The proliferation of video chat has been positive for the video telephony market as well. Examples of such use are emerging everywhere and traffic is starting to grow.
What is more natural than taking video telephony to the center of residential life - the place where people spend their time and the location of the large screen - the TV?
With broadband access in every home, high-definition on-TV video telephony has the potential to become a killer application.
What does it require?
Video telephony is well defined and widely used in the context of the IP Multimedia Subsystem (IMS). The codecs and protocols typically used in the IMS to carry video telephony are:
- Signaling: SIP
- Transport: RTP, 3G-324M
- Video: H.264 baseline profile, MPEG4 simple profile, H.263 baseline profile
- Wireline voice: G.711, G.729
- Wireless voice: AMR, EVRC
However, IP set-top-boxes do not typically support these codecs and protocols, creating the need to perform codecs and protocol conversions when bridging between IMS video telephony and IP-based television services (IPTV).
To support video telephony connectivity in an IP set-top-box (STB), some capabilities need to be integrated into the STB, while others need to be provided by the network operator as part of the infrastructure:
- Video: An IP-STB is capable of receiving H.264 main profile in standard definition (SD) resolution. IMS video is typically carried in a H.264 baseline profile, in resolutions from QCIF (144x176) up to VGA (640x480). An infrastructure gateway is required to bridge between these different codecs and profiles. In the opposite direction, from the home to the IMS network, an RTSP-based camera is typically added to the screen or as part of the STB. Conversion between the video presentation of the RTSP camera and the codecs used by the IMS is thus required.
- Audio/Voice: IMS video typically uses narrowband voice codecs, while IPTV typically uses wideband audio codecs such as AAC. An infrastructural gateway is required to provide transcoding between codecs such as G.711 in the IMS network and the AAC in the IPTV network.
- Transport: The IMS uses RTP as its primary transport protocol, while in IPTV, an MPEG2-transport stream is used for sending video from the core network to the STB. A gateway is required to bridge between RTP and MPEG2-TS.
- Signaling: SIP is the primary signaling protocol for video telephony on the IMS side. On the TV side, the STB manufacturers will integrate SIP as well. Since media conversions need to be performed in the infrastructural gateway, a back-to-back SIP user agent must be part of that gateway in order to maintain one set of protocols on the IMS side and a second set of protocols on the TV side.
