How
GPRS Works
The
General Packet Radio Service is a mobile data upgrade to a GSM mobile
phone network. This provides users with packet data services (similar
to the Internet) using the GSM digital radio network. Each voice circuit
in GSM transmits the speech on a secure 14kbps digital radio link between
the mobile phone and a nearby GSM transceiver station. The GPRS service
joins together multiple speech channels to provide higher bandwidth
data connections for GPRS data users. The radio bandwidth remains the
same, it is just shared between the voice users and the data users.
The network operator has the choice of prioritizing one or the other.
GPRS users will also benefit from being able to use
GPRS while traveling as the GSM system should transparently hand over
the GPRS connection from one base station to another.
Radio Interface
Each GSM radio transceiver uses Time Division Multiplexing
to deliver eight voice circuits on one radio channel. Each radio site
may have one or more transceivers to provide sufficient channels to
end users (maximum numbers are limited by many factors including - operators
radio license, interference with other nearby GSM cells, cost of equipment,
capacity of radio site infrastructure etc.)
A GPRS user may theoretically use all voice channels
on one transceiver - (8 * 14 kbps) but radios to support this are not
available and the operators will probably reserve at least some channels
for voice circuits.
Each 14kbps channel may be shared by multiple 'connected'
GPRS users (many users will be connected to the network but transmitting
very little data). As a user's data requirements grow, they will use
more of the available capacity within that timeslot, and then more available
timeslots up to the maximum available or the maximum supported by their
device.
In general the higher the data rate, the
more power the mobile device will use and the shorter the battery life
and the higher the transmitted RF power. If you are using GPRS with a
mobile phone, do not keep it near your ear for long periods while data
transfers are taking place.
GPRS Mobile devices
The key use for GPRS is to send and receive
data to a computer application such as Email, web browsing or even telemetry
(telemetry refers to devices not being controlled by humans such as cash
point machines or traffic monitoring cameras etc.). To use GPRS the service
is 'dialed' in a similar manner to a standard data call (though there
is no phone no.) at which point the user is 'attached' and an IP address
is allocated. From then on data can flow to and from the Internet until
either the network unattaches you (maybe because of a time-out, fault
or congestion) or you manually unattach.
Mobile workers usually have a mobile phone,
when this includes GPRS then it can also be used to transfer data to an
connected computer.
Some of the key issues are:
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Using GPRS will not stop you making or
receiving voice calls. |
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Current phones will usually suspend the
data session while a voice call takes place. |
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Battery life will be reduced when using
GPRS. |
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The data needs to be connected with your
computer. |
The three standard methods to connect your computer to
GPRS mobile phone are:
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Infrared - available on most business
mobile phones - just align the IR. port on the phone with the IR.
port on the Laptop. |
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Data-cable - reliable and doesn't
require the careful alignment of IR. which may be difficult when traveling |
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Bluetooth - My preferred solution
- often difficult to set up but once its configured Bluetooth provides
a very convenient connection. Bluetooth is available for connecting
to Laptops via USB, PC-cards or CF-cards in addition to cards for
PDAs such as those offered by PALM. Older Compaq IPAQs will require
an expansion jacket but newer Pocket PC devices usually include a
suitable expansion port (check at the time of purchase). One very
important point is that Bluetooth devices are very low powered so
do not drain your computer battery or phone battery too much. Many
people will be tempted by the all-in-one phone/PDA, but consider will
you be happy with the relatively short battery life, large size and
weight and unreliability of many PocketPC devices. |
GPRS data cards are also available, the issues here are:
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Fully integrated solution |
|
Best in Laptops with PC card expansion
slots |
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GPRS will drain your battery so expect
reduced life |
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You can subscribe to a different network
than your GSM voice supplier |
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GPRS data cards will have their own SIM
card and hence will need another subscription to your mobile network |
GPRS Roaming
In the short term don't
expect to be able to roam to many countries with GPRS, many networks are
still negotiating to set up roaming agreements. Technically there are
two type of GPRS Roaming
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Home Network Roaming - Here all
data is transmitted from wherever you connect to a GPRS network to
your home GPRS network where it is connected to the Internet or your
company LAN as if you were indeed in your home country. |
|
Local Network Roaming - Data is
just connected to a local Internet connection point and will be subject
to local conditions for security and performance. |
GPRS users would be advised to ensure they also are able
to use either GSM or High Speed GSM data (HSCSD) to retrieve their data
when traveling because of the changing state of GPRS roaming agreements.
They can either phone their ISP or RAS server on their home network or
subscribe to an ISP which provides local access points in each country
visited.
GPRS Security
The radio interface is considered to be relatively
secure being controlled by the GSM network's security - (SIM card + HLR).
Security issues arise when data needs to leave the GPRS network to be
delivered to either the Internet or a company LAN.
Internet connectivity is the cheapest and
most common - and here you can take charge of security by encrypting sensitive
data. If your GPRS network supplier allows it you can set up encrypted
VPN connections to your company systems - though there could be a performance
hit. Treat the connection as a standard dial-up Internet connection to
an ISP and take similar security precautions.
Network Connectivity
As a business GPRS user you will have a choice
of methods to connect to the GPRS network - by far the most common method
will be via the Internet. For larger users you may connect your company
LAN to the GPRS networks using leased lines or Frame Relay virtual circuits.
Internet
Your company probable already has an Internet
connection (though you may need more capacity if you add many GPRS users)
and this provides a quick and easy way of connection to GPRS.
The key problem is to deliver your data SECURELY
to your users, using strong encryption such as with SSL (128 bit) or VPN
(162 bit).
For secure company Email access you have
a number of choices. These include:
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VPN firewalls - this will provide secure
access to everything on the company LAN from GPRS and other Internet
users. |
|
Microsoft Mobile Information Server |
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WAP interfaces to your Email system e.g.
Peramon |
|
POP server - set up a company POP server
to provide Internet based Email, make sure to enable additional security
if required. |
Employees (often senior managers) often bypass
a companies security systems by redirecting to personal Internet Email
accounts which provides them with a quick fix to mobile connectivity.
Leased Lines
Leased lines provide the most secure method of connecting
to GPRS but are traditionally expensive and have long contract periods.
(Min 1 year)
The protocol over the leased line would normally be
frame relay but it is possible you could use ATM with some networks.
You do not really need any CPE (Customer Premises Equipment) supplied
by your GPRS network supplier, just a spare Frame relay port on an existing
router. There may be economies to be made if you also use the leased
line to carry standard voice and data and bulk SMS in addition to the
GPRS traffic - in which case your network supplier will provide a device
to route these onto your network. They may also try to sell you consultancy
to design this interface - shop around to get the best solution.
Keep costs down by connecting to a geographically close
connection point to the chosen GPRS network. Not all networks have the
same number and location of connection points (GGSNs in GPRS terms).
Frame Relay
If
you already have a frame relay connection with one of the key UK network
suppliers then adding an addition PVC (Private Virtual Circuit) to one
of the GPRS networks will make a cost effective solution, even if you
have to increase the size of the link.
Ask your network supplier
about availability figures as it is important they have redundant connections
to the chosen Frame supplier.
Further Reading
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