15-02-2011, 11:11 AM
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INTRODUCTION
Mobile computing means different things to different people.
Ubiquitous, wireless and remote computing .
Wireless and mobile computing are not synonymous. Wireless is
A transmission or information transport method that enables mobile computing.
MOBILE COMPUTING FRAMEWORK:
Mobile computing is expanding in four dimensions
(a)Wireless delivery technology and switching methods:
• Radio- based systems
• Cellular communications
• Wireless packet data networks
• Satellite networks
Infrared or light based mobile computing
(b)Mobile information access device:
• Portable Computers
• PDA
• Palmtops
© Mobile data internetworking standards and equipments:
• CDMA
• IrDA
(d) Mobile computing based business application:
Dreams behind mobile computing:
Location based services:
• Elements of location based services:
Geocoding:
This is a task of processing textual address to add a positional co-ordinate to each address. These co-ordinate are then indexed to enable the address to be searched geographically in ways such as “find me my nearest”.
• Latitude: the first component of a spherical cell based system used to record positions on the earth‘s surface. Latitude which gives the location of a place north or south of the equator, is expressed by angular measurement ranging from 0 at the equater to 90 at the pole.
• Longitude: latitude, the location of a place east or west of a north south line called the prime meridian, is measured in angles ranging from 0 at the prime meridian to 180 at the international date line . the international date line passes through Landon ’s Greenwich observatory, uk.
Map content :
Proximity searching: this is very important element of LBS.
Routing and driving directions: it is a interaction between the users location and a planned destination. Routes can be calculated and displayed on the map and driving directions can be provided according to shortest distance or the fastest route.
Rendering: this is a production of maps for display onto the screen of the device. Rendering images are typically personalized according to the specific LBS request.
GPS in LBS world
The global positioning system is a network is a network of 24 Navstar satellites orbiting earth at 11000 miles. Dod has established it at the cost of about US $ 13 billion, access to GPS to all users including those in other countries. GPS provides specially coded satellite signals that can be processed by GPS receiver. Basically GPS works by using four GPS satellite signals to compute positions in three dimensions In the receiver clock.
Operation control system has the responsibility for maintaining the satellite and its proper positions.
How GPS finds where you are:
Complex error correction used by satellite to determine the accurate speeds.
Here are some techniques to make improvements in LBS system.
• Time of arrival: here the differences in the time of arrival of the signal from the mobile to more than one base station are used to calculate the location of the device.
• Angle of arrival: AOA is a system that calculates the angle at which a signal arrives at two base stations from the handset, using triangulation to find location.
UBIQUITOUS COMPUTING
Firstly introduction of pervasive computing is necessary
Pervasive computing: this implies that computer has the capability to obtain information from the environment in what it is embedded and utilized to dynamically build model of computing.
Input interface of pervasive computing utilizes “Multimodal “interface and that means developing systems that can recognize voice and gestures.
WHAT IS UBIQUITOUS TECHNOLOGY?
Ubiquitous computing is intangible-physically, figuratively, literally, living and working environments embedded with computing devices in a seamless, invisible way.
True ubiquitous computing involves devices embedded transparently in our physical and social movements, integrating both mobile and pervasive computing.
Ubiquitous computing represents a situation in which computers will be embedded in our natural movements and interactions with our environments both physical and social. UC will help to organize and mediate social interactions wherever and whenever these situations might occur.
UC TECHNOLOGIES
UC represents amalgamation of quite a number of existing and future technologies like “mobile computing, pervasive computing, wearable computing, embedded computing location, context-aware computing technologies” fulfill the dreams of bringing UC into reality.
Software Infrastructure and Design Challenges for UC Applications
Ubiquitous computing applications will be embedded in the user’s physical environments and integrate seamlessly with their everyday tasks.
• Task dynamism- UC applications, by virtue by virtue of being available everywhere at all times, will have to adapt to the dynamism of user’s environment and the resulting uncertainties .in these environments; user may serendipitously change their goals or adapt their actions to a changing environment.
