Answer to Question #248767 in Computer Networks for Michael Sampson

Question

Describe the steps involve in a Distributed Coordination Function using a simple carrier sense multiple access algorithm with an interframe space delay to transmit frames in a Wireless LAN

Answer 1

Distributed Coordinated Function is the default mode used to share the physical medium. It is used in both ad hoc and infrastructure networks. A station that is willing to transmit data first waits during DCF Interframe Space. If any signal is not detected at the physical layer, CCA is sent to the MAC layer, and the base station still wait during content window. If no signal has been detected during this time, the base station sends to the receiver a Request to Send, this control frame contains Duration field and the MAC address of the transmitter and receiver which contains the estimated time of the first MAC fragment to determine their Network Allocation Vector. In this stage base stations are not allowed to transmit data to avoid collisions then the receiver sends a Clear To Send Control frame that indicates to the transmitter that it is ready for receiving the signal. If this packet is too large, it can be cut into several MAC fragments that are successively sent onto the channel. The receiver acknowledges each fragment by sending an Acknowledgment frame. When the transmitter has not received the Acknowledgment of some fragment, it retransmits fragment again. All frames contain a field indicating the estimated transmission duration of the next fragment, which allows to update the Network Allocation Vector of all adjacent base stations. Short Interframe Space separates each frame to avoid any overlap. At the end of the transmission, the reservation procedure begins again, and another user can transmit