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One of the most important functions of an intelligent workstation is to provide a state-of-the-art user interface to distributed resources. One aspect of such an interface is virtual terminal support for both local and remote applications with a range of requirements, including graphics. To ensure good response for remote applications, in particular, the bulk of user interaction must be handled local to the workstation. Therefore, the terminal management software on the workstation must provide object modeling as well as viewing facilities, in contrast to most contemporary graphics systems. One way of doing this is to support structured display files. It is equally important to support simultaneous access to multiple applications; thus the terminal management software must provide window system Lscilities. Lastly, since the terminal management software should present a common interface to both local and remote applications, the workstation itself should be regarded as a multifunction component of the distributed system and not strictly as a terminal or a personal computer. This paper presents the system architecture and protocols necessary to achieve these goals and evaluates an existing implementation.

A major reason for the rarity of distributed applications, despite the proliferation of networks, is the sensitivity of their performance to various aspects of the network environment. Contrary to much popular opinion, we demonstrate that CPU speed remains the predominant factor. With respect to network issues, we focus on two approaches to performance enhancement: (1) Improving the performance of reliable, byte-stream protocols such as TCP; (2) the use of high-level protocols that reduce the frequency and volume of communication.

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A major reason for the rarity of distributed applications, de,;pite the proliferation of networks, is the sensitivity of their performance to various aspects of the network environment. ContraD, to much popular opinion, we demonstrate daat CPU speed remains the predominant factor. With respect to network issues, we focus on two approaches to performance enhancement: (1) Improving the performance of reliable, byte-stream protocols such as TCP; (2) the use of high-level protocols that reduce the frequency and volume of communication.© 1984 ACM 0-89791-136-9/84/006/0116 $00.'75 116 extensive interaction between the various parts of the distributed system, implying that care must be taken to avoid having the network communication become a bottleneck."Ire V distributed operating system (V-System) being developed at Stanford supports distributed graphics applications of the sort just dcscribed [2,4,9]. This paper describes experience gained with the V-System with respect to various factors that affected those applications' performance. Section 2 describes the V-System environment. Section 3 describes the observed performance behavior of distributed applications. The five subsequent sections analyze various factors in some detail, including the effects of processor speed (Section 4), issues in graphics protocol design (Section 5), general issues in transport protocol design (Section 6), and a detailed discussion of one parucular transport protocol, namely, ARPA Internet TCP [13] (Section 7). Conclusions are drawn in section 9. Software Architectu reThe V-System consists of a distributed kernel and a distributed set of ~rver processes. The distributed kernel provides networktransparent interprocess communication based on synchronous message-passing. ~ It consists of the collection of kernels resident on the participating machines. The host kernels are integrated via a low-overhead inter-kernel protocol (IKP) that supports transparent interprocess communication between machines [4].Servers include device servers, storage servers, virtual graphics terminal servers, exception servers, and network servers. The following section discusses network services in some detail.Lastly. a standard program environment has been defined, the principal instance of which is a C program library. The C library includes runtime support for standard C and UNIX-like library functions to facilitate the porting of existing C programs. NetworkServicesThe V-System supports network transport through three different protocol families. The standard means of communication between hosts on the same local network is by means of the inter-kernel protocol (IKP) mentioned above. IKP provides a reliable dataeram service; packets are delivered, but duplicates are not suppressed. 2 IKP is implemented directly on top of the datalink level and is used by.each host's kernel whenever interprocess communication is requested with a non-local process. Reliable byte-streams (henceforth referred to as V I/O connections) are provided external to the kernel by means of a...