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Wireless Fundamentals 3 – Personal Area and Mobile Networking

Chapter 6 of Mobile Commerce and Wireless Computing Systems By Elliott, G. and Phillips, N.

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Personal Area and Mobile Networking

Bluetooth

Personal Area Network

Information Appliance

PersonalIntelligent Gateways Personal

Operating Space

Environments

Service Discovery

Channels

Piconet

uPnP

Timeslots

Establishing Connection

Frequency Hopping

Wire Replacement Technology

Salutation

Domestic

JINI

Master

Slave

Scatternet

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Personal Operating Space

Refer to the space around a person within the wireless-enabled devices they carry can communicate, but it can also be applied to appliances in that environment

Environments can also define their own wireless-network operating space, either to support and enhance the operation of personal devices within them or to provide smart environment control, security or monitoring services

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Activity on POS

List all the electrical devices in your home that are, or could be, operated with remote devices. Try and come up with at least ten. If each of these devices could communicate with a handheld device such as a PDA, what services should they provide?

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Personal Information Appliances Devices such as PDAs and mobile telephones,

personal CD players, and digital still or movie cameras

Wireless capabilities offer the potential for further change

Using a PAN, a single massive storage appliance can function as a file server for any number of different specialist personal devices whose form can then be adapted to best suit their function – playing music, taking pictures

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Personal Information Appliances Personal

Mobile phone, PDA, camera and MP3 Domestic

Washing machine, fridge, tv, boiler

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Personal Area Networks (PANs) A PAN is a network that supports the interoperation of

devices in personal space. They are small networks of devices with short-range,

low-power and low-cost wireless interaction capabilities.

Information appliances: mobile phone, personal CD player and PDA, and embedded information appliances will reside in radios, TVs, VCRs, washing machines, central heating and air conditioning units.

It can also be a network that moves about, linking the swarm of information devices about a person with each other and with other devices they meet along the way.

As the network moves about in the world, devices are constantly coming into and going out of range.

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Environments

Mobile wireless environments Personal, PAN, or a car environment, or commercial, on a public

transport service vehicle Provide workflow and knowledge management in order to maximize

service and customer satisfaction Static wireless environments

In a predefined area or location, i.e. home and office using wireless network such as 802.11 and HiperLAN to provide access to the Internet and home or office network

Airports, hotels,and restaurants offer E-mail facilities to their users. A wireless approach is much more cost-effective than wire-based

solutions.

Respond to devices that enter it or that it meets

Control an area based on sensed activity

Mobile

Control an area based on activity and location

Biddable

Smart

Static

Respond to devices that enter it

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Environments

Smart spaces Monitor the behaviour that is taking place within them and

respond appropriately to support and enhance that behaviour e.g. automatic heating and lighting controls

To share information between appliances in the space but not with the personal devices of the people within it.

Biddable spaces Reactive, offer a set of services to anyone who asks Selective to who or what devices they recognize and will respond

to e.g. POS about a wireless-enabled domestic appliance

Respond to devices that enter it or that it meets

Control an area based on sensed activity

Mobile

Control an area based on activity and location

Biddable

Smart

Static

Respond to devices that enter it

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Personal Area Network Intelligent Gateways

A gateway is a network connection between two types of networked computer system, such as a PC LAN and a mainframes. The gateway provides suitable translation services between the two systems.

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Personal Area Network Intelligent Gateways

The wireless nature of a PAN means that the same resource sharing that was the main economic driver behind LAN development can be applied to personal devices.

The gateway is intelligent in that it can sense the availability of any wireless LAN and WAN in the locality of the PAN and establish a connection with any other device that is similarly connected, whether wired or wireless.

If there are a variety of networks available then the gateway will be capable of determining the ideal network for the data transfer requirements of the accessing device and balancing this against power, priority and pricing consideration as appropriate.

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Bluetooth Technology

Consist of hardware, in the form of a radio antenna and Radio Frequency (RF) transceiver logic on a chip and a set of protocols with which a host of information appliance can interface with Bluetooth unit

Based on 802.11 ad hoc network standard and also has a lot in common with the Infrared data transfer standard IrDA

Is ideal for linking together the devices in a room Link devices without wires, making it easier to install and

rearrange equipment, but it offers much more than simple wire replacement

Bluetooth devices can discover each other as they come into range and negotiate to share services.

A Bluetooth-enabled PDA in a department store might become aware of a Bluetooth port from which it can download a store plan and which it can query about where to find things – it might have to ‘pay’ for this service by also downloading an advert for the store’s latest promotion.

