The challenge of designing an efficient Medium Access Control (MAC) protocol and analyzing it has been an important research topic for over 30 years. This thesis focuses on the performance analysis and enhancement of MAC protocols, particularly the random access protocols. Performance of the two widely known random access MAC protocols the IEEE 802.3 MAC protocol that employs the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, and the IEEE 802.11 MAC protocol that uses the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol, are first studied. They are analyzed using a new analytical approach proposed in this thesis. The new approach is based on the idea that the service process of a MAC protocol can be modeled by a Phase-Type (PH) distribution. This way, the arrival process as well as the service process of the actual protocol can be described by a certain multidimensional continuous time Markov chain. The advantages of this novel technique over the traditional approach for performance analyses of MAC protocols are that: (i) it provides a unified model for the analysis of MAC protocols; (ii) it significantly simplifies the analytical model of a MAC protocol which makes it possible to include a more complex and realistic traffic model without compromising the protocol details; (iii) vast knowledge is available on the analysis of a continuous time Markov chain, which allows for more insight to the performance of a MAC protocol. Extensive demonstrations of the use of the approach on performance analyses of MAC protocols are provided, some of which conducted under realistic bursty traffic conditions.

As a result of the performance analyses, it is found that the IEEE 802.3 MAC protocol exhibits relatively low and unattractive performance, especially when it is operated at 1Gb/s data rate. In response to this finding, two new protocols are introduced in this thesis. Firstly, we introduce a novel technique, Reservations by Interruptions, to provide an efficient reservation scheme for CSMA/CD. The resulting protocol is named CSMA with Reservations by Interruptions (CSMA/RI). Performance of CSMA/RI is evaluated and compared with CSMA/CD. The stability of CSMA/RI is also studied. In addition, two realistic scenarios, namely the saturation and disaster scenarios, are used to demonstrate the performance advantage of CSMA/RI. Furthermore, performance analyses based on the new approach under realistic traffic conditions are performed to show the performance benefit of CSMA/RI. Our analytical results show that CSMA/RI always offers better performance than CSMA/CD, and in some cases, the delay performance of CSMA/RI approaches that of a perfect scheduling G/D/1 system. A performance comparison between CSMA/CD, CSMA/RI as well as the token ring protocol is provided. Finally, some implementation issues and limitations of CSMA/RI are addressed.

The second MAC protocol introduced in this thesis is called the Request Contention Multiple Access (RCMA) protocol. RCMA is a distributed gigabit MAC protocol. It is designed to operate in the passive star optical network such as the 10BASE-FP version of Ethernet at a gigabit data rate. Unlike the existing IEEE 802.3z Gigabit Ethernet MAC protocol that employs CSMA/CD, RCMA is efficient and stable for a wide range of user numbers based on our study under the saturation scenario. Moreover, RCMA can easily accommodate service differentiation within the MAC layer with no additional overhead. In terms of implementation, it does not appear to be difficult. The implementation of RCMA may lead to a cost competitive yet efficient solution for the future gigabit LANs.