IP Multicasting
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Transcript of IP Multicasting
Overview
• Introduction• Multicast Applications• Unicast, Broadcast and Multicast• Multicast Addressing• Multicast Address Mapping• IGMP• IGMP Packet Format• IGMP Message Types
Introduction to IP Multicast
• Why multicast?• When sending same data to multiple receivers
• Better bandwidth utilization
• Lesser host/router processing
• Receivers’ addresses unknown
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
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
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.
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
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
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
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
Leave Report
When a host sees that no process is interested in a specific group G, it sends a leave report.
General Query Message
Membership report and leave report are not enough to maintain the membership information.
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 Explainedhttp://www.thegeekstuff.com/2013/05/ip-multicasting/
• [5] IP MULTICASTINGhttp://www.dcs.gla.ac.uk/~lewis/networkpages/m05s08multicast.htm