Wlan Technologies And Standards Computer Science

Add: 23-11-2017, 12:19   /   Views: 140

Wireless Local Area Networks (WLANs) are increasingly at hand in corporate and residential indoor environments. WLAN is not a single radio technology, several different technologies fall into the category called WLAN. This study endeavors to spotlight particularly on the existing industry standard for IEEE 802.11b as the representative example of the WLAN family of technologies.

3.1.1 Radio frequency technologyGeneral

RF has turn out to be the effective technology for largest division of today's WLANs. Radio signals are able to transmit in all routes with a distance ranging from a few meters to a number of kilometers. These features provide an extremely realistic in circumstances at a place of wide or long-range coverage which is necessary although they befall sticky whilst the signal's propagation desires to be restricted. Because of the uncontrollable destination of radio signals, this makes this medium to be vulnerable unobserved interception and utilization.

Each and every undefended radio passage be able to be examined by means of extensively existing radio equipment by any person positioned within the array of the transmitter; though it is significant to make a note of that amplifiers as well as specific antennas be able to use exclusively by the side of the receiver location on the way to enhance the effectual array of radio signals, therefore basically scheming the transmitter power is not satisfactory to restrict the broadcast of signals.

Spread Spectrum

Standard RF transmission vulnerabilities have been claimed because of the advancement of spread spectrum communication technology. Dissimilar narrowband systems that broadcast a dominant signal going on a solitary frequency, spread-spectrum systems broadcast a small power signal with a wide variety of frequencies. The signal is widening as per the pre-established constraints or models that as well-known by the receiver as a result to facilitate recovery of the signal. These transmission methods enable additional resistance to noise and interference and are not as much of vulnerable to jamming and informal interception. In the case of WLANs, the hardware should be conscious of the signal dispersal parameters so as to receive a spread-spectrum signal; as a result these parameters are pre-programmed into the hardware chipsets employed on the way to assemble these products.

Though all the above chipset be recommended to be enhanced keen on unconnected WLAN AP and workstation hardware, it is to be predictable so as the tools as well as techniques are building up for make use of these pre-programmed receivers for the function of intercept spread-spectrum WLAN communications. Various such tools are liberally obtainable on the Internet, and consequently none of the spread spectrum technologies is required that is to be reflected to be enough to protect a WLAN.

A few signal-spreading strategies have existed with progress though the systems that are conquest in the WLAN field are:

1. Frequency Hopping Spread Spectrum (FHSS)

2. Direct Sequence Spread Spectrum (DSSS) and

3. Orthogonal Frequency Division Multiplexing (OFDM)

In 802.11 WLANs, FHSS and DSSS are placed with the unique spread-spectrum technologies. The perception of spreading spectral use all the way through frequency hopping is quite easy to understand; DSSS is main supporting element on the mathematical principle of convolution and endow with a greater data throughput and a higher immunity to interference than FHSS. OFDM is a multi-carrier wideband modulation scheme that provides constant better data throughput as well as it is greatly further resistant on the way to interference than the preceding plans. 802.11n launched OFDM+MIMO, which prolong to make use of the unchanged 2.4 GHz frequency band as well as fundamental modulation plan of OFDM, excluding add techniques for using multiple transmitters and receivers while taking into account temporal and spatial characterization of the RF environment. This in effect amplify the presented bandwidth by means of a practice known as "channel bonding" (combining multiple adjacent channels into one large channel) to additional amplify range.

3.1.2 WLAN System Architecture

The WLAN protocol discussed in this research effort is based on the IEEE 802.11 standard. The standard defines a medium access control (MAC) sub layer and three physical (PHY) layers. Despite the different radio technologies, all WLAN systems are commonly used to transport IP datagram. The goal of the IEEE 802.11 standard is to describe a WLAN that delivers services commonly found in wired networks. The IEEE 802.11 architecture consists of several components that work together to provide a Wireless LAN (WLAN) connectivity that is transparent to the upper layers. The Basic Service Set (BSS) is the basic building block of an 802.11 WLAN. A station (STA) is the component that connects to the wireless medium. The station may be mobile, portable, or stationary.

A station provides the following WLAN services: authentication, privacy, and delivery of the data (MAC service data unit). The BSS, shown in Figure 2-13, is a set of stations that communicate with one another. When all the stations in the BSS can communicate directly with each other and there is no connection to a wired network, the BSS is called an Independent BSS (IBSS). An IBSS is also known as ad-hoc network, which is typically a short-lived network with small number of stations in direct communication range.

3.2 802.11 Standards


The U.S. Federal Communications Commission (FCC) in 1985 come to a decision to release the Industrial, Scientific, and Medical (ISM) bands, working at 902 to 928MHz, 2.4 to 2.483GHz, and 5.725 to 5.875GHz, which is completely intended for unlicensed public utilization. This commission satisfied demands of commercial communication and in addition sparked the improvement of WLAN technology. The Institute of Electrical and Electronics Engineers (IEEE) established the 802.11 WLAN standard [1] in 1997 in an effort to regulate wireless LAN products developing the ISM band. This standard has since been adopted by the International Organization for Standardization / International Electro technical Commission (ISO/IEC).

