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UAX12 Outline of operation. Local calls: The sub picks up his receiver,
which seizes a free connecting circuit (the allotter moves on to a free
connecting circuit so that it is ready for the next call). On receipt of dial
tone the sub dials the first digit of the local number (which is always a 2).
The switch steps up to level two, where the vertical marking wipers operates a
relay, which establishes local calling conditions. The switch now restores to normal
and is ready to receive the last two digits of the local number, upon which it
acts as a normal 2/10 PBX hunting final.
Outgoing level ‘9’ calls: These calls are
to the parent automatic exchange. The sub dials 9, which steps the selector up
to level 9 where it proceeds to hunt for a spare junction. As there is no
discriminating signal (as used for level 0 calls), the relay set extends loop
calling conditions to the junction, which establishes a call to the automatic
equipment at the parent exchange. The impulses dialed at the Uax being repeated
by the relayset over the junction.
Outgoing calls on other levels 6-8 are done in a similar way to the above, but are for calls to adjacent exchanges (auto or manual) One exchange being available on each level, with PBX hunting over the junctions. Incoming calls: Incoming junctions are terminated on early-choice contacts of the banks of the linefinders, which reduces the hunting time. If dialing occurs before the linefinder has found the junction, busy tone (and flash) is transmitted. If the called subs line is free, ringing conditions are given. If the sub is engaged, busy tone (and flash) is transmitted. At this point the parent exchange operator may ‘trunk offer’, by operating the ringing key, by operating this key again ringing is applied to the subs line. |