larry@kitty.UUCP (Larry Lippman) (08/03/85)
> Remember Data Access Arrangements? Those boxes the phone company > used to make you buy to ``protect the telephone system''? Those things > had lightning and surge protection. Now that Ma Bell is no longer watching > out for you, you have to worry about these things yourself. Welcome to > deregulation. That's no great loss - the DAA's were absurdly complex and sucked anyhow. The telco mindset at the time was "God help us if the customer had access to tip and ring." What has *really* changed now are modem designs, which have in many cases become totally solid-state and therefore more suspectible to surge voltages. It used to be that data sets (like the WECO 103) used relays for ringup detection, loop current detect, and loop closure control; relays required a fair amount of surge *energy* to open a winding and were therefore quite resistant to the real world. Now all of these functions have been replaced with solid-state optocouplers which are still much more vulnerable to damage that the old relay counterparts. Larry Lippman Recognition Research Corp. Clarence, New York UUCP {decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry {rice,shell}!baylor!kitty!larry syr!buf!kitty!larry VOICE 716/741-9185 TELEX {via WUI} 69-71461 answerback: ELGECOMCLR "Have you hugged your cat today?"
jbn@wdl1.UUCP (08/05/85)
Remember Data Access Arrangements? Those boxes the phone company used to make you buy to ``protect the telephone system''? Those things had lightning and surge protection. Now that Ma Bell is no longer watching out for you, you have to worry about these things yourself. Welcome to deregulation. Nagle
hes@ecsvax.UUCP (Henry Schaffer) (08/07/85)
> > Remember Data Access Arrangements? Those boxes the phone company > > used to make you buy to ``protect the telephone system''? > Now all of these functions have been > replaced with solid-state optocouplers which are still much more vulnerable > to damage that the old relay counterparts. > > Larry Lippman An auto answer modem we've used has a full-wave bridge rectifier across the line. I think it's used to detect the ringing voltage, and probably also to make ring-tip reversals make no difference. The problem is that it tends to get blown during lightning weather. --henry schaffer