Data link layer protocols in wireless computer networks

Bartłomiej Zieliński


The monograph is devoted to the construction and analysis of the properties of the data link layer protocols in wireless networks In the initial part, data link layer tasks, especially in wireless computer networks, are cha-racterized. Next, the aim of the monograph is formulated and a review of presented problems is given. The main part of the monograph is dfvided into three chapters. The first chapter is devoted to medium access protocols in wireless networks, especially ad-hoc networks. In this part, phenomena present in wireless network that have influence on MAC protocols operation, have been characterized. Next, collion avoidance and detection methods for wireless networks have been presented. On the basis of their operation, the con-ditions that allow to use collision detection in wireless diffuse infrared networks have been determined. Two collision avoidance methods behaviour in a mobile ad-hoc network is also compared and the criterion of control frames exchange-based collision avoidance method effectiveness is given. Next, contention MAC protocols for wireless networks are presented. In these protocols, the aforementioned collision avoidance and detection methods are used. For selected protocols, performance comparison in various operating conditions, including those typical for wireless networks, is presented. Selected protocols have been also imple-mented is a smali, experimental wireless networks, in which their properties have been meas-ured. The experimental results are different from the theoretical ones, which may show that in the network there are some phenomena not tak en into account in the theoretical model. The second chapter is devoted to the amateur Packet Radio network together with AX.25 protocol and TNC controllers used as network adapters in this network. In this part, AX.25 protocol operation is presented according to its 2.2 version with emphasize to the differences to the earlier version (especially widely used 2.0). The chapter presents also TNC operation rules, their hardware structure and software functions. On the basis of AX.25 protocol descriprtion an analytical model has been created; it allows to estimate protocol efficiency, ef-fective throughput and transmission delays. Using this model, protocol parameter influence on its performance has been analysed for both radio link types, opearating at different transmission rates. A similar model of TNC controller is also presented; it allows to estimate TNC influence on throughput and delays, and to estimate TNC buffer capacity that guarantees sender-side transmission continuity. Numerous tests performed in an axperimetal Packet Radio networks are also presented. Results show strong dependency of effective network parameters on TNC processing power as well as software-dependent AX.25 protocol implementation details. The third chapter is devoted to IEEE 802.11-comatible wireless local area networks. In this chapter, network topologies and selected elements of physical and data link layer are presented, such as: PLCP frame formats, data link layer frame formats, types and exchange rules in various medium access modes (DCF, PCF, EDCA, HCCA) and selected network manage-ment elements. Block acknowledge mechanism is also described. A separate part of the chapter describes 802.1 ln amendment that was finished during writing of this monograph (November 2009). In this fragment, PLCP frame formats as well as frame aggregation (A-MSDU and A-MPDU) methods are discussed. These mechanisms are then analysed for their influence on protocol performance under various conditions. On the basis of protocol description, an analytical model known from literaturęehas been extended. It allows estimate protocol performance, effective throughput and throughput upper limit for all considered data transmission methods.


wireless network; network topology; computer network

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