Performance of a nonblocking space-division packet switch withcorrelated input traffic

This work studies the performance of a nonblocking space-division packet switch in a correlated input traffic environment. In constructing the input traffic model, the author considers that each input is a time division multiaccess (TDM) link connecting to multiple sources. Every source on a link supports one call at a time. Each call experiences the alternation of ON and OFF periods, and generates packets periodically while in ON period. The stochastic property of each call does not have to be identical. Packets from each individual call are destined to the same output. The output address of each call is assumed to be uniformly assigned at random. The author derives both upper and lower bounds of the maximum throughput at system saturation. His study indicates that, if the source access rate is substantially lower than the link transmission rate, the effect of input traffic correlation on the output contentions can generally be ignored. Also, the analysis of each input queue becomes separable from the rest of the switch. The same study is carried out with nonuniform call address assignment     

Nonuniform traffic analysis on a nonblocking space-division packetswitch

The nonuniform traffic performance on a nonblocking space division packet switch is studied. When an output link is simultaneously contended by multiple input packets, only one can succeed, and the rest will be buffered in the queues associated with each input link. given the condition that the traffic on each output is not dominated by individual inputs, this study indicates that the output contention involved by packets at the head of input queues can be viewed as an independent phase-type process for a sufficiently large size of the switch. Therefore, each input queue can be modeled by an independent Geom/PH/1 queueing process. Once the relative input traffic intensities and their output address assignment functions are defined, a general formulation can be developed for the maximum throughput of the switch in saturation. The result indicates under what condition the input queue will saturate. A general solution technique for the evaluation of the queue length distribution is proposed. The numerical study based on this analysis agrees well with simulation results     

Performance analysis of nonblocking packet switch with input andoutput buffers

The performance of nonblocking packet switches such as the knockout switch and Batcher banyan switch for high-speed communication networks can be improved as the switching capacity L per output increases; the switching capacity per output refers to the maximum number of packets transferred to an output during a slot. The N×N switch with L=N was shown to attain the best possible performance by M.J. Karol et al. (1987). Here a N×N nonblocking packet switch with input and output buffers is analyzed for an arbitrary number of L such that 1⩽L⩽N. The maximum throughput and packet loss probability at input are obtained when N=∞     

Performance trade-offs in input/output buffer design for a non-blocking space-division packet switch

Performance trade-offs in buffer architecture design for a space-division packet switching system is studied. As described in Figure 1, the system is constructed by a non-blocking switch fabric and input/output buffers. The capacity of the non-blocking switch fabric is defined by the maximum number of packets, denoted by m, which can be simultaneously routed from multiple inputs to each output. The buffer size at each input is considered to be finite, equal to K. The emphasis here is placed on the input packet loss probability for systems constructed by different ms and Ks. From the performance point of view, we conclude:

• (a) choosing m = 3 or 4 is sufficient to exploit the maximum utilization of a non-blocking switch fabric
• (b) introducing input buffers of moderate size K significantly reduces the packet loss probability.

     

The knockout switch under nonuniform traffic

The knockout switch is a nonblocking, high-performance switch suitable for broadband packet switching. It allows packet losses, but the probability of a packet loss can be kept extremely small in a cost-effective way. The performance of the knockout switch was analyzed under uniform traffic. In this paper, we present a new, more general analytic model of the knockout switch, which enables us to evaluate the knockout switch under nonuniform traffic. The new model also incorporates the effects of a concentrator and a shared buffer on the packet loss probability. Numerical results for nonuniform traffic patterns of interest are presented     

Performance of a broadcast packet switch

The results of a simulation study undertaken to evaluate a high-performance packet-switching fabric supporting point-to-point and multipoint communications are presented. This switching fabric contains several components, each based on conventional binary routing networks. The most novel element is the copy network, which performs the packet replication needed for multipoint connections. Results characterizing the performance of the copy network are presented. Several architectural alternatives for conventional binary routing networks are also evaluated. For example, the performance gains obtainable by using cut-through switching in the context of binary routing networks with small buffers are quantified. One surprising result is that networks constructed from nodes with more then two input and output ports can perform less well than those constructed from binary nodes. This result is quantified and explained     

The maximum throughput of a nonblocking space-division packetswitch with correlated destinations

We propose a discrete-time queueing network model for space-division packet switches, in which the destinations of consecutive packets may be correlated, and different input traffic may have different destination distributions. We show that for switches under saturation, the steady-state probabilities have an approximate product-form solution. The solution is very accurate for real applications where the average packet sizes are often more than 10 times the number of bytes that can be transmitted in one time slot     

Cell loss analysis and design trade-offs of nonblocking ATMswitches with nonuniform traffic

