Hussein M. Alnuweiri

Analytical Modeling of Contention-Based Bandwidth Request Mechanism in IEEE 802.16 Wireless Networks

The IEEE 802.16 wireless metropolitan area network (WMAN) standard is a promising and cost-effective, last-mile wireless technology for the provision of broadband Internet access to end users. In this paper, we present an accurate analytical model that describes the contention-based bandwidth (BW) request scheme of the 802.16 standard, which is also known as WiMAX, for the persistent and nonpersistent request generation cases. We first model the contention procedure with a Markov chain, taking into account the exponential back-off procedure as well as the waiting time for a BW assignment and the possible timeout for lost messages. The accuracy of the model is then evaluated by comparing it with simulation results for a wide range of values of the parameters involved. We use this model to accurately calculate the capacity of the contention slots in delivering BW requests, from which the average access delay is also found. These measures are used to determine a proper configuration for the efficient operation of the contention-based BW request scheme. The proposed model provides a useful analytical tool for devising adaptive configuration mechanisms for the contention access mode of the 802.16 medium access control (MAC) layer.

A Link Adaptation Scheme for Efficient Transmission of H.264 Scalable Video Over Multirate WLANs

In this paper, we propose a cross-layer optimization scheme for delivery of scalable video over multirate wireless networks, in particular the popular 802.11 based wireless local area network (WLAN). The 802.11 based networks use a link adaptation mechanism in the physical layer (PHY) to maintain the reliability of transmission under varying channel conditions. When channel condition worsens, the reliability is maintained by employing more robust modulation and coding schemes, at the cost of reduced PHY bit rate. The reduced bit rate will result in lower available throughput for applications. For scalable video streaming applications, the conventional solution to this problem is to reduce the video bit rate by dropping the higher enhancement layers of the scalable video. We show in this article that the video quality can be improved, if the link adaptation scheme uses more intelligent reliability criteria and adjusts the PHY parameters used for delivering each video layer, according to the relative importance of that layer. Our scheme achieves better video quality without increasing the traffic load of the WLAN. For this purpose we present temporal fairness constraints and formulate an optimization problem for assigning different PHY modes to different layers of scalable video; the solution to this problem provides a set of PHY configuration parameters that achieve the highest possible video quality while meeting the admission control constraints in the network. Performance evaluations demonstrate that our method outperforms the existing mechanisms.

A framework for optimizing the cost and performance of next-generation IP routers

The explosive growth of Internet users, the increased user demand for bandwidth, and the declining cost of technology have all resulted in the emergence of new classes of high-speed distributed IP-router architectures with packet-forwarding rates of the order of gigabits, or even terabits, per second. This paper develops an analytical framework for modeling and analyzing the impact of technological factors on the cost-performance tradeoffs in distributed-router architectures. The main tradeoff in a distributed router results naturally from moving the main packet-forwarding and processing power from a centralized forwarding engine to an ensemble of smaller forwarding engines, either dedicated to or shared among the line cards. Processing packets in these smaller engines can be much cheaper (by as much two to three orders of magnitude) than in a centralized forwarding engine. Therefore, the main goal of our modeling framework is to determine an optimal allocation of processing power to the forwarding engines (in a distributed router) to minimize overall router cost while achieving a given level of packet-forwarding performance. Two types of router models are analyzed using the proposed framework: a distributed-router architecture and parallel-router architecture.

Performance of new link state advertisement mechanisms in routing protocols with traffic engineering extensions

The prevalent use of best-effort topology driven IP routing protocols with shortest path calculations can often lead to serious imbalance of packet traffic distribution when least cost paths converge on the same set of links, leading to unacceptable delays or packet loss even in the presence of feasible paths over less utilized links. Recently proposed enhancements to common routing protocols are promising to overcome such shortcomings by providing the means to distribute link state information that is more pertinent to traffic engineering in routed networks. This article presents several key results on the performance of the recently proposed OSPF-TE, with particular emphasis on OSPF-TE protocol traffic overhead and the impact of new link state advertisement triggering mechanisms on traffic-engineered routing accuracy.

