The Wireless World
In the wireless world, the distinctions between LAN and WAN or between public and private networks are less clearly defined. Radio waves don't respect legal boundaries or even physical walls, meaning that private transmissions can spill over into the public space. The first effect of this has been to expose private data to all comers, thanks to unencrypted wireless LANs. In the future, it could change how people access the Internet or make phone calls.
The companies that run wireless networks want people to use the public WAN. Their vision of the future is something similar to that shown in Figure 1.1, where each wireless device has its own separate, long-distance connection. This means that users have to pay the companies for access and that the devices can be used almost anywhere. A cell phone user can travel many miles while making a call, often without the connection being broken.
Wireless WAN: Devices communicate with base station several km away.
Many people have an alternative vision, shown in Figure 1.2. This uses a small LAN access point within the home or office, connected via a fixed network to the Internet and the phone system. Cordless phones and wireless-equipped computers communicate with the access point, which aggregates all their voice and data together and sends it over a single connection. The advantage of this is that it's cheaper—one connection costs less than many—and can achieve higher data rates, thanks to the shorter range of the wireless signal and the high capacity of the fixed network. The disadvantage is that the phones and computers can't be carried out of range of the access point while maintaining a connection.
For narrowband voice, the WAN philosophy seems to be winning: Many people in Europe have a mobile as a "primary" phone, using it for all calls, even when at home. The same is beginning to happen in North America, though only for long-distance calls. This is partly because the cell phone is more convenient and partly because aggressive competition keeps cell phone charges relatively cheap, whereas fixed telephony is often run by a de facto monopoly.
For broadband data, the situation is reversed. No WAN technologies can yet match the speed of wireless LANs, so many people prefer to set up their own wireless LAN and connect it to some kind of high-speed fixed-access technology. This is usually a cable in the ground, as shown in the figure, but in future may be a point-to-point wireless system, such as a laser beam. It's also possible that the WAN and LAN will converge as mobile operators set up wireless access points of their own.
Wireless LAN: Devices communicate with access point less than 100 m away.
Cell Phone Generations
The present hype is around third-generation (3G) phones, which will provide most of the advanced services planned until at least 2010. But it's worth looking at the other generations and the features they offer:
- 1G. First-generation phones are analog, meaning that they send information as a continuously varying wave form. They can be used only for voice and have highly variable call quality, thanks to interference. Another serious disadvantage is that they are very insecure; snoopers can listen in on calls with a simple radio tuner or can even charge calls to another person's account.
Almost no new 1G networks are now built anywhere in the world, but the phones to use with them are still manufactured. Europe and Japan both gave them up in the 1990s, upgrading to digital systems. North America is not as far advanced, but it's moving in the same direction: At the beginning of 2002, about 30% of U.S. subscribers relied on 1G phones, down from twice as large a proportion two years earlier. They are more popular in some parts of Africa and South America, thanks to their low cost, but even there, they will soon be squeezed out by second-generation (2G) and even 3G technology.
- 2G. Second-generation phones convert all speech into digital code, resulting in a clearer signal that can be encrypted for security or compressed for greater efficiency. Most also include some kind of simple text messaging, as well as support for Centrex-style services, such as voice mail and Caller ID. The most popular is the Global System for Mobile Communications (GSM), but several others are used around the world. They can send data, but usually at less than 10 kilobits per second (kbps); by comparison, most modems achieve a real speed of at least 30 kbps. Some data-only devices, such as two-way pagers, are also considered to be 2G, because they send a digital signal at relatively low speeds.
Most cellular operators are upgrading their 2G networks to higher data speeds, theoretically more than 100 kbps but more realistically those of a fast modem (about 40 kbps or less). These are referred to as 2.5G, because they are significantly better than existing 2G systems but less advanced than the more futuristic 3G. As well as offering higher data rates, they often use packet-switching for data, a more efficient way of sharing a connection between many users. This is the same system used by the Internet, so it makes interconnection between the phone and the Internet easier.
Some 2.5G upgrades don't try to reach higher data rates, instead adding the capability for specific applications. Wireless Application Protocol (WAP) and i-mode both use a compressed version of the Web to fit into a mobile phone's slow data rate and small screen. Location technologies can find a user's exact position, intended both for emergency calls and for services such as maps.
- 3G. Third-generation systems will provide a variety of advanced services, including data transfer at up to 2 megabits per second (Mbps) and videoconferencing. Instead of phones, many terminals will be small computers or PDAs (personal digital assistants) with built-in Web browsers and possibly other applications, such as word processors, spreadsheets, and address books. They will include small keyboards, handwriting recognition, and, eventually, voice recognition.
Like many new technologies, 3G has initially been disappointing. The first data rates of the first terminals are only 64 kbps, less than those once envisaged for 2.5G, let alone 3G. Many companies admitted that the expected 2 Mbps would be available only for users standing right next to a base station tower. These initial services are sometimes referred to as 3G lite. At the other end of the scale, many researchers are working on enhancements to 3G that they claim really will reach the hoped-for data rate and beyond. These are known as 3.5G.
Figure 1.3Many 3G terminals will also be able to link to a PAN, which links all the devices in a very small area, such as a room or even a person's pocket. The most promising technology for this is Bluetooth, which puts a very low-power radio into a single microchip. Bluetooth's designers envisage a chip inside almost all household devices, as shown in Figure 1.3, enabling them all to connect to the Internet via a 3G terminal.
Wirelessly networked home.
- 4G. Fourth-generation networks are already in the labs, with Japanese operator NTT DoCoMo planning to offer the first commercial services in 2006. They will offer very high data rates, perhaps as much as 100 Mbps, enabling new services that have not yet been invented. They will also be focused primarily on data, using packet-switching for all traffic and replacing basic voice service with video or even virtual reality.
Many wireless LAN technologies already come close to 4G's hoped-for data rates, though they don't offer the service guarantees or roaming capability that users of cell phones expect. If these can be added to wireless LANs, 4G may actually arrive earlier than expected.
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