In the years that followed the publishing of the original 802.11 standard, new task groups were assembled to address potential enhancements to the standard. So far, nine amendments to the standard have been ratified and published by the distinctive task groups. These ratified supplements will now be discussed in a somewhat chronological order.
802.11b Amendment
Although Wi-Fi consumer market continues to grow at a tremendous rate, 802.11b compatible WLAN equipment gave the industry the first needed huge shot in the arm. In 1999, the IEEE Task Group b (TGb) published the IEEE Std.
802.11b-1999, and it was later amended and corrected as IEEE Std. 802.11b-1999/Cor1-2001. The Physical layer medium that is defined by 802.11b is strictly direct sequence spread spectrum (DSSS).
The frequency space in which 802.11b radio cards can operate is the unlicensed 2.4 to 2.4835 GHz ISM band. The TGb Task Group’s main goal was to achieve higher data rates within the 2.4 GHz ISM band.
802.11b radio cards accomplish this feat by using a different spreading/coding technique called Complementary Code Keying (CCK) and modulation methods using the phase properties of the RF signal. 802.11 cards used a spreading technique called the Barker Code .
The end result is that 802.11b radio cards support data rates of 1, 2, 5.5 and 11 Mbps. 802.11b systems are backward compatible with the 802.11 DSSS data rates of 1 Mbps and 2 Mbps.
The transmission data rates of 5.5 and 11 Mbps are known as High-Rate DSSS (HR-DSSS) . Once again, understand that the supported data rates refer to available bandwidth and not aggregate throughput.
802.11a Amendment
During the same year the 802.11b amendment was approved, another very important amendment was also ratified and published as IEEE Std. 802.11a-1999.
The engineers in the TGa Task Group set out to define how 802.11 technologies would operate in the newly allocated Unlicensed National Information Infrastructure (UNII) frequency bands.
802.11a radio cards can transmit in three different 100 MHz unlicensed frequency bands in the 5 GHz range, as shown in list below. The 2.4 GHz ISM band is a much more crowded frequency space than the 5 GHz UNII bands.
Microwave ovens, Bluetooth, cordless phones, and numerous other devices all operate in the 2.4 GHz ISM band and are potential sources of interference.
- UNII-1 (lower) - 5.150 GHz – 5.250 GHz
- UNII-2 (middle) - 5.250 GHz – 5.350 GHz
- UNII-3 (upper) - 5.725 GHz – 5.825 GHz
In addition, the sheer number of 2.4 GHz WLAN deployments has often been a problem in environments such as multitenant office buildings. One big advantage of using 802.11a WLAN equipment is that it operates in the less crowded 5 GHz UNII bands.
Eventually the three UNII bands will also become crowded. Regulatory bodies such as the FCC are opening up more frequency space in the 5 GHz range. 802.11a radio cards operating in the 5 GHz UNII bands are classified as clause 17 devices.
As defined by the 802.11a amendment, these devices are required to support data rates of 6, 12, and 24 Mbps with a maximum of 54 Mbps. With the use of a spread spectrum technology called Orthogonal Frequency Division Multiplexing (OFDM) , data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps are supported in most manufacturers’ radio cards.
It should be noted that an 802.11a radio does not have to support all of these rates and a vendor may have a different implementation of data rates that is not compatible with another vendor.
It should also be noted that 802.11a radio cards cannot communicate with 802.11 or 802.11b radio cards for two reasons. First, 802.11a radio cards use a different spread spectrum technology than 802.11/802.11b devices. Second, 802.11a devices transmit in the 5 GHz UNII bands, while the 802.11/802.11b cards operate in the 2.4 GHz ISM band.
The good news is that 802.11a can coexist with 802.11 or 802.11b/g cards in the same physical space because these cards transmit in separate frequency ranges. In Figure below, you see an access point (AP) with both a 2.4 GHz 802.11b/g radio and a 5 GHz 802.11a radio.
Many enterprise wireless deployments run both 802.11a and 802.11b/g networks simultaneously.
