With increasing popularity of wireless networking technologies, a large number of wireless networks have been deployed. Mainly two wireless networks exist, namely WLAN (WLANs with access points or ad hoc WLANs) and PANs.Demand for wireless LAN hardware has experienced phenomenal growth during the past several years. Users connecting notebook computers to networks at work and to the Internet at home as well as at coffee shops, airports, hotels, and other mobile gathering places are common examples . Wi-Fi technology is most commonly found in notebook computers and Internet access devices such as routers and DSL or cable modems. In fact, more than 90 percent of all notebook computers now ship with built-in WLAN.A WLAN network provides high-speed data communication in restricted coverage areas at a relatively Low cost. Bluetooth has become widely famous and is used almost everywhere. It has become a standard feature of mobile phones and laptops Wireless keyboards, wireless mouse and wireless printers, Transfer of pictures, files, audio, and video between Bluetooth enabled devices. This paper firstly talks about the W-LAN and functions of layers, Benefits and applications and secondly about the Bluetooth and its uses and respective Bluetooth technology.
WLAN
There are many wireless technologies deployed these days (both in 2g and 3g), PANs (Personal Area Network) like Bluetooth and WLANs(wireless local area network, a-dhoc or with access points). Common examples are laptops connected to internet at home,coffee house,airports,universities and offices. These days almost all laptops computers are equipped with WLAN technology.
Institute of Electrical and Electronics Engineers (IEEE) in 1997 approved the first wireless LAN standard 802.11 and the maximum available speed was up to 2mbps.
However in 1999 both, 802.11a and 802.11b were approved by IEEE but 802.11b products came before 802.11a. Although the maximum speed in the 802.11a was 54mbps unlike in802.11b in which the speed was limited only to a mere 11mbps as compared to 802.11a. Still 802.11b became popular and came in market before 802.11a because it used Direct sequence Spread Spectrum(DSSS) technology. 802.11a used the Orthogonal Frequency Division Multiplexing(OFDM) It is a efficient method of transmission and increases the dats rate. DSSS is easier toimplement and so became the chief cause that IEEE802.11b products appeared in market first. 802.11b ,nowadays, is popularly known as Wi-Fi.Later on in June 2003 802.11g was introduced . It provided with the higher bandwidth .Nowadays, 802.11g is supported by most of the computer network hardwares.
BENEFITS
It allows the user to move the terminal without getting disconnected to the network.Think of a person in office is working on a computer which has a wired internet connection and the terminal cannt be moved after a certain possible limit, but when it comes to Wi-Fi equipped laptop, the user canfreely move anywhere as long as the termin al is under the coverage area of network.
Coverage range: RF and IR waves communivating over a distance depends upon the product design and path of propagation. In indoor environment, walls , heavy and solid objects block the path of IR. Hence most WLANs use the RF, RF penetrates most of the indoor surfaces. The typical range of WLAN is about 100 metres but it can be increased.
Less complicated: User doesn’t need to have a typical knowledge of WLANs . It is more or less same as in case of a wired LAN.
One of the biggest advantage of WLAN is that there is no need to pull cables and so it can be deployed very fast without any complications in term of time and money. Moreover many physical environments doesn’t support wiring, so WLAN is best suited for such areas.
Installation cost of a WLAN is much less than the traditional wired LAN because no wires and labor are required to deploy a WLAN.
MAC LAYER
MAC layer is a common medium access control specified by MAC layer . Anumber of functions are provided by MAC layer, which supports the operation of WLANs.
Two forms of medium access are defined by 802.11 standards, Distributed Coordination Function (DCF) and Point Coordination Function (PCF).
While transmitting , a counter resident which is called Network Allocation Vector(NAV) holds the value of time to send a frame based on a frame already sent before. If NAV is zero, then only a station can send a frame. Based on the frame length and data rate, a time is calculated needed to transmit that frame. Then this time is placed in duration field of the frame. After receiving this frame i,e. The time required, a station uses this value for setting the NAVs.
