2-wire T1?

It does connect to a smartjack then from the smartjack it goes to my cisco router with a CSU/DSU card, just as a normal T1 would.

Jason

Why be annoyed? Main reason the performance we are getting from the T1 appears sub-par. Granted I need to do further investigating and have concrete evidence to justify that, and that is what I am working on.

~ I moved my smartjacks lastnight and found that the T1 is only 2 wires. ~ (It is from an McLeodUSA.) I have NEVER seen a T1 that was not 4 wires ~ and still was a T1. The line is indeed 1.544 mbit. ~ ~ The only telco data service, at those speeds, that I am aware of that ~ runs on 2 wires is xDSL. Is this HDSL or some other flavor?

Sounds like HDSL2.

~ If it is DSL I will be p$#$#d. I am not paying T1 prices for a DSL ~ line, thank you very much.

I don't get it - assuming that you're getting good T1 service with good latency, low BER, no slips - what do you care whether your T1 is carried in the long haul over one pair, two pair, fiber or baling wire? What difference does it make?

Aaron

I would guess it is HDSL. GTE (and maybe US West/Qwest also, it's been 7 years ago) used to install a lot of our T1 circuits with HDSL between the telco's CO and our cellsites. It was a lot faster for them to provision the circuit and in a few cases there was a very limited number of copper pairs available where we needed the circuits. We never had any problems with it, or at least no more than we did with 'real' T1 spans. I would guess at the CO it jumped on to one of thier DS3's to be long hauled back to our MTSO which was several hundred miles away.

I think the big reason you are paying a T1 rate rather than DSL is the level of service you get. A regular DSL customer might be left waiting days for a problem to be fixed whereas a T1 customer (even if that T1 is using HDSL) probably gets a 2 or 4 hour response time

24x7x365. Plus I'm sure there are guarantees involved that the bandwidth will in fact be 1.544mbps 24x7x365 where DSL gets those "up to XXXXkbps" speeds.

See also:

HTH

Don't panic. That sounds like HDSL/2.

T1 was developed in the 1960s and was designed to be implemented using

1960s digital logic. Things have advanced a little in the past 40 years, and HDSL is a modern replacement for T1. The original HDSL did 1 Mb bidirectional on two wires, HSDL/2 can do a full T1 and maybe even E1 on two wires. It really is the functional equivalent of a T1, using more sophisticated modulation underneath on one pair rather than two.

Incidentally, the choice of traditional T1 vs. HDSL is up to the local LEC who delivers the last mile, not the long distance carrier from whom you might have ordered the circuit. I was looking at the local cell tower (it's OK, I'm the landlord) and noticed that the LEC provisioned their first T1 as a T1 and the second as HDSL, on the same panel.

Regards, John Levine, snipped-for-privacy@iecc.com, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be,

Mayor "I dropped the toothpaste", said Tom, crestfallenly.

T-1 physically separates TX and RX, officially on separate COAX cables, often run on separate twisted pairs.

McLeodUSA is in the 'bottom feeder' business. it's anybody's guess what they're delivering. The CPE used, and the line interface on it, _will_ tell the tale.

Simple, you did not buy a T1.

You bought a DS1. A DS1 is a data format, moving certain bits at 1.544 Mb/s.

In days of old, DS1 was carried only on T1, a *facility* that used special cable {usually}, two pairs, and repeaters every 6000 ft. That technology, by the way, goes back to 1962. Yes, sixty two.

More recently, there have been a lot of ways to carry those DS1 bits. An obvious one: in a DS3, with 27 other DS1's. Another is over SHDSL [ITU-T Rec. G.991.2] and likely more, I think HADSL or is it HDSL.

All use dedicated pairs, not shared with POTS.

Why be annoyed? What you get with DS1 vs DSL is not just the DS1 bitrate, but a quality of service from the carrier. Iffen you get that, as spec'd, why should you care if it uses 1 pair, 2 pair, or subspace transceivers stolen from the Vulcans?

