Giới thiệu tổng quan về multicast

Introduction to multicast

Spencer TsaiMobile Communication & Broadband Network Lab

CSIEFu-Jen Catholic University

Introduction to Multicast

• Overview

• IGMP

• Multicast Routing on the Internet

• Multicast Routing between Domains

• Reference

Host

Router

． Point to point

． N receivers, send n times

． Not suitable for group communication

Receiver

Host

Router

． 1 sender and n receivers

． N receivers, only send 1 times

． Suitable for group communication

Receiver

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

Multicast Characteristic

• RFC 1112

• Each multicast group identified by

class-D IP address

• Receivers can present anywhere

• Receivers can join and leave anytime

• Sender don’t need to be a member

• No membership list exist, use routers to manage groups

IP Multicast Address

•Multicast address range

Class D IP Address-higher order 4 bits are set

1 1 1 0 Multicast address

1 1 0 Net ID

8 16 24 32

Examples of permanent groups

All DVMRP routers in a subnet 224.0.0.4

Not allocated 224.0.0.3

Routers with RIP Version 2 in a 224.0.0.9

All routers in a subnet 224.0.0.2

All systems in a subnet 224.0.0.1

Reserved 224.0.0.0

Architecture of Multicast

Sender

Router

IGMPIGMP version 2Multicast Routing

• Overview

• Multicast Routing on the Internet

• Multicast Routing between Domains

• Reference

•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

IGMP – Join a Group

•Joining members sends report

•Different hosts can join different multicast group

Multicast Router

224.2.2.3

ReportReport

224.2.2.2

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)

IGMP – Maintaining a Group

suppress

224.2.2.2224.2.2.2

Report

•Two steps:

First, router sends general query

Second, member send report

Multicast RouterGeneral query to

224.0.0.1

IGMP – Leaving a Group

General query to 224.0.0.1

Multicast Router

•Router continue to send general query periodically

•Members silently leave group

• No report receive by router

•Group times out

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 is

selected as the actual Querier

• The other routers are Non-Querier

• Overview

• IGMP

• Multicast Routing between Domains

• Reference

Multicast Routing on the Internet

• Like RIP, maintains a routing table

• Uses RPF(Reverse Path Forwarding)

– The first data is flooded to the entire network – No members or terminating membership, do pruning

DVMRP (cont.)

• Graft is used to reconnect an old area or

connect a new area

• MOSPF

– Local group membership must be known in the routers– A separate multicast tree has to be calculated for each

R Domain

Domain

Domain Backbone

AS

Multicasting-Dense Mode (PIM-DM)

• Members are not widely distributed,

density of group member is very high

• Uses flooding, pruning and graft

• Similar to DVMRP

– Without the routing information exchange part – Differs in some details

Graft

Multicasting-Sparse Mode (PIM-SM)

• Based on that systems are located far away from each other, density of group member is low=>B.W tends to be small

• Membership is based on explicit join

operations

• Data is sent to the rendezvous point

PIM-SM (cont.)

• Bootstrap routers distribute information

about rendezvous points

PIM router PIM router PIM router

Multicast border router

Non-PIM enabled domain

PIM resister data unit

• C ore- B ased T rees( CBT )

• Based on concept of rendezvous point, in this

case called cores

• Uses a bidirectional multicast tree

– PIM is unidirectional

• Use of Hello mechanism

• Restriction to one rendezvous point

• Bootstrap mechanism

• Overview

• IGMP

• Multicast Routing on the Internet

• Reference

Multicast Routing Between

Domains

Multicast Domain

BGMP Router

Multicast Domain

BGMP Router

Multicast

BGMP Router

Multicast Domain BGMP

Router BGMP routing

Multicast Routing Between

Domains (cont.)

– Based on CBT and PIM-SM(avoid flooding) – BGMP join and prune data unit are transmitted over TCP

– Multicast routing can throughout the internet by using BGMP

– Connection between multicast domain autonomous system

• Multicast Communication, writed by

Ralph Wittmann and Martina Zitterbart, Morgan Kaufmann publish