Statistical multiplexing and mix-dependent alternative routing inmultiservice VP networks

We consider problems in traffic integration and routing for virtual path (VP)-based multiservice networks. The objective is to exploit statistical multiplexing among various traffic types in order to improve system utilization. Difficulties arise due to statistical multiplexing since a connection's bandwidth requirement depends on the characteristics of the interfering traffic. We first consider whether segregating heterogeneous traffic with different quality of service (QoS) requirements on separate VPs is desirable. Next we consider routing heterogeneous permanent connections given a predefined traffic type mix onto multiple VPs between a source destination pair. We show that it is not necessarily advantageous to have each VP carry every traffic type. In fact, perhaps surprisingly, an optimum solution to this problem suggests that only a small number of traffic types, or even homogeneous traffic, need be present on each VP. Based on this observation, we propose a simple alternative routing algorithm with routing sequences depending on the traffic mix     

Statistical multiplexing with loss priorities in rate-basedcongestion control of high-speed networks

Statistical multiplexing with loss priorities is a central element in ATM-based B-ISDN. Cell priorities arise from the marking schemes employed by the access regulators to identify excess cells, which are dropped during periods of congestion, Also, in real time applications, such as hierarchically coded voice and video, cells are assigned priorities which correspond to their importance to service quality, so that when congestion occurs only the least important are dropped. The authors present a stochastic fluid model of statistical multiplexing with loss priorities. Each Markov modulated fluid source generates streams of different priorities. The burstiness of each stream and the correlation between the priority streams are captured in the mode. The loss priority is implemented by selectively discarding cells of certain priority classes when the buffer content exceeds a corresponding threshold. To handle high dimensional source models, the authors develop an algebraic theory for the efficient computation of the spectrum of the statistical multiplexing system, which generalizes previous results for on-off sources. It is shown that to obtain the solution of the statistical multiplexing problem with J priority classes, J different 1-class problems need to be solved, together with a system of linear equations which describe the behavior of the stationary distribution at the thresholds. The numerical results demonstrate the manner in which i) the threshold level controls the tradeoff between delay of higher priority cells and the loss probability of lower priority cells, and ii) the buffer size controls the loss probability of higher priority cells     

A buffer allocation scheme for ATM networks: complete sharing basedon virtual partition

Buffer allocation to provide an efficient and fair use of the available buffer spaces is critically important for ATM networks. A complete sharing with virtual partition (CSVP) strategy for buffer management at a multiplexer or an output port of an output buffered switch is proposed and analyzed. The total buffer space is partitioned based on the relative traffic loads (measured or estimated). Virtual partition allows a newly arriving cell belonging to an oversubscribed type to occupy the spare space of an undersubscribed type, and to be overwritten when necessary. Using a fluid flow approach, a set of partial differential equations with a triangular stability region is established to characterize the dynamics of a system supporting two traffic flows. Under a buffer full condition, the system behavior is described by a set of non-homogeneous ordinary differential equations. The cell loss probability for each traffic type is obtained by solving the ordinary differential equations. Numerical examples indicate that by appropriately selecting the partitions, the CSVP method may be used to provide differential cell loss rate requirements by the different traffic types     

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.     

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     

Statistical multiplexing with a variable number of servers

A statistical multiplexing system that varies dynamically between a single-server system and an m-server system is analyzed. It is shown that the system has the same mean response time as a single-server system and that it betters the mean waiting time of an m-server system.     

Optical time division multiplexing: systems and networks

The recent advances in optical time division multiplexed (OTDM) systems and components research show the technique to be highly suited to the generation and transmission of high capacity data on a single optical carrier. This approach uses a single wavelength to carry capacities of at least 40 Gb/s. Such systems are based on a clock frequency and tributary data rates which are easily accessible using electronic components. Short optical pulses are used in a return-to-zero data transmission format with temporal interleaving to map a number of optical data channels into a single electronic clock cycle. It is an approach that can be used to achieve extremely high data-rate bit interleaved systems. This article summarizes the developments in this field and outlines a possible methodology to evolve transport networks to encompass the potential that both WDM and OTDM have to offer     

Subcarrier multiplexing in optical communication networks

The bandwidth capability of optical communication networks continues to increase. Optical fibres have low attenuation windows of many thousands of gigahertz and individual optical sources can now be modulated at rates well above 20 GHz. This is much faster than the switching rates of the electronic components needed to achieve multiplexing in applications such as time division multiplexing (TDM). Subcarrier multiplexing, which uses analogue intensity modulation of optical sources with readily available microwave components, can provide an elegant method of using the optical bandwidth and is capable of graceful evolution for future networks     

Optical multiplexing in fiber networks: progress in WDM and OTDM

WDM systems are maturing and are in use in real point-to-point applications. The technology has also become of interest in the development of all-optical networks, and in this context the performance of WDM can be more critical. In some networks, multiple-access demands that a large number of channels be deployed over long distances, and in these cases the performance of WDM may be degraded by crosstalk arising from fiber nonlinearity. Other problems arise from non-ideal components such as optical amplifiers, switches, and multiplexers/demultiplexers, Much activity in WDM has been understanding its limitations and improving component performance, Some of the limitations imposed may be overcome by the use of OTDM, and research in this area continues to be of interest and importance. However, OTDM is less mature, and much activity is concerned with the realization of robust subsystems such as sources and demultiplexers. It is likely that in the longer term networks will employ a combination of WDM and OTDM     