That's because most 'T1' service is now delivered via SDSL. It's cheaper for the telco's to put out there because they don't need all the amplifiers, etc. associated with a true T1.

So THAT is something to gripe about. Document it and bitch. Don't worry about the man behind the curtain.

Having been in the ISP biz for 14 years, I'd say 99% of my DS1 installs have been on HDSL or HDSL/2 delivered from the LEC. That's been dealing with Qwest/McLeod/AT&T/MCI/Sprint, and some others that are probably all folded back into at least one of the above.

Its the rare case where we'll go in for an install and find a real T1 and that only happens in the Downtown regions, blocks from the CO. LECs have been deploying DS1 circuits over HDSL for at least the last 12 years.

I usually get the best performance out of HDSL/2 circuits (ie. single pair from the LEC into the Smartjack).

If this is an Internet DS1, the ISP has lots to do with your preformance over it. Ie. some of the worst performance gets to be when your ISP provisions the T1 circuits out of a DSLAM and backhauls everything back into their main POP somewhere half-way across the country over some long haul ATM UBR PVCs along side their RADSL and SDSL customer base.

The best would be provisioned directly out of a well-connected POP with no back-hauling.

UUNet brings in our 2 T1's on 2 wires each. And UUNet is *not* a bottom feeder.

HDSL2

Depends on the DSL service in use. If it is HDSL2 that is a full T1 you are getting. Being that you have a smartjack and not a dsl modem, kinds of indicates you do indeed have a T1.

Cheaper maybe, but the end location still has to be within a certain distance to the CO. The reason for HDSL on T1 links is the fact that the telco's are running out of copper pairs in the cable distribution plant.

I doubt if the original poster tested his line for slips and errors, or even B8ZS/AMI configuration of the line. It may be that he has noticed a delay or reduced bandwidth from his ISP connection. Even with a full T1 to a location, depending on how many users are attached to that T1 depends on the available bandwidth available to each desktop. If his internal network is small, and not very busy, he would need to check the quality of his ISP connection to his T1. The ISP is more than likely where the congestion is occuring.

From the above description, jumping to this conclusion is wrong. Especially since his line rate is 1.544mbit.

For an end user to get a DS1, he has to get a T1 to his drop. For all practical purposes DS1 and T1 are one and the same.

While the history time frame is correct, you forgot to add that at this time T1's were used primarily for interoffice links. Very few end subscribers were able to order or get T1 links. At this time only the organizations with very high bandwidth requirements were able to tie into the telco's on a T1 level.

DS3 is just another level of the multiplexing scheme used.

24 dso's make a t1, 28 t1 makes a t3, etc. This is all based on TDM multiplexing.

And what do you mean by subpar. Have you even placed a T-berd on the span and checked for errors, slips and frame errors. Or does you network just seem to be slow, which could be an issue of congestion, even though the above errors if present would also contribute to a congestion problem due to packets being resent. First step I would do if you know your T1 on your end is not overloaded with users, is check your span from the telco with a T-berd, and see how your performance is. If your span runs clean to the telco, and to the far end, it could be your ISP has the congestion issues.

HDSL is able to run a T1 on one pair of wires due to the modualtion scheme used in HDSL. On a microwave radio you can get from one to 8 T1's on one radio path. As you jump up in cost this can increase to DS3 and OC12 rates over a microwave radio.

That seems to be more of an opinion than the equipment they are using. Being that I have no option of trying out service from McLeod up here in Alaska, I cannot say that just because they use HDSL for their T1's that they are a bottom feeder.

Just a question. Do you know what a smart jack is doing?? And now that you add that you are using CSU/DSU ports on your router, it is more than likely that you are indeed using a full T1, unless you are ordering fractional T1 from the local service, at which point you may not be getting all 24 DS0's on the T1. But you would know if you had ordered a fractional T1 so I do not think this is the case.

Exactly, with the number of copper pairs becoming almost impossible to get, HDSL comes in to rescue the telcos from the increasing demand of T1 service with a decreasing supply of copper pairs.