• Device Heterogeneity and Resource Constraints – the omnipresence of UC applications is typically achieved by either making the technological artifacts (devices) move with the user or having the applications move between devices tracking the user. In both cases, applications have to adapt to changing technological capabilities in their environment.
• Computing in a Social environment – another major characteristic of UC technology is that it has a significant impact on the social environments in which it is used. An introduction of a UC environment implies the introduction of sensors, which irrevocably have an impact on social structure.
Research Challenges:
• Semantic modeling – A fundamental necessity for an adaptable and composable computing environment is the ability to describe the preferences of users and the relevant characteristics of computing components using a high level semantic model.
Ontology can be used to describe user’s task environment ,as well as their goals ,toanable reasoning about a user’s needs and therefore dynamically adapt to changes .the research challenges in semantic modeling include developing a modeling language to express the rich and complex nature of ontologies, developing and validating for various domains of user activity.
• Building the Software Infrastructure – An effective software infrastructure for running UC applications must be capable of finding ,adapting and delivering the appropriate applications to the user’s context.
• Developing and Configuring Applications – Currently services are being described using a standard description language and in the future, using standard ontologies.such semantic descriptions could enable automatic composition of services, which in turn enables an infrastructure that dynamically adapts to tasks.
• Validating the user experience – the development of effective methods for testing and evaluating the usage scenarios enabled by pervasive applications is an important area that needs more attention from researchers.
Design of user interfaces for UC
the mobile access is the gateway technology required to make information available at any place and at any time. In addition the computing system should be aware of user’s context not only to be able to respond in an appropriate manner with respect to the user’s cognitive and social state but also to anticipate needs of the users.
Speech recognition, position sensing and eye tracking should be common inputs and in the future, stereographic audio and visual output will be coupled with 3D virtual reality information. in addition heads-up projection displays should allow superposition of information onto the user’s environment.
UC technologies benefits
The most profound technologies are those that disappear and weave themselves into the fabric of everyday life until they are indistinguishable from it. It will have profound effect on the way people access and use services that only make sense by virtue of being embedded in the environment.
Infrared Data Association
LAN Access Extensions for Link
Management Protocol
IrLAN
Introduction
The creation of the IrDA protocols and their broad industry support has led to IrDA-compliant infrared ports becoming common on laptop computers. With the IrDA approval of the higher media speeds of 1.15 and 4 megabits per second (Mbps), the infrared page link is becoming fast enough to support a network interface. This document describes a protocol, conforming to the IrDA specifications, that has these features:
•Enables a computer with an IrDA adapter to attach to a local area network (LAN) through an access point device that acts as the network adapter for the computer.
•Enables two computers with IrDA adapters to communicate as though they were attached through a LAN.
•Enables a computer with an IrDA-compliant adapter to be attached to a LAN through a second computer that is already attached to the LAN (the second computer must also have an IrDA-compliant adapter ).
The proposed protocol, the infrared LAN (IrLAN) protocol, should allow for interoperability of all devices supporting the protocol.
Design Goals
The IrLAN protocol has these design goals:
•The IrLAN protocol deals with the issues associated with running legacy networking protocols over an infrared link. It supports three different operating modes that represent the possible configurations between infrared devices and between infrared devices and an attached network.
•From a client operating-system perspective, the IrLAN protocol must be implemented completely as a set of network media-level drivers. No modification of the existing network protocols should be necessary.
•The IrLAN protocol must not impose excessive processing constraints on access point devices, which may be implemented with slower processors than typically found in modern computers.
Definition of Terms
The following technical terms are used in this document.
Control channel
An IrLMP communication channel used by the client and offered by the provider to allow for the setup and configuration of a data channel .
Data channel
An IrLMP communication channel used by the client and provider to exchange LAN-formatted packets .
Frame (or media frame)
A block of data on the media. A packet may consist of multiple media frames.
IAS (information access service)
Part of the IrDA protocol suite, the IAS is a standard IrLMP client that implements a local store of configuration information. Information is stored under a primary key called the class and under subkeys in each class called attributes. The class may only contain subkeys, each of which is unique in the class, and each subkey may contain a corresponding value, which may be a string or an integer. Multiple objects of the same class are allowed, and each object in the IAS may be read by a remote station
supporting the IAS protocol.
