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Introduction to Wireless LAN
Wireless LAN stands for Wireless Local Area Network. It is also called LAWN ( Local Area Wireless Network ). WLAN is one in which a mobile user can connect to a Local Area Network (LAN) through a wireless connection. The IEEE 802.11 group of standards defines the technologies for wireless LANs. For path sharing, 802.11 standard uses the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance). It also uses an encryption method i.e. wired equivalent privacy algorithm.
Advantages of WLANs
o Flexibility: Within radio coverage, nodes can communicate without further restriction. Radio waves can penetrate walls, senders and receivers can be placed anywhere (also non-visible, e.g., within devices, in walls etc.). o Planning: Only wireless ad-hoc networks allow for communication without previous planning, any wired network needs wiring plans. o Design: Wireless networks allow for the design of independent, small devices which can for example be put into a pocket. Cables not only restrict users but also designers of small notepads, PDAs, etc. o Robustness: Wireless networks can handle disasters, e.g., earthquakes, flood etc. whereas, networks requiring a wired infrastructure will usually break down completely in disasters. o Cost: The cost of installing and maintaining a wireless LAN is on average lower than the cost of installing and maintaining a traditional wired LAN, o Ease of Use: Wireless LAN is easy to use and the users need very little new information to take advantage of WLANs.
Disadvantages of WLANs
o Quality of Services: Quality of wireless LAN is typically lower than wired networks. o Proprietary Solutions: Due to slow standardization procedures, many companies have come up with proprietary solutions offering standardization functionality plus many enhanced features. o Restrictions: Several govt. and non-govt. institutions world-wide regulate the operation and restrict frequencies to minimize interference.
o Global operation: Wireless LAN products are sold in all countries so, national and international frequency regulations have to be considered. o Low Power: Devices communicating via a wireless LAN are typically power consuming, also wireless devices running on battery power. o License free operation: LAN operators don't want to apply for a special license to be able to use the product. The IEEE 802.11 standard, commonly known as Wi-Fi, outlines the architecture and defines the MAC and physical layer specifications for wireless LANs (WLANs). Wi-Fi uses high- frequency radio waves instead of cables for connecting the devices in LAN. Given the mobility of WLAN nodes, they can move unrestricted within the network coverage zone. The 802.11 structure is designed to accommodate mobile stations that participate actively in network decisions. Furthermore, it can seamlessly integrate with 2G, 3G, and 4G networks. Important Terminologies of IEEE 802.11 Architecture Station: Stations (STA) comprise all devices and equipment that are connected to the wireless LAN. It can be of two types: Wireless Access Point (WAP): WAPs or simply access points (AP) are wireless routers that bridge connections for base stations. Client: Examples include computers, laptops, printers, and smartphones. Access Point : It is a device that can be classified as a station because of its functionalities and acts as a connection between wireless medium and distributed systems. Distribution System: A system used to interconnect a set of BSSs and integrated LANs to create an ESS. Frame: It is a MAC protocol data unit. SSID (Service Set Identifier): It’s the network name for a particular WLAN. All-access points and devices on a specific WLAN must use the same SSID to communicate. SDU: It is a data unit that acts as an input to each layer. These can be fragmented or aggregated to form a PDU. PDU: It is a data unit projected as an output to communicate with the corresponding layer at the other end. They contain a header specific to the layer. Network Interface Controller: It is also known as network interface card. It is a hardware component that connects devices to the network.
Independent BSS
Independent Basic Service Set
In the IBSS configuration, also referred to as independent configuration or ad-hoc network, no single node is required to act as a server. The stations communicate directly with one another in a peer-to-peer basis.
Extended Service Set
ESS connects multiple BSSs and consists of several BSS cells, which can be interlinked through wired or wireless backbones known as a distributed system
Architecture for IEEE 802.11 Configuration Roaming: In an environment with multiple access points (like a large office building or campus), a device can move from the range of one AP to another and still maintain its connection. Authentication and Association: Before a station can send or receive data frames on a WLAN, it needs to establish its identity with an AP. Services provided by the WLAN IEEE defines 9 services that need to be provided by the WLAN:
Service Provider Used to Support
Association Distribution System MSDU delivery Authentication Station LAN access and security De- authentication Station LAN access and security
Points to remember for Bluetooth: Bluetooth Transmission capacity 720 kbps. Bluetooth is Wireless. Bluetooth is a Low-cost short-distance radio communications standard. Bluetooth is robust and flexible. Bluetooth is cable replacement technology that can be used to connect almost any device to any other device. The basic architecture unit of Bluetooth is a piconet.
