John Higdon <john@bovine.ati.com> (04/06/90)
George Horwath <motcid!horwath@uunet.uu.net> writes: > 2) Depending on how bad glare is/ground start trunk availability/costs/etc., > loop start trunks can be marked as one-way incoming or one-way > outgoing but now more trunks are needed. This feature also depends on > the brand of PBX. In the real world of modern CO switches (1ESS or newer) glare is a negligible problem. Unlike SXS and crossbar, electronic/digital switches apply ring current simultaneously with the connection to the called party. Once any PBX sees that ring, the trunk is instantly taken out of the pool for outside calls. Therefore, even systems with loop start trunks need not segregate the available lines for incoming vs outgoing. (It may not seem as though ring is applied instantly, since all electronic/digital switches will at least occasionally provide ringback which is out of phase with the actual ring voltage cadence applied to the called line.) John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
toddi@nsr.bioeng.washington.edu> (04/11/90)
This information on ground-start vs. loop-start has been great -
thanks all. How 'bout some more details, please? F'rinstance:
Whats the difference in the phone sets for ground start vs loop start?
(Does anyone even make a ground-start phone, or do they always get
"converted" to loop by the PBX's?)
For example, how would you use a butt set to connect and place a call
on a loop start line? Do you need an earth-ground connection, or
temporary earth-ground connection?
If you were to build a ground-start phone, would it need three wires?
Also, are ground-start lines available from all CO's? Are they the
same cost (typically) as a "business" POTS/loop-start line?
Are ground-start lines ever used for residential service? Were the
grounds required on old phones just for the ringer?
Todd Inch, System Manager, Global Technology, Mukilteo WA (206) 742-9111
UUCP: {smart-host}!gtisqr!toddi ARPA: gtisqr!toddi@beaver.cs.washington.edujohn@bovine.ati.com (John Higdon) (04/12/90)
Todd Inch <gtisqr!toddi@nsr.bioeng.washington.edu> writes: > Whats the difference in the phone sets for ground start vs loop start? > (Does anyone even make a ground-start phone, or do they always get > "converted" to loop by the PBX's?) Except for some lineman's sets, there are no "ground-start phones". Ground-start trunks are for PBXs and other complex equipment, not for ordinary telephone sets. > For example, how would you use a butt set to connect and place a call > on a loop start line? Do you need an earth-ground connection, or > temporary earth-ground connection? Yes, it's as simple as that. You put a phone across the line in an "off-hook" condition, then momentarily apply ring ground until dial tone is seized. > If you were to build a ground-start phone, would it need three wires? Yes, but why bother? > Also, are ground-start lines available from all CO's? Are they the > same cost (typically) as a "business" POTS/loop-start line? Ground-start lines and trunks are generally available in the US. In California, it matters not whether you order ground-start or loop-start. There is no difference in cost. If you wanted ground-start on your home phone it would be no problem. The difference in cost (other than the difference between res. and bus. service) comes from whether you want "design" circuits or not. Start type is not the factor. There is a significant charge to change from one to the other on an existing line, however. > Are ground-start lines ever used for residential service? Were the > grounds required on old phones just for the ringer? Ground-start has nothing to do with the ringer. I have had friends who had ground start lines in their homes, but it was primarily for toy value, or to service their prized vintage PBX. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
macy@cwjcc.ins.cwru.edu (04/13/90)
In article <6111@accuvax.nwu.edu> John Higdon writes: Telecom-Digest: Volume 10, Issue 235, Message 7 of 11 >>George Horwath <motcid!horwath@uunet.uu.net> writes: >> 2) Depending on how bad glare is/ground start trunk availability/costs/etc. >> loop start trunks can be marked as one-way incoming or one-way >> outgoing but now more trunks are needed. This feature also depends on >> the brand of PBX. >In the real world of modern CO switches (1ESS or newer) glare is a >negligible problem. Unlike SXS and crossbar, electronic/digital >switches apply ring current simultaneously with the connection to the >called party. Once any PBX sees that ring, the trunk is instantly >taken out of the pool for outside calls. Therefore, even systems with >loop start trunks need not segregate the available lines for incoming >vs outgoing. (It may not seem as though ring is applied instantly, >since all electronic/digital switches will at least occasionally >provide ringback which is out of phase with the actual ring voltage >cadence applied to the called line.) John, what you say should be true. Immediate ring is supposed to be a feature on those new-fangled electronic CO's, but it doesn't seem to work that way every time. On most CO's, one of the design parameters involves distributing the ringing load on the ring generator supplies. This is done by only ringing a portion of the lines at once...usually in four or five split groups. The "clocking" (if you will) of the groups always running, so when a line is to be rung, the CO assigns it to one of these groups (using whatever logic it has been given to select which group) and the line rings when the ring cycle time (1 on, 4 off) comes around. This is almost the same situation that would occur in Xbar and SXS offices. The primary difference is what happens during the glare interval ... some electronics CO's are not supposed to "land" the call until the ring cycle begins. Now, one of the features that came out with the more sophisticated Xbar system, and was to be continued with ESS was immediate splash