Before monitoring the LEDs or referring to the section on Symptoms and Solutions, check the following: Verify that the cables are securely connected and not physically damaged. If damage is apparent, have the user replace the cable.

Verify that the ISDN cable is properly connected to the ISDN modem and the ISDN wall jack. The ISDN modem will not operate if connected to an analog telephone wall jack. Make sure that the ISDN modem is connected directly into the ISDN wall outlet without connection to any intermediate telephone equipment (an NT1 device is not required with the 3Com Impact).

Verify that the power cord is connected to the ISDN modem and an electrical outlet.

Verify that the correct ISDN telephone number and switch type were configured.

Verify that the SPID was configured correctly.

If the user is experiencing operational inconsistencies, monitor the Test, D channel, and B channel LEDs to isolate problems.

Monitoring the Test LED

Press the reset button and observe the Test LED. During power-up self-test, the Test LED flashes. If the LED goes off, the test has been successful.

If the Test LED flashes and remains lit for more than a few minutes, there is an internal failure. Notify 3Com that the ISDN modem has failed the self-test, and order a replacement. Follow the RMA policy sent with your equipment.

Monitoring the D channel LED

Observe the D channel LED. If the user is connected to a live digital ISDN line, the D channel LED remains lit for up to a few minutes after the self-test and then begins to flash. When the D channel LED flashes, it indicates that the ISDN signal is present and it is attempting to synchronize with Pacific Bell's Network.

When the D channel LED goes out, it indicates that a valid communication channel has been established and the user can place calls. If the D channel LED does not go out, refer to Evaluating Symptoms and Solutions.

Monitoring the B Channel LED(s)

Attempt to place a call and observe the B channel LED(s). The B1 and B2 LEDs flash amber for a voice call or green for a data call during the call establishment phase. They then remain continuously amber or green once the connection is established. If they do not remain continuously amber or green, refer to Evaluating Symptoms and Solutions.

TEST LED remains lit for more than a few minutes

There has probably been an internal failure. Notify Telamon or 3Com Technical Support that the ISDN modem has failed the self-test and order a replacement.

D channel LED remains lit for more than a few minutes

There may be a poor physical connection to the Pacific Bell Network or the line may not have been properly provisioned. If the telephone wires at the user's site appear to be satisfactory, they should call Pacific Bell 611 repair to have a remote test done on the line from the serving central office. If the line test shows trouble, Pacific Bell will dispatch assistance.

D channel LED continues to flash for more than a few minutes

If the D channel LED continues to flash for more than a few minutes, there is probably a mismatch between the settings of the ISDN line and the ISDN modem configuration.

Verify the telephone number and SPID (if required). If the D channel LED continues to flash, call Pacific Bell to verify the SPID and telephone number and ensure that Pacific Bell has configured the ISDN line properly.

B channel LED(s) does not remain green

If the user is unable to establish a data call, the cause may be one of the following:

There may be a problem with the computer's application software. Carefully monitor the B1 and B2 LEDs while attempting a call. These LEDs flash during call establishment and then remain green once the connection is established. If neither LED flashes, ensure that the computer is turned on and operational, and that the application software has sent an AT dial command in the proper format.

The local or toll telephone company may be incompatible. Contact Pacific Bell and have them verify that the user can dial a data call to the destination telephone number.

A connection has been established, but data cannot be sent.

If the user is able to establish a data call, that is, the B1 or B2 green LED remains lit and the user receives a CONNECT message, but the user cannot send data, there may be an interoperability mismatch between the local and remote applications. Make sure that the local and remote data applications have communications capability and are properly configured.

Upon power up, both the TEST and D channel LEDs flash

A previous firmware download probably did not complete successfully. Download the firmware. Note: While downloading firmware to the 3Com Impact digital modem, if the serial cable is disconnected or if the PC crashes, the firmware download will continue where it left off once the cable is reconnected or the PC is restarted. (A message box appears asking the user to confirm continuation of the firmware upload.)

