SCOTT, THE FOLLOWING POSTS SHOULD BE VERY INTERSTING TO YOU ON POSSIBLY WHY NONE OF OUR CALLERS HAVE BEEN ABLE TO ACHIEVE FULL 28.8 RATES... JUST THE INFO ON BANDWIDTH TRANSMISSION OF DATA IN PHONE LINES SHOULD BE WORTH THE LOOK SEE..... LOOK FOR THREE LINES OF ********* 's TO SEE BEGINNING OF POSTS... I PUT THE MODEM ONES FIRST ! BY THE SYSOP OF MOG-UR'S BBS: =========================================================================== BBS: The MOG-UR'S EMS Date: 08-11-94 (08:16) Number: 229 From: TOM TCIMPIDIS Refer#: 39683 To: ALL Recvd: NO Subj: 28.8k Connects? Conf: (2) TechInf-LO --------------------------------------------------------------------------- MP> I would like to ask if the 28.8.k connection is as rare as it seams MP> me. I have seen a 28.8k connect only once, and during a transfer, i MP> seamed to drop to maybe 26.4k. As on a compressed file, I reciived MP> little more than 2900 cps. I was wondering what you might suggest t MP> improve line conditions in my house, I have 2 data lines, that have MP> the past gave good troughput with 16.8k connects, and 21.6k connects MP> Also, I would like to know if v.34 would improve the line condition MP> needs for a 28.8k connect? Is the v.FC protocol more demanding? MP> Thank you for your time... A 28,800 bps V.FC/V.34 link requires 3200 Hz bandwidth, from 320 - 3520 A 26,400 bps V.FC/V.34 link requires 3000 Hz bandwidth, from 375 - 3375 A 24,000 bps V.FC/V.34 link requires 2800 Hz bandwidth, from 467 - 3267 by contrast.. A 21,600/19,200/16,800 link needs a usable bandwidth of only 2400 Hz, from 600 - 3000 Hz. This is the same amount required for 9600/V32 & 14,400/V32-bis. Alas, while many domestic phone lines can easily support the requirement of V.32, V.32bis and V.32-terbo, some may not have sufficient bandwidth to support V.FC and V.34 at *FULL* SPEED. This, in a nutshell, is what you (and others) are experiencing. Compared to V.32/bis/terbo, 28,800 bps requires 33% more bandwidth, 26,400 bps requires 25% more bandwidth and 24,000 bps needs 17% more bandwidth. This additional bandwidth has to be there from end to end, from one modem to the other. Either you have it or you don't - your modem is telling you. As the domestic telephone companies race to install fiber optic cables, the bandwidth situation should gradually improve. The only suggestions for 'at-home' modeming is to try disconnecting *ALL* telephonic devices attached to the phone line. This includes: extension phones, answering machines, fax machines, caller-id boxes, line-in-use indicators, cordless phone base units, demon dialers, lightning spike protectors or line filters like those commonly found in PC Desktop master-switch power directors. If any of this helps, then start plugging things back in one-by-one until the culprit is found. Your mileage will vary. --- ž QMPro 1.52 ž MOG-UR'S EMS ž Internet: sysop@mogur.com ž =========================================================================== BBS: The MOG-UR'S EMS Date: 08-11-94 (19:09) Number: 230 From: TOM TCIMPIDIS Refer#: NONE To: ALL Recvd: NO Subj: Modem statistics screen Conf: (2) TechInf-LO --------------------------------------------------------------------------- For those of you without a V.FC or V.34 modem, this is what the Modem Stats (Door 13) screen looks like on such a connect. This screen was captured on a call from a line in my home to a node of the BBS and represents a good, clean connection and line. Protocol LAPM Modulation V.34 Compression V42BIS 2048/32 Speed 28800 Link Timeouts 0 Carrier Freq (Hz) 2000/2000 Link Naks 0 Symbol Rate 3200/3200 Blers 0 Retrains Requested 0 Blocks resent 0 Retrains Granted 0 Chars lost 0 Fallback Enabled Chars sent 2560 HST Line Reversals 0 Chars Received 0 HST Equalization Long Blocks sent 152 Trellis Code 32S-2D/32S-2D Blocks Received 33 Nonlinear Encoding OFF Octets sent 2407 Precoding ON Octets Received 37 Shaping OFF Preemphasis Index 5/4 Frequency (Hz) Level (-dB) Rx/Tx Level (-dB) 30/18 1025 25 Roundtrip Delay mS 2 3025 29 Current Call 00:00:39 3325 31 SV: 08/02/94 DSP: 08/04/94 3375 33 3475 36 08-05-94 20:44 Caller 5 3625 42 USRSTATS Version 2.34B For the those of you who care about such things, it should be noted that modems essentially become deaf at a level of -43 dB... Thus, a frequency response for a given frequency at a level of -43 dB or less (higher number is less) is unusable by a modem. A poor signal to noise ratio or excessive harmonic distortion can also cause a reduction in connect speed even if you have adequate frequency response. -Tom =========================================================================== BBS: The MOG-UR'S EMS Date: 08-17-94 (18:47) Number: 236 From: TOM TCIMPIDIS Refer#: NONE To: ALL Recvd: NO Subj: About my cps rates... Conf: (2) TechInf-LO --------------------------------------------------------------------------- I am often asked what the optimum cps rates are for different bps rates so here is a list. These are the maximum theoretical rates for each bps using Zmodem and transferring a ziped (uncompressable) file. Actual rates will generally be up to about 5% less due to modem and computer system overhead. Connections not using MNP or V.42 error correction (typical of older 1200 and 2400 baud modems) will achieve cps rates 