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Testing for loop start vs ground start

Testing for loop start vs ground start

Testing for loop start vs ground start

Hello all,
I am a complete newbie to this side of telephony. We are implementing new tele/data service to our client and testing the circuit tomorrow. We had a cut-over planned for the following day, but unfortunately the provider decides they can't schedule a port of numbers until 1 week after the install day. For a reason I do not understand, my boss tells me that if the clients lines are loop start we aren't in any trouble (meaning we can cut-over the following day without worrying about the lack of porting). My job is to go there tomorrow and test the new circuit, and then with a butt-set test for either loop starts or ground start. No problem with testing the new circuit, but tbh, I barely know what I'm doing regarding the loop starts. Can anyone help?

RE: Testing for loop start vs ground start

Bring your test set and a piece of cross connect wire with you.

Connect your test set to line 1, make sure it is idle, and go off-hook. If you get a dial tone, the line is loop start. If you do not get a dial tone, try touching the ring lead of the line to a ground. If there are ground start trunks there will be a ground somewhere nearby. If you get a dial tone after grounding, then the lines are ground start.

Old school POTS lines at a house are an example of loop start trunks. the telephone company will send a dial tone when it senses current is flowing through a device (i.e., when a handset is lifted off of the set).

Ground start trunks are usually found in sites with high call volume or when a guaranteed means of sensing disconnect is needed. Current does not flow unless the Telco gets a grounded on the ring side. This was to help prevent glare (when an outside caller would accidentally seize an incoming call) or for voice mail systems to get a positive disconnect signal when a caller hung up.

What is important here is that if your equipment provides loop start and the PBX was configured expecting ground start, the site will receive calls fine since the 90VAC ring gen will trigger a call to the PBX. The site, however, will not be able to call out.

Sometimes the PBX can be reprogrammed to use loop start trunks if the cards and the programming will allow it. Otherwise, you would have to change your side to provide what the PBX expects.

They are definitely "old school" but they do have their uses. There is a car parts place I service that had to covert TO ground start because they were always accidentally answering incoming calls when they called out. I had to see that for myself. The site had an incredible call volume for the size.

This article explains it pretty well...

http://pbxbook.com/other/trunks.html#GS-Outgoing Call

RE: Testing for loop start vs ground start

Let me start with this question. By new "circuit" are you speaking about a full T1 or are these standard POTS lines? A buttset alone won't be much help to you if the circuit is a T1.

If these are POTS lines, you should be able to draw dialtone by clipping the leads onto the + and - pins/screws and going offhook for Loopstart.

If the POTS lines are configured as Groundstart, you won't be able to pull dialtone without briefly touching the end of a piece of grounded wire to the "Ring" pin/screw.

If these are trunks on a T1 circuit, you would need to plug the T1 into a D4 channebank in order to break out the individual channels for testing.

I love2 "FEATURE 00"

RE: Testing for loop start vs ground start

If I understand the scenario correctly - the existing lines are POTs and the new service will introduce PRIs from a T1.

RE: Testing for loop start vs ground start

If that is correct, then it negates everything posted so far. A PRI/ISDN circuit and trunks cannot be tested using a simple buttset. You would have to connect the circuit to the telephone system and do some programming to facilitate the testing of the 23 "B" channels.

I love2 "FEATURE 00"

RE: Testing for loop start vs ground start

So I understand the PRI from a T1 part and Dexman asked an excellent question here.

So we can help you get the right answer, what will the handoff be from the Telco for the voice? The service providers here provide a similar service where Internet and voice are bundled into a PRI. The provider will install equipment (I have seen Adtran 908 and Outburst boxes) and then hand off the voice to us as either a PRI or Loop Start trunks or even both types depending on the customer's needs. The Service Providers in our area don't even provide Ground Start but that might just be a peculiarity here since they are so rare no one wants to deal with them. ~ Mike

RE: Testing for loop start vs ground start

I am testing the existing POTs lines, though.

RE: Testing for loop start vs ground start

Ah...If you are testing the existing POTS lines, then all of the prior posts are back in play.

I love2 "FEATURE 00"

RE: Testing for loop start vs ground start

We are not trying to confuse you here, lol...

Dexman is performing due diligence so we can help you succeed. These are the possible scenarios.

If the Telco is providing internet and voice from a PRI (or multiple PRIs) they will install some type of equipment that will sit between the actual T1 and the customer's equipment. There will be an Ethernet port for the customer's router and, hopefully, IP setup information has been provided. In this scenario, the old trunk type is not at all relevant since PRI is a completely different signaling and physical interface.

The voice will have either PRI in which case Dexman is correct in the sense you will need a physical interface on the PBX and programming for it or POTS, probably Loop Start, in which case your testing of the original trunks will determine compatibility.

We have seen Murphy so many times on jobs we try to plan for all contingencies... Hopefully we end up saving you time in the field.

In closing, it is not a good idea to connect your toner or test set to a T1 or PRI interface. Some of them put out 130V and I have fried a toner. They will also give you a really good zap! It won't kill you but it will sure wake you up and draw out some expletives! ~ Mike

RE: Testing for loop start vs ground start

Perhaps I explained it wrong. Let me try it this way.
- Customers existing equipment: POTs
- New equipment coming in: T1 - PRI
Tomorrow: I am going to test the new equipment, NOT cut them over to it.
Wednesday: We planned to cut them over to the new equipment, however now the provider cannot port the numbers over. My boss believes we can get the customer to continue working on the POTs, through some magic he knows, if they are Loop Start.
Hence, tomorrow: I am also going to test if their existing POTs are loop start or not.

RE: Testing for loop start vs ground start

OK, OK, LOL...

We are overthinking the plumbing and stopping up the drain. All you needed to know was the difference in LS vs GS and that has been well and truly answered, lol..

Please forgive me. As tech support for my customer I have seen every conceivable (and some not so conceivable) situations.

In my time zone, it is time for a beer so I am signing out.

Good luck tomorrow and you are indeed well armed with the knowledge needed. ~ Mike

RE: Testing for loop start vs ground start

Thank you very much, I totally get it. Enjoy that beer - you are much help.

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