loopback plug for testing a T1 circuit 1

1-4 2-5 as found here
We get the jacks from Graybar as an Allen Tel. Leviton doesn't make them.

LkEErie

btw. Save yourself some time with the Graybar guy.

AT-635CX

1-4 2-5 is the pin out

Many of us use the RJ48X with the built in loop at both ends,so when one end is un-plugged it is auto-loop backed at that end to the other. And will plug into the Box at the MPOE that houses the circuts using RJ45 plugs


This is so the T-1 does not go down once extended to the demark.

Just plug your tester into one biscuit at either end when nothing is connected and the test is a lot easier.

Remember to use a data cable when testing (568B)

1=w/o
2=o/w
4=blu/w
5=w/blu

1=transmit

2=recieve

4=recieve

5=transmit

Good Luck

Has been in the cabling business for about twenty years and is now the Sr PM for a cabling company located in the Los Angeles area.
Also a General Class Amatuer Radio Operator.

To correct the previous post for lead designations for a T1 8-Position Modular Jack hardware wired for RJ48C/X:

PINS Lead
1 R1 \
2 T1 / RECEIVE FROM THE NETWORK
4 R \
5 T / TRANSMIT TO THE NETWORK
7 shield ground*
8 shield ground* * when provided

This is the wiring arrangement you will find on both the NIU and a separate Modular Jack equipped installation. The RJ48X wiring arrangement and equipped Modular Jack provides a physical loopback when the Modular Plug is removed.

The loopback function is a convenience for Telco, some provision it others do not. Sometimes there are problems with the "digital loopback" of the NIU. It is helpful when troubleshooting and running tests with DS1 test equipment. If you have the expertise and/or the test equipment it is helpful to the field techs also.

....JIM....

If you need a DB15 loopback

1->3
9->11

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The latest survey shows that 3 out of 4 people make up 75% of the population.

The original point and click interface was a Smith & Wesson.

Red meat is not bad for you, it is the green fuzzy meat that is bad.

Just remember, if it is an unclocked T1 you can only loop back from/to the en dthat is clock master.

For this reason I strongly recommended using a T1 clocked by the Telco - in that case you can loop in either direction.

If you ask a better question you will get a better reply. Be specific so we can help!

If in the future you "cant remember" especially out on a jobsite with no docs, you just need to short all Tips and all Rings on any jack you have available (i.e. usoc, 568A, 568B, doesn't matter). No memory of pinouts needed.

connect all tips - wh/bl,wh/or,wh/gn,wh/br together. and connect all rings bl/wh,or/wh,gr/wh,br/wh together. You just made a DS1 loopback jack the fast/easy way!

-CL

lopes1211,

That would depend on how the other end is connected!


ISDNman,

Can you explain? Any DS1 not connected to a switch or equivalent has no clock source until equipment is connected. When I used to turn up DS1 end links, both Telco and I could loop the NIU at the other end. I used A T-BERD all the time on point-to-point DS1s. The only clock source was the test equipment until it was put into service. At least in California there is nothing at the CO end to loop up, unless the carrier people put up a manual loop @ the DSX-1 or in the Digital Cross-Connect.

....JIM....

Nope. polarity does not matter on ds1's. shorting all tips together, then seperately shorting all rings together will ensure TX and RX is looped. Been doing it for 15 years. Please explain "depends on ho the other end is connected" as there is only 1 way to connect a ds1.

-CL

Jim,

If the T1 does not go through a CO (which is a rare case)it would be unclocked.

In that case (just like a limited distance modem) one CPE (lets call it site A)would be configured for internal clock for TX. RX clock would also be from the internal clock (most equipment in my experience cannot use separate clocks for TX and RX).

At the other end (Site B). the CPE would be set to recover clock and to use recovered clock for TX.

If we loop back site B A gets signal back and since this is synchronous to the TX clock (since it IS the TX clock) there are no clock slips.

However, if we loop back site A site B will have no TX clock since its TX clock is the recovered RX clock.

