4.8 Calls transcoding

4.8 Calls transcoding

General description

The calls transcoding feature (Fig. 1, 2) enables VoipSwitch to route and connect calls when the call origination and termination have no common audio codec.
The transcoding process is fully transparent for calling clients. It is performed by the VoipBox module which can also be installed on several additional servers to increase the capacity of transcoding calls concurrently.
VoipSwitch distributes transcoding calls automatically among available VoipBoxes.

Fig. 3 shows an example of a tested configuration where 1 VoipBox server is used for calls transcoding from 2 VoipSwitch servers. It is recommended to use a separate network to interconnect VoipBox with VoipSwitch servers. A 1 Gbps network connection should be used when transcoding more than about 200 calls. However, it depends on transcoded codecs. VoipBox requirements: CPU: Intel XEON E5430 @ 2.66 GHz (4 core) RAM: 4 GB OS: Windows 2008 server 64-bit Network: 100 Mbps Tested results: G729 to AMR: Max. 160-150 transcoded calls G711u to AMR: Max. 160-150 transcoded calls G729 to G711u: Max. 240-250 transcoded calls

A single transcoding module (Fig. 4) supports 100 calls and must be enabled in the Voipswitch.exe file. It is available from VoipSwitch version: 985.897 and VoipBox: 280.

Configuration

• voipbox_config.xml configuration file

  
  

  It is required to set up the listeners used for transcodning and the codecs payload value. One listener uses one thread which can be assigned to a CPU core. In the case of an 8-core CPU, listeners can be started on the subsequent ports with the step=2, eg. 2058, 2060, 2062, etc.

  Example voipbox_config.xml file:

  Fig. 5, 6 shows VoipBox running with the properly configured listeners for transcoding.
  
  
  

• Additional configuration required for calls recording, calls interception and transcoding

  
  

  This link describes the required configuration for the calls transcoding feature. It also enables the use of several VoipBoxes to increase the calls transcoding capacity.

  
  
  

• AMR codec payload

  
  Verify if the AMR codec stored in the VoipSwitch database has the payload value defined as 108;
  if not use the SQL query below:

  
  
  

• Clients configuration

  
  VSM supports transcoding configuration for clients (Fig. 7) from the version 2.1.125.
  Available options are:
  

  • Not allowed
    
  • Transcode to match every destination
    
    

    Remember to enable (tick) the option "Use client codec" and select those codecs which are not supported by the client device or dialer but can be used at the termination side.

    
    
    
    

    
    Examples of how to enable/disable transcoding for Retail clients by database SQL queries:
    
    

    Enable transcoding

    
    

    Disable transcoding

See also

Figures