Milosh V. Ivanovich

On TCP performance enhancing proxies in a wireless environment

TCP performance enhancement in wireless access networks is an important ongoing area of research. It is known that the hostile nature of the wireless channel and the mobile nature of wireless users interact adversely with standard TCP congestion control mechanisms [1], causing a drastic reduction in throughput. This article surveys a selection of different approaches to managing TCP performance over wireless links, and presents the results of simulation and field trial results of a novel TCP performance enhancing proxy over diverse cellular radio access technologies based on the GSM, cdma2000, and UMTS standards. The proposed TRL TCP performance enhancing proxy has the advantages of being completely transparent to both TCP endpoints and tunable to different access technologies, and frequently achieves the maximum throughput available from any of the studied radio access technologies.

User-perceived quality of service in wireless data networks

For so long, the term quality of service (QoS) has been a pursuit area for network engineers trying to dimension wireless networks to run in the most efficient way possible. Of late, there has been a trend reversal, looking at the user perceptions of the network performance to decide where dimensioning can have the greatest impact. This paper demonstrates the importance of defining the concept of user-perceived QoS and linking this to specific wireless data network parameters for some anticipated valuable applications. It has been shown that a quantitative rating can be obtained for a variety of important factors in the assessment of service quality, and mapped to specific values of multiple network parameters. We found QoS to be application-specific, where various applications require different levels of network performance to satisfy users. The role of physical location was also examined, investigating the influence of being indoors versus outdoors on the user perception of QoS.

A survey of MAC based QoS implementations for WiMAX networks

We present a comprehensive survey of proposed Quality of Service (QoS) mechanisms in the Media Access Control (MAC) sublayer of WiMAX based wireless networks. QoS support in WiMAX is a fundamental design requirement, and is considerably more difficult than in wired networks, mainly because of the variable and unpredictable characteristics of wireless links. We discuss various QoS architectures, signaling mechanisms and admission control techniques proposed in the WiMAX research literature, summarizing the operation of each, and providing comparative evaluations that include advantages and limitations.

Performance between circuit allocation schemes for half- and full-rate connections in GSM

This paper considers three circuit allocation schemes for half- and full-rate connections in the Global system for Mobile Communications (GSM): best fit, repacking, and fair repacking. Analytic numerical methods are used to investigate each schemes blocking probability behavior. The analysis is based on a reduction of the state space to a manageable size. Fair repacking is found to be the fairest and most efficient. However, the best-fit scheme, while being somewhat less efficient and fair, is simpler to implement. The effect on quality of service (QoS) of voice dropouts related to intracell handover (repacking) was found to be negligible.

Evaluation of priority and scheduling schemes for an IEEE 802.14 MAC protocol loaded by real traffic

We study a new scheme for provision of priorities within the framework of a MAC protocol which is a potential candidate of the (as yet unpublished) IEEE 802.14 standard. A comprehensive simulation study, based on real traffic traces, shows that this new method provides better protection for the high priority traffic than an earlier proposed scheme. Except for physical and MAC layer overheads, the scheme exhibits comparable behaviour to that of an ideal multiplexer, for traces with very diverse correlation structures. The significance of using realistic (correlated) traffic streams for modelling purposes is demonstrated and discussed.

Models for pre-emption of packet data by voice in slotted cellular radio networks

Cellular radio networks supporting both circuit switched voice and packet switched data services aim to maximise the resource utilisation through efficient sharing of the resource. These sharing algorithms can use pre-emption to give voice service priority over data, thus preserving the grade of service for voice at the expense of delaying data calls. This paper develops models for a pre-emptive voice and data system, with a particular focus on GPRS. The model is based on an assumption of independence between the voice and data traffic. These models allow estimates of (i) the probability that a voice call causes pre-emption of a data call, as well as (ii) the probability that a data call will be delayed due to either being pre-empted by a voice call while in progress or due to not finding free resources at its initial attempt. The results show that a Poisson model for data traffic gives the best results for pre-emption probability when compared with measurements taken from a GSM/GPRS network.

A study of deadlock models for a multiservice medium access protocol employing a Slotted Aloha signalling channel

Medium access protocols for HFC and wireless ATM networks often use a collision based capacity request signalling channel which may rely on the slotted Aloha multiaccess principle. This paper studies the performance of a p-persistence slotted Aloha contention resolution algorithm (CRA), subject to extreme interstation correlation, by means of a discrete-time Markov chain analysis. We examine in detail the conditions leading to a deadlock-a situation where the time to collision resolution becomes unacceptably high and the system is practically unstable. We analyze two disaster scenario deadlock models, and study the effect of channel error probability, signalling traffic load, and the contention resolution algorithm used. We show that the key factor of the CRA is the collision rate and not channel errors. We propose and test three signalling channel capacity allocation schemes. We identify the best-performing of these three schemes as the cyclic contention mini-slot (CMS) sharing employing multiple CMSs per data slot. Finally, we demonstrate the need for implementation of an added scheme, which dynamically adjusts the p-persistence parameter.

Channel allocation methods for half and full rate connections in GSM

This paper considers five circuit allocation schemes for half and full rate connections in GSM. Analytic numerical methods are used to investigate each schemes blocking probability behaviour. Two members of the repacking family of schemes, repacking with perpetual half slot reservation and repacking with random reservation, are found to be the fairest in terms of blocking probability, and have the highest network utilisation (efficiency). However, the best fit scheme, while being somewhat less efficient and fair, is simpler to implement and does not incur voice dropouts related to intracell handover.

Intelligent Automated Diagnosis of Client Device Bottlenecks in Private Clouds

We present an automated solution for rapid diagnosis of client device problems in private cloud environments: the Intelligent Automated Client Diagnostic (IACD) system. Clients are diagnosed with the aid of Transmission Control Protocol (TCP) packet traces, by (i) observation of anomalous artifacts occurring as a result of each fault and (ii) subsequent use of the inference capabilities of soft-margin Support Vector Machine (SVM) classifiers. The IACD system features a modular design and is extendible to new faults, with detection capability unaffected by the TCP variant used at the client. Experimental evaluation of the IACD system in a controlled environment demonstrated an overall diagnostic accuracy of 98%.

Worst case signalling traffic for a multi-service access protocol

Modern multi-service medium access protocols use a collision based capacity request signalling channel. Such signalling channels may be based on the slotted Aloha multiaccess principle. This paper studies the performance of slotted Aloha subject to extreme inter-station correlation by means of a discrete-time Markov chain analysis. We study conditions whereby the time to collision resolution becomes unacceptably high (defined as deadlock). Three signalling channel management schemes for alleviating the deadlock problem are evaluated. Of these, the cyclic contention mini-slot (CMS) sharing technique employing multiple CMSs per data slot is the one that extends the protocols useable load region the furthest. We find that implementation of a scheme, which dynamically adjusts the p-persistence parameter towards its optimal value, is desirable. Both error free and error prone conditions are studied. The results highlight the fact that the critical signalling load is largely unaffected by the presence of errors, so that even in extremely error prone environments, the limiting performance factor is still the collision rate.