Line Link Functions
When a subscriber lifts the receiver a line relay associated with the
line link frame primary switch vertical to which the line is connected
operates. The operation of the line relay notifies the line link
controller that a call is being originated. The controller identifies
the calling line by determining the horizontal group, vertical column,
and vertical file in which the line is located.
District Junctor Selection
It also connects itself to one of several sender link controllers
with which the line link frame is associated. The two controllers
function together to select an idle district junctor. The selection is
made from one of the groups of ten district junctors which has an idle
line link back to the calling line and an idle sender link to a sender
subgroup which has an idle sender. District junctor groups having at
least two idle junctors are preferred.
Subscriber Sender Selection
Coincident with the selection of a district junctor, the sender link
controller is selecting an idle sender. This selection is made from
subgroups having an idle sender link to the selected district junctors.
Preference is given to those subgroups having two or more idle senders.
Dial Tone
Following these selections, crosspoints are closed on the line link
frame primary and secondary switches connecting the customer's line to a
district junctor and at the same time crosspoints are closed on the
sender link primary and secondary switches to connect the district
junctor to a sender. Over these paths the tip and ring of the customer's
line are now connected to a subscriber's sender. The sender sends out
dial tone, indicating that it is ready to receive dial pulses.
District Link Frame Indication
The sender also registers the number of the link frame involved,
receiving this information from the sender controller.
Dial
The subscriber now dials the office code and directory number of the
called subscriber. The sender counts the dial pulses and registers all
digits dialed on the register switch.
Originating Marker Selection
As soon as the office code is registered, the sender signals the
originating marker connector which connects the sender to an idle
originating marker cutting through a large number of leads over which
the sender and marker exchange information.
Marker Decoding
The marker receives from the sender the district frame number and the
office code dialed. It decodes this information and sends back to the
sender the information it needs to complete its part in handling the
call.
Marker Test of Trunks
From the route relay assigned to the office code the marker
determines the pair of office frames on which the trunks to the desired
office are located. The route relay also provides information as to the
trunk level and the start and stop test points within that level.
Through connector relays at the office frame, the marker gains access to
the specified trunk locations, tests, and selects an idle trunk.
Marker Channel Test
The marker gets access to the office links that serve the selected
trunk through connector relays at the office link frame. It also gets
access to the district link that serve the district junctor and office
junctors leading to the office frame on which the selected trunk is
located. Access to both the office links and office junctors is obtained
through the district frame connector relays. From this combination of
links and junctors the marker selects an idle district link which has
access to an idle office junctor which in turn has access to an idle
office link which appears before the selected trunk.
Channel Closure
The marker now operates the select and hold magnets on the district
and office link frames necessary to complete this channel from the
district junctor to the selected trunk. This also provides a path from
the subscriber sender to the trunk since the sender was cut through to
the district junctor. The marker now has completed its functions and
releases. [phew!]
Incoming Trunk in Terminating Office
This outgoing trunk is connected to an incoming trunk in the
terminating office.
Terminating Sender Selection
The incoming trunk when signaled by the subscriber sender, will cause
the terminating sender link controller to select an idle terminating
sender and to connect it to the incoming trunk.
Called Number Transferred to Sender
The two senders are now connected. The called number is transferred
from the subscriber sender to the terminating sender where it is
recorded on a register switch. With this information transferred the
originating sender has completed its functions and releases.
Terminating Marker Selection
The terminating sender now signals the
terminating marker connector which connects an idle terminating marker
to the sender cutting through the leads over which information is
passed. The marker receives the called number and the incoming frame
number from the sender.
Block Relay Selection
The terminating marker translates this number
as being in a block of 100 numbers and finally as being in one of five
blocks of twenty lines in the selected block of 100 numbers. By means of
cross- connections, the marker will then operate its marker connector
relays in the proper number group, the proper hundreds block relay and
through it the twenty block relay associated with twenty consecutively
numbered lines, one of which is the called number.
Called Line Test and Location
The twenty block relay operates and
cuts through to the marker a number of control leads which give the
necessary information regarding the line and its location. The marker
then tests the called line to determine whether it is busy or idle. If
busy, the marker will set the incoming trunk so that the calling
subscriber will receive busy tone. (The marker will then release
immediately).
Line Choice Selection
If idle, the marker will determine from cross
connections on the block relay frame whether it is an individual or PBX
line, whether tip or ring party ringing is required, in which line
choice, on which one of the four line link frames of the choice and in
which horizontal group of the line link frame the called line 'is
located.
Marker Channel Test and Closure
From the line location information,
the marker, by way of a line choice connector and line junctor
connector, is able to test the line links that serve the horizontal
group in which the called line is located. Knowing the incoming link
frame to which it must connect, the marker tests the line junctors
between this frame and the line link frame. At the incoming link frame,
connector relays give the marker access to the links available to serve
the incoming trunk. From this combination of links and junctors, the
marker selects an idle incoming link with access to an idle line junctor
which in turn has access to a line link serving the horizontal group in
which the called line is located. The marker will then operate the
primary and secondary select and hold magnets on the line link and
incoming link frames necessary to close this path between the incoming
trunks and the called subscriber.
Apply Ring
The marker also sets the incoming trunk to apply proper
ringing to the called line. The marker and terminating sender now
release.
Line Supervision
The incoming trunk applies ringing current to the
called line and, when the called party answers stops, the ringing and
signals the district junctor that the called party has answered, so that
the correct charge may be made. The calling subscriber may now talk to
the called subscriber, the district junctor applying talking battery to
the calling subscriber, and the incoming trunk to the called subscriber.
At the end of the conversation, the two parties will hang up, and all
circuits will release.