WiFi
IEEE 802 standards deal with Local Area Network & Metropolitan Area Network. The services and protocols specified in IEEE 802 map to the lower two layers of the seven-layer OSI networking reference model (Physical and Data Link).
IEEE 802.3 for Ethernet
IEEE 802.15 for Bluetooth
IEEE 802.11 for WLAN & Mesh (WiFi certification) [WiFi/WLAN/Wireless Ethernet]
Wireless Local Area Network (WLAN) channels are accessed using IEEE 802.11 protocols, under the trademark WiFi Technology. The 802.11 standard provides several distinct radio frequency ranges for use in WiFi communications: 900 MHz (802.11 ah), 2.4 GHz (802.11 b/g/n/ax), 3.6 GHz (802.11 y), 4.9 GHz (802.11 j), 5 GHz (802.11 a/h/j/n/ac/ax), 5.9 GHz (802.11 p) and 60 GHz (802.11 ad/ay) bands. Each range is divided into a multitude of channels.
WiFi frequencies
High freq -> More speed -> Less range -> High power signal more losses, More channels
Low freq -> Less speed -> More range -> Less channels
2.4 GHz Band
- It is unregulated ISM band (Industrial, Scientific and Medical)
- Used by 802.11 b/g/n/ax
- Fourteen channels (starting from 2412 MHz), spaced 5 MHz apart from each other, except for a 12 MHz space before channel 14. (1, 6 and 11 are non overlapping channels)
- It is most congested band with other equipment such as, cordless, microwave, bluetooth, zigbee, baby monitors, walkie-talkies, Routers, Laptops, Remote Control toy-car etc.
5 GHz Band
- It is a UNII band (Unlicensed National Information Infrastructure). It is also used by Military/Civil establishments (Weather) for Radar Radio equipments (must support Dynamic Freq Selection-DFS and Transmit Power Control-TPC to avoid interference with Radar Radios).
- Used by 802.11 a/h/j/n/ac/ax
- WiFi 802.11 a/n/ac generally use 5.725 -5.825 GHz
How WiFi network works
Wi-Fi network uses radio waves to communicate with each other among devices (Use unlicensed part of the radio spectrum). An access point to the internet connection can be installed through the Wi-Fi hotspot. This access point acts as base station. With this access point, an antenna is physically connected to conventional wired Ethernet network and serves as a bridge to the wireless network.
The actual performance of the network depends upon the signal pattern and the number of obstacles in the area.
To indicate the wireless within the area, an access point itself announces through broadcasting, a Service Set Identifier (SSID) approximately 10 times per second. The SSID indicates the name of the network. PCs that are within the range and has equipped with a wireless network interface card can receive the SSID, associate with WLAN and request an IP address that will allow them to connect to the local network, surf the internet and view network folders.
WiFi Network Topologies
AP-based Topology (Infrastructure Mode)
- BSS configuration - Basic Service Set (BSS)
- A single Access Point (AP) and its roaming Nodes. AP hears each Nodes, but Nodes can't hear each other.
- Nodes communicate through AP
AP contains standard IEEE 802.11 conformant MAC and PHY interface to the wireless medium and provides access to the distribution system for associated stations. Through an AP, BSA-RF coverage is provided (Basic Service Access is the area of the radio frequency (RF)).
- ESS configuration - Extended BSS (EBSS)
- Multiple APs with respective roaming Nodes (forming individual BSS) and the Distribution System (DS) connecting APs (i.e. connecting BSS with wired network). A Node can roam from one BSS to other BSS.
- It is formed by 2 or more BSS, with 10-15% overlap within ESA cell to allow roaming
ESA consists of two or more BSA (Extended Service Access).
Peer-to-peer Topology (Ad-hoc Mode)
- Ad-hoc configuration - Independent BSS (IBSS)
- Ad-hoc group of roaming Nodes, communicate with each other without connection to a wired network. (like hotspot)
- AP is not required
- Nodes within a cell can communicate directly with each other
Point-to-multipoint bridge Topology
- LAN from one connection to LAN to other connection, which require a clear line of sight
Hidden Node Problem in BSS
AP can hear all Nodes in BSS, and all Nodes can hear AP. But Nodes can't hear each other.
So multiple Nodes can start transmitting at the same time. If they are using the same channel then frame will collide and participating Nodes will not know about it.
Only receiver AP can help to avoid collision using 4-way Handshake for Collision Avoidance between AP and a Node
AP <---(RTS+DestAddr+MsgDuration)--- Node
AP ---(CTS)---> Node (Others receive then back off for duration and set NAV register)
AP <---(DATA)--- AP
AP ---(ACK)---> Node)
RTS=Ready To Send
CTS=Clear To Send
NAV=Network Allocation Vector
WiFi Security Components
- Authentication
It is about keeping unauthorized users off from the network.
- User Authentication
In user authentication, the username and password is required. There exist risk of sending data before the secure channel is established and level to passing eavesdropping by attackers.
