2-wire T1?

Never on coax cables. Always on twisted pair.

None of those are actually a T1. A T1 is a particular facility for twisted pair cable, using a particular line coding scheme. That is very different than HDSL, microwave, or fiber optic cable.

An accurate assessment!

Using todays terminology I would have to disagree. You have 3-4 T1's coming into your building. Your contract with the telco more than likely calls them T1's. For all practical purposes there is no difference between calling it a T1 or a DS1. DS1 is the line format for a T1. You can order a T1 as AMI or B8ZS, with AMI being almost obsolete.

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Floyd, as the following link, and content from the page listed. You can see that the terminology between T1 and DS1 is bluring. Today DS1 and T1 can and are used to describe the same thing. You no longer see many people ordering unframed T1 to just get a line speed of 1.544, must are ordering A T1 with 24 DS0'S. The issue of HDSL2 came up because the original poster said his T1 only had one pair, which is what HDSL would use in order to utilize copper pairs in a more efficient manner, especially where the copper pairs are scarce.

What Is a T1 or DS1 Circuit? T1 or DS1 is a high-speed data circuit with four wires, two of which are used for transmitting and the other two for receiving. The T1 or DS1 is capable of transmitting and receiving data at a rate of about 1.5 million bits-per-second (BPS). Thus, the T1's data transmission rate is more than

100 times faster than a PC modem operating at 14,400 BPS.

I will no longer complain of some of the wiring rooms/closets I am presently working on after seeing that picture. That is the picture you use of what not to do. Getting back to the issue of T1/DS1 yes T1 is the facility, but a lot of common usage of the terms is blending T1 and DS1 to be one and the same. While the old timers know that there are definite differences, with the DS1 being a well established standard, and I still have some old copies of some Bellcore/telcordia documentation on that standard somewhere around here. The point is especially among the IT people now moving over to the telecom side, T1 and DS1 are being used to mean the same circuit.

Dana... you're disagreeing with a couple old farts that have 3 times the experience that you do. David probably has 4 times...

It is not a matter of having a discussion to see who is right or wrong. It's a simple case of you should be asking David more questions so that you can understand what is wrong with what you've said. Don't even begin to presume that you are going to "correct" something he says... that isn't going to happen.

(Trust me... he's been gently correcting me for maybe 15 years now.)

In another post you mention (a mythical beast) a T1 on a microwave or a fiber optic. As an exercise which will demonstrate the problem with definitions that you have, try explaining what you get if you order a "T1 using B8ZS" that is provisioned on either a microwave or a fiber.

Just exactly *how* does one implement B8ZS (with bipolar violations) over either the microwave or the fiber?

The answer is that it can't be done. Indeed, on some wire facilities it can't be done either! (How can it happen on any multilevel encoded wire facility?)

Those facilities might well deliver a 1.544Mbps data rate, but they *can't*

*be* a "T1 using B8ZS".

Of course the DS1 interface can and does implement B8ZS...

TDM is "Time Domain Multiplex"... T carrier.

FDM is "Frequency Domain Multiplex"... L carrier is one example of many (O, N, K, J all being Bell designs, with others like Lenkurt either copying those or using other formats).

The other distinction is that TDM is digital and FDM is analog.

So I'm certain that we can implement B8ZS on a DS1 interface, but I still want to hear how you implement B8ZS over a microwave link. Those bipolar violations are hard to do with QAM... ;-)

And it can't be a T1 if it can't have B8ZS encoding!

I know you two are old farts with a boatload of experience. I am only stating how it is now.

True.

What I said goes back to the original poster who was stating T1's cannot go to end locations on one pair, when of course HDSL2 does indeed do just that.

Not trying to correct him at all, just trying to show what the original poster is trying to say about his T1.

The microwave or fiber being the transport the T1 takes.

Funny Floyd. Same way Ma Bell used her long haul, long distance microwave backhaul. What was that called "AT&T LONG LINE" or something like that.

Are you sure you meant B8ZS instead of bipolar??

And you can have a T1 with AMI. As our network does. We have fiber (fmt150 multiplexer) with both B8ZS and AMI on the same circuit pack (4 t's) and on our even older Rockwell 2003 multiplexer we have some groups of 4 T's sent up for AMI and some for B8ZS. And our newer microwave radios have the provision for wayside T1's that can be provisioned as either AMI or B8ZS.

For LineType, select T1 ESF B8ZS Clear, T1 ESF AMI 62411, T1 D4 B8ZS Clear, or T1 D4 AMI 62411. The default is T1 ESF B8ZS Clear.

