الفهرس 
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Abstract
Local area networks (LAN) are a special case of computer communication networks limited in geographic area . The study of these networks incorporates many fields such as networks’ hardware ( network’s cards, interfaces, plugs, etc.) , networks’ switching and routing, and networks’ software (referred to as Netware) .
Beyond all these , lies an important aspect in engineering a computer communication network which is the network performance . Performance analysis of the network helps the designer to grasp a rough estimate of the network size and its behavior under different load demands.
In this thesis , we present measures for performance evaluation of local area networks. A technique developed by Daigle [21] was reviewed for evaluation of packets’ waiting time in case of multiple classes users with fixed message lengths . The expression of the packets’ waiting time was modified to serve multiple class users with random number of packets and variable length messages .
The thesis is divided into six chapters
Chapter one: Gives a general look on the Integrated Services Digital Networks (ISDN), scans the computer communication networks and discusses the various LAN topologies and protocols
Chapter two: Presents a brief survey of the International Standards Organizations . The Open System Interconnected (OSI) model is presented as well as the physical level interface interface plugs, transmission medium)
Chapter three: Contains Medium access control (MAC) techniques for LANs and a comparison between the two most commonly used MAC techniques [CSMNCD and Token Passing] is made.
Chapter four : It discusses the performance analysis of computer networks. Measures of LANs performance are presented as well as the development of an expression for thenetwork throughput in case of CSMAlCD and Token Passing.
Chapter five Contains the model studied in this thesis . Discusses the effect of variation of the number of stations and offered load on the performance ofLANs . It also studies the effect of the frame length on the performance through two approaches . Chapter six Gives a final concept of the results obtained and further research to be
conducted in this area.
The main results are :-
1- Network performance depends on the number of stations and offered load fordifferent medium access control techniques ( CSMAlCD and Token Passing)
2- For different MAC techniques, the variable frame length has little impact on the performance .
3- Longer frame lengths yield better throughput for shorter messages and do not affect the longer messages delay characteristic in case of multiple classes users.