Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!casbah.acns.nwu.edu!accuvax.nwu.edu!nucsrl!telecom-request From: Barton.Bruce@camb.com (Barton F. Bruce) Newsgroups: comp.dcom.telecom Subject: Re: Device Given to me With "Data Lines" Message-ID: <16460@accuvax.nwu.edu> Date: 25 Jan 91 10:48:43 GMT Sender: news@accuvax.nwu.edu Organization: Cambridge Computer Associates, Inc. Lines: 130 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 71, Message 1 of 7 In article <16347@accuvax.nwu.edu>, tel@cdsdb1.att.com writes: > Any time we order a "Data Line" for our computers here, we are given a > device to put inline between the modem and the phone jack. It is a > box about 4 X 2 X 1 inches, has one two-pair modular cord to plug into > ... > My question is: What is this box, what does it do, and what do FLL and > PROG stand for? Anytime I ask the techs what they are for, they have > Tom Lowe AT&T Bell Labs Holmdel NJ tel@hound.ATT.COM 908-949-0428 ^^^^^^^^^ A user will now tell how the Bell System and FCC set this mess up. Arminger and others like Suttle are all licensed by YOUR company to produce such devices. You will find corresponding WE-xxx numbers for your products that they make with AA-xxx numbers and Suttle has SE-xxx ones, too. Arminger is heavier into data related special jacks then Suttle. Anyway, this has lots of history that I will partly skip, but the simple part of it is that modems are not supposed to hit the CO with a signal hotter than -12dbm. Originally modems all were from the phone company, and THEY set the xmit level internally with dip switches. When users were finally allowed to plug in modems, a way was devised to let the jack set the signal level. Any modem worth its salt today can receive signals that my bad ears can barely hear. But when this was planned, there was a scheme devised whereby the installing phone company could install a data jack that would program the transmit signal level for a modem with an external resistor the installer would select supposedly after determining the loop loss to the CO. That is your PROG switch position. Some modems were assumed to be too dumb to be programmed, and you could run with a fixed pad that killed some signal level for BOTH transmit and receive. They were assumed to xmit at -4dbm, and the pad would cut the level to what was needed. The transmit side of this was cut to 'protect' the network, but padding the receive side was/is totally STUPID. There is a third option the modems have and that is 'permissive' mode. It is assumed that there will be at least 3db loss on a CO line, and so any modem is 'permitted' to transmit at a fixed -9dbm (to hit the CO at no higher than -12dbm). Permissive mode is what all normal modems pluging into RJ11 jacks are using. I never saw a modem ordered or equipped for FLL (fixed loss loop) operation, but there were specs on how to do it. Some of the old modems came with instructions for the telco to set the levels internally, or you set them for 0 dbm internally and used a special cord for the external PROG or FLL or PERM jack setup. If you had loss set inside and externally you would have too much. Typically the adapter cord to make a programmable modem a FLL one included the 866 ohm resistor for -4dbm needed in FLL mode, and the adapter cord for permissive mode included the 5490 ohm resistor needed to transmit at -9dbm. The cord for programmable mode simply connected the resistor in the jack to the modem. Your jack with cord, etc is probably Arminger's AA-330A Universal Data Station Adapter. The center two wires from the RJ11 cord go to the center two of the eight-wire data jack, so any RJ11 modem plugged into this could as well be just plugged in without this. Pins 1 + 2 go to the internal PAD and then to incoming T + R via that switch when thrown to FLL position. The resistor for PROG mode is across 7 + 8. This adapter's resistor is set for -9dbm, and the unit effectively converts OLD FASHION FLL or PROG mode modems into PERmissive ones and is an FCC registered device (APZ9P9-67263-AD-N the Ren is 0.0B in PROG, and the PAD makes Ren = 2.5B in FLL mode). On telco installed data jacks, I have NEVER seen different resistors installed whether the jack is near the CO or miles from it. The installers always put in just one value. In the real world now, NO ONE needs this nonsense. If you have OLD modems that need this, maybe buy an eight-wire jack and stick your OWN resistor in and run in programmed mode set for -9dbm (i.e. run it in permissive mode). Certainly don't BUY this sort of over priced factory nonsense adapter. New modems will run in permissive mode and that is fine. Use RJ11 jacks. In some areas you seem to need to order a data jack just to get a data quality line. Then get an RJ45S (the programmable jack with out the FLL switch - but they may 'provide' it by giving you the universal model that HAS the switch). The RJ41S function DOES include the FLL Pad, and typically is provided by an AA-97A (1-9) (that 1-9 is for loop loss of 1 to 9 dbs - each number you order comes with a different resistor and pad) and nine different order numbers!, and costs about $18. The AA-97B only does RJ45S (PROG) function (no FLL switch) and comes with eight resistors (one order #) and costs about the same. Those two are the same size box, but a newer jack that looks like a fat RJ11, but also takes the eight wire plugs is the AA-97B1. It also comes with the kit of eight resistors (NO resistor is used for the highest loss setting) and costs about $8. The same jack bought as a generic JACK is under $4, and you can get the resistor for -9dbm xmit (the 3db loop loss resistor) for pennies elsewhere. Use 5,490 (or near that) ohms. If you are stuck with telco installed FLL switches, TAPE them into the PROG position. NEVER use FLL, it is a dumb and obsolete idea. Remember any normal (permissive) modem plugs into an RJ11, but also works fine in the eight-wire jacks but hardly needs them. History lesson: xmit level resistor loop loss range 0 (short) 12 or more db -1 150 ohm 11-12 -2 336 10-11 -3 562 9-10 -4 866 8-9 -5 1,240 7-8 -6 1,780 6-7 -7 2,520 5-6 -8 3,610 4-5 -9 5,490 3-4 -10 9,200 2-3 -11 19,800 1-2 -12 (open) 0-1 Personally, I get data lines in on RJ21X jacks mixed in with general phone lines. The 25 pairs there come out on the AMP connector and go to MY-OWN CO quality 3 electrode gas tube + diodes lightning protection (I like Porta System's Delta series, but NTI/Cook, AT&T, and Reliable all make this sort of thing), and then it goes to modular patch or 66 punch and then to internal voice or data or whatever we need on OUR wires. Modems plug into RJ11 jacks. Period.