Modems

One of the primary uses for portable computers is to keep in touch with the home office. The traditional method for remote access is to use a modem, but nowadays an increasing amount of remote communication is done with a broadband connection, such as DSL or a cable modem, attached to a network interface in the laptop. It is not uncommon to find hotels, coffee shops , and airports that offer high-speed connections. In addition, some areas of the country offer wide-area high-speed wireless connections. For the near future, however, travelers will have to assume that in many cases the only communication mode available to their laptops is the slow but usually dependable dial-up modem connection.

Although we may have all used a modem, some of us may not know exactly how it works. Traditionally, a modem works by modulating a stream of digital pulses into an audio signal. The process is similar to the way a radio transmitter modulates relatively low-frequency speech and music into a high-frequency carrier wave. On the other end of the connection, the modem then demodulates the audio signal to obtain the original stream of digital pulses . The name modem in fact derives from its function: mo dulate, dem odulate.

The maximum speed that can be obtained using a modulation/demodulation technique is 33Kbps, the speed provided by the V.34 modems that became available in the mid-1990s. In 1998, the V.90 modem standard attempted to bypass this speed restriction by avoiding the modulation step for one half of the communication path. Because typical Web usage requires much more data being sent downstream from the Web site to the Web viewer, this mode was speeded up to 56Kbps by using pulse-code modulation ”a method similar to that used to encode data on a CD-ROM disc. The upstream path , which usually handles less data, continued to be limited to 33Kbps.

Unfortunately, even a simple modem connection cannot be taken for granted. Most hotel rooms in the United States provide an easily accessible phone-line connector for use with a laptop modem. But a few do not. In fact, many places still exist where finding a phone line to plug in to can be a real challenge. Products are now on the market, however, that can help you overcome these problems, even if you are traveling overseas.

V.92 Modems

Ever since the dawn of personal computers in the 1970s, we have seen continual and dramatic advances in modem speeds. Now, however, with the popularity of broadband DSL connections, modem advancements seem to have stalled. The latest modem standard, called V.92, was introduced by the International Telecommunication Union in July of 2000 and represented only a minor advancement over the previous V.90 standard.

The older V.90 standard for modems provided data rates up to 56Kbps over Plain Old Telephone Service (POTS) lines. The V.92 added the following enhancements:

• An increase of more than 40% in the maximum data rate in the upstream direction (toward the network) to a new maximum of 48Kbps on the best connections

• Significantly quicker startup times on recognized connections

• The ability to put the modem "on hold" when the network indicates that an incoming call is waiting

To increase effective modem speeds further, the ITU recommended a new data-compression standard called V.44, based on the LZJH compression algorithm developed by Hughes Network Systems. This technique gives an improvement in compression of more than 25% beyond the existing ITU recommendation V.42bis. The ITU expects a data-compression ratio in the region of 6:1 for a typical Web-browsing connection. The net result should be an effective data throughput rate in excess of 300Kbps, compared with typical values of 150 “200Kbps today, thus significantly reducing download times and speeding up Web browsing.

As most modem users will agree, the actual data rates seen over typical phone lines are below these estimates and indeed well below those available from DSL technologies. The V.92 standard has the advantage, however, of not requiring any special installation on the part of the network provider, leaving upgrades solely up to the direct control of ISPs and users.

Although broadband connections are the preferred communication type for most users, the fact is that in most of the world, modems will be the state of the art for some time to come.

Because of the popularity of modems and their low cost, almost all of today's notebooks are equipped with them as standard. They are sometimes installed as mini-PCI cards. In the recent past, manufacturers would install a combination mini-PCI card that included both a modem and a network interface card (NIC). As the development of new modem standards has slowed and the probability of new standards in the near future has decreased, we now have seen V.92 modem circuitry integrated directly onto the motherboard of the laptops.

There are, however, a number of older laptops not equipped with modems. These systems can be equipped with external modems connected by a serial cord, but a much more portable approach is to insert a PC Card modem into one of the laptop's PCMCIA slots.

PC Card Modems

Most current laptops have internal modems installed in them. In previous days, however, the only way to equip a notebook computer with a modem was to use a modem in the form of a PCMCIA or PC Card.

Of course, a Type II PC Card is only 5.5mm (0.19 inches) thick, which does not leave enough room for a standard RJ-11 phone line connector. To provide this connection, manufacturers came up with three different solutions:

• The dongle or pigtail ” This is a relatively short piece of cable with different connectors at each end. One of these connectors is flat enough to attach to the PC Card modem. The other is a RJ-11 phone connector. Early dongles were only a few inches long and had an appearance that gave rise to the nickname pigtail . These cables had a female phone connector and were designed to be used with a standard phone cable. More recent dongles have a much longer cable and terminate in a male connector that can be plugged directly into a phone jack without the need for an additional cable (see Figure 12.1). Dongles were very popular with modem manufacturers, especially because users would continually lose them and pay sometimes as much as $99 to replace them. Nowadays, dongles can be purchased for as little as $19 from companies such as Computer Heaven.

