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New Member

T38 Fax issue with CCM 5.0

'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




Re: T38 Fax issue with CCM 5.0

Could you verify if the The service parameter "Strip G.729 Annex B (Silence Supporession) from Capabilities is

set to TRUE on both servers

New Member

Re: T38 Fax issue with CCM 5.0

What do you mean by your statement? I don't understand


Re: T38 Fax issue with CCM 5.0

That is a parameter in CCM Service PArameters

Could you please provide detail CCM traces

to see where might be the failure

Include calling, called number, timestamps and behaviour

New Member

Re: T38 Fax issue with CCM 5.0

The design is like this:-


I noticed that the CCM software MTP is not supported T38 fax relay. So, we introduced the hardware MTP that is Cisco AS5350XM which is also doubly support the T38.

Regarding the DP & MRGL, I have read that "any endpoint whether ATA or trunk that participates in the T.38 fax call needs to use a MGRL that includes the 'hardware' MTP". We have already did that, put the hardware MTP in the Multicast_MRGL and assigned it to Muticast_DP to the ATA. For the SIP trunk, we put the hardware MTP in the Unicast_MRGL and assigned it to BWTC_PSTN_DP.

But not only fax calls failed, the voice calls cannot be made as we checked the MTP box, and assigned only hardware MTP on it.

For local fax, the fax calls is successfully made. We just untick the MTP box at the SIP trunk, and fax calls can be made.

But for international calls that need early offer, i think we need the MTP for the call to be started as voice than switched to T38.

For international fax, when we are using software MTP in the DP for endpoint and SIP trunk, MTP are checked at the trunk, I notice that the calls are through, the fax tone is detected, the fax machine shown that:-

1) fax response recognized

2) determine exchange rate 14400bps

Then, the connection is lost. Suppose for successful fax, after No.2, it will fax the contents to the remote side.

Can you take a look on the CCM traces I've attached to you? There is incoming message from SSW to the CCM "request time-out". Is it the calls have been established and getting drop by any party or else?

Noted that the fax calls are from 13324220 to international number 0060380243462

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