What is Demarcation point?
The demarcation point is the boundary between the network the carrier maintains and the network the customer maintains. Anything on the carrier side is the carrier's responsibility to repair. Anything on the customer side is the customer's. In US telecommunications rules, 47 CFR 68.3 uses the term for the point of demarcation or interconnection between a provider's facilities and the customer's wiring.
In practice the demarc is a physical item: a network interface device on a building, a jack or patch panel in a telecom room, or a handoff port in a carrier hotel or colocation meet-me room. In an office building, it often sits near the main point of entry. In a data center, it is commonly the handoff port or patch panel where a cross-connect ends.
Because it is a boundary, an extension of the demarc is sometimes needed to carry the circuit from the entry room to the customer's equipment. This is wiring on the customer side, normally installed by the customer's cabling contractor. The exact location and who owns each segment is set by the carrier contract and the building, so confirm it in writing before a service goes live.
How it shows up in practice
- Mark the demarc clearly on the floor plan and on the panel with a label, so engineers know where carrier responsibility stops.
- Before opening a ticket with a carrier, test on the customer side of the demarc. A loopback or a known good device at the handoff helps show which side has the fault.
- A scope for a new circuit should list the demarc location, the cable type and the route from the demarc to the equipment.
- Keep the demarc extension documented: cable IDs, panel ports, and the date of any changes.