The Simulation Of Random Access Technique Based On OPNET

In communication network, whenever two or more users are transmitting on the sharing channel simultaneously, there will be a collision and the data can't be received correctly. In the case, packets may have to be retransmitted until they are correctly received eventually. In reality, building up links between any two users is impossible. The basic reason is the follows: firstly, the cost is expensive, besides that, it is difficult to extend, the last question is that the utilization of links is very low. In correspondence network, the definition of multiple access protocol is how to solve the question that the links can server all the users with sharing resources efficiently and fairly.This thesis is based on the network of sharing medium, which mainly discusses random access technique which also belongs to the contention-type access protocols. Many of these protocols, like Aloha, CSMA protocols and so on. At first giving the introduction to these systems, then building up models of ALOHA and CSMA based on OPNET 10.0, compare simulation results with theories.So far, CSMA/CD, CSMA/CA is popularly used in Ethernet and WLAN, Then giving explains to the back-off algorithm and collision splitting which is used in them. At last we do simulation of CSMA/CD and CSMA/CA in Ethernet and WLAN.For network' MAC, CSMA/CD and CSMA/CA can wok rightly on light traffic load, when traffic is heavy, it takes to the shortage of high delay and low utilization. The goal of the thesis is to perfect insufficient effective. In addition, capturing phenomena in Ethernet and back-off algorithm in WLAN cannot Guarantee the equal access for users. In response to the features above, the followings put forward a new adaptive back-off algorithm and distributed algorithm, reduce collision or conflict.With the development and popularization of audio and video multimedia, more and more higher requirement is put forward. To reach the goal of 5W (whoever, whenever, wherever, whomever, and whatever), there is a parallel requirement with development in wire and wireless field.