Note that the 3Com Impact digital modem must remain powered up throughout firmware download and recovery. If for whatever reason the unit is powered down, the unit is no longer usable and must be returned.

Both B1 and B2 flash when the D channel lights

The ISDN modem baud rate is set to 230.4 Kbps. Ensure that the computer's COM port supports 230.4 Kbps or change the COM port setting of either the computer or the ISDN modem so that both devices are set to the same COM port rate.

Q: Is compression supported?

A: Compression is not currently supported.

Q: Can the 3Com Impact External Digital Modem coexist with my analog modem inside my computer?

A: Yes and if the user only has one telephone outlet, remember to plug the internal modem's telephone cable into the 3Com Impact's analog port. (If the user has another telephone line outlet the user could plug the modem's phone cable into it.) Also, ensure that different COM ports are used.

Q: Is it possible to have a 56 Kbps/64 Kbps connection and a modem (3Com Impact digital modem's internal analog modem) connection simultaneously?

A: No, the user cannot make an ISDN and an analog call through the data port on the digital modem simultaneously.

Q: How can I tell if I have established a Multilink call?

A: Both of the B channel LEDs on the digital modem's front panel, B1 and B2, will be illuminated green. Note that if the software displays a connection speed while establishing the call, it will only show a 56 Kbps or 64 Kbps connection, not 112 Kbps or 128 Kbps.

Q: How do I disable Multilink PPP?

A: To disable Multilink PPP, uncheck the Multilink PPP box located on the Configuration screen of the digital modem software. Click Config or Update Configuration to update the change.

Or, the user can use terminal emulation software to send the following AT command to the digital modem: ATS80=0. By default Multilink PPP is enabled. (ATS80=1)

Q: What if I have to dial two telephone numbers to establish a Multilink PPP call?

A: Sometimes the destination the user is calling requires two separate telephone numbers to establish a Multilink PPP call. If this is the case, either enter that second telephone number in S register 81 (S81=up to 15 digits), or, if the user is running release 2.02, type the following command: ATD [telephone number 1] & [telephone number 2].

Q: While attempting a Multilink PPP call, why is it that I can establish one B channel connection, but not the second?

A: There are several reasons why this may occur. Check the following: Ensure that Multilink PPP is enabled by checking the Multilink PPP check box in the Configuration screen or by sending the command ATS80=1 to the digital modem. Ensure that the equipment the user is dialing into supports Multilink PPP. (If the user is trying to dial into the Internet, check with the Internet Service Provider.) Call the telephone company and check the ISDN line settings. Ensure that data is supported on both B channels, that the circuit-switched data limit is 2. The user may have to dial two telephone numbers to establish a Multilink PPP call. This would be a requirement of the equipment the user is dialing into. If the destination the user is calling requires two telephone numbers for Multilink PPP, either include that second telephone number in S register 81 (S81=up to 15 digits), or, if the user is running release 2.02, type the following command: ATD [telephone number 1] & [telephone number 2]. If the user is running Windows 95 or Windows NT, try disabling CHAP by sending the command ATS84=1 to the digital modem. If the user is not running Windows 95 and CHAP is supported, send the command ATS84=0 (enable CHAP) to the digital modem.

Q: Can I place a voice call while a Multilink PPP call is active?

A: Yes, the digital modem supports Dynamic Bandwidth Allocation (DBA). With DBA, the user can place a voice call while a Multilink PPP call is established. The digital modem will free one of the B channels for the voice call once the user lifts the telephone handset. The Multilink PPP call is uninterrupted; however, throughput will be reduced until the second B channel is reallocated. Once the user replaces the telephone handset, the B channel will be restored to the Multilink PPP call.

Q: What minimum requirements must my IBM or IBM-compatible PC meet?

