lec13 - ECE 333: Introduction to Communication Networks...

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1 ECE 333: Introduction to Communication Networks Fall 2002 Lecture 13: Medium Access Control I Introduction Static Allocations 2 In Lecture 1, we classified links as either broadcast or point-to-point. With a broadcast link, more than two users share the same transmission media. At times an entire network, in particular a LAN, will consist of a single broadcast link connecting a group of users 1 . In this case we refer to the network itself as a broadcast network . A broadcast link is also called a multiaccess channel. In such a channel, 1. A transmitter can be heard by multiple receivers 2. A receiver can hear multiple transmitters. The first point implies that a technique is needed to decide which receiver(s) a transmitted packet was meant for. A direct way to accomplish this is through addressing , i.e., each receiver is assigned an address in the form of a unique bit sequence, and this address is then added to the header field, before sending a packet. Regarding the second point, if two transmitters transmit at the same time, their signals may interfere or collide and not be recoverable at the receiver. A method is needed to share the broadcast link among the various transmitters and avoid such collisions; this is called the medium access control (MAC) problem. We will examine various solutions to this problem in the next several lectures. Before discussing these solutions in detail, we first describe several situations where broadcast links arise. We then look at where the medium access control problem is commonly addressed in a layered network architecture. Next we categorize the possible solution approaches, and begin discussing some specific approaches. 1 The primary reason LANs have been designed this way is that it is a very cost effective approach for connecting together a group of users in a small geographical area.
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3 Examples of broadcast links: In the following we mention a few representative examples of broadcast links, several other examples will be provided in later lectures. Shared Bus:
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This note was uploaded on 10/12/2009 for the course ECE ECE 333 taught by Professor Randallberry during the Fall '02 term at North-West Uni..

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lec13 - ECE 333: Introduction to Communication Networks...

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