What Is A Point Of Demarcation?

Point of demarcation

You might have heard the term “point of demarcation” used in reference to telecommunications. But what is the definition of one?

A point of demarcation is the point in the physical wiring where the public telephone network ends, and the private residential or organizational telephone network begins. It makes it clear who is responsible for which portion of the network in terms of upkeep and maintenance. In network installation, each individual private network within the building must physically be wired into the point of demarcation.

This point is also variously known as the demarc, dmarc, network boundary point, and demarcation point.

How did points of demarcation become the standard, and how exactly do they factor into network installations and networks at large? Keep reading to find out how the demarc functions in telecommunications.

Demarcation point in telecom history

Unlike other aspects of network installations, demarcation points have a somewhat dramatic origin. They actually exist due to a 20th-century antitrust lawsuit against AT&T. 

The American Telephone and Telegraph Company was founded in 1886, and it and its subsidiaries rapidly expanded to become the majority supplier of both telephone service and, through its subsidiary Western Electric, most telephone equipment in the United States.

Because the company essentially owned their customer’s wiring, customers had no choice but to use AT&T for their phone service. It was, in fact, a monopoly. This state of affairs came to be known as the Bell System, with AT&T often derisively called “Ma Bell.”

In 1956 other, smaller telecommunication companies began to file lawsuits against AT&T, and eventually in 1974 the Department of Justice itself filed an antitrust lawsuit against the company. This suit ended in a settlement in 1982, which declared that by January of 1984, AT&T must divest itself of the ownership of its regional subsidiaries, which would then function as independent companies. 

This opened the playing field to competition from other telecom companies, and allowed third-party manufacturers of phone equipment. Americans could now choose to have both a different telephone provider than AT&T, and different equipment than that of Western Electric.

And this is where the necessity for a demarcation point arose–a clearly indicated point where the phone company’s property ended, and the private citizen’s or private business’s property began.

Point of demarcation meaning

Functionally, a network demarcation point makes it easy to determine who is responsible for repairs and maintenance of cabling and equipment.

This is why it’s important to be aware of the point and to know where it is: so that if it falls on the customer side and thus onto customer responsibility, they can address the issue as soon as possible.

IT professionals have also taken advantage of this physical boundary to add surge protectors at that point, which protects the private network from surges on the public network.

Demarcation points are useful in troubleshooting, since they make it easy to disconnect a network from the larger network for testing and repairs.

There are also specialized network security features and redundancies that can be installed at the demarcation point, depending on the needs of the customer.

fiber optic

Point of demarcation for business

Not every point of demarcation is alike. The three most common demarcs for business phones are Network Terminal Interfaces, Smartjacks/Intelligent Network Interface Devices, and Optical Network Terminals. 

Regardless of which type it is, demarcs will be located at the Main Distribution Frame, or MDF, of the building in question.

Also learn more about the Different Types of Network Installation

Network Terminal Interfaces

These NIDs are commonplace and have the most basic features. They are mostly used in residential networks.

They come in the form of a small box that is weatherproofed and contains surge protectors, circuit protection, a test jack, and terminals for wiring. Their ratings are regulated by the FCC and which rating you need depends on the scale of your building and its network.

Network Terminal Interface

Intelligent Network Interface Devices/Smartjacks

INIDs are a more advanced version of NIDs, and are appropriate for more complex network setups such as triple play providers and T1 lines. These demarcation points are usual in business network settings.

NIDs have fairly basic wiring, but INIDs use circuit boards and signal boosters. They also usually include an alarm system that both customers and system providers can key into.

Optical Network Terminals

These demarcation points provide the highest speeds thanks to the inclusion of fiber optic cables–essentially, they take the signal from the local ISP and immediately speed it up to the benefit of the rest of the private LAN.

But they do require outside power, in addition to backup batteries in case of the system power outage.

Demarcation extension

In many commercial settings, the physical location of the private customer network can be quite a ways from the service provider network.

In a vertical office building or skyscraper, for instance, businesses on higher floors are far removed from the point of demarcation down on the ground floor.

Or, in a business with a large campus, the network boundary point for the service provider may be at a distance from where the buildings begin.

Cases like these require a demarc extension, which is pretty much what it sounds like–cable installation to bring the demarc point closer to the customer network.

The point of demarcation is not the most complex component in a network, but it plays an important role in allowing customers, businesses, and organizations to choose the telecom provider and equipment that best meets their needs.

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The Network Installers is a low voltage electrical contractor that provides data cabling, network installation, fiberoptic installation, and WIFI installation. We've been serving commercial customers since 2008 with exceptional quality, consistency, and professionalism.


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