MOBILE COMPUTING
ABSTRACT:
Mobile Computing is an umbrella term used to
describe technologies that enable people to access network services
anyplace, anytime, and anywhere. Ubiquitous computing and nomadic
computing are synonymous with mobile computing. Information access via a
mobile device is plagued by low available bandwidth, poor connection
maintenance, poor security, and addressing problems. Unlike their wired
counterparts, design of software
for mobile devices must consider resource limitation, battery power and display size. Consequently, new hardware and software techniques must be developed. For example, applications need to be highly optimized for space, in order to fit in the limited memory on the mobile devices. For Internet enabled devices, the good old TCP/IP stack cannot be used; it takes too much space and is not optimized for minimal power consumption. Given the plethora of cellular technologies that have emerged in such a market, it becomes extremely difficult to provide support for inter-device communication. A new hardware technology solution, Bluetooth, has been proposed to overcome this barrier. Any device with a Bluetooth chip will be able to communicate seamlessly with any other device having a similar chip irrespective of the communication technologies they might be using. For the sake of explanation, an analogy can be drawn between the Java Virtual Machine and Blue tooth. In this article we give an overview of data communication networks and describe in detail the Bluetooth technology that was developed to provide wireless interconnect between small mobile devices and their peripherals. Finally, we look at the applications of Mobile Computing in the real world. INTRODUCTION Mobile Computing: A technology that allows transmission of data, via a computer, without having to be connected to a fixed physical link. Mobile voice communication is widely established throughout the world and has had a very rapid increase in the number of subscribers to the various cellular networks over the last few years. An extension of this technology is the ability to send and receive data across these cellular networks. This is the principle of mobile computing. Mobile data communication has become a very important and rapidly evolving technology as it allows users to transmit data from remote locations to other remote or fixed locations. This proves to be the solution to the biggest problem of business people on the movemobility. DATA COMMUNICATIONS Data Communications is the exchange of data using existing communication networks. The term data covers a wide range of applications including File Transfer (FT), interconnection between WAN, fax , electronic mail, access to the internet and the World Wide Web . Data Communications have been achieved using a variety of networks such as PSTN, leasedlines and more recently ISDN (Integrated Services Data Network) and ATM (Asynchronous Transfer Mode). These networks are partly or totally analogue or digital using technologies such as circuit - switching, packet - switching etc. Mobile communications overview Circuit switching implies that data from one user (sender) to another (receiver) has to follow a pre-specified path. If a link to be used is busy, the message can’t be redirected, a property which causes many delays. Packet switching is an attempt to make better utilization of the existing network by splitting the message to be sent into packets. Each packet contains information about the sender, the receiver, the position of the packet in the message as well as part of the actual message. There are many protocols defining the way packets can be send from the sender to the receiver. The most widely used are the Virtual Circuit-Switching system, which implies that packets have to be sent through the same path, and the Datagram system which allows packets to be sent at various paths depending on the network availability. The introduction of mobility in data communications required a move from the Public Switched Data Network (PSDN) to other networks like the ones used by mobile phones. PCSI has come up with an idea called CDPD (Cellular Digital Packet Data) technology which uses the existing mobile network (frequencies used for mobile telephony). Mobility implemented in data communications has a significant difference compared to voice communications. Mobile phones allow the user to move around and talk at the same time; the loss of the connection for 400ms during the hand over is undetectable by the user. When it comes to data, 400ms is not only detectable but causes huge distortion to the message. Therefore data can be transmitted from a mobile station under the assumption that it remains stable or within the same cell. Introduction - What is Bluetooth? Bluetooth is the name given to a technology standard using short-range radio links, intended to replace the cable(s) connecting portable and/or fixed electronic devices. The standard defines a uniform structure for a wide range of devices to communicate with each other, with minimal user effort. Its key features are robustness, low complexity, low power and low cost, which make it especially suited to mobile handheld devices. The technology also offers wireless access to LANs, PSTN, the mobile phone network and the Internet for a host of home appliances and portable handheld interfaces. The standard has achieved global acceptance such that any Bluetooth device, anywhere in the world, can connect to other Bluetooth devices in its proximity, regardless of brand. Bluetooth enabled electronic devices connect and communicate wirelessly via short-range, ad hoc networks called piconets. Each unit can simultaneously communicate with up to seven other units per piconet. Moreover, each unit can simultaneously belong to several piconets. These piconets are established dynamically and automatically as Bluetooth devices enter and leave the radio proximity. Motivation for Bluetooth The motivations for Bluetooth come from both technology push and market pull. The ability