Streaming video and audio is the commonly used technology behind webcasting. The protocols applicable in this case are RTP (Real-time Transport Protocol) over UDP (User Datagram Protocol). Most webcast solutions are based on these protocols.
The Internet standard protocol for transport of data real time, including video and audio is RTP. This is used for Internet telephony, which is an interactive service, as well as for media-on-demand. RTP consists of two parts: a data and a control part. The control part is also known as Real-time Transport Control Part (RTCP).
Support of applications such as continuous media (audio and video webcasts) including content identification, loss detection, security and timing reconstruction is provided by the data part of RTP, which is a thin protocol.
Webcast support for real-time conferencing of various sized groups within an internet is provided by the Real-time Transport Control Part. Multicast-to-unicast translators are supported by this, as are support for audio and video bridge gateways and source identification. Also supported is the synchronization of various streams of media. Quality of Service feed-back to the multicast group from receivers is also offered.
RTP relies on resource reservation protocols such as RSVP (ReSerVation Protocol) and does not address the issue of resource reservation or quality of service control. Resources are reserved along data paths at each node as a result of RSVP requests. This is true for webcast recording and for video webcasts as well.
User Datagram Protocol (UDP) is a core member of a set of internet protocols, called the Internet Protocol Suite. With UDP, datagrams (messages) can be sent from computers to an IP (Internet Protocol) network host. This can be done without prior communications to set up data paths or communication channels. A transmission model that is simple is used by UDP, without handshaking dialogues for ensuring data integrity, reliability or ordering. In a real-time system, where packets dropping are not an option as compared to delayed packets, UDP is used. This is true for all time-sensitive applications. In such cases, Stream Control Transmission Protocol (SCTP) or Transmission Control Protocol (TCP) is used as error control facilities at the interface level of the network.
Servers that answer a small number of queries from a large number of clients find the UDP’s stateless nature useful. UDP is also compatible with multicasting (send to all subscribers) and packet broadcast. UDP is used by network applications like online games, Trivial File Transfer Protocol (TFTP) and streaming media like VoIP (Voice over Internet Protocol).