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·GPRS. |
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| 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.
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.
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:
The three standard methods to connect your computer to GPRS mobile phone are:
GPRS data cards are also available, the issues here are:
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
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.
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.
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.
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:
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 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).
If you already have a frame relay connection with one of the key Ask your network supplier about availability figures as it is important they have redundant connections to the chosen Frame supplier. |
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Because everybody is different and has different requirements, we will start off by outlining what we see as key features you should consider when selecting a new business mobile phone. There are features such as Bluetooth that you may not need today but will be invaluable as you become more ‘connected’ with the wireless data world. Features you should consider include:
Everyday we are seeing more and more connectivity options for PDAs of all types, some come with built-in GPRS or Bluetooth, or have expansion slots or connectors where you can plug in a cable or Bluetooth radio. Most come with IR. One Box Solution PDA manufacturers are beginning to include GPRS radios within their PDAs. We (at GPRShelp) originally had a Trium Mondo which provided an insight into what these devices were capable of. Now there are many far more advanced solutions such as the HP Jonarda 568 which has a built in GPRS mobile phone and PocketPC 2002 operating system. Palm are about to launch their Tungsten W which adds a GPRS phone and mini keyboard to the familiar PALM operating system. The big question remains, do you want to stick your PDA up to your ear to make phone calls or rely on the hands-free kit. If you upgrade either of the above devices with a Bluetooth radio you could possibly use a hands-free Bluetooth headset – but after trying all these solution I am sticking to using Bluetooth to connect my IPAQ to my T68i, or my Desktop PC with a TDK Systems Bluetooth adapter. Remember your phone comes with a good car kit, good battery life, is very reliable even though it is frequently dropped, and is small enough to fit in your shirt pocket. PDAs are not always as reliable – especially the PocketPC powered versions, both my IPAQ 3870 and Jonarda often require resetting after software errors. 1) get a data only SIM for the PDA from your network supplier or The second combination is my preferred solution as the battery life of your PDA is relatively unaffected by the low-power Bluetooth, you have a single SIM/account for your phone and it still works in your car. The PDA will connect/synchronize whenever you are within range 5-10m and it all happens automatically. Two Box Solution This is the traditional way of connecting your PDA with a GPRS enabled mobile phone. Pretty clunky if you have to plug in a cable or align the IR. ports but works well for the occasional use. As soon as you switch on Bluetooth this solution flies – your PDAs battery life is not reduced significantly and you still have a good mobile for all that voice traffic. Even if you have an older PDA without Bluetooth it is usually an easy process to upgrade by plugging in a Bluetooth expansion module – this will work with many PDAs including the market leading Compaq IPAQs and PALMs. Once you have Bluetooth it is an easy step to connect to other Bluetooth devices – get yourself a:
With a laptop you have a choice of how to connect to GPRS, these include: IR. - Works fine as long as the phone and laptop IR. windows are aligned (OK on a desk but often difficult on the train or in the car). Cable - Again this works fine but you do have to plug it in when you want to use it. Some data cables can be as expensive as a Bluetooth adapter. Bluetooth - This has to be the most versatile as you can connect with your phone for GPRS and synchronization of its address book, and you can connect with your PDA for synchronization. You can also use it as a wireless LAN card for connecting to a Internet enabled desktop computer running Internet Connection Sharing. Bluetooth may integrated into your laptop if it is fairly new or may easily be upgraded with either a USB or PC card Bluetooth adapter. GPRS PC Data Card - The latest GPRS data cards provide four uplink slots and four downlink slots – this is far higher than we are likely to see from a mobile phone. The result is that you will benefit from faster Internet access and much faster sending of emails or FTP than you would get from a two-box solution. The downside is the cost of the card and you will also require an additional SIM card. Most data cards provide a voice circuit but this is of limited use as it will only work with the Laptop powered up. |
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The fundamental data speeds for most mobile data connections is much slower than that achieved with LANs, wireless LANs or even Dial-up connections using a 56k modem. For Email and messaging use, these slow speed should not be a problem, but for Internet/Intranet access the user experience will be poor unless the system is configured properly and the (Intranet) site designed efficiently. The three choices for mobile data are Circuit Switched Data (called CSD or GSM Data), High Speed Circuit Switch Data (called HSCSD or High Speed Data) or GPRS (General Packet Radio Service). To summarize real world data rates for these services:
* In the UK High Speed Circuit Switched Data (HSCSD) is only available from ** These are the maximum rates achievable – GPRS users share bandwidth with other GPRS and Voice users which will often restrict the data rate. New terminals using more timeslots will increase these maximums. One of the key differences between using GPRS and the other forms of mobile data – GSM CSD or HSCSD is that with GPRS you share the radio bandwidth with other users. Congestion will soon reduce the speed of you connection during busy times during the day and in busy locations. The GSM CSD and HSCSD provide a fixed speed connection though you need to dial up each time it is used and then disconnect at the end of the data call. Another point in favour of GPRS is that many networks have introduced compression systems to speed up delivery of Internet content to browsers. Transparent to the user, sites appear quicker with the apparent speed of the connection being much faster than the actual speed – some manufacturers claim a five times improvement in speed.
As e-mail is not real time, speed only becomes an issue when sending and receiving large attachments. Sending is particularly difficult as many terminals only have a single channel uplink running at 9-14kbps. Some GPRS providers are offering email compression software that provides loss-less compresion on the GPRS network for incoming emails. Outgoing emails are under your control so it is easy to compress with one of the common utilities to produce a ZIP or CAB file. If you fall back to one of the dial up data services when GPRS is busy or unavailable (e.g. when traveling to countries without a roaming network), you must be careful how often you set you Email application to check for emails. Though the call may be short there is often a minimum charge, and checking every five minutes will soon produce a big bill.
To achieve the best performance you should 1) Choose a network with good compression/optimization for WWW browsing. Not all networks will have this but it can make web browsing approximately 5 times faster – often better than a dial-up connection. 2) Purchase a terminal (phone or PC data card) with a GPRS radio that utilise as many timeslots as possible – some devices were 1 timeslot up (from the phone to the network) and two slots down, more recent devices are 1 up and four down, making web browsing far more usable. 3) Watch out for congestion on the radio network. As there are a fixed number of radio timeslots shared between all voice + data users, during busy periods the GPRS performance will drop dramatically. The performance of the GPRS connection may be monitored with a useful free utility call DUNMON which provides a graphical display of up and down data speeds. 4) Configure your email application with care to avoid unecessary bills if using a dial-up mobile service (CSD, HSCSD). |