1. ACLI Configuration Guide
  2. Transcoding
  3. T.140 to Baudot Relay

T.140 to Baudot Relay

The T.140 to Baudot Relay feature uses the Oracle® Enterprise Session Border Controller's transcoding resources to relay T.140 text messages to Baudot tones and vice versa. The T.140 Protocol is used for multimedia text conversation over IP and is designed as a replacement for TDD devices. Baudot tones are a common protocol in the US in Telecommunications Device for the Deaf (TDD). Details of the protocol implementation are available in TIA/EIA-825-A. The T.140-Baudot relay is a regulatory requirement, and is specified for both emergency and non-emergency traffic. This feature is only available on Acme Packet 4600 and 6300 with transcoding hardware.

T.140 to Baudot transcoding entails that one call leg is provisioned with a Baudot-capable codec, and the other call leg accepts T.140 in the SDP. Additionally, the T.140 side includes an audio stream. Once this scenario is established, the call may begin as audio-to-audio. At any point forward, T.140 may be received on one call leg or Baudot tones may be received on the other call leg. Each text indication will be transcoded to its compliment on the other side of the call. When T.140 <-> Baudot tone transcoding is active, the existing audio stream is preempted.


The system's transcoding hardware detects baudot tones in the incoming audio stream and generates T.140 packets on an outbound text stream. In the reverse direction T.140 packets will be detected on the text stream and Baudot tones will be generated on the appropriate outgoing audio stream.

T.140 to Baudot relay is invoked when an outbound codec-policy removes any text "m=" line from the egressing offer. The processing also removes all non-Baudot-tone capable codecs from the egress SDP offer. If at this point no Baudot-capable codecs remain in the SDP, the call is torn down.

Baudot Tones capable codecs:
  • PCMA
  • PCMU
  • EVRC
  • EVRC0
  • EVRC1
  • EVRCB
  • EVRCB0
  • EVRCB1

Codec Policy Configuration for T.140 to Baudot Relay

To support T.140 to Baudot relay, configure the allow-codecs parameter in the codec-policy with text:no. This value causes the Oracle® Enterprise Session Border Controller to strip any "m=text" occurrence in the outbound INVITE and enable T.140 to Baudot transcoding. When SDP passes through the Oracle® Enterprise Session Border Controller and a text "m=" line is removed on the egress side of the call, then T.140-baudot relay/transcoding will be invoked for that call.

Unlike other transcodable codecs, T.140 is not valid in add-codecs-on-egress parameter.

Limitations

The following scenarios are not supported:

  • Configuration of T.140 in add-codes-on-egress
  • Hairpin calls (T.140 - Baudot Relay - T.140)
  • Lawful Intercept
  • SRTP for T.140

T.140 to Baudot Relay Examples

This section includes two examples; access-side call initiation and core-side call initiation. The following codec-policy is applied to the Core-side realm. 
ACMEPACKET (codec-policy)#
name T140-to-tone
allow text: no *
add-codecs-on-egress PCMU

Figure 14-1 Call Initiated from the Access-side

Figure 14-2 Call Initiated fom the Core with T.140 reINVITE