In article edg@ocn.com (Ed Goldgehn) says: > T-1's require TWO pair of copper. ISDN (BRI) requires ONE pair of > Copper. Since a Primary Rate (not Access) Interface rides on a T-1 > (in the US) Carrier, TWO copper pairs are required. Your "ordinary" > telephone line can support 144 Kbps (BRI ISDN) - not just the 30 Kbps > that you might get from analog technology -- that was an apple and > orange comparison. Technically, BRI ISDN is 2-64K B chanels, 1 16K D channel and another 16K channel for Telco maintenance use totaling 160K or 80K baud capacity. Not nitpicking, just thought you might like to know that. And the above is the NORMAL configuration, there are several others. Also, BRI ISDN can go upto 18, 000 feet from the actual serving office before it requires any type of regenaration. And talking about T-1 facilities, there is a new type called HDSL. It stands for High Density Subscriber Loop. It is a FULL Duplex 768K on two NON conditioned copper pairs that provides the 1.54mbit speed. The 18,000 ft limit can be surpassed by a regenarator. The bridge tap allowed is <2K ft. AND there is NO separation needed in the cable. AND it works! :) [I was skeptical at first when I saw one] Why use them? CHEAP to install. The cable does not need to be conditioned for T-1 carrier. No span repeaters or group separation is needed. Thusly an enginerring job is not required. The original poster is from England and the telco's over there are vastly different in there usage of copper and fiber. Scott Darling Telco installer ------------------------------ From: balcroan@netcom.com (Butch lcroan/.nameBalcroan Lilli) Subject: Re: What is a T1 Line? Organization: NETCOM On-line Communication Services (408 261-4700 guest) Date: Thu, 29 Dec 1994 17:37:40 GMT Joseph H Allen (jhallen@world.std.com) wrote: > In article , L S Ng > wrote: >> The reason why T1 can run at 1.5Mbps plus whereas your ordinary telephone >> line can run only at 30kbps is because of a low pass filter! Low pass >> filters are inserted at the end of the ordinary telephone lines for two >> reasons: to improve speech quality and (more importantly) to limit your >> modem speed! The reason for the filters is to prevent some carrier above 3300HZ from entering the A to D convertor and being multiplexed into the T1 which runs at 1.5MHZ . The reason for this is numerous and preceded In article , L S Ng > wrote: >> The reason why T1 can run at 1.5Mbps plus whereas your ordinary telephone >> line can run only at 30kbps is because of a low pass filter! Low pass >> filters are inserted at the end of the ordinary telephone lines for two >> reasons: to improve speech quality and (more importantly) to limit your >> modem speed! Well, not quite. Typically, a voice call that goes through a digital circuit (which is true for almost all non-local calls these days) gets fed into some variant of an FXS or SLIC, which breaks the analog conversation down into a 56k data stream. Once broken down into that neat little stream -- which often happens before you even get to the CO in many urban areas -- the call is placed into a data channel on a T1. So, you see, the fact that you have telephone service doesn't guarantee you your own copper even a foot past the premises. We happen to be in a nice, modern building, so the total length of the copper is only about 150 feet, from the telephone room, across the warehouse, and down into NJ Bell's "shack". From there, it does right into a fibermux, and it's a 56k stream on a DS3 before it hits the sidewalk. If I make a long distance call, it goes digital before it even leaves the switch. In some cases, your already-digitized call may be packetized for some sort of cell-relay arrangement. In this case, you don't even have a time slice on a DS1 anymore, unless you're actually talking. So, when I ring up someone in another city, I'm not actually paying for a straight copper run from one end to the other -- I'm just buying bandwidth for the period that I use it. > I think there's more to it that that. At 1.5Mbps (a signal needing > >3MHz bandwidth) the crosstalk should be pretty severe in a large > bundle of twisted pairs. This would prevent you from giving T1s to > everyone. Certainly given the state of some of the wiring that's out