Thomas London

Environments as first class objects

We describe a programming language called Symmetric Lisp that treats environments as first-class objects. Symmetric Lisp allows programmers to write expressions that evaluate to environments, and to create and denote variables and constants of type environment as well. One consequence is that the roles filled in other languages by a variety of limited, special purpose environment forms like records, structures, closures, modules, classes and abstract data types are filled instead by a single versatile and powerful structure. In addition to being its fundamental structuring tool, environments also serve as the basic functional object in the language. Because the elements of an environment are evaluated in parallel, Symmetric Lisp is a parallel programming language; because they may be assembled dynamically as well as statically, Symmetric Lisp accommodates an unusually flexible and simple (parallel) interpreter as well as other history-sensitive applications requiring dynamic environments. We show that first-class environments bring about fundamental changes in a languages structure: conventional distinctions between declarations and expressions, data structures and program structures, passive modules and active processes disappear.

Broadband Gigabit Research and the LuckyNet Testbed

This paper describes the motivation, architecture, initial applications, and objectives for LuckyNet, an AT&T Bell Labs gigabit research network. Building upon the B-ISDN infrastructure of SONET transport and the ATM packet protocol, LuckyNet will provide a fertile testbed for investigating: broadband applications, network architectures, gigabit packet switches and LANs, high-throughput protocols and interfaces, and network services and operations (including addressing, routing, signaling, control and security).LuckyNet is a heterogeneous network that has as one of its major objectives the demonstration that diverse classes of user traffic (i.e., video, voice, data, and image), as well as control and management information can efficiently utilize a single ATM infrastructure. Another goal is to provide users with gigabit-per-second network access. Initial applications provide 155 Mbps access and include video conferencing, document retrievaL low-latency processor-sharing, and Ethernet interconnection. We expect that this will be followed by FDDI interconnection and multimedia conferencing, with the long-range goal of identifying and supporting gigabit-per-second applications. Extensions to other locations and interworking with NREN sites (e.g., AT&T Bell Labs XUNET II) are anticipated. The network already links the Holmdel and Crawford Hill Laboratories (via optical fiber) and the Crawford Hill and Murray Hill Laboratories (via microwave radio) at 2.5 Gbps.

Parallelism, persistence and meta-cleanliness in the symmetric Lisp interpreter

Symmetric Lisp is a programming language designed around first-class environments, where an environment is a dictionary that associates names with definitions or values. In this paper we describe the logical structure of the Symmetric Lisp interpreter. In other interpreted languages, the interpreter is a virtual machine that evaluates user input on the basis of its own internal state. The Symmetric Lisp interpreter, on the other hand, is a simple finite-state machine with no internal state. Its role is to attach user input to whatever environment the user has specified; such environments are transparent objects created by, maintained by and fully accessible to the user. The interpreters semantics are secondary to the semantics of environments in Symmetric Lisp: it is the environment-object to which an expression is attached, not the interpreter, that controls the evaluation of expressions.This arrangement has several consequences. Because environments in Symmetric Lisp are governed by a parallel evaluation rule, the Symmetric Lisp interpreter is a parallel interpreter. A Symmetric Lisp environment evaluates to another environment; a session with the interpreter therefore yields a well-defined environment object as its result. Users are free to write routines that manage these interpreter-created objects - routines that list the elements of a namespace, coalesce environments, maintain multiple name definitions and so on precisely because environment objects may be freely inspected and manipulated. Because a named environment may contain other named environments as elements, interpreter-created objects may be regarded as hierarchical file systems. Because of the parallel evaluation semantics of environments, the interpreter is well-suited as an interface to a concurrent, language-based computer system that uses Symmetric Lisp as its base language. We argue that - in short - a basic semantic simplification in Symmetric Lisp promises a correspondingly basic increase in power at the user-interpreter interface.

LuckyNet: an overview

A description is presented of the motivation, architecture, initial applications, and objectives for LuckyNet, a wide-area AT&T Bell Labs gigabit research network. LuckyNet is a heterogeneous network that has as one of its major objectives the ability to provide users with gigabit-per-second network access. Initial applications provide 155 Mbps network access and include video conferencing, document retrieval, low-latency processor-sharing, and LAN interconnection.<<ETX>>

The Liaison network multimedia workstation

A description is given of a workstation architecture, Liaison, that solves the high bandwidth problem for real-time video and allows the exploration of these communications issues. By distributing the workstations intelligence over a high-performance network, both the computation and communication load are shed to other processors on the network. The Liaison display performs only the low-level functions of acquiring and displaying images, whereas the remainder of the workstations functionality is performed by a pool of distributed processors. Initial experiences with this architecture using a prototype monochrome workstation have provided insight into the issues surrounding the control and processing of communications-intensive applications.<<ETX>>

Applications of superimposed coding to partial-match retrieval

Experimental information-retrieval systems for telephone directory assistance and for filing office correspondence utilizing a superimposed-coded partial-match-retrieval scheme have been implemented. This extended-hash-code methodology permits the integration into the system of such user-oriented features as overlapping the query input and database search processes to give rapid apparent response, continual feedback to the user of the progress of the search, and abbreviation of keys by truncation. Simple coding and retrieval logic allow updating and rapid response to be achieved easily in either software or hardware realizations. The flexibility of the technique offers special advantages when casual users with fragmentary and ill-formulated queries need to approach a computerized information-retrieval system.

Communications-intensive workstations

The introduction of gigabit local area networks and the resultant proliferation of multimedia applications will require fundamental changes in the design of computer workstations. The workstation is implemented as a distributed application on a local area network in order to focus on communications issues. A single processor is dedicated to the low-level functions of acquiring image and audio streams from the network and sending keyboard and mouse information to the network. The display processor receives only bitmap images of data to be displayed. Higher level functionality, like that provided by the X-window system, is handled by other processors in the network. To demonstrate the feasibility of this architecture, a prototype monochrome (bilevel black and white) workstation was built that is able to simultaneously display several windows with 30 frame/s video, each arriving from a different processor via a local area interconnect. The feasibility of interleaving real-time video images across multiple disks on different processors to provide sufficient throughput for full-motion video is demonstrated. A simple method provides video and sound which are synchronized with each other and which flow smoothly.<<ETX>>