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

• Formed in 1999
• Establishes international standards for interoperability and backwards compatibility
  • 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
• Consists of hundreds of companies around the world
• Enforces the use of standards for network connections and device connectivity

Components required

• Device needs a wireless network adaptor
• Station: the combination of a computer and interface controller
• All stations share a single radio frequency communication channel
• Each station is tuned in on this frequency to pick up transmissions
• Transmissions are received by all stations within range of the WAP
• WAP usually connects to a router but this can be part of the router itself

Security

Security protocols and certification programs used to secure wireless networks:

• WPA: Wi-Fi Protected Access
• WPA2: Wi-Fi Protected Access II

WPA

• Older, replaced by WPA2

WPA2

• Built into wireless NICs
• Provides strong encryption of data transmissions
  • 128-bit key generated for each packet sent

Allow lists (prev. whitelists)

• Some network admins use MAC address allow lists to control who is allowed on the network
• The opposite of an allow list is a deny list, which specifies the MAC addresses of devices not allowed on the network
• Allow lists and deny lists were previously known as white- and black- lists respectively, but use industry-wide has generally declined over the racist connotations the terms have

SSID

• SSID: Service Set Identification
• Service Set Identification (SSID): A locally-unique informal name given to a network to identify it
• Broadcast of SSID can be disable to hide network from most users
  • Not completely hidden - network still visible in specialist tools or visible as ‘Hidden network’

CSMA/CA

• 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
• Collision avoidance not always possible due to the ‘hidden nodes’ problem
• Hidden node: A node that can be heard by the WAP but not by another node trying to transmit data
• Relies on acknowledgements to know that data has arrived successfully

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

With RTS/CTS

• Counteracts the problem of ‘hidden nodes’
• RTS signal: Request to Send signal
• CTS signal: Clear to Send signal

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

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