How do you test for T-1?

[snidercomm]

Techs,

I have a customer who has asked us to verify some jacks to make sure the T-1 is present. They asked specifically "test for t-1 tone at jack". How is this done?

What type of tester would be used by a non telco technician to veryify a t-1 tone at the jack? I am not worried about the smart jack, I would be testing the jack that had been extended from the d-mark to the server area.

I have been working with phones and pc's for many years now and had never heard the terms "testing for t-1 tone", I had a vain hope this meant to just slap a butt set into the jack and see if I hear something, I realize that would be too easy. I also wondered if they meant an actual toner probe...Im confused.

Any help would be mucho welcome...

SCSTEK

 

[mattKnight]

UM T1 Tone

T1/E1 are digital protocols. You will need a ISDN analyser to check the jack for presence of signal.

You could try plugging a PBX trunk card in to it, if the card synchronises, t1 is present, but I guess, that is putting the cart before the horse!

Hope that helps

Matt

 

[executone]

They are anting you to plug a T-1 analyzer in, like a Tbird.
If you have another active T-1. You can plug that equipment into the smart jack, or if you have a DSU plug it in to verify active. If the jack is where Telco equipment is, you could look at circuit card to verify circuit is comming into building. Good Luck!!

 

[snidercomm]

Techs,

I have been told that a high pitched warbling tone can be heard at the T-1 jack. I have no idea through what source the sound can eminate from. The jack itself has no physical way of making a noise. I am still wondering if this is done with an amplified probe. They are not referring at all to any type of spectrum/bandwidth analysis.

Any more thoughts?

 

[daronwilson]

I think you can only hear the high pitched warbling tone on a full moon.

No, really, it is a digital service. I haven't listened to one with an amplified probe, I dunno exactly how to describe what you might hear. However, this is not a test of much except the customers lack of knowledge.

I've not seen an ISDN tester that would allow you to test T1 circuits, that would be a cheap alternative to the proper test gear, but they are considerably different protocols and electrical terminations.

So you have two choices:

1. Use an active component such as you PBX or CSU/DSU to terminate the T1 and test it.

2. Install a loopback plug in the jack in question and go to the other end of the T1 and see if you can loop it back and test that way.

Or, optionally I guess you could unplug the cable at the NIU and run a test on the cable from the NIU to the jack itself and make sure that cable and jack are good, but the best test would be some kind of operational test. You could test cable from the NIU to the jack for DC continuity and still have problems with your T1 depending on the length and type of the cable.

Hope this helps, good luck!


It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[executone]

What they are talking about is; If you hook a Butt set(telephone Technicians Test set) to the jack in monitor mode (since the circuit is digital ) you will hear a high pitch squal sound. All this tells you is that the jack is wired to equipment. It does not tell you if it is working or not. Good Luck!!

 

[snidercomm]

Techs,

To executone especially...Yes that is what I thought...I thank you for confirming this.

I love this forum!

 

[daronwilson]

Well yes, you could hear noise, I've 'tested' them before on accident in a splice box, but a couple points to consider.

First, if you have a current model buttset, you may experience the feature built in to prevent you from doing exactly that. Many are data sensitive and they emit a beeping tone when it senses data so you don't clip into someones data circuit by mistake and take thier T1 down.

Second, again this is hardly a test of the circuit. If you open the jack and listen, is the "squal" present on both pairs (transmit and receive?) I don't want to pull one down to check, though I am now curious, but I believe you only hear the whine on one pair. If that is the case, your test confirms that...well, what does it confirm other than there is a noise on that pair?

Third, this likely only test a portion of the circuit, unless you can tell by the tone that you have both transmit and receive pairs there. I guess I can't decode digital data well enough to tell my customer that their T1 jack is all fine by listening to a buzz on a buttset.

All in all it is certainly good information. I've not had anyone ask me to test their T1 in that manner, but I suppose it does give you a basic indication that something is present on the jack.

Thanks for the discussion! It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[snidercomm]

Techs,

This test was in no way meant to indicate any quality of the signal. It is only to verify that the signal is at the customer jack. If the pairs are wired improperly no tone will be present on the butt set. It is not really a test of the t1 itself, more a test of the wiring to the jack. I had suspected that the butt set was the answer, thats why I mentioned it initially. I know myself that testing for DSL presence on a line is a matter of lifting a non filtered phone and listening for the hiss of the digital signal. It appears when using the butt on monitor, you can test for T-1 as well in a similiar manner. Giving the tech a simple audible indication that the signal is there or not.

P.S. ALL digital signals consist of pulsed and modulated frequencies that DO make a noise, even freqs over 20khz, which is supposed to be above the normal human range of hearing, can sound like wind, squeal, hum or a hiss.

SCSTEK

 

[daronwilson]

Hmm, I guess I respectfully have to disagree.

>If the pairs are wired improperly no tone will be present >on the butt set. It is not really a test of the t1 >itself, more a test of the wiring to the jack.

