Interfacing Aspects

Interfacing technologies
Respective significance of Fitaly, Tegic T9, Octave methods of keyboards vis-à-vis traditional QWERTY layout based keyboards / keypads, in the context of mobile handheld devices:

§Fitaly

•Merit / Significance:
Speeds up input of text, letters selected as per likely occurrence frequencies and ensuring minimization of inter-letter travel distance (to no more than 2 positions), supports 220 ANSI/ISO Latin- 1 character set, supports accents, available in on-screen as well as mechanical forms

•Demerit:
 Specific to English language‟s estimated usage patterns, needs to be practiced for a while before use, needs to learn „sliding‟ for accents‟ use etc.

§Tegic T9:
•Merit / Significance: 
Requires lesser number of keystrokes for textual input due to support for predictive text by combining use of dictionary and linguistic rules‟ embedding, resolution of word-ambiguity is supported through prompts, available in on-screen as well as mechanical forms
•Demerit: 
Requires sizeable software support and computing resources (instruction cycles and memory)

§Octave:
•Merit / Significance:
Commands available to support multiple language dictionaries, available in on-screen as well as mechanical forms although second form is more popular, gesture-based iconic support for certain insertions, word-recognition supported by dictionary, ability to resolve stroke-ambiguity with the help of dictionary

•Demerit: 
Requires sizeable software support and computing resources (instruction cycles and memory)

Memory management

§Support for protected Virtual Memory Management (upto 32 MB per process), special heap-support for File System / Registry / Object Store <max. size of Object Store:256 MB>
§Security:
§Support for cryptography with a Crypto Library+ Crypto API, support for SD and Smart Cards §Footprint:
§About 400 kb for the OS Core / Kernel
§About 3 MB with Kernel + all modules
§About 8 MB with Kernel + all modules + MS Word / PowerPoint / IE etc.
§User-interface:
 §Simple, intuitive, generally consistent, Menu-driven, Iconic
§User management:
§Designed for single user support only
 §Energy-awareness aspects:
 §Support for energy-saving enabled at the kernel level

Operating System Aspects

Operating Systems for Pervasive Computing Environments
•Types of Operating Systems 
O Classification based on location of functionalities:
§Centralised OSes
§Networked OSes
 §Distributed OSes

O Support for security through full encryption and certificate management, secure protocols (HTTPS, SSL and TLS), WIM framework and certificate-based application installation
o Support for content development options for C++, Java (J2ME) WAP etc.;

O Support for variety of user inputs – generic input mechanism supporting full keyboard, 0-9*# (numeric mobile phone keypad), voice, handwriting recognition and predictive text input.
•Variants of Microsoft Windows
O Windows XP Embedded
O WinCE

Memory Technologies

•Register class elements
•Cache memory elements
•Primary Memory elements
oRAM 
§SRAM
§DRAM
§Ut-RAM
§MRAM
§FRAM
§MBM

oROM
•Secondary Memory
oFlash Disks
oMagnetic Disks
oOptical Disks
oMagento-Optical Storages
oMagentic Tape Storage

Processor technologies

•Intel‟s SpeedStep processor technology

Intel‟s SpeedstepTM technology based processors and their successors are capable of:

•Changing the internal clock frequencies
•Adapting core voltage to changes in power supply
•Switching of selective parts of the CPU cores / CPU on or off depending on whether the current calculations require them to be available
•Using the reduced the clock rate and voltage of the processor core while on batteries, leading to significant power saving.
•Switching between these modes is transparent to user and is usually fast <however, while the system is connected to external power supply, the full clock rate and core voltage is available to processor resulting into maximum performance>
•Transmeta‟s Crusoe processor technology
 •Total number of transistors are reduced in an attempt tosave the power consumption

GSM Network Subsystem

•MSC (Mobile Services Switching Center) acts like a normal switching node and provides the connection to the fixed networks (such as the PSTN or ISDN).

 •HLR (Home Location Register ) contains information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. There is logically one HLR per GSM network •VLR (Visitor Location Register) contains selected information from the HLR, necessary for call control and provision of the subscribed services and each mobile currently located in the geographical area controlled by the VLR. 

•EIR (The Equipment Identity Register) is a database that contains a list of all valid mobile equipment on the network,

•AuC (The Authentication Center) is a protected database: secret key of SIM GSM uses TDMA/FDMA to share the limited radio spectrum wherein the FDMA part divides frequency of the not more than 25 MHz B/W into 124 carrier frequencies spaced 200 kHz apart.; and Each of these carrier frequencies is then divided in time, using a TDMA scheme. GSM is a circuit-switched digital network. 

