How Far Does Cable Fiber Go?

Following up on last week's question about why cable companies are buying fiber-to-the-home gear when they already have a DOCSIS 3.0 architecture that they claim is good enough to compete with Verizon, here is the first of a few background posts on the existing cable architecture.

Today, most cable deployments in the U.S. use a "Hybrid Fiber Coaxial" (HFC) architecture, meaning that they use a combination of fiber optic cable and coaxial cable to deliver video, Internet, and voice services to customers.  Coaxial cable is that shielded, cylindrical cable you plug in to the back of your set-top box, while fiber optic cable is a really really skinny glass thread that most folks have never seen (see picture of dozens of fiber optic threads).  The fiber optic cable is used to extend a the cable HFC network to a neighborhood with anywhere from a couple hundred to up to 2,000 homes, where the fiber is connected to an optical node and the signal is converted from optical to electrical (see diagram below). 

Once the signal is in electrical form it is transmitted downstream on coaxial cable, using radio frequencies (RF).  That coaxial cable goes through splitters so that individual coaxial cables can serve individual homes. The coaxial cable also goes through trunk amplifiers and line amplifiers to make sure the signal is still strong enough by the time it reaches your home.  Without the amplifiers, in many cases the signal strength would drop to levels too low to be detected by your set-top box or cable modem. 

That's part of the reason for the HFC architecture...if the cable operators tried to deliver signals from the headend all the way to your house on coaxial cable, they would be spending a lot of money on amplification, because of the distance limitations inherent in sending a signal down a coaxial cable.  Instead, cable operators use fiber optic cable to get the signal close to a neighborhood, because fiber optic networks use light rather than electricity, and light has better long-distance propagation characteristics. 

Okay, so cable operators are already using fiber optic cable to get the outskirts of your neighborhood, and then they use coaxial cable to go the rest of the way to your house.  In my next post on this topic, we'll look closer at the differences between fiber optic cable and coaxial cable.

Comments

[sezer]

Fiber Optic Cabling -Training - Technical Support (Training) - Information Web Site - - http://fiberoptic-cable.blogspot.com