In some cases upstream exchanges do not support the delegation of call forwarding to external ISDN users, often due to the unclear situation about who carries the call charges. For this reason, call forwarding between external subscribers is always handled by the LANCOM VoIP router.
- An external subscriber A (external SIP, ISDN) makes a call to an internal user B (SIP, ISDN).
- B makes a further call to an external subscriber D (ISDN or analog).
- The local user B then forwards the call (with consultation) to A.
- If both external users A and D use different protocols (SIP, ISDN), the LANCOM VoIP router assumes responsibility for managing and converting the data.
- If both external users A and D use SIP, the LANCOM VoIP router is unable to forward the call.
Note: Requires that the VoIP PBX fully supports Transfers in SIP (re-invites).
