Difference Between Outside Plant (OSP) and Premises

Posted on by FS.COM

Fiber optics is used in communications, lighting, medicine, optical inspections and to make sensors. But fiber optic is not always same. Such as outside plant (OSP) and premises cabling.

“outside plant” fiber optics as used in telephone networks, CATV, metropolitan networks, utilities, etc.

“premises cabling “fiber optics as found in buildings and campuses.

Outside Plant (OSP)

Telephone companies, CATV and the Internet all use lots of fiber optics, virtually all of which is singlemode fiber and most of which is outside buildings. It hangs from poles, is buried underground, pulled through conduit or is even submerged underwater. Most of it goes relatively long distances, from a few hundred feet to hundreds of miles.

Outside plant cables often have very high fiber counts, up to 288 fibers or more. Cable designs are optimized for the application: cables in conduit for pulling tension and resisting moisture, buried cables for resisting moisture and rodent damage, aerial for continuous tension and extreme weather and undersea for resisting moisture penetration. Installation requires special equipment like pullers or plows, and even trailers to carry giant spools of cable.

Splice and test

Long distances mean cables are spliced together, since cables are not manufactured in lengths longer than about 4-5 km (2.5-3 miles), and most splices are by fusion splicing. Connectors (generally SC or LC styles) on factory made pigtails are spliced onto the end of the cable. After installation, every fiber and every splice is tested with an OTDR.

If this sounds expensive, you are right! The installer usually has a temperature controlled van or trailer for splicing and/or a bucket truck. Investments in fusion splicers, OTDRs and other equipment can be quite expensive.

Premises Cabling

By contrast, premises cabling – cabling installed in a building or campus – involves shorter lengths, rarely longer than a few hundred feet, typically with fewer fibers per cable. The fiber is mostly multimode, except for the enlightened user who installs hybrid cable with both multimode and single mode fibers for future high bandwidth applications.

Splice and test

Splicing is practically unknown in premises applications. Cables between buildings can be bought with double jackets, PE for outside plant protection over PVC for building applications requiring flame retardant cable jackets, so cables can be run continuously between buildings. Today’s connectors often have lower loss than splices, and patch panels give more flexibility for moves, adds and changes.

Most connectors are SC or ST style with LC becoming more popular. Termination is by installing connectors directly on the ends of the fibers, primarily using adhesive or sometimes prepolished splice techniques. Testing is done by a source and meter, but every installer should have a flashlight type tracer to check fiber continuity and connection.

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