drears@pica.army.mil (Dennis G. Rears (FSAC)) (10/23/90)
Can anybody tell me what is meant by A/A1 control for key telephone systems? Also what is a 1A2 key system? A reference would aalso be good. Dennis
john@bovine.ati.com (John Higdon) (10/26/90)
"Dennis G. Rears (FSAC)" <drears@pica.army.mil> writes: > Can anybody tell me what is meant by A/A1 control for key telephone > systems? Also what is a 1A2 key system? A reference would aalso be > good. A 1A2 key system is the formerly ubiquitous arrangement found in small businesses. Typically the phones had a thick cable and six buttons across the front that represented outside lines and would light when the line was in use. For larger operations, there were ten, twenty, even thirty-line phones. Various types of intercoms were available. Actually, these systems are still available new if you don't mind basics. The A/A1 leads for each line controlled what the KSU (central unit) did with the line. The A lead is the actual control lead and the A1 is ground. When you come off-hook on a line, the A/A1 pair is closed through the switchhook. This causes the light to come on. When you hang up, the pair opens and the light goes out. Now for the magic. If you open the pair without opening the Tip/Ring pair (as the HOLD button does) then the KSU will sieze the line and wink the light. You may then open the Tip/Ring pair (button pops up) without losing the call. Reclosing the A/A1 pair and the Tip/Ring pair (pushing the button back down) re-accesses the line. If the line is ringing (light flashing), then closure of the A/A1 pair signals an answer. As far as a reference goes, I learned what I know about 1A2 from Direct Experience (tm). Data sheets that come with KSUs pretty much assume you know all about it (or don't care), since they only tell you where the wires go. Back when I learned 1A2, this was all handled by the telephone company and ordinary people had "no legitimate need" for such information, hence there weren't many references. It is probably a different story now. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
vances@xenitec.on.ca (Vance Shipley) (10/26/90)
In article <13966@accuvax.nwu.edu> drears@pica.army.mil (Dennis G. Rears (FSAC)) writes: > Can anybody tell me what is meant by A/A1 control for key telephone >systems? Also what is a 1A2 key system? A reference would aalso be >good. When you say "key telephone systems" I assume you mean "electronic key telephones" (EKT). The predecessor to todays EKT's was the 1A2 key. The 1A2 key telephone system can be recognized (and spotted nearly everywhere) by the familiar 500/2500 type desk set with a larger base and six buttons at the front. One button is red and the others are clear. The red button is the hold and the others are line appearances or even intercom. The line cord for these sets is a 25-pair cable (sometimes 16-pair). Each line appearance uses 3-pair (although two wires used as return grounds could be skipped, using a common ground for return). The six wires are T/R,A/A1,LG,L. These are; Tip and Ring of the CO line, A and A1 control (wired to the button in the set, a normally open contact which is closed when the line button is depressed), Lamp Ground and Lamp (the power to light the lamp in the button). When a line appearance button is depressed at a set the A1 lead signals the KSU that it is in use. The KSU lights the lamps for all other appearances of that line (with the L lead). Note that the actual CO line is always available at every set, it is only neccesary to signal the KSU to light the lamps. Now the hold key would be the subject of another lengthy article! The application of A/A1 control in an EKT system allows the integration of EKT and 1A2 on the same lines. When a user on the 1A2 grabs a line the LED associated with that line on the EKT's will light. But before you think that this is a useless feature in today's telecom world think of the other uses to put it to. Most hayes compatable modems include A/A1 control! You can use your modem on a line that is on the EKT system and other users will not be able to break in, their LED's will be lit. How about those credit verification terminals, fax machines and TDD's? If you don't have an A/A1 control pair on your terminal you can run down to Radio Shack and buy a cheap little box which senses when the CO line is in use and trips a relay providing A/A1. (I hope these are still available). For a reference you might try Radio Shack for a book called "Understanding Telephone Electronics". This is actually a very good reference on the history and operation of telephones and the network. Vance Shipley SwitchView - The Linton Technology Group (519)746-4460 vances@ltg or ... uunet!watmath!xenitec!ltg!vances
BRUCE@ccavax.camb.com (Barton F. Bruce) (10/27/90)
