Headend? How does all of this stuff work?
Without going into detail beyond the scope of this document, our system works as follows.
All signals for your area originate from the headend, our central distribution facility. At this
location, we have a significant amount of equipment which comes together to send out the
signal to your home. The most notable one is the Cable Modem Termination System, or
CMTS. This piece of equipment communicates with all the modems in a given area to send
their data out to the internet at large. Each CMTS has a number of cards in it, more or less
small computers which handle smaller scale communications, servicing approximately
500-1000 customers each. Scaling down from there, each card has several upstreams
attached to it, which are the lines that go to individual areas. The upstream level is the
level at which we diagnose outages. Referring to the previous question, if 10% of
customers on an upstream are offline, they are considered to be in an outage. Each
upstream goes out to the area it services, where it splits to local nodes. The nodes then
split to the level of distribution in a block, and the lines distribute either via underground
lines to pedestals or aerial lines to individual homes. As you can see, this is a lot of cable.
When a problem comes up, we have to trace it down to the affected customers, determine
where the issue is occurring, and then fix the issue.