802.11g
Another amendment that generated a lot of excitement in the Wi-Fi marketplace was published as IEEE Std. 802.11g-2003. The IEEE defines 802.11g cards as clause 19 devices, which transmit in the 2.4 to 2.4835 GHz ISM frequency band.
The main goal of the TGg Task Group was to enhance the 802.11b Physical layer to achieve greater bandwidth yet remain compatible with the 802.11 MAC. To achieve the higher data rates, Extended Rate Physical OFDM (ERP-OFDM) technology is used exactly as defined in the 802.11a amendment.
Therefore, data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps are possible using OFDM technology, although once again the IEEE only requires the data rates of 6, 12, and 24 Mbps. To maintain backward compatibility, the DSSS data rates of 1, 2, 5.5, and 11 are supported as well.
The 802.11g amendment defines the use of several PHYs but requires support for both DSSS and ERP-OFDM. The good news is that an 802.11g AP can communicate with 802.11g client stations as well as 802.11b stations.
The ratification of the 802.11g amendment triggered monumental sales of Wi-Fi gear in both the small office, home office (SOHO) and enterprise markets because of both the higher data rates and the backward compatibility with older equipment.
Spread spectrum technologies cannot communicate with each other, yet the 802.11g amendment mandates support for both DSSS and ERP-OFDM. In other words, ERP-OFDM and DSSS technologies can coexist, yet they cannot speak to each other.
Therefore, the 802.11g amendment calls out for a protection mechanism that allows the two technologies to coexist. The goal of the 802.11g “protection mechanism” is to prevent ERP-OFDM radio cards from transmitting at the same time as DSSS radio cards.
The 802.11g amendment also specifies other optional technologies, including Packet Binary Convolutional Coding (PBCC). This technology is optional and is rarely used.
802.11d
The original 802.11 standard was written for compliance with the regulatory domains of the United States, Canada, and Europe. Regulations in other countries might define different limits on allowed frequencies and transmit power.
The 802.11d amendment, which was published as IEEE Std. 802.11d-2001, added requirements and definitions necessary to allow 802.11 WLAN equipment to operate in areas not served by the original standard.
Country code information is delivered in fields inside two wireless frames called beacons and probe requests. This information is then used by 802.11d compliant devices to ensure that they are abiding by a particular country’s frequency and power rules.
The 802.11d amendment also defines other information specific to configuration parameters of a Frequency Hopping (FHSS) access point. FHSS parameters such as hopping patterns might vary from country to country, and the information needs to be once again delivered via the beacon or probe response frames.
This information would only be useful in legacy deployments using FHSS spread spectrum technology.
802.11F
The IEEE Task Group F (TGF) published IEEE Std. 802.11F-2003 as a recommended practice in 2003. The original published 802.11 standard mandated that vendor access points support roaming.
A mechanism is needed to allow client stations that are already communicating through one access point to be able to jump from the coverage area of the original AP and continue communications through a new access point.
A perfect analogy is the roaming that occurs when using a cellular telephone. When you are talking to your best friend on the cell phone while driving in your car, your telephone will roam between cellular towers to allow for seamless communications and hopefully an uninterrupted conversation.
Seamless roaming allows for mobility, which is the heart and soul of true wireless networking and connectivity. In Figure below, you see a station downloading a file through AP-1 from an FTP server residing on a wired network backbone. Please note that the access points have overlapping areas of coverage.
As the station moves closer to AP-2, which has a stronger signal, the station may roam to access point 2 and continue the FTP transfer through the portal supplied by the new access point.
Although the handover that occurs during roaming can be measured in milliseconds, data packets intended for delivery to the station that has roamed to a new access point might still be buffered at the original access point.
In order for the buffered data packets to find their way to the station, two things must happen:
- The new access point must inform the original access point about the station that has roamed and request any buffered packets.
- The original access point must forward the buffered packets to the new access point via the distribution system for delivery to the client who has roamed.
