A new packet delay analysis for the IEEE 802.11b protocol is developed by extending throughput analysis introduced by Bianchi. This analysis is validated by comparison with simulation results using the OPNET TM simulation package. Packet delay results are presented as a function of a number of stations and packet size for basic access and RTS=CTS medium access mechanisms. The proposed analysis identifies when the RTS=CTS mechanism achieves lower packet delay with respect to the basic access mechanism and becomes highly beneficial for the performance of IEEE 802.11 WLANs. Introduction: Wireless local area networks (WLANs) are one of the fastest growing areas in data communications and networking, and have witnessed a tremendous development over the past few years [1] . The IEEE working group proposed the 802.11 protocol [2] to deal with the modern wireless connectivity needs. The IEEE 802.11 protocol is a carrier sense multiple access with collision avoidance (CSMA=CA) MAC protocol using binary exponential backoff. The fundamental technique to access the medium is called distributed coordination function (DCF). DCF defines two access mechanisms to employ packet transmission, the basic access and the Request-To-Send= Clear-To-Send (RTS=CTS). A station with a packet to transmit senses the medium activity. If the medium is idle, the station transmits. If the medium is sensed busy, the station persists to monitor the medium until it becomes idle for more than distributed inter-frame space (DIFS) time period. To minimise collisions the station waits a random backoff interval before transmitting the data packet. If the collision probability is high and the packet size is longer than a threshold, the RTS=CTS reservation scheme is used. In this case, short RTS and CTS packets are exchanged to reserve the medium prior to the transmission of the long data packet. The RTS=CTS scheme shortens collision duration and copes with hidden stations. In this Letter a mathematical analysis is developed that calculates the average packet delay for both medium access mechanisms. Our analysis extends the approach in [3, 4] by utilising the same Markov chain model for calculating the average packet delay. We present results, which specify the threshold packet size above which the use of the RTS=CTS mechanism is superior to the basic access. As the RTS=CTS efficiency depends on the packet collision probability, which increases for large networks, we evaluate the dependency of the RTS=CTS threshold on network size. Furthermore, we identify the network and traffic conditions where the RTS=CTS mechanism enhances the performance of the IEEE 802.11 MAC protocol.
Chatzimisios, P., Boucouvalas, A. C., & Vitsas, V. discussed Packet delay analysis of IEEE 802.11 MAC protocol REF by extending some throughput analysis in order to identify when the RTS/CTS mechanism achieves lower packet delay with respect to the Basic Access Mechanism.
Packet delay analysis of IEEE 802.11 MAC protocol
Electronics Letters
Mathematics