SGSN (the Serving GPRS Support Node) keeps track of the location of the mobile within its service area and send/receive packets from the mobile , passing them on, or receiving them from the GGSN. GGSN (Gateway GPRS Support Node) converts the GSM packets into other packet protocols (e.g. IP /X.25) and sends them out into another network.

•GPRS users can share the resource (Radio link) which is used only when users are actually sending or receiving data. 

•GPRS is based on GMSK which is a modulation technique known as Gaussian minimum-shift keying. It can support a theoretical upper limit of speed up to 171.2kbps as against the GSM „s9.6Kbps.

 •In GPRS, a channel that is 200kHz wide, is divided into 8 separate data streams, each carrying maximum 20kbps(14.4kbps typical) whereas in GSM we use only one channel.

Connectivity Aspects

Role of communication architectures in pervasiveness
•The pervasive computing system needs at least two basic elements to be pervading everywhere they are required to pervade:
O Computing elements to take care of computational needs; and,
O Communication elements to interconnect these computing elements either through wires or wirelessly (with / without mobility).

•From the end user‟s perspective and in many a practical situations, the wireless communication based mobile computing is becoming increasingly important.
•From the back-end systems‟ viewpoint, however, due to its sheer traffic volume, low error rates, better noise immunity and low cost, the wire line communication based computing still remains an attractive option. •Therefore, hybrid architectures will possibly continue to exist even though end users may not be even aware of it. Identifying multi-technology mobile communication architectures of relevance
•Several generations
•Gradual enhancements
•Coexistence & transition

Pervasive Computing Devices

Device Technology for Pervasive Computing include Power-provisioning technologies, Display technologies, Memory technologies, Communication technologies, Processor technologies, Interfacing technologies, Sensor Technologies and Authentication Technologies.

Technology Aspects

Low-power Device Technologies 

Since many of the devices involved in the pervasive computing environment may have to be small in size and may have to live on their battery / power units, consumption of lower power, extension of power provisioning period etc. assume critical significance. In addition, prevention from excessive heating also requires attention. Power requirements can be reduced by several means right from material selection and chip-level designing to software designing and communication system designing. Power provisioning technology including the Battery design technology plays a very important role in the process.

Batteries as Power Provisioning Devices 

•Key issue: Size and weight of the batteries versus the power capacity and price 

•Bottleneck: Relatively slower advances in the battery technology compared to those in other fields like display and storage technologies 

•Major choices available: Nickel-Cadmium (NiCd: 12-27 hrs. standby time), Nickel-Metal-Hydride (NiMH: 16-37 hrs. standby time), Lithium- Ion (Li-ion:21-50 hrs. standby time), Lithium-Polymer Cell based batteries (> 60 hrs. standby time, flexible shapes) etc.

Elements of Pervasive Computing Systems

Pervasive Computing is a technology that pervades the users‟ environment by making use of multiple independent information devices (both fixed and mobile, homogeneous or heterogeneous) interconnected seamlessly through wireless or wired computer communication networks which are aimed to provide a class of computing / sensory /communication services to a class of users, preferably transparently and can provide personalized services while ensuring a fair degree of privacy / non-intrusiveness.

It may also be seen as the as the technology that is a combination of Personal computing technology and one or more of the following:
 •Internetworking technology
•Invisible computing technology
•Wearable computing technology
•Mobile Computing Technology

Elements of Pervasive Computing Systems
Components of Infrastructure for Pervasive Computing include Mobile computing devices, Fixed computing devices, Multimode RF Mobile communication infrastructure <Fixed-to-Mobile and Mobile-to-Fixed communication system interfaces>,Trust system (security and privacy), Protocol stacks and Personalized service frameworks.

