Dial Back isn't always secure

[D Levenson]

Multiple-hop call forwarding IS permitted, at least it is in the
local ESS / ESSX switches with which I have dealt here in NJ.  What
prevents endless forwarding in the case of circular forwarding is as
follows: If line A forwards its incoming calls to line B, then A
will appear busy to other incoming calls, for the duration of any
call it has forwarded to B.  In other words, if you dial A's number
and the call is forwarded to B, then if you or anyone else dials A's
number, a busy signal will be returned if your call to B via A is
still in progress.  A circular forward loop can only be established
between telephones served by physically separate central offices.
In this case, any call dialed to any member of the circular list
will hunt once around and reach a busy signal!

Dave Levenson
ATT-IS, Holmdel