GPRS - A Key Step For The Mobile Internet

All right, let's put our teeth into yet another acronym. To many of us it might appear that all these Internet and wireless technologies make a scene of furious and diverse competitors, all fighting for market acceptance and penetration. In this article, the Author will show how today's mobile systems migrate smoothly into the 3G (3rd Generation) wireless systems of the future. A key step in this migration is GPRS, General Packet Radio Services, due at the end of 2000. This article will show that this technology will make the use of the Mobile Internet much easier, and that it is not competing with IP, WAP or whatever your favorite acronym might be. The article's first half explains the basics at a high level, while the second half starts to move into some details.

Always Online

The wireless/mobile/cellular systems of today are sometimes called 2G (2nd Generation) systems, with the first being the early analog systems. With the boom of the Internet and the massive spread of both computers and cellular phones, it is likely that we will want to get access to more than voice services and applications when we are on the go.

The Mobile Internet is something that has started over the last year, with WAP, Wireless Application Protocol (Europe, USA), Palm.net (USA) and I-Mode (Japan). What WAP does to the cell phone is what the web browser did to the computer. It enables non-Rocket-scientists to access the information anytime, anywhere and on any device. WAP is an open standard that is now rapidly spreading throughout the world. If you want to use WAP today, you will connect to the servers with a cell phone using circuit switched data. That works much like computer modems, where you dial in to an ISP (Internet service provider), do your e-mail and surf the web and then disconnect. If you want to do it again, you have to dial in again. Compare that to the connection some of us have at work or at school, where your connection to the Internet is always there, always online. The web browser starts as quickly as a word processor, and the remote Internet services are just one click away. That is exactly the functionality that GPRS adds to the cell phones and the Mobile Internet, enabling the user to be always connected, always online (without necessarily having to pay by the minute). The functionality means a tremendous change in the way we will use the cell phone and probably also the home PC. In order to clarify this new feature, this example shows how the same application, getting a last-minute trip, changes with GPRS.

Home PC: You go home to your PC and check the website where they have offers on cheap tickets. You dial in, wait and then you can check what is available and what the price is. If you're in luck, the site might even have e-mail alerts that will tell you when something comes up (most of us will have to dial in every hour to check if we have gotten that mail).

Cell phone today: With a WAP phone, you can do access a similar site and check if something interesting comes up. You dial in, check if there are any offers, no matter where you are. That procedure is then repeated until you find something interesting.

Cell phone with GPRS and WAP: The GPRS phone is always online, so you can access the site with the tickets, anywhere and anytime. You click on the kind of preferences you want (Hawaii, Max $300, Sometime in May). The application that handles the last-minute tickets can then keep that request in mind and notify you whenever something comes up. You can walk around relaxed, not bound to a single location or forced to check something on a regular basis.

So, GPRS is the network (like you have a modem at home) and WAP makes the access easy, robust and efficient (like a web browser + much more).

An upgrade to existing systems

GPRS is not a completely new system, but rather an upgrade that empowers existing GSM and TDMA networks (US: PacBell, Voicestream, AT&T etc, Europe and Asia: Everywhere but in Japan and a few other spots). This means that you are still going to have the same functionality for voice calls and it is even possible to have simultaneous voice and data for some handsets. This smooth migration also means that you are going to enjoy the same coverage for GPRS as for present cellular networks, as opposed to building a completely new network from scratch. That way, your present phone will work in the future as well, but you will need a new handset in order to access the new features.

An integral part of 3G wireless systems

3rd Generation wireless systems will bring high speed multimedia services to the Mobile Internet. You will not only be able to surf the web fast, and download e-mail. You will also see a million new applications where high quality voice, text, pictures and interaction is blended. The always-online functionality for most of these 3G systems (WCDMA, EDGE) will be reused from GPRS. So, in the same way that operators are upgrading to get GPRS functionality this year, they will upgrade in 2001,2002 to get full 3G functionality. The packet data functionality of these systems is GPRS. Also, the future systems are built bottom up to facilitate compatibility with GPRS, so once again, the devices you buy now will work in the future as well.

A view of a GPRS end-to-end

The picture shows the architecture where individual nodes have been taken out. Starting from the left you will have a GPRS enabled handset. That can be just about anything, from a laptop with a GPRS PC-card, a handheld computer (like the Ericsson MC218) that talks to a GPRS mobile via Bluetooth (short range radio), a feature phone (like the Ericsson R380), to a phone centric WAP phone (R320). The transmission speed when using GPRS is very much determined by the capabilities of the handset. The two main properties are the number of timeslots (each timeslot is the capacity equivalent of a voice call, thus around 10kbps per timeslot) and the class of the handsets.

