The mobile machines, which are essentially client PCs, "talk" to a server on a wired LAN using these access points. An access point simply acts as an intermediary between the wireless PC and the wired LAN.

During the last three years, we saw a mushrooming of technologies and their related applications designed for mobile telephony. Applications such as mobile-commerce and virtual gaming are now becoming possible due to 2.5G (Generation) and 3G technologies. Technologies such as General Packet Radio Service (GPRS), a 2.5G technology that is a stepping-stone to 3G Universal Mobile Telecommunications System (UMTS), are beginning to transform the way we interact with our favorite voice/data transmission device called the cell-phone. The revolution continues, with Japan and US leading in research and development of hyper-speed content rich mobile solutions that are envisioned as 4G deliverables.

With increased usage of wireless devices such as pagers, cell-phones, Personal Digital Assistants (PDAs), it became necessary to explore the application of wireless technologies in the confines of enterprise-wide computing. In 1997, IEEE ratified the 802.11 as a standard that promised the movement of PCs without any wires within a Local Area Network (LAN). The beauty of this standard was that it created LAN environments running on radio waves. 802.11 was designed to provide 1 and 2 Mbps data rates. In 1999, similar variations called 802.11a and 802.11b were confirmed. With two distinct data transmission rates for 802.11a and 802.11b, this technology has started to draw the attention of IT groups that have dedicated "move and install teams". These teams are primarily focused on moving and "cabling" their users’ PCs on a departmental LAN.

What and How?

To keep technology structured and interoperable, IEEE adopted 802 series of protocol standards for LANs. The 802 series deals with the lowest layers 1 and 2 of the ISO Reference Model. Protocols 802.2, 802.3, 802.4 and 802.5 deal with the physical and link layers. More specifically, 802.2 is the Logical Link Control (LLC) protocol, whereas 802.3, 802.4 and 802.5 are Medium Access Control (MAC) protocols. The lowest layers are network dependent and therefore must understand low-level protocol associated with the data communications network connecting two devices.

Technology for wireless LAN has been around for over ten years, but it has started to gain respect and popularity with the arrival of the 802.11 family of protocols – the specifications 802.11, 802.11a and 802.11b. This is primarily because it has been simplified and standardized by IEEE. Strong support exists for this technology due to reasons such as Non-Line-of-Sight (NLoS) transmission, freedom to move PCs within a reasonable periphery and integrated encryption. Wired Equivalency Privacy (WEP), the encryption algorithm, is included in the 802 standard. Some vendors, such as Cisco have released products based on 128-bit encryption (Aironet 350), thus substantially reducing the security risk.

Even though 802.11, 802.11a and 802.11b, use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CD) "listen before you talk" scheme as path sharing protocol, 802.11 and 802.11b specs are for wireless Ethernet LANs, and 802.11a is suitable for wireless ATM. 802.11b transmits signals between 2.4–2.483 GHz, the unlicensed section of the spectrum targeted for Industrial, Scientific and Medical (ISM) industry. The original 802.11 encodes signals using Direct Sequence Spread Spectrum (DSSS). Using DSSS technology the 0s and 1s are modulated with a second pattern called the chipping sequence, thus generating streams called chips. The data transmission rates varies with 802.11 supporting 2 Mbps, and 802.11b peaking at 11Mbps due to a Complementary Code Keying (CCK) modulating method that supports a higher data rate. 802.11b sends 64 chips in one burst, achieving a data rate of 11Mbps while 802.11a specification is capable of supporting up to 54Mbps. The table above shows both standards with their respective distinct characteristics.

In 802.11 architecture, the mobile nodes communicate with other nodes through fixed network access points. The mobile machines, which are essentially client PCs, "talk" to a server on a wired LAN using these access points. An access point simply acts as an intermediary between the wireless PC and the wired LAN. It serves a group of users within several hundred feet by transmitting and receiving signals over radio waves from a group of PCs.

When a PC is moved from one "cell" or place to another, its access point also changes. In cellular terminology this is called a hand-off. A hand-off does not involve any technical support for the PC and it is fully transparent to the user of the PC, making a PC completely mobile.

The appeal for 802.11 exists because the standard is from IEEE, supports higher-speed networks similar to wired LANs, and is cost effective. The access point transceivers can be bought for $1000, along with transceivers for desktop and laptop PCs for up to $200. The standard also supports interoperability, a main concern for LAN administrators. To top all this, the standard is completely wireless, thus giving complete mobility freedom to PCs without any strings attached.

Data coming over a dedicated link out of the telecom carrier, enters the corporate router through modem and then encryption device. Once packets arrive into the enterprise network, the switch pushes them on to the right destination. For example assume that PC1, server A and printer A are all connected and accessible on a wired local area network running ethernet. Also, available on the network are PC2 and PC3 through a radio-link via access point device that is connected to the ethernet. A network may have multiple access points, each communicating with several laptops, desktops or PDA devices. Each access point acts just like a base station in the world of cellular communications. When one PC moves from one area to the other, a migration from current base station to the next base station occurs. The PC is "handed off" to the next base station.

A new PC issues a request for authentication, which is acknowledged by the network by sending a block of random text. The PC encrypts the packet and radios it to the access point. This way authentication is established. More illustratively, the PC sends a Ready-To-Send (RTS) packet to the access point. In return, access point sends a Clear-To-Send (CTS) signal. On receiving it, PC sends data that is acknowledged by the access point.