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Understanding the network.pdf - Back to Home

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Because all <strong>the</strong> nodes on <strong>the</strong> <strong>network</strong> are connected <strong>to</strong> one ano<strong>the</strong>r across a<br />

common transmission medium, an access control mechanism is required. The<br />

access control mechanism makes it possible for each node <strong>to</strong> have access <strong>to</strong> <strong>the</strong><br />

medium <strong>to</strong> transmit data signals. Contention-based mechanisms function on access<br />

demand, which results in <strong>the</strong> chattiest hosts dominating <strong>the</strong> segment. A<br />

non-contention-based mechanism provides an opportunity for each host <strong>to</strong> have<br />

equal access <strong>to</strong> <strong>the</strong> medium.<br />

Contention-Based Access<br />

Network contention is a difficult problem. If nodes cannot send or receive data,<br />

<strong>the</strong>re is no point <strong>to</strong> having a computer <strong>network</strong>. With star and bus <strong>network</strong><br />

<strong>to</strong>pologies, <strong>the</strong> Carrier Sense Multiple Access with Collision Detect (CSMA/CD)<br />

method is used for access control. With CSMA/CD, pro<strong>to</strong>col forces only one<br />

workstation <strong>to</strong> send data at any time (see Figure 1.6). Without this mechanism, all<br />

<strong>the</strong> hosts would send <strong>the</strong>ir data at <strong>the</strong> same time.

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