Media Access

Question 1

What can 802.11 cant do?

Answer 1

It cannot detect if collision occurs

Question 2

What is DCF?

Answer 2

Distributed Coordination Function

It is a mandatory access mode of 802.11 standard

Question 3

What are the main components of DCF?

Answer 3

InterFrame Space IFS
Duration/ID Field
Carrier Sense Physical and Virtual
Random Back-Off Timer

Question 4

What is IFS?

Answer 4

Interframe Space

Time period between Wireless Transmissions

Question 5

Types of IFS

Answer 5

Reduced Interframe Space
Short Inteframe space
PCF interframe space
DCF interframe space
Arbitration interface space
Extended interframe space

Question 6

Types of Carrier Senses?

Answer 6

Physical Carrier Sense
performed by stations not transmitting or receiving
listens for traffic
Virtual Carrier Sense
Uses NAV
Stations can not transmit unless the NAV value is 0

Question 7

What is NAV?

Answer 7

Network Allocation Vector

Question 8

What is CSMA / CD?

Answer 8

start - if the packet is ready - transmit - colission detected - backoff

Question 9

What is CSMA / CA?

Answer 9

start - construct frame - is it idle? - transmit RTS - cts received? - transmit application data - end

Question 10

What is physical carrier sense?

Answer 10

Performed constantly when a station is not transmitting or receiving
Checks if the channel is busy

Question 11

Two purposes of physical carrier sense?

Answer 11

Determine if a frame transmission is inbound for a station to receive
Determine if the medium is busy

Question 12

What is a random back off timer?

Answer 12

Final timer used prior to transmission

Question 13

What is PCF?

Answer 13

Point Coordination Function
Optional 802.11 media access method
uses a form of polling
AP acts as a Point Coordinator

Question 14

What is HCF?

Answer 14

Hybrid Coordination Function
Combines capabilities from DCF and PCF
Creates two channel access method EDCA
HCCA