Proxima, Libra firmware ver. 2.12.xx
rev. 2.12.01
12. Glossary
DTMF (Dual Tone Multi Frequency) is the name of tone signalling
used in telephone devices. It is also known as TouchTone®. DTMF is an example
of MFSK (Multiple Frequency Shift Keying).
DISA (Direct Inward System Access) is the name of a functionality offered by
PBX telecommunications systems, enabling you to call an extension user without
going through an operator.
Having connected with a given PBX server, a user hears a announcement recorded
by the server’s owner and while or after listening to it, dials the desired extension
number using a telephone with DTMF tone dialling.
A drawback of this system is that the caller pays for the call from the moment the
DISA device answers the phone, i.e. they pay for the time that passes until the
phone is answered after the extension number has been dialled.
DDI (Direct Dial-In (Europe) or Direct Inward Dialing (USA)) is the name of a
function offered by PBX servers, enabling you to call an extension user directly.
A PBX server user is provided by the operator with at least 10 telephone numbers
and each of them is assigned to individual server extension users. For example, in
the case of 7-digit numeration, a user receives 100 numbers in the 1234500-
1234599 range. 12345 functions then as the server number, while the last two
digits are used as the number of an extension user. DDI numeration using the last
one or the last three digits is also possible (a user may then receive either 10 or
1000 numbers). A connection between the server and the operator’s exchange is
most often established using an ISDN line.
DDI offers the following advantages:
It makes the server operator's assistance no longer necessary and eliminates the
need of using an additional extension number.
It is also cheaper than buying from the operator a separate telephone line for each
extension user. For example, you pay the operator for a few lines only and have
100 DDI numbers at your disposal.
CLIP (Calling Line Identification Presentation) is a service that consists in
presenting the caller's number on the telephone display (or on a special telephone
snap-in’s display). This service is available for both land line and mobile networks.
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