Presentation of the desired exit number

In the event that a user wishes to present himself with his own exit number when calling on the ISDN network, some conditions must be met: one of these is that the exit number belongs to the range of numbers managed by his operator. The operator can in fact assign more than one number to the same socket, whether they are present in a multi-number socket, whether they belong to a pass-through selection service.

Each socket can only come out with its numbers and the ISDN gateways (eg Mediatrix) do not know which they are, limiting themselves to sending the call request on the ISDN bus. It will be the boss that will show up with its main number (leader). If necessary, the gateway can indicate which of the numbers of the socket to use as the presentation number, but in no case can it indicate a number unrelated to the socket: if it did, the socket would ignore the request by presenting itself with the main number.
Only by activating the automatic search service for a fee, it is possible to manage all the studs as a single resource and thus share all the numbers of the individual studs on all of them.

If a user sets an exit number other than the numbers assigned by the operator, it is up to the operator to solve the problem by replacing this number (in jargon called CLIP), with one of the numbers (typically the leader) of the range of numbers assigned by contract. In some cases the operator has the right to submit a different number but only as an additional service. In several cases we have seen that the operator instead refuses the call, but this is contrary to the law.

The technical standard that regulates the CLIP service on the ISDN network (Calling Line Identification Presentation) is ETSI EN 300 092-1, which can be downloaded from

In paragraph 8.3.1 it is in fact specified how, in the presence of a foreign number presented by the caller:

the network shall use a default number associated with the calling user.
The network shall set the screening indicator to "network provided".

This means that the operator must discard the foreign number, replacing it with a default number and set a flag on the Calling Party Number which says that the information has been set by the control panel (otherwise the indication would be “user provided”).

Any other operation, in particular rejecting the call, is based on nothing and is not allowed.

The cases in which these anomalies may occur occur when the exit number configured in the gateway associated with the operator is set to specified by the Caller. With this setting, when a user makes a call, the number presented to the network is the one indicated as “exit number” in the user’s profile. So far, nothing strange if the user’s exit number is chosen from one of the numbers assigned by the operator.

The problem, on the other hand, arises when the user’s GUI is set to call their mobile phone (use mobile on direct or group call …). In this scenario, when the gateway has chosen to use the caller’s number as the exit number, the latter will not be the exit number of the user who triggered the call to his own mobile phone, but the original number of the caller, ie who initiated the call: if this is another user with their correct exit number, there will be no problem, but if this is an external caller, his exit number will be presented. Obviously this will be presented to the operator and the aforementioned legislation should come into play: the number is not among those belonging to the operator, so the operator must replace it, but not reject the call. If the call is rejected, you must contact the operator.

The VOIspeed PBX applies the same behavior even with VoIP operators, which, although not required to comply with the aforementioned legislation, which only concerns the ISDN world, could easily apply the same mechanism. Instead in these cases it may happen that they reject the call with a message like:

403 From user does not match authenticated user

or let the call pass quietly, presenting the original number of the external caller, as in the case of Voicetrading.