IP multicast

1. IP Multicast

2. Introduction Multicast communications refers to one-to-many or many-to-many communications. Unicast Broadcast Multicast

3. What is Multicast? Multicast allows the source to send a single copy of data, using a single address for the entire group of recipients. Routers between the source and recipients use the group address to route the data. The routers forward duplicate data packets wherever the path to recipients diverges.

4. Component of Multicast service There are three essential components of the IP Multicast service: IP Multicast Addressing IP Group Management Multicast Routing

5. Multicast Addressing Multicast groups are identified by IP addresses in the range 224.0.0.0 - 239.255.255.255 (class D address) Every host ( more precisely: interface) can join and leave a multicast group dynamically no access control Every IP datagram send to a multicast group is transmitted to all members of the group no security Sender does not need to be a member of the group The IP Multicast service is unreliable . . . IP Multicasting only supports UDP as higher layer There is no multicast TCP !

6. Multicast Groups The set of receivers for a multicast transmission is called a multicast group. A multicast group is identified by a multicast address A user that wants to receive multicast transmissions joins t he corresponding multicast group, and becomes a member of that group. After a user joins, the network builds the necessary routing paths so that the user receives the data sent to the multicast group

7. Multicast Routing Protocol 1) Internet Group Management Protocol (IGMP) 2) Protocol Independent Multicast Sparse Mode (PIM-SM ). 3) Protocol Independent Multicast Dense Mode (PIM-DM ). 4) Distance Vector Multicast Routing Protocol (DVMRP ). 5) Bi-directional PIM (BIDIR-PIM ).

8. Internet Group Management Protocol (IGMP) IGMP provides three basic functions for IP multicast networks: • JOIN: An IGMP host indicates that it wants to receive information from (“become a member of”) a multicast group. • LEAVE: An IGMP host indicates that it no longer wishes to receive information from a multicast group. • QUERY: An IGMP router can ask the hosts which groups they are members of. This is done to verify a JOIN/LEAVE request or to look for error conditions. There are 3 version of IGMP IGMPv1:- Hosts can join multicast groups. There were no leave messages. Routers were using a time-out based mechanism to discover the groups that are of no interest to the members. IGMPv2:- Leave messages were added to the protocol. Allow group membership termination to be quickly reported to the routing protocol, which is important for high-bandwidth multicast groups. IGMPv3:- Major revision of the protocol. It allows hosts to specify the list of hosts from which they want to receive traffic from

9. Properties of Routing Protocol Four of the most important features of multicast routing protocols are the following. • Whether they use opt-in or opt-out routing protocols. • Whether they use source-based or shared trees. • The methods they use to find the upstream router.

10. Difference between OPT-IN & OPT-OUT Protocol Opt-in Protocols: Opt-in or sparse protocols are designed on the assumption that most subnets in the network will not want any given multicast packet

11. Difference between OPT-IN & OPT-OUT Protocol In opt-out or broadcast-and-prune or dense protocols, it is initially assumed that every router on the network wishes to receive multicast data, and data is sent to all routers. Routers wishing to remove themselves from the multicast tree must then send a Prune message to the upstream router.

12. Source Based Tree protocol 1) Source based tree protocol build a separate tree for each source that send data to multicast group. 2) Router wishing to join the multicast group must specify both the source and the group of the multicast data. 3) The advantage of sourced based tree protocol are that multicast data path are always efficient and they benefit from a simpler configuration.

13. Shared Based Tree Shared tree protocol build a single tree is used for all source for a multicast group. The tree is rooted at some selected node called rendezvous point. The root of each shared multicast tree must be selected in some manner such as pre - configuration.

14. PIM-Spare Mode PIM-SM is opt-in multicast routing protocol . PIM-SM by default used shared based trees with the trees rooted at a router called Rendezvous point (RP) for a group . Data is send to an (RP) via encapsulation in PIM control message sent by unicast.

15. PIM-Dense Mode PIM-DM is opt-out multicast routing protocol. PIM-DM uses source-based trees to distribute data. It assumes that the receivers for any multicast group are distributed densely. Links on which the data is not required are removed from the tree using PIM Prune messages. PIM-DM support source based tree.

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