Table 5.1 (continued)
NAME DOCUMENT SUBJECT
Session Announcement
SAP RFC 2974 Session Announcement Protocol
Session Invitation
SIP RFC 3261 Session Initiation Protocol
Security Mechanisms
for the Internet
Security RFC 3631 Internet Security Threats and
ProtectionMulticast Protocols
IP multicast is not yet implemented in most public IP networks, but it is an
important concept to discuss with regard to Internet multimedia. The Internet
multimedia conferencing architecture [5] was initially developed on experi-
mental Internet multicast networks in the early 1990s. The initial application
was the audiovisual transmission of IETF meetings to online attendees around
the world, an application that is continued without interruption to the present.
IP multicast is the most efficient procedure to distribute data and multimedia
to large groups of users by locating the distribution function in the IP network
layer and, thus, making it available to any type of application. IP multicast also
absolves applications from establishing any type of communications between
senders and receivers, since joining a multicast group is all that is required.
The IP multicast address is the unique identifier for senders and receivers to
join a multicast session. Multicast is also highly scalable, since the data repli-
cation is delegated to the edge of the network as required by traffic patterns.
Multicast Address Allocation
Multicast addresses are allocated from a pool of Class D IP addresses that are
reserved for multicast. Most multicast address allocations are implemented at
present in a static manner with manual configuration. However, work is in
progress to dynamically allocate multicast group addresses and to provide
directory services for multicast groups.
We will use Table 5.1 as guide to provide a short overview on Internet multi-
media and real-time communications.
Real-Time Internet Multimedia 85