20% lower than those listed. Modem protocol: V.FC V.34 V.32bis V.32terbo V.32 HST BPS CPS 1200 144 X X X X X X 2400 288 X X X X X X 9600 1152 X X X X X X 12000 1440 X X X X X 14400 1755 X X X X X 16800 2016 X X X X 19200 2304 X X X 21600 2592 X X X 24000 2880 X X 26400 3168 X X 28800 3510 X X All the protocols and rates shown above are presently supported by MOG-UR'S on all nodes using USR Dual Standard V.Everything modems. However, experience nationwide during beta testing on a variety of systems by a variety of persons has shown that only about 10% achieve a 28.8 connect, 40% achieve a 26.4 connect and 40% achieve a 24.0 connect. The remaining 10% receive a 21.6 connect or lower. See earlier messages in this conference for a discussion of why this is so and how the telephone company enters in to the picture. =========================================================================== BBS: The MOG-UR'S EMS Date: 09-09-94 (10:09) Number: 245 From: TOM TCIMPIDIS Refer#: 12731 To: ALL Recvd: YES Subj: 8/25 V.34 code Conf: (2) TechInf-LO --------------------------------------------------------------------------- BB> Yes, but my available bandwidth here (using -43 as the threshold BB> benchmark) should not allow beyond a 24K or maybe at best a very BB> occasional 26.4K connect, which is exactly what I used to get. Howev BB> I now get solid 28.8 connects everytime which tells me that they mus BB> now be able to get a usuable signal from levels well below -43... BB> Whatever the reason, it is a most impressive performance. With the USR Courier Flashrom 08/23 code (and later) they've enabled the 1829 Hz carrier frequency, thus shifting the entire envelope down 91 Hz lower when conditions warrant, for an additional 182 Hertz of bandwidth. This may be where you're achieving those 3200 Hz bandwidth calls. Now if the modem can't find the bandwidth in the attic it looks for it in the basement. The -43 level threshold is still there. Not 100% sure, but I think the modems -may- be able to do this envelope shifting independently, transmit versus receive. Isn't V34 neat? -Tom =========================================================================== BBS: The MOG-UR'S EMS Date: 09-09-94 (10:39) Number: 246 From: TOM TCIMPIDIS Refer#: 12748 To: ALL Recvd: NO Subj: 8/25 V.34 CODE Conf: (2) TechInf-LO --------------------------------------------------------------------------- RH|I am seeing that the V.34 code is not reporting correct connect |rates.. I have seen my comm. program reporting one thing but the bbs |says something else... sometime my comm. program will say 21.6 and |the bbs says 24.0 sometime it is reversed.. Today, I called myself |and I said 19.2 on the comm program and PCBoard reporte 26.4... The |transfer rates seem to point out the higher rates, no matter what it |says it connected at... Which I guess is good, (Grin)... There is nothing incorrect about what the V.34 modems are reporting. V.34 incorporates ASL (adaptive speed leveling) which allows one side (transmission or receive) of the connection to be higher than the other. All you have to do is examine an ati6 after (or during) a call (or use Door 13 online here) to see this. When I call from work to my bbs, my comm program reports a 28800 connect while the bbs reports 26400. What that means is *my* receive is 28800 and the bbs's receive is 26400. Both speeds MAY be the same but they do not HAVE to be the same. This is one of the many big advantages of V.34 over V.FC. -Tom *************************************************************************** *************************************************************************** *************************************************************************** =========================================================================== BBS: The MOG-UR'S EMS Date: 06-20-94 (09:17) Number: 208 From: TOM DEVLIN Refer#: 10650 To: DOUG HAIRE Recvd: NO Subj: New 28.8 Modem Conf: (2) TechInf-LO --------------------------------------------------------------------------- DH>Yes, the need for extra capacity at a low price is the basic reason for DH>the SLC usage. My area is growing quickly and is in a very rual area of DH>the county. There is insufficient outside plant (cables) to support the DH>amount of growth we have. Since we are also in a transition to fiber, DH>there is a problem with expanding the existing metallic wiring to handle DH>the growth. Converting it to SLC systems is a good method until the DH>fiber comes in... Then you see the SLC's as a temporary expediant, right? There was (as I'm sure you recall) a lot of talk in the Field Trial conference about the effect SLC's were having on connect speeds, you seem convinced that they *should* allow a 28.8K connect but other folks noticed a direct correlation between connect rates and the presence (or absence) of a SLC in the path. DH>I already have two V.everythings (one on the board and one personal). I DH>get some interesting results when calling from home and office. When DH>calling from my home voice line into the BBS (call is routed to the CO DH>and back), I get 26400 bps connects. Is it possible to have a SLC in the circuit on an in-and-out connect like that? You say they are used for inter-office expansion but would something similar ever be used to expand