CSMA CA

Carrier Sense Multiple Access with Collision Avoidance is the physical layer access control method used in IEEE 802.11 (Wi Fi) wireless LANs. The wireless nodes cannot transmit and receive at the same time and due to the very nature of the wireless medium, all the nodes cannot receive all the packets on the medium. Due to these two main limitations, CSMA/CD access control protocol cannot be used in wifi technology.

This video talks about necessity of new protocol and explains CSMA/CA access control in detail. Collision avoidance is used to improve the performance of CSMA by attempting to be less "greedy" on the channel. If the channel is sensed busy before transmission then the transmission is deferred for a "random" interval. This reduces the probability of collisions on the channel.

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CSMA/CA can be supported with Request to Send (RTS) and Clear to Send (CTS) packets optionally to reserve the channel. This kind of access control method is called as Virtual Carrier Sensing method, and it is implemented at MAC layer.

Amit Vartak, 27 is working in wired and wireless security fields since last 3-4 years. His current area of interest includes IEEE 802.11 (Wi-Fi) suite of protocols, vulnerabilities in these protocols and countermeasure for those vulnerabilities. Working on cutting edge tools and technology always keeps him busy. He has contributed from concept level to final prototyping for the presentations in Defcon 2007 (The Emperor Has No Cloak - WEP Cloaking Exposed) and Toorcon 2007 (Caffe latte attack). He holds 2 patents with USPTO (current status: Patent Pending) and a few papers in IEEE journals on wireless protocol vulnerabilities. Prior to this, he was working on MEMS (Micro Electro Mechanical Systems) and has published a few papers in SPIE and ICMAT. (Yeah… kindda orthogonal fields… but technology really doesn’t limit the talent :) He did his masters in Electrical Engineering from one of the premier institutes in India, Indian Institute of Technology, Bombay (IIT-Bombay) and his under graduation, from University of Mumbai in Electronics and Telecommunication Engineering. He is currently working with AirTight Networks Inc. as a team lead in technology group since last 3 years.You can get in touch with him at amitcv[at]gmail[dot]com