Modem Keeps Dropping Signal

Chances are it was not provisioned properly. Could be the mac address was input wrong. Try giving service a call again and have them double check it.

Reply to
Dr Feelgood
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SNR a little low, but still should work.

Check all your connections and make sure you have good contact. What devices do you have prior to the modem from the outside in ? How long is your run to the modem ? If all if well, you may want to try a swap on the modem.

Reply to
$Bill

I'm in the SF Bay Area, zip 94070. I swapped out my RCA DCM245, which couldn't handle the new, higher speeds, for a Motorola SB5101 at the Comcast walk-in store. I now have the new speeds, but every hour or so, the modem drops the signal. The online light stays solid, but I'm no longer connected to the internet. I have to power cycle.

Here's my modem stats for the new SB5101: Downstream Frequency 705000000 Hz Signal To Noise Ratio 27.8 dB (RCA was 35.2) Power Level -5.5 dBmV (RCA was -7.5)

Upstream Channel ID 4 Frequency 24800000 Hz Power 34.0 dBmV (RCA was 32)

I've got a truck roll for Saturday morning to check line (that's what Comcast wants to do), but it seems odd that this happened immediately after putting the new SB5101 into service.

I don't understand if this is a coincidence that the S/N dropped, or if the new modem could be the problem.

Reply to
Bruce

"Dr Feelgood" wrote in news:oNWdnc89S7RvjzzenZ2dnUVZ snipped-for-privacy@comcast.com:

If that were the case, I don't think I'd even get a connection.

Crap, just dropped again. Won't come back online without a power cycle.

Reply to
Bruce

Not necessarily.

Remember that both your computer and the modem have their own IP addresses. Your computer may be getting a valid IP address because it's MAC address is already on your account. When the modem comes online for the first time, it should get an IP address that will only allow local access, but once it's provisioned, it will get an IP address that will allow access to the Internet. The problem is that the IP address is initially assigned at the direction of the provisioning system. It is a very short lease. When it comes time to renew the lease, if the provisioning process has not finished, the regular DHCP server won't recognize the modem as being allowed to have a full-access IP address. Your online light will remain lit, but you'll have no access to the Internet.

It should be easy for this to be fixed. A customer service rep can repush, or refresh, the information on the account, after which the DHCP server for your node will now know to give your modem a full-access IP. Assuming your modem's MAC is correct in the records (which it probably is if you are able to get, and re-get, the temporary IP address that allows you to keep getting online over and over again for that hour time period.)

Reply to
Warren

In my area (eastern WA. state) Comcast offers the moto. modem along with one by the name of AMBIT, I saw it at a comcast booth in a home show & asked for it when I moved, It is much smaller about the size of a dsl modem and appears to be fast, I went from connect speeds of 3-4,000 to 7-9,500 whith the change (granted I did move but from a new neighborhood to one with nuch older lines).....we get 8,000 as cable subscribers here....anyway, since you are renting your modem and having problems with the Moto. you might check into it.

Reply to
Bob H

"Warren" wrote in news: snipped-for-privacy@comcast.com:

Thanks Warren and Dr. FG. I have had them push a new config file twice, but this time I asked them to check the MAC. It was correct. Comcast suggests possibly a bad modem out of the box, and to swap before the truck roll on Saturday. I'll try to get back to the Comcast store before then...

Thanks again.

Reply to
Bruce

I'm running an owned DCM 235r I bought back in 2000 and getting the full 8 meg and then some. I just wish Comcast would take the UL to a full meg.

Thousands of users are using the rental SB5101's without a problem. Double check your physical connections.

Is the truck roll still scheduled for tomorrow?

Reply to
Dr Feelgood

"Dr Feelgood" wrote in news: snipped-for-privacy@comcast.com:

Yep, the truck roll is still scheduled for Saturday (tomorrow) morning.

If interested, check out this thread. It discusses the Motorola SB5101 and possible firmware problems.

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Thanks, Bruce

Reply to
Bruce

They changed the downstream to 256 QAM. The SNR is too low to support reliable communication. You need to have a tech investigate. you may need a new drop, or they need to set up the amplifiers in your neibhorhood, as -5.5dB should get you somewhere around 35dB SNR or so, unless you are at the end of a very long cascade.

Good luck.

Reply to
Eric

Hopefully your tech showed today. If not...

The Singal To Noise Ratio can go as low as 1 (in theory), but will never happen given the noise that is present in your AC lines. !?! Does your cable run along multiple AC power cables?

The drop in value from the moto is an improvement, given it has lowered your S/N, it has also improved your Power Level (Rx), but this will only be temporary over time the AGC (Auto Gain Control) circuit in the modem will burn itself out, if too low.

The RCA modem reading was -7.5, given the correction of the AGC, your Rx is closer to and possibly lower than -10 dBmv, which is not realiable.

There are numerous reasons why the modem will lose sync with the system...keep an eye on the status lights on the modem when it happens.

Power, RX, TX, On Line and Data...

Power is a given RX is Recieve and very specific to the signal level at the modem...first to lock in sync TX is Transmit...second in sync On Line...full sync with system and first to go if splitters in the line Data...Rx/Tx to PC ehternet.

Hope this helps..

BigDaddyRhino

Reply to
BigDaddyRhino

You are confusing SNR with something else. High SNRs are good, low is bad. Check out "Shannon's Law" for the details of how SNR and bandwidth relate to information transfer rates.

Shannon's law can tell you the minimum theoretical SNR required for a given information rate across a channel with a certian bandwidth. With DOCSIS 256 QAM modulation on a 6 MHz channel, an SNR of about 30db or higher is required. 64 QAM (lower data rate), buys us another 6db of SNR, so the minimum is around 24db.

-Gary

Reply to
Gary

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