Bluetooth Architecture:
The architecture of Bluetooth defines two types of networks:
- Piconet
- Scatternet
Piconet:
Piconet is a type of Bluetooth network that contains one primary node called the master node and seven active secondary nodes called slave nodes. Thus, we can say that there is a total of 8 active nodes which are present at a distance of 10 meters. The communication between the primary and secondary nodes can be one-to-one or one-to-many. Possible communication is only between the master and slave; Slave-slave communication is not possible. It also has 255 parked nodes , these are secondary nodes and cannot take participation in communication unless it gets converted to the active state.
Scatternet:
It is formed by using various piconets. A slave that is present in one piconet can act as master or we can say primary in another piconet. This kind of node can receive a message from a master in one piconet and deliver the message to its slave in the other piconet where it is acting as a master. This type of node is referred to as a bridge node. A station cannot be mastered in two piconets.
Bluetooth protocol stack:
- Radio (RF) layer: It specifies the details of the air interface, including frequency, the use of frequency hopping and transmit power..
- Baseband Link layer: The baseband is the digital engine of a Bluetooth system and is equivalent to the MAC sublayer in LANs
- Link Manager protocol layer: It performs the management of the already established links which includes authentication and encryption processes.
- Logical Link Control and Adaption (L2CAP) Protocol layer: It is also known as the heart of the Bluetooth protocol stack
Disadvantages:
It can be hacked and hence, less secure. It has a slow data transfer rate: of 3 Mbps. It has a small range: 10 meters. Bluetooth communication does not support routing. The issues of handoffs have not been addressed.
Applications:
It can be used in laptops, and in wireless PCs, printers. It can be used in wireless headsets, wireless PANs, and LANs. It can connect a digital camera wirelessly to a mobile phone. It can transfer data in terms of videos, songs, photographs, or files from one cell phone to another cell phone or computer. It is used in the sectors of Medical health care, sports and fitness, Military. Multiple Access Protocols in Computer Network The Data Link Layer is responsible for transmission of data between two nodes. Its main functions are- Data Link Control Multiple Access Control Data Link control – The data link control is responsible for reliable transmission of message over transmission channel by using techniques like framing, error control and flow control. For Data link control refer to
1. Random Access Protocol: In this, all stations have same superiority that is no station has more priority than another station. Any station can send data depending on medium’s state( idle or busy). It has two features: 1. There is no fixed time for sending data 2. There is no fixed sequence of stations sending data The Random access protocols are further subdivided as: (a) ALOHA – It was designed for wireless LAN but is also applicable for shared medium. In this, multiple stations can transmit data at the same time and can hence lead to collision and data being garbled. Pure Aloha: When a station sends data it waits for an acknowledgement. If the acknowledgement doesn’t come within the allotted time then the station waits for a random amount of time called back-off time (Tb) and re-sends the data. Since different stations wait for different amount of time, the probability of further collision decreases. Slotted Aloha: It is similar to pure aloha, except that we divide time into slots and sending of data is allowed only at the beginning of these slots (b) CSMA – Carrier Sense Multiple Access ensures fewer collisions as the station is required to first sense the medium (for idle or busy) before transmitting data. If it is idle then it sends data, otherwise it waits till the channel becomes idle. However there is still chance of collision in CSMA due to propagation delay. or its time slot to send data. (c) CSMA/CD – Carrier sense multiple access with collision detection. Stations can terminate transmission of data if collision is detected.
Vehicles o For personal communication, a universal mobile telecommunications system (UMTS) phone might be available offering voice and data connectivity with 384kbit/s. o For remote areas, satellite communication can be used, while the current position of the car is determined via the GPS (Global Positioning System). o Vehicle data from buses, trucks, trains and high speed train can be transmitted in advance for maintenance. Emergency o Video communication: Responders often need to share vital information. The transmission of real time situations of video could be necessary o Push To Talk (PTT): PTT is a technology which allows half duplex communication between two users where switching from voice reception mode to the transmit mode takes place with the use of a dedicated momentary button. It is similar to walkie-talkie. o Audio/Voice Communication: This communication service provides full duplex audio channels unlike PTT. Public safety communication requires novel full duplex speech transmission services for emergency response. o Real Time Text Messaging (RTT): Text messaging (RTT) is an effective and quick solution for sending alerts in case of emergencies. Types of text messaging can be email, SMS and instant message. Business Travelling Salesman o Directly access to customer files stored in a central location. o Consistent databases for all agents o Mobile office o To enable the company to keep track of all the activities of their travelling employees. In Office o Wi-Fi wireless technology saves businesses or companies a considerable amount of money on installations costs.
