GTE Omni Si Database Technical Practices Issue 1 Manual

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RELEASE28.0 RLTs (Release Link Trunks) are used to minimize the
LINK TRUNKS
number of interconnecting trunks required to connect a main
system with branch systems for CAS operation and to provide the
control and features required by this integral configuration. Both
the CAS main and the branch must have the special capability of
using 
RLTs. Additional hardware and revised data base
distribution are required to incorporate 
RLTs into the system.
However, 
RLTs are not tied up for the duration of the CAS call
but are available when needed. They allow the interchange of
control functions between two systems without the need for any
additional interconnections and appear transparent to the users.
Incoming calls to the branch PABX are identified by differential
audible tones heard by both end users and through seizure of the
RLT associated with the main system. An audible ring is
returned from the PABX station to the telephone instrument. The
CO trunk-to-station connection at the branch is still set up and
ringing continues at the station.The attendant “holds” the caller
at the branch, and connects the call. The RLT releases to idle
condition for RLT-2WGS (Wire Ground Start). (The branch end
RLT-2WGS should provide open tip and ring leads to the main
PABX end during the idle state).
When the call is answered, the branch end RLT-2WGS stops
ringing within 100 msec. of receiving the answer signal. Ringing
is tripped during both the silent and ringing intervals. The branch
end PABX detects the answer signal from the RLT-2WGS and
passes it to the connecting circuit (i.e., PABX-CO trunk) to
cause CO ringing to trip and cut through the transmission path for
talking. When an answer is detected, the branch PABX times for
300 msec. and then transmits, via the 
RLT-2WGS, through the
appropriate call information tone to the CAS attendant, followed
by cut-through of the transmission path between the calling
party and the RLT-2WGS. After answer and until disconnect,
the branch end RLT-2WGS provide up to 425 ohms resistance
to ground on the tip lead, and -48 VDC loop battery through up
to 425 ohms resistance on the ring lead.
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OMNI PBAX (MAIN)
1BRANCHES
CENTRAL OFFICE TRUNKS
Figure 28.1Release Link TrunksIf a call is directed to an idle station but the station is not
answered within the selected time-out interval, the system
recalls the attendant by means of a preselected idle RLT. On
recalls, the appropriate audible signals are extended to the
attendant to identify the type of call. The tone is heard only by the
attendant because the system delays cut-through long enough
to permit any required audible signal to be sent to the main
location before the calling party is connected. If the station is not
answered before the attendant answers, the seized PRLT signals
the attendant with the appropriate audible tone. The call is then
reconfigured to a three-way mode in which the local station
continues to ring while the attendant and the trunk party converse
over 
ringback tone. If the trunk party does not wish to wait for the
selected line to answer, the attendant flashes off the original
called number. The attendant then redirects the call by a second
flash and redialing. Alternatively, the station can answer after the
attendant has been recalled; the attendant then releases the
PRLT and causes the trunk and line to remain connected while
the PRLT is made available for reuse. The same procedure
applies when the line rings for an additional recall period.
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The functions of the PRLTs can be summarized as follows:
The branch system uses the PRLT to send supervisory and
information signals to the CAS Main, and receives supervisory
and address signals from the CAS equipment to direct call
switching at the branch location. Only the branch can seize the
PRLT to initiate the sequence. The system can extend stations
or tie trunks to outgoing trunks via the PRLT if this feature is
required.
The system supports a maximum of 16 PRLTs.
Refer to the system functional block diagram found in TL-130300-1001. The PRLT trunks are connected into the system
via an FB-17251 -A PRLT card. Each card can support four
PRLTs.Each PRLT can be dialed up for testing. The CAS branch
system provides the cross-connecting arrangements so that
telephones can be used for terminating the PRLTs at the branch
location. This arrangement permits calls to be answered locally
when the equipment at the main location fails, or the trunk
facilities fail and no local console has been provided.
SVR 5210Each PRLT in the system has an assigned access number
permitting the main location to make loop-around test calls to
verify performance of both PRLT and main locations are being
properly done. The main location accesses the branch system
via a designated Tie trunk. The branch system is directed by
dialing the PRLT access number to connect the Tie trunk to the
selected PRLT for extension back to the main location. Two
lOO-msec bursts of tones signal the CAS attendant of a test call.
Test calls can also be originated from the branch location by
special stations class-marked in the data base as maintenance
lines.
During the talking state, the RLT-2WGS circuit interprets a
substained increase in the external DC resistance across the T
and 
R leads from less than 1,300 ohms to greater than 20
kilohms for greater than 1 second as a disconnect indication. If
the calling party abandons the call before answer supervision is
received from the CAS Main location, the RLT-2WGS send a
disconnect signal to the call distributor by opening the T and 
Rleads.
