bnelson@ccb.bbn.COM (Barry Nelson) (04/20/87)
In response to: > Can anyone explain why REN's (...) come in "A" and "B" flavors? > On my many instruments I see old-fashioned phones are > usually 1.0A, and flimsy electronic jobs are 0.5B or 1.5B. I have dreamed up > something about whether it uses the real AC to drive a bell (A?) or runs an > electronic tweeter (B?). Do you add them all together anyway, and why do they > bother telling you which flavor? Not quite. The letter following the Ringer Equivalent Number (REN) is the Ringing Type letter representing the frequency range for which the REN is tested. It may be one of A through Q or, in special cases, Z. Furthermore, REN is based upon loop or ground start modes and the on-hook impedence range of the loop. One must reference several diagrams and tables to figure out what to test and then compute the largest of several methods to arrive at the REN for each listed Ringing Type for each phone option. Type A is 20 or 30 Hz (+/- 3 Hz), 40-130 vrms, 1400 ohms (1000 ohms at 30 Hz). Type B is 15.3 to 68.0 Hz, 40-150 vrms, 1600 ohms (looks like a harder test) Types C through P are other segments of 15.3 to 68 Hz with volts from 54 to 150 and impedences all limited to 1600 ohms. Type Q is 20 Hz +/- 3 Hz, 40-130 vrms, 1400 ohms. Type Z does not comform to these on-hook characteristics and requires consent from the local telco (which is by no means guaranteed). The limitation for REN is stated as follows: "68.312(f) All registered terminal equipment and registered protective circuitry which can affect on-hook impedance shall be assigned a Ringer Equivalence. The sum of all such ringer equivalences on a given telephone line or loop shall not exceed 5; ... " It appears that they don't discriminate totals based upon Ringing Type, although I suspect the Telco knows what RT they send you and can use your REN and RT designators against you in certain situations (if you give it to them), notwithstanding their ability to empirically determine your instrument and loop characteristics. Reference 47 CFR part 68.312 if you would like to know more. Caution: It's sometimes a little dry compared to reading a hex core dump of the same length. "This document contains statements of opinion by the author which are not attributable to BBN Communications Corporation or its management." Barry C. Nelson / Network Consultant / International Certifications BBN Communications Corporation