  Figure 12.1. An example of a dongle used to connect a PC Card modem to a phone jack. (Photo from Computer Heaven, Inc., www.computerheaven.com.)

  

• The XJACK connector ” This is an ingenious connector that looks like a cross-section of a typical RJ-11 phone jack. It is so thin that it can slide in and out of a PC Card modem. The phone line attaches in a vertical direction. When the phone line is not connected, the jack can be pushed back into the PC card, thereby protecting it. The only problem with the XJACK connector is that it can be damaged by excessive tension on the phone line, such as when someone trips over it. But it is easier to replace a broken modem card than to replace a notebook that has gone crashing to the floor.

• The Type III card ” Perhaps the simplest way to connect a phone line to a thin Type II PC Card is to use a thick Type III card instead. It turns out that a Type III card, which is so thick it takes up two Type II card slots, can accommodate both a standard RJ-11 phone jack and an RJ-45 LAN connector.

Even though most of today's notebooks already have a modem installed internally, some people would benefit from carrying around a spare PC Card modem as well, especially if the modem has special features, such as the ability to handle international phone systems or voice calls. A PC Card modem is extremely light and often comes in handy if the laptop's internal modem ever stops working.

Winmodems

Many modems are not really modems at all but simply enhanced connectors. These so-called "Winmodems" depend on Windows programs that instruct the laptop's CPU to do all the processing that the modem normally does. These modems have gotten better, partly because today's Pentium processors are so powerful that they can easily accommodate the relatively slight amount of work required by a 56Kbps modem. Winmodems are inexpensive, often less than half the cost of a real modem, but they are dependent on Windows. In general, a real modem still outperforms a Winmodem and also has the benefit of working under DOS, Linux, or any other non-Windows environment.

Caution

Some phone lines can be hazardous to the health of your modem. Many hotels and offices use digital PBXs for their telephone systems. These systems typically carry more current than standard analog phone lines. This power is needed to operate additional features on the telephone, such as message lights and LCD displays. Unfortunately, this additional current can permanently damage the tiny modems found in PC Cards or integrated onto the motherboard of your laptop. Visually, there is no way to tell whether a phone system is digital or analog, because they both use the same standard RJ-11 connectors.

To avoid frying your laptop's internal modem, you can purchase a line-testing device ”usually called a Modem-Saver ”for about $30 that plugs in to a wall jack and measures the amount of current on the circuit. It then informs you whether it is safe to plug in your modem.

If the line is not safe, you may still use it with your laptop's modem, but only with certain protection. A company called Konexx (www.konexx.com) sells a device for about $130 that plugs in to the handset jack on a standard phone and protects your modem from any dangerous currents on a digital PBX system.

Wireless Modems

The traditional modem is indeed a handy tool, but its usefulness disappears as soon as you move more than about 10 feet away from a phone jack. A wireless networking adapter lengthens your communications leash to about 200 feet, but the number of wireless networks is still relatively small. All this effectively means that for most of the world's surface area, your laptop is incommunicado ”unless of course you have a wireless modem.

There are basically three ways to connect a wireless modem to your laptop. The first is to use a cellular modem, usually in a PC Card format. As the name implies, these devices rely on the increasingly omnipresent cellular phone networks and can be used anywhere you can get cellular phone coverage. The second approach is to use your cell phone itself as a cellular modem. The third option is only for those who frequently travel outside the cellular phone coverage: using a satellite phone as a modem.

Note that all wireless modems have traditionally suffered from a speed penalty. Until fairly recently, wireless modems typically operated at a speed of only about 14.4Kbps or less.

In recent years the press began promoting so-called third-generation or 3G cellular technology. (The first cellular generation was analog and is usually referred to as AMPS , or Advanced Mobile Phone System . The second generation was digital and is based on one of several technologies, such as TDMA, CDMA, and GSM.) The new 3G technology promised high-speed data communications; in some cases the claims were as high as 2Mbps. More reasonable claims touted 384Kbps. In actual fact, the "3G" systems that have appeared to date are capable of a maximum data rate of only about 128Kbps or even just 56Kbps. Because of this, they are sometimes referred to as 2.5G systems . Although still slow by wired networking standards, 3G systems are still an order of magnitude better than previous wireless and WAN standards.

Circuit-Switched Versus Packet-Switched Connections

Most wireless modems make connections in two ways. The first is circuit-switched mode , which is identical to the traditional dial-up connection on a wired modem. Here, the user dials a connection to a host system, communicates for a given amount of time, and then disconnects the call.

The second is packet-switched mode . With this type of connection, the wireless modem is in effect always connected to the host system, in much the same way a home computer is always connected to the Internet via DSL or a cable modem. Data is sent back and forth in packets.

