A Technical Assistance Center, or TAC, is a department within a company that's primary purpose is networking, or an ISP. The TAC also works closely with a company's Network Operations Center, or NOC. A TAC can only monitor items with a return signal, such as a modem or a MTA. Forward-only systems, such as cable boxes, are currently not monitored. The purpose of a TAC is to support customers with technical issues regarding the equipment developed/delivered by the company which delivers the TAC support.
References
Technical assistance center Wikipedia(Text) CC BY-SA