Wireless LAN

LAN(local area network) It is a communication network that interconnects variety of devices and provides means of information exchange among these devices Its scope may be a small room, a building or a cluster of buildings

WLAN(Wireless LAN) LAN that makes use of wireless transmission media is called as wireless LAN i.e. WLAN Instead of being an alternate it may be called as extension to LAN It is used to provide final connectivity of few meters between backbone wired network and end mobile users

MCU WAP MCU – Master Control Unit WAP – Wireless Access Point Node-1 Wireless transmission medium

Access point : Should have NIC (Network Interface Card) Hub antenna : located at center or corner Line of sight : not necessary but desirable Frequency used may be Licensed (require high length of paper work from FCC) Unlicensed (does not require paper work but suffers inference from barcode , scanners etc) Standards used may be de-facto ( approved by individuals or organizations that don’t have national international recognition) De-jure(approved by nationally internationally approved organizations)

Advantages Flexibility Planning Installations Robustness Scalability Cost Improved productivity and service

Disadvantages Quality of service Proprietary solutions Restrictions Safety and security

Applications

Design and principle of operation

Configurations of WLAN Infrastructure WLAN Ad hoc WLAN

Infrastructure WLAN

communication take place between node(user) and AP No direct communication between Nodes AP act as bridge AP takes care of all network Functionality so nodes can be Simple two small networks can form single big logical network Flexibility is less

Ad hoc WLAN Or Peer to peer WLAN

communication take place directly between nodes Access point is not present Here the clients need to take care of network functionality, hence nodes are complex two nodes can communicate with each other only if they are in range they are quite flexible , for setting up fast network such as for meetings ,Conferences etc

comparison Ad hoc WLAN Infrastructure WLAN Communication take place directly between nodes AP is not present Complexity of each node is higher as it need to implement MAC mechanism, mechanism to handle hidden or exposed terminal to provide certain quality of service Communication take place through AP and no direct communication between nodes AP act as a bridge between wired and wireless network All the network functionality lies in the AP point and hence client remain quite simple

Ad hoc WLAN Infrastructure WLAN Nodes that are not in direct range of each other can also communicate through AP Two small networks can be combined to form a larger logical network Flexibility is less Eg: hyperlan Nodes that are in each others range can only communicate Such network expansion is not possible in Ad hoc WLAN More flexible Eg: Bluetooth

Micro cell and roaming

Transmission technologies Wireless LAN Transmission technologies Or Types of wireless LAN

Wireless LAN transmission technologies Or Types of wireless LAN Infrared WLAN Radio WLAN Spread spectrum Narrow band

Infrared WLAN Strengths and weakness constructed using infrared portion of spectrum Strengths and weakness strengths: unregulated spectrum infrared shares some properties of visible light -diffusely reflected by light colored objects . Thus ceiling reflection can be used to provide coverage of entire room. -infrared cant penetrate , hence can be protected against eavesdropping

spectrum virtually unlimited hence high rates possible equipments used are LED and photo diode which are simple and inexpensive IR data transmission generally use IM so the detector needs to detect only amplitude which quite simple electrical devices does not cause any interference

Weakness: background radiation, e.g. ssunlight, indoor lighting appear as noise. Line of sight is compulsory as it cant penetrate Increase in transmitter power is also limited by concerns of eye safety

Transmission techniques of IR: Directed Beam IR Omni-directional Diffusion

1) Directed Beam IR Point-to-point links Range depends on power and focusing -Can be kilometers -Used for building interconnect within line of sight Indoor use to set up token ring LAN IR transceivers positioned so that data circulate in ring

2) Omni directional IR Single base station within line of sight of all other stations -Typically, mounted on ceiling Acts as a multiport repeater Other transceivers use directional beam aimed at ceiling unit

3) Diffused directional IR Transmitters are focused and aimed at diffusely reflecting ceiling IR striking the ceiling are reradiated and picked up by the receiver in the area