drears@pica.army.mil (Dennis G. Rears (FSAC)) asks about A/A1 and 1A2: A 1A2 key system is the electronic replacement for the 1a1 all relay ones that preceeded them. This is a relatively simple system that typically has a KSU supporting 4, 6, or 13 cards. Each card is wired in series with T+R going to the phones. The card does several things. It can detect ringing and start a local interrupter (to have ringing and lamp flashing for many lines all in step) and connect the flashing lamp service to the lamp lead for that line. It will light that lamp lead steady if a phone is picked up by noticing that the A lead for that line and the A1 lead (local signal ground, and the pair-mate to the phone's A lead for line 1) have been connected. If the current through the T+R path breaks and then the A A1 connection breaks, (normal hangup sequence) the card knows you are hanging up and the lamp goes out. If the A-A1 connection is broken BUT the current is still flowing from Tip to Ring, the line card knows you want to go on hold (things are in this state when you have the hold button bottomed). The card immediately switches a 135 ohm 5 watt (typical) resistor across T+R to simulate a phone off hook to hold the line up. The card also starts the interrupter and switches the wink supply to that lines lamp ckt. The card monitors loop current on hold and if it drops (the far end probably hung up) drops the hold. The timing of this can be extended to bridge short duration opens such as those caused by call waiting by a strapping option usually involving adding a cap. Answering machines and modems sometimes have the A + A1 leads so they can light the light and trip local ringing, etc. if used behind such a 1A2 key system. A non A A1 equipped device can be supplemented with an adapter that watches for loop current and gives the A A1 signal. Answering machine manufactuorers that no longer include A A1 support often suggest a source for such a device if they don't offer it themselves. Does this give you enough, or do you have some specific other questions? There are also probably many similar answers someone could point you to in the archives.
kaufman@neon.stanford.edu (Marc T. Kaufman) (10/28/90)
In article <14050@accuvax.nwu.edu> "Barton F. Bruce" <BRUCE@ccavax. camb.com> writes: >A 1A2 key system is the electronic replacement for the 1a1 all relay >ones that preceeded them. This is a relatively simple system that >typically has a KSU supporting 4, 6, or 13 cards. Each card is wired >in series with T+R going to the phones. The card does several things. >It can detect ringing and start a local interrupter (to have ringing >and lamp flashing for many lines all in step) and connect the flashing >lamp service to the lamp lead for that line. Ah, yes. Long ago another engineer and myself used to go into the basement of the radio station we worked at, and manually engage the relays. We would set up ring on some or all ten lines, then put a few on hold. This was at 2 AM, and the night DJ thought he was the only one in the building. We could hear him crashing about all over the building, trying to find who was using the phones. Marc Kaufman (kaufman@Neon.stanford.edu)
IZZYAS1@oac.ucla.edu (Andy Jacobson) (10/28/90)
In V10, #765, "Barton F. Bruce" <BRUCE@ccavax.camb.com> responds to drears@pica.army.mil (Dennis G. Rears (FSAC)): >If the A-A1 connection is broken BUT >the current is still flowing from Tip to Ring, the line card knows you >want to go on hold (things are in this state when you have the hold >button bottomed). The card immediately switches a 135 ohm 5 watt >(typical) resistor across T+R to simulate a phone off hook to hold the >line up. So, if that is all there is, where would this resistor be on a 400D, 400G or 400H card? Would it be possible to simply put a high Z or xformer isolated source across it and create your own music on hold circuit? That would certainly be alot cheaper and less trouble than buying one of those adaptor kits that companys like Tellabs sells.
john@bovine.ati.com (John Higdon) (10/29/90)
Andy Jacobson <IZZYAS1@oac.ucla.edu> writes: > So, if that is all there is, where would this resistor be on a 400D, > 400G or 400H card? Would it be possible to simply put a high Z or > xformer isolated source across it and create your own music on hold > circuit? That would certainly be alot cheaper and less trouble than > buying one of those adaptor kits that companys like Tellabs sells. The resistor is easy to spot. It's the only five watt resistor on the card. Music on hold is nothing more than bridging audio across that resistor, usually with a transformer. But also bear in mind that you will have to provide isolation between lines; you wouldn't want two of your customers getting together while on hold and discussing an alternative to your goods or services. The isolation usually consists of the fact that each line is driven by a separate amplifier. This prevents audio from the caller from backing up through the MOH system and being heard by other callers on hold. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !