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。     

Cell multiplexing in ATM networks

Formulates, analyzes, and compares several connection multiplexing algorithms for a multiplexer residing in the equivalent terminal of the asynchronous transfer mode (ATM) layer at the user premise. The primary goal is to find an algorithm that efficiently combats the cell delay variation (CDV) introduced by the multiplexer. Several performance criteria are examined, one of which is unique to ATM networks. This one is the proportion of arriving cells that do not conform to the traffic contract of the connection. The conformance is being tracked by a generic cell rate algorithm (GCRA) recommended (but not mandatory) by CCITT. Other criteria are the classical buffer requirements and the cell delay. Service fairness among connections is also evaluated with respect to each performance criterion. The impact of the following five multiplexing policies on the performance criteria are evaluated for constant bit rate (CBR) traffic sources. The policies are first in, first out (FIFO), round robin (RR), least time to reach bound (LTRB), most behind expected arrival (MBEA), and golden ratio (GR). Extensive numerical examples reveal that there is no single policy that is best across all criteria. With respect to cell conformance, most behind expected arrival (MBEA) emerges as the preferred one. FIFO is best with respect to cell delay, except for high utilizations where RR dominates. The LTRB is marginally better than all other policies with respect to buffer requirements     

Optimal algorithm for scheduling CBR traffic in ATM switches

A non-blocking input buffered ATM switch that supports CBR and ABR traffic using a TDM scheduler frame is considered. A new TDM scheduler algorithm (largest-first) for CBR traffic is compared with four others, based on the evenness of the distribution of unused timeslots in the scheduling frame. An even distribution of unused slots minimises the average latency and jitter for ABR traffic. Simulation results show that largest-first allocation is the best     

Per-stream jitter analysis in CBR ATM multiplexors

Constant bit-rate (CBR) traffic is expected to be a major source of traffic in high-speed networks. Such sources may have stringent delay and loss requirements and, in many cases, they should be delivered exactly as they were generated. A simple delay priority scheme will bound the cell delay and jitter for CBR streams so that in the network switches CBR traffic will only compete with other CBR traffic in the networks, In this paper we consider a multiplexor in such an environment. We provide an exact analysis of the jitter process in the homogeneous case. In this case we obtain the complete characterization of the jitter process showing the inaccuracies of the existing results. Our results indicate that jitter variance is bounded and never exceeds the constant 2/3 slot. It is also shown that the per-stream successive cell interdeparture times are negatively correlated with the lag 1 correlation of -1/2. Higher order correlation coefficients are shown to be zero. Simple asymptotic results on per-stream behavior are also provided when the number of CBR streams is considered large. In the heterogeneous case we bound the jitter distribution and moments. Simple results are provided for the computation of the bound on the jitter variance for any mix of CBR streams in this case. It is shown that streams with a low rate (large period) do experience little jitter variance. However, the jitter variance for the high-rate streams could be quite substantial     

Engineering ATM networks for congestion avoidance

With the combination of telecommunication, entertainment and computer industries, computer networking is adopting a new method called Asynchronous Transfer Mode (ATM) networking. Congestion control plays an important role in the effective and stable operation of ATM networks. Traffic management concerns with the design of a set of mechanisms which ensure that the network bandwidth, buffer and computational resources are efficiently utilized while meeting the various Quality of Service (QoS) guarantees given to sources as part of a traffic contract. In this paper, the most widely recognized congestion control schemes for ABR service are investigated. Some of these schemes show either lack of scalability or fairness while other well‐behaved schemes may require a highly complex switch algorithm that is unsuitable for implementation in cell‐switching high‐speed ATM networks. A new and improved congestion control scheme is proposed to support the best‐effort ABR traffic. This algorithm provides the congestion avoidance ability with high throughput and low delay, in addition to achieving the max–min fairness allocation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Determination of buffer capacity for payload multiplexing in SDH systems

This paper presents a method for multiplexing C-3 payload according to the ITU-T recommendations G.707, G.708 and G.709. Our technique eliminates signal rate variations, which occur in various multiplexing structures in the synchronous digital hierarchy (SDH) networks, by using a buffer. Calculations related to the buffer capacity for C-3 payload are also presented in this paper. The proposed methodology is expected to be an efficient solution for multiplexing C-3 and other containers in the SDH networks. © 1997 John Wiley & Sons, Ltd.     

