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 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.



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


Starting with version incoming multicast audio will be displayed by an icon in the title bar on phones with monochrome displays. On all other phones the text "PA" will be shown in the status message line.

Example monochrome display:

  • On high resolution monochrome display (D745, D305, D315, D345): File:Multicast_snom_icon_font.png
  • On high low monochrome display (e.g. 710, 715, 720, D725): File:Multicast_snom10x10font.png‎

Example color display (760, D765, D375):


On 8.7.5 the status message text "PA" will be shown on all phone types.

Multicast Zones

The concept of Multicast Zones is introduced in version 10.1.x. The configuration is done on the web interface the same as before, with the addition of Zone names.


A new keyevent type F_ZONES is added, so that a function key can be configured for the Multicast Zone feature, using the web interface as shown below.


An example showing the idle screen of D375:


The above softkey will bring up the Multicast Zones screen on the phone interface.


The user can select the zone on which to start the outbound multicast stream. The first number is the zone number, and corresponds to the keypad shortcut. For example, user presses 2 to select Zone 2.


Note: key 0 corresponds to zone 10.

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