It is very clear to network architects that video is going to be the killer application for enterprises and the Internet. However a lot of network architects came from pure networking background and thus may not have the knowledge of the video protocols and standards.
The two major standards that tell us how to run video are SIP and H.323. I will be discussing H.323 today.
I found that the H.323 tutorial written by Intel hosted on IEC website is an excellence paper to help network architect to understand the basics of H.323.
The following are some H.323 terminologies what network architect should know:
Terminals are simply the end video hosts. It could be a laptop, video phone, large screen TV, etc. A H.323 must supports G.711 audio codec, all other codecs optional. Of course your terminals will need to be able to support one of the video codes in order to act as an video endpoint.
A H.323 gateway is a device the connect the H.323 network to some other non-H.323 networks. For example, if you want to have a video conference call between a terminal on a h.323 network and a terminal on a SIP network, you will need a H.323 gateway. Gateway provides call setup/release as well as media conversion services. Gateway is not needed if the terminals are all on the same H.323 network.
A zone is a collection of H.323 gateways, terminals and MCU and gatekeeper. A zone can only have one gatekeeper. A zone can cross subnet boundary.
Although you can have H.323 terminals talking to each other without gatekeeper, an H.323 network without gatekeepers are very limited in its functionality. Also, if a gatekeeper is present, the terminals must use the gatekeeper. Gatekeepers is the brain of the H.323 network. It provides addressing, authentication, authorization, call-routing, accounting, bandwidth management and other features. Gatekeepers do not process the actual video streams.
You can use a Cisco Router as an H.323 gatekeeper, make sure the IOS has an “x” on its name. i.e.: c2600-ix-mz.122-11.
Multipoint Control Units (MCU)
You will need a MCU if you want to run video conference with more then 2 terminals. The job of a MCU is to determine CODEC for the terminals and manage video conference resources. Video streams could be routed and processed by the MCU in some setup.
Gateway, gatekeeper and MCU can be deployed in the same physical hardware, or each could be deployed as a dedicated device on an H.323 network.
H.225 consists of call signaling and RAS (Registration, Admission, and Status). When a terminal needs to call another terminal, or want to join a video conference, it uses H.225 to communicate with the gatekeeper, or other terminals.
H.245 is a control procotol. It is used to exchange terminal capabilities and creation of media channels.
Real-Time Transport Protocol (RTP)
The payloads of video stream are carried by RTP packets, and then encapsulated by UDP. RTP provides payload-type identification, sequence numbering, timestamping, and delivery monitoring.
Real-Time Transport Control Protocol (RTCP)
RTCP is the control protocol for RTP. It provides feedback on the quality of the video streams, among other functions.