Solution for this is, to establish encrypted channel before sending username & password.
- Server Authentication
In server authentication, the digital certificate is used and within the client software the validation of the digital certificate occurs automatically.
- Privacy
Wireless Protected Access (WPA) is a standard based specification, interoperable security enhancement that strongly increases the level of data protection and for existing access control and future wireless LAN systems.
For security & safeguard, it has 802.1X Access Control & IEEE 802.11i
Firewalls and anti-virus software protect network from uninvited users & keep information secure.
Though,
The most common wireless encryption standard, Wired Equivalent Privacy (WEP) has been broken even if the correct configuration is set up.
Typically, Wi-Fi Access Point is set to default to an open (encryption-free) mode.
WiFi Version numbers
Source:
#) "Wi-Fi now has version numbers, and Wi-Fi 6 comes out next year"
#) "Next-generation 802.11ax wi-fi: Dense, fast, delayed"
Following 802.11 standards are growing to supply a higher data rates and better quality of service. These standards also defines the bands used by wireless network and also defines the modulation technique.
In 802.11g, using the OFDM technique data rates drastically.
But 802.11b was preferred as least expensive & better performance, instead of more expensive 802.11g.
MIMO (Multiple Input Multiple Output)
- Receive and/or Transmit simultaneously through multiple antennas
- 802.11 defines many "MxN" MIMO configurations (i.e. AP with M transmit & N receive antennas)
- MIMO uses an advance signal processing techniques
- Spatial Multiplexing/Multipath Diversity
- Divide outgoing signal into multiple pieces (spatial stream)
- Each piece is transmitted through different antenna
- Receiver re-assembles back the original stream
- Multiplexing two/multiple spatial streams into single channel (radio frequency) effectively doubles the capacity
- and thus maximizes data rate
IEEE 802.11a
Less interference in the 5GHz band appears, means it is potential for more reliable transmission.
Some of the countries have other uses of 5GHz band, such as military and air traffic control, so therefore this band is not globally accepted and to be used in the ISM applications. But in some cases, this band can be used inside the building with limited power. In the U.S, the band 5GHz is treated as other 900MHz and 2.4GHz ISM bands. One advantage of the IEEE 802.11a is that it operates with the same data rate (54Mbps) as IEEE 802.11g but it escapes sometimes due to crowded with the 2.4GHz channels.
IEEE 802.11g
This standard is more expensive, sp it is preferred to go for the least expensive and better performance which is 802.11b.
IEEE 802.11ax
Faster speed & better performance when handling a multitude of device.
Bunch of technical improvements, which add up to a transmit rate now at up to 11 Gbit/s
Up to 30 percent faster top speeds over its forebear.
Uses a suite of new and extended technologies to solve some of WiFi's more enduring problems, including client density and latency.
With four times as much data deliverable simultaneously to multiple clients and latency cut by 75 percent, the user experience should be much improved.
Also retains full backwards compatibility with older standards -- an essential feature, but one that comes at a cost.
In particular, 802.11ax may solve one of technology's greater ironies -- that any large conference dedicated to wireless communication has unusable WiFi. The same problem occurs at stadium events, busy concourses, and large events. An 802.11ax access point (AP) will not have much greater throughput than the 1Gbps or so that an 802.11ac device could manage, but it can split that total efficiently between many more simultaneous connections.
Radio : At the base of the 802.11ax innovation tree is the way it handles radio frequencies. It has to use the same spectrum allocations on 2.4GHz and 5GHz as before, with sets of 20MHz-wide channels that can be grouped together in blocks up to 160MHz wide. But within those 20MHz channels, 802.11ax subdivides the frequency space into 256 subchannels -- four times more than the 64 subchannels previously used. This improves the resolution with which a link can cope with interference, frequency-dependent fading and so on.
The greater density of narrower subcarriers gives 802.11ax more flexibility to control each channel, equalising characteristics with more precision and allocating groups of subchannels to many clients simultaneously.
A bigger change is in the way 802.11ax uses the subchannels. Before, all subchannels were used in parallel to talk to an individual device, which monopolised the channel until it was handed over to another device. 802.11ax allocates subchannels into resource units (RUs) that can be used to talk simultaneously with multiple 802.11ax clients -- up to nine on one 20MHz channel, or 74 on a 160MHz channel group. This means much lower latency and fairer distribution of bandwidth between 802.11ax clients. The AP can send clients trigger frames that query what sort of service is required, while the clients reply with buffer status reports that the AP uses to allocate RUs.
The old 64-subcarrier system was called Orthogonal Frequency Division Multiplex (OFDM) -- 'orthogonal' meaning the frequencies were related to each other so as to minimise interference between subcarriers. The new 802.11ax version is called Multi-User Orthogonal Frequency Division Multiple Access (MU-OFDMA). This may prove useful if you go to the wrong sort of pub quiz.
References:
2) "WiFi Explained in Detail | Wifi 802.11 a, b, g, n, ac" https://www.youtube.com/watch?v=M6E87su5vR0