The paradigm of a traditional wired network protocol stack is a hierarchy of services provided by each individual layer, but the ability of such paradigm to handle an error-prone physical medium is severely compromised in wireless networks. Several approaches, including cross-layer techniques, have been developed to address this problem. While much cross-layer research endeavour focused on interactions of the lower layers, in this paper, we present a cross-layer technique that involves the transport and MAC layers. In particular, our approach allows the MAC layer of a WiMAX network to be made aware of the network congestion condition perceived by TCP at the transport layer. This cross-layer technique allows the scarce radio resource to be distributed in a more intelligent fashion among the stations in the network. More specifically, our resource allocation scheme at the MAC layer adapts to the congestion window sizes passed down from TCP. We have developed analytical and simulation models to understand the dynamics of the proposed technique and quantify the resulting performance gains. Our results show that our proposed algorithm delivers a better performance in average end-to-end delay, file download time, and throughput when the traffic intensity of the network is moderate to high.

The evolution of 3G Code Division Multiple Access (CDMA) network towards higher data rates is through the introduction of High Speed Downlink Packet Access (HSDPA) enhancement to the existing 3rd Generation Partnership Project (3GPP) standards. In this paper, an access control protocol is proposed for an integrated voice, video and non real-time data traffic on the forward link (cell-site to mobile). The protocol involves predicting the residual capacity available for the HSDPA traffic. This paper evaluates the performance of three video traffic models in predicting the number of data packets that could be scheduled at the next time slot. All three video traffic models exploit the frame properties of Motion Picture Experts Group (MPEG) traffic. The traffic models are based on Markovian, Autogressive (AR) and two-sided Markov Renewal Model (TSMR) processes. The performances of the proposed estimation schemes are compared with estimation scheme using static guard margin. Findings of this paper can be used to improve the downlink performance of non-real time data traffic in the presence of MPEG video traffic in 3G CDMA networks.

OLSR (Optimized Link State Routing), a table-driven proactive protocol, standardized (RFC3626) for Mobile Ad-hoc Networks (MANETs), only works properly if participating nodes cooperate in routing. Hence, if nodes inject invalid messages or withhold critical messages, routing protocol integrity may be compromised - the protocol will fail to consistently provide each node with the accurate MANET topology. Opportunities, therefore, exist to provide intrusion detection in OLSR based MANETs by detecting anomalies in OLSR semantics. In this paper we implement and analyze an Intrusion Detection System (IDS) in which each MANET node evaluates such non-conformances locally, and thereafter infers & detects possible attacks on the routing protocol. We quantify the effectiveness of the IDS in terms of false positive and false negative detection rates. Although our discussion and implementation is based on OLSR, the techniques can be applied to any link-state routing protocol.

The AODV (ad hoc on-demand distance vector) routing protocol performs on-demand route discovery that minimizes the signaling overhead on the wireless channel at the expense of larger session setup delays. While large delays may be acceptable at session set up, they are certainly undesirable during handoffs when the session is already in progress. Our previous work addressed the problem of session handover delay within an ad hoc network connected to the Internet at large via IPv6 MANET gateways. This paper presents an extension of that earlier work by addressing another shortcoming of the AODV routing protocol - the often high overhead involved in maintaining (refreshing) active routes incurred by the active monitoring of a user-mode AODV routing daemon. A Linux kernel-based port of the AODV6 routing daemon and gateway component was developed to minimize the demands placed upon the individual mobile node's processing capabilities. A real test-bed is implemented and performance benchmarks are presented to demonstrate the viability of the proposed architecture.

The Achilles' heel of video over wireless services continues to be the limited bandwidth of wireless connections and short battery life of end-user handheld devices such as cell-phones and PDAs. Efficient coding and compression techniques are required to meet the QoS (quality of service) requirements of such services while effectively managing the aforementioned resources. H.264, the latest coding and compression standard from ITU-T, is currently dominating the field by offering a flexible architecture and compression gain of up to 50%. The compression efficiency in H.264, however, is achieved at the expense of processing time. With demands for video-streaming and video-conferencing over wireless growing rapidly, the performance of H.264 for wireless and mobile platforms, in terms of picture quality, bit-rate, and battery power consumption needs to be benchmarked, and the H.264 operating modes most suitable for these services need to be determined. This paper proposes strategies to reduce the complexity of various H.264 operations. Using the knowledge of the context of the scenes in the video sequences, unimportant regions in the frames are isolated and unnecessary processing is avoided. Experimental results, obtained using a test-bed, are presented to demonstrate the viability of the proposed strategies in minimizing the battery power consumption by H.264 while maintaining desired frame quality and low bit-rate.

