Ethernet And Wireless

Question 1

What is the transmission algorithm for Ethernet?

Answer 1

CSMA/CD
- Send data if idle,
- Detect collisions and send jamming,
- Use exponential back off

Question 2

What is the transmission algorithm for WiFi (802.11)?

Answer 2

CSMA/CA:
- Send RTS,
- Wait for CTS,
- Transmit frame,
- Wait for ACK

Question 3

How are the transmission algorithms for Ethernet and Wifi(802.11) the same or different?

Answer 3

Same:
- Both check the channel is idle before sending

Different:
- Ethernet detects collisions
- WiFi avoids them using RTS and ACKs

Question 4

When the transmission algorithm for Ethernet and WiFi (802.11) has a collision, what happens?

Answer 4

Ethernet:
- Sender sends a jamming signal and retries after a random back off

WiFi:
- No ACK is received, sender retries after random back off

Question 5

What is the hidden node problem?

Answer 5

2 nodes can’t hear each other but collide when transmitting data

Question 6

What is the exposed node problem?

Answer 6

Nearby nodes hold off on sending data because they’re aware of other nodes and detect transmissions from them, even if their own messages won’t cause issues so things slow down for no reason

Question 7

What are the differences between the base station model and the mesh network/ad hoc network model for wireless network topologies?

Answer 7

Base Station: mobile nodes communicate through a fixed central base station using connection to the internet to communicate to other nodes

Mesh/Ad Hoc: peer nodes forward messages through each other without the base station