MAC LAYER FUNCTIONS
Scanning: two types of scanning is defined by 802.11 standards . They are Active and Passive scanning . In order to find the best access point signal,Passive scanning is deployed and it is mandatory as well. Radio NIC receives the becons which were sent by access points and the radio NIC scans the becons and checks for the signal strength.
Active scanning is quite similar to Passive scanning with the difference that the process is initiated by radio NIC by broadcasting a probe frame.
Authentication: two types of authentication. In open system authentication, which is mandatory, authentication request frames are sent to the access point by a radio NIC. The approval or disapproval of authentication is sent back with an authentication response frame.
Fragmentation: Division of data packets into smaller frames is enabled by fragmentation function. It avoids the retransmission of large frames . Less overhead is required to transmit a smaller frame than a large frame.
DCF(Distributed coordination function)
This is the basic MAC Protocol. It deploys:
CSMA/CA and
A random backoff time. Acknowledgement (ACK frame) is used by traffic. If no ACK is received by sender , it senses that some data packets are missing and an acknowledgement to retransmit the missing frame is scheduled.
Before transmission a station checks if the channel is idle or some other station has requested the transmission. If the channel is idle for the time equal to Interframe Space(IFS),it transmits the packet. If some other station has requested the transmission than the other stations wait until the channel becomes free.
For DCF , three IFS are defined:
SIFS(Short IFS)
PIFS(Point Coordination Function IFS)
DIFS(Distributed Coordination Function IFS)
SHORT IFS
Of all IFS it is the shortest and has the maximum priority.
PIFS
Its length is more than SIFS but less than DIFS and its main function is to issue polls.
DIFS
It performs the function of medium delay.
Request to send(RTS) and clear to send(CTS) are the virtual sensing mechanisms and these govern the transmission. The whole procedure is like, prior to transmission a station sends the RTS ( a short pulse) to the receiving station to inform about the transmission. And if the other station is ready to accept packet it sends the clear to send(CTS) packet.
PHYSICAL layer
Three physical layers are defined by the IEEE 802.11 : one infrared and two spread spectrum.
These supports data rate of upto I mbps and 2 mbps. Direct Sequence Spread Spectrum and Frequency Hopping Spread Spectrum(FHSS) are the two spread spectrums. One interesting thing to note is that different data rates. For 1 mbps 16-ppm and for 2 mbps 4-ppm is used. Main reason for different data rate is to minimize the added complexity by 2mbps data rate and it assures that at both data rates, the basic pulse is same.
To carry the MAC Protocol Data Unit simultaneously with the feature of physical layer is the most important function of PHYSICAL layer frame.
MOBILE AD HOC NETWORKS
In AD Hoc networks no fixed infrastructure is needed and it represents an evolution in terms of wireless networking. In this type of network, mobile nodes are joined together to form a group of devices and the devices within the group can communicate with each other in a seamless way. It can have either a hierarchical topology or a flat topology. If all the nodes are on the same level of communication , than this type of topology is flat topology. All the nodes of the ad hoc network are organized into clusters. There is one node called the cluster head which controls the respective clusters.
USES OF WLAN
High speed Internet without any hassle of wired workspace. For example, within a home or a office, everyone can use the internet through the same modem
No wiring cost, saves time and easy to install.
New workstations can be added any time at any point.
Visitors to any enterprise can connect to the internet with very little configuration.
Transmitting Voice over WLANs: The solution to the problem of being in constant touch with each other is to use WLAN to transmit voice.
In a Hotel, where the spread workers to different places need to respond quickly..
In retail stores , if a customer asks for some item, the employer can communicate to the person in inventory to check for the availability of the item.
In offices , where quick help is needed like police or ambulance services.
BLUETOOTH
Bluetooth came into existence in 1994 in order to replace the cables and to connect accessories with wireless links to mobiles and computers.
Why it is called Bluetooth?? : The Bluetooth project was originally started in Scandanavia, so it was named after the10th century monarch Harald Bluetooth, to regard the monarch, who united the Norway and Denmark.