In practical ATM switch design, a proper dimensioning of buffer sizes and a cost effective selection of speed-up factor should be considered to guarantee a specified cell loss requirement for a given traffic. Although a larger speed-up factor provides better throughput for the switch, increasing the speed-up factor involves greater complexity and cost. Hence, it may not be cost effective to increase the speed-up factor for 100% throughput. Moreover, with a given buffer budget, an increase in the speed-up factor beyond a certain value only adds to the cell loss. The paper addresses design trade-offs existing between finite input/output buffer sizes and speed-up factor in a nonblocking ATM switch. Another important issue is the adverse effect on cell loss performance caused by nonuniform traffic (different traffic intensity and unevenly distributed routing). The paper analyzes cell loss performance of ATM switches with nonuniform traffic, and examines the effect of each nonuniform traffic parameter. The authors also provide an algorithm for effective buffer sharing that alleviates the performance degradation caused by traffic nonuniformity     

Scheduling nonuniform traffic in a packet switching system withlarge propagation delay

Transmission algorithms are introduced for use in a single-hop packet switching system with nonuniform traffic and with propagation delay that Is large relative to the packet transmission time. The 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 algorithms are based primarily on sending transmission schedules to the receivers immediately before transmitting each data packet multiple times so that the receiver can maximize the number of packets it captures. An algorithm based on matchings in a random graph is shown to provide mean total delay divided by mean propagation delay arbitrarily close to one, as the propagation delay tends to infinity     

Throughput analysis, optimal buffer allocation, and trafficimbalance study of a generic nonblocking packet switch

A general model is presented to study the performance of a family of space-domain packet switches, implementing both input and output queuing and varying degrees of speedup. Based on this model, the impact of the speedup factor on the switch performance is analyzed. In particular, the maximum switch throughput, and the average system delay for any given degree of speedup are obtained. The results demonstrate that the switch can achieve 99% throughput with a modest speedup factor of four. Packet blocking probability for systems with finite buffers can also be derived from this model, and the impact of buffer allocation on blocking probability is investigated. Given a fixed buffer budget, this analysis obtains an optimal placement of buffers among input and output ports to minimize the blocking probability. The model is also extended to cover a nonhomogeneous system, where traffic intensity at each input varies and destination distribution is not uniform. Using this model, the effect of traffic imbalance on the maximum switch throughput is studied. It is seen that input imbalance has a more adverse effect on throughput than output imbalance     

Performance of two-stage shared fiber delay line optical packet switch under bursty traffic

Packet contention is a major issue in an optical packet switching network. It is not a trivial task to resolve contention due to lack of optical RAM technology. This article proposes a two-stage shared fiber delay line (FDL) optical packet switch for contention resolution. In this article, shared FDLs are used to buffer optical packets, in which a pool of buffer memory is shared among all switch output ports. Most of the existing optical buffering schemes are output-based which require a huge number of FDLs as well as a larger switch size that incur extra implementation cost. However, a shared buffering approach is considered in this article in order to reduce implementation cost. In this article, FDLs are implemented in two stages using an extremely simple auxiliary switch. The proposed switch architecture leads to more efficient use of buffer space. The superiority of the proposed switch architecture has been established by means of extensive simulations. The performance of the proposed switch is investigated under bursty traffic. Simulation result shows that the proposed switch can achieve satisfactory performance at the price of a reasonable amount of FDLs. Moreover, the significance of the proposed switch is confirmed by simulation.     

Using a packet switch for circuit-switched traffic: a queueingsystem with periodic input traffic

Consideration is given to the effects of time-multiplexed stream traffic on the performance of a store-and-forward packet switch. Substantially reducing the amount of buffering in the switch results in only a small probability that an existing circuit will be disrupted during the length of its connection. For example, with a circuit-switched frame of length 1000 and 100% loading, reducing the buffer size from 999 packets to 83 results in only a 10^-6 circuit-disruption probability     

Performance of a packet switch with crossbar architecture

A packet having a crossbar architecture with M inputs and N outputs is considered. Following earlier work, the theoretical capacity of such a switch is found in terms of the throughput of a closed queueing network. A state-dependent server model that approximates the rate at which the switch is transferring packets as a function of the work backlog (the number of packets queued at the switch inputs) is then developed. In this way, the model reflects the fact that such a switch tends to function more efficiently as the work backlog increases. This model yields an accurate method for approximating the entire distribution of the work backlog, as well as mean queue lengths and waiting times     

Analysis of a delay-dependent priority discipline in an integratedmulticlass traffic fast packet switch

