10.1.2 External numbers
A user's external number defines the number on which he can be reached from an external phone. This external number must come from the public number range, which is supplied by the relevant telephone service provider. This number range must have been assigned to the SwyxServer through the number configuration of its associated trunks.
These are usually number ranges which are supplied via the SwyxServer's analog or ISDN connection to the public telephone network by the relevant service provider (e.g. Deutsche Telekom, Arcor, etc), but also by a VoIP telephony provider. It is often a contiguous number range, such as from +44 20 1234 100 to +44 20 1234 199, which differs only in the last part of the number.
Each of the numbers from this range can be assigned to exactly one user, so that he can be called on the assigned number by external subscribers.
 
You can also assign an external number to a user that contains less or more digits than the defined numbers range. In this case, overlaps during the call transfer may occur.
If two users have been assigned the external numbers +44 4777 28 and +44 4777 288 for example, any external calls for one of the two users are only signalized to the first user. Any longer number will not be decoded by the system, as soon as a dialed number corresponds to an assigned number.
 
Several external numbers for one user
It is also possible here to assign more than one external number to a user (10.3 Mapping of numbers). This makes it possible—especially in installations with networked Swyx sites—to assign a user external phone numbers from different locations, through which the user can be reached from outside the system.
Example:
For example, a user who works at a Swyx location in Germany can have, in addition to their external phone number at the German location, another external phone number from a networked Swyx location in England. If a call is received at this English phone number, it is routed to the appropriate user via the connected Swyx system in Germany. When a user makes an outbound call to an external subscriber in England, the call can then be routed through the Swyx installation in England to the public telephone network connected there and on to the appropriate subscriber, so that the called subscriber in England sees the user’s external English phone number. Such a configuration not only enables a company to save costs by using the appropriate local gateways at its networked Swyx locations, but also significantly enhances its public image through the "local presence" of its employees at various locations.
If you only want to be able to reach a user by phone internally—that is, within the Swyx installation—you do not need to assign an external phone number. In this case, the user can only be reached directly by other users within the Swyx installation (including those at other networked locations) via their internal phone number (see below), but not by calls from the public telephone network or the Internet.
Format of the external numbers
In general, external numbers are always given in the canonical format:
+<country code><area code><number>
Example: +44 20 4777100
These are public numbers (numbers on the ISDN or analog connection). SIP providers also offer public numbers, which need to be mapped to a country or a location.