- This topic has 4 replies, 1 voice, and was last updated 14 years, 8 months ago by hope4agape.
17th May 2006 at 16:18 #30965Chris BerndGuest
Symptoms- Voice in one direction sounds like its “your talking in a barrel”. DTMF tones are not being passed. (Laymen’s terms when calling an auto attendant you can’t dial an extension). Voice quality severely deteriorated.
Cause- Telecom equipment, Cisco or VOIP equipment Not grounded, Ground drain connected on T-1 interface cable on both sides.
Fix- Isolate Ground on one end going into VOIP Equipment that has the CODEC’s. RJ-48 pins 3 6 Ground return, DB 15 pins 2 & 4 Shield ground drain. Ground Cisco router or other VOIP equipment to Ground following the procedures of the manufacturer. Make sure that NIU and all Telecom Equipment is also Grounded externally.
The lessons of the Legacy D-4/ TDM Network devices are being ignored and it is causing massive issues. Early on in the deployment of TDM’s and D-4 Channel Banks. The manufacturers and field representatives faced these same issues that are infecting the VOIP deployments now.
The Root Cause analysis is that analog to digital conversion uses ground as its reference . Yet along the same circuitry and circuit paths the same ground is being used to drain excess energy. The voltage that is put on the ground circuits and then follows least path resistance to ground. Which without external paths is back through the circuitry to the point of “reference ground”. (Minor difference of energy on a ground create a ground loop causing further issues.)
You might be thinking wait this is VOIP, that is true but there is still an analog network out there. Where the VOIP equipment attaches to a PRI or DS-1 (T-1). At some point you go from VOIP to Analog to D-4 (Digital) and this is where the problem occurs.
When a CODEC is looking at at analog wave form and converting that into a digital output signal . Any energy on its reference (Ground) is translated into either a higher or lower level. If you are reading 1600 HZ and converting that to 00100111. The First step is to determine what is 1600 HZ. With Ground as reference 0 then you can make the conversion easy. But if you add +.002 V or -.03 V to the ground that interferes with the ability to accurately convert the signal.
The fix then is to isolate the grounds in the circuit that are reference from those that are drain. On a T-1 interface the pins are 3 & 6 on an RJ-48 that is used to drain excess energy from the cable. If it is attached at both ends then the excess energy is following the path back into the router and into the reference. Remove the pins or these wires from the router side and leave them attached on the NIU. The NIU should have an external ground that is attached to the building and excess energy will follow this path. Further Follow the manufactures procedures and attach a ground between the router and building reference. This will provide a path for excess energy out of that equipment.
(just a minor note use smaller wires towards the equipment then towards the building. IE if the building common ground point is using 6 awg then use 10-12awg to ground the equipment.19th May 2006 at 12:19 #30966Saul BejaranoGuest
Check the -law on your compand type, make sure that you are using u-law with T1 and a-law with E1.
Saul20th May 2006 at 15:53 #30967Chris BerndGuest
problem is very sporadic and comes and goes in two diverse networks.
While setting up the wrong PCM compression algorthym would cause some of the same issues. Depending on latency they would be constand and not coming and going.
I neglected to mention that this was a spordiac problem were the circuits work for a while then the problems come up.
until the DSP is reset then they go away until next time.
Since Telco is defaulted to U-law, if you inadvertently set for A-law the problems would be ongoing from the start depending on latency.
While a ground loop or energy on a reference would be spordiac.
Not to mention I have one working site and two that are experincing the problem. I sought to find a differnce between the sites.
The Site that never experinced the problem was grounded at least on the Telco side.
The two sites that had the problem, the Telco side had no grounds connected. Worse the installer left a two foot 10awg ground cable hanging in the air on teh telco (NIU) equipment.
Can you say Antenna ?
I grounded one of the sites that was having the problem and left the other as it was.
The problem was showing up every 2-4 weeks and so far has not resurfaced at the grounded site.
Time well tell but after 90 days if the grounded site has not experinced any more issues then the problem is resolved.8th June 2006 at 17:10 #30968Saul BejaranoGuest
Normally is a work-or-no work scenario, this scenarios where EMI could be the cause of your problem has a trick or I may say a question, why it happens only in one direction? it should affect both right?
I do not think is caused by incorrrect grounding.9th June 2006 at 05:12 #30969hope4agapeGuest
why it happens only in one direction? it should affect both right?
It will not show up on a voip to voip call, It shows up in a voip to Digital world.
Were you go from outbound on a Pri, DS-1, E-1 then it is a digital signal.
On the other end were it is being converted A/d in the telco world it is allways Grounded.
There is nothing in the telco word that would ever be ungrounded because they already had these issues years ago.
But Ground issues can come across and noise, they can effect one side or both and they come and go and can change right in the middle of troubleshooting which is why they are so aggravating.