06-11-2012 04:12 AM
Every couple months or so, I'll be unable to connect to the internet. Today was one of those days. I have a Motorola Surfboard SB5101U modem. When this occurred, the send light was constantly blinking. I did all the basic steps, unplug/ re-plug modem and router, connect PC directly to modem,etc. Nothing. Then I ran ipconfig /release, ipconfig /renew. Still nothing. I then called Comcast and the guy said the signal wasn't getting to the modem.
Then later that night, my modem is back online, without any intervention on my part. The problem resolves itself every time I've run into this connection problem with this modem. I've posted some details from a site I found on another post in the forum.
Signal to Noise Ratio; 34.6 dB
Power Level: -12.4 dBmV
Channel ID: 7
Power: 54.0 dBmV
On the same website was a log page. I found the following warning and critical messages:
Received Response to Broadcast Maintenance Request, But no Unicast Maintenance o
Started Unicast Maintenance Ranging - No Response received - T3 time-out
DHCP WARNING - Non-critical field invalid in response
Can anyone tell me what the root cause of the connection problem may be?
06-11-2012 09:06 AM
Your signals are significantly out of spec -- this is causing your problems. Usually this is caused by too many splitters or bad/substandard wiring.
Generally, an acceptable signal range for a modem is:
Downstream (forward path): -7 to +7 dBmV.
Upstream: (return path): >40 dBmV but <50 dBmV . Some systems tolerate levels as low as 35 dBmV.
Signal to Noise Ratio (SNR): >33 dB (higher is better)
The operational range of modems is generally much greater than the desired range, so it's not unusual to have a modem operating outside of the specified range.
06-12-2012 06:24 PM
Thanks for the reply.
I'm assuming you were referring to the downstream signal when stating the signals are out of spec. During the outage, why was the 'Send' light blinking on the cable modem instead of the 'Receive' one if the downstream signal was too weak? The 'Receive' light stayed lit.
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