to pack ever more transistors on a small area of silicon has made small-embedded devices capable of running complex protocols. Various techniques are available to connect these embedded devices to the Internet, thus forming the so-called "embedded Internet". Significant progress has been made in developing small and cheap sensors that can pick up useful signals from the user environment without user interaction or explicit command. This has opened up the possibility for creating a "ubiquitous computing" environment. In this environment, the devices are controlled and activated by a combination of intelligent systems and strategically located sensors that work without explicit user support. The facility to automate depends heavily on the ability of devices to communicate wirelessly with each other, with more intelligent central servers, information repositories, sensors and actuators. Bluetooth can provide a solution to this requirement. The available technology-IrDA OBEX is based in infrared links that are limited to line of sight connections. Bluetooth is further fuelled by the demand for mobile and wireless access to LANs, Internet over mobile and other existing networks, where the backbone is wired but the interface is free to move. Now days there is also the commercial need to provide "information push" capabilities, which is important for handhelds and other such mobile devices and this has been partially incorporated in Bluetooth. Bluetooth's main strength is its ability to simultaneously handle both data and voice transmissions, allowing such innovative solutions as a mobile hands-free headset for voice calls, print to fax capability, and automatically synchronizing PDA, laptop, and cell phone address book applications. The Basic Bluetooth System Architecture The system architecture for Bluetooth is briefly described here. The system design has been segmented into various almost independent layers for conceptual ease of description. These layers are described in detail in the core Bluetooth specifications. The design specifications also describe certain properties for certain common classes of applications to be implemented over Bluetooth to achieve uniformity across diverse manufacturers. These are described in profiles of the Bluetooth Specification. Overview of the Protocol Stack The basic protocol stack consists is shown in Fig .1. The figure shows that the protocol stack consists of a radio layer at the bottom that forms the physical connection interface. The base band and Link Manager Protocol (LMP) that reside over it are basically meant to establish and control links between bluetooth devices. These three bottom layers are typically implemented in hardware/firmware. The Host Controller layer is required to interface the Bluetooth hardware to the upper protocol-L2CAP (Logical Link Control and Adaptation Protocol). The host controller is required only when the L2CAP resides in software in the host. If the L2CAP is also on the Bluetooth module, this layer may not be required as then the L2CAP can directly communicate with the LMP and base band. Applications reside above L2CAP. The following subsections give a brief description of each layer. Radio layer This link operates in the unlicensed ISM band around 2.4GHz and uses spread spectrum communication. The band extends from 2400 to 2483.5 MHz in a vast majority of countries and this whole range is utilized for optimizing the spectrum spreading. For spread spectrum, the frequency hopping (FH) technique is used. As multiple uncoordinated networks may exist in this band and cause interference, fast FH and short data packets are used. This is because the error rate may be high, especially due to strong interference from microwave ovens that operate at this frequency. CVSD coding has been adopted for voice, which can withstand high bit error rates. Also the packet headers are protected by a highly redundant error correction scheme to make them robust to errors. Base band The base band is the layer that controls the radio. This layer provides the frequency hop sequences. Base band also takes care of lower level encryption for secure links. The packet handling over the wireless link is the responsibility of base band. Two types of links can be established: • SCO: Synchronous Connection Oriented. These links are meant for synchronous data typically voice. • ACL: Asynchronous Connection less. These links may be used for data transfer Applications , which do not require a synchronous link. The base band provides the functionalities required for devices to synchronize their clocks and establish connections. Link Manager Protocol The basic functions of LMP can be classified as: • Piconet management • Link configuration • Security functions A piconet is a group of devices connected to a common channel, which is identified with its unique hop sequence. One of the devices, usually the one which first initiated the connection is the master. Up to seven other devices can be actively connected to this master, and many more could be connected in a low power "parked" state. The devices on one piconet can communicate with each other over SCO or ACL links. The master, with the help of Link Managers on each device, manages the channel sharing. Devices can be part of many piconets at the same time (Fig 2). The LMP provides the functionality to attach/detach slaves, switch roles between a master and a slave and to establish ACL/SCO links. LMP also handles the low power modes-hold, sniff and park, designed to save power when the device does not have data to send. Link configuration tasks include setting link parameters, Quality of Service and power control if the device supports it. Authentication of devices to be linked and managing link keys is also taken care by LMP. Host Controller Interface The basic structure showing how the host controller layers are fitted into the protocol stack is shown in Fig.3. For many devices, the Bluetooth enabling module may be added as a separate card, for instance, on a PC or a