Ethernet Networking

Ethernet Networking

Ethernet Networking means networking with Ethernet Technology.

Ethernet is a contention media access method that allows all hosts on a network to share the same bandwith of a link.

Ethernet is widely used because it is compatible with new technologies like fast ethernet and gigabit ethernet, and troubleshooting is easier and less expensive.

Ethernet uses CSMA/CD (Collision Sense Multiple Access / Collision Detection), a protocol that helps devices share the same bandwith,without having two devices transmit at the same time ina network medium.

CSMA/CD was created to overcome the problem of collision, that used to occur when packets were transmitted from two different nodes at the same time.

Working of an Ethernet:

When a host wants to transmit a packet over the network, first it checks for the presence of digital signals on the wire. If it is clear, it starts transmitting; while transmitting it monitors if any other device is trying to transmit, if any other host is trying to transmit, it sends a jam signal (busy signal). The other host responds to the busy signal by waiting for sometime before attempting to transmit again. If collision keeps occuring for 15 tries, the node attempting to transmit will then get timed-out.

So, when a collision occurs on an Ethernet LAN, following happens:

             

            1.       A jam signal informs all the devices that a collision occurred.

            2.       The coliision invokes a random back-off algorithm.

            3.       Each device on the Ethernet segment stops transmitting for a short while until the timer expires.

            4.       All hosts have equal priority to transmit after the timer expires. (After the timer has expired, it works  on First come, First served basis)

Disadvantages of CSMA/CD:

          

            1.       Delay

            2.       Low throughput

            3.       Congestion

Half Duplex Ethernet:

It uses CSMA/CD, to prevent collisions and permit retransmission if a collision occurs. It is used maily for HUBS, which is a One Collision Domain. It uses only one wire, through which it can either transmit or receive at a time.

Full Duplex Ethernet:

Generally meant for Bridges and Switches, or point-to-point connection. It has two wires, one for transmitting and the other for receiving. No collision occurs here.

 Note: Half Duplex Ethernet shares a collision domain and provides a lower throughput than Full Duplex which has a private collision domain and higher effective throughput.

Point to Remember:

             

             1.       No Collision occurs in Full-Duplex

             2.       A dedicated Switch port is required for each Full-Duplex node

             3.       The Host NIC and the Switch port must be capable of operating in full duplex.

 Thank You.

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