John A. Trotter

Interrupt-based hardware support for profiling memory system performance

Fueled by higher clock rates and superscalar technologies, growth in processor speed continues to outpace improvement in memory system performance. Reflecting this trend, architects are developing increasingly complex memory hierarchies to mask the speed gap, compiler writers are adding locality enhancing transformations to better utilize complex memory hierarchies, and applications programmers are recoding their algorithms to exploit memory systems. All of these groups need empirical data on memory system behavior to guide their optimizations. This paper describes how to combine simple hardware support and sampling techniques to obtain such data without appreciably perturbing system performance. The idea is implemented in the Mprof prototype that profiles data stall cycles, first level cache misses, and second level misses on the Sun Sparc 10/41.

SWAN: a mobile multimedia wireless network

The SWAN (Seamless Wireless ATM Network) is an experimental indoor wireless network that instigates the combination of wireless access with multimedia networked computing in an indoor setting. It is based on room-sized pico-cells and mobile multimedia endpoints. It enables users carrying multimedia endpoints, such as personal digital assistants (PDAs), laptops, and portable multimedia terminals, to seamlessly roam while accessing multimedia data resident in a backbone wired network. The network model of SWAN consists of base stations connected by a wired asynchronous transfer mode (ATM) backbone network, and wireless ATM last hops to the mobile hosts. SWAN is one of the first systems to realize the concept of a wireless and mobile ATM network. Mobile hosts as well as base stations are embedded with custom-designed ATM adapter cards called FAWN (Flexible Adapter for Wireless Networking). FAWN uses off-the-shelf 2.4 GHz industrial, scientific, and medical (ISM) band radios. After giving an overview of the SWAN network model, and discussing the challenges in making ATM wireless and mobile, the article describes the first phase implementation of SWAN hardware and software. This initial implementation provides connectivity over the wireless last hop. We have investigated both native-mode end-to-end ATM communication across the wired ATM backbone and wireless ATM links, and transmission control protocol (TCP) and user datagram protocol (UDP) communication using Internet protocol (IP) over wireless ATM in the wireless link with IP forwarding and segmentation and reassemble modules at the base stations.

TeleWeb: loosely connected access to the World Wide Web

Abstract The development of the World Wide Web (WWW) has made people reliant on continuous, high-speed, low-cost networks in order to get work done. Ideally, one should be able to browse the Web anytime, anywhere, whether connected to such a network or not. This paper describes the design of TeleWeb, a system we are building to support this goal. We believe that fine-grained cost control is crucial and have developed a “reactive architecture” that supports user-specified adaptation under various operating conditions. There are four key features to TeleWebs architecture: costs are made visible to the user through annotated HTML; budget monitoring warns the user when operations exceed pre-specified limits; actions may be postponed and later triggered when conditions are met; and finally, user customization and system configuration values may automatically adapt according to the changing conditions of use. These mechanisms work together to provide an asynchronous, email-style of browsing in which users can work disconnected from a cache of documents, or trade off communication cost against information needs.

SWAN: an indoor wireless ATM network

The SWAN (seamless wireless ATM network) project investigates architectural aspects of networks containing mobile hosts. The network model includes base stations connected via a wired, ATM infrastructure and a wireless, ATM last hop to a number of mobile hosts, ranging in computational and functional abilities from personal digital assistants to notebook computers. The FAWN (flexible adaptor for wireless networking) network interface card was developed as part of the implementation of a small SWAN network. It provides wireless, ATM channels using off-the-shelf FHSS modems which operate in the 2.4 GHz industrial, scientific and medical band, and use a sequence of radio channels of 1 MHz bandwidth to provide up to 625 kb/s raw bit rate. The first phase of the implementation has been completed and provides basic wireless ATM connectivity. This paper presents an overview of the SWAN network, followed by a description of the implementation which has been built to validate our initial architectural design.

A testbed for mobile networked computing

The rapid deployment of wireless access technology, along with the emergence of high speed integrated service networks, promises to provide users with ubiquitous access to multimedia information in the near future. We are building an experimental testbed system, SWAN (Seamless Wireless ATM Network), to mimic this emerging networking environment. Our wireless access network is organized according to a nanocellular design with base stations serving as a gateway for communication between the wired network and the mobile hosts in a cell. Normally, a mobile host sends and receives traffic through the base station in its current cell. But SWAN also supports direct ephemeral networking between a limited number of cooperating mobile hosts within a small domain. The heart of the testbed is a networking subsystem, FAWN (Flexible Adapter for Wireless Networking) that interfaces the standard PCMCIA bus to an RF modem. The FAWN interface is used with a PC or workstation connected to a wired backbone network or a portable device such as a laptop or palmtop computer. In addition, a user interface consisting of an LCD display, audio I/O, and a bar code reader has been built. When interfaced with FAWN this results in a portable wireless multimedia terminal.

