Link Layer Flashcards
List and explain 3 Link layer services
1- framing datagram by encapsulation
2- reliable delivery between adjacent nodes
3- error detection
What does the Link Layer do?
Transferring datagram from one node to another.
Where is the link layer implemented?
In each and every host
Name two error detection methods the link layer uses and explain.
1) Single bit parity- detects single bit errors
2) 2-dimensional bit parity- detects and corrects single bit errors
What is cyclic redundancy check?
Code added to data which is used to detect errors.
What are the 2 types of links?
- Point to point
- Broadcast
What is collision?
This happens in broadcast links where a node receives two or more signals at once
How do we manage collision?
Multiple access protocol
What does channel partitioning MAC protocols do? give 2 examples
Divides A channel into smaller pieces. (TDMA)Time Division Multiple Access, (FDMA) Frequency Division Multiple Access
What do random access MAC protocols do? give an example
Detects collisions and recover eg. Slotted ALOHA, CSMA
Give an advantage and a disadvantage to Slotted ALOHA
+ Simple
- Collisions wastes slots
How does CSMA work?
If channel sensed idle, transmit entire frame. If channel sensed busy, defer transmission. Collisions may still occur.
Whats CSMA/CD?
Collision detection within a short amount of time
Name 2 taking turns protocols
1) token passing
2) polling
What’s a MAC(or LAN or Ethernet) address?
Gets frames from one interface to another physically-connected interface. e.g. 1A-2F-BB-76-09-AD
What’s ARP(Address Resolution Protocol) table?
Allows you to determine an interfaces MAC address given it’s IP address
What is a Star network topology?
One where ethernet switch is in the center and each link runs an ethernet protocol
List 2 characteristics of ethernet?
- Unreliable
- Connectionless(no handshaking)
How do ethernet switches know which hosts can be reached through which interfaces?
Self learning, recording sender and location pair in a switch table
Whats the difference between Switches and Routers? In the context of computer network layers
Routers– network layer device
Switches– link layer device