Bluetooth technology is an open standard specification particularly for small distances based upon radio frequency. It is comparatively cheap wireless networking system. It connects portable devices to laptops such as wireless keyboards and wireless mouse. Bluetooth technology has reduced the cost, it has improved security and the functions and operation performed by it are same as carried by cables by mobile travellers.Bluetooth was designed to be a secure just like a cable( which supports every function done by a cable) and it must have the cost same as that of the cables.
The main reason why Bluetooth was created was to replace cables. Various mobile devices communicate to each other after framing a quick ad-hoc “Piconetâ€. When a Bluetooth radio is connected to another Bluetooth radio, a Piconet is formed. Than , through 79 channels, both the radios are hopped together. By providing a unique hopping pattern for each piconet, large number of piconets are supported by the Bluetooth radio system.
A laptop equipped with Bluetooth , which is very common these days , can connect to internet via a Bluetooth mobile phone. In this case Personal Access Point is the mobile phone.
BLUETOOTH COMPONENTS
There are four major components:
Antenna/rf component
Bluetooth radio and Baseband
Bluetooth software Protocol Stack
The application itself
Antenna/RF
A unique solution is implemented for each device in RF and antenna design.
Bluetooth Radio and Baseband
It is the hardware transceiver that performs the function of implementing the Bluetooth Radia specifications. The radio transceiver is a part of this unit which can transmit and send data and it consumes very low power. It operates in 2.4GHz frequency band.Just by increasing power by 10 db, the coverage area is increased roughly by 50 metres.
The baseband has mainly two units, the Link Controller used to perform baseband protocols and Low-layer Link routines.
Bluetooth Software Protocol Stack
It is more or less thought as a driver code .If we want to send and receive some information from the Bluetooth device , it is this code which helps.
Apparently the Bluetooth silicon manufacturers are unable to provide a Bluetooth antenna with the device itself. A lot of specialized skills are required to ensure that the Bluetooth radio will work in the specified specifications.The antenna is not provided purchasing a Bluetooth module.
The protocol stack has a number of components but the major ones are the Logical Link Control and Adaptation Protocol (L2CAP), Human interface Device, TCP/IP, the service discovery protocol, the host control interface and Link manager.
Bluetooth Protocols
Link Manager: The LM setup the connection configuration. It also ebsures the connection and security during the connection between the devices.In a Piconet, the LM decided the master and slave and even the LM switches the master and slave.
L2CAP: Reassemble and segmentation , multiplexity of protocols and quality of services are the various services provided by the L2CAP. Protocol multiplexing is the use of several protocols simultaneously.
Segmentation and Reassemble is a kind of service . In it, the higher layer protocol packets are segmented and thebluetooth packets are reassembled again after transmission after segmented from higher layers.
Audio and Telephony Control: These are linked protocols. Telephony control , as the name suggests, controls the calls and audio. It connects and disconnects a call. Telephony links have some different path, other than the L2CAP-to-LM path and are established as synchronous links.
Human Interface Device(HID): Brings the fashion of cordless computers , keyboards, joysticks , gaming devices like the sony PSs and wireless mouse are part of this protocol.
TCP/IP: TCP/IP being the most fundamental and most vital protocols are widely supported by applications. But handling ad hoc networking is one of the key problems with TCP/IP.
Host/Controller Interface(HCI): It is often implemented as an internal software interface.
USES
Bluetooth has become widely famous and is used almost everywhere. It has become a standard feature of mobile phones and laptops.
Wireless control between a mobile phone and a blurtooth handsfree.
Sending some information to many users at the same time having Bluetooth enabled devices.
Wireless keyboards, wireless mouse and wireless printers are becoming famous, are based on Bluetooth.
Transfer of pictures, files ,audio ,video between Bluetooth enabled devices( this is the OBEX protocol) object exchange.
Using mobile phone as a wireless modem for dial up internet .
Often implemented in traffic control devices , GPS receiver and medical equipments.
CONCLUSION