Absolutely incorrect. Lets look at things here. A jack for T1 service has 8 pins on it. I've only owned 8 buttsets over the years...but none of them had 8 pin modular plugs on the end. So, to test we either have to use a banjo type adapter which breaks out all 8 pins to something you can clip your buttset onto, or you open up the jack and clip the buttset onto the pins you choose. The fact that you can open the jack, find two wires and hear a tone on them in no way means those two wires are on the right pins. So, it is not a valid test of the wiring of the jack. Let's say the jack was terminated RJ48S, using pins 1,2 and 7,8. You are likely expecting the jack to be terminated RJ48C using pins 1,2 and 4,5. Certainly you can see that being able to hear a bit of digital noise on a pair does not prove the jack is wired correctly.

>I know myself that testing for DSL presence on a line is >a matter of lifting a non filtered phone and listening >for the hiss of the digital signal.

That hissing noise can be a good indication of DSL, and you are testing a single pair service that does not require a return pair to function as does the T1 service. Also, being a single pair, if you have hissing noise on the only pair involved, and it is on the center two pins of the jack, not too many things can be wrong with the wiring of the jack.

>It appears when using the butt on monitor, you can test >for T-1 as well in a similiar manner. Giving the tech a >simple audible indication that the signal is there or not.

Yes, generally you will be able to hear if there is a digital signal on a pair, but in this situation it only indicates that you have some digital signal on a pair.

>P.S. ALL digital signals consist of pulsed and modulated >frequencies that DO make a noise, even freqs over 20khz...

I beg to differ with this one as well. Modulation is the process of varying some characteristic of an electrcial wave. I'm a little curious if you could hear anything on my 300 baud digital serial connection?. I understand what you mean, but if I am turning off and on the voltage on a pair of wires, that may not create a noise you can hear.

In summary, it may be possible to detect the presence of a digital signal with the buttset. Simply connecting the buttset in monitor mode (assuming that the buttset is not 'datasafe') to the pair that has digital data on it will likely yield some noise (tho I do not think I can differentiate between T1, DDS, Ethernet, Serial, etc.). Generally this would not be considered a valid method of testing the wiring of a jack. I guess, if asked, I would listen and tell the customer that there is a digital signal there. Would I tell the T1 is definately working at that jack? No. I don't like going back at 11pm on Friday when they try to cut over and finding out that it wasn't wired right. If I showed up along with my competition and the customer asked us to check the T1 jack, and I clip on with my buttset and say "sounds like there is a T1 there" and my competition grabs a CSU/DSU and plugs it in and says "nope, we are missing the recieve pair" or he loops it back and finds he can't complete a loopback test, who do you think the customer is going to believe?




It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[snidercomm]

Techs,

First off, if you read the initial post carefully you will see rather plainly the customer requested this action. They are a national IT outsource company who must have some reason for requesting this. They want it they got it, I personally dont care if they want me to come in and dance an Irish jig beside a 30 yr old mainframe, as long as I get my money next Friday.

Lets be real the "test" is a joke and must be based on some aspect like..."if there is at least some type of signal there then our tech can rearrange the wires on site"...based on bad experiences or something.

I half wonder if they are getting some new dsl/fractional t1 hybrid type deal where they ARE only using one single pair for tx/rx.

Your absolutely right about the jack and plug aspects. I basically wrote them before I had written here and asked then what they were talking about as well. They wrote back almost the same time saying to use a butt set. I wrote back to here some of what they said on the "test"



___III___III_______IIIII___III___III______IIIII
T={________________________.001___________________}

Each "I" represents a binary "1" or voltage pulse of undetermined amplitude...each "_" is a binary "0" equating to no volatge pulse. This is what a pulsed modulation looks like. Varying the speed or number of pulse bursts is the modulation on the digital electronic signal. It makes a frequency, frequency is just a measure of how often something happens, and it also makes a noise.

http://www.tpub.com/neets/book12/49l.htm

I mean I absolutely dont wish to banter about the audible aspect of it. The truth is that using brand new digital frequency generators when you plug a speaker onto a volatage output you can hear the sound directly. Even after you go well abouve 20khz you can still detect the rise or fall of the frequency even up to a Mhz. I would have thought it utterly impossible also but its true. Try it. I have worked at design and proto level on many types of micro boards, no one can tell me they dont squeal. (no its not a "deliverence" type of thing at the test bench) All they are is tiny little capacitors and resistors at the core of it, subject to the same laws of physics as their older, bigger cousins. Meaning they get hot and they make noise.

If any of this made sense I apologize, I do honestly appriciate the advice.

 

[daronwilson]

Oh it all makes sense, and yes if the customer requests it then by all means do it and take their money. I'm not going to try and convince you that digital circuits are noise free, what I was trying to explain was use of an analog test set (buttset) to verify digital operation is less than effective. Reminds me of Austin Powers trying to play a CD on an old phonograph. Oh yeah, you will get some noise, but you get little assurance of what it is.

My point was simply that testing a T1 jack with a buttset will not verify the presence and function of a T1 circuit. If you have a digital circuit present and can hear the noise produced by it, great. I guess it seems like observing a well lit light bulb in the house and saying 'yup, got 120 volts and 60 cycles'. Your light bulb really can't give you that much information.

It was a good discussion, thanks for bearing with me, and the link to the PCM explanation was nice as well. I just hate to see someone come through and read answers and head off with a buttset to 'verify T1's' because someone said it was the right thing to do on tek-tips.

Good luck, next time I install one before I hook it up I'm going to listen in different combinations and see what I hear.

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com