Procedures for Megaco/H.248 controlled Voice Media Gateways for Autonomous Switchover to Fax Relay Service
draft-leurs-megaco-t38-callflows-00

Abstract

This document describes the handling of realtime fax calls in Megaco/H.248 controlled MGs. The call setup and capability negotiation is done with support of the control domain with Megaco commands. The switch over to fax or modem, upon detection of the relevant tones, is done in an autonomous way, without intervention of the control domain. In the Appendix, the Megaco messages for a call setup scenario with capability negotiation are shown, to point out the structure of the to the transmitting MG. Switching to T.38 is done after reception of V.21 flags. In the other flows, T.38 is not enabled, both MGs switch to the fallback case, fax pass-through mode. This document is based on the superior framework (reference [2]). The reader should be familiar with [2]. SDP sessions in the local and remote descriptors. Call flow diagrams are given as example: In the first flow, a T.30 CNG tone is generated by the transmitting terminal, the transmitting MG signals the detection towards the receiving MG. Switching to T.38 is done by both MGs as soon as possible. In the second example, a T.30 CED tone is sent by the receiving terminal. As this tone is no clear indication that a FAX will be sent, the receiving MG will switch to VBD after signaling this event

Authors

An Leurs
Carsten Waitzmann
Annette Schwarz

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)