laptop, the Bluetooth hardware may be added as a PCI card or a USB adapter. Hardware modules usually implement the lower layers-radio, baseband and LMP. Then the data to be sent to LMP and baseband travels over the physical bus like USB. A driver for this bus is required on the "host", that is the PC, and a "host controller interface" is required on the Bluetooth hardware card to accept data over the physical bus. Bluetooth Security: The Bluetooth system is intended to be used as a uniform interface to all of a person's information sources and will thus be expected to transfer sensitive personal data. Security of the data is thus understandably an important issue. Further, Bluetooth devices are expected to be omnipresent and at some places the access to these devices by public users may have to be restricted. This calls for authentication procedures to be provided. As the channel used is wireless and the packets being transmitted are available to all members of a piconet, the security initialization communications should not send any information that can allow an unauthorized device to know the secret authentication keys.The basic structure. The procedures for security use four values: the device address (which is public), a privateauthentication key (128 bits), private encryption key (8-128 bits, configurable) and a random number. As the keys have to be secret, they cannot be obtained by inquiry. The security procedure requires a secret PIN to be known to the user (or stored by his application) for accessing a particular device. The main steps in the procedure are:An initialization key is generated using the PIN, the length of the PIN, a random number and the device address. The dependence on the device address makes it more difficult for a fraudulent device to try a large number of PIN’s, as each has now to be tried with different device addresses. The claimant may also carry out verification on the verifier using a similar procedure as above. Each Bluetooth unit has a unit key, installed in its non-volatile memory. The device now uses the initialization key to encrypt this unit key and sends it to the other device that decrypts it using the initialization key exchanged earlier. The second device may add its own unit key to the unit key of the first device and generate a combination link key if both the devices are capable of handling this. Otherwise the unit key of one of the devices is treated as the link key. The link key is communicated to the first device. The initialization key is discarded. An encryption key is now generated from the link key, a random number and another number obtained from a fixed procedure. Both the devices can generate this encryption key as all the required information is known to both devices. This key with some modification as described later, is used to encrypt data payloads. The link key is remembered. If another link is to be established between the two devices at a later time, this link key can be directly used. This eliminates the need to send keys over the channel again. Thus, data can be transmitted securely with minimum user interaction. Establishing a connection in Bluetooth: This section describes the basic procedures to be followed by two or more Bluetooth devices to start a connection between them. For example, a person walks in to a hotel lobby and wants to access her email over her Bluetooth enabled device, which could be a laptop ora Personal Digital Assistant. What would she have to do? Depending on implementation, she would be clicking on a menu or an email application icon. The device would automatically carry out the following steps, (except perhaps for the authentication step if the device has come to the environment for the first time): Inquiry: The device on reaching a new environment would automatically initiate an inquiry to find out what access points are within its range. (If not, it'll do so when the email application asks for a link.) This will result in the following events: - All nearby access points respond with their addresses. - The device picks one out the responding devices. Paging: The device will invoke a baseband procedure called paging. This results in synchronization of the device with the access point, in terms of its clock offset and phase in the frequency hop, among other required initializations. Link establishment: The LMP will now establish a link with the access point. As the application in this case is email, an ACL link will be used. Various setup steps will be carried out as described below. Service Discovery: The LMP will use the SDP (Service Discovery Protocol) to discover what services are available from the access point, in particular whether email access or access to the relevant host is possible from this access point or not. Security: If the access point restricts its access to a particular set of users or otherwise offers secure mode communications to people having some prior registration with it, then at this stage, the access point will send a security request for "pairing". This will be successful if the user knows the correct PIN code to access the service. Competing Technologies: Besides Bluetooth many other technologies exist that provide similar or related services. A quick glance comparison between these technologies is presented below. Peak Data Rate Range Relative Cost Voice network support Data network support IEEE 802.11 2 Mbps 50m Medium Via IP TCP / IP IrDA 16 Mbps < 2m Low Via IP Via PPP Bluetooth 1 Mbps < 10m Medium Via IP and cellular Via PPP HomeRF 1.6 Mbps 50m Medium Via IP and PSTN TCP / IP Coexistence Of Bluetooth with Other Technologies. Some issues to be considered in the design of the higher layers were that the Bluetooth module should be easily integratable into any existing device that may benefit from being connected. Further, for rapid acceptance into the market, it should be possible for existing applications developed over conventional protocols to be easily portable to the Bluetooth platform. In addition, other wireless initiatives like