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102 Dialogic
®
Global Call IP Technology Guide — November 2007
Dialogic Corporation
IP Call Scenarios
3.4.4 Receiving T.38 Fax Without an Established Audio Session
This scenario describes the reception of T.38 Fax in a media session that does not have audio
already established. The application first opens a Media device and a T.38 Fax device and
configures “Manual” operating mode. See Section 4.26.2, “Specifying Manual Operating Mode”,
on page 322 for more information on manual mode. When the application receives a T.38 fax
request, a GCEV_OFFERED event with T.38 extension information is received.
If the application accepts the call, the T.38 Fax device is associated with the Media device before
the T.38 call is answered. Figure 43 shows the scenario diagram.
Notes: 1. The GCEV_OFFERED event with T.38 extension information is only generated if the following
requirements are met. For H.323, the incoming message must be a Q.931 Setup message with
data terminal capability only. For SIP, the incoming message must be an INVITE message with
an SDP that has an image media descriptor only. If this condition is not met, the
GCEV_OFFERED event does not include any T.38 extension information. This limitation
prevents the T.38 server from receiving the T.38 request in H.323 slow start or in a SIP no SDP
INVITE request.
2. The application must not use both Dialogic
®
Global Call API and Dialogic
®
IP Media Library
API functions on the same device. The Dialogic
®
IP Media Library API calls (ipm_) in
Figure 43 are shown for informational purposes only. Global Call interacts with the IP Media
Library on behalf of the application.
Figure 43. Receiving T.38 Fax Without an Established Audio Session
IPML
Remote Device Capable of
Signaling and T.38
App
gc_OpenEx(:N_iptB1T1:M_ipmB1C1)
Receive SETUPw/TCS/INVITE with FAX IP
address and RTP Port number
Call Connected
FAX
fx_open(dxxxB23C1)
T.38 Data via RTP
GC/cclib
GCEV_OFFERED(IPSET_FOIP,IPPARM_T38_OFFERED)
gc_AnswerCall()
gc_SetUserInfo(IPSET_FOIP, IPPARM_T38_CONNECT)
dev_Connect(ipmB1C1, dxxxB23C1)
Ipm_GetLocalMedia(T.38)
Ipm_StartMedia(T.38)
Fx_recvfax()
GCEV_ANSWERED
gc_SetConfigData(IP_MANUAL_MODE)