Analog Cellular Communications

Connecting your modem to an analog cellular telephone using a 3Com Megahertz cellular cable gives you freedom from land lines, enabling you to send and receive data and faxes without being tied to a physical phone line. This section explains how to use your modem's cellular functions.

Supported Cellular Phones

3Com Megahertz modems can support certain models of Motorola, Nokia, Ericsson, AT&T, Radio Shack, and other leading cellular phones (see the 3Com Web site at www.3com.com for updated lists of supported phones).

NOTE: Before you can use a cellular phone with your modem, you must obtain the correct 3Com direct-connect cellular cable. If you need to order a cellular cable, go to the 3Com web site at www.3com.com to access our Parts Fulfillment Center.

What to Expect from Analog Cellular Data Transmissions

Analog cellular phones use radio frequencies for transmission and are subject to the same signal impairments as other radio devices. They do not generate dial tones or busy signals and decode touch tone or pulse dial signals. Your modem is designed to overcome this situation.

You cannot control any of the following cellular characteristics:

A large portion of the cellular voice channel is reserved for out-of-band signaling, reducing the bandwidth on the cellular network, which can result in distortion or signal loss.
Voice compression techniques on some cellular networks can cause loss of bandwidth, resulting in slower data transmission.
The mobile telephone exchange may send a signal over the control channel, commanding the telephone to reduce its transmission power, possibly resulting in dropped data lines.
The mobile telephone exchange may send messages to, or request information from, the telephone on the voice channel while the data link is established. Either of these requests can temporarily disrupt data communications or cause the line to be dropped.

To ensure that your transmission quality is as high as possible, do the following:

Use cellular protocols whenever possible. These will be set up automatically on the modem when you plug in the 3Com direct-connect cellular cable. Always use error correction and data compression to receive and send the highest quality transmissions.
Use cellular modem pools if available. Contact your cellular carrier or service provider to see if cellular modem pools are available in your area. This service is accessed by dialing the prefix *DATA (*3282) before the number you are dialing.
Make sure the signal is as strong as it can be. Refer to your cellular phone's manual for a description of signal strength and an explanation of how to read the signal strength bars. If the signal is not strong enough to support a voice call, it will not handle data transmission.
Pull the antenna out to its full length and point it in several different directions until you find the strongest signal. Try putting the phone in a vertical position and moving it closer to a window.
Laying the phone on a metal surface during transmissions causes interference.
Large objects like mountains or even a car hood can cause the signal to be reflected back to you or block the signal from reaching the phone.
Be sure the cellular phone's battery is fully charged while you are sending or receiving faxes or data. If the low battery message blinks during transmission (signaling it is running out of power), disconnect the transmission, attach a fully charged battery, and redial.

Connecting the Modem to a Cellular Phone

CAUTION: Transmitting data or faxes from a moving vehicle may result in sub-optimal performance or loss of connection.

With the cellular Cable ID feature, just plug in the 3Com direct-connect cellular cable and the modem recognizes the phone that you are using.

Follow these steps to connect the cables:

Insert the modem into the computer.
Be sure your computer is powered up.
Enter your communications software package.
Connect the 3Com direct-connect cellular cable to the phone. The phone's power should be off.
Connect the other end of the cellular cable to the modem. You will hear three ascending tones in rapid succession, indicating that the Cable Sensor recognizes the cable and the modem is configured for the phone. If your software is in terminal mode, the message "<Manufacturer> Cable Attached" will appear.
Turn the cellular phone on if the modem has not already turned it on. If you have a digital cellular phone, switch it to analog mode (refer to your phone's user manual for instructions).

The phone is now ready to use.

Cellular phone connection:

Automatic Cable Sensor

When a cellular cable is not inserted, the modem is in landline mode. When a cellular cable is inserted, a three-tone ascending beep will sound, the message "<Manufacturer> Cable Attached" will appear (if you are in terminal mode), and the modem will automatically go into cellular mode.

If a cable is attached that the modem does not recognize, the message "Unrecognized Cable Attached" will appear if you are in terminal mode.

NOTE: Before you can use a cellular phone with your modem, you must obtain the correct 3Com direct-connect cellular cable. If you need to order a cellular cable,go to the 3Com web site at www.3com.com to access our Parts Fulfillment Center.

NOTE: No AT command string is needed to put the modem into cellular mode. Because of the Automatic Cable Sensor feature, the initialization string is automatically sent when the cable is attached.

When the cellular cable is removed, the message "Cable Removed" will appear if you are in terminal mode and the modem will automatically return to land line mode.

Using Cellular Protocols

If you are not sure what cellular protocols the modem with which you are connecting supports and you are having trouble getting a good connection, set AT&N4 to limit the startup rate to 4800 bps. This setting maximizes throughput and minimizes the risk of losing the connection.

Enhanced Throughput Cellular (ETC)

The purpose of ETC is to combat particularly harsh line conditions that can arise during cellular and rural transmissions to produce optimum cellular performance.

ETC offers the following features:

Improves the initial connection success rate.
Automatically calculates optimal transmission speeds to compensate for cellular telephone signal distortion in the following categories:

The modem connection begins at the optimal speed that will ensure a strong connection, then moves to the highest possible speed during transmission.
Establishes a reliable link during noisy call setups.
Continuously adjusts transmission speeds throughout the connection, supplying the highest possible speed with the greatest reliability that the line can support at any time.
Improves link and transmission performance under adverse conditions. Detects errors during transmission and resends the packets.

Uses signal line conditioning to ensure line conditions provide maximum throughput.

Connecting to the Internet Over Cellular

Connect to your Internet provider using a landline connection. Most Internet service providers (ISP) are not set up to support and maintain a cellular connection.

If you need to connect to an ISP with a cellular phone system, contact your local carrier to see if they provide a cellular modem pool (usually by prefixing the number you are dialing with *DATA (*3282).

If a modem pool is available, follow your carrier's instructions for connecting with the modem pool. Contact your ISP through the modem pool. If not, carefully follow the ISP procedures in "Connecting the Modem to a Cellular Phone" in this section.

NOTE: Cellular functions are not currently compatible with V.90.

Cellular Dialing

Cellular dialing functions work the same as landline functions (see "Dialing" in Transmitting Data).

If you are dialing manually and you do not require a personal identification number (PIN) and your phone number is 555-5555, enter:

ATDT 5555555

If you are dialing manually and your cellular phone requires that you enter a PIN and your PIN is 1234, enter the phone number, three commas (you may need fewer or more commas, each representing a two-second delay), an exclamation point, three more commas, then the PIN number. For example, if your PIN number is 1234, enter:

ATDT 5555555,,,!,,,1234

Enter these numbers into a dialing directory the same way as they are shown above.