T.38

NSE (Named Signaling Events) is a proprietary protocol to switch from voice to Passthru, without involving SIP. It uses a proprietary event, based on Named Telephony Events (NTE), (see 3.5 Payload Format from RFC2833). So NTE is not proprietary, but NSE is.

TelcoBridges and NSE

TelcoBridges implementation currently only support NSE events:

192 (switch to passthru)
193 (disable echo)
194 (switch back to voice)

References

• RFC 2833
• NSE article