line capacity in or out of a CO? Possible at a site remote from the actual Central Office? DH>When I call from my office (about 16 miles as the crow flies), I DH>get only a 24000 bps connect. Dumps of the various displays show no DH>real difference in conditions. Does that include the ATY7 screen? I'm convinced that there's some valuable information there if we could understand it. DH>However, from the office, I go through a PBX to a local CO (in the DH>same building) to my home CO so there's more room for problems. Yeah, any time you add *anything* to the link you increase the possiblity of problems. I frequently see better LD connects than to "local" boards that are an office or two away. This was also true with V.32Bis, HST and terbo, I saw fewer Blers on LD calls than calls to a couple of local boards. DH>I have passed the data on to a friend who works in Southern Bell Keep us posted... DH>It's real hard to get any sympathy for the telcos when your complaint DH>goes: DH> I can't seem to get any better than 24000 bps connections on my DH>voice line. Once V.34 is "officially" approved I'm going to try the "I'm using a protocol the was approved internationally for use on voice grade lines, why aren't *your* lines up to snuff?" line. Be interesting to see what they say. DH> In fact, it's hard to get any sympathy from my friends with 14.4's ... DH> [g] Sadly true... DH> ž SLMR 2.1a #40 ž Why does 14400 bps seem so slow now? ROTFL! I still remember my first 14400 HST connect, I just couldn't believe it. Now, if I call a board that's still "stuck" at 14400 it seems like it takes an enternity for anything to happen. How soon we get spoiled... --- * BCSUTI Version 1.3 * The Warm Boot ž Waterford, MI ž (810) 683-8032 * PostLink(tm) v1.20į WARMBOOT (#1003) : RelayNet (tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 06-20-94 (19:40) Number: 209 From: BILL GARFIELD Refer#: 10827 To: DOUG HAIRE Recvd: NO Subj: New 28.8 Modem Conf: (2) TechInf-LO --------------------------------------------------------------------------- TD> I've heard a fair amount about SLC's lately, I get the feeling that TD> we're going to be seeing a lot more of these as the phone companies TD> scramble to add capacity, true? DH>Yes, the need for extra capacity at a low price is the basic reason for DH>the SLC usage. My area is growing quickly and is in a very rual area of DH>the county. There is insufficient outside plant (cables) to support the DH>amount of growth we have. Since we are also in a transition to fiber, But fiber or copper, the SLCs are here to stay. The old SLC96 is giving way to the new SLC5 and SLC2000. (higher capacity) TD> Do you think that a properly set up SLC should allow 28.8K connects? No. Contrary to what some will tell you, an SLC-96 operating in either Mode 1 or Mode 2 provides only 56-kilobit voice channels, not 64k bps. They are 64k bps capable, but only in Mode 3. Mode 3 is not used for switched voice applications. SLC = Subscriber Loop Concentrator. SLC-96 "Mode 1" is for high capacity voice applications, normally in commercial settings. A Mode 1 SLC-96 is provisioned with four (4) 1.544 megabit T1 lines (and sometimes a 5th for failsafe). It can also be provisioned with a fiber DS-2. But whether fiber or copper, the Mode 1 SLC-96 is capable of providing 96 -simultaneous- 56 kilobit voice paths. SLC-96 "Mode 2" is used typically in residential areas where the likelihood that more than 50% of the households would be using their phones at any one moment in time is very remote. In Mode 2 the SLC-96 is provisioned with only two (2) T1 lines, but no compression takes place. It still serves 96 subscribers, though only 48 can be off hook (talking) at any one time. Again, these are 56-kilobit channels, not 64k. In either Mode 1 or Mode 2 an SLC-96 uses "robbed bit signalling" to carry in band all status information such as E&M signalling states. Before we put this to bed I think we need to have a crash course in T1 digital transmission techniques. A T-1 line or Span as they are sometimes called, runs at a composite data rate of 1.544 megabits. For a SLC-96 loop concentrator, the line format is AMI (alternate mark inversion). It uses an 8-bit character interleaved Time Division Multiplexing (TDM) pulse code modulated (PCM) format. There are 24 time slots (channels) on a standard T1 line. Each time slot (channel) is divided into 8-bits and sampled at an 8-kilobit rate to provide twenty-four 64k bps channels plus a single-frame synchronization bit per frame (193 bits per frame total times 8k bps sample rate = 1.544 megabits). - It's easier to follow drawn out on a white board, but follow along, we're almost there... One of the rules (laws) of this signalling format is the zeroes density rule. We can have no more than 15 consecutive "zeroes" before we -must- output a "one". To prevent violation of the zero density rule, the 7th bit of any 8-bit byte must be altered. This is of no consequence for voice transmission but means data is effectively restricted to 7/8ths of the maximum 64k bps, or 56 kilobits max. It is possible to achieve "clear channel" 64k bps speed but doing so requires that we use binary 8-zero substitution (B8ZS) instead of the altername mark inversion (AMI) format. Use of B8ZS in a T1 