Monday, January 24, 2011

Starting a Wireless Mesh Network Simulation

This blog was part of my daily journal when I was doing my thesis during my graduate work. It might be of help to someone doing his own.

Initially, to get the feeling of mesh networking in network in simulator 2 (ns2), I set up 5 pairs of nodes using the multi-rate implementation of 802.11b as shown below:

(4) ------------------------------------> (9)

(3) ------------------------------------> (8)

(2) ------------------------------------> (7)

(1) ------------------------------------> (6) +
(0) ------------------------------------> (5) +
|<-------------- 5m ------------------> |
datarate 11mbps (mode 11mb)
basicrate 1mb
routing protocol, AODV

Sending rate increases from 0.1mb, 0.4, 0.8, 1, 1.6, 2.2 mbps at times 0, 5, 10, 15, 20, 25 s respectively.
When I set up the network above and running the simulation, the nodes seemed to drop all packets right at the routing layer. One of the error said NRTE “no route ”, something that was impossible, because when only a pair would exchange data, they could find each other.

In this case, the most probable reason that all packets got dropped was that it took longer time for the mesh network routing algorithm to converge in building the network topology. Packets got dropped because the nodes have no routes for the packets being sent, as suggested by one of the errors NRTE (no route to destination). So I went back to the 5 pair mesh network set-up.

True enough, after re-scheduling transmissions of data, and aiding the nodes to build first their routing table, all node-pairs were able to exchange data. Convergence time really was longer in the multi-rate implementation (than in the default implementation). To aid the routing algorithm in building the routing topology, for the first twenty (20) seconds of the simulation, I let one node at a time send two small dummy packets every 4 seconds. Then letting, cbr applications, burst at the 30th second. Consequently, transmission and reception of cbr packets converge between the 60th and 70th second of the simulation, i.e., when all pairs are able to transmit fairly the same amount of packets.

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