Indra Widjaja

IEEE 802.11 Wireless Local Area Networks

The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler.

MATE: MPLS adaptive traffic engineering

Destination-based forwarding in traditional IP routers has not been able to take full advantage of multiple paths that frequently exist in Internet service provider networks. As a result, the networks may not operate efficiently, especially when the traffic patterns are dynamic. This paper describes a multipath adaptive traffic engineering mechanism, called MATE, which is targeted for switched networks such as multiprotocol label switching (MPLS) networks. The main goal of MATE is to avoid network congestion by adaptively balancing the load among multiple paths based on measurement and analysis of path congestion. MATE adopts a minimalist approach in that intermediate nodes are not required to perform traffic engineering or measurements besides normal packet forwarding. Moreover MATE does not impose any particular scheduling, buffer management, or a priori traffic characterization on the nodes. This paper presents an analytical model, derives a class of MATE algorithms, and proves their convergence. Several practical design techniques to implement MATE are described. Simulation results are provided to illustrate the efficacy of MATE under various network scenarios.

Performance of output-buffered banyan networks with arbitrary buffer sizes

A report is presented on a queueing analysis and a simulation study of a switch fabric based on a buffered banyan structure whereby buffers are placed at the output links of each switching element. When buffers are located at the input links, it is well known that maximum throughput is limited to approximately 0.45 under a uniform input traffic pattern. This bottleneck is due to the head of the line (HOL) contention at each switching element and is intrinsic to input queueing. The authors propose a buffered banyan switch built from smaller knockout switches which are output-buffered switches. With small knockout switches as the basic switching elements, the complexity of the overall switch fabric is manageable and no internal clock speedup is required. Furthermore, it is shown that with the proposed output-buffered banyan switch, a maximum throughput of 1 can be achieved.<<ETX>>

Conditional overflow probability and profile curve for ATM congestion detection

Many systems in ATM environments require the queue to be monitored for impending congestion before it happens. We characterize impending congestion by measuring how long the queue length has exceeded a certain threshold. Based on the idea of the profile curve, we introduce a new performance measure called the conditional overflow probability which gives a quantitative measure on the congestion state. We develop a matrix analytic method to compute the conditional overflow probability and the profile curve, and present a corresponding algorithm to estimate the two measures using real traffic data.

Connection admission control for PRMA/DA wireless access protocol

Next generation wireless communication systems will handle a wide range of services such as voice, video, and data. In this multi-service scenario, major technical issues are concerned with the selection of a suitable media access control (MAC) protocol and provision of adequate quality of service (QoS) to network users. We introduce a wireless media access control (MAC) protocol which is capable of transporting broadband traffic and providing seamless connectivity to ATM (asynchronous transfer mode) networks. Our protocol, having an air interface comparable to ATM, adopts a dynamic channel allocation scheme which enables expeditious network access and utilizes bandwidth resource efficiently for a mixed voice/video/data traffic environment. Simulation results presented here show the effectiveness of wireless access scheme, QoS provision, and dynamic channel allocation in terms of key performance metrics such as: throughput, cell loss-rate, call access delay, and cell transmission delay.

Performance aspects of IEEE 802.11 wireless local-area networks

We are on the threshold of witnessing an explosion of portable and mobile terminals capable of sending and receiving multimedia traffic. Currently, the standard being worked out by the IEEE 802.11 committee to support wireless connectivity in the local area network appears to be the most promising one. IEEE 802.11 protocols support both scheduling and random access techniques operating simultaneously, called point coordination function (PCF) and distributed coordination function (DCF), respectively. In this paper, we study the interactions between PCF and DCF when voice and asynchronous data traffic needs to be supported. We investigate the dimensioning problems of various parameters, and provide the general rule of thumb of the default values.

Burst-level admission control protocols with multirate traffic and arbitrary network topology

In this paper, we investigate the performance of two burst-level admission control protocol for ATM networks that are based on simple random access techniques: fell-and-wait and tell-and-go. We develop an analytical model based on reduced load approximation to obtain throughput, end-to-end transfer delay and blocking probability characteristics far an arbitrary network topology with multirate traffic. We discuss the performance of these two protocols under varying propagation delays and peak bit rates. We discuss how the presence of multirate traffic introduces the issue of fairness into these burst-level admission control protocols, a phenomenon not observed previously.

QoS Control in Next-Generation networks[ Guest Editorial]

The three articles in this special section are devoted to quality of service control in next generation networking.

Fast IP routing with VC-merge-capable ATM switches

Recent work on building fast IP routers has emphasized on integrating ATM switching with IP routing. One critical issue is concerned with ways to map IP routing information to ATM labels. VC merging allows many routes to be mapped to the same VC label, thereby providing a scalable mapping method that can support tens of thousands of edge routers. VC merging requires reassembly buffers so that cells belonging to different packets intended for the same destination do not interleave with each other. We investigate the impact of VC merging on the additional buffer required for the reassembly buffers and other buffers due to the perturbation in the traffic process. The main result indicates that VC merging incurs a minimal overhead compared to non-VC merging in terms of additional buffering. Moreover, the overhead decreases as utilization increases, or as the traffic becomes more bursty.

Fairness of burst-level admission control protocols

Burst-level admission control protocols have been proposed to perform access control to sources that exhibit high burstiness and need not require real-time delivery. To this end, two broad approaches of burst-level admission control can be classified. In the first approach, called tell-and-go, the source transmits its messages immediately in the form of bursts as soon as it receives the message from its application layer. In the second approach, called tell-and- wait, the source first reserves the bandwidth along the virtual circuit using a short request message. The burst is transitted only after the requested bandwidth has been allotted. In this paper, we analyze the performance of both protocols taking into consideration of the fact that the sources are heterogeneous, an important assumption which is absent in all previous analyses. We show that sources which request a higher peak bit rate encounter higher blocking probability, resulting in lower throughput. We then propose a solution to fix this fairness problem so the equitable performance is achieved.