3Com DIGITAL MODEM

3-4 CHAPTER 3: TROUBLESHOOTING

■If you are unable to establish a data call, carefully monitor the

B-1 and B-2 LEDs while attempting a data call. The B-1 and

B-2 LEDs ﬂash green during the data call establishment

phase. They then remain continuously green once the data

connection is established.

■If neither of the B-1 or B-2 LEDs ﬂashes green, check to make

sure that your computer is turned on and operational, that

your 3Com Impact digital modem cable is properly

connected and not damaged, and that your application

software has sent an AT dial command in the proper format.

Depending upon the location of the destination call you are

dialing, there may be an incompatible local or toll telephone

company. Though this is less likely, if you suspect a telephone

company problem in dialing local or toll data connections,

contact your local telephone company and have it verify that

you can dial a data call to the destination telephone number.

7If you are able to establish a data call, in which the B-1 or

B-2 green LED remains lit and you receive a CONNECT

message at your application software, but you are unable

to send data, then it is possible that:

■There is a difference in the local and remote B channel

data rates.

■There is a mismatch in the data communications

protocols.

■There is an interoperability mismatch between the local

and remote applications.

■Make sure that the local and remote data applications have

communication capability and are properly conﬁgured.

Once you have veriﬁed that communication capability

exists, make sure that the B channel call data rate is the

same as the remote destination call data rate. The default B

channel data rate used by the digital modem is 56 Kbps.

Under some circumstances, the data rate may be

increased to 64 Kbps at both ends of the connection.