I am new to DOCSIS and CMTS. We have a CMTS at work.
We have been asked to perform a ranging test on cable modems.
Can you briefly explain what ranging is so that a novice like myself can understand it? Right now the CMTS only has 1 Upstream and 1 Downstream.
Thanks
Jobin
Is ranging telling the CM to tune to a different upstream frequency or downstream frequency by setting values in the cable modem and then the CMTS communicating with the cable modem to let it do so?
the cmts is constantly communicating with the modems, having it adjust it's transmit levels and staying or going to different frequencies. when the modem first starts it's registration it scans the downstream to find a docsis channel. info on the channel(s) gives the modem information in regards to return frequencies it listens to. so if your downstream is at 555Mhz and returns are 30 and 35Mhz for example, the modem will transmit at 30Mhz, increasing it's power level until the cmts replies to increase or lower it's transmit level to hit the receiver at the correct level. the increasing or decreasing it's power level until it hits the receiver at the correct receive level is ranging. since your new, rule of thumb to save yourself allot of headaches... docsis spec for modems is receive power level of 0 +/- 15 and max transmit level of 61 (depends on modulation).
make sure all the modems are 0 +/- 10 dbmv and don't transmit over 52 dbmv.
~Carl