multiplexor requires that all channel service units, central ofice equipment and test equipment be strapped for this option. It is not commonly used in SLC-96 equipment. In theory, if I understand all this smoke & mirror magic, the max speed one can expect running data over a Mode-1 or Mode-2 voice channel on an SLC-96, under the most favorable of conditions, is 26,400 bps (due to the theoretical restrictions of Shannon's Law as applied to the reduced bandwidth of a 56 kilobit voice channel. Not what you wanted to hear, I know... --- ž OLX 3.0 ž Friends feel sorry for friends who are on an SLC-96! * USRobotics Customer Support, U.S.A., 708-982-5092 (28.8k) * PostLink(tm) v1.11 USRUSA (#174) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 06-21-94 (23:33) Number: 210 From: DOUG HAIRE Refer#: 10842 To: TOM DEVLIN Recvd: NO Subj: New 28.8 Modem Conf: (2) TechInf-LO --------------------------------------------------------------------------- DH>Yes, the need for extra capacity at a low price is the basic reason for DH>the SLC usage. My area is growing quickly and is in a very rual area of DH>the county. There is insufficient outside plant (cables) to support the DH>amount of growth we have. Since we are also in a transition to fiber, TD|Then you see the SLC's as a temporary expediant, right? There was (as Yes, that's what its purpose has become. It was envisioned as a way to handle growth on a permanent basis but it's apparent that nothing is that permanent in the telecommunications field :). TD|I'm sure you recall) a lot of talk in the Field Trial conference about |the effect SLC's were having on connect speeds, you seem convinced |that they *should* allow a 28.8K connect but other folks noticed a |direct correlation between connect rates and the presence (or absence) |of a SLC in the path. And I still feel that way (since I have managed 28.8k connects on rare occasions though they have been generally poor and unstable) in spite of Bill's explanation about the SLC's. DH>I already have two V.everythings (one on the board and one personal). I DH>get some interesting results when calling from home and office. When TD|Is it possible to have a SLC in the circuit on an in-and-out connect |like that? You say they are used for inter-office expansion but would |something similar ever be used to expand line capacity in or out of a |CO? Possible at a site remote from the actual Central Office? The SLC is not between offices, it's from CO to house/business areas (though more to rural/suburban housing than any major business area). Straight T-cxr systems are used between offices (usually in T-3 "pipes" or 1.7gbps fiber routes). DH>When I call from my office (about 16 miles as the crow flies), I DH>get only a 24000 bps connect. Dumps of the various displays show no DH>real difference in conditions. TD|Does that include the ATY7 screen? I'm convinced that there's some |valuable information there if we could understand it. I'm sure the aty7 screen would be quite useful if we had *any* idea of what it was reporting. Since we don't, it's totally useless. TD|Yeah, any time you add *anything* to the link you increase the |possiblity of problems. I frequently see better LD connects than to |"local" boards that are an office or two away. This was also true with |V.32Bis, HST and terbo, I saw fewer Blers on LD calls than calls to a |couple of local boards. When you make an LD call, the path is usually like this: home ÄÄÄ CO ÄÄÄÄ LD provider ÄÄÄÄÄÄÄ LD Provider ÄÄÄÄÄ CO ÄÄÄÄ bbs or: home ÄÄÄ CO ÄÄÄ tandem ÄÄÄÄ LD Provider ÄÄÄ LD Provider ÄÄÄ tandem ÄÄÄ CO ÄÄÄ bbs with all paths from local CO to remote CO being digital (and likely fiber). Paths across town may not take an all digital route (though most now seem to) or the route may consist of multiple links that are not properly set up. They should be improving over the next couple of years, though. DH>It's real hard to get any sympathy for the telcos when your complaint DH>goes: DH> I can't seem to get any better than 24000 bps connections on my DH>voice line. TD|Once V.34 is "officially" approved I'm going to try the "I'm using a |protocol the was approved internationally for use on voice grade |lines, why aren't *your* lines up to snuff?" line. Be interesting to |see what they say. That's the proper approach, in my opinion. A simple remark that these are designed to operate within the specs for a standard voice line should be sufficient. DH> ž SLMR 2.1a #40 ž Why does 14400 bps seem so slow now? TD|ROTFL! I still remember my first 14400 HST connect, I just couldn't |believe it. Now, if I call a board that's still "stuck" at 14400 it |seems like it takes an enternity for anything to happen. How soon we |get spoiled... See the next generation tagline ... ÄÄÄÄæ --- ž SLMR 2.1a #40 ž Drat! Only 24kbps! * Telephone Exchange 407-791-2474 V.32bis ZyXel 19200! * PostLink(tm) v1.20į TELEPHNE (#222) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 06-22-94 (04:57) Number: 211 From: TOM DEVLIN Refer#: 10851 To: BILL GARFIELD Recvd: NO Subj: New 28.8 Modem Conf: (2) TechInf-LO --------------------------------------------------------------------------- BG>There are 24 time slots (channels) on a standard T1 line. Each time slot BG>(channel) is divided into 8-bits and sampled at