Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: fmsystm!macy@cwjcc.ins.cwru.edu Newsgroups: comp.dcom.telecom Subject: Re: Loop Start vs Ground Start, a User Intro Message-ID: <6358@accuvax.nwu.edu> Date: 12 Apr 90 18:40:42 GMT Sender: news@accuvax.nwu.edu Organization: F M Systems, Inc. Medina (where's that?) Ohio USA Lines: 86 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 251, Message 8 of 10 In article <6111@accuvax.nwu.edu> John Higdon writes: Telecom-Digest: Volume 10, Issue 235, Message 7 of 11 >>George Horwath 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")