ENCS offers a SIP Trunking service to those units who wish to run their own IP-PBX. This service will connect the customers IP-PBX to the TNS SIP Core and allow full access to the PSTN (Public Switched Telephone Network) and to all other entities connected directly to it. The SIP Core utilizes the existing PSU IP network infrastructure to deliver calls to and from the customers PBX. Customers of this service will be able to keep their existing DID phone numbers. The ENCS SIP Core is fully redundant and is also considered a “vendor agnostic” service.