A.1 Single private numbering plan
24.5243GPPArchitecture, functional description and signallingHosted enterprise servicesRelease 17TS
If the UE detects that a private dialling plan is being used, it may decide to send the dial string unchanged to the network or to alter it to comply with the private numbering plan (e.g. remove all dial string elements used for private numbering detection). The resulting dial string may be sent, in the Request URI of SIP requests, using one of the following formats:
1) A TEL URI, complying with IETF RFC 3966 [21], with local number and a pre-configured fixed phone-context value.
tel:<output dial string>;phone-context=pnp.entreprise.com.
2) A SIP URI, complying with IETF RFC 3261 [22], with the user =phone parameter.
sip:<output dial string>;phone-context=pnp.entreprise.com@operator.com;user=phone.
3) A SIP URI, complying with IETF RFC 3261 [22] and IETF RFC 4967 [23], with the user =dialstring parameter (see note).
sip:<output dial string>;phone-context=pnp.entreprise.com@operator.com;user=dialstring.
NOTE: This option only applies if the dial string was not completely processed into a private number string.
4) A SIP URI complying with IETF RFC 3261 [22], where the user part contains the dialled string (possibly modified) and the domain name is specific enough to enable to network to understand that the user part contains a dialstring according to a private numbering plan or private dialling plan.
sip:<output dialstring>@pnp.entreprise.com.
In the first three cases, the phone-context value indicates that a private number is being used that belongs to the single private numbering plan.