What should the Infrastructure provide? 
•Pervasive Computing Infrastructure has to comprise of computing elements, communicating elements, sensors, actuators, and interface devices
 •Computation to be available widely and freely (not free of cost).
•Intermittent connectivity has to be a supported feature due to physical limitations pertaining to power, cost, bandwidth and network congestion.
•Bluetooth and other choices address small-distance networking issues and allow intermittent connection. •The infrastructure has to offer seamless connectivity to the devices /entities / services.
•It has to support placement and location of uniquely identifiable “information tags / track able tags” to all devices / entities in the Pervasive Computing environment.
•User‟s environment must be able to be aware of the user‟s context. Roaming Environment: An environment that allows connectivity and communication to the services outside the home zone is called a Roaming Environment. Some sample devices that may involve Roaming-based access <fixed / mobile roaming>:

Wireless session protocol

The wireless session protocol (WSP) has been designed to operate on top of the datagram service WDP or the transaction service WTP (WAP Forum, 2000e).For both types, security can be inserted using the WTLS security layer if required. WSP provides a shared state between a client and a server to optimize content transfer. HTTP, a protocol WSP tries to replace within the wireless domain, is stateless, which already causes many problems in fixed networks. Many web content providers therefore use cookies to store some state on a client machine. State is needed in web browsing, for example, to resume browsing in exactly the same context in which browsing has been suspended. This is an important feature for clients and servers. Client users can continue to work where they left the browser or when the network was interrupted, or users can get their customized environment every time they start the browser. Content providers can customize their pages to clients‟ needs and do not have to retransmit the same pages over and over again. 

WSP offers the following general features needed for content exchange between cooperating clients and servers:

● Session management: WSP introduces sessions that can be established from a client to a server and may be long lived. Sessions can also be released in an orderly manner. The capabilities of suspending and resuming a session are important to mobile applications. Assume a mobile device is being switched off – it would be useful for a user to be able to continue operation at exactly the point where the device was switched off. Session lifetime is independent of transport connection lifetime or continuous operation of a bearer network.

Capability negotiation: Clients and servers can agree upon a common level of protocol functionality during session establishment. Example parameters to negotiate are maximum client SDU size, maximum outstanding requests, protocol options, and server SDU size. 

● Content encoding: WSP also defines the efficient binary encoding for the content it transfers. WSP offers content typing and composite objects, as explained for web browsing. While WSP is a general-purpose session protocol, WAP has specified the wireless session protocol/browsing (WSP/B) which comprises protocols and services most suited for browsing-type applications. In addition to the general features of WSP, WSP/B offers the following features adapted to web browsing.

● HTTP/1.1 functionality: WSP/B supports the functions HTTP/1.1 (Fielding,1999) offers, such as extensible request/reply methods, composite objects, and content type negotiation. WSP/B is a binary form of HTTP/1.1.HTTP/1.1 content headers are used to define content type, character set encoding, languages etc., but binary encodings are defined for well-known headers to reduce protocol overheads. 

Wireless transaction protocol

The wireless transaction protocol (WTP) is on top of either WDP or, if security is required, WTLS (WAP Forum, 2000d). WTP has been designed to run on very thin clients, such as mobile phones. WTP offers several advantages to higher layers, including an improved reliability over datagram services, improved efficiency over connection-oriented services, and support for transaction-oriented services such as web browsing. In this context, a transaction is defined as a request with its response, e.g. for a web page.

WTP offers many features to the higher layers. The basis is formed from three classes of transaction service as explained in the following paragraphs. Class 0 provides unreliable message transfer without any result message. Classes 1 and 2 provide reliable message transfer, class 1 without, class 2 with, exactly one reliable result message (the typical request/response case). WTP achieves reliability using duplicate removal, retransmission, acknowledgements and unique transaction identifiers. No WTP-class requires any connection set-up or tear-down phase. This avoids unnecessary overhead on the communication link. WTP allows for asynchronous transactions, abort of transactions, concatenation of messages, and can report success or failure of reliable messages (e.g., a server cannot handle the request). To be consistent with the specification, in the following the term initiator is used for a WTP entity initiating a transaction (aka client), and the term responder for the WTP entity responding to a transaction (aka server). The three service primitives offered by WTP are TR-Invoke to initiate a new transaction, TR-Result to send back the result of a previously initiated transaction, and TR-Abort to abort an existing transaction. The PDUs exchanged between two WTP entities for normal transactions are the invoke PDU, ack PDU, and result PDU.

Wireless datagram protocol

The wireless datagram protocol (WDP) operates on top of many different bearer services capable of carrying data. At the T-SAP WDP offers a consistent datagram transport service independent of the underlying bearer (WAP Forum, 2000b). To offer this consistent service, the adaptation needed in the transport layer can differ depending on the services of the bearer. The closer the bearer service is to IP, the smaller the adaptation can be. If the bearer already offers IP services, UDP (Postel, 1980) is used as WDP. WDP offers more or less the same services as UDP.