o There is no need to physically setup wires throughout an office building, warehouse or store. o Bluetooth is also a wireless technology especially used for short range that acts as a complement to Wi-Fi. It is used to transfer data between computers or cellphones. Transportation Industries o In transportation industries, GPS technology is used to find efficient routes and tracking vehicles. Replacement of Wired Network o Wireless network can also be used to replace wired network. Due to economic reasons it is often impossible to wire remote sensors for weather forecasts, earthquake detection, or to provide environmental information, wireless connections via satellite, can help in this situation. Location dependent service It is important for an application to know something about the location because the user might need location information for further activities. Several services that might depend on the actual location can be described below: o Follow-on Services: o Location aware services: To know about what services (e.g. fax, printer, server, phone, printer etc.) exist in the local environment. o Privacy: We can set the privacy like who should get knowledge about the location. o Information Services: We can know about the special offers in the supermarket. Nearest hotel, rooms, cabs etc. Infotainment: (Entertainment and Education) o Wireless networks can provide information at any appropriate location. o Outdoor internet access. o You may choose a seat for movie, pay via electronic cash, and send this information to a service provider. o Ad-hoc network is used for multiuser games and entertainment.
A low-level networking operation, such as broadcasting via Ethernet. Broadcasting is basically limited to local area network (LAN) systems. In a LAN, however, its performance impact is more substantial in a wide area network (WAN). Internet Protocol Version 6 (IPv6) uses multicasting, rather than broadcasting, to avoid network interruption when services are required by only one or two nodes. During data transmission, IPv6 transmits data directly to devices and does not disturb network device traffic.
What is Mobile IP?
Mobile IP or MIP is an Internet Engineering Task Force (IETF) RFC 2002, De-Facto standard communication protocol. It is created by extending Internet Protocol, IP. The Mobile IP allows mobile device users to move from one network to another while maintaining the same permanent IP address. The concept and role of Mobile IP are very important in the field of mobile computing technology. The mobile IP makes the communication flawless and ensures that the communication will occur without the user's sessions or connections being dropped. Mobile IP is based on IP, so it is scalable for the Internet. Any media that supports IP can also support Mobile IP.
Introduction to Mobile IP Technology
In IP networks, when a device is within its home network, the routing is based on the static IP addresses. The device within a network is connected through normal IP routing by the IP address assigned on the network. It is the same as how a postal letter is delivered to the fixed address on the envelope. The mobility function of the Mobile IP is performed on the network layer rather than the physical layer.
The architecture of Mobile IP Technology
The components of the Mobile IP and the relationship among them are specified in the following image:
This is the architecture of Mobile IP technology. It consists of the following components: o Mobile Node (MN) o Home Agent (HA) o Foreign Agent (FA) o Home Network (HN) o Foreign Network (FN) o Corresponding Node (CN) o Care of Address (COA) Mobile Node The Mobile Node is a device or a user or a router that can frequently change their network positions without changing its original IP address. Examples of mobile nodes are cell phone, personal digital assistant (PDA), laptop, etc. whose software enables network roaming capabilities. Home Agent The Home Agent is a router on the home network. It serves as the anchor point for communication with the Mobile Node. Foreign Agent The Foreign Agent is a router that provides several services such as tunneling data-grams whenever a mobile node visits a foreign network. It
Applications of Mobile IP The mobile IP technology is used in many applications where the sudden changes in network connectivity and IP address can cause problems. It was designed to support seamless and continuous Internet connectivity. It is used in many wired and wireless environments where users have to carry their mobile devices across multiple LAN subnets. What is Wireless Application Protocol (WAP)? WAP stands for Wireless Application Protocol. It is a protocol designed for micro-browsers and it enables access to the internet in mobile devices. It uses the markup language WML (Wireless Markup Language and not HTML), WML is defined as an XML 1.0 application. It enables the creation of web applications for mobile devices. In 1998, WAP Forum was founded by Ericson, Motorola, Nokia and Unwired Planet whose aim was to standardize the various wireless technologies via protocols. WAP protocol resulted from the joint efforts of the various members of WAP Forum. In 2002, WAP forum was merged with various other forums in the industry resulting in the formation of Open Mobile Alliance (OMA) WAP Model The user opens the mini-browser in a mobile device. He selects a website that he wants to view. The mobile device sends
the URL encoded request via network to a WAP gateway using WAP protocol. The WAP gateway translates this WAP request into a conventional HTTP URL request and sends it over the internet. The request reaches to a specified web server and it processes the request just as it would have processed any other request and sends the response back to the mobile device through WAP gateway in WML file which can be seen in the micro-browser. WAP Protocol stack
- Application Layer: This layer contains the Wireless Application Environment (WAE). It contains mobile device specifications and content development programming languages like WML.
- Session Layer: This layer contains Wireless Session Protocol (WSP). It provides fast connection suspension and reconnection.
- Transaction Layer: This layer contains Wireless Transaction Protocol (WTP). It runs on top of UDP (User Datagram Protocol) and is a part of TCP/IP and offers transaction support.