Now, if you wanted to test this line you could put a pair of T-berds on the line with each configured to use internal Clock for TX and recovered clock for RX. In this case you would have separate clocks west and east.

Most of my troubleshooting is long distance and most of my customers have no T-berd so loops to/from the CPE is the only option we have.

But keep in mind that most CPE cannot use two clocks simultaneously. IN this case there will be slips if the incoming data is not clocked to the same clock as the outgoing data.

To my mind having a network clocks (which after all is a highly stable clock(strata 2 or 3)). In this case both CPE are recovering clock and using recovered for Tx.

In this case no matter how you loop it the clock is the same.

NOTE: I suspect that some (maybe most?) equipment automagically switchs to internal clock if there is no incoming signal, meaning in that case loops from the far would work even if this device is set to use recovered clock. But this could become a ring-around-a-rosie scenario.

I hope this makes sense. All I know is I have had a few cases where unclocked T1's failed to be easily troubleshot with out changing the clocks just to allow loopbacks and that gets messy in a hurry.

Cheers

Rolf



ISDNman,

Can you explain? Any DS1 not connected to a switch or equivalent has no clock source until equipment is connected. When I used to turn up DS1 end links, both Telco and I could loop the NIU at the other end. I used A T-BERD all the time on point-to-point DS1s. The only clock source was the test equipment until it was put into service. At least in California there is nothing at the CO end to loop up, unless the carrier people put up a manual loop @ the DSX-1 or in the Digital Cross-Connect.

....JIM....

If you ask a better question you will get a better reply. Be specific so we can help!

ISDNman,

I understand what you are saying to a point, the same thing I said, but when you order a point-to-point DS1 ckt prem-to-prem Telco provides NO clock timing into the DS1. The only time you get Telco's strata clocking is when the DS1 is connected to a CO switch, Channel Bank, or Digital Cross-Connect system, like the Tellabs 5300, etc. In my example one of the ends has to provide clocking be it internal or whatever source clock it can use and the other end is set for RX clock and sends it back to the other end.

I agree with you the strata clock source is the best when available. Keeping the network in time is very important!

This can be a challenge to someone not familiar with timing in a DS1 network.

....JIM....

JIm,

since when don't 95% of T1 terminate on a digital cross connect at the very least?

Of course I have built a few limited distance modems using DS1 over copper, but that is not a T1 from the Telco by my book.

I had one customer that had a 75 miles T1 that had no clock on it. Obviously he could/should have had it.

I guess local practices must vary widely!

So, I guess we agree you should ask for it, and if the Telco refuses then go with whatever they can give you!

Cheers



If you ask a better question you will get a better reply. Be specific so we can help!

You're both right in a way. If you want true clocking to a ckt then a CO switch or DXC 3/1/0 will be involved.
Yes most if not all ckts will go through a DXC however in 3/1 system a true clock is not being applied. You guys are looking at this on 2 different angles as to what clocking is. Here's how I see it.. If a PBX is connected to a CO via a t-1 and it's set to internal clock the line will have slips. If two PBX's are trunked together via a t-1 private line and one isn't set to master and the other to slave the line will have slips. Let's so if I confused the issue further

This is the case I am talking about. And if you ask for it usually it can be clocked and therefore both would be set to slave.

I like to ask for it because it makes troubleshooting easier, particularly since the equipment at both ends is made by my employer and therefore I need to sectionalize to one end or the other if the line is ok.

>>If two PBX's are trunked together via a t-1 private line and one isn't set to master and the other to slave the line will have slips. Let's so if I confused the issue further <<

If you ask a better question you will get a better reply. Be specific so we can help!

The example that artesian2000 gave, is the reference that I have always used. In California none of the Telcos or IXCs that I have ordered facility from have ever "inserted" clocking on a high capacity circuit, except for DS3 or higher. All of the riders on the DS3s I worked on had NO clocking unless one end terminated on a CO switch, CO Channel Bank or equivalent. In fact if I remember correctly, in the Access Handbook, it mentioned something about this not being an orderable item for any point-to-point DS1 facility.

So in that case one has to set a master clock source for one end.

....JIM....

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