2.05 - Ethernet

Question 1

What is Ethernet?

Answer 1

Ethernet is one of the two dominant technologies in the mordern networked world. It primarily focuses on LAN. Formal name of wired ethernet is IEEE 802.3

Question 2

What is the formal name of wired ethernet?

Answer 2

IEEE 802.3

Question 3

Name

The IEEE full form

Answer 3

Institute of Electrical and Electronic Engineers

Question 4

Explain

History of Ethernet

Answer 4

It was first devised in 1970s indenpendently of any organisation. Later it was adopted by IEEE and their 802 commitee took responsibility of developing its protocol. The standard has evolved through 5 generations.

Question 5

What are the 5 generations the Ethernet went through?

Answer 5

1. Standard / Traditional
2. Fast
3. Giga bit
4. 10 Giga bit
5. 100 Giga bit

Giga bit represnts the data transfer speed capability

Question 6

Describe

The original Ethernet

Answer 6

It was implemented on a LAN bus configuration or star configuration with a hub as the central device. Messages went sent as a broadcast. Since it shared the same medium, collisions occured, corrupting data. Therefore used the CSMA/CD method.

Question 7

What was the central device of the star configuration in the original ethernet?

Answer 7

A hub

Question 8

What was the type of transmission used in the orginal ethernet?

Answer 8

Broadcast

Question 9

What had to be done after a message was recieved by the end systems in the original ethernet?

Answer 9

The destination address needed to be checked to see if it was the intended end system

Question 10

Why was using a shared medium a disadvantage when using the original ethernet?

Answer 10

Because collisions would occur which corrupts the data and causes the transmission to be unrealiable

Question 11

How do collisions occur?

Answer 11

When two end systems send signals at the same time, the voltage associated with the transmssion interfere with each other and causes corruption of individual messages.

Question 12

Name

CSMA/CD full form

Answer 12

Carrier Sense Multiple Access with Collision Detection

Question 13

Decribe

The CSMA/CD method

Answer 13

1. Check the voltage on the transmission medium
2. If this indicates activity, wait a random time before checking again
3. If no activity is detected, start transmission
4. Continuously check for a collision
5. If no collision is detected, continue transmission.
6. If a collision is detected, stop transmission of the message and transmit a jamming signal to warn all end-stations; after a random time, try again

Question 14

Decribe

The modern Ethernet

Answer 14

Modern Ethernet is switched, and the star configuration has a switch as the central device, controlling transmission to specific end systems. Each end-system is connected to the switch by a full-duplex link, so no collision is possible along that link. Because there might be high levels of activity, the switch needs to be able to store an incoming message in a buffer until the cable is free for the transmission to take place. Since collisions are now impossible, CSMA/CD is no longer needed

Question 15

What is the difference in the star configuration between the orignal an modern Ethernet?

Answer 15

Orginal used a hub as the central device but the modern uses a switch

Question 16

Why are buffers used in the modern ethernet?

Answer 16

Because there might be high levels of activity, the switch needs to store an incoming message in a buffer until the cable is free for the transmission to take place. Therefore no collisions can occur.

Question 17

Why are no collisions possible in the links of the modern ethernet from the end systems to the switch?

Answer 17

Because it uses full duplex links

Question 18

Are CSMA/CD used nowadays?

Answer 18

Even though some legacy Ethernet LANs are still operating, modern ethernet do not need CSMA/CD therefore it isnt being used.