Posted in AudioCodes

AudioCodes SBC Voice Transcoding Example Configuration

Diagram

transcoding_diagram

Scenario

  • Enterprise LAN users in LAN #1 served by SIP entity server #1:
    Voice coder: G.711
    SIP transport protocol: UDP
  • Enterprise LAN users in LAN #2 served by SIP entity server #2:
    Voice coder: G.729
    SIP transport protocol: TCP

As the two SIP entity servers use different voice codecs, you need to configure the SBC to perform transcoding between the servers. In the example, the codec support is as follows:
 SIP Entity Server #1 uses G.711 A-law or G.711 μ-law, and does not allow any other coder in the SDP offer-exchange coder list
 SIP Entity Server #2 uses G.729

The configuration for the example uses the following terms related to coders:
 Extension Coders: Voice codecs supported by the SIP entity. The SBC adds these coders to the SDP offer sent to the SIP entity. Extension coders are required for transcoding when the two communicating SIP entities support different coders (i.e., supported coders do not appear in the SDP offer).
 Allowed Coders: Coders that are permitted to be listed in the SDP offer that the device sends to the SIP entity. This is required for SIP entities that accept only SDPs that include specific coders (for whatever reason). The Allowed coders would include the Extension coder as well as other coders.

Step 1: Add Extension Coder Groups for SIP Entities

A Coder Group (or Extension Coder Group) defines the codecs supported by the SIP entity. Even if the original SDP offer does not include the coder supported by the SIP entity, the SBC adds it to the SDP before sending it to the SIP entity.
In the example, you need to configure a Coder Group per SIP entity server with the supported coder:
 SIP Entity Server #1 – G.711 A-law and G.711 μ-law
 SIP Entity Server #2 – G.729

Configuration tab > VoIP menu > Coders and Profiles > Coders Group Settings

Coder Group for SIP Entity Server #1

transcoding_g711

Coder Group for SIP Entity Server #2

transcoding_g729

Step 2: Add Allowed Coders Group for SIP Entity Server #1

In the example, SIP Entity Server #1 allows only the G.711 A-law and G.711 μ-law coders to be listed in the SDP offer sent to it by the SBC. If other coders are listed in the SDP, the SBC removes them before sending them to the SIP entity. Therefore, you need to configure an Allowed Audio Coders Group with these coders.

Configuration tab > VoIP menu > SBC > Allowed Audio Coders Group

Allowed Audio Coders Group for SIP Entity Server #1

transcoding_g711_allowed

Step 3: Add IP Profiles for SIP Entities and Assign their Coder Groups

An IP Profile defines a set of configuration settings that can be assigned to specific calls. In the example, you need to configure an IP Profile for each SIP entity server and assign it the supported codec (i.e., Coder Group) that you configured in the previous steps:
 SIP Entity Server #1: Supports only G.711 (A-law and μ-law) and does not allow other additional coders to be listed in the SDP. Therefore, the IP Profile must be assigned the following:
• Extension Coders Group (Index 1): G.711 (A-law and μ-law)
• Allowed Audio Coders Group (Index 0): G.711 (A-law and μ-law)
 SIP Entity Server #2: Supports only G.729, but accepts SDPs listing other additional coders. Therefore, the following configuration is required:
• Extension Coders Group (Index 2): G.729

Configuration tab > VoIP menu > Coders and Profiles > IP Profile Settings

IP Profile for SIP Entity Server #1

transcoding_row1

IP Profile for SIP Entity Server #2

transcoding_row2

Step 4: Assign IP Profiles to SIP Entity IP Groups

To associate the voice coders with the SIP entity servers, you need to assign the previously configured IP Profiles to the IP Groups of the SIP entities.

Note: IP Profiles should already been created for SIP entities.

Configuration tab > VoIP menu > VoIP Network > IP Group Table

Assigning IP Profile to IP Group of SIP Entity Server #1

transcoding_sipentity1

Assigning IP Profile to IP Group of SIP Entity Server #2

transcoding_sipentity2

That’s it!

 

 

 

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