Multicast

Integrated Network Services

Almerindo Graziano

Introduction

• New applications• Type of communications• Shortfalls of Unicast• Multicast

– IP Multicast– IP Multicast sessions– Example

• Conclusions

New Applications

• Improved computer systems

• New types of applications:

– Point-to-Multipoint

– Multipoint-to-Multipoint

• Computer networks do not keep the pace

Multiple-Destination Applications

• Videoconferencing

• Remote seminars

• Transmission of corporate messages to employees

• Live transmission of multimedia training

• Communication of stock quotes to brokers

• Transmission over networks of live TV or radio news

Unicast

• Problems of using Unicast:– Lack of Bandwidth

– Need more powerful workstations

– Difficult to manage with multiple destinations

• A possible solution:– Multicast

DN

D1

.

.

.

.

.

S

D2

D

BT = B BT = N x B

S: SourceD: RecipientBT: Total Bandwidth involvedB: Bandwidth required by one recipient

Unicast Transmission

• IP Multicast (Steve Deering 1989, RFC112)

• Greatly reduces the used bandwidth

• Reduces the load on the servers

• It’s receiver initiated

• Introduces the concept of Session

IP Multicast

IP Multicast•Host groups (logical addressing)

•Multicast Sessions

•IGMP (Internet Group Management Protocol)

•It works better on broadcast media

IP Multicast Addresses

• Class D Internet Protocol addresses:

– 224.0.0.0 to 239.255.255.255

• 224.0.0.0 to 224.0.0.255 are reserved:

– 224.0.0.1 is all host groups

– 224.0.13.0 to 224.0.13.255 for Net News

R R R

Internetwork

Sender

BT = B BT = BBT = B

Receivers

R

BT = B

S: SourceD: RecipientBT: Total Bandwidth involvedB: Bandwidth required by one recipient

Multicast Transmission

IP multicast over 802 LANs

• IP unicast address MAC address

• IP Multicast address multiple MAC addresses?– IEEE assigns 01-5E-00-00-00 to the IETF for

Multicast– Low-order 23 bits of IP Multicast address low-

order 23 bits of MAC address 01-5E-00-00-00– Mapping is not unique

MAC address format

8 7 6 5 4 3 2 1

U/L I/G

Manufacturer

OU

I

Byte 1Byte 2Byte 3Byte 4

Byte 5Byte 6

Mbone (IP Multicast Backbone)

• Virtual network layered on top of the Internet (IETF July 1992)

• Is made of multicast island

• Communication between islands is achieved via tunnels

Multicast Router

Tunnels

MulticastIsland

LAN

Mbone Topology

Mbone Map (1994)

MRA MRB

LAN A LAN B

Tunnelling

Transmission on the Mbone

References

• http://www.mbone.com

• http://www.ipmulticast.com

• http://www.video.ja.net/mice