∙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.