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Bluetooth Technology

The requirements of a device that can achieve this clearly go beyond simply determining their capabilities, negotiating terms for use of those capabilities and creating the network to support that use.

A Bluetooth-enabled device includes both specialist hardware and software to manage the interface.

The hardware consists of 3 modules: the Radio Frequency (RF) transceiver, the Link Controller and the IO Manager.

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Bluetooth Technology

The hardware consists of 3 modules: the Radio Frequency (RF) transceiver, the Link Controller and the IO Manager.

The radio transceiver operates in the 2.4GHz range; the transceiver and its antenna can both be made very small so that they can easily be incorporated into a device quite unobtrusively.

The main functionality of the devices is access using three core protocols: the Logical Link Control and Adaptation Protocol (L2CAP), the Service Discovery Protocol (SDP) and the Radio Frequency CoMMunication Protocol (REFCOMM).

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Bluetooth Technology

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Bluetooth Technology The L2CAP provides the main interface to higher-level protocols. It is essentially the bottom half of the data link layer of the ISO

OSI model and corresponds to the MAC Layer of the 802 standard.

L2CAP converts between the digital electrical signals and the baseband signal and vice versa.

The SDP supports operations concerned with discovering and getting information about the identity and characteristics of the services offered by other devices and informing them of the characteristics of its devices.

RFCOMM is the actual cable replacement technology. It provides transport capabilities for all high-level services that use serial line as the transport mechanism.

Transmission and reception is achieved through the antenna that forms the ‘air interface’ of the unit.

Transmission is over a band of frequencies in the 2.4 GHz range. Each device uses the whole band in each transmission, by employing a frequency-hopping techniques that overcomes noise in the environment.

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Bluetooth Radio Frequency Channels 3 meanings:

Refer to the 79 RF-channels 1MHz apart. Refer to a particular, pseudorandom hopping sequence

through 79 RF-channels Refer to five logical channels used for control and co-

ordination Synchronous Connection-Oriented (SCO)

transmissions are point-to-point transmissions between master and slave. Transmissions are made in reserved time-slots determined by the master unit when it set up the link

Asynchronous Connection-Less (ACL) is a multi-cast link where transmissions provide packet-switched connections between a master and all connected slaves.

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Piconets A piconet is a small ad hoc network of Bluetooth-

enabled devices. Up to eight devices can be joined together in a

Bluetooth piconet – 1, and only 1, of these must be the master that controls the communications for the duration of their co-operation; the other units are referred to as slaves.

Slaves in a piconet have no direct communication with each other.

All communication is between the master and each slave in turn.

Each device in the piconet has a simple three-bit address (hence the eight-device limit).

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Network Master and Slaves in a Piconet The role of the master is to synchronize communication by

determining a common time for the start of a time-slot sequence and to determine common pseudo-random frequency-hopping scheme.

Typically a device wishing to make use of a service will naturally take the master role and the device offering the service will be the slave.

All the slaves in a piconet have to adjust their timings to match the master.

Resembles that a star network with the master playing the role of hub.

Slaves have an automatic built-in right to overthrow their masters and reverse the relationship.

It is possible fro a slave to be the master of a piconet without giving up the role of slave in another.

However, 2 units cannot be both master and slave to each other. Nor a slave become a master of one of its masters other slaves.

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Scatternets - Piconet

A slave in one piconet will become a master of another or a master of a piconet will become a slave in another. These relationships create extended networks, in principle, allow communications between devices in different piconets through these gateway devices.

A highly structured pyramid network with a supreme master who has 7 slaves, each of which is in turn a master with 7 slaves of piconets are called ‘scatternets’.

Due to lower power consumption of devices, call-forwarding is not supported.

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Scatternets

Lacks of research on incidental capability – re-configurable computerized units that need sporadic contact with other which will establish a connect, do the business and close a connection.

Devices come and go. These needs a different set of rules for

maintaining it s list.

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Establishing and Maintaining Wireless Connections – Different Contexts (1) An environment such as a room in the home

where devices change infrequently. A new device needs to introduce itself and learn

about its neighbours or a device will be removed from the room either for an extended period or permanently.

The same set of mobile devices will come and go in the room and all devices will ‘know’ each other. They will have each other’s ID and capabilities listed.

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Establishing and Maintaining Wireless Connections – Different Contexts (2) An environment with a number of conventionally

networked, static communication devices with a high throughput of mobile devices, such as in a department store, airport or hotel. The static devices might collect data on each device and

count how often and when they visit but there is a very low expectation that any particular device will be present at any particular time so they will always need to ask who is there before they can make a connection.