Figure below illustrates these two needed tasks.
Although the original 802.11 standard calls for the support of roaming, it fails to dictate how roaming should actually transpire. The IEEE initially intended for vendors to have flexibility with implementing proprietary AP-to-AP roaming mechanisms.
The 802.11F amendment was an attempt to standardize how roaming mechanisms work behind the scene on the distribution system medium, which is typically an 802.3 Ethernet network using TCP/IP networking protocols. 802.11F addresses “vendor interoperability” for AP-to-AP roaming.
The final result was a recommended practice to use the Inter Access Point Protocol (IAPP). The IAPP protocol uses announcement and handover processes that result in how APs inform other APs about roamed clients as well as define a method of delivery for buffered packets.
802.11h
Published as IEEE Std. 802.11h-2003, this amendment defines mechanisms for dynamic frequency selection (DFS) and transmit power control (TPC) that may be used to satisfy regulatory requirements for operation in the 5 GHz band in Europe. DFS is used for spectrum management of 5 GHz channels for 802.11a radio cards.
The European Radiocommunications Committee (ERC) mandates that radio cards operating in the 5 GHz band implement a mechanism to avoid interference with radar systems as well as provide equable use of the channels. The DFS service is used to meet the ERC regulatory requirements.
The dynamic frequency selection (DFS) service provides for the following:
- An AP will allow client stations to associate based on the supported channel of the access point. The term associate means that a station has become a member of the AP’s wireless network.
- An AP can quiet a channel to test for the presence of radar.
- An AP may test a channel for the presence of radar before using the channel.
- An AP can detect radar on the current channel and other channels.
- An AP can cease operations after radar detection to avoid interference.
- When interference is detected, the AP may choose a different channel to transmit on and inform all the associated stations.
TPC is used to regulate the power levels used by 802.11a radio cards. The ERC mandates that radio cards operating in the 5 GHz band use TPC to abide by a maximum regulatory transmit power and are able to alleviate transmission power to avoid interference.
The TPC service is used to meet the ERC regulatory requirements. The transmit power control (TPC) service provides for the following:
- Stations can associate with an AP based on their transmit power.
- Designation of the maximum transmit power levels permitted on a channel as permitted by a regulations.
- An AP can specify the transmit power of any or all stations that are associated with the access point.
- An AP can change transmission power on stations based on factors of the physical RF environment such as path loss.
The information used by both DFS and TPC is exchanged between stations and access points inside of management frames. Although the 802.11h amendment was ratified specially to address compliance with European regulations in the 5 GHz band, many vendors have also applied TPC and DFS-like services to radio cards operating in the 2.4 GHz ISM band.
802.11i
From 1997 to the year 2004, there really was not much defined in regard to security in the 802.11 standard. Two key components of any wireless security solution are data privacy (encryption) and authentication (identity verification).
For seven years, the only defined method of encryption in an 802.11 network was the use of 64-bit static encryption called Wired Equivalent Privacy (WEP).
WEP encryption has long been cracked and is not considered to be an acceptable means of providing data privacy. The 802.11 standard defined two methods of authentication. The default method is Open System authentication, which verifies the identity of everyone regardless.
Another defined method is called Shared Key authentication, which opens up a whole new can of worms and potential security risk. The 802.11i amendment, which was ratified and published as IEEE Std. 802.11i-2004, has finally defined stronger encryption and better authentication methods.
The intended goal was to better hide the data flying through the air while at the same time place a bigger guard at the front door. The 802.11i security amendment is without a doubt one of the most important enhancements to the original 802.11 standard due to the seriousness of properly protecting a wireless network.
The major security enhancements addressed in 802.11i are as follows: Data privacy Confidentiality needs have been addressed in 802.11i with the use of a stronger encryption method call Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP), which uses the Advanced Encryption Standard (AES) algorithm.
The encryption method is often abbreviated as CCMP/AES, AES CCMP, or often just CCMP. The 802.11i supplement also defines an optional encryption method known as Temporal Key Integrity Protocol (TKIP), which uses the RC-4 stream cipher algorithm and is basically an enhancement of WEP encryption.
