What the heck is this 802.11 && 802.11b??

802.11 is a standard proposed by the Institute of Electrical and Electronics Engineers (IEEE) for Wireless Local Area Networks (WLANs). The idea for this standard ,is like any standard, to give manufacturers of WLAN products be it software or hardware manufacturers a shared and compatible foundation to begin developing products. The initial 802.11 PAR (Project Authorization Request) states, "...the scope of the proposed [wireless LAN] standard is to develop a specification for wireless connectivity for fixed, portable, and moving stations within a local area." The PAR further says, "...the purpose of the standard is to provide wireless connectivity to automatic machinery and equipment or stations that require rapid deployment, which may be portable,handheld, or which may be mounted on moving vehicles within a local area."To date, wireless LANs have been primarily implemented in applications such as manufacturing facilities, warehouses, and retail stores. The majority of future wireless LAN growth is expected in healthcare facilities, educational institutions, and corporate enterprise office spaces. In the corporation, conference rooms, public areas, and branch offices are likely venues for WLANs. So this standard should enable interoperability among the embedded components or adapters in mobile devices.

802.11b proposed recently takes advantages of the technological advances since 802.11 and allows increased data rates, throughput and security . It's implementation and operation are the same however.


How can multiple PCs communicate on the same WLAN ??

The fundamental access method of the 802.11 MAC is known as Carrier Sense Multiple Access with collision avoidance, or CSMA/CA. CSMA/CA works by a "listen before talk scheme". This means that a station wishing to transmit must first sense the radio channel to determine if another station is transmitting. If the medium is not busy, the transmission may proceed. The CSMA/CA scheme implements a minimum time gap between frames from a given user. Once a frame has been sent from a given transmitting station, that station must wait until the time gap is up to try to transmit again. Once the time has passed, the station selects a random amount of time (called a backoff interval) to wait before "listening" again to verify a clear channel on which to transmit. If the channel is still busy, another backoff interval is selected that is less than the first. This process is repeated until the waiting time approaches zero and the station is allowed to transmit. " This type of multiple access ensures judicious channel sharing while avoiding collisions ".




What kind of networks can be created using this 802.11 thingie ?



There are two differnt architectures proposed by IEEE for this standard, that is ad-hoc and infrastructure.
Ad-hoc
Ad-hoc or on the fly networks are created using no fixed tranmitters/receivers nodes. It is basically a network created by wireless PCs coming together and through cooperation forming a network. For example, in a weekly stockholder meeting which for some reason is held in different locations week to week such a network would be suitable. All stockholders bring their PCs and can thus establish an ad-hoc wirless LAN. To maintain order within the network a master/base station can be elected.
fig.1 shows an ad-hoc network
Infrastructure
Infrastructure is a fixed network made up of Access Points. These Access Points transmit and receive data within a certain range and so when inside the radio range of an Access Points a user is effectively connected to the LAN. This means I can roam outside my office,and aslong as I'm within the range of one of my company's Access Points I am still connected to the LAN.
fig.2 shows an infrastructure network



802.11: Performance

The IEEE 802.11 standard places specifications on the parameters of both the Physical (PHY) and medium access control (MAC) layers of the network. Below is a pic of the 802.11 and the ISO model.







"The Physical layer, which actually handles the transmission of data between nodes, can use either direct sequence spread spectrum, frequency-hopping spread spectrum, or infrared (IR) pulse position modulation. IEEE 802.11 makes provisions for data rates of either 1 Mbps or 2 Mbps, and calls for operation in the 2.4 - 2.4835 GHz frequency band (in the case of spread-spectrum transmission), which is an unlicensed band for industrial, scientific, and medical (ISM) applications. " (1)

" The new standard proposed ie 802.11b allows data rates pf up to 11Mbps. To support very noisy environments as well as extended range, 802.11b WLANs use dynamic rate shifting, allowing data rates to be automatically adjusted to compensate for the changing nature of the radio channel. Ideally, users connect at the full 11 Mbps rate. However when devices move beyond the optimal range for 11 Mbps operation, or if substantial interference is present, 802.11b devices will transmit at lower speeds, falling back to 5.5, 2, and 1 Mbps. Likewise, if the device moves back within the range of a higher-speed transmission, the connection will automatically speed up again. Rate shifting is a physical-layer mechanism transparent to the user and the upper layers of the protocol stack ". (2)


Security

The only problem with using radio as a carrier is that any one within a certain radius could potentially intercept secret information. Unlioke wired ethernet where wire tapping is less likely anyone witha similar WLAN network card can recieve a WLAN's transmissions.

" 802.11 provides for both MAC layer (OSI Layer 2) access control and encryption mechanisms, which are known as Wired Equivalent Privacy (WEP), with the objective of providing wireless LANs with security equivalent to their wired counterparts. For the access control, the ESSID (also known as a WLAN Service Area ID) is programmed into each access point and is required knowledge in order for a wireless client to associate with an access point. In addition, there is provision for a table of MAC addresses called an Access Control List to be included in the access point, restricting access to clients whose MAC addresses are on the list.

