Telecom Jargon for Layer 1 & 2 of the OSI Model

From LECs and lit buildings to fiber splices and MPOEs, this post provides a glossary of telecom jargon as it relates to layer 1 and layer 2 of the OSI model.

glossary dictionary
Matt Pinto

Mar 17, 2022


The telecom industry is famous for a lot of things; for being the most important industry, for being the most hated industry, and for being the most jargon-ful industry. 

Whether you’re a network engineer tasked with keeping the internet up and running for your company or you’re an IT procurement analyst buying services, your day is bound to be jam packed with telecom and networking jargon. And confusion is nothing to be ashamed of - even the most experienced networkers run into terms, new or (super) old, that they haven’t heard of before. 

I’ve worked in telecom for 25+ years and wanted to share my personal glossary of telecom jargon. I split up the glossary as the jargon relates to the layers of the OSI model and I’ll be releasing it in a series right here on the Lightyear blog. 

Telecom & the OSI Model: Layer 1 & 2

The Open Systems Interconnection (OSI) model is used to describe the seven standard layers that are used to communicate in a computer system network. Telecommunications takes place across all seven layers of the OSI model, and there are different types of telecom providers at each layer (some span across many or all layers, as well).

This series of the Telecom Jargon Glossary refers to the elements of telecommunications that sit at layer 1 and layer 2 of the OSI model. 

Layer 1 of the OSI model is referred to as the “physical layer” where an actual, touchable medium is used to transmit data from one place to the other.

Layer 2 of the OSI model is referred to as the “data link layer” where the data is transmitted between the nodes on the network that are physically connected via Layer 1. This layer breaks data into packets and moves them based on the network protocol. 

Before we dive into the jargon, I should point out that this blog is covering Layer 1 and 2 telecom jargon as it relates to the physical, wired links. Wireless links (LTE, 5G, Fixed Wireless, satellite) operate on Layer 1 and 2 very similarly to wired links, but in order to keep this blog at a reasonable length we are saving that for a separate post. 

Telecom Provider Layer 1 Jargon

Telecom Provider Nicknames

There are telecom providers at every layer of the OSI model. Here we discuss the providers who own the fiber or cable in the ground that your data is transmitted over. 

While you may be used to referring to your telecom provider using explicative terms, this section covers some of the more common technical terms (aka jargon) used to describe the layer 1 telecom providers. 

If you manage the network for your company, you should know the local Cable Company (CableCo) and the Local Exchange Carrier (LEC). Most regions have both a CableCo and a LEC. 

Cable Company (CableCo) 

The CableCo is your local provider of telecommunications services primarily in the form of television services. As demand for internet connectivity has grown and technological advances have been made, CableCos have begun to service traditional internet connectivity needs over their network infrastructure as well. CableCo’s mode of physically transporting data ranges from DSL to copper, coax and fiber (more on these in the next section). 

Local Exchange Carrier (LEC)

The Local Exchange Carrier (LEC) is the company that provides telecom services in your area historically over copper. Current trends see most LECs abandoning their copper plant (T1, DSL, and POTS) and replacing them with fiber based services.  Although it will still be some time (maybe never) before copper is fully phased out it’s important to know of this trend before investing heavily on equipment that would integrate with copper entrance facilities.

ILEC: Incumbent Local Exchange Carriers are the companies who used to hold a regional monopoly in your area for providing telephony services. The ILEC monopolies in the USA came undone when the United States Congress passed the Telecommunications Act of 1996. The original ILEC in the United States was AT&T. AT&T still operates as an ILEC in several areas. Other major ILECs in the United States include Centurylink, Frontier Communications, Windstream, Verizon, Claro, and several others.

CLEC: Competitive Local Exchange Carriers are telecommunication providers that compete with the larger LECs and have their equipment connected to the LEC. In some instances, they are able to provide more competitive pricing. CLECs are now also building their own fiber networks and offering more cloud-based services. Examples of CLECs in the United States include Cogent Communications, Inc., Granite Telecommunications, LLC, and TelePacific Communications.

Layer 1 Provider Specific Terms

Lit Building vs Not Lit Building 

A lit building is one that already has telecom services in place (i.e. the fiber is already installed). It’s preferred to install services at lit buildings because it means that no construction is required to service the location. 

Just because a building is lit, that does not mean that your specific provider has fiber installed at this location, it just means that a provider has fiber there. 

If you require Lumen fiber at a building that is lit with only AT&T fiber (this might happen to you when expanding an MPLS network), Lumen will need to build its fiber to this location which of course comes at a cost; this is an expensive and time consuming process. For more on this topic, check out our guide to telecom installation fees.   

On-Net vs Off-Net

An On-Net provider is a telecom company that is able to facilitate your entire build or project at a certain location. It’s preferred to work with on-net providers because it means that your traffic will be traversing solely that provider’s network. 

If the provider is not able to facilitate your entire project and your traffic is required to traverse Type 2 circuits (aka a different provider’s network), this provider is considered to be Off-Net.  

Type 1 vs Type 2

Your service is considered Type 1 when the provider builds the network and service to become your on-net provider, and your traffic traverses their network solely. 

Type 2 service is when the provider doesn’t own the infrastructure, but rather they lease the network infrastructure from a third party to service your location. If your provider is Type 2, this should be clearly identified in their SLAs. 

When procuring Type 2 circuits, be sure to diligence the cost. As Type 2 providers are essentially resellers, there’s bound to be an MRC mark-up.

Telecom Network Layer 1 Jargon 

Transport Type

Transport type refers to the physical mode of moving data on your network and comes in a few flavors - copper, coax, and fiber (and wireless, which we will discuss in a separate post).

