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LBI-39076B OPERATION
38
• Radio-originated call - a call from a radio using an
EDACS repeater site, through a telephone line
connected to that EDACS repeater site, to a
telephone.
• Line-connected GTI - the GTI unit connected to the
telephone line for the interconnect call being
described.
• Channel-connected GTI - the GTI unit connected to
the radio channel for the interconnect call being
described.
Note that a line-connected GTI and a channel-
connected GTI may be the same physical GTI unit or
different physical GTI units. Although each GTI unit is
capable of being connected to one line and to one channel,
the Site Controller computer makes each radio channel and
telephone line assignment, based on availability and the
constraints of its active database configuration, not on
whether they share the same GTI unit.
Detection of telephone hang-up depends on signaling
provided to the line-connected GTI. To determine if a line
provides the necessary signaling, connect a scope across the
line to monitor the DC voltage. At the end of the call, there
must be a loss of voltage for 100 milliseconds or more.
Telephone hang-up typically can be detected on End-to-End
with battery removal (many COs now provide this type of
line, but it cannot always be ordered), E&M Type 1, and
DID lines. Telephone hang-up typically cannot be detected
on PBX lines and microwave links (which emulate end-to-
end lines).
Telephone-Originated Call
The sequence of steps for a telephone-originated local
interconnect call is as follows:
DETECTING THE CALL
1. Somewhere in the telephone system, a user dials the
telephone number of a subscriber line connected to a
GTI unit.
2. The line-connected GTI detects the call by sensing the
presence of a ringing voltage (or an E-lead signal), and
sends a message to the Site Controller indicating that a
call has been detected by this GTI unit.
3. The Site Controller checks to see if it is permitted to
add another telephone interconnect call. (There may be
a limit on the number of telephone interconnect calls
allowed at any one time.)
If the Site Controller is not permitted to add another
telephone interconnect call, it lets the call go
unanswered. This ends the sequence here.
4. If the Site Controller is permitted to add another
telephone interconnect call, it checks to see if that line
number is dedicated to a specific LID. (See Dedicated
to Unit field in System Manager screen 14.)
If the line number is dedicated to a specific LID, go to
step 19.
5. If the line number is not dedicated to a specific LID, the
Site Controller checks to see if a channel-terminating
GTI is available to collect overdial digits. (The Site
Controller will check the GTI on the Control Channel
first and if available, use it for this operation.)
If no channel-terminating GTI is available, the Site
Controller lets the call go unanswered. The caller
should hang up and try again after 3 ringbacks. This
ends the sequence here.
ANSWERING THE CALL
6. If a channel-terminating GTI is available, the Site
Controller allocates it for digit collection.
7. The Site Controller sends a message to the line-
terminating GTI, directing it to answer the call.
8. The line-terminating GTI answers the call and lights the
“LINE CONNECTED” indicator on its front panel.
9. The Site Controller directs the line-terminating (now
line-connected) GTI to apply dial tone to the line.
10. The Site Controller directs the line-connected GTI to
look for DTMF or dial click (pulse) signals.
11. The Site Controller starts a rapid polling mode of
operation to poll the Master GTI more frequently than
usual. The fast polling is used during the anticipated
dialing process to speed the processing of the dialed
digits. The Site Controller will fast poll for the DTMF
Digit Detection Duration (forced to 20 seconds when
ELI is selected) to collect the digits. The call will be
disconnected if the DTMF digits are not collected
within this time.
12. The caller hears the dial tone from the line-connected
GTI, and starts sending DTMF digits indicating whether
the call is analog or digital, if it’s to a group or
individual, and what the ID of the individual or group
is.