Information Technology Reference
In-Depth Information
If . . .
-
Long-distance calls have problems, but local ones do not (or vice versa)
-
Calls at certain times of day have problems
-
Calls from specific remote exchanges have problems
Then . . .
You might be getting bad circuit paths through the Public Switched Telephone Network.
2.
Long distance doesn't work well or at all, but local calls work fine.
If . . .
Long distance calls are bad but local calls are good.
Then . . .
-
Double-check to make sure that the digital line connects into a digital switch, not a channel bank
-
Check with telcos to examine the circuit paths used for long distance
3.
Some calling areas have problems
If . . .
Calls from specific geographical regions/exchanges tend to have problems
Then . . .
Learn the network topology from the telco. If multiple analog-to-digital conversions (caused by
nonintegrated SLCs or analog switches) are used to serve an area, V.90/K56flex modem connects
will be impossible, and V.34 may be somewhat degraded.
ISDN Operations
Integrated Services Digital Network (ISDN) refers to a set of digital services that is available to end
users. ISDN involves the digitization of the telephone network so that voice, data, text, graphics, music,
video, and other source material can be provided to end users from a single end-user terminal over
existing telephone wiring. Proponents of ISDN imagine a worldwide network much like the present
telephone network, but with digital transmission and a variety of new services.
ISDN is an effort to standardize subscriber services, user/network interfaces, and network and
internetwork capabilities. Standardizing subscriber services attempts to ensure a level of international
compatibility. Standardizing the user/network interface stimulates development and marketing of these
interfaces by third-party manufacturers. Standardizing network and internetwork capabilities helps
achieve the goal of worldwide connectivity by ensuring that ISDN networks easily communicate with
one another.
ISDN applications include high-speed image applications (such as Group IV facsimile), additional
telephone lines in homes to serve the telecommuting industry, high-speed file transfer, and
videoconferencing. Voice, of course, will also be a popular application for ISDN.
Many carriers are beginning to offer ISDN under tariff. In North America, large local exchange carriers
(LECs) are beginning to provide ISDN service as an alternative to the T1 connections (digital carrier
facilities provided by telephone companies) that currently carry bulk wide-area telephone service
(WATS) services.
