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T.38 connected to UC500 issue

I'm trying to enable T.38 Fax in my network environment using UC520. The setting is something like this:

Fax 1 -- UC520 -- CCM -- VOIP -- PSTN -- Fax 2

Cisco UC520 (using CME) is the originating gateway for fax 1 to send T.38 fax. It is going to the Cisco Unified Call Manager 5.0.4 through SIP trunk.

T.38 has been enabled at the remote terminating gateway, which is using a 3rd party gateway. The receiving fax machine, Fax 2, is currently able to receive fax from other normal fax machine (PSTN & VOIP), but not from Fax 1.

Currently normal voice call can be made from fax 1 (when FXS port is connected to an analog phone) to all the numbers in VOIP and also to all PSTN numbers (local&international). Incoming call can also be received in fax 1.

However, when testing fax call, both Fax 1 and Fax 2 are not able to receive/send fax to each other. In other words, If Fax 1 made a call to Fax 2, there is a ringing tone at the other end but it will just go idle after a while and unable to respond to the fax call.

Therefore, I need some help to check if the following configuration at UC520 is correct, or is there any other way to enable T.38 at the CCM? Currently only SIP trunk to UC520 is configured on the CCM.

Thank you in advance.



voice service voip

allow-connections sip to sip

no supplementary-service sip moved-temporarily

no supplementary-service sip refer

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw


registrar server expires max 3600 min 3600

localhost dns:BWTC.local



voice class codec 1

codec preference 1 g711ulaw


voice-port 0/0/0

ring cadence pattern01

description **FXS Port To Fax Machine**

station-id number 13324400


dial-peer voice 2 voip

description **T.38 SIP Trunk To CCM**

destination-pattern [0-9].......T

session protocol sipv2

session target ipv4:

incoming called-number .T

dtmf-relay h245-signal

codec g711ulaw

fax-relay ecm disable

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

no vad


dial-peer voice 10 pots

destination-pattern [0-9].......T

fax rate fax

no digit-strip

port 0/0/0

forward-digits 0




registrar ipv4: expires 3600