IrLAN client (or client)
The station in an IrLAN page link that is using the IrLAN services of a provider to set up an IrLAN link. The client is the active component in the IrLAN protocol; it issues requests to the IrLAN provider to establish a data page link and to configure the link.
IrLAP (Infrared Link Access Protocol)
A protocol, based on the HDLC protocol, designed to control an infrared link. IrLAP provides for discovery of devices, their connection over an infrared link, and reliable data delivery between devices.
IrLMP (Infrared Link Management Protocol)
A multiplexing protocol designed to run on top of IrLAP. IrLMP is multipoint-capable even though IrLAP is not. When IrLAP becomes multipoint-capable, multiple machines will be able to communicate concurrently over an infrared link.
Infrared LAN access point device
A network adapter with an infrared page link to the LAN client . Conceptually, the infrared page link is the bus that the LAN card resides on.
LAN
A local area network.
LSAP (logical service access point)
A unique 1-byte identifier used by IrLMP to multiplex and demultiplex packets sent using IrLAP. Clients of IrLMP logically open an LSAP and then attach it to a remote node, or receive attachment from a remote node. Clients typically advertise their LSAP to other clients by writing entries in the local IAS.
NIC (network interface controller)
A piece of hardware designed to transmit and receive packets on a LAN network.
Packet
A block of data that is transmitted or received over the media . The media may break a packet down into several media frames to deliver it.
Primary station
A term used in IrLAP to specify the station that is controlling the infrared link. The other side of the page link is where the secondary station resides (or secondary stations reside). No secondary station can transmit without receiving permission from the primary station.
IrLAN Provider (provider)
The station in an IrLAN page link that is providing the IrLAN protocol interface.
Secondary station
A term used in IrLAP to specify a station that is controlled by the primary station. The secondary station can send when it receives permission from the primary station.
TinyTP
A lightweight protocol, supporting flow control and segmentation and reassembly, that is designed for use over an IrLMP connection.
Window size
One of the parameters negotiated between the two infrared nodes as part of establishing an IrLAP connection. The window size specifies the number of consecutive IrLAP frames that a node can transmit before it must allow the other node an opportunity to transmit. The maximum IrLAP window size is seven frames.
Overview
The IrLAN protocol is a “sided” protocol that defines a two-channel interface between a protocol client and a protocol server. An IrLAN provider is passive. It is up to the IrLAN client to discover and then attach to the provider and open up a data channel over which LAN packets can be transmitted and received. In IrLAN peer-to-peer mode (which is also described in “Access Methods”), each station has both an IrLan client and provider. There is a race to determine which node will open the Data channel. This race condition is resolved by the protocol in State Machines described later in this document.
The client begins setting up the connection by reading an object’s information in the provider’s IAS. The object specifies an IrLMP LSAP for the “control channel.” The client connects to the control channel and uses the control channel to negotiate thecharacteristics of a data channel. Once the data channel has been negotiated, it is opened and then configured. All configuration is handled through the control channel. The data channel is used solely for the transmission and reception of packets formatted for the LAN. The IrLAN protocol defines a graceful close, but it is seldom used because it would require user intervention to initiate a disconnect. Typically, the connection will close down “ungracefully” through an IrLAP connection timeout. Both the control and data channels use the TinyTP protocol for segmentation and reassembly of packets
and for flow control.
Access Methods
The IrLAN protocol is intended to support these modes of operation:
•Access point
•Peer-to-peer
•Hosted
Access Point Mode
An access point device is hardware supporting both a LAN network interface controller (NIC) and an infrared transceiver. For communication over the infrared link, the access point device runs a protocol stack that conforms to the IrDA standards and runs the IrLAN protocol over the IrDA stack. The access point device implements a network adapter for the client using infrared as the bus for accessing the adapter.
The following illustration shows the access point mode of operation.