an 8-kilobit rate.... BG>....This is of no consequence for voice transmission but means data is BG>effectively restricted to 7/8ths of the maximum 64k bps.... BG>In theory, if I understand all this smoke & mirror magic, the max BG>speed one can expect running data over a Mode-1 or Mode-2 voice channel BG>on an SLC-96, under the most favorable of conditions, is 26,400 bps (due BG>to the theoretical restrictions of Shannon's Law as applied to the BG>reduced bandwidth of a 56 kilobit voice channel. I've saved your message for further study but this is *finally* starting to make sense! Shannon says that you need to sample at a frequency of (at least) twice the data rate. An 8K samples/second rate should still allow the 3600 V.FC frequency to pass but that 7/8 figure (which I've *never* seen before) gives us a top frequency limit (assuming a "brick wall" low pass filter) of 3500 cps. Presto! A 26.4K connect! Does anyone know what frequencies V.34 will use? --- * Channel 1(R) * 617-354-7077 * Cambridge MA * 100 lines * PostLink(tm) v1.11 CHANNEL1 (#15) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 06-23-94 (19:33) Number: 212 From: BILL GARFIELD Refer#: 10842 To: TOM DEVLIN Recvd: NO Subj: New 28.8 Modem Conf: (2) TechInf-LO --------------------------------------------------------------------------- TD>Then you see the SLC's as a temporary expediant, right? There was (as >I'm sure you recall) a lot of talk in the Field Trial conference about >the effect SLC's were having on connect speeds, you seem convinced >that they *should* allow a 28.8K connect but other folks noticed a >direct correlation between connect rates and the presence (or absence) >of a SLC in the path. Tom, my contacts inside Southwestern Bell say that everything from the technology standpoint is "temporary". The SLCs will likely remain for the forseeable future. The new SLC's (SLC-5 and SLC-2000) represent only the latest technology is subscriber loop concentrators, or "pair gain devices" as most telcos refer to them as. The concept is still the same - a device intended to bring hundreds of telephone circuits to an area which is either: (A) Too far from the switching office for conventional copper, or (B) Rapidly outgrowing the capacity of existing cabling, or (C) A newly platted subdivision A single SLC-96 can bring 96 phone lines into an area and use only 4 pairs of conventional copper wires to make it happen. It can do this out to 50 miles from the switching office, though a T1 repeater is required every 6,000 feet. As far as 28.8k modem performance is concerned, a SLC-96 configured for Alternate Mark Inversion has to "steal" 1/8 of each channel's timeslot to conform with the T1/D4 AMI format. Therefore we could logically say by so doing that it also robs 1/8 of the available bandwidth. This has no effect on voice transmission, but when the modem is looking for bandwidth, a 1/8 reduction in the timeslot equates to a 12« percent reduction in bandwidth and easily 1 rung off of the speed ladder. During the 28.8 Courier beta trials we experienced this loss of bandwidth and reduction in speed capability every time we encountered T1/D4 analog-to-digital and then back digital-to-analog conversion (which happens at each end of a T1/D4 interface). As the SLC-96 was designed around D4 channel bank technology, it behaves similarly. I can route my call over 2,800 miles of 100% digital (B8ZS) circuits and back to another modem across the room and GUARANTEE that we'll have a solid 28,800 bps connection every call. I can send the same call out to Southwestern Bell through a D4 channel bank and a 3 mile loop and guarantee that you will never, ever see a connection faster than 26,400 (that will hold in). --- ž OLX 3.0 ž CONNECT 21600/ARQ/V32/LAPM/V42BIS - 2500 cps!! YEAH!! * IBM Net Connection <> Indpls., IN <> (317)882-5575 21.6 Duals All Lines * PostLink(tm) v1.20į IBMNET (#5) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 06-30-94 (10:14) Number: 216 From: TOM TCIMPIDIS Refer#: 11055 To: ALL Recvd: NO Subj: A quick review Conf: (2) TechInf-LO --------------------------------------------------------------------------- This message was from BILL GARFIELD to ALL originally in conference USRobot-RI on MOGUR (The MOG-UR'S EMS) and was forwarded to you by TOM TCIMPIDIS ---------------------------------------- A quick review.... Although we've spoken of these SLC-96 remote terminals as a device which combines (multiplexes) 96 telephone circuits onto two or four broadband high speed synchronous lines (T-1 lines), perhaps another word or two of explanation is in order. These "slicks" or "remote terminals" or "pair gain" devices as they are called, (names used interchangeably) are not simply a single stand-alone piece of gear. Rather several of them will be installed in a "hut" or small building. This hut is normally a non-obtrusive building, about 10' X 20' that blends into its surroundings. Chances are most folks have seen them but not known what's inside. The phone company tries to locate these near the center of a new (normally) residential subdivision. These then become the "local hub" for all neighborhood phone service out to about 3 miles or so in all directions from the hut. No "switching" is done in these remote terminal huts. Their