CSMA Simulation

by Choongmin Lee on May 29, 2011

Compare the two common MAC protocols, CSMA/CD and DCF (CSMA/CA) using simulation.

Model

• Each node generates data packets according to a Poisson process with rate λ.
• No transmission errors.
• For DCF, propagation time is assumed to be the same for all pairs of nodes; when a node begins to transmit, some times later all the other nodes know it at the same time. This is not true for CSMA/CD, for which each node is equally spaced on the bus and propagation times for each pair of nodes are proportional to their distance.

Parameters

MAC:	CSMA/CD DCF
Number of nodes N:
Packet arrival rate λ:
Buffer size:
Packet size:	octets
Transmission rate:	bps
Maximum propagation time:	μs
Slot time:	μs
Interframe gap:	bits
Air propagation time:	μs
Slot time:	μs
SIFS:	μs
DIFS:	μs (= SIFS + 2 × SlotTime)

Simulation

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Tip: Click the nodes to generate packets independently of the random processes.

Results

Number of nodes	Packet arrival rate (pkts/s)	Throughput (pkts/s)	Mean packet delay (ms)	Collision probability	Packet drop rate 1	Packet drop rate 2