Video Support

Overview

The SBC Core supports two types of Video sessions:

1. Vanilla video session comprising one audio and video stream.
   
   
2. Interactive video session involving audio, video, and a second video stream for channel sharing (see H.239 Video Channel Sharing for details). For example, an interactive video session using Desktop Share uses a second video stream to share the slides as well as control the protocol deciding who presents the data (BFCP).

The SBC Core supports the following features:

Video Support Per Call Scenario

Call Scenario	Audio	Video	Presentation			FECC
			BFCP/UDP	BFCP/TCP	H.239
SIP-SIP					N/A
SIP-H.323
H.323-H.323			N/A	N/A

Media features such as Network Address and Port Translation (NAPT) processing and SRTP are supported for video streams as well. Policy controls are available to manipulate the Video Codec list (refer to Codec List Profile - CLI or Media - Codec List Profile (EMA ) for configuration details), SDP video "media line" related bandwidth attribute and packet marking for QoS of video streams. To allow video peering and conferencing flows, the SBC can relay a set of SDP attributes at the audio "media level" (refer to SIP Trunk Group - Media - CLI or SIP Trunk Group - Media (EMA)) and session level (see SIP Trunk Group - Signaling - CLI or SIP Trunk Group - Signaling (EMA)).

For SBC 7000 video performance details, refer to SBC 7000 Performance Metrics.

To see CLI global statistics examples audio vs. video configurations, see the "Command Examples" section of Show Status Global page. 

SIP-SIP Video

The SBC manages peering video flows and conferencing in the following manner.

The SBC relays most attributes and lines in the SDP corresponding to Video, BFCP and FECC streams. Only a small set of attributes/lines are manipulated to relay media through the SDP, for example:

• C line
• a=sendonly/recvonly/inactive/sendrecv
• a=crypto
• b=TIAS/AS

If relaying certain attributes/lines is undesirable, use SIP Message Manipulation (SMM) to delete those particular attributes.

To facilitate video peering and conferencing flows, the SBC relays SDP attributes at the media and session level using the flag sdpAttributesSelectiveRelay.

The CLI syntax is shown below.

% set addressContext default zone INTERNAL sipTrunkGroup SIP_INT media sdpAttributesSelectiveRelay <disabled | enable>

This flag controls the selective relay of unknown SDP attributes at the session level, and selective relay of unknown SDP attributes in core audio stream.

The example scenarios below depict the effects of enabling/disabling this flag to session, core and video streams:

sdpAttributesSelectiveRelay Flag Impact to Video Streams

Scenario	SDP Stream Offers	Flag On			Flag Off
		Session	Core	Video	Session	Core	Video
1	Audio only	relayed	relayed	--	dropped	dropped	--
2	Audio only, and then...	relayed	relayed	--	dropped	dropped	--
	Audio + Video	relayed	relayed		dropped	dropped
3	Audio + Video	relayed	relayed		dropped	dropped
	Audio + Video	relayed	relayed		dropped	dropped

The SBC Core also offers control over the TCP port range for the relayed BFCP-TCP streams.

The Video and other conference-related streams are allowed to pass through when the Packet Service Profiles on both call legs allow video (non-zero maxVideoBandwith value as shown in example below).

% set profiles media packetServiceProfile INGRESS videoCalls maxVideoBandwith 2000
% set profiles media packetServiceProfile EGRESS videoCalls maxVideoBandwith 2000

The “Floor Control” feature is the process by which access to a shared resource, or shared whiteboard, is controlled by granting access to participants in a multiparty communication session using the Binary Floor Control Protocol (BFCP) whereby a separate TCP connection is used for each BFCP session.

SIP-H.323 Video

The SBC Core supports SIP-H.323 interworking for audio, video, presentation (BFCP/H.239) and FECC. The following functionality is supported:

• Mapping of the call setup and tear down sequences
• Maintaining the H.323 and SIP state machines
• Negotiating terminal capabilities
• Opening and closing media channels
• Reserving and releasing call-related resources
• Processing of mid-call signaling messages
• Handling of services and features

H.323-H.323 Video

The SBC Core supports H.323-H.323 video peering scenarios, for example H.323-H.323 call with an audio and video stream. Unlike SIP video where all codecs are relayed through the SBC, H.323 only supports a subset of SIP video codecs (refer to Supported Codecs and Transcoding).

A video stream is allowed to pass through if the Packet Service Profiles on both call legs allow video (non-zero maxVideoBandwith value as shown in above example.

H.239 Video Channel Sharing

H.239 protocol allows sharing graphical content such as presentation slides, applications, complete desktops or other external video sources with other conference participants. The content is treated as a second video stream provided by one source and distributed to all other participants in a conference.

Far End Camera Control

The SBC supports Far End Camera Control (FECC) in controlling a remote camera's pan, tilt and zoom functions. The remote control aspect of a video conferencing system supporting FECC usually provides arrow keys for controlling pan and tilt and two separate keys for controlling the camera zoom. Camera control can be applied to either the local or remote camera. In the latter case, the video conferencing system generates far end camera control messages and sends them to the remote party. The remote party may act on reception of these messages by adjusting the camera's pan, tilt and zoom.

• Usage of FECC in the context of H.323 is defined by Annex Q of ITU-T Rec. H.323 which details how H.281/H.224 messages are used and sent over an RTP/UDP/IP transport.
• RFC 4573 supports offer-answer when requesting a ``h224'' media type stream for use with H.281 over H.224 with SDP-based media negotiation making it possible to negotiate a H.224 session as described in H.323 Annex Q between a SIP client and an MCU in an interoperable way.

Video Codecs

Video Codecs SIP

The SBC relays all video codecs by default using static or dynamic payloads.  

Video Codecs H.323

References