الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Studying the performance characteristics of a LAN before putting it into use is very important for network designer to adjust various parameters of the network at the planning stage. The common approaches to performance evaluation apply analytical models, simulation models or hybrid models. There is some factors affecting the networks performance like , the transmission rate, number of stations , packet length and traffic intensity. The term network performance means studying the effect of such factors on the network delay (the time spent from one station start to send a message to another station till the another station receives this message) . Four network protocols (token ring , token bus , CSMA/CD and star) are investigated in this thesis. Numerical results are performed for each protocol using both analytic and simulation models. A comparison study is carried out between numerical results for the four protocols to conclude the difference between the numerical results of the simulation model and analytical model for each protocol, to show the validity of the simulation model. Moreover theoretical performance analysis for the CSMA/CA as it is used in IEEE802.11 wireless LANs is carried out. Analytical approach for CSMA/CA protocols in wireless LANs with finite number of stations is adopted. The presented numerical results highlight the characteristics of both CSMA/CA methods (Basic , RTS/CTS) and define how their performance depends on various factors that affect the network performance. The security of computer networks is also investigated. That includes how to build a secure network, the security elements and security tools and techniques, In addition to security vulnerability. A case study is presented to explain the computer networks security, also the applied security features in the case study is discussed.