Download Wireless Fundamentals 3

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
Intelligent Gateways
Environments
Personal
Personal
Operating
Space
Personal
Area
Network
Domestic
Information
Appliance
Wire
Replacement
Technology
Master
Bluetooth
Channels
Piconet
Slave
Frequency
Hopping
Establishing
Connection
Scatternet
Service
Discovery
Salutation
uPnP
Timeslots
JINI
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Personal Operating Space
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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
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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
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Personal
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Mobile phone, PDA, camera and MP3
Domestic
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Washing machine, fridge, tv, boiler
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Personal Area Networks (PANs)
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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
Static
Biddable
Smart

Respond to
devices that
enter it
Respond to devices
that enter it or that
it meets
Control an area
based on
sensed activity
Control an area
based on activity
and location
Mobile wireless environments
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Mobile
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
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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.
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Environments
Static
Biddable
Smart

Respond to
devices that
enter it
Respond to devices
that enter it or that
it meets
Control an area
based on
sensed activity
Control an area
based on activity
and location
Smart spaces

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Mobile
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
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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
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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
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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
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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
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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
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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
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3 meanings:
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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 coordination
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 multicast link where transmissions provide packetswitched connections between a master and all
connected slaves.
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Piconets
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A piconet is a small ad hoc network of Bluetoothenabled 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
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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
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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, callforwarding is not supported.
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Scatternets
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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.

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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.

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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
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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
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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
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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
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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
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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 pseudorandom sequence minimizes the chance of interference between
two piconets in the same space.
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Time-slots
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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.
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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
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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
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Two concerns: integrity and privacy
Integrity
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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
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Error correction enables a
certain number of errors to
be both detected and
correction so that there is
no need for retransmission.
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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
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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
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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
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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
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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
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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 subsystem 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)
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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)
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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
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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.
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