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The manner in which the call is completed varies according to
the status of the local line selected. If the call is successfully
terminated, immediate ringback tone is transmitted to the CAS
Main and the CAS attendant operates the RELEASE pushbutton.
The RLT interprets this as an on-hook condition, the system
then reconfigures the call and connects the incoming trunk to the
destination station.
The four-wire E&M RLT provides audio frequency transmission
via the T, R and 
Tl, Rl leads, while supervisory signals are
transmitted over the M lead (outgoing) and the E lead (incoming).
The T, 
R and Tl, Rl leads do not carry DC signals. The CAS
Branch PABX trunk circuit sends a seizure by replacing the
ground potential on the M lead by -48 VDC battery potential.
The seizure is received at the CAS Main location as a change of
state on the E lead from open to ground. The E lead at one end
of the interconnecting facility always indicates the state of the M
lead at the other end of the facility. Disconnect at either end of
the facility is signaled by connecting ground to the M lead at the
disconnecting end. The other end of the facility receives the
disconnect as a change of state on the E lead from ground to
open. The four-wire E&M RLT reflects an idle state at the
branch PABX as a ground on the M lead, causing the CAS Main
to receive an open on the E lead. The CAS Branch PABX
reflects an outgoing seizure condition by applying -48 VDC
battery to the M lead (removing ground).
After sending a seizure, the branch PABX should interpret the
appearance of ground on the E lead as answer supervision
indication from the main location. Upon receipt of answer
supervision, the branch PABX performs the following functions:
l Return answer supervision (trips ringing) to the CO trunk
(if involved).
0 Time for 300 msec, followed by transmittal of the appropriate
call information tone to the centralized attendant, followed by
cut-through of the voice transmission path between the calling
party (i.e., CO trunk) and the attendant. During the talking
state, the branch PABX should maintain -48 VDC battery on
the M lead and continue to monitor ground on the E lead.
During the talking state, the branch PABX interprets a
momentary open of the E lead (i.e., 300 to 1,000 msec) as a
flash. During the talking state, the branch PABX interprets an
E lead open of greater than 1 second as a disconnect signal.
If the calling party abandons the call before the attendant
answers the call, the branch PABX replaces the -48 VDC
battery on the M lead with ground, thereby transmitting a
disconnect indication to the main location.
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29.0 The Tl digital trunk link allows the system to receive and
transmit time-division-multiplexed 
Tl carrier data to and from a
channel bank at the far end. A 
Tl digital data link can support 24
channels of multiplexed Tl-type data. The two-line (transmit
and receive) 
Tl trunk link provides the same traffic capabilities
as 24 individual analog trunk lines. The 
Tl digital trunk link
(Figure 29.1) consists of the 
Tl interface cards at the system
end, a channel bank at the far end, and a 
Tl span in between.
I .TRANSMISSIONFACILITY SPANLINEISVR 5210
Figure 29.1Tl-Type Digital Trunk Link
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The Tl interface is compatible with WECO D2 and D3 signaling
format channel banks or Siemens Transmissions Systems 9002A
(24) or 9002B (48) channel banks at the far end. The far-end
channel bank interfaces with loop-start, ground-start, or 
E&Mtrunks that can be connected to any standard telephone and
most data terminals, to a system, or to a CO that supports 
Tl-type communications. Two systems can be connected via a 
Tllink without the use of a channel bank at either end. The 
Tlinterface is joined directly to the local terminating shelf repeater
and does not require a channel bank or A/D to D/A converters in
the system end (Figure 29.1).
Supervisory signaling information is transmitted every sixth frame.
During the signaling frame, the least-significant digit is borrowed
from the voice information coding and used to indicate the
signaling condition of each channel. Alternate signaling frames
are designated as A and B, respectively, called A and B
signaling. When a customer-related interface is used, such as
a FX ground start or FX loop start, the A signaling frame provides
on-hook/off-hook information. The B signaling frame provides
ringing information and special conditions.
S-282CAUTION
Because the removal of a loop-start channel at the CO is not
detected by the Tl-type interface it is recommended that the use
of 
loop-stsrt channels for Tl interface be avoided.
The removal of a loop-start channel unit at the CO is not
detected by the Tl-type interface cards. Therefore, it is
recommended that use of the loop-start channel interface be
avoided for 
Tl applications. Removal of a ground-start channel
unit at the CO causes the GD (Ground-Detected) sense point,
bit 7, in the FX trunk sense word to become true, making the
associated trunk busy to the system. When this occurs, the
associated trunk-busy lamp on the Attendant Console lights.
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