RFC 1193 (rfc1193) - Page 2 of 24
Client requirements for real-time communication services
Alternative Format: Original Text Document
RFC 1193 Requirements for Real-Time Services November 1990 different pairs of entities: every layer (with the support of the underlying layers) provides a service to the layer immediately above it and is a client of its underlying layers. In this paper, our considerations generally apply to any client-server pair. However, most of them particularly refer to human clients (users, programmers) and to the ways in which such clients express their communication and processing needs to the system (e.g., interactive commands, application programs). This type of client is especially important, since client needs at lower layers can be regarded as translations of the needs expressed by human clients at the top of the hierarchy. When the client is human, the server consists of the entire (distributed) system, including the hosts, their operating systems, and the networks interconnecting them. As for the generic term, performance, we will give it a fairly broad meaning. It will include not only delay and throughput, the two main network performance indices, but also reliability of message delivery. Real-time communication is concerned with those aspects of quality of service that have to do with performance in this broad sense. The term guarantee in this paper has a rather strong legal flavor. When a server guarantees a given level of performance for the communications of a client, it commits itself to providing that performance and to paying appropriate penalties if the actual performance turns out to be insufficient. On the other hand, the client will have to obey certain rules, and will not be entitled to the requested performance guarantees unless those rules are scrupulously obeyed. In other words, client and server have to enter into a contract specifying their respective rights and duties, the benefits that will accrue, the conditions under which those benefits will materialize, and the penalties they will incur for not keeping their mutual promises. We believe that a legal viewpoint is to be adopted if serious progress in the delivery of communication services (not only the real-time ones) is desired. Utility services, as well as other kinds of service, are provided under legally binding contracts, and a mature computer communication utility cannot fail to do the same. In the field of real-time communication, such a contract will by definition include performance guarantees. Real-time services may be offered in any kind of network or internetwork. Some of their predictable applications are: (a) digital continuous-media (motion video, audio) communication: lower bounds on throughput and upper bounds on delay or delay variability or both are needed to ensure any desired level of output quality; in the interactive case, both the values of delay and delay variabilities have to be Ferrari
