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Tl Posts:

Posted - 7/16/2000 8:53:36 AM  Show Profile  Email Poster  Edit Message
Hey people:

one quick question. I have a USR 56K ISA Internal modem, non win-modem. It is great... except for one thing.

Every once in a while, the internet connection will just stop dead in its tracks. The computer is still linked up, but no data will flow at all. Then all of a sudden, it will restart again and race along.

I've tried bumping down the speed of the modem, that didn't work. Everything my ISP has tried has failed. I NEED HELP!!!!! :)

Tl Posts:

Posted - 7/16/2000 12:37:59 PM  Show Profile  Email Poster  Edit Message  v.Richards Homepage
Sounds to me like the problem is most likely your ISP or beyond.

Try other ISP(s).

(Make sure it isn't the modem by checking ATi6 after connection for RETRAINS.... retrains can also cause 5-10second data-flow interruptions.)


Edited by - v.Richard on 7/16/00 12:39:12 PM

Tl Posts:

Posted - 11/15/2000 4:31:08 AM  Show Profile  Email Poster  Edit Message
I have seen this behaviour quite a lot. We have a number of full time connections to ISP's in different cities. In two of these locations it will be going fine, then suddenly, zero thu put then sometimes it recovers. The modem remains online and there are no outward signs of distress. It can go for 5 minutes or two weeks between incidents. It can always be cleared by disconnecting the modem and reconnecting. Out Telco has looked at some of the error stats from within his Cisco routers and they suggest a "retrain storm" is occuring. We have replaced the modems with different brands 3 times in both locations. In one location we have shifted our telephone line from a System 12 exchange to an AXE (which is a different type and manufacterer and thus probably has different DAC's ADC's and associated software) with no significant improvement.

We have done heroic telephone line testing and checking including full group delay analysis and stability tests.

The only common thing I suspect is the Rockwell chipset and the CISCO routers at the ISP, which in our case is the Telco.

So no, it is not your imagination, and I suspect it is fairly common, but most users just go mutter, disconnect, reconnect and away they go again.

My view is that there is a software problem involving the retrain function, either in the modem or the telephone exchange ADC (analogue to digital converter) and DAC (digital to analogue converter) and the CISCO routers which control the Telco side of the connection. I suspect some sort of feedback loop condition in which both side start clearing their throats and each is unable to correctly respond to the other because it is itself trying to retrain.
Edited by - ian on 11/15/00 4:41:05 AM

Tl Posts:

Posted - 11/17/2000 7:58:34 AM  Show Profile  Email Poster  Edit Message  v.Richards Homepage
If the modem were retraining - it would be reported in the modem diagnostic screen (at i6 for all USR modems);

If you leave the speaker on at the client modem, you will be able to hear retrains, null speedshifts, etc.

It has been my experience, especially calling to Ascend servers, to have intermittent total loss of connectivity even though the modems are connected fine, not retraining, not experiencing any errors, etc - it appears as if the RAS gear beyond the modem (ie, the server side networking) has 'broken'; hanging up and redialing solves the problem - it can be minutes, hours or days before it happens; on days it does happen, it's likely to happen more than once;
I think this is beyond the modem.
I wrote an item in the 'Who Knows....' section of a newsletter many months ago describing this as well and asked who knows and who has this happen to them.... Did not get any replies....

As for "retrain storm" - what is that?!? I don't understand how a Cisco router behind the server side modem could even know if a modem is retraining; I would think that it knows only whether the port is giving a Clear-To-Send signal or not;

I do know from my observation when this happens to me, my [external modem with lights] is OK, and IS sending data; nothing is coming back from the server modem; What would be interesting is to know what's happening from a diagnostic standpoint at the server-side modem and the RAS driving that modem....


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