(Twisted Pair) Copper Cabling 

While iron and steel were the metals used in the first telephone systems of the 1880s, copper quickly became the standard medium due to its high electrical conductivity and corrosion resistance. Copper transmits data by sending electrical signals over the cable. 

Copper continues to fall out of vogue as it has lower bandwidth and distance capabilities and is subject to interference more than the alternatives - fiber and coax. 

Coaxial Cable

Coaxial cable or simply “coax” is essentially enhanced copper cabling, where insulation and a conduction shield enable the cable to transmit data over greater distances. Due to these relative benefits, Coax is in greater use today than copper. 

Fiber Optic Cable

Fiber optic cable or simply “fiber” is the optimal transport medium available today. Fiber cables contain strands of glass fibers that carry telecommunication signals via pulses of light which results in much more efficient transmission than copper and coax. The physical Fiber cabling is also lighter weight and more flexible than copper and coax, adding to its attractiveness.

There are two types of fiber cables that are utilized for telecommunications: single-mode fiber (SMF) and multi-mode fiber (MMF).

Point to Point or P2P 

Point to Point or P2P refers to the network topology of your layer 1 telecommunications network. This is a network that connects point A to point B in a direct link. 

P2P can also refer to the type of connection you are procuring (traditional fiber vs waves over fiber) which is a layer 2 application of P2P (discussed in the next section).  

Dark Fiber 

Dark Fiber or wholesale fiber refers to unlit fiber lines that are leased out by the telecom provider to end users. End users can harness dormant or dark fiber by installing their own electronics on the fiber. 

Fiber Splice Point

An important thing to know about fiber is that just because you have fiber installed on your street does not mean that you are able to utilize that fiber. That’s because of the splice points. 

A splice point is where two strands of fiber optic cable are connected together. 

When procuring fiber, it’s helpful to know where the nearest splice point or access point for your providers’ fiber is, as this is where you will be able to actually connect to the network. 

Right of Entry (ROE) 

The Right of Entry (ROE) refers to the permission the telecom provider needs to receive from the property owner in order to install your services and use power in the meter room. 

If you own the property where construction needs to take place, you will receive the ROE documents directly from the provider and can execute them. If you are a tenant, you will need to engage your landlord in order to get the services installed. 

Utility Easement 

A utility easement is the section of private property where utility companies have the right to access for water, power, gas, sewage, and telecommunications needs. 

This term is relevant for layer 1 telecommunications as it relates to the location that providers are able to install their services. The utility easement is blocked off by the local municipality and will border all property types.  For example, even my personal piece of property around my home has a 6’ utility easement around the entire perimeter. Utility providers are not required to obtain any special permitting to construct on utility easements. 

The thing that does need to be obtained are construction permits.  The permitting process is the longest pole in the tent in many telecom installation situations.  Construction cannot even start until the appropriate municipalities authorize permitting. It is possible to pay for expedited telecom installations, but they are never guaranteed, and the need for permitting is a big part of that.  

Telecom Network Layer 2 Jargon

Wavelength Services

Wave Services are a type of Layer 2 wide area networking technology that takes place over fiber optic cable. 

Wave providers use dense wavelength division multiplexing (DWDM) technology that allows for multiple, private, high-capacity circuits to be delivered over a single fiber strand. The network interface device (NID) connected to your fiber by the carrier is what runs the DWDM technology and defines the network protocol of your wavelength services (which is most traditionally ethernet). 

Handoff details

Handoff details concern where the connection from the carrier’s network goes to the customer hardware. Fiber or electrical—electrical is a fancy way to say Ethernet. Handoff rarely has an implication on price. What you do see is sometimes there’s inflexibility due to physical limitations as well as carrier policy. Sometimes electrical just isn’t an option due to distance limitations or speed requirements. So if you’re an old network with old boxes, your electrical transport might not be able to peer with the carrier.

Demarc or Demarcation Point 

The demarcation point (aka demarc) is where your telecom network services interface with the provider’s services. In other words, this is where the carrier’s responsibility ends and the customer’s local network starts.

There are two common terms regarding demarc location discussed below.

Minimum Point of Entry (MPOE)

The Minimum Point of Entry or MPOE is the point where the telecom providers’ wiring enters your location. 

When working with the LEC, it is common that they will only deliver services to the Minimum Point of Entry of your location. The location of the MPOE in most buildings is the 1st floor telecommunications closet.

Extended Demarc

In many cases, it is the end user / customer’s responsibility to extend the demarc from the MPOE to wherever the customer equipment is in the building.

In other situations, demarc extension can be requested and often granted by the service provider.  In many cases, the service provider will provide specifications that need to be met in order for them to extend the demarc.

A common extended demarc request would be something like, 

“Extend demarc from MPOE 1st floor meter room to customer’s telecom backboard on the 4th floor suite 410.”  

A common response from the service provider would be, 

“Provide conduit with inner duct from the MPOE to suite 410 backboard with available 2’x2’ plywood backboard coated in fire suppressant paint, #6 ground, and isolated 120VAC power outlet.”  

Metro Ethernet 

Metro Ethernet is a transport network that provides P2P (or multipoint) connectivity over a metropolitan area network (MAN). Carriers commonly use this as a method to bring services back to their Point of Presence (POP) and then layer on additional services.  More on this when we go over Layer 3 of the OSI model.

Virtual Local Area Network (VLAN)

A Virtual LAN is a group of network nodes that are connected as if they are part of a single local area network, but in reality they make up one or several LANs which are segmented together. This virtual segmentation reduces network traffic delays by utilizing bridges and switches to control the traffic.  

To be continued… 

As mentioned above, this post just dips into the world of telecom and networking jargon.

I hope you found it helpful. Look out for future posts on telecom jargon as it relates to the other layers of the OSI model. 

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