of ring. This feature put a brief splash of ring out on the line just as the call "landed". This works well, but many newer CO's seem to drop this feature when they are busy. You often hear a funny, mis-timed "ring-ring" when the call lands, the splash of ring occurs and then the normal ring timing cycle takes over. In the past few years, I notice that fewer CO's have this feature. I wonder if they are phasing it out in the new generics? Another problem is intentionally slow ring sense in key systems and PBX's. Several people have mentioned in the Digest that their phones make an odd sound (a beep or click) and any line loop status indicators they have blink in the middle of the night. This is caused by the telco's automatic line test equipment, which changes the voltages on the line when it scans the line. This test scan voltage change can look like the first part of a ring to a phone system, and if the system is not properly designed, a false incoming ring state will occur. (Just try and get the telco to take the blame on this one! I have a couple of residence key systems that had this problem, and it was a real fight with the telco to prove it!)) So most phone equipment manufacturers design their equipment to ignore the first 0.5 second of ringing. Some even ignore the first ring altogether (Ugly! Ugly!) to prevent false rings. The better designed PBX's will prohibit an outgoing call from seizing a trunk during this 0.5 second interval, but its not too common. So, ground start lives, and will be with us for quite a while yet. It should be noted that I find very few lines give loop disconnect supervision anymore, except in older offices. The telco will sometimes give you loop (CPC) disconnect on a loop start line, on request, but don't count on it. Ground start is still the only reliable way to prevent call collisions and get reliable disconnect. Macy M. Hallock, Jr. macy@NCoast.ORG uunet!aablue!fmsystm!macy F M Systems, Inc. {uunet!backbone}!usenet.cwru.edu!ncoast!fmsystm!macy 150 Highland Drive Voice: +1 216 723-3000 Ext 251 Fax: +1 216 723-3223 Medina, Ohio 44256 USA Cleveland:273-3000 Akron:239-4994 (Dial 251 at tone) (Please note that our system name is "fmsystm" with no "e", .NOT. "fmsystem")
Don Lewis <del@thrush.mlb.semi.harris.com> (04/14/90)
In article <6358@accuvax.nwu.edu> fmsystm!macy@cwjcc.ins.cwru.edu writes: >Now, one of the features that came out with the more sophisticated >Xbar system, and was to be continued with ESS was immediate splash of >ring. This feature put a brief splash of ring out on the line just as >the call "landed". This works well, but many newer CO's seem to drop >this feature when they are busy. You often hear a funny, mis-timed >"ring-ring" when the call lands, the splash of ring occurs and then >the normal ring timing cycle takes over. This reminds me of a problem I was having with my home phones. Periodically, I would get one of these funny rings, then silence. It sounded sort of like someone had called and hung up on the first ring. I found out that if I answered the phone anyway, the party calling me was still on the line. I believe sometimes I didn't get a ring at all. Trying to explain this to the repair people was usually interesting. What was frustrating was that this tended not to be very reproduceable, and when the repair person called back it would work fine. Usually they would then go off and check it out anyway, and then it would work for a few months before breaking again. It seems to be fixed now, it's been working ok for the last nine months or so. Don "Truck" Lewis Harris Semiconductor Internet: del@mlb.semi.harris.com PO Box 883 MS 62A-028 UUCP: rutgers!soleil!thrush!del Melbourne, FL 32901 Phone: (407) 729-5205
John Higdon <john@bovine.ati.com> (04/14/90)
fmsystm!macy@cwjcc.ins.cwru.edu writes: > John, what you say should be true. Immediate ring is supposed to be a > feature on those new-fangled electronic CO's, but it doesn't seem to > work that way every time. > [...] > Another problem is intentionally slow ring sense in key systems and > PBX's. Ah, this is where you have me! While I experimentally determined that my CO (a 1ESS) hit the called line with ring voltage immediately 100% of the time, sometimes it was very short indeed, sometimes not even enough to be seen by my KX-T1232 (which is very quick). So if that first ring is missed, it would be several seconds before the next ring would come along and glare could easily occur. > So, ground start lives, and will be with us for quite a while yet. Just so there's no doubt, the two ITT3100s that I take care of have nothing but ground-start trunks (and design trunks at that). That is of course the real professional way to go. Naturally, glare is never a problem and the system has positive sense of when dial tone is actually seized. This makes things go much faster when the ARS works. But there is a sad truth. Ground-start is a USA phenomenon. As I'm sure our non-US readers will confirm, ground-start is not generally available worldwide. (I'm sure it's available in Canada.) It might be interesting to find out where, other than North America, a PBX user can hook up to ground-start circuits. > It should be noted that I find very few lines give loop disconnect > supervision anymore, except in older offices. The telco will > sometimes give you loop (CPC) disconnect on a loop start line, on > request, but don't count on it. Ground start is still the only > reliable way to prevent call collisions and get reliable disconnect. More and more, I am hearing that telcos are becoming sensitive to this. There are just too many devices out there that depend on loop current interruption for disconnect. Every switch used for CO service is capable of providing it, assuming that it is equipped with the proper line cards and the correct programming options are invoked. Repair service will listen to you now about that. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !