1 - History of Ericsson - History of Ericsson

Fig. 6 X 8454
Part of the ARM 20 equipment at Bogota
-31S544
the caller replaces. Since the metering pulses are sent at random, the called
subscriber's answer and the first metering pulse may not coincide.
For the semiautomatic trunk traffic two-digit codes are used for calling the
trunk operator. Subscriber-dialled trunk numbers include a single-digit trunk
access code, a usually three-digit group area code, and the directory number.
All digits are dialled in one sequence without needing to wait for a new dial
tone after obtaining a trunk line.
The operators' positions at the automatic trunk exchanges are of cordless
type with keysets. The operators' position equipments and cord pairs terminate
on the trunk switching equipment.
Outgoing trunk calls are usually handled at the demand position. The calls
are switched automatically to a free cord pair at a free operator's position
and the operator switches it to the trunk network via the same cord pair.
Through-connection is not effected until the period counter has been switched
into the circuit. The latter starts when the called subscriber answers and stops
when the caller replaces his handset.
For demand service calls verification of the caller's number is adopted only
for a li'mited number of connections by call-back to the subscriber. The operators'
positions for non-delay working can be individually blocked against
demand calls and used exclusively for delay traffic if required by the traffic
conditions on certain trunks at certain times.
Some trunks, principally manual trunks, are not designed for automatic
traffic. Calls on these routes are therefore handled at special delay and transit
positions at the superior automatic trunk exchange. These positions have the
same traffic facilities as the demand positions but are also equipped for tying
of the manual circuits to specific cord pairs. This implies that the circuits are
blocked against incoming automatic calls and are accessible only to the
operator to whose position the circuits are tied. Connections of this kind
can be established and cancelled form the operator's position, and a tied circuit
can be loaned to another operator. When the tfe-up is cancelled, calls on the
route can be switched automatically.
The incoming traffic from the manual circuits requires an assistance operator
at the automatic trunk exchange. A call on a manual trunk which is not tied
to a particular operator is indicated at the delay and transit positions. Via
13