Wireless LAN Simulation IEEE 802.11 MAC Protocol Lab 4 Networks and Communication Systems Department TA. Maram Almuhareb Wireless LAN Simulation IEEE 802.11 MAC Protocol

Outline Project Description IEEE 802.11 MAC Protocol Simulation Performance Analysis 4 Dec, 2002 Simulation of a Wireless LAN

Project Goals MATLAB simulation Performance Analysis - Number of Nodes - DCF (Distributed Coordination Function) - No Propagation Delay Performance Analysis - Number of Nodes - Range - Packet Size - RTS/CTS RTS: When a node has a data packet to transmit, it first broadcasts a small packet called a Request-To-Send (RTS) packet. 2) CTS: When the intended recipient on the WLAN receives an RTS packet, it broadcasts a small Clear-To-Send (CTS) packet. 3) ACK: Acknowledgement packet sent from the receiver to the sender upon successful completion of the data exchange. 4) CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a protocol in which (a) a carrier sensing scheme is used, (b) a data station that intends to transmit sends a jam signal, (c) after waiting a sufficient time for all stations to receive the jam signal, the data station transmits a frame, and (d) while transmitting, if the data station detects a jam signal from another station, it stops transmitting for a random time and tries again 4 Dec, 2002 Simulation of a Wireless LAN

DCF DCF - CSMA/CA is a DCF Salient features - Medium sharing through CSMA/CA - Allows one STA to use the medium - Random Back off interval before retransmission - Refinement – RTS/CTS packets 4 Dec, 2002 Simulation of a Wireless LAN

IEEE 802.11 MAC Protocol Also known as CSMA/CA 802.11 CSMA (no collision detection) Sender If the channel is idle for DIFS seconds - Transmit DATA packet If the channel is busy - Backoff Receiver If DATA packet received - Return ACK after SIFS seconds Source Destination DIFS DATA SIFS ACK 4 Dec, 2002 Simulation of a Wireless LAN

CSMA/CA (Collision Avoidance) - RTS/CTS Implementation IEEE 802.11 MAC Protocol CSMA/CA (Collision Avoidance) - RTS/CTS Implementation Sender transmits an RTS packet Receiver responds with a CTS packet Purpose of CTS packet - Reserves channel for sender - Notify other stations Source Destination DIFS RTS SIFS CTS SIFS DATA SIFS ACK Goal – Avoid “Hidden Node” collisions 4 Dec, 2002 Simulation of a Wireless LAN

MATLAB Simulation Old Simulation - Implemented CSMA (No RTS/CTS) New Simulation - Includes RTS/CTS exchange - Simulates CSMA/CA 4 Dec, 2002 Simulation of a Wireless LAN

Output

Analysis 4 Dec, 2002 Simulation of a Wireless LAN

References Simulation of an 802.11 Wireless Network: http://ipsit.bu.edu/sc546/sc546Fall2002/wireless /index.htm