Protocols
IPTV covers both live TV (multicasting) as well as stored video (video-on-demand, or VoD). The playback of IPTV requires an IP connected device, typically a personal computer or smart phone, or tablet, or game-console, or the traditional set-top box connected to a TV. Video content is typically compressed using either a MPEG-2 or a MPEG-4 codec and then sent in an MPEG transport stream delivered via IP multicast in case of live TV or via IP unicast in case of video on demand. IP multicast is a method in which information can be sent to multiple computers at the same time. The H.264 (MPEG-4) codec is increasingly used to replace the older MPEG-2 codec.
In standards-based IPTV systems, the primary underlying protocols used are:
- Live IPTV uses IGMP for connecting to a multicast stream (TV channel) and for changing from one multicast stream to another (TV channel change). IP multicast operates within LANs (including VLANs) and across WANs also. IP multicast is driven by Protocol Independent Multicast (PIM), which allows for distribution of mulitcast streams (TV channels) from their source all the way to the customer who wants to view them.
- VOD uses UDP or RTP protocols for channel streams and control is done using the Real Time Streaming Protocol (RTSP).
- A network personal video recorder, like VOD, uses UDP or RTP for IPTV streams and RTSP for end-user control communications.
A telecommunications company IPTV service is usually delivered over an investment-heavy walled garden network.
Local IPTV, as used by businesses for audio visual AV distribution on their company networks is typically based on a mixture of:
- Conventional TV reception equipment and IPTV encoders
- IPTV gateways that take broadcast MPEG channels and IP wrap them to create multicast streams.
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