Mobile devices that are frequently used to assist their users with shopping and travel might have geographic awareness, to know where they are, and the addresses of the static devices in different locations with services of interest.

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Establishing and Maintaining Wireless Connections – Different Contexts (3) An environment where most of the interaction

is between a person’s personal mobile devices, e.g. headset, MP3 player, mobile phone, etc., whose addresses are well known to all devices, but where occasionally devices need to interact with unknown, static or mobile devices, e.g. to make a payment or exchange a business card or to negotiate a service such as Interact access or E-mail facilities.

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Establishing and Maintaining Wireless Connections – Different Contexts (4) An environment where a personal mobile

device is regularly engaging with other static and mobile devices, e.g. a vehicle guidance system or a PDA being used to navigate a shopping precinct, or members at a trade convention engaged in electronically enhance networking.

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Establishing and Maintaining Wireless Connections – Wireless Operating Modes 4 basic states:

Unnconnected (Default state) Connecting Active Low Power

In unnconnected state, there is a only STANDBY mode, it can receive/issue INQUIRY, and PAGE requests.

INQUIRY message is issued when it wants to find out what devices are in range.

INQUIRY message includes details about itself, such as ID and type information.

Bluetooth uses a type system so that manufacturers can specify the types of device it is appropriate for different appliances to communicate with.

The INQUIRY can also elicit basic details about the purpose and functioning of any device that responds and give that device information about its own purpose and functioning.

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Creating Network Connection in Bluetooth 1 To create a connection a device sends a PAGE message to the

particular device that it wishes to connect to. The initiating device broadcasts a message that includes the

address of the device it wants to connect to. It first sends the message using 16 of the standard 32 wake-up

hop frequencies. If it cannot find its target, it sends the message using the remaining 16 hop frequencies.

Once a connection has been established, the devices in the new piconet are in the active state.

In the active state, there are transceiving and connected modes. In the transceiving mode, data is passed between master and

slave. In the connected mode, only control and synchronization signals

are exchanged, but the device actively listens for data all the time.

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Creating Network Connection in Bluetooth 2 In a dynamic environment, devices will frequently issue INQUIRY

messages to keep themselves up to date on their environment. Often they will not actually establish connection unless a

particular unit is able to supply a service requested by a user application or an application has requested that data is communicated to a particular device.

In static environment where piconet membership is likely to be fairly constant, networks might be set up and remain fro extended periods of time, even if no communication is taking place. For this situation, devices can enter the power-saving state. In each low-power mode the salve remains synchronized with the

piconet, but they vary in how engaged they are and, therefore, in how quickly they can resume fully active membership again.

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Creating Network Connection in Bluetooth In Sniff mode a device listens to the master as normal but at a

reduced rate. A master can decide to put a device in Hold mode if it knows that

there will be no data to exchange; alternatively a slave can demand to be put in Hold mode.

A slave might enter Hold mode in one piconet so that it can create another piconet in order to make use of a service; when that service is complete it can return by existing Hold.

In Sniff and Hold modes a device is still a full member of the piconet and can easily return to full participation.

A parked device will occasionally listen to the master device resynchronize its clock and listen to broadcast message. Parking provides a way for a master device to deal with more than 7 other devices at a time.

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The Physical Connection

Bluetooth uses frequency-hopping in time-slots with short packages and Forward Error Correction in order to maintain efficient data transfer through multiple channels in noisy environments.

Separate logical channels are maintained through the use of time-slots synchronized to the clock of the master device.

Every device uses the full breadth of the available frequency band by hopping in a coordinated but pseudo-random fashion between 791 MHz channels.

The frequency-hopping reduces the interference from noisy appliances such as microwave ovens, while the use of a pseudo-random sequence minimizes the chance of interference between two piconets in the same space.

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Time-slots

The communicating devices agree to divide time into fixed-length periods and each period is assigned a unique identification number.

Time-slots can then be distinguished by simple properties of the numbers assigned to them to form separate logical channels. For instance, even-numbered slots can be reserved for the master

device to communicate to its slave devices. A particular slave device might then be assigned every twelfth pair of

slots for its communication. It listens for packets from the master every 23rd time-slot and uses every

24th time-slot to respond.

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Frequency-hopping

Bluetooth divides a broadband of frequencies 791 MHz channels and hops to a new frequency after transmitting or receiving a single packet on each channel.

The hop sequence follows a pseudo-random pattern. Devices employ a limited hop sequence composed of a subset of all

available frequencies to scan their environment while in unnconnected states.