Home networks: a standards perspective

An overview of home networks, as defined by the Home Networking and IT (HNIT) Division of the Consumer Electronics Association (CEA), is presented in this paper. HNIT's membership includes consumer electronics executives, marketing and market research professionals, engineers, and standards developers, which provide a broad perspective on this subject. The article first introduces the rational behind the definition. From that baseline, it moves on to review some of the most critical issues home networks must address so as to meet the expectations of content and service providers-and ultimately those of the consumer. With that foundation, the article provides an overview of each of the major home networking protocols and standards, as well as their respective strengths and weaknesses. Also included is a discussion of the interrelationships between the major standards and industry specifications: in other words, how they will work together to create a seamless home network environment     

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.     

Dense wavelength division multiplexing networks: principles andapplications

The very broad bandwidth of low-loss optical transmission in a single-mode fiber and the recent improvements in single-frequency tunable lasers have stimulated significant advances in dense wavelength division multiplexed optical networks. This technology, including wavelength-sensitive optical switching and routing elements and passive optical elements, has made it possible to consider the use of wavelength as another dimension, in addition to time and space, in network and switch design. The independence of optical signals at different wavelengths makes this a natural choice for multiple-access networks, for applications which benefit from shared transmission media, and for networks in which very large throughputs are required. Recent progress in multiwavelength networks are reviewed, some of the limitations which affect the performance of such networks are discussed, and examples of several network and switch proposals based on these ideas are presented. Discussed also are critical technologies that are essential to progress in this field     

Evolving access networks: a European perspective

The diversity of telecommunications markets and access network infrastructure among the countries of Europe is a complicating factor in the development of effective standards for Europe's future access networks. The need for evolving access networks to make efficient use of a wide variety of existing infrastructure may at times conflict with the long-term requirement for a stable platform of self-consistent standards which allow future-proof evolution. In light of these constraints, the authors summarize progress made in the European Telecommunications Standards Institute (ETSI) toward standards for future access networks     

Subcarrier multiplexing for lightwave networks and videodistribution systems

Applications for subcarrier multiplexing include a variety of analog and digital lightwave transmission systems. An overview of the requirements and capabilities of these systems is presented by describing specific examples of the most popular system types. These examples include multiuser interactive local area networks and multichannel digital, FM, and AM-VSB (vestigal sideband) video distribution systems. Limitations imposed on each by the linearity of directly or externally modulated sources, receiver noise, and relative-intensity noise are discussed     

Overcoming interference in spatial multiplexing MIMO cellular networks

Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But spatial multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future spatial multiplexing cellular systems.     

Traffic grooming in static wavelength division multiplexing networks

Advances in wavelength-division multiplexing technology have made it possible to design point-to-point transmission systems with unprecedented per-wavelength high capacity. This capacity may be exploited to design optical networks, in which end nodes are interconnected by circuits consisting of wavelengths. Contrary to early expectations, however, most of today's end-to-end applications require only sub-wavelength bandwidth. This bandwidth mismatch makes wavelength circuits inefficient in many cases, unless multiple traffic flows are time multiplexed together on the same wavelength. This practice is often referred to as traffic grooming. In this survey the authors address the issue of achieving efficient traffic grooming in static WDM networks. A great deal of discussion is devoted to the problem of determining which network solution is the most cost effective, taking into account the network topology, volume of traffic, possible optical impairments at high transmission rates, and cost ratio between electronic and optical components.     

Alternative multiplexing and transmission strategies forinteroffice optical networks

A fundamental multiplexing and transmission issue associated with interoffice optical transmission-how traffic originating in one central office (CO) and terminating in another should be handled at intermediate sites-is addressed. Using specific network examples, as well as a general analysis of linear chains of COs, major quantitative and qualitative differences between two alternative strategies are identified. The relative difference in installed first costs between the strategies is further evaluated in terms of their sensitivity to cost trends in fiber and electronics. The general conclusion drawn is that based on several criteria such as relative first cost, uniformity of fiber cross sections, optical repeater requirements, and applications of efficient high bit rate multiplexers, a cascaded multiplexing strategy is preferable to a dedicated multiplexing strategy. However, where route growth and diversity are primary considerations, dedicated multiplexing is more economical on a first-cost basis     

Gigabit local area networks: a systems perspective

A broad overview of gigabit local area networks (LANs) is presented from a systems perspective. Motivations and technical goals of gigabit LANs and challenges of coping with highly bursty traffic and large bandwidth mismatches between network links are described. The focus is on concerns unique to gigabit LANs, especially issues that differentiate them from gigabit wide area networks (WANs), metropolitan area networks (MANs), and lower-speed LANs. Major systems issues are discussed, and possible solutions, such as the virtual-connection architecture, are presented. The hardware technology required by gigabit LANs is illustrated by SONET components