sole purpose is to gather or combine the neighborhood cluster of phone circuits together (often as many as 2,000 or more lines) which are then routed to the switching office (Central Office) via just a few high speed digital lines. In this way, the phone company is able to bring phone service to 2,400 subscribers and use only 200 copper pairs to do it. In this specific case, a 2400 line hut would contain 25 individual SLC-96 concentrators inside. If the main line between the remote terminal and the distant Central Office happens to be a fiber optic cable, a mere two strands of fiber is all that would be needed to provide service to those 2,400 subscribers. (In actual practice more than just 2 strands of fiber are used, but I'm sure you get the idea). These remote terminals provide the subscriber (you) with loop current and ringing voltages, but the actual dial tone you hear is coming from the real Central Office (switching center) several miles away. Obviously, the SLC-96 can potentially save the phone company millions of dollars with its capability to provide service to so many while requiring so few lines all the way back to the Central Office, but they can be a horrible vexation to our new technology modems. The issue is bandwidth. Our new 28.8k bps modems are hoping to see a phone line with at least 3200 Hz of bandwidth, centered on 1920 Hz and extending from 320 Hz on the low end to 3520 Hz on the high end. Any less than this and our new ultra warp speed modems may operate at something less than optimum speed. Typical bandwidth for phone service coming through a SLC-96 is about 3100 Hz in the best case and sometimes as little as 3000 Hz. Therein lies the focal point of the issue. The possible reasons for that reduced bandwidth and the effect it has on modem performance is what we've been discussing. --- ž OLX 3.0 ž OS/2 VirusScan - "Windows found: Remove it? (Y/y)" * USRobotics Customer Support, U.S.A., 708-982-5092 (28.8k) * PostLink(tm) v1.11 USRUSA (#174) : RelayNet(tm) --- ž QMPro 1.52 ž MOG-UR'S EMS ž Internet: sysop@mogur.com ž =========================================================================== BBS: The MOG-UR'S EMS Date: 07-07-94 (17:32) Number: 217 From: BILL GARFIELD Refer#: 11200 To: FRANK HABER Recvd: NO Subj: New 28.8 Modem 1/2 Conf: (2) TechInf-LO --------------------------------------------------------------------------- FH> to support customers down there). I'm here in Manhattan, where they FH> gave up gutta-percha cable insulation about five minutes ago. ROTFLMAO!! So others can share the humor in Frank's comment, Gutta-Percha is an old latex substance first discovered back in 1847. It first found use about 1851 as the insulation in the first international -telegraph- cable which ran between England and France. Gutta-Percha was also the first insulator to survive in undersea applications and was still the insulator of preference as late as 1947 when polyethylene finally began to gain acceptance. (Just how old are you Frank?) FH> This is a mostly 5ESS, big-gauge copper, lots o' crosstalk, <3mi to the FH> CO -that sort of environment. Casually calling around New York, I get FH> 28.8 about 30% of the time. The rest of the connections are split FH> evenly between 26 and 24. Pretty much what I'd expect to see in an all-copper, short loop length environment. Envious, but not enough to justify moving to the big apple. We sleep with 12-ga slide action Mossberg now. FH> Yes, the rosy glow does seem to disappear when the two modems are of FH> different makes. Yes, but that will become less of an issue with the passage of time and the maturing of the protocols. Remember the problems of the early V.32 and V.32bis modems? FH> Years ago, telcos were experimenting with adaptive PCM and FH> delta-PCM. Is that devilishness dead now? Unfortunately, No. Fortunately it also hasn't gained much popularity. To my knowledge all ADPCM stuff is limited to dedicated lease circuit applications and 'el-cheapo' tielines into hole-in-the-wall businesses with complete morons and penny pinchers as their communications consultants. Most of that crap also relies on 3rd party hardware. For those reading along, ADPCM (Adaptive Delta Pulse Code Modulation) for lack of a better description, is basically a digital circuit with compression. Most of it runs at 32k bps and has very narrow bandwidth. ADPCM works *swell* for strictly voice applications, and might have made some inroads were it not for the advent of the office fax machine about the same time (whew!). Modems and fax machines don't get along well with "compressed" phone lines, hence ADPCM has been judged unsuitable for widespread applications, thank goodness. FH> 2) You guys are debating a lot over differences of 5% in bandwidth. Actually the tussle is over a 12«% discrepancy in bandwidth. For a 28.8k bps modem which -hungers- for usable bandwidth beyond 3500 Hz, a 12«% bandwidth impairment spells the difference in achieving 28.8 versus 26.4 or 24.0 & less. My goal in conducting the discussion is not so much to cast aspersions upon the phone company as it is to -explain- to other modem users *why* some can achieve better results than others. I'm trying to help users understand that it's not the modem's fault. FH> What's the actual spec for a the