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Shift Operation

This operation shifts all the bits to the left by one position.
Example:
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This figure represents a 16-bit CRC hardware which uses 3 shift registers and 3 XOR units.

Types of Errors

CRC can check following errors better than checksum.

Vertical Errors

These occur due to hardware failure.
Example: 2nd bit of each character is damaged.

Burst Errors

These occur when a small set of bits changes due to some external interference like lightning or an electric motor starting nearby.

Frame Format and Error Detection

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If there is an error in the frame, it is rejected by the receiver.

LAN Technology and Network Topology

Introduction

In a shared medium, hardware devices need to take turns in able to communicate.

Direct Point-to-Point Communication

In this mode, each channel connects exactly 2 devices.
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Advantages

  1. The connection type of individual connections can be different.
  2. Individual connections can choose a different frame format and error detection mechanism etc.
  3. It is easy to enforce security and privacy

Disadvantages

  1. The no. of connections grow more rapidly than the no. of computers.
  2. For ‘n’ computers connections = (n^2 – n)/2.
  3. Most computers use the same physical path.
  4. Direct point-to-point communication is expensive due to a no. of connections.
  5. Another disadvantage is that adding a new computer to the network requires N-1 new connections as shown in the above figure.