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Unit - 3Wireless LANS & Virtual Circuit Networks 3.1 Wireless LANS: IEEE 802.11 ProjectWireless LANs are those Local Area Networks that use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or Wi-Fi.IEEE 802.11 ArchitectureThe components of IEEE 802.11 architecture are as follows1) Stations (STA) − Stations comprise all devices and equipment’s that are connected to the wireless LAN. A station can be of two types:Wireless Access Points (WAP) − WAPs or simply access points (AP) are generally wireless routers that form the base stations or access. Client. − Clients are workstations, computers, laptops, printers, smartphones, etc. Each station has a wireless network interface controller.2) Basic Service Set (BSS) −A basic service set is a group of stations communicating at physical layer level. BSS can be of two categories depending upon mode of operation:Infrastructure BSS − Here, the devices communicate with other devices through access points. Independent BSS − Here, the devices communicate in peer-to-peer basis in an ad hoc manner. 3) Extended Service Set (ESS) − It is a set of all connected BSS.4) Distribution System (DS) − It connects access points in ESS.
Advantages of WLANsThey provide clutter free homes, offices and other networked places. The LANs are scalable in nature, i.e. devices may be added or removed from the network at a greater ease than wired LANs. The system is portable within the network coverage and access to the network is not bounded by the length of the cables. Installation and setup is much easier than wired counterparts. The equipment and setup costs are reduced. Disadvantages of WLANsSince radio waves are used for communications, the signals are noisier with more interference from nearby systems. Greater care is needed for encrypting information. Also, they are more prone to errors. So, they require greater bandwidth than the wired LANs. WLANs are slower than wired LANs. 3.2 Introduction BluetoothIt is a Wireless Personal Area Network (WPAN) technology and is used for exchanging data over smaller distances. This technology was invented by Ericson in 1994. It operates in the unlicensed, industrial, scientific and medical (ISM) band at 2.4 GHz to 2.485 GHz. Maximum devices that can be connected at the same time are 7. Bluetooth ranges upto 10 meters. It provides data rates upto 1 Mbps or 3 Mbps depending upon the version. The spreading technique which it uses is FHSS (Frequency hopping spread spectrum). A bluetooth network is called piconet and a collection of interconnected piconets is called scatternet.Bluetooth Architecture:
Bluetooth protocol stacks:
Radio (RF) layer:
It performs modulation/demodulation of the data into RF signals. It defines the physical characteristics of bluetooth transceiver. It defines two types of physical link: connection-less and connection-oriented. Baseband Link layer:
It performs the connection establishment within a piconet. Link Manager protocol layer:
It performs the management of the already established links. It also includes authentication and encryption processes. Logical Link Control and Adaption protocol layer:
It is also known as the heart of the bluetooth protocol stack. It allows the communication between upper and lower layers of the bluetooth protocol stack. It packages the data packets received from upper layers into the form expected by lower layers. It also performs the segmentation and multiplexing. SDP layer:
It is short for Service Discovery Protocol. It allows to discover the services available on another bluetooth enabled device. RF comm layer:
It is short for Radio Frontend Component. It provides serial interface with WAP and OBEX. OBEX:
It is short for Object Exchange. It is a communication protocol to exchange objects between 2 devices. WAP:
It is short for Wireless Access Protocol. It is used for internet access. TCS:
It is short for Telephony Control Protocol. It provides telephony service. Application layer:
It enables the user to interact with the application. Advantages:Low cost. Easy to use. It can also penetrate through walls. It creates an adhoc connection immediately without any wires. It is used for voice and data transfer. Disadvantages:It can be hacked and hence, less secure. It has slow data transfer rate: 3 Mbps. It has small range: 10 meters. 3.3 Zigbee Virtual LANSIn this present communication world there are numerous high data rate communication standards that are available, but none of these meet the sensors’ and control devices’ communication standards. These high-data rate communication standards require low-latency and low-energy consumption even at lower bandwidths. The available proprietary wireless systems’ Zigbee technology is low-cost and low-power consumption and its excellent and superb characteristics makes this communication best suited for several embedded applications, industrial control, and home automation, and so on.
Advantages of WLANs Bluetooth protocol stacks: It performs modulation/demodulation of the data into RF signals. It defines the physical characteristics of bluetooth transceiver. It defines two types of physical link: connection-less and connection-oriented.
It performs the connection establishment within a piconet.
It performs the management of the already established links. It also includes authentication and encryption processes.
It is also known as the heart of the bluetooth protocol stack. It allows the communication between upper and lower layers of the bluetooth protocol stack. It packages the data packets received from upper layers into the form expected by lower layers. It also performs the segmentation and multiplexing.
It is short for Service Discovery Protocol. It allows to discover the services available on another bluetooth enabled device.
It is short for Radio Frontend Component. It provides serial interface with WAP and OBEX.
It is short for Object Exchange. It is a communication protocol to exchange objects between 2 devices.
It is short for Wireless Access Protocol. It is used for internet access.
It is short for Telephony Control Protocol. It provides telephony service.
It enables the user to interact with the application.
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