The soon to be ratified IEEE 802.11e MAC layer QoS enhancements to the 802.11 protocol are making their way into production wireless networking equipment. As greater numbers of local area networks utilize the QoS features of 802.11e, we can expect to see aggregation of these networks into larger systems capable of addressing the needs for high bandwidth, real time services. We present a practical and accurate analytical model for the saturation transmission delay of EDCA. Our model is distinguished by its ability to provide a cumulative distribution function for transmission delay and by its treatment of the post-collision period, heretofore ignored by all other 802.11 models. We prove that our model accurately predicts the cumulative distribution of transmission delay with results from the ns-2 simulator.

Compressed RTP (CRTP) is a protocol to reduce the header in the VoIP packets. It is a point to point protocol and can be readily implemented on the IEEE 802.11 wireless LAN network. This paper demonstrates the throughput improvements using the CRTP protocol on VoIP applications. The paper also proposes a negative acknowledgement mechanism to further improve network capacities in VBR traffic model. Numerical results show that the bandwidth saving for each channel could be over 25%. Packet loss rate for CRTP over WLAN is also analyzed.

OLSR (optimal link state routing) is one of the four base routing protocols being considered for use with MANETs (mobile ad hoc networks) by the lETF's MANET working group. OLSR belongs to the proactive class of routing protocols in which the connection setup delay is minimized at the expense of the heavier control traffic load on the wireless channel. Existing IETF draft proposals on OLSR does not yet address security issues. Although a PKI (public key infrastructure) based security is deemed more appropriate for MANETs including OLSR MANETs, care should be taken to ensure that such an infrastructure does not add to the already heavy control traffic load in OLSR and, as much as possible, the existing OLSR control packets are utilized to support such infrastructures as well. In this paper we describe our approach in which a PKI is tightly coupled with an OLSR MANET at the network layer level and the OLSR control packets are leveraged to support various security related activities as well. We have implemented a fully distributed CA (certificate authority) and integrated it with an existing implementation of OLSRv4 (OLSR for IP version 4). Intricate details of our implementation are presented to develop insights into the key aspects of the proposed solution.

The IEEE 802.11 Task Group E will soon approve the 802.11e standard for medium access control (MAC) layer quality-of-service (QoS) enhancements to the 802.11 protocol, and it is widely believed that these enhancements will allow 802.11 technology to form the foundation of high-bandwidth vertically integrated networks. At the heart of 802.11e is a modified contention-based access mechanism, named the enhanced distributed coordination function (EDCF). In this paper, we propose and validate an analytical model for the saturation throughput of EDCF. Key to the accuracy of our model is a treatment of the postcollision period, which has been ignored by all previous 802.11 models. With results from the ns-2 simulator, we show that our model can accurately predict throughput over a wide range of scenarios, and thereby demonstrate its usefulness as a predictive tool for use in QoS provision. With context provided by our analytical model, we discuss the primary throughput differentiation mechanisms of EDCF.

This paper presents a novel approach to integrate wireless local area network (WLANs) and mobile ad hoc networks (MANET) to the Internet protocol version 6 (IPv6) based Internet. In the proposed network architecture, the mobiles, connected as a MANET, employ the optimized link state routing (OLSR) protocol for routing within the MANET. Gateways are used to connect MANETs to the Internet. This paper extends the functionality of OLSR to support mobile IP (MIP). This functionality is essential in a scenario where a node moving into an OLSR MANET needs to auto-configure its care-of-address and to propagate a binding update message containing its new care-of-address to its home agent and its correspondent node(s) located on the Internet. Automatic mode-detection and switching capability is also introduced in each mobile node to facilitate handoffs between WLANs and MANETs. Mobility management across WLANs and MANETs is achieved through mobile IPv6 (MIPv6). A real test-bed is constructed to demonstrate the viability of the proposed approach. Results from a performance evaluation on this test-bed are presented. Efficiency of handoffs between WLANs and MANETs is measured in terms of delay and packet loss. The impact of OLSR based route discovery and packet propagation, and mobile IPv6 features such as movement detection and address auto-configuration on the handoff latency and packet loss are quantified. These performance benchmarks and metrics provide in assessment of the impact of the aforementioned system features on the QoS parameters associated with handoffs.

In this paper an access control protocol is proposed and analyzed for an integrated video/voice/data DS-CDMA (direct-sequence code division multiple access) system. The protocol involves predicting the residual capacity available to non real-time data services in the reverse link (mobile to cell-site). Each real-time voice or video call is assumed to handle bursty traffic by utilizing one or more DS-CDMA channels, in parallel, as provisioned in IS-95-B and cdma2000 standards. The arrival of new calls well as the variations in the aggregate bit-rate of the existing real-time calls, and hence the number of occupied channels with respect to time, are modeled as a two-dimensional imbedded DTMC (discrete time Markov chain) process. The state of the Markov process is predicted to compute the residual capacity or the number of data packets that could be scheduled in the next time slot. Simulation results obtained, using synthetic data, are presented to demonstrate the viability of the approach. The main contribution of the paper is that it presents a simple yet effective application of the two-dimensional imbedded Markov chain model in the access control of integrated services in the reverse link of a CDMA cell.

