All subscribers are connected to the public switched telephone network (PSTN) via the network interface device (NID) outside their house. Everything beyond the NID is the customer's responsibility (unless the subscriber has contracted with the phone company via an inside wiring service plan).
An imaginary line separates the telephone company's equipement from the customer's equipment. This imaginary dividing line is called the demarcation point or 'demarc'.
A list of all customer premise equipment (CPE) would include:
- All wiring inside the house (unless the subscriber puchased a wiring service plan)
- All "sets" (telephones/telephone handsets)
For commercial/business subscribers, additional equipment might be considered 'CPE' :
- Public Branch Exchange switches
- Punchdown blocks
- Extended wiring within the businesses premise.