Category:HowTo:Multicast Audio

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Author: Sascha Kruszka



The snom3xx, snom7xx, snom8xx, snomMP and the snomPA1 support paging via multicast IP. Currently any snom phone can use up to 10 multicast addresses. The index of the addresses is equivalent to the stream priority, 1 is lowest, 10 is highest. Streams with higher priorities will overlap those with lower priority. This description deals with firmware version 8.x.

Extended informations

You can find more Information about Multicast IP here.

Configuration of the phones

The Multicast configuration can be found in the phones web interface on advanced->SIP/RTP

- Set Multicast Support to on
- Enter a valid multicast IP-address and port, separated by colons into a index line


The default codec used by the phone when sending multicast is pcmu, with a packet-size of 20 milliseconds. Starting with version 8.6.6, you can edit these values using the following settings:

Multicast via VLC

The Video Lan Client is able to produce a Multicast RTP Stream.

NOTE: some VLC versions create RTP packets with a variable payload size this will cause choppy audio. Snom phones expect to receive an RTP stream with fixed payload size defined by the setting rtp_codec_size


vlc.exe "test.mp3" --sout "#transcode{acodec=ulaw,ab=64,scale=1,channels=1,ar=8000}:rtp{dst=,port-audio=5555}"

In this example we are streaming the file test.mp3 via Multicast IP to and Port 5555.

Multicast via FFMpeg

FFMpeg is a powerful audio encoder / decoder and can generate Multicast RTP Stream


/opt/ffmpeg/ffmpeg -re -i ./test.mp3 -filter_complex 'aresample=8000,asetnsamples=n=160' -acodec pcm_mulaw -ac 1 -vn -f rtp udp://

the switch -filter_complex 'aresample=8000,asetnsamples=n=160' is needed in order to fix the RTP palyload size.

Multicast via snom phone

The snom phones 3xx, 7xx, 8xx and MP are able to generate a muticast stream. You need to setup a function key for that.



Multicast via snomONE

SnomONE supports paging via multicast, too. For a description visit this site here

Muticast via Freeswitch

Freeswitch supports paging via multicast, too. For a description visit this site here

Multicast via Asterisk

Asterisk (>= 1.8) supports MuticastRTP channel. Please visit this page

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