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Community Member

Using Multicast with VoIP


I'm looking for any kind of ios feature, that will let me configure VoIP to a multicast destination address. I have some E&M connected devices, and I would like to send a multicast VoIP packet whenever a certain device start transmiting voice. For each E&M device I want to send the VoIP packet with a different destination multicast address.

I saw the Hoot and Holler documentation. I saw there the following:

Cisco Hoot and Holler over IP can handle many inbound voice streams, but it only

arbitrates and mixes three streams that can be heard within the hoot group.

Does that means that only three streams can coexist ? Because I need many more streams.

Can I use the following configuration without using the Hoot and Holler feature:

dialer-peer voice 1 voip

destination-pattern 111

voice-class permanent 1

session protocol multicast

session target ipv4:

Thank you,


Cisco Employee

Re: Using Multicast with VoIP

The documentation you reference means that within a single hoot group, there can be only 3 simultaneous talkers, but those talkers can change throughout the call. Basically the DSP will playout the "loudest" 3 audio streams to the voice port. You can have more than one hoot group configured per router.

I'm not sure I understand the rest of your question.



Community Member

Re: Using Multicast with VoIP

I believe the limitation to 3 or 4 streams, is imposed by the DSPs, which can only handle this much (the mixing is done on the digital voice streams). In a way it makes sense: if more than 4 people speak at the same time, nobody understands anything. The others will have to wait for their turn.

If you use VAD, packets are generated only when the users talk and you should be able to deploy this solution to as many users you want.

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