• Class A handsets can do both voice and data at the same time (simultaneously)
• Class B handsets are voice and packet data capable, but not at the same time
• Class C handsets can handle packet data only (or they can be set manually to handle one or the other)

So, a 4+1, Class B handset has packet data capabilities, but your information retrieval will be paused whenever someone calls you. The capacity will be roughly 40kbps download (receiving) and 10kbps upload (sending) maximum. It will be common to have less capacity for sending, as it consumes much more power to send than to receive. In a mobile handset you always want to minimize power consumption as high power means battery drain and heat generation.

Different vendors of handsets will have different configurations on their handsets, but three general comments are of interest for application developers:

• There will still be a huge market for small devices with small screens
• Most devices will have higher receiving speed that transmission speed
• Class B mobiles are going to be common, at least initially, as they are cost and time efficient to make.

The Network

The existing cellular infrastructure will be upgraded, mainly by adding new software. That means operators do not have to travel to remote sites but can perform centralized updates into GPRS functionality. In addition, there are certain hardware elements that need to be added in order to build the IP infrastructure needed for packet data services. The SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node) are mobile network equivalents of routers and gateways. The SGSN assigns IP addresses, tracks the movement of the user to know where to send packets and ensures that the connection is secure. The GGSN is a gateway to other networks, ISP's, dynamic IP allocation etc. The GGSN and SGSN can either be co-located or located in different parts of an IP network.

As GPRS introduces packet data into mobile systems, it will be hard to use the traditional way of calling whenever we want to use some application or web site. GPRS has full Internet functionality from day one, and thus uses IP addresses to connect to servers. IP addresses can basically be assigned in three ways:

• Fixed: IP address stored in the HLR
• Dynamic: A set of IP addresses are allocated to the GGSN domain
• Dynamic: The IP address can be allocated by and external ISP (Radius) server

The network might also restrict the capacity for a user, as you will share capacity with other users. Packet switching means that GPRS radio resources are used only when users are actually sending or receiving data. The actual number of users supported depends on the application being used and how much data is being transferred. Rather than dedicating a radio channel to a mobile data user for a fixed period of time, the available radio resource can be shared between several users. Today's voice calls and the data traffic of GPRS will be transported over the same shared set of channels over the air. This means you will see high bitrates when few people are using the network, but lower bitrates at peak hours. Theoretically it is possible to reach 115.2kbps (or 160kbps, depending on how you count), but in reality, bitrates of 10-40 kbps are more likely. GPRS main advantage will not be the high speeds, but rather the always-online functionality.

Applications

The area of Mobile Internet applications is one of the most intense in the world. The operators that have bought billions worth of equipment are now asking: What should we (and our customers, the users) use it for? It is likely going to be such an important question that it will make and break players in the business. Who wants to buy a subscription if there is nothing fun or useful to do with it? Of course, there will be a huge variety of Internet content available but that is only the start of it. The Mobile Internet applications will be so much more. Imagine what could be done if your device knew roughly where you were? The possibilities for the 'Find the closest Starbucks shop' kind of applications show where that could take us. Coming to a new city and clicking on an icon to see what is happening close to your hotel that weekend (all according to your own preset interests, of course). Also, the mobile device that you will use for all these services is much more personal than any other Internet access device. The things you will have in there will reflect your interests and personality. The personalization will take the devices into things that make life easier, not more complicated. That is also in essence what GPRS does for the applications. Where you before dialed in and waited, the information will now only be a click away. Checking the weather where you are will be as easy as looking up a number in the phonebook.

Typical GPRS applications will utilize the always online functionality to its full extent. Things that reside inside your device will do things for you, when you have better things to do. Say you want to buy stocks when the Nasdaq drops below 3000, then you can have your GPRS handset vibrate whenever that happens (while you are hanging out at the beach).

In developing applications for GPRS it is necessary to understand both the new possibilities and new challenges. The bandwidth will vary and sometimes be very low, you will temporarily lose contact with the network and there will be packet loss. Wireless networks are different and you need to consider these properties when developing applications for them.

If you are in the process of developing wireless applications, make sure to sign up as a member at http://www.gprsworld.com (membership is free and open to anyone, not just the ones currently developing for GPRS). You can also drop in at one of the Ericsson GAA test labs for tests in a wireless environment and feedback on how to optimize for wireless.

About The Author