For data encryption, the standard provides for optional encryption using a 40-bit shared-key RC4 PRNG algorithm from RSA Data Security. All data sent and received while the end station and access point are associated can be encrypted using this key. In addition, when encryption is in use, the access point will issue an encrypted challenge packet to any client attempting to associate with it. The client must use its key to encrypt the correct response in order to authenticate itself and gain network access." (3)



Shortcomings


When it comes to implementation its down to individual vendors to decide on what features are important which are not for their 802.11 products. Often many of the security features described by the standard were not implemented.

Multivendor interoperability problems
Among devices with the same Physical layer, a few key ingredients necessary to achieve multivendor interoperability are absent in the ratified standard.
1. AP-to-AP coordination for roaming
The standard does not specify the handoff mechanism to allow clients to roam from one AP to another.
2. Data frame mapping
The standard does not state how an Access Point addresses data framing between the wired and the wireless media.
3. Conformance test suite
There is no conformance test suite specified to verify that a device is compliant with the IEEE 802.11 specification. Vendor claims for compliance to the 802.11 standard will need to be ratified by a neutral third party.
Short range and Expensive
The following is a summary taken from: (4) where several tests were conducted on products who implemented the 802.11 standard of 2Mbps.

" To evaluate each product's transmission range, we established three test environments in the Center for Science and Technology at Syracuse University, a 10-year-old office and classroom building. We set up APs in a hallway and ransingle-station FTP tests between two notebook computer systems. Although the FTP client we used reported performance slightly higher than Ganymede's Chariot software, we were more concerned with each product's relative performance."

Aswell as different vendors several locations were also tested. Below are the descriptions of each
Location A
used to simulate a long-distance, open-office test environment, was approximately 250 feet from the Access Point down a long corridor.
Location B
resembling a short-distance, walled-office test environment, was in an office approximately 100 feet from the Access Point, but separated by numerous walls and corridors.
Location C
illustrating a long-distance, walled-office environment, was in a classroom approximately 150 feet away from the Access Point, again separated from the Access Point by numerous walls and corridors.

The table below shows the results for each of the products.

Testing Transmission Range for 802.11 WLANs , results displayed in (Mbps)

 

     A

      B

       C

Average

Lucent

1.54

1.42

0.9

1.29

Nortel 660

1.3

1.18

Incomplete

0.83

InTalk

1.34

1.48

0.47

1.1

Aironet 4500

1.5

1.58

0.72

1.27

MaxTech

1.3

1.49

0.7

1.16

NWN

Incomplete

1.17

Incomplete

0.39

Cabletron

1.53

1.53

0.42

1.16

Intermec

1.42

1.13

0.43

0.99

Samsung

1.34

1.36

0.27

0.99

Proxim

0.9

0.94

0.46

0.77

Symbol

1.17

1.2

0.2

0.86

BreezeCOM

1.21

1.29

Incomplete

0.84

Nortel 650

0.49

0.57

0.19

0.42

Aironet 3500

0.85

0.97

0.31

0.71

Average

1.13

1.24

0.36

 

 

The amount of coverage you can expect from a single Access Point depends on the type of environment and the nature of a vendor's implementation, especially as it relates to radio output power. In open-office, cubicle-style environments, you can easily communicate at distances of several hundred feet. But during tests in a traditional walled-office environment, there was trouble establishing connections at 150 feet. Most vendors offer optional higher-output radios and high-gain antennae for their Access Points (and sometimes for PC Cards) that let you stretch those numbers.Given the relatively modest speed and contention-based architecture of these products, distance limitations have a significant advantage: They reduce the number of nodes in a single cell, thereby improving per-station throughput. The down side, of course, is that you'll need a number of fairly expensive Access Points to cover a large building.

So 802.11 enables limited mobility within small offices and campuses, and increased mobility increases the costs substantially.


References

(1).
http://computer.org/students/looking/summer97/ieee802.htm
A Short Tutorial on Wireless LANs and IEEE 802.11 Daniel L. Lough, T. Keith Blankenship, Kevin J. Krizman
(2).
Pictures and some text were taken from http://www.3com.com/technology/tech_net/white_papers/503072a.html
Entitled : "What’s New in Wireless LANs: The IEEE 802.11b Standard"
(3).
http://www.proxim.com/wireless/standards/80211wp.shtml
(4).
http://www.networkcomputing.com/1006/1006r22.html
(5).
http://www.wireless-nets.com/whitepaper_overview_80211.htm
(6).
http://www2.itworld.com/cma/ett_article_frame/0,,1_1844.html
Mobile computing
Securing 802.11 wireless LANs