Host groups: A multicast extension to the Internet Protocol (RFC0966)
Original Publication Date: 1985-Dec-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
S.E. Deering: AUTHOR [+1]
This RFC defines a model of service for Internet multicasting and proposes an extension to the Internet Protocol (IP) to support such a multicast service. Discussion and suggestions for improvements are requested. See RFC-988.
Network Working Group S. E. Deering Request for Comments: 966 D. R. Cheriton Stanford University December 1985
Host Groups: A Multicast Extension to the Internet Protocol
1. Status of this Memo
This RFC defines a model of service for Internet multicasting and proposes an extension to the Internet Protocol (IP) to support such a multicast service. Discussion and suggestions for improvements are requested. Distribution of this memo is unlimited.
This memo was adapted from a paper  presented at the Ninth Data Communications Symposium. This work was sponsored in part by the Defense Advanced Research Projects Agency under contract N00039-83- K-0431 and National Science Foundation Grant DCR-83-52048.
The Internet task force on end-to-end protocols, headed by Bob Braden, has provided valuable input in the development of the host group model.
In this paper, we describe a model of multicast service we call host groups and propose this model as a way to support multicast in the DARPA Internet environment . We argue that it is feasible to implement this facility as an extension of the existing "unicast" IP datagram model and mechanism.
Multicast is the transmission of a datagram packet to a set of zero or more destination hosts in a network or internetwork, with a single address specifying the set of destination hosts. For example, hosts A, B, C and D may be associated with multicast address X. On transmission, a packet with destination address X is delivered with datagram reliability to hosts A, B, C and D.
Multicast has two primary uses, namely distributed binding and multi-destination delivery. As a binding mechanism, multicast is a robust and often more efficient alternative to the use of name servers for finding a particular object or service when a particular host address is not known. For example, in a distributed file system, all the file servers may be associated with one well-known multicast address. To bind a file name to a particular server, a client sends a query packet containing the file name to the file server multicast address, for delivery to all the file servers. The
Deering & Cheriton [Page 1]
RFC 966 December 1985 Host Groups: A Multicast Extension to the Internet Protocol
server that recognizes the file name then responds to the client, allowing subsequent interaction directly with that server host. Even when name servers are employed, multicast can be used as the first step in the binding process, that is, finding a name server.
Multi-destination delivery is useful to several applications, including:
- distributed, replicated databases [6,9].
- conferencing .
- distributed parallel computation, including distributed gaming .
Ideally, multicast transmission to a set of hosts is not more complicated or expensive for the sender than transmission to a single host. Similarly, multicast transmission should not be more expensive for the networks and gateways than traversing the shortest p...