RightFax T38 with stcapp controlled FAX

[DANIEL COHEN-LAROQUE]

I have a RightFax connected to a CUCM v6 through a SIP trunk. VGs are configured for T38 with fallback cisco protocol. Some faxes are connected directed on FXS on VG, and controlled by CUCM via STCAPP service protocol.

OK: from RightFax --> Fax Rx/Tx to/from PSTN work OK.

PROBLEM: from RightFax --> Fax Rx/Tx to/from STCAPP fax cannot negotiate T38 (see attached wireshark trace: not acceptable media)

Here is the config:

stcapp register capability 0/3/0 both

stcapp ccm-group 1

stcapp

voice class codec 1

codec preference 1 g711alaw

codec preference 2 g711ulaw

voice-port 0/3/0

cptone CH

timeouts ringing infinity

caller-id enable

dial-peer voice 415800 pots

service stcapp

port 0/2/0

dial-peer voice 415801 voip

description TEST T38

preference 1

voice-class codec 1

incoming called-number 415800

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

no vad

WORKAROUND:

I managed to send fax by forcing the CUCM to reroute to the VG via H323, by inserting a new route pattern (9.415800 predot) and a creating an additional dial-peer on the VG:

dial-peer voice 415802 pots

preference 1

destination-pattern 415800

port 0/2/0

--> SUCCESS !! T38 is negotiated correctly

--> Does anyone having an idea of what can cause this problem ?

--> Does anyone having succeeded in making T38 call to STCAPP controlled fax in a similar set-up ?

[Nicholas Matthews · Accepted solution]

SCCP does not support protocol based T38. You would need to use SIP/H323/MGCP for this functionality to work.

As well, there are almost no additional features gained by a fax machine for a SCCP controlled port rather than MGCP. Or SIP/H323 if you don't mind configuring things on the gateway.

-nick

[DANIEL COHEN-LAROQUE]

Hi Nick,

thanks for your reply. Now I understand the protocol mismatch error...

For FXS/SCCP on voice gateways, I see following advantages: 1. customer can control line parameter directly from CUCM (like MGCP), and 2. SRST support (not possible with MGCP, right?)

I guess it makes sense to keep SCCP, and had transtation/partition to redirect inbound T38 calls from the rightfax SIP trunk to VGs via H323 (already configured for PSTN).