• T1 ESF B8ZS Clear indicates the NI port will have a line type of T1, a framing format of ESF, a line coding format of B8ZS, and a clear density.

• T1 ESF AMI 62411 indicates the NI port will have a line type of T1, a framing format of ESF, a line coding format of AMI, and a density of 62411.

• T1 D4 B8ZS Clear indicates the NI port will have a line type of T1, a framing format of D4, a line coding format of B8ZS, and a clear density.

• T1 D4 AMI 62411 indicates the NI port will have a line type of T1, a framing format of D4, a line coding format of AMI, and a density of 62411.

And to add even more confusion here is some text in the book T-1 Networking written by William Flanagan, and published by CMP copyright of 1997 for latest edition. In chapter 2 on page 29 we have this "The term T-1 originated with the phone company as a very specific type of physical equipment: selected cable pairs and digital regenerators at

6,000ft intervals. The term has become somewhat corrupted in common usage, and now T-1 refers to the DS-1 rate more than the cable system." And this is the point I am trying to raise. Today for all practical purposes when someone says T-1 they are really refering to the DS-1 signal level and not the carrier system.

Western Multiplex for example had made a line of radios in the 2 and 5Ghz bands that offered from 1 to 8 T-1's on one radio. These radios can be provisioned as AMI or B8ZS. So in reality we are talking about one and the same thing a DS-1 which the original poster had called a T-1.

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Nope.. you're incorrectly mixing terms.

I strongly disagree... T1 is a *facility*; DS1 is a data format. I have 3-4 DS1's coming into my building. The newer ones are 1-pair H[A]DSL. The oldest is 2-pair T1. ALL are DS1.....

If you are in big building with a fiber hub downstairs [or for that matter, a smaller one such as the Phone Room from Hell at there's a fiber hub just out of sight on the floor there.] then you can get DS1 with no T1 or H[A]DSL transport.

No. TDM multiplexing was L-carrier, not T-carrier.

[corrects my thinko about L-carrier and 'TDM'. It's late.]

Well, not necessarily. Edison had patents on analog TDM systems, for example. I would not be terribly surprised if few or none were actually _used_ anywhere.

And that guy who raced Elisha Grey to the patent office was working on FDM for the digital telegraph system.

I've got no idea what you mean by that. What is "long haul, long distance microwave backhaul" supposed to mean? And other than the fact that AT&T Long Lines was the department that operated the microwave systems, what has that go to do with it?

I still want to hear what you think the method is for implementing B8ZS encoding over a microwave link! As you've stated, T1's come with either AMI or B8ZS... and B8ZS involves encoding 8 consecutive 0 bits with a sequence that includes two bipolar violations. So just how do you encode BPV's on a microwave link?

(The secret, of course, is that you *don't*.) It is implemented for the DS1 interface segment, only.

So what happens if you have a "T1" over a microwave and one end is configured for B8ZS while the other end is configured for AMI?

B8ZS *is* a bipolar encoding. Just as AMI is. But B8ZS uses BPV's, and you can have BPV's on a wireline facility but not on a microwave or a fiber. The B8ZS encoding applies *only* to the DS1 interface.

Sure. Which should tell you also that you can't have a T1 over a microwave, because microwave channels don't use AMI. The DS1 interface does though!

Dana... are you still a union member, helping to keep my retirement fund healthy? :-)

Around here, SBC won't sell you a 4 wire T1 even if you insist. All of them are now 2 wire. And yes, they are HDSL.

Doing business with Alan Ralsky qualifies as bottom feeding in my book. Which they HAVE done in the past...

Ah yes, Groups, Supergroups, Mastergroups, Supermastergroups [or was it Mastersupergroups]..

I yearn for the sound of a sweet hetrodyne.....

Now, N Carrier... THAT was a technology.. Who needs a furnace when you have kilowatts full of 'firebottles' to keep you warm? And the glow.. with some cardboard and foil to reflect it, you could make a fireplace for Santa to come down..

I am, by any measure, jaded. But when the employee opened that door, I physically recoiled in horror and shocked her with my language.

You can not see the worst of it. About 85% of the jumpers are dead in place. There are routers and hubs HANGING from loops of duct tape. NOTHING ANYWHERE has a correct tag.

Said to be Abe Lincoln's favorite joke:

A) How many legs does a dog have, if you call a tail a leg?

B) Four. Calling a tail a leg doesn't make it one....