You are confusing preamble which refers to V21 preamble with CED tone. You would not switch to T38 on CED detection since that same tone is also used by modems. CNG tone and v21 preamble are specific to G3 fax machines and should trigger a T38 switch.
The originating side would detect CNG (if it occurs) on its analog interface causing a switch to T38 via a re-invite. If CNG was not generated by the originating GW, then the terminating GW will detect v21 preamble on its analog interface and send the t38 re-invite. Donnie Петр Кравченко <[EMAIL PROTECTED]> Sent by: [EMAIL PROTECTED] 02/14/2006 03:56 AM To SIP-implementors <[email protected]> cc Subject [Sip-implementors] t38: fax detection I have a questions. In case, when fax is detected after voice session setup, which side must setup the session ? I'm in doubt with 2 recomedations. ITU-T T.38 Ammedment 2 Annex says: D.2.2.4: ... Upon detection of facsimile by the ___emitting___ gateway, a SIP INVITE request is sent to the receiving gateway.... As i understood, this must be performed on CNG detection. draft-mule-sip-t38callflows-02 shows in all voice-to-fax examples that the re-invite is sent on detection of preamble (CED?). 1. What way is correct/preferrable ? And exactly, what tone must be detected whith GW (CNG,CED) ? 2. Are examples in draft-mule-sip-t38callflows-02 applicable whith voice sessions on formats other than 711a/u ? ITU-T T.38, section 6.2: ... The following signals are not transferred between gateways but are generated or handled locally between the gateway and the G3FE: CNG, CED, .... 3. So, _HOW_ the fax receiving side can detect the preamble, whenever it fax session setup signals must not be tranferred ? _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