frequency response of a subscriber The numbers I've seen are 300 to 3000 Hz within +2 and -8 dB over the whole range, referenced against 'milliwatt' (1004 Hz) injected at +/-0 dBMO at the serving office. This is a very generous spec, and it's unlikely that anyone's subscriber loop will actually be found to be out of tolerance. LD circuits are spec'd at 300 to 3400 Hz (CCITT G.132). This might also explain why we hear occasional reports of users getting higher connect speeds on an LD call than on a call down the lane. The shape of the bandwidth response curve will generally be 'humped', depending on loop length and whether or not it's loaded cable (loaded meaning with load coils, used to improve frequency response on long cables). At the high end, the subscriber loops going through the SLC-96 and other pair-gain devices will start stonewalling around 3300 Hz. Though the subscriber loops are spec'd at 300~3000, we all know that in actual practice most of them perform better, but not many perform as well as we'd like them to. As the North American telephone infrastructure gets rebuilt and upgraded to fiber over the next few years, the remaining bandwidth issues should gradually begin to disappear. FH> I'm inferring from your messages that the "proper" line level is FH> -20 or -22, that V.34's equalization makes that "zero," and that the I'm not privvy to what the manufacturer expects to see. Most can tolerate moderate level swings down to about -43 at which point the receiver becomes deaf. These new V.FC and V.34 modems can do some magic with the levels (preemphasis and transmitter offset) to help compensate for "normal" high end rolloff characteristics, but are helpless in trying to find a signal down in the mud below -43 or trying to find bandwidth which just isn't there to find. cont'd next message... --- ž OLX 3.0 ž Shopping tip: Shoes are only $.85 at bowling alleys. * USRobotics Customer Support, U.S.A., 708-982-5092 (28.8k) * PostLink(tm) v1.11 USRUSA (#174) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 07-07-94 (17:32) Number: 218 From: BILL GARFIELD Refer#: NONE To: FRANK HABER Recvd: NO Subj: reply cont'd... 2/2 Conf: (2) TechInf-LO --------------------------------------------------------------------------- Continued from previous message... FH> Could you discuss group delay a little bit? Is there a situation FH> where the simple response curve in the frequency domain could be OK, and FH> phase errors could bollix V.34? Admittedly, analog loops are getting FH> less and les important, but we still have loading coils and other old FH> stuff in use here. Hmmm... Definition time again. For those reading along, "Group delay" is the distortion resulting from the non-uniform speed of transmission of one frequency versus another frequency in the same cable. Normally it's not an issue until we get involved with LD calls or excessively long subscriber loops, usually beyond 18,000 feet. Load coils are a blessing in flattening out the frequency response curve in those long loops but extract another penalty at both the high and low frequencies, slowing one range of frequencies down a few microseconds while not affecting another range. To answer the question, yes, group delay can adversely impact modem performance if it is sufficiently large. I don't know what the modem can tolerate, however. Perhaps one of the USR guys can take up the discussion for a moment here. (Oh puhleeze?) FH> Could someone define a "bridge tap" so someone with a general EE FH> background can understand it? You're the second one to ask that question in as many days. They can be anywhere, but seem to proliferate in multi-family apartments and older commercial buildings. In telco-speak a circuit is said to be "bridged" if that same circuit appears in two or more locations. The term differs from "looped" in that a bridge connection (or tap) has an actual physical connection to the main feeder cable in two or more locations, often thousands of feet apart. In a looped cable, the cable pair may "appear" in two or more locations but it's integrity has not been violated by a physical connection having been made to it. Bridge taps can be sources of imbalance (hum) and static. It's a connection to the line that is redundant and doesn't need to be there to get your service to you. It's a potential problem waiting to happen. Locating bridge taps usually requires use of a device known as a TDR (Time Domain Reflectometer) to "scope the line". Getting them removed requires a service order for a conditioned line ($$$). FH> What are the "fast connect" options for V.34? V.FC takes a FH> looong time to negotiate, sometimes, and makes a really obnoxious set of FH> noises You haven't heard "obnoxious" until you hear a genuine V34 handshake! FH> day, call setup time becomes a big factor. USR already is one of the FH> best "fast handshakers" in the V.32 world. Can you do that with V.34? Oh Mr. Frankiewicz, HELP!!! FH> In V.34, are we still supposed to "train down" when we want to drop FH> the connection, and twiddle our thumbs. If we use &D3, will we still FH> wind up in a Swiss jail (g)? As part of the error correction protocol in both MNP as well as V42/LAP-M there is a unique Link Disconnect Frame which is sent by the modem. Another compliant