CTI Products NCB/EM with External PSTN Modem - Manual (Page 58)

CTI Products, Inc. NCB-EM User Guide
Appendix G. Modem Notes 52
Telecom Regulations
Telecom regulations require that certain operational restrictions be enforced by an external modem that may
result in operation (or lack thereof) not in line with user expectations. The most notable of these are blacklisting
and delay-before-auto answer.
Blacklisting (Forbidden Lists)
Blacklisting prevents re-dialing to the same telephone number multiple times in rapid succession if a successful
connection has not been made with the distant modem. The parameters governing the blacklisting vary from
country to country, but in general, there is some delay imposed before a number just dialed without successful
connection can be re-dialed. Refer to the user documentation supplied with the modem for current
specifications (under the section covering “Forbidden Lists” or “V.25bis Operation”). Diagnosis of this
situation can be accomplished by using the “Query Command Progress” function of NCBCON. In the “last
characters from modem” parameter, if the dialing string (starting with “ATDT”) is followed immediately by
“NO CARRIER”, then the number has been blacklisted and may be dialed at a later time or not at all, depending
on the country. In general, to clear the blacklist before normal time expiration, the modem must be power-
cycled.
Delay Before Auto-Answer
Some countries require a minimum number of rings (or fixed time delay) before auto-answering. The NCB
attempts to set auto-answer after 1 ring, but some countries will be forced to 2 or more rings. Refer to the user
documentation supplied with the modem for current specifications (under the section covering “V.25bis
Operation).