IGMP procedure.

Hi,

Can any one explain in brief how a IGMP( V2 and V3) works in network..

say i have a set up like this.


IP TV ----........

---

router

---

multicast router --- Internet

case 1:
When i switch on TV and i choose espn, i'm not the first person to join ESPN mulitcast group ( this is from Router's perspective).

Later i tend to choose a diffrent channel say Star Sports.. so how would this switching occur...

case : 2
I'm the first person to choose ESPN channel, (From routers perspective...)

can any one help me... what messages are sent ( like Join, Query, leave) and what exactly do they contain.. I read RFC but i dint get an exact picture how this happens in real scenario.

Thanks in advance..
-Manjunath.

Hi,

I'm a bit rusty on this but here goes...

Case 1:

There are 2 way this can be handled depending upon the multicast intelligence of the router

In the first case the router is aware of multicast traffic and configured to manage local multicast groups (IGMP Proxy).

1) Your TV sends JOIN ESPN message upstream destined for the multicast router.

2) Your local router should intercept the IGMP message and see that you have requested access to multicast group ESPN

3) Router checks to see if Multicast group is already streamed to itself.

4) Router finds ESPN is already streamed, so multicasts the stream to your connection.

When you change channels.....

1) JOIN STARSPORTS message sent upstream.

2) Router connects your IPTV to stream

3) IPTV sends LEAVE ESPN to router

4) Router disconnects ESPN stream from your connection


Case 2: 1st to join a group

1) Your TV sends JOIN ESPN message upstream destined for the multicast router.

2) Your local router should intercept the IGMP message and see that you have requested access to multicast group ESPN

3) Router checks to see if Multicast group is already streamed to itself and finds it is not.

4) JOIN ESPN is (unicast) from router to mulitcast router.

5) Multicast router connects ESPN stream from internet to your router.

6) Router forwards ESPN stream to your IPTV.

Periodically Query messages will be sent by the multicast router to your router to ensure all streamed channels are still being watched.

I think this is basically correct...but am open to corrections.

R