A demarc extension, also called an extended demarc, is the cabling that carries a circuit from the carrier’s demarcation point to the customer’s equipment somewhere else in the building. The carrier often ends its responsibility in a shared telecom room near where its cable enters the building. If your router or firewall is in your suite on another floor, something has to bridge that gap, and that something is the demarc extension.
At a glance
- A demarc extension connects the carrier’s hand-off to your equipment when the two are in different places.
- It may be done by the carrier, the building’s preferred contractor or your own cabling vendor, depending on the building and the order.
- Copper Ethernet suits short runs; fiber is common for longer runs, higher speeds and paths between floors.
- Who installs it usually decides who maintains it and whether the carrier’s SLA covers it.
- Unplanned extensions are a common cause of delayed install dates and surprise charges.
What problem it solves
In many multi-tenant buildings, carriers bring their cable to the minimum point of entry and place their demarc there, often in a basement or ground-floor telecom room. That suits the carrier: it serves every tenant from one room and keeps its equipment in a controlled space. It does not get the circuit to your equipment.
Without a planned extension, a carrier can complete its installation and report the circuit as delivered while your office still has no service. The extension closes that last stretch inside the building. Planning it ahead keeps install day on schedule, makes sure the cable suits the speed you bought, and settles who to call when it fails.
How it works
Survey. Someone walks the path from the demarc to your equipment: risers, conduits, ceilings and any floors or tenant spaces in between. The survey sets the distance, the cable type and any building approvals needed.
Cable choice. Twisted-pair copper Ethernet is common for short runs and lower speeds, within its distance limit of about 100 meters. Fiber handles longer runs and higher speeds, and is often preferred in risers between floors. The carrier’s hand-off port, such as a copper RJ-45 or an optical port, also shapes the choice, since both ends must match or use a media converter.
Installation. The installer pulls the cable along the approved path, terminates both ends, labels them with the circuit ID, and tests the run. In buildings with existing structured cabling, the extension may use spare riser pairs or fibers, with patching at each telecom room.
Ownership and support. If the carrier does the extension, it may treat it as part of the circuit and move its effective demarc to your suite. If the building or your vendor does it, the extension is your inside wiring and the carrier will usually test only to its own demarc. Either can work; what matters is that everyone agrees before install day.
Building rules. Landlords often control riser access, require approved contractors, or charge for space in shared pathways. Leases sometimes say who owns existing inside wiring, so check the lease along with the carrier order.
For help planning internet circuits into a new or moving office, see our Dedicated Internet Access solution page.
When it matters for buyers
- Moving into a new office. Ask the landlord where carriers terminate and what riser paths are available to your suite.
- Ordering any new circuit. Confirm whether the quote includes an extension, and to which room.
- Upgrading speed. An old copper extension may not carry a faster service; check before you order a higher tier.
- Adding a second carrier. If both circuits share one extension path, they share one point of failure inside the building.
- Troubleshooting. If the carrier tests clean to its demarc, the extension is the next place to look.
Questions to ask vendors
- Where will your demarc be, and is an extension to our equipment included in this quote?
- If you do the extension, will you maintain it and include it in the SLA?
- What cable type will the extension use, and will it support the speed we ordered and future upgrades?
- What building approvals, contractors or riser fees are needed, and who arranges them?
- How will the extension be labeled and documented at both ends?
- If we use our own cabling vendor, what hand-off port and specifications do they need to meet?
How it differs from the demarcation point
The demarcation point is the boundary where the carrier’s responsibility ends. A demarc extension is the physical cabling from that boundary to your equipment. If the carrier installs and maintains the extension, it may effectively move its responsibility to your suite; if someone else does, the original demarc stays where it was and the extension is yours. When reading an order, look for both: where the demarc is, and how the circuit gets from there to your rack.