, only send 1 times

Suitable for group communication

Receiver


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Benefits of Multicast

Saves bandwidth by enhancing network

efficiency in distribution of data

Group communication and services

Supports distributed applications

distance learning

videoconferencing

Reduces the cost to deploy applications


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Multicast Characteristic

RFC 1112

Each multicast group identified by class-

D IP address Receivers can present anywhere

Receivers can join and leave anytime

Sender dont need to be a member No membership list exist, use routers to

manage groups


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IP Multicast Address

Multicast address range

Class D IP Address-higher order 4 bits are set

224.0.0.0 ---239.255.255.255

1 1 1 0 Multicast address

1 1 0 Net ID

8 16 24 32

IP system

1 0Net ID

IP system

0 Net ID IP system

Class D

Class C

Class B

Class A


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Examples of permanent groups

All DVMRP routers in a subnet224.0.0.4

Not allocated224.0.0.3

Routers with RIP Version 2 in asubnet

224.0.0.9

All routers in a subnet224.0.0.2

All systems in a subnet224.0.0.1

Reserved224.0.0.0


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Architecture of Multicast

Sender

Router

Receiver

IGMP

IGMP version 2

Multicast Routing


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Outline

Overview

IGMP



Reference


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IGMP

Internet Group Management Protocol (IGMP)

Group management within edge networks

RFC 1112 IGMP version 1

RFC 2236 IGMP version 2 (widely uesd)

Similar to the ICMP(Internet Control Message Protocol)

Router sends query to their directly hosts to manage group

membership

Different Hosts may join more than one multicast group


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IGMP Join a Group

Joining members sends reportDifferent hosts can join different multicast group

Multicast Router

Host 1 Host 2 Host 3

224.2.2.3

ReportReport

224.2.2.2


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IGMP General Query


General query to

224.0.0.1

Multicast Router

Router periodically sends general query to

224.0.0.1(all systems in a subnet)


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IGMP Maintaining a Group

suppress


224.2.2.2224.2.2.2

Report

224.2.2.2 224.2.2.2

Two steps:First, router sends general query

Second, member send report

Only one member needs to send report

Multicast RouterGeneral query to224.0.0.1


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IGMP Leaving a Group


General query to224.0.0.1

Multicast Router

Router continue to send general query periodically

Members silently leave groupNo report receive by router

Group times out


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IGMP - Querier Selection


MRouter 11.1.1.1

MRouter 21.1.1.2

Initially, all routers are querier and send query

Then, only one router with the lowest IP address isselected as the actual Querier

The other routers are Non-Querier


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Outline

Overview

IGMP



Reference


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DVMRP

MOSPF

PIM-DM

PIM-SM

CBT


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DVMRP

Distance Vector Multicast Routing Protocol(DVMRP)

Distance vector algorithm that determines theshortest path (hop count)

Like RIP, maintains a routing table

Uses RPF(Reverse Path Forwarding)

The first data isfloodedto the entire network

No members or terminating membership, dopruning


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DVMRP (cont.)

Graftis used to reconnect an old area orconnect a new area

Member to source

Graft ack. Indicates that a graft has beenreceived correctly

Source to member

Designated forwarder

First, lowest metric to a source

Second, lowest IP address


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MOSPF

Multicast Extensions to Open Shortest PathFirst

OSPF Hello

Synchronize database description

Link state advertisement

MOSPF Local group membership must be known in the routers

A separate multicast tree has to be calculated for eachpair consisting of sender and group G(S,G)


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MOSPF (cont.)

Autonomous System

BR

BR

BR

R

Boundary AS

router

R

Domain

Domain

Domain

Backbone

AS


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PIM-DM

Protocol Independent Multicasting-Dense Mode (PIM-DM)

Members are not widely distributed,density of group member is very high

Uses flooding,pruningand graft

Similar to DVMRP Without the routing information exchange part

Differs in some details


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

Initial


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

Flooding


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

Pruning

Pruning

Pruning

Pruning


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

Steady state


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

A receiver is joining

Graft

Receiver 2

Graft


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PIM-DM (cont.)

Source

B

Receiver 1

C

A

D

E

Receiver 2

Steady state


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PIM-SM

Protocol Independent Multicasting-Sparse Mode (PIM-SM)

Based on that systems are located faraway from each other, density of groupmember is low=>B.W. tends to be small

Membership is based on explicit joinoperations

Data is sent to the rendezvous point


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PIM-SM (cont.)

Bootstraprouters distribute information

about rendezvous points

PIM router

PIM router PIM router

Bootstrap router

Multicast

border

router

Non-PIM

enabled domain

PIM domain


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PIM-SM (cont.)

Sender

PIM Router 2

Receiver

Data

IGMP join

PIM joinPIM Router 1

Rendezvous

PIM Router 3

PIM join

PIM join

PIM resisterdata unit


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PIM-SM (cont.)

Sender

PIM Router 2

Receiver

PIM Router 1

Rendezvous

PIM Router 3 delete

PIM join

Pruning data unit

Data


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CBT

Core-Based Trees(CBT)

Based on concept of rendezvous point, in this

case called cores Uses a bidirectionalmulticast tree

PIM is unidirectional

Use of Hello mechanism Restriction to one rendezvous point

Bootstrap mechanism


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Outline

Overview

IGMP



Reference


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Multicast Routing Between

Domains

Multicast

Domain

BGMP

Router

Multicast

Domain

BGMP

RouterMulticast

Domain

BGMP

Router

Multicast

Domain

BGMPRouter

BGMP routing


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Multicast Routing Between

Domains (cont.) BGMP(Border Gateway Multicast Protocol)

Based on CBT and PIM-SM(avoid flooding)

BGMP join and prune data unit are transmittedover TCP

Multicast routing can throughout the internet by

using BGMP Connection between multicast domain

autonomous system


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Reference

Multicast Communication, writed byRalph Wittmann and Martina Zitterbart,

Morgan Kaufmann publish http://www.ietf.org/html.charters/pim-

charter.html

http://www.cs.ucsb.edu/~almeroth

http://www.cisco.com

http://www.cs.wisc.edu/~lhl/

Introduction to Multicast

Documents

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