IrDa OBEX, WAP and HomeRF should also be able to interoperate with this standard. Keeping this in view, interface points where existing protocols may be used over the Bluetooth platform have been provided. Applications of Bluetooth • By installing a Bluetooth network, you can do away with the complex and tedious task of networking between the computing devices; yet have the power of connected devices. • Each Bluetooth device could be connected to 200 other devices making the connection of every device with every other possible. Since it supports both point to point and point to multipoint it will virtually make the maximum number of simultaneously linked devices unlimited. • Bluetooth technology increases the freedom of connecting the peripherals wirelessly. • Bluetooth technology promotes portability of devices. • Bluetooth technology supports automatic messaging. • Devices like Watch pad and Cyber phone can be connected with other devices through bluetooth. The future for Bluetooth Bluetooth has a good future ahead because it meets a basic need of connectivity in close proximity, is the result of initiatives of nine leading communications and computer industry vendors including companies like 3-COM, Ericsson, Lucent, IBM, Intel, Microsoft, Nokia, Toshiba etc. According to one market research report, Bluetooth technology is expected to be built into over 100 millions devices before the end of 2002. As a result of success of WAP (Wireless Application Protocol), adoption of smart phones and handheld devices, Bluetooth will have tremendous effects on everyday life. Bluetooth is one of the key technologies that can make the mobile information society possible. The seamless connectivity promised by Bluetooth makes it possible to explore a range of interactive and highly transparent personalized services which were even difficult to dream of because of the complexity involved in making various devices talk to each other. Already many Bluetooth pilot products have rolled into the market backed by big vendors, which indicates the acceptance of the technology. Over the long term manufacturers will also benefit from the ability to replace multiple connection ports with a single Bluetooth module, gaining economies at the production level. APPLICATIONS OF MOBILE COMPUTING In many fields of work, the ability to keep on the move is vital in order to utilise time efficiently. The importance of Mobile Computers has been highlighted in many fields of which a few are described below: Emergency Services :Ability to recieve information on the move is vital where the emergency services are involved. Information regarding the address, type and other details of an incident can be dispatched quickly, via a CDPD system using mobile computers, to one or several appropriate mobile units which are in the vicinity of the incident. In courts :Defense counsels can take mobile computers in court. When the opposing counsel references a case which they are not familiar, they can use the computer to get direct, real-time access to on-line legal database services, where they can gather information on the case and related precedents. Therefore mobile computers allow immediate access to a wealth of information, making people better informed and prepared. In companies :Managers can use mobile computers in, say, critical presentations to major customers. They can access the latest market share information. At a small recess, they can revise the presentation to take advantage of this information. They can communicate with the office about possible new offers and call meetings for discussing responds to the new proposals. Therefore, mobile computers can leverage competitive advantages. Stock Information Collation/Control :In environments where access to stock is very limited ie: factory warehouses. The use of small portable electronic databases accessed via a mobile computer would be ideal. Data collated could be directly written to a central database, via a CDPD network, which holds all stock information hence the need for transfer of data to the central computer at a later date is not necessary. This ensures that from the time that a stock count is completed, there is no inconsistency between the data input on the portable computers and the central database. Credit Card Verification :At Point of Sale (POS) terminals in shops and supermarkets, when customers use credit cards for transactions, the intercommunication required between the bank central computer and the POS terminal, in order to effect verification of the card usage, can take place quickly and securely over cellular channels using a mobile computer unit. This can speed up the transaction process and relieve congestion at the POS terminals. Electronic Mail/Paging :Usage of a mobile unit to send and read emails is a very useful asset for any business individual, as it allows him/her to keep in touch with any colleagues as well as any urgent developments that may affect their work. Access to the Internet, using mobile computing technology, allows the individual to have vast arrays of knowledge at his/her fingertips. Paging is also achievable here, giving even more intercommunication capability between individuals, using a single mobile computer device. THE FUTURE With the rapid technological advancements in Artificial Intelligence, Integrated Circuitry and increases in Computer Processor speeds, the future of mobile computing looks increasingly exciting. Use of Artificial Intelligence may allow mobile units to be the ultimate in personal secretaries, which can receive emails and paging messages, understand what they are about, and change the individuals personal schedule according to the message. This mobility aspect may be carried further in that, even in social spheres, people will interact via mobile stations, eliminating the need to venture outside of the house. Indeed, technologies such as Interactive television and Video Image Compression already imply a certain degree of mobility in the home, ie. home shopping etc. Using the mobile data communication technologies discussed, this mobility may be pushed to extreme. The future of Mobile Computing is very promising indeed, although technology may go too far, causing detriment to society
