The document provides a comprehensive overview of IP multicasting, detailing its benefits such as improved bandwidth utilization and reduced processing for hosts and routers. It explains the differences between unicast, broadcast, and multicast transmission methods, as well as multicast addressing and the Internet Group Management Protocol (IGMP) for managing group membership. Additionally, it covers IGMP message types and packet formats, outlining how hosts communicate with routers to maintain multicast group membership.

1. IP Multicasting
SCS 3004 - Networking Technologies

2. Overview
• Introduction
• Multicast Applications
• Unicast, Broadcast and Multicast
• Multicast Addressing
• Multicast Address Mapping
• IGMP
• IGMP Packet Format
• IGMP Message Types

3. Introduction to IP Multicast
• Why multicast?
• When sending same data to multiple receivers
• Better bandwidth utilization
• Lesser host/router processing
• Receivers’ addresses unknown

4. Multicast Applications
• Many applications transmit the
same data at one time to multiple
receivers
• Broadcasts of Radio or Video
• Videoconferencing
• Shared Applications
• Advertisement, Stock, Distance
learning
• Synchronizing of distributed
database, websites

5. Unicast, Broadcast and Multicast
• Broadcast: One sender, all the others as receivers
• Unicast: One sender and one receiver
• Multicast: One sender (potentially many senders), many receivers
Unicast Broadcast Multicast

6. Unicast, Broadcast and Multicast
Host
Router
Unicast
Host
Router
Multicast
With 3 receivers, sender must
replicate the stream 3times
• Source transmits one stream of
data for n receivers
• Replication happens inside
routers and switches
• WAN links only need one copy of
the data, not n copies.

7. Multicast Addressing
• All Class D addresses are multicast addresses:

8. Multicast Addressing
• The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive
• 224.0.0.1 :- signifies every system on a subnet
• 224.0.0.2 :- signifies every router on a subnet
• Multicast addresses can only be used as destination
• No ICMP error messages can be generated for multicast datagram

9. Multicast Address Mapping

10. Internet Group Management Protocol - IGMP
• How hosts tell routers about group membership
• Routers solicit group membership from directly
connected hosts
• RFC 1112 specifies first version of IGMP
• IGMP v2 and IGMP v3 enhancements
• Supported on UNIX systems, PCs, and MACs

11. IGMP Protocol
• Router: sends IGMP query at regular intervals
• Hosts belonging to a multicast group must reply to query if wishing to join or
stay in the group.
• host sends an IGMP report when it joins a multicast group (Note: multiple
processes on a host can join. A report is sent only for the first process).
• No report is sent when a process leaves a group

12. IGMP Message Types

13. IGMP Packet Format
Ethernet Header IP Header IGMP Message
14 Bytes 20 Bytes 8 Bytes
Type Max Resp. Time Checksum
Group Address
8 bits 8 bits 16 bits

14. Membership Report
Host or a router can join a group

15. Leave Report
When a host sees that no process is interested in a specific
group G, it sends a leave report.

16. General Query Message
Membership report and leave report are not enough to maintain the
membership information.

17. Reference
• [1] YouTube. “Lecture - 32 IP Multicasting”. Youtube.com. [Online]. Available
https://www.youtube.com/watch?v=TApIo_BiX6U [Accessed: 3 Aug2014].
• [2] YouTube. “Cisco Live 2014: IP Multicast Concepts, Design and Troubleshooting
(Melbourne)”. Youtube.com. [Online]. Available https://www.youtube.com/watch?v=l9RJdrdjDU8
[Accessed: 3 Aug2014].
• [3] Overview of IP Multicast
http://www.cisco.com/en/US/tech/tk828/technologies_white_paper09186a0080092942.shtml
• [4] What is IP Multicasting? Concept of IP Multicast Address Explained
http://www.thegeekstuff.com/2013/05/ip-multicasting/
• [5] IP MULTICASTING
http://www.dcs.gla.ac.uk/~lewis/networkpages/m05s08multicast.htm