6.4 - Wireless Networking, CSMA &SSID Flashcards
What is Wi-Fi?
A wireless networking technology providing high-speed Internet and network connections
How do devices connect to the internet?
Via a WAP (wireless access point)
What is needed to connect to a wireless network?
ISP (Internet Service Provider)
Modem and wireless router (often combined)
Device with a NIC
What is a Service Set IDentifier? (SSID)
Identifies each network by a unique name
- must be used by all devices on that network
- can be set manually or automatically
- can be hidden to make it harder to detect
- can be set to broadcast to wireless devices in range of the wireless access point
Why are wireless networks less secure?
- unauthorised users can be hard to spot
- transmitted data can be easily intercepted
How can the wireless networks be made more secure?
Have protocols:
WPA
WPA2
What does WPA/WPA2 do?
Generates a 128-bit key for every packet of data sent
- very strong encryption
- usually pre-installed on wireless NIC’s
What happens if two devices transmit data simultaneously via a single WAP?
Data collisions can occur
How can you avoid data collisions?
Have a protocol
CMSA/CA
How does the CMSA/CA (carrier sense multiple access with collision avoidance) protocol work?
- a frame is assembled
If the channel is idle: - data is transmitted
If not: - wait a random time until the channel is idle
What does the carrier sense part of CMSA mean?
Each node continually listens to/tests the network frequency for the presence of a signal prior to transmitting
What does the multiple access part of CMSA mean?
Many computers attempting to transmit and compete for opportunity to send data
How does CMSA/CA work? (a lot)
- sending computer listens
- if there is already traffic on the network it waits
- when no traffic, sender issues RTS (request to send)
- WAP responds with CTS (clear to send) if it is ok to send
- the RTS/CTS signals block any other transmissions
- if CTS not received the user must wait
- once receiver has received the data it sends ACK
- sender waits for ACK so it knows data is received
- if no ACK received, sender will retransmit after a reasonable time
- ACK indicates to other devices that they can transmit
Draw the flowchart for CMSA/CA using RTS/CTS?
Start (oval)
Assemble a frame (rectangle)
Channel idle (diamond) -> no -> wait a random time (rectangle) -> back to channel idle
If channel idle == yes:
Transmit RTS (request to send)(rectangle)
CTS (clear to send) received? (Diamond) -> no -> wait a random time
If CTS == yes:
Transmit data
Stop
How does MAC address white list/filtering work?
- WAP checks MAC addresses of device trying to connect to network against list of allowed addresses
- only devices with an allowed MAC addresses are able to connect, devices without an allowed MAC addresses are not able to connect
