General

Cable Architecture

How do cable companies design their networks? Members of the ISP-Cable list sketch out the basics.

[March 7, 2000]

On the ISP-Cable list in October, GH asked for some help in understanding cable network architecture:

"We've created a capacity planning application for ISPs and gotten some interest from cable folks. I'd like to understand the architecture; can someone point me to a resource regarding how cable companies architect their networks to consolidate head-ends and where they deploy Internet access via DS-1, DS-3 or even OC-3 pipes?"

One respondent suggested a source of information:

[JP suggested] "You might find some useful information or aid at the SCTE-List (also available at www.scte-list@relay.doit.wisc.edu )."

[Ed. Note: The SCTE-LIST is an online forum run by the Society of Cable Telecommunications Engineers (SCTE). The list is dedicated to discussion of cable television and telecommunications from the technological perspective.]

A number of respondents reported that they had actually done such designs:

[FK wrote] "There's nothing about the cable architecture that imposes unique requirements. I've done such designs, but I don't know of any publicly available resource for the same. Cisco may have resources for designing the head-end. I think they are pretty much a monopoly in this area."

One respondent outlined two basic cable modem systems:

[TM agreed] "The concept is quite simple. Most cable companies have one of two setups. The simplest explanation of the first is that it uses one head-end with all the High Frequency Cable (HFC) coming back to it. This is quite simple if you're using DOCIS equipment with one Cable Modem Termination System (CMTS) per 14,000 homes passed or 500 homes per node. These connect to a switch, then out to the net. The second setup uses multiple head-ends with dedicated dark fiber and Ethernet transceivers connecting the head-ends, so basically you just extend your LAN."

[TM added] "The one thing you need to keep in mind is until you hit a few DS3 the bandwidth on your cable network will always be higher then your Internet bandwidth. We have a product from Allot Communications which, based on how much bandwidth is being used overall, will allocate bandwidth to each customer based on priorities/rules and such."

—End