Interleaving schemes for ATM multiplexing of MPEG video sources

The authors analyse the performance of two interleaving schemes, called frame-oriented and cell-oriented, for statistical multiplexing of MPEG video sources. Simulations using two long MPEG sequences show that there is a trade-off in cell loss probability and delay jitter when selecting the interleaving scheme     

Capacity allocation in statistical multiplexing of ATM sources

Discusses the allocation of the available capacity of a statistical multiplexer to serve a number of heterogeneous on-off sources, with the cell loss rate as the performance criterion. In order to avoid using potentially lengthy simulations, the authors have derived computationally efficient bounds and asymptotic approximations for the cell loss rate. The union of all partitions of the available capacity which satisfies the capacity bound and the performance criterion is defined as the capacity region. Both linear approximation and nonlinear approximation of the capacity region are investigated. It is shown that the linear approximation is reasonably accurate when the activity factors of the sources are not too high (less than 0.8). For the case where the linear approximation appears too optimistic, a simple nonlinear approximation for determining the capacity region is suggested. The accuracy of the method is demonstrated using numerical examples     

Speedup and buffer division in input/output queuing ATM switches

The capacity of a switch is built out of two factors: space parallelism and speedup. A switch has space parallelism if more than one input port can transmit simultaneously. Speedup is the ratio of the switch's internal link speed over the incoming link speed. An input-queuing switch uses only the first factor (space parallelism), and a share-medium or a share-memory output queuing switch uses only the second factor (speedup). However, to build a large switch, both factors are normally used. A large switch's capacity can be built with less space parallelism (the space factor), but more speedup (the time factor), or vise versa. Buffers are needed at both the input and the output ports. In this paper, we show how to divide the buffers between the input and the output queues and how the optimal division is affected by the (space, time) combinations.     

Optimal buffer management policies for shared-buffer ATM switches

Shared-buffer ATM switches can have severe cell loss under asymmetrical or heavy loading conditions, which makes buffer management essential. In this paper, we study the shared-buffer system under the class of all work-conserving pushout policies and derive the properties of the optimal policy, which gives the least-average expected total cell loss probability. In a 2×2 system with independent identically distributed Bernoulli arrivals, we show that the optimal policy can be characterized by a single threshold. In the case of correlated arrivals, modeled by a discrete batch Markovian arrival process, the optimal policy has multiple thresholds, one for each phase of the arrival process. For the N×N shared buffer ATM switch, we are unable to prove optimality of any policy, but we study the system via simulations. We provide a dynamic buffer management policy and compare its performance with that of static threshold-type policies     

Physical performance limits for shared buffer ATM switches

Performance studies, linking ATM switch capabilities to physical limitations imposed by integrated circuit technology, have been scarce. This paper explores trends in circuit capabilities, and makes projections toward the 0.25-μm technologies that will be available to all switch designers in the year 2000. The limits imposed by circuit technology are applied to shared buffer ATM switches. We determine requirements and physical limits for buffer capacity, buffer throughput, chip I/O throughput, and power dissipation. As a result, we are able to project chip counts, aggregate switch throughputs, and switch dimensions. As well, performance capabilities of single-chip shared buffer switches are estimated. A single-chip shared buffer switch implemented in 0.25-μm technology will be capable of an aggregate throughput of 1.3 Tb/s, will accomplish almost arbitrarily low cell loss rates for bursty traffic, and may be integrated together with translation tables supporting hundreds of connections per port     

A hybrid analysis/simulation for ATM performance with application to quality-of-service of CBR traffic

A discrete time queueing model for the performance of an ATM system is analyzed using matrix analytic methods. Time is segmented into slots with each slot equal to the transmission time of one ATM cell. The ATM system is modeled as a single server queue with Markovian arrivals and service time equal to one slot. The arrival process includes as a special case the superposition of on-off sources, possibly heterogeneous. The queueing model is of the M/G/1 type. By exploiting the structure of the M/G/1 type Markov chain, the complexity of the solution to the problem is reduced to only the inversion of a 2×2 matrix irrespective of the size of the Markov chain. This simplification allows us to investigate Constant Bit Rate (CBR) traffic performance (or quality-of-service) issues through a hybrid analysis/simulation approach. Specifically, we analyze the impact of on-off background traffic on the probability of consecutive cell losses, cell delay variation, and traffic shaper or playback buffer underflow and overflow probabilities of CBR traffic sources.     