Efficient coding and mapping algorithms for software-only real-time video coding at low bit rates

This paper presents efficient coding and mapping algorithms that lead to a significant speed improvement in low bit rate H.263/H263+ video encoding while maintaining high video-reproduction quality. First, by exploiting the statistical properties of low resolution and slowly varying video sequences, we reduce significantly the computation times of the most computationally intensive components of video coding, particularly the discrete cosine transform, the inverse discrete cosine transform, quantization, and motion estimation. We also map some of the single instruction multiple data (SIMD)-oriented functions onto Intels MMX architecture. The developed algorithms are implemented using our public-domain H.263/H.263+ encoder/decoder software. Using the above algorithms, our H.263/H.263+ baseline video-encoder implementation can encode more than 15 fps in QCIF resolution on a Pentium MMX 200-MHz computer.

Analysis of Burst Transmission in IEEE 802.11e Wireless LANs

Transmission opportunity, or TXOP, is a channel control method introduced in the IEEE 802.11e wireless LAN standard for improving channel utilization. In this paper, we propose an analytical model to evaluate the performance of TXOP as a method for achieving efficient burst transmissions in IEEE wireless LANs. We show how the model can be used to estimate the throughput of different access categories as a function of the TXOP limit value, and how to calculate the total throughput achieved under basic-access and RTS/CTS access modes. We also show that improved service differentiation can be achieved by using a novel scheme based on TXOP thresholds. Our model demonstrates how the combined used use of TXOP with other MAC parameters can lead to higher aggregate throughput and improved service differentiation.

A fuzzy constraint-based routing algorithm for traffic engineering

We propose a low-complexity constraint-based routing algorithm for traffic engineering in packet networks that route end-to-end packet flows. The proposed fuzzy routing algorithm (FRA) modifies the well-known Dijkstras single-source shortest paths algorithm by using fuzzy-logic membership functions in the path-cost update process. The main objective of FRA is to reduce path-request blocking and increase overall network utilization. To achieve this objective, the algorithm computes new routes based on network-wide load balancing constraints. Simulation results show that FRA outperforms several earlier algorithms in terms of load balancing and path-request blocking.

Realizing MPEG-4 streaming over the Internet: a client/server architecture using DMIF

The paper presents the implementation of an MPEG-4 Streaming System for the delivery of multiple elementary stream presentations containing audio-visual objects. This system has been tested with the MPEG-4 demonstration software implementation (IMI), but it is in fact a generic platform for multimedia presentation delivery. The signalling and delivery layer of this system implementation conforms to the recommendations made by part 6 of the MPEG-4 standard, Delivery Multimedia Integration Framework (DMIF). We present the issues involved in designing our DMIF-based streaming server and the levels of abstraction required. The system enables interactive media streaming across the Internet through its Data and Control Planes. It also implements a source based rate control system, a Synchronization Layer packetizer and a signalling mechanism.

Traffic engineering with distributed dynamic channel allocation in BFWA mesh networks at millimeter wave band

Inherent difficulties in millimeter-wave radio operations, such as higher atmospheric attenuation, especially during rainy times, motivated the use of mesh architecture in millimeter-wave band for broadband fixed wireless access (BFWA) networks. When used with highly directional antennas, these mesh networks also provide better frequency reuse. In a recent proposed architecture for such networks, a link can have multiple radio channels. However, to provide traffic engineering with scalability, it is needed to develop a distributed dynamic channel allocation algorithm to allocate channels to these links. This paper proposes a distributed dynamic channel allocation algorithm that is scalable and able to provide traffic engineering if invoked periodically. The proposed solution provides traffic engineering by optimizing link capacities by adding or removing channels from a link while maintaining interference constraints, based on current network conditions. Simulation results suggested that proposed algorithm performs better than a solution based on fixed channel allocation

Quality of service support over switched Ethernet

This paper investigates the performance of switched-Ethernet LANs when transporting real-time video streams. Our study covers several switched-LAN topologies that employ switches with different capabilities. Such capabilities include the use of shared versus dedicated ports and single versus multi-priority access buffers in the switch ports. As an example, we consider the transport of several medium and low packet video streams that correspond to video conferencing activities over a switched LAN. Our results show the impact of LAN switch parameters on the delay and loss performance of real-time video streams.