具有大容量缓存器的ATM网络交换节点的接入允许控制

本文讨论了ＡＴＭ网络交换节点的缓存器容量较大时,如何实现实时接入允许控制的问题。我们从大量的计算机模拟的结果中发现,对于符合负指数分布的马尔可夫ＯＮ／ＯＦＦ单一类型或多类型信源,在信元及系统的其它参数保持不变的条件下,信元丢失概率和丢失率,只取决于缓存器容量与信元平均突发长度的比值。本文从“生灭过程”出发加以了证明。     

Loss performance analysis of an ATM multiplexer loaded withhigh-speed on-off sources

The performance of an asynchronous transfer mode (ATM) multiplexer whose input consists of the superposition of a multiplicity of homogeneous on-off sources modeled by a two-state Markovian process is studied. The approach is based on the approximation of the actual input process by means of a suitably chosen two-state Markov modulated Poisson process (MMPP), as a simple and effective choice for the representation of superposition arrival streams. To evaluate the cell loss performance, a new matching procedure that leads to accurate results compared to simulation is developed. The application limits of the proposed method are also discussed. The outstanding physical meaning of this procedure permits a deep insight into the multiplexer performance behavior as the source parameters and the multiplexer buffer size are varied     

Performance analysis of an ATM multiplexer loaded with VBR trafficgenerated by multimode speech coders

Multimode coders are able to exploit the different characteristics of the speech waveform and to take into account the different peculiarities of background noise, thus allowing improvements in both signal reconstruction and network-offered load. In this context the variable rate code excited linear prediction (VR-CELP) coding, that is, a multimode variable bit rate (VBR) coding based on the CELP technique, has been introduced in the literature and is currently being considered for use in various applications, especially in the third-generation UMTS cellular systems. The target of the paper is to introduce an efficient and accurate framework allowing a network designer to analyze the impact of multimode VBR speech coding on the quality of service (QoS) provided by a wireless/wired ATM network. In order to capture the coder output characteristics, we propose to model a VR-CELP voice source by using a switched batch Bernoulli process (SBBP). More specifically, three models are introduced and compared in terms of accuracy and simplicity in determining network performance. As a result of the comparison, a four-state model has been chosen as the best tradeoff. The model is then used to analytically derive the loss probability and the jitter probability density function of an ATM multiplexer loaded by a number of VR-CELP sources. Finally, the proposed paradigm has been assessed in a case study where we demonstrate that, for a given output ATM link capacity and for a number of telecommunication services involving voice transmission, VR-CELP coding performs better than traditional on-off coding     

与多媒体信源模型弱相关的ATM复接器监管方案

本文提出一种与信源模型弱相关的复接器监管方案－－采用模糊漏桶控制方法改变令牌产生速率,对多媒体信源接入实施动态带宽分配。用ＭＭＢＰ模型及其合成讨论了该方案的可能性给出了模糊控制方案和规则,计算机仿真表明,在多个不同速率不同特性的语音、图像、数据信源接入时延该方法能很好地满足低时延低丢失的要求,提高带宽利用率,傅诉异步和编者复用特性被有效、充分地利用。     

Analysis of DQLT scheduling policy for an ATM multiplexer

This letter suggests a modified priority scheduling policy for the asynchronous transfer mode (ATM) multiplexer, which is called DQLT. In the dual queue length threshold (DQLT) method, there exist two queues: (1) Q₁ is for nonreal-time traffic and (2) Q₂ is for real-time traffic and each queue has its own threshold to adaptively control the buffer congestion. If Q₁ is congested over the threshold T₁ one cell at the head of Q₁ moves into Q₂ in a slot time. It is shown that the DQLT method gives intermediate performance between those of minimum laxity threshold (MLT) and queue length threshold (QLT) policy, but its control method is quite simpler     

An error-controlled approximate analysis of a stochastic fluid flowmodel applied to an ATM multiplexer with heterogeneous on-off sources

