Last week, two people asked me the same question. My8-year-old daughter and a guy who I work with basically wanted to know howcould a single wire, a single piece of coax cable both provide TV programminginto my TV and also carry Internet traffic? How does that work?
Well, instead of thinking it as a single cable or a singlechannel, think of it as a highway where you can allocate a certain amount ofbandwidth for each need that you have. What the cable company does is typicallyassign 6 MHz of bandwidth for each channel. So you think about this road. TheCNN road gets 6 MHz and, you know, USA gets 6 MHz, ESPN gets 6 MHz, you get theidea, specific allocations. So you have separate bandwidth channels within thiscable.
Now, if you are also using Internet access with your cablecompany, what they do is take one of these unused channels and give you that...allocate that bandwidth for you for traffic. But they have 2 differentallocations for incoming traffic and outgoing, traffic typically that goes intoyour PC gets an entire channel 6 MHz. On the other hand, most cable companieswere strict. The bandwidth for traffic that comes out of the Internet to 2 MHz.That enables them to control their cost. It also enables them to discouragepeople from running commercial Web sites onto residential accounts. So that'show they carry the traffic there and this 6 MHz path is usually sufficient foranyone's use for home use on the Internet.
You have to remember though, just because you've got 6 MHzcoming from the street into your house, it doesn't mean you're going to getthat much when it comes in because even though they have allocated this whole 6MHz, you're sharing Internet access with everyone on your neighborhood that'sriding that infrastructure. So even though this path is pretty wide, your throughputwhen you actually get in and out of your machine could be considerably lessthan this if there's a lot of contention in the neighborhood.