there. With good-quality copper and proper termination, 10mhz signalling (a la 10baseT) is achievable for decent distances today, and I think most people expect both the bandwidth and distance to grow, with the price of the equipment coming down. It's the long-haul bandwidth that's expensive, and the equipment that it takes to switch it. >> Has anyone ever used/seen a PRI? The above is just a guess because I >> have not seen/used one. PRI/T1 are, I heard, usually run over 2 copper >> pairs (4 wires). This means that your ordinary telephone line should >> at least be able to run at 1 Mbps per pair. > The loss at 1Mbps on both twisted pair and coaxial is pretty high. > This means you would need lots of repeaters. I don't think with voice > that you need any repeaters between home and local office. So at the > very least, they have to add lots of repeaters everywhere. If users want more bandwidth, the carriers seem quite eager to bring it in. I don't expect we're really going to see a big drop in the cost of high-capacity private circuits anytime soon, though, unless someone comes out with an application to use it. >> 2Mbps is the limit of working in full duplex mode. In some >> applications such as video/TV, it is possible to pump more than 6Mbps >> down the copper wires. This technique is known as ADSL (Asymmetrical >> Digital Subscriber Loop) and it is half duplex. British Telecom was >> blocked by Bristish Government last month from using this technology >> for broadcasting TV over the old copper telephone networks to home. >> The technology is ready but the bureaucrats are not. > I'd really like to see a detailed technical description of how this is > done. Perhaps they transmit at a different carrier on each pair in > the bundle? I really don't see how else they would get rid of the > cross-talk. I'm not familiar with the technique, but I'd guess it's analogous to the v.42 compression used by commercial modems; you put intelligent equipment at each end that can spot and tokenize repetitive data streams. Dave O'Shea dave_oshea@wiltel.com Technical Development Manager 201.236.3730 WilTel Communications Systems Did I *say* I'm a WilTel spokesman? ------------------------------ From: mpd@adc.com (Matthew P. Downs) Subject: Re: What is a T1 Line? Date: 29 Dec 1994 14:29:42 GMT Organization: ADC Telecommunications lsn92@ecs.soton.ac.uk (L S Ng) writes: > Edward F. Munro writes: >> If T1 is 24 X 64K on 4 wires, and ISDN is 2 X 64K, then why do you only get >> 4 X 64K when you use 2 ISDN links? Is there a way to get 2 ISDN lines and >> set yourself up with T1 bandwidth?!? > I thought T1 has now been repackaged by the telephone companies as > ISDN Primary Access or Primary Rate ISDN (PRI), consisting of up to 24 > B channels (1.5Mbps) in North America or 30 B channels (2Mbps) in 'the > rest of the world'. T1 is just a line format. PRIMARY rate uses this in order to make higher rate connections. The underlaying technology even to primary rate is a T1 line with 24 DS0's each at 64 kbps. > Originally T1 or Primary Access were used only within the telephone > networks (from one local exchange/central office (CO) to another), but > now it seems that, by packaging it as PRI, such rate now runs from CO > to customers premises (your office/home). Each T1 link is essentially > either a copper pair or an coaxial cable. The reason why T1 can run at > 1.5Mbps plus whereas your ordinary telephone line can run only at > 30kbps is because of a low pass filter! Low pass filters are inserted > at the end of the ordinary telephone lines for two reasons: to improve > speech quality and (more importantly) to limit your modem speed! Who has telephony via coax right now in the field? Right now each one is either a copper or optical fiber connection. There is a difference between coax and fiber. These filters are not to limit your modem speeds, but to protect you 64 kbps channel from others. So you don't hear the cross talk on your line! This was done a long time before modems were ever thought of ... > So remember this: when you ask for ATM from your telephone company, > make sure you get an optical fibre. Or they would give you a copper > coax for 150Mbps and ask for more money when you need to 'upgrade' it > to 