Exploring – IEEE 802.11: Why so many letters?

The IEEE 802 family of standards deals with Local Area Networks and Metropolitan Area Networks. The first meeting of the 802 LAN/MAN Standards Committee (LMSC) was held in February of 1980. As a result, it is widely associated with 80-2.(1980-February) It was the next available number so this is more of a coincidence than anything.

The 802.11 working group is responsible for all aspects of Wireless Local Area Networks. The two layers at the heart of 802.11 are the medium access control(MAC) layer and the physical(PHY) layer.

This brings us to the topic of discussion. Why are there so many different letters associated with 802.11? It would seem that 802.11 would be 802.11. The letters at the end of the working group represent the version of the standard. Each subsequent revision will use the following letter in the alphabet. Some letters are not used. This is to avoid confusion with other standards or because they look like numbers. 802.11x is not used as it looks too much like 802.1X. It is also commonly used to identify all the 802.11 versions. 802.11l looks like 802.111 or 802.11i which would be confusing. 802.11o would also be confused with 802.110.

To make it even more confusing, there are roll-up standards. When there are a handful of letter-based standards the IEEE 802.11 working group will roll all the standards into a year based roll-up standard. This will often times include an earlier roll-up standard and an alphabet soup of some of the latest letter-based standards. See below for dated roll-ups and their associated standards.

— 1999 edition
— 802.11a-1999 (Amendment 1)
— 802.11b-1999 (Amendment 2)
— 802.11b-1999/Corrigendum 1-2001
— 802.11d-2001 (Amendment 3)
— 802.11g-2003 (Amendment 4)
— 802.11h-2003 (Amendment 5)
— 802.11i-2004 (Amendment 6)
— 802.11j-2004 (Amendment 7)
— 802.11e-2005 (Amendment 8)

— 802.11-2007
— 802.11k-2008: Radio Resource Measurement of Wireless LANs (Amendment 1)
— 802.11r-2008: Fast Basic Service Set (BSS) Transition (Amendment 2)
— 802.11y-2008: 3650–3700 MHz Operation in USA (Amendment 3)
— 802.11w-2009: Protected Management Frames (Amendment 4)
— 802.11n-2009: Enhancements for Higher Throughput (Amendment 5)
— 802.11p-2010: Wireless Access in Vehicular Environments (Amendment 6)
— 802.11z-2010: Extensions to Direct-Link Setup (DLS) (Amendment 7)
— 802.11v-2011: IEEE 802.11 Wireless Network Management (Amendment 8)
— 802.11u-2011: Interworking with External Networks (Amendment 9)
— 802.11s-2011: Mesh Networking (Amendment 10)

— 802.11-2012
— 802.11ae-2012: Prioritization of Management Frames (Amendment 1)
— 802.11aa-2012: MAC Enhancements for Robust Audio Video Streaming (Amendment 2)
— 802.11ad-2012: Enhancements for Very High Throughput in the 60 GHz Band (Amendment 3)
— 802.11ac-2013: Enhancements for Very High Throughput for Operation in Bands below 6 GHz (Amendment 4)
— 802.11af-2013: Television White Spaces (TVWS) Operation (Amendment 5)

Once everything is rolled up into a dated standard, all of the previously published amendments and revisions are then retired.

Now that we have navigated by the global 802.11 map, let’s zoom in and take a look at some of the individual standards.

