Fiber Optic Cabling Installation for Backbone and Campus Networks

Where fiber belongs in a commercial building or campus#

Fiber optic cabling carries the backbone of a commercial network: the links between the MDF and each IDF in a building, the links between buildings on a campus, and the links from the carrier entrance to the equipment room. It also shows up in the horizontal where copper cannot reach, such as a camera pole in a parking lot or a warehouse endpoint 200 meters from the nearest IDF.

We design, install, splice, terminate and test fiber as part of a structured cabling system or as a standalone backbone upgrade in an existing building. Telelink Business Services is a licensed C-7 Low Voltage Systems Contractor, CSLB License #472017. The optical backbone is usually bid under Division 27 13 23.

Single-mode OS2 or multimode OM3, OM4, OM5: how we choose#

The first design decision is the fiber type, and the answer depends on distance, the optics your switches will use, and how long you plan to keep the cable in the wall.

Single-mode OS2 has a small core, roughly 9 microns, and carries light at 1310 nm or 1550 nm. Distance is not a practical constraint inside a building or across a campus, and OS2 supports 10 Gb/s and 100 Gb/s links over kilometers. The optics cost more than multimode optics at the same speed, though the gap has narrowed. OS2 is the right choice for campus links between buildings, for any backbone that may need to run 40 or 100 Gb/s later, and for links longer than the multimode limits below.

Multimode OM3, OM4 and OM5 have a 50 micron core and use 850 nm optics that are cheaper and lower powered. Distance is the constraint. OM3 supports 10 Gb/s to 300 meters. OM4 supports 10 Gb/s to 400 meters and 40 or 100 Gb/s to shorter distances using parallel optics. OM5 is wideband multimode designed for short wavelength division multiplexing, which lets one pair of fibers carry several wavelengths, and it supports the same distances as OM4 for the common optics. Multimode is common for in-building riser backbones where the longest run is a few hundred meters.

Fiber	Core	10 Gb/s reach	Typical use
OM3	50 µm	300 m	Existing in-building backbones, extensions to match
OM4	50 µm	400 m	New in-building riser backbones
OM5	50 µm	400 m, SWDM capable	In-building where higher speeds on duplex fiber are planned
OS2	9 µm	10 km and beyond	Campus links, carrier entrance, future 40G and 100G

Where the spec leaves the choice open, we usually recommend OS2 for anything between buildings and either OM4 or OS2 inside the building, priced both ways so the owner can decide. We also recommend more strand count than the day-one need. Twelve strands where you need four costs a little more in cable and almost nothing more in labor, and it saves a second pull later.

Riser backbone and campus backbone design#

In-building backbone follows the star topology in ANSI/TIA-568: each IDF is linked directly to the MDF. Riser cable runs in a shaft or in sleeves through each floor, in a pathway that protects the cable from the other trades, and terminates in a fiber enclosure in each room. We use riser rated (OFNR) or plenum rated (OFNP) fiber cable depending on the space, as required by Article 770 of the California Electrical Code (Title 24, Part 3).

Campus backbone links buildings through underground conduit, existing utility tunnels, or, in some cases, aerial plant. We design the route, the conduit and innerduct sizing, the pull points and the cable type, and we coordinate the trenching and conduit installation with the GC and the electrician. Outside plant cable is armored or gel-filled and is not listed for use inside a building beyond a short distance from the entrance, so we plan the transition to indoor rated cable or a splice enclosure at the entrance facility.

For every backbone link we calculate the loss budget before we order cable. The budget adds the cable attenuation for the length, the maximum loss per mated connector pair (0.75 dB in ANSI/TIA-568.3-D), and the maximum loss per splice (0.3 dB). Then we compare the total against the power budget of the optics you plan to use. If the link does not close with margin, we change the design on paper, not after the cable is pulled.

Fusion splicing, connectors and enclosures#

Fiber is terminated one of three ways on our jobs, and the spec usually decides which.

Fusion splicing to factory-terminated pigtails. The cable strands are fusion spliced to pigtails with factory-polished connectors, and the splices are protected in a splice tray inside the enclosure. This gives the lowest and most consistent loss per termination, and it is how we terminate most backbone and outside plant cable.