The stochastic fluid flow approach is applied to the analysis of the cell loss performance of an ATM multiplexer. The input traffic stream offered to the multiplexer is the superposition of heterogeneous on-off sources with independent and exponentially distributed on and off times. The focus is on the numerical investigation of the steady-state behavior of models involving very large state spaces. To this end, an efficient algorithm for the evaluation of tight upper and lower bounds of the cell loss probability is developed. The algorithm allows a significant reduction of the computational burden, while yielding a guaranteed overestimate of the error implied by the proposed approximation of the cell loss probability. Numerical results are presented both to assess the tightness of the proposed bounds and to gain insight into the behavior of heterogeneous traffic mixes. The main conclusion, from the multiplexer performance evaluation point of view, is that it is not convenient to mix very different traffic streams in a completely shared FIFO buffer, without some kind of control     

A prototype broadcast-and-select photonic ATM switch with a WDMoutput buffer

A rack-mounted prototype of a broadcast-and-select (B and S) photonic ATM switch is fabricated. This switch has an optical output buffer utilizing wavelength division multiplexed (WDM) signals. The WDM technology solves. The cell-collision problem in a broadcast-and-select network and leads to a simple network architecture and the broadcast/multicast function. The prototype can handle 10-Gb/s nonreturn-to-zero (NRZ) coded cells and 5-Gb/s Manchester-coded cells and has a switch size of four. In this prototype, the level and timing design are key issues. Cell-by-cell level fluctuation is overcome by minimizing the loss difference between the optical paths and adopting a differential receiver capable of auto-thresholding. The temperature control of delay lines was successful in maintaining the phase synchronization. Using these techniques, we are able to provide a WDM highway with a bit error rate of less than 10^-12. Fundamental photonic ATM switching functions, such as optical buffering and fast wavelength-channel selection, are achieved. We show our experimental results and demonstrate the high performance and stable operation of a photonic ATM switch for use in high-speed optical switching systems as an interconnect switch for a modular ATM switch and an ATM cross-connect switch     

A new priority control of ATM output buffer

A new ATM output buffer management strategy with priority control function is proposed, based on four types of cell classes. This strategy can use system resource more effectively, meet the quality of service (QOS) requirements (i.e. cell loss probabilities and delay characteristics) of different services, and also can reduce the complexity of buffer. Furthermore, overload from lower priority traffic doesn't degrade the performance of higher priority traffic (i.e. cell loss rate and cell delay characteristics).     

Queuing analysis of shared‐buffer ATM switches with grouped output channels

Shared buffering and channel grouping are powerful techniques with great benefits in terms of both performance and implementation. Shared‐buffer switches are known to have better performance and better utilization than input or output queued switches. With channel grouping, a cell is routed to a group of channels instead of a specific output channel. In this way, congestion due to output contention can be minimized and the switch performance can therefore be greatly improved. Although each technique is well known by itself in the traditional study of queuing systems, their combined use in ATM networks has not been much explored previously. In this paper, we develop an analytical model for a shared‐buffer ATM switch with grouped output channels. The model is then used to study the switch performance in terms of cell loss probability, cell delay and throughput. In particular, we study the impact of the channel grouping factor on the buffer requirements. Our results show that grouping the output channels in a shared‐buffer ATM switch leads to considerable savings in buffer space. Copyright © 2001 John Wiley & Sons, Ltd.     

Switched bath Bernoulli process (SBBP) and the discrete-timeSBBP/G/1 queue with application to statistical multiplexer performance

A doubly stochastic point process is proposed and analyzed. It is a switched batch Bernoulli process (SBBP) for modeling bursty and correlated input to discrete-time queuing systems. Through the investigation of the counting process, statistical characterization measures of the SBBP are explicitly obtained. A discrete-time single-server queue with SBBP input and general service time (SBBP/G/1) is then considered. The SBBP/G/1 queue has a potential applicability to a statistical multiplexer in the network. The supplementary variable technique is used to obtain the probability generating functions of performance measures in the SBBP/G/1 queue. It is shown how the SBBP is suitable for analyzing a discrete-time queue with bursty and correlated input     

