atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's t1 timing issue

need some expert advice on what a telco tech called a timing issue. we have an asterisk pbx with a digium t1 card and it has been dropping a number of calls over the last two days and we're not sure what the cause is.

we had a verizon tech come on site yesterday to test the pri and he said that he was seeing a timing issue. he recommended that we restart the pbx which eliminated the issue but he only tested for a minute after the restart so i'm not convinced that there isn't some other issue. before we restarted the pbx he actually told me that he noticed a number of errors on the circuit but he wasn't sure if they were related to the timing issue.

does anyone have any recommendations as to where we should go from here?

Timing, network synchronization, clocking...whatever you want to call it, simply means that your DTE and the carrier have to agree on a common clock in order to pace out the bits that make up the voice calls. Telcos ALWAYS have more reliable clocks than your own gear, so this value is almost always set to "Network".

Look for related programming parms in your DTE and set it for "Network"; this will force the box to derive it's timing from the carrier.

I'm hoping that James will chime in here as I do not know what the Asterisk folks have chosen to rename this parameter. "Zap Omega", perhaps? They call T1 trunks "Zap" trunks, so why not? Those Asterisk people want to change everything

thanks for replying. i asked the telco to do some more intrusive testing so hopefully they will find something.

our asterisk system is a turn key box distro called switchvox. it doesn't allow you to view the inner workings of asterisk but you can set the timing provider and it is already set to network.

i'm beginning to think that there must be something wrong with the t1 card in the server....

If you have a T1, pri or otherwise that teminates in a Telco switch you must time off them. If you are having slips it can only be your problem not Telco's. If Telco had a timing problem they'd would be effecting everybody. Reseting your equipment will only work for awhile as it will eventually get out of sync again.

Pure slips will not cause errors, but massive errors can cause slips. So in answer to the Telco telling you he doesn't know if the timing issue cause the errors that answer would be no it wouldn't. So if he was seeing errors and slips it wouldn't be strictly a timing issue and Telco would need to check further.

so timing issues can only be on my side? that would really suck, i have no where to get a replacement card until after we open up tuesday morning which means that we will have more dropped calls. is there any way that the something down stream could be causing the slips?

i'm still going to try to get the provider to come out again. the tech connected his laptop to the smart jack and had 37 errors over a 24hr period. it seemed like a lot to me but i didn't think to get him to monitor a little longer while he was there.

37 errors is NOT a lot in a 24 hour period. My experience is that if there is some major problem you'll have about 20,000 errors in the first 2 seconds.

When I tested Microwave circuits we used to be allowed 1 error in 24 hours. Otherwise we had to tear the circuit down and try it again. We once did a pair of T-3 backup circuits for Bell Atlantic that ran through a repeater site across the Hudson before they got to their final destination. We could get that one down to about 5 errors in a 24 hour period and they were thrilled.

Microwave of course could take errors if a bird flew in the path of the beam. I don't think you're having that problem (the circuit isn't partially wireless, is it?), but 37 errors while not good is probably not even noticeable. Remember a T-1 is 1.544 million bits per second. That's about 92 million bits per minute, 5.5 billion bits per hour and approximately 133 billion bits per day. (I think I've got the math right.) So you've got 37 bad bits and 133 billion good ones.

You want to get it fixed, but not to agonize.

Sam

That's not enough errors, it takes massive errors to cause a circuit to slip. I would think your timing option is incorrect rather than a bad card.

No. I worked many years in a T-1 center and never once saw anything but CPE equipment cause slips. It's simple the timing source (Telco) can't be out of time. The same thing can happen CO to CO if the slave end is optioned incorrectly.

Also those errors the tech saw could have been cause by previous remote testing. When he said timing issue did he actually see slips? If not what was he basing his statement on?

first he used some software from his laptop and that is where he was seeing the slips. he then connected a t-bird to the circuit and did not see any errors. the tech was from verizon who is our local lec, but our t1 is thru att so we ended up calling att to ask if they saw any errors. while we were on hold for att, the verizon tech connected a serial cable to the smart jack and that is where he saw the errors over the 24hr period.

any ideas what could screw up the timing on the asterisk box? it was running fine for months without any issues before this then all of a suddent we start having issues.

R u sure you are set to time from the network, not. Internal, also if a t3 is hitting up u may see timing errors