Choosing which mode to use depends on what type of data will be transmitted and how the cellular phone company is charging for the service. Circuit-switched connections are usually charged on a per-minute rate. Packet-switched connections are charged usually by the megabyte of data transferred. If the cellular company charges a low fee for each voice call or if you tend to surf the Internet only for short, intensive batches, a circuit-switched connection is best. If, however, your cellular company charges you a low per-megabyte rate or if you tend to connect intermittently several times throughout the day, you should opt for a packet-switched connection.

PC Card Wireless Modems

As for most other laptop peripherals, the best form factor for wireless modems is the PCMCIA or PC Card. The original PC Card cellular modems actually consisted of two cards. For example, the Sierra Wireless AirCard modem, which became available in 1997, comprised two Type II PC Cards, one of which was a more-or-less standard modem, and the other a cellular adapter. In 1999, Sierra Wireless was able to shrink the device down to a single Type II card for Windows CE handheld devices, and later for Windows notebooks. As 2.5G and 3G cellular networks come on line, wireless modems have begun incorporating this technology and have taken advantage of the higher transmission speeds. One of the newest wireless modems on the market is the Sierra Wireless AirCard 750, pictured in Figure 12.2. This device can communicate at a maximum rate of 56Kbps on cellular systems that support this feature. With the addition of a headset, this card can also function as a cellular phone.

Figure 12.2. The Sierra Wireless AirCard 750 cellular modem, which is available for T-Mobile GSM-based cellular systems, among others.

The advantage of a PC Card cellular modem is that it's a relatively simple system. There are no wires, external components , or dongles hanging off the laptop. The only visible sign of the modem is the PC Card's flexible antenna that sticks out the side of the laptop.

Some PC Card cellular modems have an added advantage of being able to carry voice communications as well. With these modems, you could use the internal microphone and speaker of your laptop and have, in effect, a mobile speakerphone. For more private conversations, you could plug in a small headset that combines headphones and a microphone.

Connecting a Modem to a Cell Phone

Some laptop modems have the ability to connect to a cell phone as well as to a standard phone line. This group includes both built-in modems as well as PC Card modems. Unfortunately, however, most modems are not cellular capable, in which case you must purchase a PC Card cellular-capable modem to use. 3Com and others make modems that work with most of the popular cell phones on the market using the traditional AMPS or GSM service. For example, I use a Nokia 6100 series phone, which is supported by the 3Com CXM756 (56K Data/Fax/Cell) modem. To use this, I need a cable, which 3Com also sells. Most of these modems use the Microcom MNP10EC protocol, which is designed to handle the signal changes and handoffs common in cellular operation. Even with the cost of the cellular-capable modem and the cable between the modem and the cell phone, this is a very cost-effective approach because it involves only a single cell phone bill each month.

Using a Cell Phone as a Wireless Modem

Some of the more recent cell phones have a built-in cellular modem. In many cases this built-in modem is used to enable the phone to access specially designed Web sites. The Audiovox phone shown in Figure 12.3, for example, supports data transfers at a maximum burst rate of 256Kbps (depending on the cellular system where the phone is used). Typical data-transfer rates are 56Kbps in packet-switched networks and 14.4Kbps in circuit-switched networks.

Figure 12.3. The Audiovox CDM8300 Tri-Mode Digital CDMA2000 1X cellular phone, one of many that now include a cellular modem capable of being attached to a laptop.

As is the case with the previous approach, this is a cost-effective technique, enlisting your existing cell phone for double duty as both a phone and a modem. The only extra cost is a cable that connects your cell phone to your laptop's USB or serial connector. Originally these cables were expensive, often costing $99, but as cell phones have become more popular, third-party companies have been offering low-cost cables. This cable, by the way, can also be used for transferring phonebook and calendar information back and forth from your cell phone to your laptop.

The great advantage of using a cell phone as your wireless modem is that you will be charged for only one monthly cellular bill. If you use a PC Card cellular modem along with a cell phone, you are charged a monthly bill for each.

Note

Note that not all cell phones can function as cellular modems. Before you buy your next phone, check whether this feature is supported.

The disadvantage of using a cell phone as a modem is the awkward cable clutter involved with this approach. Your laptop will now have a cell phone attached to it, dangling at the end of a fragile and expensive cable like a miniature ball and chain. However, if the Bluetooth wireless standard discussed later in this chapter becomes more popular, this cable can be eliminated. Instead, your cell phone and laptop will communicate with each other via a radio-frequency connection. Unfortunately, Bluetooth has been slow to the market. Also, the relatively few Bluetooth-compatible products that have appeared have been expensive.

Using a Satellite Phone as a Wireless Modem

Laptop users who will be traveling outside cellular coverage can still keep in touch by using a satellite phone, such as those sold by GlobalStar. As is the case with cellular phones, some satellite phones can be connected to a laptop and then function as a satellite modem. All you need is the particular accessory cable for that phone to enable it to connect to a laptop's serial port. Note, however, that there's a price for this freedom. The maximum data rate for this type of connection is only 9.6Kbps.