User`s guide

Dialogic
®
System Release 6.0 PCI for Windows
®
Release Update, Rev 62 — January 30, 2008 216
Dialogic Corporation
1.52.2.4 SIP SlowStart Mode (Calling UA Answers SDP)
When a SIP application sets the optional SlowStart parameter, it specifies that the INVITE
message it sends will not contain SDP, so that it is up to the called UA to offer SDP which
the calling UA will subsequently answer. In SIP terminology, this is known as delayed offer.
Figure 19. SIP Early Media, Calling UA Answers SDP
1.52.3 Early Media with Non-Global Call Applications
The ipm_ModifyMedia( ) function can be used to implement early media from non-Global
Call applications (i.e. directly from IPML). Function reference information is given below.
gc_MakeCall( )
Calling
App
Called
App
IP
CCLib
IP
CCLib
GCEV_ALERTING
GCEV_CONNECTED
GCEV_EXTENSION
(EXTID_MEDIAINFO - RX)
GCEV_EXTENSION
(EXTID_MEDIAINFO - TX)
GCEV_EXTENSION
(EXTID_MEDIAINFO - RX)
GCEV_EXTENSION
(EXTID_MEDIAINFO - TX)
GCEV_DETECTED/OFFERED
GCEV_ANSWERED
GCEV_ACCEPT
gc_AcceptCall( )
gc_AnswerCall( )
Unidirectional media
streams are enabled
before each respective
GCEV_EXTENSION
(MEDIAINFO) event
is dispatched upon
receiving SDP offer.
180 Ringing
200 OK
("m=" , "m=" , ...)
m
n
INVITE [no SDP]
ACK
("m=" , "m=" , ...)
m
n
Pre condition: Both line devices are IDLE. Called party has executed gc_WaitCall().
"SlowStart" is enabled.
Post condition: Call is connected.
If only one Rcv codec
was specified in SDP
offer, unidirectional
receive stream is
enabled when SDP
is offered.
Unidirectional media
streams are enabled
before each respective
GCEV_EXTENSION
(MEDIAINFO) event
is dispatched upon
receiving SDP answer.