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| Forums | USR | Those Pesky Null-Shifts | Watch |
| Author | Topic |
| Arcane Tl Posts: 5 USA | Posted - 6/17/2000 4:32:20 PM    Hi,  Ok, here it goes... For the last 6 months (there 'bouts), I have been having continuous retrains for anything around a connection of 49k. So I step down the connect speed to 44k, (thanks to v.Richard's great website I was able to do that!) now I hear (M2) null-shifts at about every 15 to 20 seconds and one full retrain just after the initial connection. Throughputs average 3.5 to 4k. This is about the max good connection rate I can get without retrains. Even when I lower the connect speed more, I still hear null-shifts. Yes I have tried other ISPs, both local and distant with the same results. I have also installed the latest modem driver (from Gateway). So my questions are: Below is a typical 44k connect, about 30 minutes long. As far as I can tell, everything looks good except for the number of retrains. ////////////////////////////////// U.S. Robotics 56K Voice Win Link Diagnostics... ////////////////////////////////// Thanks in advance, Edited by - Arcane on 6/18/00 1:02:21 PM |
| Daveman_750 Tl Posts: 86 USA | Posted - 6/18/2000 6:04:36 AM  I would try DISABLING SPEEDSHIFTS. To do that, the lucent command is %e0. It might and might not also be the command for 3COM. Your line, with EXCELLENT frequency response, SNR, etc. is very good. And you've got 2 RBS links so try some diff. numbers and see if they have less. No digital pad. Most if not all integrated SLCs use digital pads as far as I know, although i don't know for sure. If i'm right, you must be within a half mile of the CO. Should get ~50.6 to 52K with this line. |
| v.Richard Tl Posts: 6222 USA | Posted - 6/18/2000 9:49:58 AM The 2 RBS links may be problem - indicated by the 2N in status line. Try calling tollfree/toll call, & other local ISPs to see if you have the report of 2N on ALL calls. There is no way I know of to disable null speedshifts w/ USR modems (other than to disable 56k). They happen because the modem thinks the line quality is better than it "really" is. A good explanation of shifting/retraining is found in the Soltel pdf docs referred to in my Lastest Updates yesterday - http://808news.com/56k/latest.htm The retrain after initial connect is due to the modem not correctly identifying impairments on your line. Also note the --0 (indicating an unusual pad); Try connecting w/ HyperTerminal, and examine the status line BEFORE the retrain. (Either disconnect before the retrain and give it i11, or use +++ to go to command mode and examine i11) - see if impairments detected are different. http://808news.com/56k/diag3com.htm Aloha, |
| Arcane Tl Posts: 5 USA | Posted - 6/20/2000 7:56:30 PM Sorry it has taken me so long to get back, but these 12 hour work shifts are killers.  I've tried several local and long distance ISPs, and it looks like the impairments are, for the majority, at 1N. I still see the --0 with all of the ISPs I called. I do think I'm close to the CO, but I'm not sure. I was also unable, like you said, to disable retrains with my modem. As for the initial full retrain at the beginning, there was no change in the impairments before or after. Is there nothing I can do for this RBS problem short of changing ISPs? I am somewhat happy with my throughput, but not happy with the constant null-speedshifts. The only thing I haven't tried is to unplug every phone outlet in the house. If you think this could be the problem, I will try it. Thanks Again and Aloha, |
| Arcane Tl Posts: 5 USA | Posted - 6/27/2000 7:11:28 PM I signed up with one of those free ISPs, Freewwweb. I get a 1N with them but still have to throttle back to 44Kbs to stop retrains. At 44Kbs I still get the null-speedshifts at 15-20 second intervals. I'll post the new readings when I get the chance at home. By-The-Way... Freewwweb looks pretty good so far. No banners, no software needed, and throughput isn't too bad. I may just cancel my local $20/month ISP if this works out. I also found the CO, It's about 3.5 miles away. I guess that explains the good signal strength. |
| Arcane. Tl Posts: 3 | Posted - 6/27/2000 11:11:15 PM Here is what I'm getting with Freewwweb; boy that's hard to type.
===================== I would love to stop those null-speedshifts if at all possible without lowering my connection rate. ------ |
| v.Richard Tl Posts: 6222 USA | Posted - 7/4/2000 12:39:27 PM Your i11 indicates 2 RBS links in your call path. This is not good. I would check the i11 for RBS links when you call other #s, local & toll. www.808news.com/56k/diag3com.htm Null shifts are common w/ USR modems and happen because the modem thinks it can do better - then it can't, and keeps cycling. You might be able to stop this using s-register setting related (examine ats? for all s-register settings) The full retrain shortly after connection would indicate you may want to limit the max speed to even a lower rate. Also check your y11 results. Aloha, |
| Arcane Tl Posts: 5 USA | Posted - 7/11/2000 2:48:51 AM I couldn't find any ats commands that would stop null-speedshifts. (I hope you meant ats& vice ats?, I couldn't get ats? to work)I posted above that most other ISPs I called did NOT show more than one RBS link. (above post 'Arcane.' is me also) Also notice that there were no retrains with Freewwweb ISP. I still see the null-speedshifts every 15-20 seconds though. I do not want to lower my connect speed because it seems like the best tradeoff between throughput and nulls. I guess I am at a stopping point...so |
| v.Richard Tl Posts: 6222 USA | Posted - 7/14/2000 10:45:41 AM The stats on your last connection don't look too bad to me. If and when your telco upgrades the digital portion of their net that is introducing the RBS impairment, you may get slightly better connection. I wouldn't be so concerned with the null speedshifts: let's say if you limit your connect to 36k you eliminate them - would your throughput be better or worse? The answer is that usually throughput will be better with the higher rate and a moderate amount of 'errors'. Note, too that your 44k connect has near-zero blers; It's also possible that you may get better throughput with a rate of 45.3k or 46.6k and a higher # of errors. It is possible that other devices connected to your phone line prevent your modem from achieving best performance. I would definitely suggest connecting the modem to the demarc if possible which will disconnect all other wiring/devices - www.808news.com/56k/demarc.htm Aloha, |
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