for mobile devices must consider resource limitation, battery power and display size. Consequently, new hardware and software techniques must be developed. For example, applications need to be highly optimized for space, in order to fit in the limited memory on the mobile devices. For Internet enabled devices, the good old TCP/IP stack cannot be used; it takes too much space and is not optimized for minimal power consumption. Given the plethora of cellular technologies that have emerged in such a market, it becomes extremely difficult to provide support for inter-device communication. A new hardware technology solution, Bluetooth, has been proposed to overcome this barrier. Any device with a Bluetooth chip will be able to communicate seamlessly with any other device having a similar chip irrespective of the communication technologies they might be using. For the sake of explanation, an analogy can be drawn between the Java Virtual Machine and Blue tooth. In this article we give an overview of data communication networks and describe in detail the Bluetooth technology that was developed to provide wireless interconnect between small mobile devices and their peripherals. Finally, we look at the applications of Mobile Computing in the real world. INTRODUCTION Mobile Computing: A technology that allows transmission of data, via a computer, without having to be connected to a fixed physical link. Mobile voice communication is widely established throughout the world and has had a very rapid increase in the number of subscribers to the various cellular networks over the last few years. An extension of this technology is the ability to send and receive data across these cellular networks. This is the principle of mobile computing. Mobile data communication has become a very important and rapidly evolving technology as it allows users to transmit data from remote locations to other remote or fixed locations. This proves to be the solution to the biggest problem of business people on the movemobility. DATA COMMUNICATIONS Data Communications is the exchange of data using existing communication networks. The term data covers a wide range of applications including File Transfer (FT), interconnection between WAN, fax , electronic mail, access to the internet and the World Wide Web . Data Communications have been achieved using a variety of networks such as PSTN, leasedlines and more recently ISDN (Integrated Services Data Network) and ATM (Asynchronous Transfer Mode). These networks are partly or totally analogue or digital using technologies such as circuit - switching, packet - switching etc. Mobile communications overview Circuit switching implies that data from one user (sender) to another (receiver) has to follow a pre-specified path. If a link to be used is busy, the message can’t be redirected, a property which causes many delays. Packet switching is an attempt to make better utilization of the existing network by splitting the message to be sent into packets. Each packet contains information about the sender, the receiver, the position of the packet in the message as well as part of the actual message. There are many protocols defining the way packets can be send from the sender to the receiver. The most widely used are the Virtual Circuit-Switching system, which implies that packets have to be sent through the same path, and the Datagram system which allows packets to be sent at various paths depending on the network availability. The introduction of mobility in data communications required a move from the Public Switched Data Network (PSDN) to other networks like the ones used by mobile phones. PCSI has come up with an idea called CDPD (Cellular Digital Packet Data) technology which uses the existing mobile network (frequencies used for mobile telephony). Mobility implemented in data communications has a significant difference compared to voice communications. Mobile phones allow the user to move around and talk at the same time; the loss of the connection for 400ms during the hand over is undetectable by the user. When it comes to data, 400ms is not only detectable but causes huge distortion to the message. Therefore data can be transmitted from a mobile station under the assumption that it remains stable or within the same cell. Introduction - What is Bluetooth? Bluetooth is the name given to a technology standard using short-range radio links, intended to replace the cable(s) connecting portable and/or fixed electronic devices. The standard defines a uniform structure for a wide range of devices to communicate with each other, with minimal user effort. Its key features are robustness, low complexity, low power and low cost, which make it especially suited to mobile handheld devices. The technology also offers wireless access to LANs, PSTN, the mobile phone network and the Internet for a host of home appliances and portable handheld interfaces. The standard has achieved global acceptance such that any Bluetooth device, anywhere in the world, can connect to other Bluetooth devices in its proximity, regardless of brand. Bluetooth enabled electronic devices connect and communicate wirelessly via short-range, ad hoc networks called piconets. Each unit can simultaneously communicate with up to seven other units per piconet. Moreover, each unit can simultaneously belong to several piconets. These piconets are established dynamically and automatically as Bluetooth devices enter and leave the radio proximity. Motivation for Bluetooth The motivations for Bluetooth come from both technology push and market pull. The ability to pack ever more transistors on a small area of silicon has made small-embedded devices capable of running complex protocols. Various techniques are available to connect these embedded devices to the Internet, thus forming the so-called "embedded Internet". Significant progress has been made in developing small and cheap sensors that can pick up useful signals from the user environment without user interaction or explicit command. This has opened up the possibility for creating a "ubiquitous computing" environment. In this environment, the devices are controlled and activated by a combination of intelligent systems and strategically located sensors that work without explicit user support. The facility to automate depends heavily on the ability of devices to communicate wirelessly with each other, with more intelligent central servers, information repositories, sensors and actuators. Bluetooth can provide a solution to this requirement. The available technology-IrDA OBEX is based in infrared links that are limited to line of sight connections. Bluetooth is further fuelled by the demand for mobile and wireless access to LANs, Internet over mobile and other existing networks, where the backbone is wired but the interface is free to move. Now days there is also the commercial need to provide "information push" capabilities, which is important for handhelds and other such mobile devices and this has been partially incorporated in Bluetooth. Bluetooth's main strength is its ability to simultaneously handle both data and voice transmissions, allowing such innovative solutions as a mobile hands-free headset for voice calls, print to fax capability, and automatically synchronizing PDA, laptop, and cell phone address book applications. The Basic Bluetooth System Architecture The system architecture for Bluetooth is briefly described here. The system design has been segmented into various almost independent layers for conceptual ease of description. These layers are described in detail in the core Bluetooth specifications. The design specifications also describe certain properties for certain common classes of applications to be implemented over Bluetooth to achieve uniformity across diverse manufacturers. These are described in profiles of the Bluetooth Specification. Overview of the Protocol Stack The basic protocol stack consists is shown in Fig .1. The figure shows that the protocol stack consists of a radio layer at the bottom that forms the physical connection interface. The base band and Link Manager Protocol (LMP) that reside over it are basically meant to establish and control links between bluetooth devices. These three bottom layers are typically implemented in hardware/firmware. The Host Controller layer is required to interface the Bluetooth hardware to the upper protocol-L2CAP (Logical Link Control and Adaptation Protocol). The host controller is required only when the L2CAP resides in software in the host. If the L2CAP is also on the Bluetooth module, this layer may not be required as then the L2CAP can directly communicate with the LMP and base band. Applications reside above L2CAP. The following subsections give a brief description of each layer. Radio layer This link operates in the unlicensed ISM band around 2.4GHz and uses spread spectrum communication. The band extends from 2400 to 2483.5 MHz in a vast majority of countries and this whole range is utilized for optimizing the spectrum spreading. For spread spectrum, the frequency hopping (FH) technique is used. As multiple uncoordinated networks may exist in this band and cause interference, fast FH and short data packets are used. This is because the error rate may be high, especially due to strong interference from microwave ovens that operate at this frequency. CVSD coding has been adopted for voice, which can withstand high bit error rates. Also the packet headers are protected by a highly redundant error correction scheme to make them robust to errors. Base band The base band is the layer that controls the radio. This layer provides the frequency hop sequences. Base band also takes care of lower level encryption for secure links. The packet handling over the wireless link is the responsibility of base band. Two types of links can be established: • SCO: Synchronous Connection Oriented. These links are meant for synchronous data typically voice. • ACL: Asynchronous Connection less. These links may be used for data transfer Applications , which do not require a synchronous link. The base band provides the functionalities required for devices to synchronize their clocks and establish connections. Link Manager Protocol The basic functions of LMP can be classified as: • Piconet management • Link configuration • Security functions A piconet is a group of devices connected to a common channel, which is identified with its unique hop sequence. One of the devices, usually the one which first initiated the connection is the master. Up to seven other devices can be actively connected to this master, and many more could be connected in a low power "parked" state. The devices on one piconet can communicate with each other over SCO or ACL links. The master, with the help of Link Managers on each device, manages the channel sharing. Devices can be part of many piconets at the same time (Fig 2). The LMP provides the functionality to attach/detach slaves, switch roles between a master and a slave and to establish ACL/SCO links. LMP also handles the low power modes-hold, sniff and park, designed to save power when the device does not have data to send. Link configuration tasks include setting link parameters, Quality of Service and power control if the device supports it. Authentication of devices to be linked and managing link keys is also taken care by LMP. Host Controller Interface The basic structure showing how the host controller layers are fitted into the protocol stack is shown in Fig.3. For many devices, the Bluetooth enabling module may be added as a separate card, for instance, on a PC or a laptop, the Bluetooth hardware may be added as a PCI card or a USB adapter. Hardware modules usually implement the lower layers-radio, baseband and LMP. Then the data to be sent to LMP and baseband travels over the physical bus like USB. A