A continually growing number of businesses and technology consumers exchange increasing amounts of information has result in evolving very rapidly local area networks (LANs) as the communication infrastructure that meets their fundamental needs and demands. As a consequence, to design, develop, and deploy a LAN, it is often necessary to perform an accurate measurement campaign (including interconnection topologies, transmission media, and access protocols) so as to ensure that the LAN with its parameter settings provides the needed throughput for the intended users. Among these examinations, network access protocols play vital role in the adoption of the network. To this end, the design of an efficient and reliable Medium Access Control (MAC) protocol requires careful understanding and tuning of its various key parameters to achieve the optimum performance in any actual environment.The two commonly MAC protocols used in LANs are the IEEE 802.3 and the IEEE 802.11 MAC protocols that are employed by Ethernet and Wireless LANs respectively. Ethernet occupies the Carrier Sense Multiple Access with Collision Detection (CSMA/CD), while wireless LAN devotes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). These CSMA protocols have randomness property that may direct the transmission to a possible collision which in turn requires that the stations (users) involved in the collision to abort their unsuccessful transmissions to be re-transmitted again according to a specified contention algorithm (e.g., the Truncated Binary Exponential Backoff – BEB algorithm). As a result of this randomness feature is that MAC protocol may suffer from harmful performance degradation. The work here deals with the performance evaluations of both IEEE 802.3 and the IEEE 802.11 MAC protocols. Performance results are presented by considering some protocol analysis assumptions. The analysis is considered under the two extremely heavy load conditions – the saturation and disaster scenarios. Under saturation scenario, the objective is to examine the fundamental limit of the protocol; while under disaster scenario, the contribution is on examining the response of the protocol to a certain failure recovery. The results present the relative estimate (or different levels of relation) between Ethernet and wireless LAN system throughputs. Results demonstrate that to achieve an acceptable performance level of the IEEE 802.3 protocol, the number of active stations in a network may be limited. On the other hand, the results present that the IEEE 802.11 MAC protocol performs reasonably well under a certain load condition with a good selection of the protocol parameters (e.g., initial backoff window size and maximum number of backoff stages). Moreover, the performance achieved by IEEE 802.11 MAC protocol which use four-way handshaking access scheme is, even, better than those achieved by the use of basic access method.