Filtering information is passed from the client to the access point device to minimize the transmission of unwanted traffic over the infrared link. In this case, the access point device assigns a unique UNICAST address to each client connecting to the device.
It is quite reasonable to expect future implementation of access point devices to support multiple concurrent clients connecting to the LAN. In this case, each client would be assigned a unique LAN address, and the access point device would likely use a NIC supporting multiple concurrent UNICAST addresses.
Peer-to-Peer Mode
The IrLAN protocol peer-to-peer mode allows nodes running network operating systems that are peer-topeer capable to create ad-hoc networks. The following illustration shows the peer-to-peer mode.
In peer-to-peer mode, there is no physical connection to a wired LAN. Filtering information can still be sent to the provider during the connection setup process. The filters allow the provider to lower traffic when both peers are not running the exact same protocol suites. Also, the filters can lower traffic in the case of
point-to-multipoint traffic.
In peer-to-peer mode, each peer must provide a Server Control LSAP in addition to its Client Control LSAP and Data LSAP. Each Client Control LSAP connects to its peer’s Server Control LSAP. This allows each node to establish and control its peer’s Data LSAP using the command set described herein.
Hosted Mode
In hosted mode, the provider has a wired network connection, but has multiple nodes attempting to communicate through the wired connection. The following illustration shows hosted mode.
Unlike access point mode, both the host machine and the client(s) share the same NIC address in host mode. To make host mode work, the host must run special bridging and routing software that will handle the proper routing of packets. The algorithms used in this mode are highly protocol-dependent.
IrLAN IAS Object Specification
When a client connects to a provider, it looks in the provider’s IAS for the object with the “IrLAN” class.
The client reads the following attribute information for the IrLAN object to determine which LSAP the IrLAN control channel resides on.
IrDA:TinyTP:LsapSel:<LSAP>
For compatibility with Plug-n-Play operating systems, peer nodes, access points and hosted mode hosts must advertise the LAN and PNP hint bits in the discovery process. Access points should report PnP ID *PNP8294 in their PnP IAS entry. Peer nodes should report PnP ID *PNP8389 in their PnP IAS entry.
TinyTP Considerations
In the IrLAN protocol, both the control and data channels use the TinyTP protocol for segmentation and reassembly of packets and for flow control. The use of TinyTP involves these elements:
•Maximum assembled frame size
•Flow control
Maximum Assembled Frame Size
TinyTP allows for the fragmentation and reassembly of packets, which may span several IrLMP frames.
During the setup of the TinyTP connection, a maximum assembled frame size is negotiated between the two sides.
The IrLAN protocol currently defines support for access to the 802.3 (Ethernet) and 802.5 (token-ring) LANs. (In the future, this protocol may be modified to support additional media types.) The assembled TinyTP frame should be large enough to support the maximum frame size for the media.
•For 802.3 (Ethernet), the assembled TinyTP frame size is 1,518 bytes.
•For 802.5 (token ring), the assembled TinyTP frame size is 65,535 bytes. Because token ring permits a smaller upper bound on the frame size, depending on the adapter technology in use, a 2,045-byte assembled frame size is acceptable for 802.5 support. A smart token-ring IrLAN implementation will scale the media frame size to fit well in an integer number of TinyTP frames, which depends on the negotiated frame size. Examples of such scaling are shown in the following table.
Flow Control
TinyTP specifies a flow control mechanism based on extended credit; that is, during the setup of a TinyTP connection, each side informs the other of a number of outstanding “credits,” where each credit represents a TinyTP packet that may be sent to the side extending the credit. Each time a packet is sent, the sending side assumes that the receiving side has one less resource available for receiving packets. If the sending side
reaches the point where it determines the receiving side has no resources left because all credits have been consumed, it will stop transmitting until more credit is extended. The receiving side will extend more credit as resources are freed up on the receiving side.
When this flow mechanism operates in conjunction with IrLAP, it can lead to under-utilization of the link.This typically happens when the credit extended by a receiver is smaller than the window size negotiated by IrLAP. This results in the send window not being filled, and the page link turns around as a consequence more often than it needs to. If at all possible, the receiver should extend at least enough credit so that the transmitter can always fill an IrLAP window. The current maximum IrLAP window size is seven frames.
