The Institute of Electrical and Electronics Engineers (IEEE) is the professional society that creates and maintains standards that we use for communications, such as the 802.3 Ethernet standard for wired networking.
The IEEE has assigned working groups for several wireless communication standards. For example, the 802.15 working group is responsible for personal area network (PAN) communications using radio frequencies. Some of the technologies defined within the 802.15 standard include Bluetooth and ZigBee.
Another example is the 802.16 standard, which is overseen by the Broadband Wireless Access Working Group; the technology is often referred to as WiMAX. The 802.11 Working Group comprises 250+ wireless companies and has over 650 active members.
It consists of standing committees, study groups, and numerous task groups . For example the Standing Committee-Publicity (PSC) is in charge of finding means to better publicize the 802.11 standard. The 802.11 Study Group (SG) is in charge of investigating the possibility of putting something new into the 802.11 standard.
Various 802.11 task groups are in charge of revising and amending the original standard that was developed by the MAC Task Group (MAC) and the PHY Task Group (PHY).
Each group is assigned a letter from the alphabet, and it is common to hear the term “802.11 alphabet soup” when referring to all the amendments created by the multiple 802.11 task groups.
Quite a few of the 802.11 task group projects have been completed and amendments to the original standard have been ratified. Other 802.11 task group projects still remain active and exist as draft amendments. We will discuss the original 802.11 standard, the ratified amendments, and draft amendments of various 802.11 task groups.
Overview of the IEEE 802.11 Standard
The original 802.11 standard was published in June 1997 as IEEE Std. 802.11-1997, and it is often referred to as 802.11 Prime because it was the first WLAN standard. The standard was revised in 1999, reaffirmed in 2003, and published as IEEE Std. 802.11-1999 (R2003).
The IEEE specifically defines 802.11 technologies at the Physical layer and the MAC sublayer of the Data-Link layer. By design, the 802.11 standard does not address the upper layers of the OSI model, although there are interactions between the 802.11 MAC layer and the upper layers for parameters such as quality of service (QoS).
The PHY Task Group (PHY) worked in conjunction with the MAC Task Group (MAC) to define the original 802.11 standard. The PHY Task Group (PHY) developed three Physical layer specifications:
- Infrared (IR) - Infrared technology uses a light-based medium. Although an infrared medium was indeed defined in the original 802.11 standard, the implementation is obsolete. More information about modern implementations of infrared can be found at the Infrared Data Association’s website at www.irda.org.
- Frequency Hopping Spread Spectrum (FHSS) Radio frequency signals can be defined as narrowband signals or as spread spectrum signals. An RF signal is considered spread spectrum when the bandwidth is wider than what is required to carry the data.
Frequency Hopping is a spread spectrum technology that was first patented during World War II. Frequency Hopping 802.11 radio cards are often called clause 14 devices due to the clause that referenced them in the original 802.11 standard.
- Direct sequence spread spectrum (DSSS) Direct sequence is another spread spectrum technology that is frequently used and easiest to implement. DSSS 802.11 radio cards are often known as clause 15 devices.
As defined by 802.11 Prime, the frequency space in which either FHSS or DSSS radio cards can transmit is the license free 2.4 GHz Industrial, Scientific, and Medical (ISM) band. DSSS 802.11 radio cards can transmit in channels subdivided from the entire 2.4 to 2.4835 GHz ISM band.
The IEEE is more restrictive for FHSS radio cards, which are permitted to transmit on 1 MHz subcarriers in the 2.402 to 2.480 GHz range of the 2.4 GHz ISM band. Chances are that you will not be working with older legacy 802.11 equipment since most WLAN deployments use technologies as defined by newer 802.11 amendments.
WLAN companies had the choice of manufacturing either clause 14 FHSS radio cards or clause 15 DSSS radio cards. Because spread spectrum technologies differ, they cannot communicate with each other and often have a hard time coexisting.
Spread spectrum signals are analogous to oil and water because they do not mix well. Therefore, it is important to understand that an 802.11 DSSS radio cannot communicate with an 802.11 FHSS radio.
The majority of legacy WLAN deployments used frequency hopping, but some DSSS solutions were available as well. What about bandwidth? Data rates defined by the original 802.11 standard were 1 Mbps and 2 Mbps.
Keep in mind that a data rate is the available bandwidth and not actual throughput . Due to medium access methods, aggregate throughput is typically 1/2 or less of the available data rate bandwidth.
