GPRS is a packet-switched service built on the existing Global System for Mobile (GSM) communication voice network. GSM was primarily designed for voice services.

A GSM channel contains eight timeslots (a portion of time allocated to transmit data), with each timeslot dedicated to each circuit-switched call. Traditionally, when using Circuit Switched Data (CSD) — which is explained in more detail in What Is CSD/HSCSD? later in this chapter — you can only use a maximum of one timeslot. With GPRS, timeslots can be assigned dynamically, and you can use more than one single timeslot. This results in increased throughput, which was was previously not possible with CSD. Also, because timeslots are only allocated when required, more users can be supported at any one time.

GSM networks have more worldwide coverage than any other cellular technologies, such as CDMA and PDC (Personal Digital Cellular) used in Japan. In Asia and Europe, the frequencies used for GSM are 900 and 1800 MHz. In North America, it is 1900 MHz. Phones that support these three frequencies are known as tri-band phones. Examples of tri-band phones are the Sony Ericsson T68i and the Nokia 6610.

GPRS uses multiple timeslots for sending data. In theory, GPRS can use up to eight timeslots, but physical constraints (such as the number of users currently on the network as well as the coverage quality) have placed the number to a maximum of five, with one or two timeslots reserved for upstream communications (leaving three or four for downloads).

There are altogether four encoding schemes used in a GPRS network. Table 8-2 shows these and their data rate per timeslot as well as their maximum data speed for eight timeslots. The encoding scheme to be used is determined by the service provider and depends on factors such as the quality of the channel (the radio link between the GPRS device and the base station). CS-1 has the highest reliability (but the lowest data rate) and CS-4 has the least reliability (but the highest data rate).

Each GPRS device also belongs to a particular class. A class determines the number of timeslots used for downloading and uploading. The manufacturer of the GPRS device determines the class of a device.

Table 8-3 shows the 29 classes for GPRS devices. Each class has a designated number of timeslots used for downloading and uploading. The maximum slots column lists the maximum number of timeslots that a device can use simultaneously for downloads and uploads.

To put these numbers into perspective, let’s take an example and illustrate how all these numbers determine the throughput of a GPRS device.

The Nokia D211 GPRS PC card is a Class 6 device (I talk more about this card in the next section). This means that it has 3 timeslots allocated for downloads (sometimes referred as 3+2, for 3 timeslots for downloads and 2 timeslots for uploads). If I use the Nokia D211 in Singapore and myISP supports the CS-2 coding scheme, then the maximum downstream speedof the D211 is (13.4 Kbps x 3), giving a maximum download speed of 40.2 Kbps.

GPRS devices fall into three categories:

GPRS devices are commonly called " GPRS terminals.” These come in different shapes and sizes, but can be grouped into the following categories:

A constantly updated list of GPRS terminals can be found at http://www.gsmworld.com/technology/gprs/terminals.shtml.

GPRS phones

Many new mobile phones support GPRS for data access. Two such phones are the Sony Ericsson T68i and the Nokia 6610 (see Figure 8-1).

Figure 8-1. The Sony Ericsson T68i and the Nokia 6610 (shown with the kind permission of Sony Ericsson; copyright Sony Ericsson 2003)

Using a GPRS-enabled phone, you can access WAP applications on your mobile phone. You can also connect your Windows XP computer to your mobile phone (through Bluetooth or infrared) and use it as a GPRS modem. You can then access the Internet.

What Is a SIM Card?

A SIM is a smart card placed inside a GSM phone that identifies the user account to the network. It handles tasks such as authentication and acts as data storage for user data such as phone numbers, Short Message Service (SMS) messages, and network information. Figure 8-2 shows a SIM card inserted into a mobile phone.

A SIM card may also contain applications that run on the phone.

Tip

Chapter 6 and Chapter 7 discuss how you can use Bluetooth and infrared connections to connect to your GPRS-enabled phone for Internet access.

GPRS modem

For dedicated data access, you can use a GPRS modem. This is usually a PC card that allows you to make data calls. To use a GPRS modem, you need to insert your Subscriber Identity Module (SIM) card into your phone or PCMCIA card; it also requires a subscription to the data service provided by your ISP. The Sierra Wireless Aircard® 750 (see Figure 8-3) is a GPRS modem card that supports GPRS data access in addition to GSM voice calls and SMS messages.

Figure 8-2. A SIM card inserted into a mobile phone

Figure 8-3. The Sierra Wireless Aircard 750

GPRS modules

GPRS modules are commonly used by vertical application developers such as value-added service providers and equipment manufacturers.

The Sony Ericsson GM47/GM48 (see Figure 8-4) is a radio device that can be incorporated into other devices such as a vending machine, an alarm monitoring system, etc. It allows systems developers to build GPRS (and GSM) functionality into their systems.

Figure 8-4. The Sony Ericsson GM47/GM48 GSM module (shown with the kind permission of Sony Ericsson; copyright Sony Ericsson 2003)

The Sony Ericsson GM29 (see Figure 8-5) uses the GM47/GM48 hardware module. The GM29 is marketed as a GSM/GPRS modem. It is a Class B (4+1) device with an RS232 connection.

