Advanced input queuing is an attractive, promising architecture for high-speed ATM switches, because it combines the low cost of input queuing with the high performance of output queuing. The need for scalable schedulers for advanced input queuing switch architectures has led to the development of efficient distributed scheduling algorithms. We introduce a new distributed scheduling algorithm, FIRM, which provides improved performance characteristics over alternative distributed algorithms. FIRM achieves saturation throughput 1 with lower delay than the most efficient alternative (up to 50% at high load). Furthermore, it provides improved fairness (it approximates FCFS) and tighter service guarantee than others. FIRM provides a basis for a class of distributed scheduling algorithms, many of which provide even more improved performance characteristics.

FIRM: a class of distributed scheduling algorithms for high-speed ATM switches with multiple input queues

Presents a new scheduler, the two-dimensional round-robin (2DRR) scheduler, that provides high throughput and fair access in a packet switch that uses multiple input queues. We consider an architecture in which each input port maintains a separate queue for each output. In an N/spl times/N switch, our scheduler determines which of the queues in the total of N/sup 2/ input queues are served during each time slot. We demonstrate the fairness properties of the 2DRR scheduler and compare its performance with that of the input and output queueing configurations, showing that our scheme achieves the same saturation throughput as output queueing. The 2DRR scheduler can be implemented using simple logic components, thereby allowing a very high-speed implementation. >

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Two-dimensional round-robin schedulers for packet switches with multiple input queues

A new model of nonuniform traffic is introduced for a single-hop packet-switching system. This traffic model allows arbitrary traffic streams subject only to a constraint on the number of data packets which can arrive at any, individual source in the system or for any individual destination in the system over time periods of specified length. The nonuniform traffic model is flexible enough to cover integrated data networks carrying diverse classes of data. The system model is rather general, and includes passive optical star wavelength-division networks. Transmission algorithms are introduced for a single-hop packet-switching system with such nonuniform traffic and with propagation delay that is negligible relative to the packet length. The algorithms are based on collision-free scheduling of packets using graph-matching algorithms since the global state of the system is known to all stations at any time.

Scheduling nonuniform traffic in a packet-switching system with small propagation delay

We consider the fundamental delay bounds for scheduling packets In an N times N packet switch operating under the crossbar constraint Algorithms that make scheduling decisions without considering queue backlog are shown to incur an average delay of at least O(N) We then prove that O(log(N)) delay is achievable with a simple frame based algorithm that uses queue backlog information This is the best known delay bound for packet switches, and is the first analytical proof that sublinear delay is achievable in a packet switch with random inputs

/pdf/logarithmic-delay-for-n-times-n-packet-switches-under-the-3dso1hkskc.pdf

Logarithmic Delay for $N \times N$ Packet Switches Under the Crossbar Constraint

A combined random/reservation multiple access (CRRMA) scheme for packet-switched communication over a global beam satellite with on-board processing is proposed and analyzed. Channel time is divided into contiguous slots; each slot contains N minislots for transmission of request packets and N' minislots for data. With N substantially smaller than the number of earth stations, collisions will occur in request packet transmissions. Two channel access algorithms for the CRRMA model are proposed: uncontrolled channel access (UCA) and controlled channel access (CCA). UCA is simpler but has an inherent stability problem particularly when the number of minislots N is small. The CCA algorithm restricts the transmission of request packets for new arrivals to take place only when the slot is in the FREE state. With N = 3 , the CCA algorithm exhibits good delay-throughput characteristics. As N increases, the UCA algorithm offers stable operation. For N \geq 5 the simpler UCA algorithm is preferred over CCA.

Combined Random/Reservation Access for Packet Switched Transmission Over a Satellite with On-Board Processing: Part I--Global Beam Satellite

In this paper, we examine the problem of time-slot assignment in an SS/TDMA system operating in a packet-switched environment. We seek to assign time slots in order to minimize average packet waiting time and in order to maximize transponder utilization. We show that an assignment which achieves both objectives exists and develop a branch-and-bound algorithm to find it. In addition, we suggest several heuristics which require much less computational effort and give very close to optimal results. We derive theoretical bounds on the performance of these heuristics and perform simulation trials to show that, on average, the heuristics are very much better than their bounds suggest, and are, in fact, extremely close to optimal.

I. Gopal

Papers

Minimizing Packet Waiting Time in a Multibeam Satellite System