A VC-based API for renegotiable QoS in wireless ATM networks

Quality of service (QoS) support for multimedia applications has been widely discussed in the context of high speed wired networks. As interest increases in wireless ATM networks that extend the connection to a wireless endpoint, the issue of QoS over a wireless link has to be addressed. We focus on the provision of QoS at the application level in a wireless environment. Our work includes the design of an application programming interface (API) that allows applications to specify and renegotiate the QoS level during a call; as well as the implementation of such API in a wireless ATM testbed: the SWAN system. Experiments are performed to verify the efficiency of this scheme, and the results reveal quality control for multimedia applications despite changing network conditions.

Module replication for fault-tolerant real-time distributed systems

This paper considers the problem of replicating and scheduling periodic tasks in a multiprocessor system, under timing and dependency constraints. The objective is to maximize the probability of successful completion (logically correct execution, within the time constraints) of all the tasks in the system. The authors assume a precedence graph that is general with chain, AND, OR and loop subgraphs. To achieve high probability of successful completion of the tasks in the system, several modules (that constitute the tasks) are chosen for replication and executed, regardless of whether a failure actually occurs or not. The replicated modules are chosen in an optimal way, and are added to the set of the executable tasks only if that increases the probability of successful completion. The failure model of the modules in the system is general and realistic. The allocation scheme assigns the original and the replicated modules to the processing nodes of the system, and determines their starting time as well as the schedule for communication among them. Their results improve upon the work done previously.

Hardware-software architecture of the SWAN Wireless ATM network

The SWAN (Seamless Wireless ATM Network) system provides end-to-end ATM connectivity to mobile end-points equipped with RF transceivers for wireless access. Users carrying laptops and multimedia terminals can seamlessly access multimedia data over a backbone wired network while roaming among room-sized cells that are equipped with basestations. The research focus on how to make ATM mobile and wireless distinguishes SWAN from present day mobile-IP based wireless LANs. This paper describes the design and implementation of the ATM-based wireless last-hop, the primary components of which are the air-interface control, the medium access control, and the low-level ATM transport and signalling.The design is made interesting by its interplay with ATM; in particular, by the need to meaningfully extend over the wireless last-hop the service quality guarantees made by the higher level ATM layers. The implementation, on the other hand, is an example of hardware-software co-design and partitioning. A key component of the wireless hop implementation is a custom designed reconfigurable wireless adapter card called FAWN (Flexible Adapter for Wireless Networking) which is used at the mobiles as well as at the basestations. The functionality is partitioned three-way amongst dedicated reconfigurable hardware on FAWN, embedded firmware on FAWN, and device driver software on a host processor. Using an off-the-shelf 625 Kbps per channel radio, several of which can be supported by a single FAWN adapter to provide multiple channels, per-channel unidirectional TCP data throughput of 227 Kbps (or, 454 Kbps bidirectional) and per-channel unidirectional native ATM data throughput of 210 Kbps (or, 420 Kbps bidirectional) have been obtained.

Parallel model evaluation for circuit simulation on the PACE multiprocessor

Device model evaluation, an essential part of a circuit simulator, is a compute-intensive task. A multiprocessor-based circuit simulator that ignores the parallelization of model equation formulation (LOAD), and just parallelizes the solution (SOLVE) of the equations will seriously degrade the simulation performance. This paper describes methods of parallelizing the LOAD part of a circuit simulator on PACE (Parallel Architecture for Circuit Evaluation) a distributed memory multiprocessor designed at AT&T Bell Laboratories. This is integrated with the parallel SOLVE algorithms given in our earlier work. Load balancing and minimization of interprocessor communication are used as the primary objectives of the parallel LOAD heuristics studied. Performance results, using the prototype PACE system, on benchmark circuits show the feasibility of our approach.<<ETX>>

Multimedia information processing in the SWAN mobile networked computing system

Anytime anywhere wireless access to databases, such as medical and inventory records, can simplify workflow management in a business, and reduce or even eliminate the cost of moving paper documents. Moreover, continual progress in wireless access technology promises to provide per-user bandwidths of the order of a few Mbps, at least in indoor environments. When combined with the emerging high-speed integrated service wired networks, it enables ubiquitous and tetherless access to and processing of multimedia information by mobile users. To leverage on this synergy an indoor wireless network based on room-sized cells and multimedia mobile end-points is being developed at AT&T Bell Laboratories. This research network, called SWAN (Seamless Wireless ATM Networking), allows users carrying multimedia end-points such as PDAs, laptops, and portable multimedia terminals, to seamlessly roam while accessing multimedia data streams from the wired backbone network. A distinguishing feature of the SWAN network is its use of end-to-end ATM connectivity as opposed to the connectionless mobile-IP connectivity used by present day wireless data LANs. This choice allows the wireless resource in a cell to be intelligently allocated amongst various ATM virtual circuits according to their quality of service requirements. But an efficient implementation of ATM in a wireless environment requires a proper mobile network architecture. In particular, the wireless link and medium-access layers need to be cognizant of the ATM traffic, while the ATM layers need to be cognizant of the mobility enabled by the wireless layers. This paper presents an overview of SWANs network architecture, briefly discusses the issues in making ATM mobile and wireless, and describes initial multimedia applications for SWAN.