Let’s start at the very beginning. A very good place to start, the 1997 standard. The original standard is sometimes referred to as 802.11 prime or 802.11 legacy. With this standard, the world was introduced to many of the foundational topics surrounding wireless local area networks. We are introduced to the contention mechanism carrier sense multiple access protocol with collision avoidance.(CSMA/CA) The standard includes the authentication, association, reassociation, encryption, power management and point coordination function(PCF has not ever been implemented) provisions.
We learn from the original standard many of the definitions we still use today when defining the various components of the wireless local area network. Some of these definitions include…
Access Point: A station that provides access to a distribution system through a wireless channel.
Association: The process by which an AP to Station mapping is created which allows the station to communicate with the distribution system services.
Authentication: The process by which a Station identifies itself as a member of a set of stations allowing it to associate with another station.
Basic Service Area: The coverage of a basic service set. In laymen’s terms, the AP coverage.
Basic Service Set: The set of stations controlled by a single coordination function. Think of this like the group of stations that are associated with a single AP on a single SSID.
Beacon: Transmission scheduled at specific interval which provides data about the device one each SSID and its capabilities. Also used for transmission synchronization.
Clear Channel Assessment: Function that detects whether the physical medium is clear or currently busy.
Distributed Coordination Function: The coordination function that is used by the various stations in a basic service set to coordinate access to the shared resource. A contention method.
There are many more terms that are still used in our modern 802.11 networks that are still commonly used.
Now that we have covered some of the ways the standard has remained the same, let’s consider some of the ways this standard offered some aspects that are no longer used.
The original standard was designed for infrared devices using baseband communications and radio transmissions in the 2.4 GHz band. The modulation techniques use for encoding data on the radio channel were frequency-hopping spread spectrum and direct sequence spread spectrum. Both of the different modulation techniques could yield a data rate of 1 Mbps and 2 Mbps. Infrared allowed 2 Mbps optionally.
Two types of authentication are available in the legacy standard. Open system authentication is the most basic form of authentication. Any station that requests authentication will be authenticated. The other method is shared key authentication. This method uses the deprecated Wired Equivalent Privacy (WEP) keys to establish a secured session. WEP is no longer a secure standard and should not be used on a modern Wi-Fi network. More recent standards will not even allow the faster modulations when WEP is used. Modern 802.11 networks no longer use FHSS with Gaussian Frequency Shift Keying or infrared. Direct sequence spread spectrum is still supported for legacy devices. There are significant performance drops by allowing DSSS devices to coexist on a modern network.

This standard is also commonly referred to as 802.11 legacy or prime. It is a revision to the 1997 standard. As such, the documents are nearly the same with only slight variations and clarifications made between the two revisions. FHSS, DSSS, and infrared communications are all supported. Infrared communications are transmitted between 850 nm and 950 nm. Direct sequence spread spectrum operates within a 22 MHz wide channel bandwidth in 2.4 GHz. Differential binary phase shift keying (DBPSK) is used to obtain a data rate of 1 Mbps. Differential quadrature phase shift keying (DQPSK) is used to obtain a data rate of 2 Mbps. The early standards set the stage for the Wi-Fi Alliance certifications. There were so many different PHY layer options and so many varying implementations of the standard that equipment was not capable of interoperating reliably. This lead to Wi-Fi Certified certification to ensure that equipment was interoperable.

Now the alphabeterrific fun begins. The 802.11a standard was the first standard to allow devices to transmit in the 5 GHz frequency range. This standard is 5 GHz only. We are introduced to the unlicensed national information infrastructure (U-NII) bands. We were also introduced to a new modulation technique known as orthogonal frequency division multiplexing (OFDM). OFDM is a powerful way to stack individual carriers together allowing them to occupy the same bandwidth but not to interfere with each other. Quadrature amplitude modulation (QAM) is added to encode data on the carriers. Data rates of 6,9,12,18,24,36,48 and 54 Mbps are possible. These rates are achieved using BPSK, QPSK, 16-QAM and 64-QAM. This standard was not widely implemented at first. It was ahead of its time in many ways. The shortage of equipment capable of operating in this band and the added cost made it less attractive to many of the users. 802.11a was the foundation for the 802.11g standard that was very popular as the strengths of OFDM were adopted into the 2.4 GHz band.

This standard was one of the first to find widespread adoption. 802.11b introduced high rate direct sequence spread spectrum (HR/DSSS). In addition to the 1 and 2 Mbps, devices could now connect at data rates of 5.5 and 11 Mbps. This was done by adding complementary code keying (CCK). More data could be encoded on the 22MHz DSSS channel. A shortened preamble was also included. This standard only operated in the 2.4GHz band. An optional modulation of packet binary convolutional coding (HR/DSSS/PBCC) was introduced. It never found widespread adoption.

When learning about this standard, think domain-d. The 802.11d standard is concerned with conforming to the rules within each regulatory domain. Each country makes its own rules concerning how RF devices operate. Additional elements are added to existing frames, like the beacon frame, which tell devices what country the device is operating in. This allows devices to also meet the requirements of the regulatory domain and to roam between regulatory domains.

The extended rate phy (ERP) standard was very popular in the 2000s. This standard is a PHY amendment that operates in the 2.4 GHz band. 802.11g adapted OFDM from 802.11a into the 2.4GHz band with many of the same technical parameters ported over. The following data rates were available…
ERP-DSSS: 1 and 2
ERP-CCK: 5.5 and 11
ERP-OFDM: 6, 9, 12, 18, 24, 36, 48, and 54
ERP-PBCC: 5.5, 11, 22, and 33
DSSS-OFDM: 6, 9, 12, 18, 24, 36, 48, and 54
With so many different rates, this standard clarifies multirate support. Dynamic rate switching is where devices will change the modulation and coding scheme to increase throughput when signal is good and to decrease throughput when signals are not so good. The fact that all devices must be able to understand the broadcast traffic and management traffic, the lowest order modulations are typically used for transmitting. This significantly impacts throughput on a channel. This is why OFDM only is best practice for modern networks.

