Wireless networking, CSMA, and SSID

Wi-Fi

Wi-Fi

A local wireless technology enabling devices to connect to the Internet via a WAP

WAP

Wireless Access Point

Wi-Fi Alliance

Organisation consisting of hundreds of manufacturers that establishes international standards for interoperability and backwards compatibility and enforces the use of standards for network connections and device connectivity

Interoperability

The ability of different systems, devices, applications, or products to connect and communicate with each other in a coordinated way without effort from the end user

Backwards compatibility

The ability for a product or technology to interoperate with an older, legacy system or technology

When was the Wi-Fi Alliance formed?

1999

What components are needed for wireless communication?

• Device - wireless network adapter

• WAP

• Router (to connect to the Internet)

Station

The combination of a computer and interface controller

WPA

Wi-Fi Protected Access

WPA2

Wi-Fi Protected Access II

Wi-Fi Protected Access (WPA)

A wireless security protocol previously used to secure wireless networks, replaced by WPA2

Wi-Fi Protected Access II (WPA2)

A wireless security protocol built into wireless NICs used to secure wireless networks

How many bits are allocated to each key generated for each packet sent on a network secured by WPA2?

128

Allow list

A list specifying the MAC addresses of devices permitted to join a network

Deny list

A list specifying the MAC addresses of devices not permitted to join a network

SSID

Service Set Identification

Service Set Identification (SSID)

A locally-unique informal name given to a network to identify it

Why does disabling the broadcast of a network’s SSID not completely hide a wireless network?

The network is still visible in specialist tools and, on some devices, visible as ‘Hidden network’

CSMA/CA

Carrier Sense Multiple Access/Collision Avoidance

Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)

Protocol for carrier transmission in wireless LANs for avoiding collisions occurring on a data channel

Why is collision avoidance not always possible using CSMA/CA?

The ‘hidden nodes’ problem

Hidden node

A node that can be heard by the WAP but not by another node trying to transmit data

Outline the steps for transmitting data using CSMA/CA without RTS/CTS

1. Node listens for signals to determine whether another node is transmitting

2. If signal detected

   1. Wait for random period of time for other node to stop transmitting

   2. Listen again

3. If no signal is detected, start transmitting data

4. Node continues listening to the channel

5. If node detects collision

   1. Stop transmitting

   2. Wait random amount of time

   3. Try again

Why is RTS/CTS used with CSMA/CA?

Counteracts the problem of ‘hidden nodes’

RTS signal

Request to Send signal

CTS signal

Clear to Send signal

Outline the steps for transmitting data using CSMA/CA with RTS/CTS

1. Node listens for signals to determine whether another node is transmitting

2. Signal detected → waits for random period of time for node to stop transmitting → listen again

3. If no signal is detected, transmit an RTS signal

4. When channel is idle, WAP sends a CTS signal back to the node

5. Start transmitting data