FOA Guide 

Topic: Optical LANs (OLANs)

Fiber To The Desk/Fiber To The Office

Table of Contents: The FOA Reference Guide To Fiber Optics

Optical LANs (OLANs) or Fiber Optic Local Area Networks (LANs)

Centralized Fiber Optic Cabling - Fiber to the Desk and Fiber To The Office 
Passive Optical LANs 

Designing And Installing Optical LANs (OLANs)
Testing OLANs  

As Ethernet network speeds grew from 10 to 100MB/s and then 1Gb/s, optical fiber was quickly recognized as a simpler way to upgrade to higher speeds and provide longer backbone connections. Both multimode and singlemode fiber were added to the cabling standards for backbones with longer lengths and multimode was added to the horizontal link but still with the same 100m length limit.

The additional bandwidth and link length capability of fiber was later recognized in the late 1990s by allowing a "centralized fiber" architecture in the standards, an architecture often called "fiber to the desk" or FTTD. Instead of several Cat 5 UTP cables, two fibers were run to the desktop where a media converter allowed devices to connect over standard Cat 5 cables. Here fiber connects the desktop directly without the electronics in the telecom closet (renamed telecom room in later versions of the standard.) Since fiber needs no intermediate electronics, the cost of equipment drops and the need for power, AC and grounds - or even the space allocated for the equipment (the telecom room) - means the cost of equipping telecom rooms goes away, easily offsetting the higher cost of the fiber electronics needed to interface to the connected device. The cost of the fiber cabling, meanwhile, had dropped and copper increased, so the cabling cost itself was often less for fiber than copper.

Here is the architecture of centralized fiber compared to normal structured cabling.

cabling architecture

When centralized fiber was introduced, the installed cost of fiber was still higher than copper and, since all the connected devices had network connections for a UTP cable with modular 8-pin connector, every device needed a media converter, increasing the cost of using fiber. Computer room switches also required fiber ports and most switch manufacuteres charged very high prices for fiber ports, making media converters often the more economic choice. These additional costs could be offset by the lack of need for services (power, grounds and AC) in a telecom closet, but many users who were upgrading already had these services available. This analysis made it hard to sell centralized fiber architecture to users except those needing longer links, additional security, immunity to interference or "bragging rights."

Several equipment vendors had a solution to the cost equation. Instead of using a media converter for each connected device, use an architecture more like copper's "zone cabling," where the fiber connected to a small switch with 2-4 ports that would spread the cost of fiber among several users, finally making the fiber cost competitive.

Fiber To The Office (FTTO)

Fiber to the office is a simple development of centralized fiber in structured cabling architecture, except it uses lower cost components designed for FTTH and singlemode fiber. Like centralized fiber, the work area switches are connected by two fibers transmitting in opposite directions for full duplex connections. The FTTH-type components are cheaper and incorporate power over Ethernet (PoE) for powering local devices.

This is the network for Terminal 3 at the Dubai Airport as designed by Cliff Walker. It uses FTTH P2P (point to point)  links to 4 port switches. FTTO was chosen in part because of the sheer size of the terminal which made copper or MM fiber unfeasible. This architecture is similar to centralized fiber optics in structured cabling standards except it uses FTTH hardware, including singlemode fiber. Here is Cliff Walker's paper on this FTTO application.

FTTO Terminal 3 Dubai 

Here is a diagram of the Dubai Airport network which covers a PC LAN, VoIP phones, Wifi access points and IP surveillance cameras all over a terminal several kilometers long. Power over Ethernet was provided from a central DC source to each of the local switches.

Dubai Airport

Here is the block diagram of a typical FTTO network.


FTTD/FTTO is a design that is familiar to most IT managers because the network electronics and management systems are traditional Ethernet and familiar to most users - in fact they are the same. Only the cable plant is different from copper networks, but the substitution of singlemode fiber gives this network practically unlimited bandwidth for upgrades.

More On OLANs

Centralized Fiber Optic Cabling - Fiber to the Desk and Fiber To The Office 
Understanding Passive Optical LANs  
Designing And Installing Optical LANs (OLANs)
Testing OLANs  

Training And Certification

FOA has an Optical LAN (OLAN) specialist certification (CFOS/L) with training available from FOA approved schools. Read more.

Here are more sources of information on Optical LANs.

The  FOA YouTube Lecture 30, OLANs, Optical LANs

There is a new trade association focusing on passive optical LANs: APOLAN



Cliff Walker's FTTO paper

3M on POLs 

TE Connectivity on Optical LAN Solutions  

Corning Cable Systems on Optical LAN Solutions 

Table of Contents: The FOA Reference Guide To Fiber Optics


(C)2014, The Fiber Optic Association, Inc.