‘Describe radio will hop the carrier frequency over

‘Describe how you would set up and maintain a wireless LAN alongside an existing wire-based system in a closely defined organization of your choice’ Since the invention of the computer, we have been witnessing major shifts in computing paradigms almost every decade. Today clusters of desktop workstations interconnected through high speed Local Area Networks constitute the core of network computing environments worldwide.

” Technological advances of the 90’s are bringing about a major change that has the potential to reshape the existing form of network computing, with the confluence of wireless and VLSI technologies, we are poised for yet another computing revolution. “. (Jim Grier ‘Wireless lans’2001) Figure (1. 0) shows a network plan of Surrey County All Girls School. The school has 2 main teaching buildings, which are separated by a recreation building but interconnected by an Ethernet LAN.

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The School Dean has decided the recreation building that has no computing facilities will be converted into a teaching facility but due to the historical nature of the building, cabling the whole building would be difficult. The floors and walls were made of very thick sandstone and historic plaster ceilings could not be easily drilled into. The only feasible solution was a wireless LAN. Wireless LAN exist in several specifications and standards, the emphasis of this solution is using IEEE 802. 11 i. e. using 2. 4 Ghz operating frequency and data rates of 1Mbps and 2Mbps. It use’s spread spectrum modulation.

There are alternatives such as HiperLAN operating in the 5 GHz radio band and data transfer rates up to 24 Mbps. Another popular one is Bluetooth, operating over 2. 4 GHz and data rates of 1Mbps. Wireless LAN’s use electromagnetic airwaves (radio in this case) to communicate network information from node to node without relying on a physical (wired) connection. The various manufacturers of wireless LAN’s have a range of technologies to choose from. The common ones include narrowband (NB), spread spectrum (SS), frequency hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS) and infrared technology (IR).

The principal one used in our solution is FHSS. It takes the data signal and modulates it with a narrow band carrier wave that hops from frequency to frequency as a function of time over a band of frequencies. For example, a frequency-hopping radio will hop the carrier frequency over the 2. 4 GHz and 2. 483 GHz. A hopping code determines the frequencies it will transmit and in which order. To properly receive the signal, the receiver must be set to the same hopping code and “listen” to the incoming signal at the right time at the correct frequency.

The major components of a wireless LAN are a wireless network interface card (NIC) and a wireless local bridge which is often referred to as an access point. The wireless NIC interfaces the appliance with the wireless network, and the access point interfaces the appliance with the wireless network with a wired network. The wireless NIC interface appliances to the wireless network by implementing a carrier sense protocol and modulating the data signal with a spreading sequence.

The end user appliances for this solution are a range of desktop computers, laptop computers and hand held p.c. ‘s. (See figure 1. 3) The solution (fig 1. 2) shows how the new system will be implemented. The main features of this wireless solution includes: using the 2. 4 GHz frequency band, high performance 1. 6 MB/s data rate, transmitting over secure FHSS technology, simple control and configuration of network, being ETSI accredited by Radio Communications Agency and fully IEEE 802. 3 compliant and protocol independent. It is fully manageable via SNMP and via special web browser software.

It is an Ethernet solution that has future options for IEEE 802.11 and IEEE 802. 11b (yet to be licensed within UK)It even offers Cable-less mobile users or fixed users within buildings Building-to-building links with zero running costs. The network operating system software is Window’s NT, hosted on a high-end server providing the file, print and application services. The network operating system will be server orientated, that is where the core application software and databases will reside. The appliances will interface via TCP/IP with the application software/database running on the NOS.

The wireless network appears to be transparent to application software and operating systems on the network. As a result, applications written for the wired Ethernet will generally run without changes over the wireless network. In the school wireless LAN configuration, the access points connect to the wired network from the fixed location using standard cabling. It then transmits via an antenna to the antenna in building 2 connected to another access point. The access point receives buffers and transmits data between the wireless LAN and the wired network infrastructure.

This single access point can support the users in that room and can function within a range of up to several hundred feet. The access point (or in this case, the antenna attached to the access point) will be mounted anywhere on the floor to provide the desired radio coverage. The end users then access the wireless LAN through wireless-LAN adapters, which are implemented as PC cards in the desktop computers, lap top computers or integrated within hand held p. c. ‘s. Due to the large number of relatively large number of access points the school users will be able to move seamlessly (called roaming) on the floor.

The access points ‘hand’ the client from one to another in a way that is invisible to the client (similar to how mobiles phones pass from one cell site to another). Extension points can also be used to further extend coverage however for this solution it was more cost effective to use extra access points. The solution will be implemented using the Proxim RangeLAN2 product range from: Unwired Solutions. Com (UK Based Company) Figure 1. 4 and fig 1. 5 shows the RangeLAN2 Network Card and Adapter, a wireless network card (NIC) is required for each client on the wireless network.