Other than the video codec, all other characteristics for a video call - for example picture size, frame rate, and the like - are not negotiated via the SDP offer and answer mechanism. In the SDP offer and answer negotiation, each party only informs the other what they can receive, not what they are going to transmit.
The internal CAC solution continues to use statically configured values for the bandwidth requirements for the video streams provided via H.323 and unknown video codecs as described.
However, bandwidth calculations for H.264 codecs, which are performed during the SDP negotiation, also take into consideration the video profile level associated with the codec. This calculation also adds a fixed percentage value depending on whether:
The transport takes place on IPv4 or IPv6 addresses.
SRTP usage is present.
The actual bandwidth being used by the video stream is constantly changing and will usually be a lot lower (up to 90%) than the maximum figure specified in the SDP offer and answer.
Due to these restrictions, the internal CAC solution uses statically configured values for the bandwidth requirements for the video streams for the different video codecs supported by Lotus Sametime Unified Telephony. The internal CAC solution also uses statically configured values for the bandwidth requirements for unknown video codecs.
The following parameters required for video bandwidth calculation can be configured on the Lotus Sametime Unified Telephony system:
The estimated bandwidth required by the video stream for an H.263 call
Possible values=32-960000 kbpsH.264 Bandwidth:
Default = 160 kbps
The estimated bandwidth required by the video stream for an H.264 call
Possible values=32-960000 kbpsUnknown Bandwidth:
Default = 64 kbps
The estimated bandwidth required by the video stream for unknown video codecs
Possible values=32-960000 kbps
Default = 128 kbps
These values are stored in the same parm file as the other bandwidth calculation parameters. In addition, these values are configurable via the Telephony Control Server Assistant.
The internal CAC solution makes the bandwidth calculations, assuming a symmetrical RTP stream. If a CAC policy has a bandwidth limit of 1 Mbps, it means that the link's upstream capacity is 1 Mbps and the downstream capacity is also 1 Mbps. Therefore, if the H.263 Bandwidth parameter is set to 160 kbps, it indicates that this bandwidth will be reserved for 160 Kbps upstream and 160 Kbps downstream.
Video CAC enhancements
Call Admission Control in the Lotus Sametime Unified Telephony has been enhanced to ensure correct bandwidth calculation for video. With HD endpoints the bandwidth used by the endpoints can be as high as 1.2 Mbit/s, providing the bandwidth is available.
Lotus Sametime Unified Telephony Video Service
To integrate Video service in Lotus Sametime Unified Telephony and to make Telephony Control Server video service aware, the following subfeatures have been added:
CDR enhancements (Call type,Bit rate etc.).
Business Group Line (control which BGL can make Video calls - this will ensure that HD conference capable lines has enough bandwidth).
Routing based on Service required. (E.g. based on Video service request (in SDP), route to Video GW.)
The IRM shall process requests for Video calls according to the following rules:
Parent topic: CAC (Call Admission Control)
- Enough Bandwidth for Both the Audio and Video Streams: The Video call is allowed (i.e. IRM sends a positive response).
- Not Enough Bandwidth for the Audio Stream: The Video call is not allowed (i.e. IRM sends a negative response with Error Code = "Insufficient Resources").
- Enough Bandwidth for the Audio Stream, Not Enough Bandwidth for the Video Stream:
- Video Tone or Announcement (i.e. MEDIA_SERVER_ANNOUNCEMENT flag is set): The Video call is not allowed (i.e. IRM sends a negative response with Error Code = "Insufficient Resources").
- New flag ("Audio only allowed when Video requested") is NOT set for the CAC Policy: The Video call is not allowed (i.e. IRM sends a negative response with Error Code = "Insufficient Resources").
- New flag ("Audio only allowed when Video requested") is set for the CAC Policy: Audio only call is allowed. In this case, the IRM modifies the SDP offer to cancel the video portion and sends back a positive response.