A Bernoulli process approximation with buffer size adjustment forthe analysis of an ATM multiplexer

The heterogeneity and the burstiness of input source traffic together with large size of the shared buffer make it difficult to analyze the performance of an asynchronous transfer mode (ATM) multiplexer. Based on the asymptotic decay rate of queue length distribution at the shared buffer, we propose a Bernoulli process approximation for the individual on-off input source with buffer size adjustment, which gives a good upper bound of the cell loss probability     

Statistical multiplexing gain for variable bit rate video codecs in ATM networks

Asynchronous transfer mode (ATM) broadband networks will support variable bit rate video codecs, which are capable of maintaining a constant picture quality. To demonstrate this capability, a prototype hardware video coder has been developed in the Siemens Central Communications Laboratories. The prototype uses interframe coding, combined with a discrete cosine transform, and is able to reproduce the original picture quality, independent of signal sources or picture material used. A gain in transmission efficiency is expected when several video sources share a common ATM channel (‘statistical multiplexing’). This paper reports on a series of measurements that have been performed using this coder for a large variety of video sources to determine the possible gain in transmission efficiency. The main results are: for realistic video phone scenes, up to about three times the number of signals can be transmitted compared to transmision with constant rate and the same picture quality, if the output signal of the coder has been smoothed over a period of one frame. Smoothing over shorter periods reduces the potential gain substantially. The statistical multiplexing gain increases with the duration of the picture sequences due to the criterion of constant picture quality. It varies very little with the acceptable packet loss rate.     

Dynamic capacity allocation and hybrid multiplexing techniques for ATM wireless LANs

We consider digital wireless multimedia LANs and timevarying traffic rates. To deal effectively with the dynamics of the timevarying traffic rates, a Traffic Monitoring Algorithm (TMA) is deployed to dynamically allocate channel capacities to the heterogeneous traffics. The TMA is implemented as a higher level protocol that dictates the capacity boundaries within two distinct framed transmission techniques: a Framed Time DomainBased (FTDB) technique and a Framed CDMA (FCDMA) technique. The performance of the TMA in the presence of the FTDB technique is compared to its performance in the presence of the FCDMA technique for some traffic scenarios. The performance metrics used for the TMAFTDB and TMAFCDMA combinations are channel capacity utilization factors, traffic rejection rates, and traffic delays. It is found that the TMAFTDB is superior to the TMAFCDMA when the speed of the transmission links is relatively low and the lengths of the transmitted messages are relatively short. As the speed of the transmission links and the length of the transmitted messages increase, the TMAFCDMA eventually outperforms the TMAFTDB.     

Approximation to M/D/1 for ATM CAC, buffer dimensioning and cellloss performance

The authors derive a new, accurate, closed form approximation for the M/D/I queue. This can be arranged to yield expressions for the cell loss probability, the admissible load and the buffer length. These expressions have a direct application to cell scale queueing in ATM networks     

Bandwidth-dependent scheduling algorithm to limit cell delayvariation for CBR traffic in ATM networks

A multiplexing control scheme is proposed for limiting the cell delay variation (CDV) caused by multiplexing of constant bit rate (CBR) traffic in asynchronous transfer mode (ATM) networks. The control scheme is based on a bandwidth-dependent scheduling algorithm. The limitation of the CDV is proved     

TDMA multiplexing of ATM cells in a residential access SuperPON

Time division multiple access (TDMA) multiplexing of ATM cells from thousands of residential customers toward the common feeder of a passive optical network (SuperPON) tree obviates the need for an equal number of optical line terminations (OLTs). All upstream transmissions converge by means of the passive splitters/combiners to just one OLT unit which serves all by time sharing. The ability to reach such a high splitting ratio became possible by the development of bursty mode optical amplifiers (OAs). In addition, OAs make possible a 100-km-long feeder which can bypass the local exchange into the first core switch, bringing further savings to both initial and running costs. These techniques allow SuperPONs to lower the access cost per customer, holding for the promise of ushering into domestic local loops the photonics revolution which has already transformed the transmission plant. These savings, however, can only be realized under the assumption that the system can accept high loading before exceeding the limits of quality of service (QoS) requirements and without distorting the egress traffic in a way that jeopardizes the statistical estimates on which ATM connection acceptance was based. Solutions to the problem of traffic arbitration, respecting the idiosyncrasies of each traffic class and suitable for fast implementation, are offered     

An analysis of statistical multiplexing in an ATM transport network

The traffic characteristics of an asynchronous transfer mode (ATM) network are analyzed by theoretical methods. A new method is proposed to express the burstiness of the cell arrival process. Both statistical multiplexing and statistical bandwidth allocation are quantitatively evaluated. When packetized video traffic and voice traffic are multiplexed, the number of multiplexable sources strongly depends on the peak bit rate of the multiplexed video sources, and statistical bandwidth allocation is ineffective without control. On the other hand, lowering the peak bit rate of video traffic effectively improves bandwidth utilization