Multimedia Server Recording and Playback Control
The Real-Time Streaming Protocol [20] is an application level protocol for the
control of the delivery of data with real-time properties (such as audio/visual
media using RTP). Readers may think of recording video sessions and replay-
ing them over the Internet with playback controls, such as found in consumer
sound and video players. The protocol is similar in syntax and operation to
HTTP/1.1, so that extension mechanisms to HTTP also can be added, in most
cases, to RTSP. However, RTSP differs in a number of aspects, such as the
following:
■■ RTSP introduces new methods.
■■ RTSP servers maintain state, contrary to Web servers.
■■ Data is carried out-of-band, such as in RTP packets.
■■ RTSP has the notion of the request URI pointing to the desired service.RTSP is similar in many ways to SIP in its approach to protocol design. Also
in common with SIP, RTSP uses web security mechanisms and can use differ-
ent transport mechanisms such as UDP and TCP.
Session Description
The Session Description Protocol (SDP) [21] is rather a session description for-
mat than a protocol. SDP is also a quite complex topic because of the many
capabilities and the issues related to NAT traversal. The description of the
session parameters is used by SIP Internet multimedia and conferencing
for session initiation. SDP will be covered in more detail in Chapter 6, “SIP
Overview.”
Session Announcements
The Session Announcement Protocol (SAP) [22] is a multicast session
announcement protocol. SAP advertises multicast sessions by stating the spe-
cific multicast address and time information, and it carries a payload that
describes the session. In some ways, SAP is analogous to the TV Guidewhere
information about the channel, time, and program is provided.
Session Invitation
The Session Initiation Protocol (SIP) is the subject of this entire book.
Real-Time Internet Multimedia 93