Figure 8-5. The Sony Ericsson GM29 GSM/GPRS modem (shown with the kind permission of Sony Ericsson; copyright Sony Ericsson 2003)

The Nokia D211 (see Figure 8-6) and D311 are multimode radio cards (PCMCIA cards) that support GPRS, CSD (Circuit Switched Data), HSCSD (High Speed Circuit Switched Data; D211 only), and 802.11b networks. It is slightly longer than a conventional wireless card and combines the best of both worlds: allowing you to access a wireless network as well as connect to the Internet through GPRS when a wireless network is not available. The beauty of the D211 is that all these functionalities are integrated in one card, which makes it ideal for road warriors. The only downside is that you cannot make voice calls using the D211; otherwise, the card would be perfect.

Figure 8-6. The Nokia D211

Configuring WLAN access

The Nokia D211 and D311 support 802.11b wireless network access. Let’s configure the card for wireless access now. Here are the steps:

1. Ensure that you have selected the Profiles function from the Nokia D211 Manager.

2. Click on the Modify tab.

3. Click on New....

4. Give your profile a name, e.g., Home Network (see Figure 8-9). Also check the connection type(s) to be used for this profile. In other words, you can use this profile to connect to a WLAN connection, GSM connection, or GPRS connection (for our example here, let’s just turn on the WLAN connection checkbox). Click Next.

Figure 8-9. Creating a new profile

SMS Craze in Asia

SMS messaging is very popular in Asia. In Singapore, teenagers can often input text faster (using numeric keypads on the phones) than you can type on a computer keyboard!

The following is an explanation of how to type messages on your mobile phone.

Each numeric key on your phone is assigned three to four alphabetic characters:

2 - a, b, c
3 - d, e, f
4 - g, h, i
5 - j, k, l
6 - m, n, o
7 - p, q, r, s
8 - t, u, v
9 - w, x, y, z

To form a word, you need to press the corresponding digits that make up the letters of a word. For example, to form the word “is,” you would press “4” three times (“i” is the third alphabet in this assignment) and then press “7” four times. This input method is commonly known as the “multitap” method.

But most mobile phones sold today support the T9 input method. T9 stands for “Text on 9 keys.” Here is how T9 works. Look for the letters that you want and press the assigned digit once. Using the same example, to form the word “is,” press “4,” followed by “7.” A phone utilizing the T9 technology has a compressed database of all the commonly used words. In this case, the database returns “is” as a likely word.

There are many cases when a particular key sequence may generate multiple words, such as the sequence “4663.” Two possible words are “good” and “home.” So, as a user you just need to select the word that you want. If a desired word cannot be found in the database, you have the option to add it in.

Try it on your mobile phone and see if you can type faster than on a keyboard!

For more information on T9 input, go to http://www.t9.com/.

TDMA

The predecessor of CDMA is Time Division Multiple Access (TDMA). TDMA operates similarly to network packet switching — it divides the signal into multiple segments, thereby allowing multiple calls to take place. Unlike CDMA, TDMA does not utilize Spread Spectrum Technology and hence the available spectrum must be divided into channels, which means fewer users are supported simultaneously than with CDMA.

1. You will be prompted to select the wireless mode (Infrastructure or ad-hoc). The SSID(s) of the available wireless networks will also be displayed (see Figure 8-10). Select the SSID of the wireless network to which you want to connect. Click Next.

   

   Figure 8-10. Selecting the wireless mode

2. On the next screen, you have the option to specify your IP address manually. We will use the IP address allocated by the wireless network. Click Next.

3. The main screen of the Nokia D211 Manager will be displayed again (see Figure 8-8). Click Select... to choose the profile to use. Select the WLAN connection type under the Home Network item (see Figure 8-11).

   

   Figure 8-11. Selecting the wireless connection

4. You should now be able to connect to the wireless network. Information about the connection, such as the connection quality and data flow, is displayed (see Figure 8-12).

Figure 8-12. Viewing the wireless connection information

Configuring GPRS access

Let’s now configure the Nokia D211 for GPRS access. For this, you need to insert your SIM card into the D211 before you can connect to the GPRS network. If you purchased the D211 or D311 along with a wireless plan from a cellular provider, the SIM card may have been installed for you. Otherwise, you will have to use a SIM card from another phone.

1. In the D211 Manager, click on Profiles, then click the Modify tab.

2. Select the profile to which you want to add GPRS access.

3. Click on GPRS (see Figure 8-13). Turn on the “Use GPRS connection with this profile” and “Specify access point name manually” options. Enter the GPRS access point name provided by your ISP.

   

   Figure 8-13. Using a GPRS connection

4. Click OK and return to the main screen by clicking on the General tab.

5. Click Select... and choose the GPRS item (see Figure 8-14).

   

   Figure 8-14. Selecting the GPRS connection

6. Click the Activate button (see Figure 8-15).

   

   Figure 8-15. Activating GPRS access

7. A Dial-up Connection window appears (see Figure 8-16). Enter your username and password (provided by your ISP).

   

   Figure 8-16. Dialing up GPRS

8. When authenticated, you should now see the operational information (see Figure 8-17).

Figure 8-17. Viewing the GPRS connection information

Messaging using SMS on the Nokia D211

One interesting feature of the Nokia D211 is the ability to send and receive SMS (Short Message Service) messages. In the Nokia D211 Manager window (see Figure 8-18), click SMS → Inbox (or any other items within the SMS menu to launch the Nokia Short Messaging window).

Figure 8-18. Invoking the SMS functionality

This window contains five main tabs: Inbox, Outbox, Sent messages, Delivery reports and Contacts (see Figure 8-19). To send a message, simply click the Send message icon and type your text.

Figure 8-19. The Nokia Short Messaging window