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

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

3. 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

4. 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

5. IEEE 802.11 MAC Protocol Also known as CSMA/CA
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

6. CSMA/CA (Collision Avoidance) - RTS/CTS Implementation
IEEE 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

7. 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

8. Output

9. Analysis
4 Dec, 2002
Simulation of a Wireless LAN

10. References
Simulation of an Wireless Network: /index.htm