A discrete-time queueing model of the shared buffer ATM switch with bursty arrivals

We model the shared buffer ATM switch as a discrete-time queueing system. The arrival process to each port of the ATM switch is assumed to be bursty and it is modelled by an interrupted Bernoulli process. The discrete-time queueing system is analyzed approximately. It is first decomposed into subsystems, and then each subsystem is analyzed separately. The results from the subsystems are combined together through an iterative scheme. The analysis of each subsystem involves the construction of the superposition of all the arrival processes to the switch. Comparisons with simulation data showed that the approximate results have a good accuracy.Supported in part by DARPA under Grant No. DAEA18-90-C-0039.Work done while on a sabbatical leave of absence at the Computer Science Department of North Carolina State University.     

Calculation and analysis of compensation buffer size in multimediasystems

In multimedia systems end to end delay jitter has a great impact on the continuity of information playback. Therefore, it is necessary to compensate for delay variations to preserve the intramedia and intermedia temporal relationships. A buffer at the destination site is often adopted to compensate for the delay jitter. In this paper, a mapping relationship from P_QoS to buffer which is used to compensate for delay variations is given based on delay jitter statistics, and its theoretical analysis is also shown. So the buffer size of a multimedia synchronization system can be determined     

Traffic studies of a multiplexer in an ATM network and applications to the future broadband ISDN

In the first part of this paper the influence of the arrival process on these three performance parameters is discussed. The values of these three performance parameters depend strongly on the utilization distribution over the input trunks of the multiplexer while the total utilization on the input trunks is fixed. If there is the same utilization on all input trunks, the values of these three performance paramters reach a maximum. This result is also valid for an ATM switching matrix with a separate FIFO buffer at each output trunk. In the second part of this paper some examples are provided of how to apply the results of these studies to the future broadband ISDN which is intended to transmit services with very high bit rates (e.g. 135 Mb/s) as well as services with very low bit rates (e.g. 64 kb/s).     

Estimation of equivalent bandwidth without modeling arrival processes for connection admission control in an ATM multiplexer

The traffic modeling is a key element in analyzing and simulating communications network. Most of the previously studied approaches to the connection admission control (cac) are based on an assumed arrival process model. However, there are some limits to apply the assumed model to the real environment. In this paper, we study a connection admission control (cac) method without assuming arrival processes in an atm multiplexer when homogeneous traffics are multiplexed. To obtain the equivalent bandwidth (eb) without modeling arrival processes, the concept of equivalent bandwidth convergence (ebc) is proposed and implemented by using the upper bound of the first derivative of cell loss rate (clr) for the load. With the ebc concept, one can avoid modeling of the arrival process and implement the cac simply and effectively. We show by numerical examples the convergence process of the average clr and the eb for voice and video traffics, and the robustness of the ebc concept.     

Design and feasibility analysis of an innovative integratedgrating-assisted add-drop multiplexer

An integrated optical add-drop multiplexer (OADM), based on a symmetric coupler with a superimposed innovative grating, is proposed. The device has, theoretically, no backreflection at the input and add ports, and does not require a critical positioning of the grating, thus simplifying device fabrication and allowing thermal tuning. Simulations for a glass-on-silica technology show the excellent performances of the proposed device, and the analysis of the sensitivity highlights the specifications that have to be met in the fabrication tolerance     

Performance analysis of a voice/data multiplexer based on Markovrenewal process modelling

Voice and data transmission on a common link is modelled as a Markov renewal process. The performance of an integrated voice/data multiplexer with arbitrary message length distribution and nongated service discipline, particularly mean data message delay, is analyzed using the model. Numerical results are presented     

