What is a Telephony Application Server (TAS)?

The TAS performs a central function in the network of all telcos.

Its task is to keep the status of the connections stable on the basis of the network protocol SIP (Session Initiation Protocol).
The TAS is the 'guardian of the service logic' and provides all essential call processing services.
These include digit analysis, call setup, call waiting, call forwarding, conference calling, call termination and additional multimedia functions.

The CreaLog SIP Application Server is a modern TAS development.
It provides telcos and network operators with effective control over calls using all current standards, enabling them to intelligently monitor, forward, transfer and initiate SIP calls.

Read more here.