Setting Video Parameters
Information About Setting Video Parameters
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Cisco Unified SCCP and SIP SRST System Administrator Guide
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During call setup for video, media setup handling determines if a video-media path is required or not. If
so, the corresponding video-media-path setup actions are taken.
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For an SCCP endpoint, video-media-path setup includes sending messages to the endpoints to open
a multimedia path and start the multimedia transmission.
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For an H.323 endpoint, video-media-path setup includes an exchange between the endpoints to open
a logical channel for the video stream.
A call-type flag is set during call setup on the basis of the endpoint-capability match. After call setup,
the call-type flag is used to determine whether an additional video-media path is required. Call signaling
is managed by the Cisco Unified CME router, and the media stream is directly connected between the
two video-enabled SCCP endpoints on the same router. Video-related commands and flow-control
messages are forwarded to the other endpoint. Routers do not interpret these messages.
Call Setup Between Two Local SCCP Endpoints
For interoperation between two local SCCP endpoints (that exist on the same router), video call setup
uses all existing audio-call-setup handling, except during media setup. During media setup, a message
is sent to establish the video-media path. If the endpoint responds, the video-media path is established
and a start-multimedia-transmission function is called.
Call Setup Between SCCP and H.323 Endpoints
Call setup between SCCP and H.323 endpoints is the same as it is between SCCP endpoints except that,
if video capability is selected, the event is posted to the H.323 call leg to send out a video open logical
channel (OLC) and the gateway generates an OLC for the video channel. Because the router needs to
both terminate and originate the media stream, video must be enabled on the router before call setup
begins.
Call Setup Between Two SCCP Endpoints Across an H.323 Network
If call setup between SCCP endpoints occurs across an H.323 network, the setup is a combination of the
processes listed in the previous two sections. The router controls the video media setup between the two
endpoints, and the event is posted to the H.323 call leg so that the gateway can generate an OLC.
Flow of the RTP Video Stream
For video streams between two local SCCP endpoints, the Real-Time Transport Protocol (RTP) stream
is in flow-around mode. For video streams between SCCP and H.323 endpoints or two SCCP endpoints
on different Cisco Unified CME routers, the RTP stream is in flow-through mode.
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Media flow-around mode enables RTP packets to stream directly between the endpoints of a VoIP
call without the involvement of the gateway. By default, the gateway receives the incoming media,
terminates the call, and then reoriginates it on the outbound call leg. In flow-around mode, only
signaling data is passed to the gateway, improving scalability and performance.
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Media flow-through mode involves the same video-media path as for an audio call. Media packets
flow through the gateway, thus hiding the networks from each other.
