atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers When is a Trunk not a Trunk?

The subject of Lines & Trunks came up in another thread and I thought I'd recount a tale from my past. (Seems to be all I've got left these days)

Once upon a time, (about 20 years ago) in a kingdom by the sea (NYC,)a handsome young man (grave exaggeration) was the Network Manager for one of America's largest banks.

The network consisted of 3 GTD-4600s all tied together with T-1s (originally the connections had been 4 Wire E&M, but they had been upgraded.) The DIDs had also been upgraded to T-1s but the OGTs (Outgoing Trunks)were still coming in on copper.

One day at the Network Hub, everyone who dialed "9" for an OGT got reorder tone. Needless to say our hero was somewhat distressed. And discomfitted. And was being screamed at by everyone who was anyone and by most people who were not.

Tests at the demarc with a butt set and a ground wire produce dial tone. Dialing 9 from the switch - no dial tone. Obviously something is wroong with the switch. Our hero is getting beat up pretty bad.

To make a long story a little shorter, excessive troubleshooting and evaluation of SMA (System Malfunction Analysis) reveal that the switch attempted to seize DT. After 375 ms of no DT, the switch gave up on tht trunk and tried the next one. After 375 ms of no DT on the second trunk, the switch returned reorder tone and printed out a SMA report (in easily readable and translatable hexadecimal format).

What was going on? According to the Bell System Red Book all ground start trunks must return DT within 250 ms. The GTE switch added another 125 ms to the timing to cover for foulups and then gave up. Hence, reorder tone.

What was wrong with the CO? Well, according to NY Telephone - nothing. What about the parameters for Trunks? Well, surprise! They felt the parameters didn't apply. Why not?

Because, while we ordered (Ground Start) Trunks, And the NY Tel Sales Department wrote the order for (Ground Start) Trunks, the Switch delivered
(Ground Start) Lines. Trunks have to deliver DT in 250 ms. Lines can deliver it whenever they feel like it. In this case about 1000 - 1500 ms. Which is why we would get DT on the demarc with a butt set and a ground wire but not on the switch.

So when is a Trunk not a Trunk? When it's a Line.

Why did we get Lines and not Trunks? Because it was too expensive to provide trunks (Blocking, traficing, CCS, Erlangs, etc. is the reason. If anybody cares, I'll start another thread on that stuff - it's a subject unto itself.)

Not only did we not get trunks, neither did anyone else in the entire City of NY! Everyone who ordered GSTs got GSLs!

I began to set up a class action law suit (my brother is an attourney). I had progressed quite a way in writing it up when I was called in to the office of the Bank's Senior Vice President for Telecommunications.

"Silverman", he said, "You will forthwith cease and desist with this lawsuit. If you continue, you will be out of a job. Immediately."

So I gave it up. Later I discovered that the Chairman of the Board of NY Tel sat on the Bank's Board of Directors.

Surprise!

To the best of my knowledge, at least in NYC, if you order an analog GST today , you will still get a connection to the Line side of the switch. A monumentally inferior connection.

So much for quality service.

And now we know when a Trunk is not a Trunk.


Sam

Even for a regular line, over a second to get dialtone doesn't sound too good. Presumably it was just down to heavy traffic conditions at the time. What was the type of serving office: X-bar, ESS?

The switch was a #1 ESS. The problem actually happened three times over the ten years I was at the bank.

We never got a straight answer as to what the problem was. Sometimes it was supposed to be an upgrade to the switch that slowed processing time, sometimes it was heavy traffic, sometimes it was just.......????

Usually we got conflicting answers depending who we were talking to.

If you were picking up your DT on a single line set, by the time you got the handset to your ear you had DT. On a regular PBX you dialed 9 and there was a long pause and then you had DT. Most people would never know that there was a problem.

In our case though, the switches were "supercharged" (for the time) networking monsters and were specifically designed to report Network problems (like no or slow DT).

But it was always my experience (and I'm sure many will argue with me) that GTE, while they were somewhat lacking in the Telephone Set department, made an excellent switch and had a higher standard of switching then the Bell System - at least in NY.


As an aside - does anyone still use Analog Ground Start Circuits?
Or have they too gone the way of the dodo?

Sam

I have just one customer left that uses ground-start trunks. I believe most payphones--which will soon be gone--also use ground-start.

When I was first cutting my teeth on System 25 and early Definity, we were told by AT&T that ordering that service was the only way to go, particularly for busy switches. That along with placing the hunt/seize order in opposite directions would eliminate glare.

The biggest negative about loop-start, as least as we were told, had mainly to do with toll fraud. But with the advent of better disconnect supervision (and the steadily declining phone rates), toll fraud isn't really an issue with loop-start anymore.

In VoIP land I had always thought that a VoIP Trunk meant allowing you to send multiple conversations through one connected stream (think of it as a line), similar to a T1. Unfortunately it looks like this is an asterisk-only feature.

It is very rare to see a ground-start line around here nowadays. I did add one to an old Mitel at a hotel a few months back. It took the telco a couple of tries, but they were finally able to deliver the line as ground-start.

The necessity for GSTs was on PBXs. Besides Glare as Tim pointed out, an even bigger problem with LSTs was with 3 party conferencing.

A calls B and then conferences in C to ask a quick question. If C is connected via a loop start line and he disconnects before A&B hang up then A&B will be conferenced in with DT, then with ROT, then with Howler and then with "There appears to be a receiver off the hook" before getting blessed silence as the line locks out.

With a GST the circuit just disconnects.

Sam

When I went to Mitel school, I was told PBX's needed GSTs to prevent glare(call-crashing to you youngsters) and to insure disconnect every time. I was told the GSTs literally communicate between the CO and the PBX, and one or the other says this is going to be used by 'me', don't try to use it. They communicated with the ground pulses, if the pulse was not answered, the asking end tried the next trunk instead of 'blindly' setting up the call at their end. Supposedly it was possible to crash a GST call, but the time frame was so small, impossible for all practical purposes. And we had problems with ATT SLIC's set up for GS. They couldn't meet the specs that ATT wrote. At least that was the story I got! And the PBX that I was installing expected the designed timing. PBX supplier said that a different brand of SLIC (Nope, I don't remember) would work, and it was a plug and play swap in the slic hut. We offered to buy them and SWB said NOPE. The only way out of it was going to L/S. Fortunately, the SLICs did support disconnect. Reliably! John C. (Not Garand)

We still have some ground-start around over here for PBX use and for BT's "Redcare" services -- Various alarm systems.

British party lines used to be ground start as well, known as "earth calling" here, although they've been extinct for a good few years now.