MacLeech
The one and only
Premium,MVM
join:2001-07-14
SoCal
edit:
March 11th, @08:26PM
| said by funchords  :What is CPD? CPD = common path distortion. It's caused when forward signals are "reflected" back onto the return path. It's more common on the coax distribution system where the forward signals are high (20 dBmV or higher) and the return attenuation is low.
It causes the return noise floor to jump up quite a bit (some times more than 20 dB). It kills the upstream SNR and causes "codeword" errors on the upstream. It usually affects every modem on the upstream CMTS port, but can be VERY intermittent and difficult to track down because it often disappears for hours or days due to being disturbed during the troubleshooting process.
If CPD is strong enough, it'll knock modems offline, if it's not it could just slow things down and cause "hiccups" occasionally because of the upstream errors.
It has a lot of possible causes: corrosion of distribution equipment, loose connectors, bad termination, faulty amplifiers, kinked cable, customer wiring issues, etc.... I've seen alot of it first hand.
This may interest you:
»cable.doit.wisc.edu/cpd/cpd2.v2.html
[edit]Posted better link. |