A discourse analysis of software documentation: implications forthe profession

To discover the similarities and differences between primary and secondary computer manuals, and to account for the popularity of the secondary texts, two best-selling books for word processing and spreadsheet programs are compared to documentation supplied by the manufacturer. A heuristic for analyzing software documentation based on cognitive and rhetorical principles is developed and applied to the corporate documentation for (WordPerfect 5.0) in contrast to Stewart's Using WordPerfect 5 from Que, and the corporate documentation from `Lotus 1-2-3' in contrast to Gilbert and Williams's `The ABC's of 1-2-3 from Sybex.' It is shown that the trade texts from Que and Sybex contain more conceptual background information than the corporate documentation and differ in their rhetorical stance: the writers provide a richer context by giving more examples for applying the software; the writers provide global and structural frameworks; the writers use persuasive marketing techniques to ease the reader's anxieties and remind them of the software's benefits; and the writers identify themselves     

A theoretical analysis of a buffer frame size conversion algorithm for audio applications ensuring minimum latency

In implementing digital signal processing (DSP) algorithms for audio real-time applications, one is frequently faced with problems regarding incompatibilities between the hardware buffer length (the internal buffer of a professional sound card) and the software buffer size imposed by the underlying algorithm (due to i.e. multirate or FFT constraints). This mismatch is solved by proper frame size conversion algorithms which inevitably introduce delay. In this context, this paper presents a buffering scheme together with a theoretical proof of the minimum delay property shown by it. Some examples derived from frequently encountered issues in DSP applications are reported.     

The design and analysis of an ATM multicast switch with adaptivetraffic controller

The paper describes several improvements to a nonblocking copy network proposed previously for multicast packet switching. The improvements provide a complete solution to some system problems inherent in multicasting. The input fairness problem caused by overflow is solved by a cyclic running adder network (CRAN), which can calculate running sums of copy requests starting from any input port. The starting point can change adaptively in every time slot based on the overflow condition of the previous time slot. The CRAN also serves as a multicast traffic controller to regulate the overall copy requests. The throughput of a multicast switch can be improved substantially if partial service of copy request is implemented when overflow occurs. Call-splitting can also be implemented by the CRAN in a straightforward manner. Nonuniform distribution of replicated packets at outputs of the copy network may affect the performance of the following routing network. This output fairness problem due to underflow is solved by cyclically shifting the copy packets in every time slot. An approximate queueing model is developed to analyze the performance of this improved copy network. It shows that if the loading on each output of the copy network is maintained below 80%, the average packet delay in an input buffer would be less than two time slots     

A new approximation for analyzing the multiplexing of bursty sources in ATM networks

This paper is concerned with the analysis of an asynchronous transfer mode (ATM) multiplexer serving bursty applications such as voice, image, and high-speed data. The model used is a GI _i /D/1 discrete-time single-server queueing system: the arrival process is a superposition of several random processes, and the departure process is a deterministic with a FCFS discipline. The difficulty in solving such a queueing system depends on the model chosen for the individual traffic sources. For the case in which the cell arrival stream from the individual sources is modeled as a Bernouli process, an exact solution is possible. The problem with such a model is that it does not incorporate the effect of burst length, which has been shown through simulation experiments to have a significant effect on the performance. A more realistic model that takes into consideration the impact of the burst length is considered in this study. In particular, an alternating-state Markov process is chosen to model the individual arrival stream.The solution of a GI _i /D/1 queueing system with the arrival process being a superposition of several renewal processes is in general intractable. This paper obtained a new approximation we refer to as the three-parameters approximation (TPA). This approximation was based on the asymptotic properties of the aggregate traffic and the congestion estimates from the simulation experiments. The TPA solution was found to be dependent on three parameters: number of sources, overall traffic intensity at the queue, and multiplexing factor. The TPA is an improvement of a previous approximation developed in analyzing packet voice system.In addition, the study determined an optimal operating point for the ATM multiplexer and the ATM switch that takes into account the tradeoff between delay and throughput. In particular, an optimal operating point is specified by the traffic loading that maximizes the queueing power. This optimal operating point is used to contrast the performance of ATM with synchronous transfer mode (STM).