Network Design elements

Our approach to designing networks is from the bottom up (starting at the customer and connecting back to the OLT). Because of this, our terminology starts at the bottom of the network and works up.

FOND designs a 3 tiered network. Rather than use terms like Drop, Distribution, Access, Feeder and Backbone which can mean different things to different customers, we just named ours Tier 1 (T1), Tier 2 (T2) and Tier 3 (T3). Each Tier has its own type of Cable, as well as its own type of Hub.

This page is mainly a glossary of terms. For more information on how to interpret a design, see How to interpret a design.


A cabinet is any above ground structure that houses equipment like splitters, patch panels or OLTs.

Tier 2 Cabinet

Cabinet, PFP, FHD, Hub, Splitter cabinet - these are some common names for these devices. The Tier 2 Hub can have a range of sizes. While it’s always called a Cabinet in our schema, in practice it can also represent a splice closure with a small number of splitters in it. This is where the primary splitters of the network reside.

See here for an example.

Tier 3 Cabinet

Central Office, Hut, Exchange and Hub are all frequently used to describe the location which houses the OLTs for the PON network. This is typically where the only active equipment will be housed in the FTTH network.

T1 Dedicated Cabinet

In cases where an address or group of addresses have more demand than the T2 Cabinet can support, FOND will place a T2 Dedicated Cabinet which reserves the correct amount of fiber. See our section on editing input data on ways to prevent unwanted T2 Dedicated Cabinets. 


A closure is a splice closure that can be buried in a Pit, or on a pole. Some Closures can house splitters, but mostly they’re used to branch cables.

T3 and T2 Closures

These closures are used to branch T2 and T3 Cable (see the section on cables below).

T1 Closure  

MST, MPT, FST, Terminal, Boundary Box, Drop terminal - these are all some of the names we hear for a device that has a similar function. The function of the Tier 1 Closure is to service the Tier 1 Cable (aka Drops) to the customer. In a distributed split network, these hubs can house the Secondary splitters.

Tier 1 Closures can also be used to branch T2 Cable.

See here for an example. 

T1 Dedicated Closure

In cases where an address or group of addresses have more demand than the T1 Closure can support, FOND will place a T1 Dedicated Demand which reserves the correct amount of fiber.  

See here for an example. 


We’ve used the term pit to encompass a range of underground structures including pedestals, flowerpots, handholes, and vaults.

See here for an example.


Any pole that is used to support a cable or any other equipment in the network.


Any type of Fiber Optic cable that’s in our designs. We have three categories: Tier 1 Cable, Tier 2 and Tier 3. 

Tier 1 Cable 

These cables connect the customer addresses back to the Tier 1 Closure. Commonly called Drop cables.

Tier 2 Cable 

This is any cable that connects the T1 Closure to the T2 Cabinet. It could be a cable that is manufactured along with the MST head, or it could be a cable that the Tier 1 Hub gets spliced into.

Fibers in this tier have typically been split.

See here for an example.

Tier 3 Cable 

This is a cable that connects the T3 Cabinet (typically where the OLT and active equipment reside) to the T2 Cabinet.

See here for an example.


Houses cable in an underground environment.


Anywhere where there will need to be trenching or boring to install conduit.


The high-level route the network takes, showing where there is cable without showing the detail of the type, size or connectivity.


Tier 1 Cables and Closures

In the image below, you can see the red T1 Closures () serving Addresses () with Tier 1 Cables ().



T1 Dedicated Closure example

In the image below, we have a design that used T1 Closures with only 4 ports. Since there are too many addresses to all be served on that road segment, FOND has just reserved 5 and 8 fibers at the left and right T1 Dedicated Closures (). 


Tier 2 Cables and Cabinets

In the image below, we can see how the T2 Cabinet () is serving the T1 Closures () with fiber via the Tier 2 Cable ().


Tier 3 Cables and Cabinets

In the image below, we can see how the T3 Cabinet () is serving the T2 Cabinet () with fiber via the Tier 3 Cable ().



Pit example

In the image below you can see that there's a Pit placed where the T1 Cable breaks out to serve an address. There's also a Pit underneath the T1 Closure that can be seen when toggling the layer on and off.