Once connections are established, the master device dictates a particular hopping sequence to follow.

Every piconet has a different hopping sequence, so the chances of the piconet channel being busy are extremely low.

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Security of Piconets or Scatternets Two concerns: integrity and privacy Integrity

Rely on various error-detection and correction schemes

Bluetooth supports a standard authentication mechanism to address this problem.

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Security of Piconets or Scatternets Error correction enables a

certain number of errors to be both detected and correction so that there is no need for retransmission. How noisy the environment

a certain number of errors to be corrected than it does to encode the same message for error detection.

Have a higher computational overload for both encoding and decoding

Error detection schemes identify that an error has occurred and ask for the data to be retransmitted. In noisy environments

where errors are common the retransmission costs of only using error detection can be much more expensive.

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Privacy

Is concerned with both accidental and intentional eavesdropping on transmissions between two devices.

The particular method of channel hopping and time divisions used in Bluetooth makes accidental eavesdropping extremely unlikely.

Bluetooth includes random number generation, encryption and encryption key management facilities to ensure secure private transmissions.

The difficulty of intercepting a Bluetooth communications is probably slightly higher than the difficulty of intercepting a wired LAN communication.

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IEEE 802.15

A set of general PAN standards developed by the IEEE.

802.15b: 3 variations to cope with the needs of particular usage models

802.15c: concern with power management and handles much higher data transfer rates but power consumption is less of an issue

802.15d: aimed at devices that have extremely limiting power constraints but also lower data transfer rate requirements

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Wireless Service Discovery and Use How can a mobile device discover what other

devices it meets have to offer? If the user of a device issues a request for a

particular service that requires the device to interact with another system, how can a device go about meeting that request?

How does a device tell other devices what it has to offer and what its owner is interested in?

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Wireless Service Discovery and Use – 3 Coordination Frameworks JINI is a Java-based solution that extends the Java distributed

systems architecture Remote Method Invocation (RMI) into the mobile domain. JINI is, obviously, language-dependent but platform- and transport-independent

Universal Plug and Plug (UPnP) is a Microsoft approach, only tangentially related to Plug and Play under Windows, that aims for language independence but is reliant on TCP/IP as a transport mechanism.

Salutation is a non-proprietary approach which aims at both language and transport independence.

3 approaches JINI emphasizes standardization, while UPnP emphasizes autonomy and Salutation attempts to walk the middle road and balance the two.

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JINI

A collection of autonomous devices in contact with one another forms a federation.

Members of a federation can become aware of each other, negotiate and cooperate together.

At least one device must be running a JINI sub-system that provides a look-up service.

The underlying assumption is that these look-up services will be provided via an access point to a conventional network or among static devices such as consumer appliances.

JINI does not provide any means for devices to configure themselves for appropriate networking.

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Universal Plug and Play (UPnP) A much lower level solution than JINI and is based around

extensions to the TCP/IP protocol that can be implemented locally using native code. (Limited to TCP/IP networks)

Provides a set of defined network protocols and allows manufacturers to develop their own APIs to implement them using any language or platform.

Simple Service Discovery Protocol (SSDP) which provides an interface for devices to announce their presence to a network and to discover other devices and their capabilities.

SSDP can work with or without a look-up service, called service in UPnP.

If a proxy service exists then all devices will use it. If no proxy service exists there is a proxy-less operating mode for them to follow.

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Universal Plug and Play (UPnP) The discovery mechanism uses HyperText Transfer

Protocol (HTTP) over UDP, unicast or multicast. The registration process sends and receives data in

HTTP format, but with special semantics such as the ANNOUNCE message and the OPTIONS message for querying.

Multicasts are sent on a reserved address to which all participating devices must listen.

Every device must have its own Unique Resource identifier and an XML file accessible through a URL. Details of both must be included in a device’s ANNOUNCE message.

The restriction to TCP/IP makes it possible for UPnP devices to obtain an IP address using DHCP.

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Salutation

Both JINI and UPnP clearly have their roots in the wired network paradigm and conceptually both are extension of established wire-based solution, i.e. RMI and PnP.

Salutations Manager (SLM) may be part of same device or of a remote device.

SLMs form ensembles or swarms of agents that coordinate with one another in order to provide services for their clients.

All requests and communications between client devices are mediated through SLM agents.

SLM agents behave in a similar way to Object Request Brokers (ORBs) in wired distributed computing systems.

SLMs discover other SLMs and exchange registration information. This process can transverse different transport media.