This amendment deals with spectrum and transmit power management. It prevents interference in the 5 GHz band to radar and satellites. From this standard we get the dynamic frequency selection (DFS) and transmit power control (TPC).

When I hear of 802.11i I think impenetrable. The standard increased the security using Wi-Fi Protected Access (WPA2) and the robust security network (RSN). It used the advanced encryption standard (AES).

When you see this lettered amendment, think Japan. This standard deals with the operation in the 4.9 to 5 GHz band in Japan.

When I see this standard, I think excellence. The e standard is used to define quality of service (QOS) on a Wi-Fi network. The standard created 4 separate access categories. AC_VO for voice operations requiring the highest QOS. AC_VI for video. AC_BE for regular data traffic and AC_BK for the lowest priority traffic. This form of QOS is probabilistic meaning that it does not guarantee a higher class will gain access to the medium first. It increases the likelihood that a higher class would gain access to the channel before the other classes.

Radio resource management (RRM) serves to facilitate the maintenance and management of the radios in a wireless network. Devices exchange information about the RF environment that allows them to make decisions about how best to operate the network. It also helps devices to roam.

Fast BSS Transition allows wireless clients to quickly roam from AP to AP without having to undergo a complete authentication exchange. This greatly improved the ability for devices to reduce latency or missed packets during a roam.

This amendment allows for high powered Wi-Fi networks to operate in the 3.65-3.7 GHz band in the USA. It operates using the 802.11a protocol. This band requires a light license. There is a nationwide non-exclusive license and a fee per base station fee.

This amendment deals with protected management frames. One of the problems with Wi-Fi is that the management information is passed without encryption. Even with the layer 2 encryption methods, only the payloads are actually encrypted. The open management frames allow attackers to hijack communications and can force clients to deauthenticate from the network causing service interruptions. By protecting the management frames, this prevents these types of attacks from occurring.

This is a PHY layer amendment that added multiple antenna support. MIMO was brought to the wireless networking world. This allowed for multiple spatial streams to significantly improve throughput and performance. This standard allowed for up to 4 spatial streams. The maximum modulation was 64QAM 5/6. There were 32 primary MCS index values and a whole bunch of mismatched modulations. Both the 2.4 and 5 GHz bands were included. RF channel width could increase to 40MHz by combining two 20MHz channels. Theoretical speeds up to 600 Mbps could be achieved.

This amendment adds wireless access in vehicular environments (WAVE). It is designed to provide roadside access via access points to devices in vehicles driving by. A way to remember this one is to think p for pavement.

Tunnelled direct link setup (TDLS) is a way for two devices that are associated with an AP to set up a direct link between each other without going through the AP to pass data directly. This keeps this traffic off the AP and theoretically increases system performance.

This wireless network management standard allows the configuration of a client device to be changed while remaining connected to the network.

When I think of the u amendment I think of ubiquitous. The idea behind Passpoint or Hotspot 2.0 is the idea that our devices can connect securely to networks spread far and wide. Information is exchanged before the connection that tells the device information about the network. Access network query protocol (ANQP) is used to exchange info between the AP and device. The device does not have to connect to the network to receive this information. The connection is also secured with WPA2 layer 2 encryption which is much more secure than connecting to an open network where hackers can listen in on your wireless traffic.

This amendment is the mesh networking amendment. When you think s think mesh.

This amendment is about prioritizing management frames.

When you see this amendment think of awesome audio. It allows for MAC Enhancements for Robust Audio Video Streaming. It is concerned with improving multicast traffic over Wi-Fi.

The way I remember this one is to think almost deaf. This is the WiGig 60GHz standard. It allows for multi-gigabit speeds. The frequency band is really high and does not cover very far. It does have a lot of promise for delivering large amounts of data over short distances.

This is a PHY layer amendment that only operates in the 5 GHz band. The very high throughput (VHT) PHY added 256 QAM modulation, multi-user MIMO (MU-MIMO) and support for up to 8 spatial streams.

The TV White Space amendment allows networks to operate in frequencies lower than 1 GHz. It is intended to be used in rural areas to provide wireless networks. It uses OFDM modulation. Stations are managed by a geolocation database (GDB) to ensure devices do not interfere with licensed TV operations.

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