This paper analyses the performance of priority based call admission control policies on the reverse link (mobile to cell-site) of DS-CDMA (direct-sequence code division multiple access) based cellular networks supporting VBR (variable bit rate) video traffic along with voice and data. Such analysis is important for estimating capacity requirements of competing services in multi-service DS-CDMA networks. In the first part of the paper, a channel utilization model is suggested for VBR video sources in which excess bits of compressed video frames are transported using an additional DS-CDMA channel. The main contribution is that an analytical expression is derived to compute the statistical multiplexing gain of such sources in DS-CDMA. In the second part of the paper, two priority-based call admission control policies are evaluated under the context of a multi-service DS-CDMA cellular network. System parameters such as call blocking probability and call dropping probability are analytically determined using multi-dimensional Markov chain analysis. A mixed loss-delay system is considered in which a rejected call from a real-time service is assumed to be lost, whereas, a denied request for the transmission of a non real-time. message may be queued. The main contribution is that the impact of user mobility is included in the analysis, and not only the active calls but also the queued calls may undergo handoffs.

We present herein an integrated and proactive capacity management solution for multi-service cellular networks. The proposed system, NetOptimize/sup TM/, continuously monitors the network and, upon detecting or anticipating QoS (quality of service) violations, determines an optimal channel allocation plan that ensures the prescribed QoS while maximizing revenue. Functionality of the system within the network management infrastructure is discussed herein. The emphasis, however, is on highlighting the QoS evaluation and capacity optimization capabilities of the system. The system adaptively builds a traffic model that takes into consideration the impact of user mobility. Using this model, the call level QoS parameters such as call blocking probability and call dropping probability are predicted and, thereafter, an effective optimization of capacity allocations to competing services, or user classes, is conducted.

Capability to optimally allocate network resources such as bandwidth is the key to the economical viability of modern telecommunication networks. Requirements such as adaptive updating of bandwidth allocations to track dynamic load variations, and preferential treatment for some services at the expense of others, based on economic considerations, however, add to the complexity of the task. We propose, herein, the framework of the ITE (integrated traffic engineering) system that caters to these requirements. Based on the current global network state, ITE projects the future network state and determines optimal bandwidth partitioning among the competing services that maximizes network revenue while maintaining prescribed QoS (quality of service) in broadband networks. Functionality of ITE within the network management infrastructure is discussed herein. The emphasis, however, is on highlighting the mathematical model, used in ITE, to analyze various bandwidth access policies, and evaluate the performance of the services in the presence of these policies. This performance evaluation derives the engineering methods that are subsequently used to plan these networks.

Wireless cellular networks are fast evolving into multi-service networks supporting narrow-band, as well as, wide-band services. The capability to optimally partition the available radio frequency spectrum among competing services is key to the economical viability of these networks. An analytical model is developed, herein, to measure the performance of various bandwidth access control policies, in terms of call level QoS (quality of service) parameters such as call blocking probability, call dropping probability and throughput, in TDMA/FDMA (time/frequency division multiple access) based multi-service cellular networks. The model also takes into consideration the impact of mobility on the QoS. Such models are essential for facilitating an effective optimization of bandwidth allocations in a cellular network supporting multiple services. Furthermore, requirements such as, adaptive updating of bandwidth allocations to track dynamical load variations, and preferential treatment for some services at the expense of others, due to revenue considerations, suggest applicability of priority based bandwidth access control policies. Some priority based bandwidth access control policies are, therefore, also proposed in this paper, and compared with conventional policies such as CS (complete sharing), CP (complete partitioning) and PS (partial sharing). Simulation results are presented that reflect upon the effectiveness of priority based policies. The main contribution of this work is the precise formulations developed to predict call level QoS parameters in a multi-service cellular network with mobile users.

portion of the traffic carried by high speed packet-switched broadband integrated services digital networks (B-ISDN). The high peak-to-mean ratio of VBR traffic, however, makes allocation of network resources, such as bandwidth, quite difficult. If bandwidth is allocated based on the peak rate, it will be highly inefficient and would, in fact, mitigate the gains of statistical multiplexing. On the other hand, choosing the mean rate means of allocating bandwidth would lead to congestion in the network, specially if multiple sources become active at the same time and start delivering video traffic into the network at their peak rates. The dynamics of the VBR traffic, coupled with the delay-bandwidth product of the high-speed networks, add to the complexity of congestion control and render conventional reactive based congestion control schemes as highly inefficient. Bandwidth allocation, based on the mean rate aided by a preventative congestion control scheme that could predict the onset of congestion, well in advance, is the desired solution. One such technique is proposed that estimates the current traffic state, predicts the future traffic states and forecasts the occurrence of congestion in the network. The emphasis is on demonstrating the applicability of least mean square (LMS) filters in estimating the current state of the VBR traffic sources accessing the networks. Some simulation results are presented.