Because a frame may not hold an entire packet, this is the actual formula for the minimum credit that should be extended for optimum throughput:
Noninteger credit values derived from the formula should be rounded up to the next highest integer value. Examples of values derived from the formula are shown in the following table.
Frame Formats
The IrLAN protocol defines the commands used on the control channel as well as the format of data on the data channel. These formats are defined above TinyTP; that is, TinyTP segmentation and reassembly and flow control is assumed to be handled by the TinyTP interface. The definitions in the following sections are for the assembled TinyTP frames.
Data-Channel Frame Formats
Frames on the IrLAN data channel are formatted the same as for their respective media.
For 802.3 (Ethernet), the format is the same as would be transmitted at the software level for an 802.3 packet.
The IrLAN data-channel frame does not contain the 802.3 FCS. This is the IrLAN data channel packet format
(the numbers in the square brackets are the number of bytes in each part of the packet):
For 802.5 (token ring), this is the IrLAN data channel packet format.
These are the same formats typically used by network protocols when talking to network drivers. Usually, the IrLAN driver will only have to reformat the descriptors for the packets for transmission on the infrared media. The driver should not have to change any of the packets contents in either the peer-to-peer or access point modes. In the hosted mode, some protocol specific transformations may have to be made.
Once the data channel is established, it is treated as the send and receive path for all frames on the emulated LAN media. All packets sent from a node are transmitted on this channel, and all packets being received will come from this channel.
Control-Channel Frame Formats
The control channel is used to perform these tasks:
•Set up a data channel connection.
•Set up configuration parameters for the data channel connection.
The control channel uses TinyTP as a flow control and segmentation and reassembly protocol. The client and provider must both support a minimum 1,024-byte assembled frame size on the control channel. If a cient must send a command that exceeds 1,024 bytes, which is highly unlikely, it must send a sequence of smaller commands of the same type that accomplish the same purpose.
A command/response protocol is used on the control channel. Currently, only client-initiated command/response pairs are defined. In the future, there may be a requirement for unsolicited responses from the provider to the client, but these requirements have not been defined. If an unsolicited response is received from the provider, the client should check the result code field, which is the first byte of the response. If the result code field is not 0xFF, indicating a valid unsolicited response, the page link should be
dropped.During a session, the client issues a sequence of request packets, each of which is immediately followed by a response from the provider. The format of the command packets and response packets are defined in the following sections.
Command Packet Structure
Each request consists of a command code, a count of parameters, and a parameter list for the command.
Command Code
A 1-byte field specifying the command to be issued on the control channel. A number of different commands are currently defined. This list may be expanded in the future. These are the valid command code values.
Parameter Count
A 1-byte value specifying the number of parameters that follow in the parameter list.
Response Packet Structure
This is the structure of a response packet generated by a provider.
Result Code
If the result code is success, zero or more parameters are returned in the response packet. If the result is nonzero, the provider must return, in its response packet parameter list, the first invalid parameter it encountered in the request packet.
These are the valid result codes.
Parameter Count
Number of parameters to follow in the parameter list.
Parameter List
List of zero or more parameters that are return values for the associated command. For a definition of the structure of a parameter list, see “Packet Parameter List Format” later in this document.
Packet Parameter List Format
The parameter list contains zero or more variable-length parameters. The number of parameters in the list is defined by the Parameter Count field in both request and reply packet headers Each parameter in a parameter list has a Parameter Name field and a Value field. The Parameter Name field identifies the content and format of the Value field. There may be more than one parameter of the same name in the same
parameter list.
The parameters in the parameter list may be in any order.
Name Length
Length of the Parameter Name field.
Parameter Name
ASCII parameter name, which is case insensitive.
Value Length
Length of the Value field.
Value
Parameter value. The format is implied by the Parameter Name field. Values that represent integers are transmitted in little endian (Intel) format. Parameters that represent nonintegers, such as network address fields, are transmitted in the same octet order that they would be transmitted on their respective media.
