Sleeping Modems

Posted on 2004-08-26
Last Modified: 2010-03-17
We are a small local internet provider of broadband connection.

We have been having a sleeping (freezing) modem issue. The equipment is a 3COM Total Controller.

The modems we seem to be having the most trouble with are Toshiba,Surfboards and Piperiders.

Could you tell me what could be causing this to happen?

Question by:Rockey98
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Expert Comment

ID: 11904706
Are these modems by any chance USB modems?  If so, you may have to disable the power management for the UBS port in your Device Manager.
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Expert Comment

ID: 11904905
The asker is concerned with possible diagnostics needed for determining causes between the head-end of a cable network and the modems in the field.  I know this because he called me to ask me this question and I asked him to post here where he can pick the brains of the top talent in the world on the matter.  We don't think these are not matters localized to the customer end.

I am a customer of this ISP.  I use a 10baseT Cat5 cable to connect the 3 com modem (Model 3CR29223, looks like a shark fin) to the cable network and still experience this periodically.  I have kept logs on the moments of downtime as I find them.  I use a Netgear Hub and Linksys Cable/DSL Router to hook up 5 systems.

The local modem and/or router lights give NO indication that service has been interrupted.  It is detected on attempting to move traffic by any application.  It is sometime preceeded by a "slow down" on the network prior to an outage.  Additionally, the modem may sometime NOT "go down" and attempt re-acquisition.  It might just start working again with no indication that there was any problem.  The problem usually goes away within a minute, not to occur again for as much as about 24 hours.


Expert Comment

ID: 11905531
It is possible that if you are a small broadband shop that you have a bad batch of modems.  TW for some time received several shipments of bad motorolla surfboard and Toshiba modems.  I do not recall the specific lot that had the bad modems, but I would check with your vendors.
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Accepted Solution

Fatal_Exception earned 500 total points
ID: 11913059
There is a lot that goes on between the head-end and the end-user...  Bad batch of modems could certainly be a problem, but as you all know, these cable signals are amplified every 1000 feet or so, depending on the cable size, etc.  Signals could be bleeding, the amps may need their chips reset and tweaked, could even be the quality of the amps in place, etc...  It has been a few years since I was in the business building these, but other than the meters available in the 90's, I don't know the new techniques they are using now for monitoring and nailing down the problems in the circuits.

I would try to narrow down the vicinity where the problems occur first, then take a long look at the lines installed.  If the drops were installed with anything but RJ6 wire, the first thing I would do is replace them (older wire installed in the 80's was rj58 I believe..:).  If they are over 200 feet, then perhaps upgrade to RJ11 wire for the drops.  And ck the attentuation on the lines.  Most signals drop off after -15 db, so that could be relevant too...

BTW:  I have several thousand feet of RJ11 if anyone wants to purchase it..!!  :)


Expert Comment

ID: 11986837
I agree with Fatal ... 80% of the problems I have experienced with cabled/broad RF networks are physical layer issues.  However, I do not believe you have a bad batch of modems, unless you got a bad batch from each of three vendors.

As Fatal suggested, observe the geographic location(s) of the failures .. preferably over a few days.  Get a good baseline for this.  You will likely see a pattern of poor performance in older installations where RJ6 is in place.... and from what I have seen, the problem is really a function of the deterioration of the jacket (sheathing), thus exposing the copper to the elements and so on.  Replace the RJ6 with beefier stuff (RJ11 a is good choice) and consider HFC to the distribution layer or even the access layer if you have the subscribership to warrant the expense.

Also, I'm ok with the Total Control box ... used them for many a dial-up ISP.  However, 3Com's CMTS blade is weak by definition because it grossly lacks detailed RF management, tuning and monitoring.  I have had great success with Cisco's uBR series in both small ISP/Community applications as well with TWC installations.  It simply boils down to the level of detail you get while the modem is ranging to the head-end for suitable COS levels.

I probably have not helped you much at this point, but would be delighted to help you troubleshoot the problem as you gather more information.

LVL 32

Expert Comment

ID: 12017217
First off lets state for the record that I am not a duplicate account,... I am an associate of the asker and I have the following update.  I am posting this for Rockey98.   Mods:  please let this act as a response from asker for abandonment considerations.  He's a local friend, and fellow EE-ite...what can I say.

Rockey98 is checking with the manufacturer's rep on this issue also and is better informed thanks to your efforts.  Your offer to assist in the continued t-shooting is greatly appreciated and will likely be needed in the near future.  Please bear with us as we gather all the needed info.

thank you all
-j-  (for rockey98)

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Expert Comment

ID: 12017795
Look forward to hearing what they have to say..  :)

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Expert Comment

ID: 12369376
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Expert Comment

ID: 12369698
The contributory element (learned just this week after much investigation) is :

  an onboard power supply backup at the pole was discharging/recharging repeatedly.
  the device condition continued to worsen until it also began causing "punchouts" in the cable signal to a group of customers.
  it actually took calling customers to find the affected area in order to find a good starting point for the action.
LVL 40

Expert Comment

ID: 12372222
Very good jade...  glad you got the ISP on this and that they were able to narrow it down..

and thanks..


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