Demarcation point
（重定向自DEMARC）
![Old and new style demarcation points in a Canadian home built in 1945. A DSL splitter has been plugged into the modern demarc (on the right). One line passes through a DSL filter before going to the old demarc, and from there to the remainder of the house.](/Images/godic/202501/08/Demarc5943.jpg")
![20th century Bell Canada demarcation point for a single phone line. The spark-gap surge protectors on the left have hex heads for easy removal. Near center, a post is connected to the house's ground. The other two connection points are for tip and ring. A test jack can be attached nearby so the home-owner or tenant can verify whether the inside wiring is at fault. Modern Bell Canada demarcation points are network interface devices](/Images/godic/202501/08/Demarc25943.JPG")
![Two network interface devices.](/Images/godic/202501/08/Network_interface_device_ameritech5943.jpg")
![Demark extension](/Images/godic/202501/08/Demarc_Extension_Single_Segment5943.jpg")
In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines who is responsible for installation and maintenance of wiring and equipment—customer/subscriber, or telephone company/provider. The demarcation point varies between countries and has changed over time.