Pre-terminated trunk cable. The cable is manufactured to length with connectors on both ends, often MPO connectors carrying 12 or 24 fibers each, and lands in a cassette that breaks out to LC duplex ports. Pre-terminated trunks install quickly and test predictably, but the length has to be right, and the pathway has to accept the pulling grip and the connector bundle.

Field-polished or mechanical connectors. Used for small counts and repairs. Acceptable where the spec allows it, but we prefer splicing for anything permanent.

LC duplex is the standard connector on modern switches and patch panels. SC is common on older equipment and some carrier handoffs. MPO is used for parallel optics and high-density trunks, and polarity has to be planned end to end so that transmit lands on receive. We document the polarity method on the drawings and label every port per ANSI/TIA-606. Enclosures are rack-mount or wall-mount, sized with spare capacity, and every strand is labeled at both ends. Corning, CommScope, Panduit and Leviton are the fiber and connectivity lines we see specified most often on California backbone work, and where the drawings name one, that is the line we install.

Outside plant, conduit and the building entrance#

Outside plant (OSP) fiber work adds civil and code items to the scope. The conduit route needs pull boxes at intervals and at every change of direction, sized for the cable and the pulling method. Innerduct inside a larger conduit protects the fiber and reserves space for a second cable. At the building entrance, the conduit is sealed against water and gas, the cable is bonded and grounded where it has metallic armor or strength members, and the transition to indoor cable or a splice enclosure happens within the distance Article 770 allows for unlisted OSP cable inside a building.

Trenching, boring and the underground conduit are usually civil or electrical scope. We provide the route, the conduit and innerduct specification, the pull box locations and the entrance detail, and we coordinate with the GC and the electrician so that the conduit is ready when the cable arrives. The bond from the entrance protector or armor to building ground is electrical scope; we show it on our submittal. In an existing campus, we survey the existing conduit with a mandrel and a pull line before we promise a cable will fit, because a collapsed duct found on pull day is a schedule problem for everyone.

Tier 1 and Tier 2 testing to ANSI/TIA-568.3-D#

Every fiber link we install is tested, and the test method matches the spec.

Tier 1 testing uses an optical loss test set (OLTS) to measure the insertion loss of every strand end to end, in both directions where specified, at the wavelengths the strand will carry (850 and 1300 nm for multimode, 1310 and 1550 nm for single-mode). Tier 1 also records length and verifies polarity. The measured loss is compared with the calculated loss budget for the link, and every strand must pass.

Tier 2 testing adds an optical time domain reflectometer (OTDR) trace of every strand. The OTDR shows each connector, splice and bend as an event along the length of the fiber, so a link that passes its total loss but has a bad splice buried in it gets caught. Tier 2 also produces the record you want in five years when a strand goes dark and you need to know where the break is. Most institutional and public agency specs require Tier 2 on the backbone. Where the spec is silent, we recommend it and price it as a line item.

We use calibrated test sets with reference cords matched to the connector type, inspect and clean every connector end face before it is mated, and deliver the OLTS results and OTDR traces in the native tester format and as PDF, one record per strand, with labels that match the enclosure and the drawing.

Touro University: a campus fiber backbone in a renovation#

On the Touro University campus building renovation in Vallejo, our scope included the fiber backbone along with network cabling, IT room buildout and wireless. The fiber tied the building’s new IT rooms together and connected the building to the campus network, and the rooms and the backbone were built while the campus stayed in session.

The project is a good example of the combination most institutional owners need: a backbone sized for the next decade of switch uplinks, rooms built to hold it, and testing that proves each strand before the IT staff moves the first switch. Our education market page covers how we approach K-12 and higher education work, and our network room buildout page covers the rooms the fiber lands in. Public agencies with similar backbone needs can read about prequalification and documentation on our government and public works page.

Next step#

Send us the backbone riser diagram, the site plan, or a description of the buildings you need to link through request a bid. We will return a design with fiber type, strand count, termination method and testing tier priced as options where the spec leaves them open. General contractors can read about our prequalification and coordination process on the for general contractors page.