Week 9 - MAC protocols & VLANs

Question 1

What are 2 examples of broadcast link-layer technologies?

Answer 1

1. Ethernet
2. Wireless LANs

Question 2

What is a MAC random access protocol?

Answer 2

Each station is treated equally (random access).

Question 3

What are the 5 categories of MAC random access protocols?

Answer 3

1. Pure Aloha
2. Slotted Aloha
3. CSMA
4. CSMA/CD
5. CSMA/CA

Question 4

What is the pure aloha procedure?

Answer 4

Depends on ACKs

Each station sends a frame when it can

Sender Time-out is 2 x Tp

Backoff time Tb is waited if ACK not received (send not successful)

Question 5

What is the difference between Pure Aloha and Slotted Aloha?

Answer 5

Slotted Aloha uses slots/frame transmission times to prevent overlapping of frames sent.

Contains collisions to a slot.

Question 6

What is CSMA?

Answer 6

Carrier Sense Multiple Access

Senses medium using energy levels.

Uses persistent methods

Question 7

What is the difference between CSMA/CD and CSMA/CA?

Answer 7

CD is collision detection
CA is collision avoidance

Question 8

What does a link-layer switch do?

Answer 8

Receives frames and forwards them to ports based on MAC address.

Question 9

How does switch self-learning work?

Answer 9

Uses switch table with ports mapped to MAC addresses.

switch learns from incoming frames.

If outgoing MAC address unknown, all unknown ports are flooded with the packet.

Question 10

How can we define multiple broadcast domains?

Answer 10

VLAN

Question 11

What are VLANs for?

Answer 11

Logical configuration
Can take multiple physical LANs and essentially create one massive VLAN switch which can logically create its own broadcast domains.

Question 12

What is a trunk port/link for?

Answer 12

Connecting VLAN switches

Question 13

What is frame tagging?

Answer 13

VLAN tag to indicate the VLANs that that the frame corresponds to when using a trunk link.