driver for this bus is required on the "host", that is the PC, and a "host controller interface" is required on the Bluetooth hardware card to accept data over the physical bus. Bluetooth Security: The Bluetooth system is intended to be used as a uniform interface to all of a person's information sources and will thus be expected to transfer sensitive personal data. Security of the data is thus understandably an important issue. Further, Bluetooth devices are expected to be omnipresent and at some places the access to these devices by public users may have to be restricted. This calls for authentication procedures to be provided. As the channel used is wireless and the packets being transmitted are available to all members of a piconet, the security initialization communications should not send any information that can allow an unauthorized device to know the secret authentication keys.The basic structure. The procedures for security use four values: the device address (which is public), a privateauthentication key (128 bits), private encryption key (8-128 bits, configurable) and a random number. As the keys have to be secret, they cannot be obtained by inquiry. The security procedure requires a secret PIN to be known to the user (or stored by his application) for accessing a particular device. The main steps in the procedure are:An initialization key is generated using the PIN, the length of the PIN, a random number and the device address. The dependence on the device address makes it more difficult for a fraudulent device to try a large number of PIN’s, as each has now to be tried with different device addresses. The claimant may also carry out verification on the verifier using a similar procedure as above. Each Bluetooth unit has a unit key, installed in its non-volatile memory. The device now uses the initialization key to encrypt this unit key and sends it to the other device that decrypts it using the initialization key exchanged earlier. The second device may add its own unit key to the unit key of the first device and generate a combination link key if both the devices are capable of handling this. Otherwise the unit key of one of the devices is treated as the link key. The link key is communicated to the first device. The initialization key is discarded. An encryption key is now generated from the link key, a random number and another number obtained from a fixed procedure. Both the devices can generate this encryption key as all the required information is known to both devices. This key with some modification as described later, is used to encrypt data payloads. The link key is remembered. If another link is to be established between the two devices at a later time, this link key can be directly used. This eliminates the need to send keys over the channel again. Thus, data can be transmitted securely with minimum user interaction. Establishing a connection in Bluetooth: This section describes the basic procedures to be followed by two or more Bluetooth devices to start a connection between them. For example, a person walks in to a hotel lobby and wants to access her email over her Bluetooth enabled device, which could be a laptop ora Personal Digital Assistant. What would she have to do? Depending on implementation, she would be clicking on a menu or an email application icon. The device would automatically carry out the following steps, (except perhaps for the authentication step if the device has come to the environment for the first time): Inquiry: The device on reaching a new environment would automatically initiate an inquiry to find out what access points are within its range. (If not, it'll do so when the email application asks for a link.) This will result in the following events: - All nearby access points respond with their addresses. - The device picks one out the responding devices. Paging: The device will invoke a baseband procedure called paging. This results in synchronization of the device with the access point, in terms of its clock offset and phase in the frequency hop, among other required initializations. Link establishment: The LMP will now establish a link with the access point. As the application in this case is email, an ACL link will be used. Various setup steps will be carried out as described below. Service Discovery: The LMP will use the SDP (Service Discovery Protocol) to discover what services are available from the access point, in particular whether email access or access to the relevant host is possible from this access point or not. Security: If the access point restricts its access to a particular set of users or otherwise offers secure mode communications to people having some prior registration with it, then at this stage, the access point will send a security request for "pairing". This will be successful if the user knows the correct PIN code to access the service. Competing Technologies: Besides Bluetooth many other technologies exist that provide similar or related services. A quick glance comparison between these technologies is presented below. Peak Data Rate Range Relative Cost Voice network support Data network support IEEE 802.11 2 Mbps 50m Medium Via IP TCP / IP IrDA 16 Mbps < 2m Low Via IP Via PPP Bluetooth 1 Mbps < 10m Medium Via IP and cellular Via PPP HomeRF 1.6 Mbps 50m Medium Via IP and PSTN TCP / IP Coexistence Of Bluetooth with Other Technologies. Some issues to be considered in the design of the higher layers were that the Bluetooth module should be easily integratable into any existing device that may benefit from being connected. Further, for rapid acceptance into the market, it should be possible for existing applications developed over conventional protocols to be easily portable to the Bluetooth platform. In addition, other wireless initiatives like IrDa OBEX, WAP and HomeRF should also be able to interoperate with this standard. Keeping this in view, interface points where existing protocols may be used over the Bluetooth platform have been provided. Applications of Bluetooth • By