Authentication 802.11i defines two methods of authentication using either an IEEE 802.1X authorization framework or preshared keys (PSKs). An 802.1X solution requires the use of an Extensible Authentication Protocol (EAP), although the 802.11i amendment does not specify what EAP method to use.
Robust Security Network (RSN) This is a method of establishing authentication, negotiating security associations, and dynamically generating encryption keys for clients and access points.
The Wi-Fi Alliance also has a certification known as Wi-Fi Protected Access (WPA2), which is a mirror of the IEEE 802.11i security amendment. WPA version 1 was considered a preview of 802.11i and WPA version 2 is fully compliant with 802.11i.
The Wi-Fi Alliance also has a certification known as Wi-Fi Protected Access (WPA2), which is a mirror of the IEEE 802.11i security amendment. WPA version 1 was considered a preview of 802.11i and WPA version 2 is fully compliant with 802.11i.
802.11j
The main goal set out by the IEEE Task Group j (TGj) was to obtain Japanese regulatory approval by enhancing the 802.11 MAC and 802.11a PHY to additionally operate in Japanese 4.9 GHz and 5 GHz bands. The 802.11j amendment was approved and published as IEEE Std. 802.11j-2004.
In Japan, 802.11a radio cards can transmit in the lower UNII band at 5.15 GHz to 5.25 GHz as well as a Japanese licensed/unlicensed frequency space of 4.9 GHz to 5.091 GHz. 802.11a radio cards use OFDM technology with required channel spacing of 20 MHz.
When 20 MHz channel spacing is used, data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps are possible using OFDM technology. Japan also has the option of using OFDM channel spacing of 10 MHz, which results in available bandwidth data rates of 3, 4.5, 6, 9, 12, 18, 24, and 27 Mbps.
The data rates of 3, 6, and 12 Mbps are mandatory when using 10 MHz channel spacing.
802.11e
Since the adoption of the original 802.11 standard, there has not been any adequate quality of service (QoS) procedures defined for the use of time-sensitive applications like Voice over IP (VoIP). Voice over Wireless IP (VoWIP) is also known as Voice over Wirless Lan (VoWLAN) and as Voice over Wi-Fi (VoWiFi).
Although deployments so exist, the QoS capabilities are typically handled at upper layers using proprietary solutions. Application traffic such as voice, audio, and video has a lower tolerance for latency and jitter and requires priority before data traffic.
The newly approved IEEE Std. 802.11e-2005 amendment defines the layer 2 MAC methods needed to meet the QoS requirements for time-sensitive applications over IEEE 802.11 wireless LANs. The original 802.11 standard defined two methods in which an 802.11 radio card may gain control of the half-duplex medium.
The default method, Distributed Coordination Function (DCF), is a completely random method of who gets to transmit on the wireless medium next. The original standard also defines another medium access control method called Point Coordination Function (PCF), where the access point briefly takes control of the medium and polls the clients.
The 802.11e amendment defines enhanced medium access methods to support QoS requirements. Hybrid Coordination Function (HCF) is an additional coordination function that is applied in an 802.11e QoS wireless network. HCF has two access mechanisms to provide QoS.
Enhanced Distributed Channel Access (EDCA) is an extension to DCF. The EDCA medium access method will provide for the “prioritization of frames” based on upper-layer protocols.
Application traffic such as voice or video will be transmitted in a timely fashion on the 802.11 wireless medium, meeting the necessary latency requirements.
Hybrid Coordination Function Controlled Access (HCCA) is an extension to PCF. HCF gives the access point the ability to provide for “prioritization of stations.” In other words, certain client stations will be given a chance to transmit before others.
The Wi-Fi Alliance also has a certification known as Wi-Fi Multimedia (WMM). The WMM standard is a “mirror” of 802.11e and defines traffic prioritization in four access categories with varying degrees of importance.
