Industrial wireless tutorials: Understand the IEEE Wi-Fi standards, what each standard provides, benefits of standardization, and Wi-Fi Alliance device certification.
In the beginning, wireless networking, like wired, had several different competing methods, using incompatible technologies and frequencies. Security was practically non-existent. Wireless was not considered seriously as a usable network technology. Market forces conspired to drive the technology toward standardization, which greatly increased its utility.
At the outset, let's understand that the standards discussed here define the protocols used at the physical and data link layers of the OSI model. All of the standards were developed and are maintained by the IEEE, specifically the 802.XX working groups, for example: IEEE 802.3 describes Ethernet, 802.11 describes Wi-Fi, and 802.15 describes Bluetooth. Standardization has allowed the technology to flourish and has eliminated problems associated with lack of interoperability.
Wi-Fi device testing
The other player in the Wi-Fi industry is the Wi-Fi Alliance, which is responsible for testing Wi-Fi devices for compatibility with standards and certifying interoperability; the familiar "Wi-Fi CERTIFIED" logo is assurance the device conforms to interoperability and security standards.
The original Wi-Fi standard, or "Wi-Fi Prime" was issued in 1997 as IEEE Standard 802.11-1997. This standard defined the three original physical layer (PHY) specifications:
- Frequency hopping spread spectrum (FHSS), now obsolete for Wi-Fi
- Infrared (IR), now obsolete
- Direct sequence spread spectrum (DSSS).
Major Wi-Fi standards
The data rates were 1-2 MBPS and operated in the 2.4 GHz ISM band regardless of what method was used. Following are the major standards that were subsequently developed:
- 802.11a: Orthogonal frequency division multiplexing (OFDM) in the 5 GHz U-NII band allowing up to 54 MBPS
- 802.11b: High Rate DSSS (HR-DSSS) in the 2.4 ISM band allowing up to 11 MBPS. 802.11b is backward compatible to 802.11.
- 802.11g: OFDM in the 2.4 GHz ISM band, allowing up to 54 MBPS. 802.11g is backward compatible to 802.11b
- 802.11n: High Throughput OFDM in both the ISM and U-NII bands, allows up to 450 MBPS with MIMO technology. 802.11n is backward compatible with 802.11g, b.
- 802.11ac: Very High Throughput OFDM (VHT-OFDM) in the ISM and U-NII bands, allows an eventual throughput of 6 GBPS. 802.11ac is backward compatible with 802.11n, g, b.
Wi-Fi security amendment
A major security amendment to be aware of is 802.11i, which describes Robust Security Network Associations (RSNAs) and the methods to achieve same. This amendment specifies the mandatory use of CCMP-AES, or Counter Mode with Cipher Chained Message Authentication Protocol — Advanced Encryption Standard. (Wireless security will be covered in a later segment.)
There are also several other amendments to the standard that modify and enhance the behavior of compliant devices:
- 802.11d: "World Mode" — automatically sets a radio to the proper local channels and power output
- 802.11h: Defines Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to avoid interference with radar or other services in the 5 GHz bands.
- 802.11e: Addresses Quality of Service (QoS) requirements to mitigate latency issues in multimedia delivery over a WLAN
- 802.11r: Defines parameters for roaming between access points in an Extended Service Set (ESS)
- 802.11w: Defines robust management frames to prevent Denial of Service (DoS) attacks.
The amendments discussed above (with the exception of 802.11ac) were rolled into the 802.11-2012 standard, which is available for free download at the IEEE website.
- Daniel E. Capano, owner and president, Diversified Technical Services Inc. of Stamford, Conn., is a certified wireless network administrator (CWNA). Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, firstname.lastname@example.org.
www.controleng.com/blogs has other wireless tutorials from Capano on the following topics:
Wireless propagation fundamentals
Radio antenna types
www.controleng.com/webcasts has wireless webcasts, some for PDH credit.
Control Engineering has a wireless page.
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