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Incoming Fax Issue on ATA 187 - T38 reInvite not sent to SBC by Terminating Gateway

Hi All,

I have some issues with incoming fax. The voice phase is successful but the switchover to fax fails. When I call the fax number it rings, connects, gives one short beep then is silent throughout the call until I drop the call.

ITSP SBC--> (SIP Trunk) ---> Cisco gateway --> (H323) ---> CallManager --> (SIP) ---> ATA 187 with latest sw version

On the gateway, when I make a call to the fax I can see the IOS MTP is in use for that call for about 6 seconds upon connect - G729 is used; the call does not change to passthrough codec. The ccm logs show the ATA sending an Invite to CallManager containing T38 in the SDP, but I don't see the T38 Invite being sent from the gateway to the SBC. Looks like it isn't switching from G729 codec to T38.

voice service voip

allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

allow-connections sip to sip

fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback none


  no h225 timeout keepalive

  h225 h245-address on-connect


  bind control source-interface GigabitEthernet0/0

  bind media source-interface GigabitEthernet0/0

  early-offer forced


dspfarm profile 3 mtp

codec pass-through

codec g729r8

maximum sessions software 250

associate application SCCP


The region on CallManager is also configured for G729.


New Member

Incoming Fax Issue on ATA 187 - T38 reInvite not sent to SBC by

Calling number: 08227598

Called Number: 0873109434

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