tldr - IEEE 802.11 standards, WLAN hardware, configurations and modes
IEEE 802.11 Standards
A set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication
Protocol Comparison
802.11ac
Cool stuff it provides
Extended channel bonding
80 or 160 MHz channel width, as compared to 40 MHz in 802.11n
Denser modulation
256-QAM used, as compared to 64-QAM in 802.11n
More MIMO spatial streams (explained below)
8 streams (8x8:8), as compared to 4 in 802.11n
Multi-User MIMO (Up to 4 clients)
4 separate receivers within an AP with multiple antennas on each receiver
Beamforming
Focuses RF energy directly at receiving client
Multiple Input, Multiple Output (MIMO)
Uses multiple transmitters and receivers to transfer data simultaneously
MIMO as pure Transmitter and Receiver Diversity (Spatial Diversity)
Same data is transmitted and received with multiple antennas
Multiple copies of the same data improves reliability of system
MIMO as pure Spatial Multiplexing
Different data is transmitted and received over multiple data streams
Increases data throughput N-fold, where N is no. of data streams
MIMO hybrid mode (Spatial Diversity & Spatial Multiplexing)
Improves reliability AND increases data throughput
Possible when there are more antennas than data streams
Example
4x4:3 MIMO
4 input and 4 output antennas over 3 data streams
Hybrid mode is possible
Frequency Bands & Channels
WLAN operates on certain frequency bands, such as 2.4 GHz and 5 GHz
Each band is divided into many frequency channels
For 2.4 GHz, many channels overlap, hence to reduce interference, adjacent WLANs should use different frequency channels
2.4 GHz channels
802.11 Channels
Bandwidth of each channel is 20 MHz and Passband between channels is 5 MHz
Only 3 non-overlapping channels
Channel 1 (2.412 GHz)
Channel 6 (2.437 GHz)
Channel 11 (2.462 GHz)
Channel Bandwidth and Passband
5 GHz vs 2.4 GHz Frequency Band
👍🏼
Relatively interference free, whereas 2.4 GHz is more prone to interference as cordless home phones and microwaves also share this band
Faster speeds with the same channel width as 2.4 GHz
23 non-overlapping channels as compared to 3 in 2.4 GHz
👎🏼
Higher frequency signals of 5 GHz do not penetrate solid objects as well as 2.4 GHz signals ∴ shorter coverage range (higher frequency => shorter coverage range)
Hardware for WLAN
Wireless Network Interface Card (WNIC)
Required for devices to access wireless networks
Wireless Access Point
Transmits and receives data
Wireless Router
Comprises of
Access Point
Switch: Connects desktops, printers, servers etc.
Router: Provide internet connection through ISP via ONT / modem
AP or wireless router has to be configured to setup a WLAN.
Identification (SSID)
Name of WLAN
Properties of SSID
Case sensitive
Alphanumeric
Max 32 characters
How it works 🤔
SSID is broadcast to all wireless devices within coverage range
Clients manually select SSID of WLAN to join
Question❓
Why is it is not effective to disable SSID broadcast?
Answer
It does not prevent anyone from accessing the network. Whoever knows the name of the SSID could easily connect to the network. A hidden SSID can be discovered using WiFi sniffing tools such as inSSIDer.
Frequency Channels
Auto - AP selects best channel
Manual - Configure which channel to be used
Channels 1 to 11 are available in Singapore
Only 1, 6 and 11 are used (non-overlapping)
Wireless Security
Types (Elaborated in week 7 notes)
Open
WEP
WPA / WPA2
WPA-Enterprise / WPA2-Enterprise
Other Configurations
IP Address & Subnet Mask
AP or wireless router is also an IP host, hence IP address and subnet mask is required
DHCP
Configure range of IP addresses to be used by DHCP server
NAT
On by default
MAC Address Filter List
Specify a list of valid MAC-addresses which are allowed to join the WLAN. Not recommended as MAC addresses can be easily found using network monitoring tools and can be spoofed
Wireless LAN (WLAN) and Wired LAN
Wireless LAN
Provides hosts with physical mobility
Servers and network resources are still connected by wired network
Wired LAN
Backbone connecting users to servers and resources
WLAN Modes
Ad Hoc
Wireless devices connect directly to each other without the use of an AP or wireless router
Independent Basic Service Set (IBSS)
Easy to set up
Optional to specify SSID & Frequency channel
Small coverage and limited users
Useful for peer-to-peer comms
Can achieve high speeds but with limited functionalities
Infrastructure
Wireless router acts as
Router: connects WLAN to the internet
Switch: connects desktops, servers, printers etc. to WLAN
AP: provide wireless connectivity to wireless devices
Basic Service Set (BSS)
Requires at least 1 AP
Uses basic AP settings: SSID, security type, encryption type
Extended Service Set (ESS)
Uses 2 or more APs
Coverage area of APs should overlap
APs must have the same SSID
Adjacent APs must have different channel frequencies
WLAN Roaming
When wireless client moves from one point to another, it looks for an AP which provides a better service
Seamless handoff occurs when the client connects to a different AP