The Physical (PHY) and Data Link layers of the Open Systems Interconnection (OSI) Basic reference model are addressed by the IEEE 802.11. The legacy standard projected three (mutually incompatible) implementations intended for the physical layer: IR pulse modulation, RF signaling using FHSS, and RF signaling using DSSS. The physical medium for data transmission is the main understandable dissimilarity among the WLAN and the customary wired LAN.

The IEEE 802.11 standard has several key amendments. Products compliant to the 802.11a, b and g amendments are in common use today, with an increasing number of products based on the "Draft 2.0" release of 802.11n. Key specifications for each of these amendments can be found in Table 1.

Previously, the primary flourishing commercial 802.11 WLAN products were submissive by means of the 802.11b standard. Both 802.11a and b amendments were in fact approved at the similar time, however since 802.11b was not as much of complex as 802.11a, products submissive through the 802.11b standard swiftly materialized whilst products beneath 802.11a merely get in touch with the market in 2002. Since that time, the 802.11g amendment which made use of the same 2.4 GHz band as 802.11b, however carried more rapidly and additional vigorous connections as well as greater range, has come to dominate the market.

Institute of Electrical and Electronics Engineers (IEEE) is responsible for developing the radio technology standards to be used by wireless LANs. These standards pertain to the 802 wireless standards including 802.11, the first one that was developed, and several variations of it.

Each standard though developed for wireless LANs serves a different purpose for the LANs, due in part to hackers, as well as others who might challenge its security for the purpose of strengthening their own enterprise security. As vulnerabilities, or holes, are found they become public knowledge and the IEEE proceeds to update the standard.

The standards (versions) listed below are the most common ones, a list of which can be found in any wireless LAN literature or in IEEE published data

3.2 IEEE 802.11 Task Groups/Amendments


Basic standard 802.11 WLANs are based on IR transport were in no way commercially put into practice and the RF-based versions experienced low transmission speed (2 Mbps). The IEEE in a while started up numerous task groups on the way to investigate a variety of upgrades to the original 802.11 core standard.

802.11a Amendment

An unlicensed 5.0 GHz frequency band explored by Task Group A, by means of Orthogonal Frequency Division Multiplexing (OFDM), functioning to attain throughputs up to 54 Mbps. The 802.11a extension [2] was fulfilled in 1999 and in 2002 vendors set in motion releasing products acquiescent to this extension. Because of the dissimilar operating band and modulation, the 802.11a standard is not rearward companionable or interoperable among the 802.11b standard. Numerous vendors are marketing dual-band, multi-standard (802.11a and 802.11b/g) APs. The 802.11a is at present licensed for use in North America and most European countries; though commercial use of 802.11a has traditionally been relatively restricted.


Task Group B explored DSSS technology to boost data rates in the original 2.4 GHz band. The 802.11b extension [3], published in September 1999, delivers raw data rates up to 11 Mbps, which gave data rate parity with the popular 10 Mbps "10Base" wired LAN systems of the day. The majority of WLAN systems in the market today follow the 802.11b standard and it is accepted throughout North America, Europe and Asia.


Task Group G permitted the enlargement of the new extension to the 802.11 standard in November 2001; the resultant amendment was approved in 2003. The 802.11g operates at 2.4 GHz with mandatory compatibility to 802.11b and uses the OFDM multicarrier modulation scheme to achieve a maximum data rate of 54 Mbps.

802.11n Amendment

As with 802.11b and g, the 802.11n standard will operate at 2.4 GHz with mandatory compatibility to 802.11b/g and uses OFDM with MIMO techniques to achieve a maximum projected data rate of 248 Mbps. As described earlier in this document, OFDM+MIMO utilize the same basic modulation as 802.11g. However it utilizes multiple transceivers with advanced techniques to compensate for both the spatial and temporal variations of the RF channel as well as the practice of "channel bonding" in order to greatly increase the range and raw data rate. The 802.11n is still in the draft stage with an expected final approval in 2010, however many "Pre-N" or "Draft-N" products have already begun emerging on the market. Consumers are cautioned when purchasing such products because, as draft-based products, they are not subject to the same interoperability testing as full-standard compliant products. As such, they are not guaranteed to be compatible with, and may not be upgradeable.

IEEE 802.11

The 802.11 operation modes

There are two operation modes defined in IEEE 802.11: Infrastructure Mode and Ad Hoc Mode.

Infrastructure mode

Figure 1: Infrastructure mode in WLAN

Ad-Hoc Mode

Figure 2: Ad-hoc mode

The 802.11 physical layerThe 802.11 Datalink layerIEEE 802.11b

Enhancements to the physical layer