A dynamic packet transmission priority discipline, head-of-the-line with priority jumps, is proposed and analyzed for a packet switch serving multiple classes of delay-sensitive traffic. It is shown that, under realistic traffic conditions, the discipline can make the tail probabilities of the delay distributions for the different classes of traffic, in excess of their respective delay requirements, approximately the same, thus resulting in fairness of service and minimization of the maximum tail probability among the different classes. Implementation of the discipline is considered to be relatively simple, and involved processing overhead is minimal     

Performance study on a WDM packet switch with limited-rangewavelength converters

We consider a slotted WDM packet switch with limited-range wavelength converters. The performance of this switch is studied using simulations with various types of data traffic. Results show that the slotted WDM packet switch with a small range of wavelength conversion capability can achieve a performance close to that of a switch with the full range of wavelength conversion capability     

Performances of the Data Vortex switch architecture under nonuniform and bursty traffic

The Data Vortex switch architecture has been proposed as a scalable low-latency interconnection fabric for optical packet switches. This self-routed hierarchical architecture employs synchronous timing and distributed traffic-control signaling to eliminate optical buffering and to reduce the required routing logic, greatly facilitating a photonic implementation. In previous work, we have shown the efficient scalability of the architecture under uniform and random traffic conditions while maintaining high throughput and low-latency performance. This paper reports on the performance of the Data Vortex architecture under nonuniform and bursty traffic conditions. The results show that the switch architecture performs well under modest nonuniform traffic, but an excessive degree of nonuniformity will severely limit the scalability. As long as a modest degree of asymmetry between the number of input and output ports is provided, the Data Vortex switch is shown to handle very bursty traffic with little performance degradation.     

Efficient scheduling of nonuniform packet traffic in a WDM/TDMlocal lightwave network with arbitrary transceiver tuning latencies

A passive-star-based, broadcast-and-select, local lightwave network which can support a limited number of wavelength-division multiplexed (WDM) channels, but serve a much larger number of nodes, is considered. Each node is equipped with one tunable transmitter and one fixed receiver, and each WDM channel is operated in a time-division multiplexed (TDM) fashion for carrying packet traffic. Bandwidth is allocated to the node pairs when traffic flow between them is nonuniform, while also accommodating transceiver tuning latency. Our approach exploits well-known results from scheduling theory to create efficient transmission schedules. Multiprocessor task scheduling heuristics that can be applied to load balancing in a multichannel network is also examined     

Performance analysis of a CDMA network with fixed overlapping sectors in nonuniform angular traffic

The problem of base station antenna assignment (BSAA) with minimum mobile transmit power (MTP) is studied for CDMA networks with fixed overlapping sector antenna architecture (FOSAA) where more than one co-located antenna is used to cover any space in the network. It is first noted that the non-FOSAA has limitations in switching users between in-cell sectors and also out-of-cell sectors in moderately-loaded networks. It is then shown that by employing overlapping sectors in FOSAA, we can exploit the flexibility of assigning a user to one of possibly many potential antenna to effectively support the nonuniform azimuthal traffic. It is also shown that the BSAA problem with minimum MTP is a special case of a general problem that was solved by Hanly and Yates. The process of dynamic cell sectoring is differentiated twofold as cell-breathing (CB) and cell-slicing (CS) and the latter can be viewed as being azimuthal discrete counterpart of the former radial scheme. The hybrid scheme, CB+CS, offers better performance in terms of minimum total MTP in a FOSAA system. Simulation results demonstrate the flexibility and effectiveness of the FOSAA system in nonuniform angular traffic.     

Performance of rearrangeable nonblocking 4×4 switch matriceson LiNbO3

The design, fabrication, and characterization of rearrangeable nonblocking 4×4 switch matrices and the development of a novel ITO (indium-tin-oxide)/Au multilayer electrode that leads to low switching voltages and low DC drift is reported. Results on electrode systems, insertion loss, crosstalk, tolerances in the coupling length, and stability obtained for eight fabricated matrices are given. In comparison to the SiO₂ buffer layers, a reduction in the switching voltage of a factor of 0.66 has been achieved. Insertion losses of fiber pigtailed modules are in the range between 4 and 7 dB. The crosstalk has still to be improved. The stability of the operating points of the switches has been analyzed, showing that the devices must be operated in closed dark housings with a passivation layer in order to avoid optical damage effects from ambient light and to protect them against physical and chemical influences     

具有反馈式光缓存的OPS节点结构性能研究

对反馈式光分组交换节点的性能进行深入分析,并针对现有反馈式光分组交换节点结构的不足,提出一种改进的反馈式光分组交换节点结构,即SMOP-TWC交换结构.最后,本文使用仿真实验的方法对SMOP-TWC交换结构的性能进行深入研究.