Chapter 5: Installation
EST3X Technical Reference Manual 131
Transmission process
The 3-MODCOM includes features that provide an appreciable level of
transmission integrity. Multiple telephone lines and multiple telephone numbers
help to ensure that a call to the receiver gets through.
The 3-MODCOM module sequences through the following basic steps to contact
the CMS receiver.
1. The 3-MODCOM seizes one of the telephone lines and puts the line on-hook
for a minimum of 3 seconds.
This cuts off any ongoing call and disconnects the line from any telephone or
dialing devices that are connected downstream.
Note: The module tries to select an unused line for its first two attempts.
2. The 3-MODCOM takes the line off-hook and waits for a dial tone.
The Line 1 or Line 2 LED indicates.
If a dial tone is not received by the configured time, the module goes on-hook,
increments the attempt counter, and continues to alternate lines and numbers
until a dial tone is acquired.
If the 3-MODCOM is configured with two telephone numbers and only one
telephone line, it will make four attempts using the first telephone number,
then four attempts using the second telephone number. This alternation of
telephone numbers continues as needed until a connection is made or the
configured number of dial attempts has been made.
Note: In areas where the telephone system has no dial tone, or where the
dial tone is erratic, you can configure the 3-MODCOM to dial without waiting
for a dial tone.
3. The 3-MODCOM dials the CMS using the programmed dialing mode and
telephone number.
4. The 3-MODCOM waits for a handshake message from the CMS, indicating
that a connection has been established.
If a handshake is not received within 40 seconds the module puts the
telephone line on-hook and waits for the configured period.
After the wait, processes 2 through 4 are repeated. If the module is still
unable to contact the receiver, it seizes the other telephone line and repeats
two attempts. If still unable to contact the receiver, it switches back to the first
telephone line and attempts to contact the receiver using the secondary
telephone number. If still unable to contact the receiver, the module continues
to alternate lines and numbers until the configured maximum number of
attempts have been reached. If the maximum number of attempts is reached,
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