Video conferencing multicast config for Microsoft OCS 2008

Unanswered Question
Feb 24th, 2009

Hi all

I'm in the process of finding out more detailed technical information on how video conferencing is implemented by OCS 2K8. Things such as typical bandwidth usage, protocol, accepted level of delays etc. What's more important are sample configuration on Cisco routers and switches (Catalyst 2950, Catalyst 4006 - CatIOS, Cisco 2811) to enable multicast efficiently. Would be great if someone can point me in the right direction.

I have this problem too.
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Jon Marshall Wed, 02/25/2009 - 09:11


This is quite a big subject. Have a look at these 2 docs

1) Overview of Multicast. Explains the basics of how multicast works

2) Quick start guide to deploying multicast -

You will want to be using pim sparse mode to route the multicast traffic, pim is covered in the above docs.

For specific devices the easiest thing to do is to go to "Products and Services" on Cisco homepage and then drill down to the device you are interested in and on that device page there will be links to the configuration docs eg. - 2950 page -

If you have a read and want further advice please come back.


vincent-n Mon, 03/02/2009 - 20:20

Hi Jon

thank you for your feedback. I've read the first two documents you shown and I think they're very useful. I do have some questions to ask you on:

- The documents do not give specific examples on multicast using REAL IP addresses. I'm guessing here that the multicast IP address would be in the range of 239.x.x.x/8.

- Using examples given in the document, the 'Source' represents the server that's hosting the multicast event (video). What application would enable me to specify a multicast address of 239.x.x.x?

- Using a real life example of Microsoft NLB running in Multicast mode, as part of the configuration, the NLB address is on the same subnet as the real IP address of the servers (eg: server1 -, server2 - and NLB This real NLB IP address is obviously not a multicast address. Has MS gone wild somewhere here?

- IGMP Snooping is enabled by default on most Cisco switches. Without specifying the correct multicast IP address format, how would you expect the switch to be able to snoop the multicast traffic?

Those are my questions for now. I'll keep everyone posted on my progress with multicast and OCS as the project move on.


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