A: An IBM or IBM-compatible PC must have the following:

• A 386, 486, or Pentium‚ processor
• An available serial communications port
• 16550 UART
• MS-DOS‚ or IBM PC DOS 3.1 or later operating system
• 640 Kilobytes of conventional memory
• Microsoft Windows 3.1X with 8 Mb of RAM
• Microsoft Windows 95 with 16 Mb of RAM
• A hard disk drive with 20 MB of free space

NOTE: For sustained performance at higher data rates (57.6 Kbps and 115.2 Kbps), it is recommended that the IBM or IBM- compatible PC serial COM port be equipped with a 16C550 UART (universal asynchronous receiver/transmitter). To determine what UART is installed in the PC, run the Microsoft‚ Diagnostic Program (msd) from the DOS prompt. In addition, for reliable high-speed serial port performance in the Microsoft Windows 3.x environment, a TurboCom driver for Windows, which replaces the standard Microsoft Windows COM driver, is included with the 3Com Impact digital modem. (TurboCom is not needed for Windows 95.)

Q: Does the 3Com Impact External digital modem work with Windows 95?

A: Yes, all the user needs is the impact.inf file which is included in the latest firmware release. If the user does have the impact.inf file, the user can find it on 3Com's FTP Site (192.156.136.12). For instructions on how to set up the digital modem using Windows 95, request document number 9658 from 3ComFacts at (408) 727-7021.

Q: Does the 3Com Impact External digital modem work with Windows NT?

A: Yes, all the user needs is the modem.inf file which is included in the latest firmware release. If the user does not have the modem.inf file, the user can find it on 3Com's FTP Site (192.156.136.12). For instructions on how to set up the digital modem using Windows NT Remote Access Service (RAS), request document number 9657 from 3ComFacts at (408) 727-7021.

Q: What minimum hardware requirements must my Macintosh computer meet?

A: The user must have a Macintosh 68030 or later system running System 7.1 or later operating system; one free serial communications (modem) port and 10 MB of available space on the hard drive.

Q: What is the maximum serial port speed for a Macintosh computer?

A: Macintosh computer serial (COM) port speed maximums vary. Refer to the Technical Information guide which came with the Macintosh computer or call Apple Support. Macintosh models with low serial port speeds can be upgraded by adding an internal card. Creative Solutions, (800) 367-8465, offers an internal card with either two or four serial ports capable of 57.6 Kbps each for a maximum of up to 115.2 Kbps or 230.4 Kbps. Note that the 3Com Impact digital modem currently supports serial port speeds of up to 115.2 Kbps.

Q: There's a physical connection between my digital modem and my Macintosh computer, but I still can't access the digital modem. Why?

A: If the user has an internal modem or Ethernet card installed in the Macintosh computer, there may be a conflict with the digital modem. COM or serial ports can only support one device at a time. Also, AppleTalk/LocalTalk might be vying for the modem port, disabling AppleTalk often helps. Before you call Pacific Bell Internet Technical Support:

Review the troubleshooting section of the User Manual.

Check all cables (ISDN phone cable between the phone jack and the terminal adapter; Serial communications cable between the computer and the terminal adapter).

If you suspect the ISDN line, contact the Pacific Bell Repair Service at 611.

If you still have to call Pacific Bell Internet Technical Support:

Please be prepared to let the Technical Analyst know any tests/procedures you have tried already.

Have your ISDN provisioning sheet handy. Please note the Switch type, SPIDs, and Directory Numbers. If you do not have this information, please contact the Pacific Bell ISDN Service Center at 800-4PB-ISDN.

Software: PBI will provide technical support to subscribers that meet our minimum system specifications using PBI provided software.

ISDN Hardware: PBI will provide full technical support on the 3Com Impact and 3Com ImpactIQ Terminal Adapter.

PBI will provide minimum support for a variety of Terminal Adapters that we have experimented with in our lab. Those being (subject to change without notice): Motorola BitSurfr Pro, US Robotics Sportster 128, Farallon Netopia, Diamond Multimedia Net Commander and the US Robotics Courier I-Modem with ISDN/V.34.