Support of feature ClipNoScreening for SIP trunks (kb3905)

The information in this article applies to:

  • SwyxWare v6.12
  • SwyxWare 6.20 Quickfix 09-02-20

[ Summary | Information ]


ClipNoScreening stands for the capability to signal two differents numbers:

  • the Network Provided Number of the caller
  • the User Provided Number (not screened)

'No screening' means that the User Provided Number will not be validated by the network provider. This number is defined by the caller himself.


To use the ClipNoScreening function via a SIP trunk, in a SIP INVITE message a P-Asserted-Identity-Header is added, which includes the number associated to the provider account. If this number corresponds with the account parameters, the call will be transferred. Otherwise the call will be rejected using the SIP error code 403.
ATTENTION: Some provider don't support P-Asserted-Identity-Header, they only use the from header. In this case ClipNoScreening cannot be used.

In SwyxWare Version 6.1x it is only possible to transfer one number as 'User Provided Number' from Server to LinkManager. Therefore a trunk specific registry key named 'SIPNetworkProvidedNumber' must be inserted under



<Trunkname> contains the name of the trunk how it is noticed in the SwyxWare Administration. The value of this key contains the subscriber number including the long distance prefix. If there are more than one trunk which should use this functionality, please create a registry key for each trunk. If there is an value which is not empty, the P-Asserted-Identity-Header gets the format


<Realm> stands for the SIP realm of the provider configuration.

The registry key can be entered in the format

<subscriber number> or <subscriber number>-<x>

<x> separated by an hyphen stands for one or more digits. In that way it is possible to address the operator (-0) or another subscriber (e.g. -123) directly.

If you want to write the URI of the Fom header in the P-Asserted-Identity-Header, it will be checked if the <subscriber number> is part of the From URI. If this is valid, the URI of the From header will be inserted in the P-Asserted-Identity-Header instead of the configured value in the registry. Otherwise the value given in the registry in format: <subscriber number><x> (without the hyphen) will be inserted.


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