Handovers for multi-media Wireless LANs (WLANs) have special requirements, unlike those in the public wireless networks. In this paper, the problems and challenges faced in a multi-media WLAN environment are presented and a multi-tier wireless cell clustering architecture is introduced. New design issues for multi-media handovers are specified and a fast, continuous and efficient hybrid handover protocol is proposed. A prototype of the proposed handover protocol is implemented into a Cambridge Fairisle ATM switch and the results are evaluated. We found that implementing transport mobility for a Wireless ATM environment is not practical as the cell re-routing function is not scalable to increasing cell rate and to the number of mobile connections. It also changes the characteristics of the traffic. Instead, the data link layer mobility implementation is found to work well. The protocol provides symmetric data disruption to traffic flows in both directions and up to seventy five intra-cluster handovers can be supported in a second. Throughout the experiment, cells arrive in sequence with no cell loss observed during the handover, up to the capacity limit of the ATM switch.

Introduction Pegasus 3 is a project of the Universities of Cambridge (GB) and Twente (NL). This is a preliminary paper whose primary function is to state the goals of the project and to describe how we plan to set about reaching them. The theme of the Pegasus project is the design and implementation of generalpurpose operating-system support for distributed multimedia applications. It is our contention that for a system to be a multimedia system, it should endow text, images, audio and video with equal status: Interpreting an audio or video stream should not be a privileged task of special functions provided by the operating system, but one of ordinary user programs. If programs with no special status can process text interactively, then processing audio or video interactively should also be done by programs with no special status. Very few, if any systems exist today that can claim to be multimedia systems in this sense. There is a wide range of multimedia appl

This dissertation considers various problems associated with the scheduling and network I/O organisation found in conventional operating systems for effective support for multimedia applications which require Quality of Service. A solution for these problems is proposed in a micro-kernel structure. The pivotal features of the proposed design are that the processing of device interrupts is performed by user-space processes which are scheduled by the system like any other, that events are used for both inter- and intra- process synchronisation, and the use of a specially developed high performance I/O buffer management system. An evaluation of an experimental implementation is included. In addition to solving the scheduling and networking problems addressed, the prototype is shown to out-perform the Wanda system (a locally developed micro-kernel) on the same platform. This dissertation concludes that it is possible to construct an operating system where the kernel provides only the fu...

The deployment of high speed, multiservice networks within the local area has meant that it has become possible to deliver continuous media data to a general purpose workstation. This, in conjunction with the increasing speed of modern microprocessors, means that it is now possible to write application programs which manipulate continuous media in real-time. Unfortunately, current operating systems do not provide the resource management facilities which are required to ensure the timely execution of such applications. This

le application-specific use of I/O devices. The architecture is applied to several representative classes of device including network interfaces, network connected peripherals, disk drives and framestores. Of these, disks and framestores are of particular interest since they must be shared at a very fine granularity but have traditionally been presented to the application via a window system or file-system with a high-level and coarse-grained interface. A device driver for the framestore is presented which abstracts the device at a low level and is therefore able to provide each client with guaranteed bandwidth to the framebuffer. The design and implementation of a novel client-rendering window system is then presented which uses this driver to enable rendering code to be safely migrated into a shared library within the client. A low-level abstraction of a standard disk drive is also described which efficiently supports a wide variety of file systems, and other applications requiring

The Fairisle project was concerned with ATM in the local area. An earlier paper [9] described the preliminary work and plans for the project. Here we present the experiences we have had with the Fairisle network, describing how implementation has changed over the life of the project, the lessons learned, and some conclusions about the work so far. 1 Introduction The Fairisle project was a three year effort at the Computer Laboratory begun in October 1989, to design and build an ATM local area network, and to investigate the architecture and management algorithms appropriate to the local area. The project included the construction of ATM switches, host interfaces, device drivers, and management software. Within the Computer Laboratory, other research projects such as multimedia, operating systems, workstation architecture and distributed systems are now using the bandwidth provided by the Fairisle network, and providing the network with real data. This paper presents a report of the...

In this paper we present several practical methods for formally verifying an Asynchronous Transfer Mode (ATM) network switching fabric using the Verification Interacting with Synthesis (VIS) tool. We produced Verilog RTL behavioral and netlist structural descriptions of the switch fabric at different levels of hierarchy and established several abstracted models of the fabric. Using various techniques presented in the paper, we provided a number of relevant liveness and safety properties expressible in CTL, and accomplished their verification in reasonable CPU time. Moreover, we performed equivalence checking between the structural and behavioral descriptions of each submodule of the implementation hierarchy.

The Desk Area Network was proposed as an architecture suitable for a multimedia workstation. This paper describes how the architecture has evolved and the demonstration workstation that has been constructed 2 . 1 Introduction Common usage of the term "multimedia" is to describe systems which incorporate both traditional computer data forms, such as text and graphics, and data forms such as audio and video. This presents new problems due to both the isochronous requirements for audio and video and the significantly higher bandwidth that is needed to transport video. The wish to link machines which use this mix of data types is one of the driving forces behind the development of high speed networks based on the Asynchronous Transfer Mode (ATM); these aim to provide the necessary performance and guarantees about the timeliness of data transfers. The Asynchronous Transfer Mode makes use of small fixed size cells to carry data through the network. It is connection oriented and each cell ...

In this paper we present our results on formally verifying the implementation of an Asynchronous Transfer Mode (ATM) network switching fabric using a new class of decision graphs, called Multiway Decision Graphs (MDG). The design we consider is in use for real applications in the Cambridge Fairisle network. We produced the description of the hardware implementation at different levels of abstraction. We then performed the verification of an abstract description model against the description of the gate-level implementation. Using this abstract model, we accomplished the verification of specific properties that reflect the behavior of the Fairisle ATM switch fabric.

ATOMIC is an inexpensive high-speed LAN built by USC/ISI. It is based upon Mosaic technology developed for fine-grain, message-passing, massively parallel computation. Each Mosaic processor is capable of routing variable length packets, while providing added value through simultaneous computing and buffering. ATOMIC adds a general routing capability to the native Mosaic wormhole routing through store-and-forward and path concatenation. ATOMIC aggregate bandwidth scales as the number of nodes increases, and it has a small interface cost. Each ATOMIC channel has a data carrying capacity of 500Mb/s. A prototype ATOMIC LAN has been constructed along with host interfaces and software that provides full TCP/IP compatibility. Using ATOMIC, 1,500 byte packets have been exchanged between hosts at an aggregate transfer rate of more than 1Gb/s. Other tests have demonstrated throughput of 5.25 million packets per second over a single Mosaic channel. The architecture is flexible both ...