Help with T.38 Fax over SIP Trunk

Unanswered Question

I have a UC520 (CME) system connected to PSTN via a SIP trunk provider. The SIP trunk supports T.38 faxing.

I have a fax server setup with StoneFax to terminate the faxes. I have setup an incoming dialpeer with one of my DIDs. upon sending a fax, the line rings once, then seems to connect, but it is just dead silence. The microsoft fax service on the fax server shows 'answering' but nothing ever happens.

I am mostly concerned about my dial-peer config.

Here is the dialpeer config that StoneFax suggests:

dial-peer voice 20 voip


destination-pattern <<DID HERE>>

session target ipv4:<<FAX SERVER IP>>:1721

dtmf-relay h245-alphanumeric

codec g711alaw

fax rate 14400

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback cisco

no vad

should this work ok over a SIP trunk? are there any other system settings i should change? I am wondering about the DTMF settings. Cisco configs usually show h245-signal, and all my voice dialpeers are rtp-nte.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)

Also one followup question, how do i create an outgoing dial-peer to be used for sending outgoing faxes, and lock it down so that ONLY the fax server uses it? i currently have several outgoing voice dialpeers setup with COR lists for call restrictions, so i want to give the fax it's own dial-peer, but make sure that none of the voice callers use it.


This Discussion