WDP offers source and destination port numbers used for multiplexing and demultiplexing of data respectively. The service primitive to send a datagram is TDUnitdata.req with the destination address (DA), destination port (DP), Source address (SA), source port (SP), and user data (UD) as mandatory parameters (see Figure 10.11). Destination and source address are unique addresses for the receiver and sender of the user data. These could be MSISDNs (i.e., a telephone number), IP addresses, or any other unique identifiers. The T-DUnitdata.ind service primitive indicates the reception of data. Here destination address and port are only optional parameters.

If a higher layer requests a service the WDP cannot fulfill, this error is indicated with the T-DError.ind service primitive as shown in Figure 10.11. An error code (EC) is returned indicating the reason for the error to the higher layer. WDP is not allowed to use this primitive to indicate problems with the bearer service. It is only allowed to use the primitive to indicate local problems, such as a user data size that is too large.

MOBILE TCP

The M-TCP (mobile TCP)1 approach has the same goals as I-TCP and snooping TCP: to prevent the sender window from shrinking if bit errors or disconnection but not congestion cause current problems. M-TCP wants to improve overall throughput, to lower the delay, to maintain end-to-end semantics of TCP, and to provide a more efficient handover. Additionally, M-TCP is especially adapted to the problems arising from lengthy or frequent disconnections (Brown, 1997).

 M-TCP splits the TCP connection into two parts as I-TCP does. An unmodified TCP is used on the standard host-supervisory host (SH) connection, while an optimized TCP is used on the SH-MH connection. The supervisory host is responsible for exchanging data between both parts similar to the proxy in ITCP

The advantages of M-TCP are the following: 

● It maintains the TCP end-to-end semantics. The SH does not send any ACK itself but forwards the ACKs from the MH. 

Proactive Routing Protocols

Destination-Sequenced Distance-Vector (DSDV)
•When X receives information from Y about a route to Z
–Let destination sequence number for Z at X be S(X), S(Y) is sent from Y
–If S(X) > S(Y), then X ignores the routing information received from Y
–If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z
–If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y)
DSDV Protocol
•Packets are transmitted between the nodes using route tables stored at each node.
•Each route tablelists all available destinations and the number of hops to each destination.
•For each destination, a node knows which of its neighbours leads to the shortest path to the destination.
•Consider a source node Sand a destination node D.
•Each route table entry in S is tagged with a sequence number that is originated by the destination node.
•For example, the entry for D is tagged with a sequence number that Sreceived from D (may be through other nodes).
•We need to maintain the consistency of the route tables in a dynamically varying topology.

DSR Optimization: Route Caching

•Each node caches a new route it learns by any means

•When node S finds route [S,E,F,J,D]to node D, node S also learns route [S,E,F] to node F

•When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S

•When node F forwards Route Reply RREP[S,E,F,J,D],node F learns route [F,J,D] to node D

•When node E forwards Data [S,E,F,J,D]it learns route [E,F,J,D] to node D

Dynamic Source Routing: Advantages

•Routes maintained only between nodes who need to communicate

–reduces overhead of route maintenance

•Route caching can further reduce route discovery overhead

•A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches

Reactive Routing Protocols

Dynamic Source Routing (DSR)
•When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery
•Source node S floods Route Request (RREQ)
•Each node appends own identifierwhen forwarding RREQ

Route Discovery in DSR
•Destination D on receiving the first RREQ, sends a Route Reply (RREP)
•RREP is sent on a route obtained by reversingthe route appended to received RREQ

•RREP includes the routefrom S to D on which RREQ was received by node D

•Node S on receiving RREP, caches the route included in the RREP
•When node S sends a data packet to D, the entire route is included in the packet header
–hence the name source routing
•Intermediate nodes use the source routeincluded in a packet to determine to whom a packet should be forwarded

Routing Protocols

•Finding a path from a source to a destination
•Issues
–Frequent route changes
•amount of data transferred between route changes may be much smaller than traditional networks
–Route changes may be related to host movement
–Low bandwidth links
•Goal of routing protocols
–decrease routing-related overhead
–find short routes
–find “stable” routes (despite mobility)