600Mbps. It is not possible to use copper coax at 600Mbps which is > why you need a piece of cheap glass wire, otherwise known as the > optical fibre by the telephone companies who want to glamorised their > product names. A lot of things are stated as fact that are not in this ... such as with SONET. They are not planning on giving any one a 150 mpbs or even 600 mbps links. Matt ------------------------------ From: stans@panix.com (Stan Schwartz) Subject: Re: '500' Numbers Finally Available Date: 29 Dec 1994 01:45:04 -0500 Organization: PANIX Public Access Internet and Unix, NYC The Toddster (todd@access.digex.net) wrote: > Hopefully, the local phone companies will reprogram their switches to > allow dialing of 1 + 500 and 0 + 500 calls. If they do not, it is my > assumption that calls can still be made via +1.800.CALL.ATT (though > this is PURELY speculation). Hopefully, INDEED! Rochester Telephone never upgraded their switches to allow for EasyReach service, and I _COULDN'T_ complete the calls through AT&T's 800 numbers either, as of the summer of '93. An AT&T rep told me that they couldn't force local phone companies to upgrade their hardware/software to handle new LD services, and they also had the same problem in Cincinnati. This was one of the many reasons I cancelled my EasyReach service. Stan [TELECOM Digest Editor's Note: Well I am sure Ameritech will be making all the needed adjustments very soon now since they are also entering the 500 arena. According to the {Chicago Sun Times} on Thursday, Ameritech has been given approval to offer their own 500 numbers for local and long distance use. As to be expected, AT&T and MCI both screamed loudly to protest, claiming Ameritech would favor itself in the form of reduced access rates (charged to its own telcos on its books) as opposed to the access rates it has already demanded from AT&T and other long distance carriers who intend to offer this service. So I don't think anyone is going to have to tell *our* telephone company here about it ... grin. Not only that, Ameritech's version is going to have a prefix for cellular customers where the caller pays for the airtime instead of the traditional method where the cellular owner pays in both directions. They are going to offer voicemail, transfer on busy/no answer and a few other goodies on their version as well, and this has gotten AT&T all the more annoyed according to the newspaper account. PAT] ------------------------------ From: Jerry Eckler Subject: Re: Newbridge Channel Bank Date: 29 Dec 1994 17:38:45 GMT Organization: On-Ramp; Individual Internet Connections tague@cwinc.win.net (Michael Tague) wrote: > where is the Newbridge company located (or phone number)? The listing in the new Dallas Yellow Pages shows the following: Newbridge Network, Inc. 14275 Midway Rd. I am not sure if this is Dallas or Addison, Texas (214) 490-4200 I think this is the home office. If not they should be able to give you the number. Hope this helps. Jerry ------------------------------ From: anadigi@cerfnet.com (William J. Dawson) Subject: Re: Newbridge Channel Bank Date: 29 Dec 1994 21:45:02 GMT Organization: Anadigicom Corporation In article , tague@cwinc.win.net says: > Could someone suggest a good -- inexpensive -- place to get a > Newbridge channel bank. Also, where is the Newbridge company located > (or phone number)? > Does anyone have any thoughts about the most cost effective channel > bank to get -- for voice use. > Our organization manufactures the Channel Bank Multiplexer, Model MUX100-1 which might meet your requirements. The MUX100-1 supports various voice interfaces such as 4-wire E&M, 2 wire FXS or FXO, etc. and converts them into either a T1 or E1 interface. The MUX100-1 can be configured to operate from either -48vdc or 115/230VAC nominal input power. Data ports are also available although you did not specify this requirement. The MUX100-1 can also be configured for signaling conversion should you require this. If you need additional information, please respond via email anadigi@cerfnet.com or to the below with your requirements: Anadigicom Corporation Ph-703-803-0400 Fax-703-803-2956 Attn: Gene Delancey ------------------------------ End of TELECOM Digest V14 #471 ******************************