installing a Bluetooth network, you can do away with the complex and tedious task of networking between the computing devices; yet have the power of connected devices. • Each Bluetooth device could be connected to 200 other devices making the connection of every device with every other possible. Since it supports both point to point and point to multipoint it will virtually make the maximum number of simultaneously linked devices unlimited. • Bluetooth technology increases the freedom of connecting the peripherals wirelessly. • Bluetooth technology promotes portability of devices. • Bluetooth technology supports automatic messaging. • Devices like Watch pad and Cyber phone can be connected with other devices through bluetooth. The future for Bluetooth Bluetooth has a good future ahead because it meets a basic need of connectivity in close proximity, is the result of initiatives of nine leading communications and computer industry vendors including companies like 3-COM, Ericsson, Lucent, IBM, Intel, Microsoft, Nokia, Toshiba etc. According to one market research report, Bluetooth technology is expected to be built into over 100 millions devices before the end of 2002. As a result of success of WAP (Wireless Application Protocol), adoption of smart phones and handheld devices, Bluetooth will have tremendous effects on everyday life. Bluetooth is one of the key technologies that can make the mobile information society possible. The seamless connectivity promised by Bluetooth makes it possible to explore a range of interactive and highly transparent personalized services which were even difficult to dream of because of the complexity involved in making various devices talk to each other. Already many Bluetooth pilot products have rolled into the market backed by big vendors, which indicates the acceptance of the technology. Over the long term manufacturers will also benefit from the ability to replace multiple connection ports with a single Bluetooth module, gaining economies at the production level. APPLICATIONS OF MOBILE COMPUTING In many fields of work, the ability to keep on the move is vital in order to utilise time efficiently. The importance of Mobile Computers has been highlighted in many fields of which a few are described below: Emergency Services :Ability to recieve information on the move is vital where the emergency services are involved. Information regarding the address, type and other details of an incident can be dispatched quickly, via a CDPD system using mobile computers, to one or several appropriate mobile units which are in the vicinity of the incident. In courts :Defense counsels can take mobile computers in court. When the opposing counsel references a case which they are not familiar, they can use the computer to get direct, real-time access to on-line legal database services, where they can gather information on the case and related precedents. Therefore mobile computers allow immediate access to a wealth of information, making people better informed and prepared. In companies :Managers can use mobile computers in, say, critical presentations to major customers. They can access the latest market share information. At a small recess, they can revise the presentation to take advantage of this information. They can communicate with the office about possible new offers and call meetings for discussing responds to the new proposals. Therefore, mobile computers can leverage competitive advantages. Stock Information Collation/Control :In environments where access to stock is very limited ie: factory warehouses. The use of small portable electronic databases accessed via a mobile computer would be ideal. Data collated could be directly written to a central database, via a CDPD network, which holds all stock information hence the need for transfer of data to the central computer at a later date is not necessary. This ensures that from the time that a stock count is completed, there is no inconsistency between the data input on the portable computers and the central database. Credit Card Verification :At Point of Sale (POS) terminals in shops and supermarkets, when customers use credit cards for transactions, the intercommunication required between the bank central computer and the POS terminal, in order to effect verification of the card usage, can take place quickly and securely over cellular channels using a mobile computer unit. This can speed up the transaction process and relieve congestion at the POS terminals. Electronic Mail/Paging :Usage of a mobile unit to send and read emails is a very useful asset for any business individual, as it allows him/her to keep in touch with any colleagues as well as any urgent developments that may affect their work. Access to the Internet, using mobile computing technology, allows the individual to have vast arrays of knowledge at his/her fingertips. Paging is also achievable here, giving even more intercommunication capability between individuals, using a single mobile computer device. THE FUTURE With the rapid technological advancements in Artificial Intelligence, Integrated Circuitry and increases in Computer Processor speeds, the future of mobile computing looks increasingly exciting. Use of Artificial Intelligence may allow mobile units to be the ultimate in personal secretaries, which can receive emails and paging messages, understand what they are about, and change the individuals personal schedule according to the message. This mobility aspect may be carried further in that, even in social spheres, people will interact via mobile stations, eliminating the need to venture outside of the house. Indeed, technologies such as Interactive television and Video Image Compression already imply a certain degree of mobility in the home, ie. home shopping etc. Using the mobile data communication technologies discussed, this mobility may be pushed to extreme. The future of Mobile Computing is very promising indeed, although technology may go too far, causing detriment to society
No comments:
Post a Comment