modem, upon recognizing the link disconnect request will drop the call virtually in an eyeblink. USRobotics modems have always issued and responded to the -MNP- link disconnect request when in MNP or HST mode. Compliance with the V42 Link Disconnect Request didn't come along in USR products until this last year (thanks in part to yours truly flaming USR on the internet for omitting the feature). &D3 is not supported in USRobotics modems. It's counterpart, S13=1, works fine in accomplishing the same task (modem reset upon loss of DTR). In an earlier incarnation, the unsupported &D3 command would emulate S13=1 but you couldn't "save" the &D3 in nvram whereas you could save S13=1. And yes, in that same approximate vintage there was a recycle trap that you could fall into until you cycled power off and back on. That's an obscure bug that -you- weren't supposed to know about. It got fixed anyway, about a year or two ago, also with no fanfare. FH> That should do it for a first cut (g). Whew! You're not trying to set me up are you? You sound like an OT with some pre-divestiture whiskers longing for the days gone by of the old panel and step office, strowger switches and of course a P.K.Neuses burnishing tool in your shirt pocket. >very wide smile< --- ž OLX 3.0 ž GUN CONTROL means using BOTH HANDS. * USRobotics Customer Support, U.S.A., 708-982-5092 (28.8k) * PostLink(tm) v1.11 USRUSA (#174) : RelayNet(tm) =========================================================================== BBS: The MOG-UR'S EMS Date: 07-12-94 (17:51) Number: 220 From: BILL GARFIELD Refer#: 11232 To: ALL Recvd: NO Subj: Conditioned Lines Conf: (2) TechInf-LO --------------------------------------------------------------------------- I know this is a resend, but Joe Frankiewicz liked the first chart so much that I was spurred on to gather even more information for it. This is the kind of line specs the phone company is talking about with "C" and "D" conditioning. "D" conditioning is sometimes referred to as High Performance Data Conditioning (HPDC). (courtesy of the Bell System Technical Journals) ŚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄæ ³ ³ Without ³ With C-1 ³ With C-2 ³ With C-4 ³ ³ ³ Conditioning ³Conditioning³ Conditioning ³Conditioning³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³Frequency Range ³ 300 - 3000 ³ 300 - 2700 ³ 300 - 3000 ³ 300 - 3200 ³ ³ in hertz (Hz) ³ +3 to -12 dB ³ +2 to -6 dB³ +2 to -6 dB ³ +2 to -6 dB³ ³ and levels ³ ³ ³ ³ ³ ³ (ref. to 1004 ³ 500 - 2500 ³1000 - 2400 ³ 500 - 2800 ³ 500 - 3000 ³ ³ Hz tone level ³ +2 to -8 dB ³ +3 to -1 dB³ +1 to -3 dB ³ +2 to -3 dB³ ³ between C.O. ³ ³ ³ ³ ³ ³ and subscriber ³ ³ 300 - 3000 ³ ³ ³ ³ premesis) ³ ³+3 to -12 dB³ ³ ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³Group Delay in ³ < 1750ęs ³ < 1000ęs ³ < 500ęs ³ < 300ęs ³ ³microseconds ³ 800-2600 Hz ³1000-2400 Hz³ 1000-2600 Hz ³1000-2600 Hz³ ³ ³ ³ ³ ³ ³ ³ ³ ³ <1750ęs ³ < 1500ęs ³ < 500ęs ³ ³ ³ ³ 800-2600 Hz³ 600-2600 Hz ³ 800-2800 Hz³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ < 3000ęs ³ < 1500ęs ³ ³ ³ ³ ³ 500-2800 Hz ³ 600-3000 Hz³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ < 3000ęs ³ ³ ³ ³ ³ ³ 500-3000 Hz³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³Impulse Noise ³ 15 counts in 15 minutes ³ Zero ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³Bit error rate ³ 1 bit error per 100,000 bits transmitted ³ Zero ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄ“ ³ ³ ³ With the addition of "D" Conditioning ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄÄÄĀÄÄÄÄÄÄÄÄÄÄÄÄ“ ³Signal to Noise ³ 24 ³ 28 ³ 28 ³ 28 ³ ³ ratio (in dB) ³ ³ ³ ³ ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³2nd harm. Dstn. ³ -25 ³ -35 ³ -35 ³ -35 ³ ĆÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ“ ³3rd harm. Dstn. ³ -30 ³ -40 ³ -40 ³ -40 ³ ĄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄÄÄĮÄÄÄÄÄÄÄÄÄÄÄÄŁ From the chart above, we see that a C-4 conditioned line provides us with the best bandwidth. "D-4" conditioning provides the enhanced bandwidth of C-4 conditioning plus a 4 dB better signal-to-noise ratio and 10 dB better 2nd and 3rd order harmonic suppression. As we've seen from many of the Y11 frequency & level reports, some people's phone lines may already meet or even exceed D-4 conditioned status. Lucky them. For the rest of us, we can either order and pay for C-4 or D-4 line conditioning or simply accept the fact that for the time being, 24,000 bps may be the best we can do. At this point I would like issue a disclaimer and in so doing make it very clear that by no means am I or anyone else advocating that anyone go out and spend the money for line conditioning! Unless you're going to be modeming over a dedicated full-period "nailed up" circuit, line conditioning will only help -your- leg of the call between you and your own local phone company. Most telephone companies will advise against conditioning of dial-up circuits just for that reason. Also, remember that conditioning merely guarantees a certain quality of line. It does *not* guarantee that your modem performance will improve. --- ž OLX 3.0 ž Guns no more cause crime than flies garbage * USRobotics Customer Support, U.S.A., 708-982-5092 (28.8k) * PostLink(tm) v1.11 USRUSA (#174) : RelayNet(tm)