PON: How It Works

PON: How It Works

Vendors now say PON, which eliminates active elements on the loop, offers cost savings up to ten times that of SONET and is reaching cost parity with DSL and hybrid fiber coax. The combination of PON and WDM increases bandwidth availability and cost advantages even further.

A PON system typically consists of an optical terminal at the customer site that terminates the optical signal and delivers voice and data; an optical switch or other device that sits at the headend or central office to send the PON protocol to the terminal at the customer premises; and the passive couplers and splitters that actually sit on the fiber loop.

The PON equipment in the loop is placed at a fiber junction to act as a T-connector would on a garden hose, splitting two fibers into eight fibers, for example, to enable multiple customers to share fibers.

Those PON devices on the loop, which can be as small as a pen, typically cost only a couple hundred dollars vs. the hundred of thousand dollars it would cost to install a SONET add/drop multiplexer and the environmentally-controlled housing and power that would have to go with it. And because PON couplers and splitters are passive, meaning they don't require power, the carrier doesn't have to do as much ongoing maintenance of the equipment because there's no need for backup power or batteries in the outside plant.

PON can decrease the spectral interference created by copper-fed applications like ADSL and DS1, which clash if put in the same cable bundles, and instead roll the DS1 onto a passive fiber. PON is also less expensive to maintain because there are no active loop devices and fiber is less expensive to maintain in the long run than is copper in any case.

PON lets carriers go into new markets and share fibers among residential and small business customers like gas stations, strip malls and smaller establishments with automatic teller machines fed by 56kbps lines. It can also enable carriers to reach buildings that are just out of reach of fiber in a metropolitan network or even in-building networks that want to bring fiber to additional customers.