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Overview

The SBC Core supports pass-through of the text media streams based on the T.140 codec. The t140Call flag is added to the Packet Service Profile to support T.140 calls.

The SBC Core supports:

  • Calls with only T.140 stream.
  • T.140 stream pass-through when it is part of multiple stream sessions (audio and Video calls).  
  • SDP update in 200 OK for T.140 streams  (controlled by the flag sendUpdatedSdpIn200Ok in the ingress IP attributes).  
  • Direct Media calls with T.140 streams.
  • Late media pass-through calls with T.140 streams.
  • Downstream forking calls with T.140 streams.
  • Ring Back Tone (RBT) call flows, all types of direct media, LI, SRTP/DTLS pass-through calls with T.140 streams.

The following session modifications are supported for the T.140 sessions:

  • Addition and/or removal of T.140 streams.
  • Modification triggered due to change in T.140 stream attributes.
  • Modification triggered due to changes in session attributes for non-T.140 stream related attributes.

The SBC does not validate, prioritize, or purge any codec or attributes received for the text media. Any validation required is performed by the endpoints.

Text Codecs SIP

 The SBC Core relays text codec by default using dynamic payloads.

Text Codecs T.140

The SBC supports the following codec for text call scenarios (Text → Text calls with an audio and video stream).

Supported Codecs for Text Calls

Codec VariantPayload Type
T.140Dynamic
T.140
  • T.140 to TTY Transcoding (DSP) for SIP
  • T.140 to TTY Transcoding support in DSPs (SBC 5400 and SBC 7000)
  • T.140-to-TTY Transcoding  for the SBC SWe. 


T140 Passthrough 

The SBC Core supports T.140 passthrough calls over GW-GW interface between the SBC (SBC-SBC).