Basics of Ethernet

Ethernet 

Ethernet is the Media access method in a network where all the device or hosts, that share data or share the bandwidth in between them. Its popular due to its scalability property.

Types: Ethernet , Fast Ethernet , Gigabit Ethernet

Basically Ethernet Uses the multiple access technique of CSMA/CD (Carrier Sense Multiple Access with Collision Detection).

Collision Domain:

Under one physical domain, when two devices transmit packet/ signal / data at a same time, a interference may happen due to the collision on the transmission medium (wire).

Output of a Collision:-

• A signal Jam
• Delay in transmission
• Traffic Congestion
• Low Throughput

Note:- Ethernet works in both Physical and Datalink Layer of the OSI Model.

CSMA/CD :-

CSMA defines by its name as Accessing the Carrier or medium by sensing . CSMA/CD works when a device wants to transmit data in a network it first checks if any other signal is presence in that medium . And if any form of signal present then it detects and waits for clearance to avoid collision of data and hence to avoid traffic jam like condition which results transmission failure or delay.

* Ethernet at the Data-link layer have the main role of Ethernet addressing or MAC addressing . Also it is responsible for framing the data or packet it receives. There are four different type of Ethernet framing used as:-

                              1. Ethernet II

                              2. 802.3

                              3. 802.2

                              4.SNAP

Ethernet Frame

Ethernet Framing consists of packet like in the given figure :-

• Preamble is the header file of the frame, a pattern of  1/ 0 which gives 5 MHz clock at the start of each packet for lock the incoming bit stream of the receiving device.
• DA is the Destination Address contains 48 bits or 6 bytes.
• SA is the Source Address also contains 48 bits or 6 bytes.
• Type is used to recognize the network layer protocol contain of  2 bytes.
• Data is then the actual data sent which contains approx 50-1500 bytes.
• FCS is Frame check Sequence at the end of the frame to monitor the CRC.(Cyclic Redundancy Check).
• Ethernet at the Physical Layer are three different types according to as :-

1. 10base2
2. 10base5
3. 10baseT

 IEEE802.3 standardized as-

10base2:10mbps up to 186 meter in length supports 30 Hosts.

10base5: 10mbps up to 500 meter in length.

10baseT: 10mbps using cat3 twisted pair cabling per 1 Host supports up to 100 meter in length.

100baseTX: 100mbps using cat5/6/7 two pair cabling per 1 Host.

100baseFX: Uses fiber cabling 62.5/125 micron multimode fiber and point to point supports 400meter.

Ethernet cabling :-

Ethernet cabling can be done three types based on the requirement as :

1. Straight-through Cable

2. Crossover Cable

3. Rollover Cable.

All cabling structures has been described at section basics of cabling in this blog .

-DR