Abstract
Despite the efficiency of the IP-multicast it has not been deployed in the whole Internet. The main reason is that the wide-area multicasting among the different autonomous systems (AS) has not been solved perfectly. The global address allocation is especially a problematic part of Internet-wide multicasting. This article addresses such problems in order to review the existing methods and the emerging research results (Hosszú, 2005).
Key Terms in this Chapter
Address Allocation: The problem of choosing an unused IP-multicast address before starting a multicast session; when the session has been finished, this address should be released.
Domain Name System (DNS): A hierarchical distributed database for mapping the IP addresses to segmented name structure and vice versa.
Source Discovery: This problem arises when a host sends a join message to a router. The router can forward this join message toward the source of the multicast group if it has information about the source. This problem is more difficult, if the joining host and the source of the group are in different ASs (see above). In this situation, the MSDP (see above) can be used in order to exchange the information about the active sources among the ASs.
Multicast Source Discovery Protocol (MSDP): This protocol makes it possible to use independent multicast routing inside the domains, while the multicast sessions originated from or to other domains reach all the participants. In each AS (see above), there is at least an MSDP protocol entity in order to exchange the information about the active sources among them. Rendezvous Point (RP)
Inter-Domain Routing Protocol: IP-level routing protocol in order to create paths through the borderrouters of the Autonomous Systems (ASs).
Application-Level Multicast (ALM): A multicast technology which does not require any additional IPmulticast routing protocol in the network routers, since it uses the traditional one-to-one unicast IP transmission. This technology is the alternative of the IP-multicast (see below).
Multicast Routing Protocol: In order to forward the multicast packets, the routers have to create multicast routing tables using multicast routing protocols. An example of the multicast routing protocol is the Protocol Independent Multicast (PIM).
Autonomous System (AS): A network where the main routers are in common administration. The Internet is composed of peering ASs, which are independent from each other.
IP-Multicast: Network-level multicast (one-tomany) technology, which uses the special class-D IPaddress range. It requires multicast routing protocols in the network routers. This technology is an alternative to the Application-Level Multicast (ALM, see above). Its other name is Network-level Multicast (NLM).