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Global Call IP Technology Guide — November 2007 371
Dialogic Corporation
Third Party Call Control (3PCC) Operations and Multimedia Support
Figure 79. OPTIONS Request with a MIME Body
5.5 Processing Intraframe Requests for Video Streams
This section provides information about processing intraframe requests for video streams. Topics
are as follows:
• Overview
• Requesting an I-Frame in SIP
• Global Call Example Code
5.5.1 Overview
When each frame of video is compressed separately, the type of compression is known as
“intraframe” or “spatial” compression. Intraframes, also known as I-frames (or I-Pictures), are
complete and independent. Video compression systems, however, typically utilize what is known
as “inter-frame” or “temporal” compression as well. Inter-frame compression takes advantage of
the fact that any given frame of video is most likely similar to the frames around it. So, instead of
storing entire frames, the coder implementation can store just the differences between certain
frames, reducing the amount of overall data that needs to be stored or transmitted. I-frames provide
a reference point for dependent Inter-frames (P pictures and B pictures) and allow random access
into the compressed video stream. When recording a video message, the first video frame stored
should ideally be an I-frame. This will insure that the playback will be begin with a visually
complete and recognizable frame.
Application A
Global Call
Library A
(IPCCLIB)
Global Call
Library B
(IPCCLIB)
Application B
gc_Extension
MSG_TYPE_SIP_OPTIONS
IPSET_SDP
OPTIONS
MIME (SDP Capabilities 0)
GCEV_EXTENSION
MSG_TYPE_SIP_OPTIONS
IPPARM_MIME_PART_BODY(SDP)
IPSET_SDP
gc_Extension
MSG_TYPE_SIP_OPTIONS_OK
IPSET_SDP
GCEV_EXTENSIONCMPLT
200 OK
MIME (SDP Capabilities 1)
GCEV_EXTENSIONCMPLT
GCEV_EXTENSION
MSG_TYPE_SIP_OPTIONS
IPPARM_MIME_PART_BODY(SDP)
IPSET_SDP
A GCEV_SIP_200_OK event
is not sent to the application
when a 200 OK is received
on an OPTIONS transaction.
SIP OPTIONS transactions
do not receive an ACK.