Routing Protocols
•Proactive protocols
–Traditional distributed shortest-path protocols
–Maintain routes between every host pair at all times
–Based on periodic updates; High routing overhead
–Example: DSDV (destination sequenced distance vector)
•Reactive protocols
–Determine route if and when needed
–Source initiates route discovery
–Example: DSR (dynamic source routing)
•Hybrid protocols
–Adaptive; Combination of proactive and reactive
–Example : ZRP (zone routing protocol)

MANETs Applications

•Industrial and commercial networks
•‘Anywhere’ communication
•Military applications
•Robust alternatives to cellular networks
•Wearable and Ubiquitous computing
•Remote satellite -based communication

Many Applications
•Personal area networking
–cell phone, laptop, ear phone, wrist watch
•Military environments
–soldiers, tanks, planes
•Civilian environments
–taxi cab network
–meeting rooms
–sports stadiums
–boats, small aircraft
•Emergency operations
–search-and-rescue
–policing and fire fighting

MOBILE AD HOC NETWORKS

Interconnected collection of wireless nodes
•Nodes enter and leave over time
•Nodes also act as routers; forward packets
•No pre-established network infrastructure
•No centralized administration
•Communication using BlueTooth and WAP

Characteristics Of MANETs

• Dynamic Topologiesand node memberships
• Host movement frequent
• Topology change frequent
• Data must be routed via intermediate nodes
• Bandwidth constraints
• Many Transmission Errors
• Energy-constrained operation

WI-FI – Wireless Fidelity

Wireless Fidelity – popularly known as Wi-Fi, developed on IEEE 802.11 standards, is widely used technology advancement in wireless communication. As the name indicates, WI-FI provides wireless access to applications and data across a radio network. WI-FI sets up numerous ways to build up a connection between the transmitter and the receiver such as DSSS, FHSS, IR – Infrared and OFDM.

Wi-Fi provides its users with the liberty of connecting to the Internet from any place such as their home, office or a public place without the hassles of plugging in the wires. Wi-Fi is quicker than the conventional modem for accessing information over a large network. With the help of different amplifiers, the users can easily change their location without disruption in their network access. Wi-Fi devices are compliant with each other to grant efficient access of information to the user. Wi-Fi location where the users can connect to the wireless network is called a Wi-Fi hotspot. Through the Wi-Fi hotspot, the users can even enhance their home business as accessing information through Wi-Fi is  simple. Accessing a wireless network through a hotspot in some cases is cost-free while in some it may carry additional charges. Many standard Wi-Fi devices such as PCI, miniPCI, USB, Cardbus and PC card, ExpressCard make the Wi-Fi experience convenient and pleasurable for the users. Distance from a wireless network can lessen the signal strength to quite an extent; some devices such as Ermanno Pietrosemoli and EsLaRed of Venezuela Distance are used for amplifying the signal strength of the network. These devices create an embedded system that corresponds with any other node on the Internet. 

Wi-Fi uses radio networks to transmit data between its nodes. Such networks are made up of cells that provide coverage across the network. The more the number of cells, the greater and stronger is the coverage on the radio network. The radio technology is a complete package deal as it offers a safe and consistent connectivity. Radio bands such as 2.4GHz and 5GHz depend on wireless hardware such Ethernet protocol and CSMA. Initially, Phase Shift Keying (PSK), a modulation method for conveying data was used, however now it has been replaced with CCK. Wi-Fi uses many spectrums such as FHSS and DSSS. The most popular Wi-Fi technology such as 802.11b operates on the range of 2.40 GHz up to 2.4835 GHz band. This provides a comprehensive platform for operating Bluetooth strategy, cellular phones, and other scientific equipments. While 802.11a technology has the range of 5.725 GHz to 5.850 GHz and provides up to 54 Mbps in speed. 802.11g technology is even better as it covers three non-overlapping channels and allows PBCC. 802.11e technology takes a fair lead by providing excellent streaming quality of video, audio, voice channels etc.

No matter where you are, you can access the world of web through your handsets and your laptops and your iPads. You might not have noticed what it is but the technology that enables you to plug in internet without any wires whether you are in a cafe, a library, a shopping mall or an airport is Wi-Fi – the wireless network also known as 802.11. The circumference where wireless technology is present and available to the users is known as Hotspot. The inexpensive, user-friendly WiFi networks are alsoobtrusive; if you do not need one you would not know there exists any. Wi-Fi could be also installed in home or offices in order to transmit information over the air without the aid of wires. In near future you would find wireless networking available in every nook and corner