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DIRECT DIALING INWARDSCALL SERVER : TELEPHONE FEATURES
Ed. 04 1/4Réf. 3EH 21000 BSAA
File
DIRECT DIALING INWARDS
DDI numbers can:
- contain up to 8 digits.
- use the numbering recovery mechanism described below.
NUMBERING RECOVERY
Description
When, in an existing installation, a new range of DDI numbers needs to be added, and the new se-
quence allocated by the public exchange overlaps the existing range, the installer can make use of the
"DDI with more than 4 digits" mechanism.
Exemple :
Consider an existing system with the DDI numbers (XX = any possible "intercity prefix", "intercity code"
and "recall prefix" – these can vary from country to country):
- XX 1 41 23 40 10 to XX 1 41 23 40 19 assigned to stations 120 to 129
- XX 1 41 23 41 00 to XX 1 41 23 41 19 assigned to stations 130 to 149
The exchange allocates the new range XX 1 41 33 40 15 to XX 1 41 33 40 24: these numbers are
assigned to stations 150 to 159.
As described below, the numbering plan does not allow:
- use of the whole DDI range available; in actual fact, in order to route a DDI number to a called
station, the system only analyzes the last 4 digits of the number received from the network and the
DDI sequences XX 1 41 23 40 10 and XX 1 41 33 40 15 have in common, the range of the last 4
digits 40 15 to 40 19.
- transmission of the exact number of the caller (see "ISDN services") since the system would require
two installation numbers (XX 1 41 23 and XX 1 41 33) in order to operate correctly, which is im-
possible.
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