The Telephony Control Server is located in the main office data center, the connection to the SIP Service Provider is achieved using the internet or the Service Provider WAN/MAN. There is no direct connection between the Lotus Sametime Unified Telephony and the service provider's SIP Server. An SBC (Session Border Controller) is used to secure and inter-work the connection.
The Service Provider uses an SBC and provides a public IP address on the outside of their SBC for the enterprise to connect to. Use of an SBC on the enterprise side of the SIP trunk is, therefore, not essential to provide connectivity to the Service Provider, but in practice most enterprises consider an SBC indispensable to secure their network (internet/WAN/MAN).
The enterprise SBC also provides the opportunity to configure SIP message header manipulations that may be necessary to satisfy service provider specific requirements. A PSTN (Public Switched Telephone Network) call would always be:
Subscriber - Lotus Sametime Unified Telephony - SBC - Provider - PSTN (or vice versa)
Parent topic: SBC (Session Border Controller)