Link Layer

Question 1

List and explain 3 Link layer services

Answer 1

1- framing datagram by encapsulation
2- reliable delivery between adjacent nodes
3- error detection

Question 2

What does the Link Layer do?

Answer 2

Transferring datagram from one node to another.

Question 3

Where is the link layer implemented?

Answer 3

In each and every host

Question 4

Name two error detection methods the link layer uses and explain.

Answer 4

1) Single bit parity- detects single bit errors

2) 2-dimensional bit parity- detects and corrects single bit errors

Question 5

What is cyclic redundancy check?

Answer 5

Code added to data which is used to detect errors.

Question 6

What are the 2 types of links?

Answer 6

• Point to point

- Broadcast

Question 7

What is collision?

Answer 7

This happens in broadcast links where a node receives two or more signals at once

Question 8

How do we manage collision?

Answer 8

Multiple access protocol

Question 9

What does channel partitioning MAC protocols do? give 2 examples

Answer 9

Divides A channel into smaller pieces. (TDMA)Time Division Multiple Access, (FDMA) Frequency Division Multiple Access

Question 10

What do random access MAC protocols do? give an example

Answer 10

Detects collisions and recover eg. Slotted ALOHA, CSMA

Question 11

Give an advantage and a disadvantage to Slotted ALOHA

Answer 11

+ Simple

- Collisions wastes slots

Question 12

How does CSMA work?

Answer 12

If channel sensed idle, transmit entire frame. If channel sensed busy, defer transmission. Collisions may still occur.

Question 13

Whats CSMA/CD?

Answer 13

Collision detection within a short amount of time

Question 14

Name 2 taking turns protocols

Answer 14

1) token passing

2) polling

Question 15

What’s a MAC(or LAN or Ethernet) address?

Answer 15

Gets frames from one interface to another physically-connected interface. e.g. 1A-2F-BB-76-09-AD

Question 16

What’s ARP(Address Resolution Protocol) table?

Answer 16

Allows you to determine an interfaces MAC address given it’s IP address

Question 17

What is a Star network topology?

Answer 17

One where ethernet switch is in the center and each link runs an ethernet protocol

Question 18

List 2 characteristics of ethernet?

Answer 18

• Unreliable

- Connectionless(no handshaking)

Question 19

How do ethernet switches know which hosts can be reached through which interfaces?

Answer 19

Self learning, recording sender and location pair in a switch table

Question 20

Whats the difference between Switches and Routers? In the context of computer network layers

Answer 20

Routers– network layer device

Switches– link layer device