Multicast Audio

Introduction

IP multicast is a technique for one-to-many communication over an IP network. The transmitter sends out packets to a specific multicast IP address. Any node (phone) listening on this IP address will receive the stream and play it in handsfree mode.

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.

Configuration of the phones for announcements

The Multicast configuration can be found in the phones web interface on Advanced → SIP/RTP.

• Turn multicast support 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:

• rtp_codec_type
• rtp_codec_size

Starting with version 8.7.3.26, you can setup the multicast address with additional options:

• speaker=(0|1): If this option is set and value is 1, then the multicast audio will be played always over speaker. If value is 0, then the current audio device will be used. If this option is not set, then value 0 is used as default value.
• interrupt=(0|1[|2(*)]):
  If this option is set and value is 1, then the multicast audio interrupts a running call. If multicast is finished, then the interrupted call continues. If value is 0, the multicast audio will only be played in idle state. If this option is not set, then value 0 is used as default value. (*)Starting with 8.7.5.75 and 8.9.3.67 the value can also be 2. If this value is set, then the call will be mixed with the multicast audio in a local conference. But this is only supported on snom7XX and snom3X5 phones.
• volmax=(0|1): If this option is set and value is 1, then the maximal volume will be used for multicast audio. If value is 0, then the current volume will be used. If this option is not set, then value 0 is used as default value.
• priority=(0..10): This option sets the priority of the multicast address. You can choose a priority between 0 and 10, where 0 is the lowest and 10 the highest priority. If the phone receives multicast from more than one configured port, then the multicast with the highest priority will be played. If they have the same priority then the multicast will be played, that was received first. If this option is not set, then a priority of 5 is used as default.

Example XML

mc_address1=239.255.255.230:5555,speaker=1,interrupt=1,volmax=1,priority=9,name=Sales

Behavior

Configuration for Streaming MP3 or WAV Files over Multicast with VLC or FFMPEG

It is possible to stream an audio file directly to the snom phones via multicast. This can be used to start pre-recorded audio announcements or automated audio warning messages. Depending on which file format your audio file is, a different streaming tool has to be used.

• If you have a wav file that you want to stream over multicast you can download https://www.videolan.org/vlc/
• If you have a mp3 file that you want to stream over multicast you can download https://ffmpeg.org/

ffmpeg works for both wav and mp3 files but vlc only works for wav files.

On the receiving phone configure:

multicast_listen=on
mc_address1=239.255.255.244:5555

On the PC or MAC in the terminal window type:

VLC

PATH/TO/VLC PATH/TO/WAVFILE --sout "#transcode{acodec=ulaw,ab=16,scale=1,channels=1,samplerate=8000}:rtp{dst=239.255.255.244,port-audio=5555}"

FFMPEG

• g711u

  PATH/TO/FFMPEG -re -i PATH/TO/MP3FILE -filter_complex 'aresample=8000,asetnsamples=n=160' -acodec pcm_mulaw -ac 1 -f rtp udp://239.255.255.244:5555

• g722

  PATH/TO/FFMPEG -re -i PATH/TO/MP3FILE -filter_complex 'aresample=16000,asetnsamples=n=160' -acodec g722 -ac 1 -f rtp udp://239.255.255.244:5555

Multicast via snom phone

The snom phones D3xx, D7xx, PA1 and MP are able to generate a muticast stream. You need to setup a function key for that.

Example

Visualisation

Starting with version 8.9.3.58 incoming multicast audio will be displayed by an icon in the title bar on phones with monochrome displays.

Example monochrome display:

• On high resolution monochrome display (D745, D305, D315, D345):

On all other phones the text "PA" will be shown in the status message line.

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.

• Page:
  How To Configure Multicast Paging
• Page:
  Multicast Audio
• Page:
  What can you do with a PA1