Week 8

Question 1

How does throughput in wireless network compare with wired network

Answer 1

Wired network offer higher and more stable throughput, ideal for heavy network task

More secure, higher throughput, lower latency, lower interference

Question 2

What factor influence throughput in wireless LANs

Answer 2

1. Signal strength and quality
2. Interference
3. Distance from AP
4. Number of users
5. Channel bandwidth
6. Network protocol
7. Network traffic
8. Antenna strength/ MIMO

Question 3

Why advertised throughput is always lower than raw data rate?

Answer 3

a. Encapsulation overhead
1. Physical overhead
2. MAC header overhead (Media access control)
3. Encryption protocols

B. CSMA/CA overhead

Question 4

Explain 802.11n advances (WIFI 4)

Answer 4

1. MIMO
2. Short guard interval
3. Channell bonding
4. Frame aggregation
5. Block acknowledgements

Question 5

Explain MIMO

Answer 5

Multiple in multiple out
- Uses multiple RF streams with multiple antenna
- Require multipath to work well

Question 6

Explain spatial multiplexing

Answer 6

Technique used in MIMO
- multiple antenna from sender and receiver
- original data is split into separate streams
- sent from different antenna and combined upon receiver through advanced signal processing

To understand, ab:c,44:4

-a: sender antenna
- b: receiver antenna
-c: number of streams

Question 7

Explain channel bonding

Answer 7

Two adjacent channel are combined, when are within a frequency range, increasing throughput

Question 8

Explain short guard interval

Answer 8

Typically found in OFDM (orthogonal frequency division multiplexing), where guard interval is placed between (data broken down) symbols to prevent intersymbol interference (ISI) due to delay multipath

Question 9

Explain channel bonding

Answer 9

A process when two adjacent channel are combined, within a given frequency range to increase output

Question 10

Explain frame aggregation

Answer 10

It aggregate multiple MAC data together to form a long MAC frame

Question 11

Explain block ack

Answer 11

Block ack is block acknowledgement, where sender and receiver send multiple frames, which receiver reply only with one block ack, containing information of frames thats received and which is not

Question 12

Explain beamforming

Answer 12

A method used to focus the network connections on a direct location, instead of spreading it omnidirectional

Question 13

Explain 802.11ah

Answer 13

Known as Wifi Halow, used for low power, long range wireless communications.

Low data rates, but far distances