ETHERNET DEVICES -BY MUJTABA FARAZ

OBJECTIVES

CSMA/CD Algorithm

Hubs

Bridges

Ether Switches

Working of Ethernet switches

CSMA/CD Algorithmo CSMA/CD logic helps to prevent collisions and also defines how to act when a

collision does occur.

Working of CSMA/CD:

Step 1: A device with a frame to send listens until the Ethernet is not busy

Step 2: When the Ethernet is not busy the sender(s) begin sending the frame

Step 3: The sender(s) listen to make sure that no collision occurred

Step 4: If a collision occurs, the devices that had been sending a frame each send a jamming signal to ensure that all stations recognize the collision

Step 5: After the jamming is complete, each sender randomizes a timer and waits that long before trying to resend the collided frame

Step6: When each random timer expires, the process starts over with step 1

Draw Backs of CSMA/CD:

It does not prevent collision rather it ensures that the Ethernet

works well even though collision occurs

Only one device can send frame at any one instant of time

The logic of waiting to send a frame until a LAN is silent makes the

Ethernet half duplex

Random timing after the jamming signal effects the speed of the

Ethernet

HUBS• Hubs are also known as repeaters with multiple physical ports

• Hubs regenerates the electrical signal that comes in one port and sends the same signal out every other ports

• Hubs has one Collision and broadcast domain

Draw Backs of Hub:

1. High collision rate2. Overall Network Performance is low3. Not efficient for big network

Network Bridgeso Bridges are intelligent devices

o They have the ability to learn MAC addresses

o Bridges divides the network into multiple collision domains

Draw backs:

1. Bridges are slow devices

2. Separate software is used learning the MAC address

SWITCHES

Ethernet switches eliminates the collisions in the network

Each port of a switch is one collision domain

Communication in a switch is full duplex

High Speed Communication

How Does Switch..Switches