SARTS Testing at Access Points Between Tandem Channel Units

Bellcore TN-TSY-000110 (Issue 1, Release 1, March 1985)

Introduction

These notes provide access point application guidelines and testing methods to permit Switched Access Remote Test System (SARTS) remote testing of circuits at access points between tandem channel units.  Tandem channel units are used for interconnecting back-to-back digital channel banks (D-banks).  The primary application of these channel units is for multi-facility trunks used in Foreign Exchange (FX) circuit applications.  These testing methods are designed to use the present capabilities of SARTS (Generics 2.4 and 2PC1).

The signaling and transmission paths at this interface are described, and step-by-step procedures for signaling are given.

Tandem Interface Configuration

The voice frequency transmission between tandem channel units is four-wire 600 ohm.  Signaling and supervision are carried through the connection on separate signaling leads, as well as simplexed onto the transmission leads.  Two signaling states are transmitted on the signaling leads and two states are transmitted on the simplex, as shown in Figure 1.

The signaling output leads from a channel unit are, an E-lead and a simplex on the T- and R-leads (the simplexed lead is called E1).  These leads follow the E-lead convention that an open is an on-hook and a ground represents an off-hook.  Signaling inputs to a channel unit are on the Ex-lead, and a simplex on the T1- and R1-leads (the simplex lead is called Ex1).  An open on these leads is detected as an on-hook and a ground an off-hook.  This signaling convention in similar to the Type V E&M-lead interface.  See Notes on the Network, BSP 781-030-100, Issue 2, December l980.

The Ex-lead is carried out of the channel bank on the M-lead, and will appear on the M-point of the distributing frame terminal block.

Access Point Configuration

A 6-wire access point should be used between tandem channel units.  Assuming the normal convention of the switch-end of the circuit at the "A" end of the circuit, the "EF" orientation should be used.  However, if the switch is at the "Z" end of the circuit, then the "FE" orientation is required to use the following methods.  The voice frequency connections that are carried through the A- and B-paths of the access point are wired in normal fashion.

The E- and Ex-leads, which are unique to tandem channel units, require special handling.  They will be connected to the TC- and RC-paths of the access point, with the E-lead of each channel unit cross-connected to the Ex-lead of the other.  This frogginq of the E- and Ex-leads must be done on the E-side of the access point, as shown in Figure 1.

Access Configuration Code

The "MBA" configuration code will be used if the access point is wired "EF" and the "MAB" code used in those cases where the "FE" orientation must be used.

Signaling Format

It is recommended that the signaling format be shown as "NON" on the 703-line of the access point data.  This signaling format is incorrect for a "MAB" or "MBA" configuration code, and it should give the tester a clue that this is an unique access point and will require special testing techniques.  The tester should replace the "NON" with the "EMF" signaling format before sending the 703-line.

Wiring Confirmation Tests

Since the wiring of the E- and Ex-leads can lead to confusion, the wiring of the access point should be tested as part of the pre-service testing of the circuit.  This can be done by checking that the equipment side channel Ex-lead is found on the E-lead at the access point, and that the equipment side Ex1-lead is simplexed on the A-pair.  These checks are made by splitting the leads and measuring for a DC voltage on the leads in the "E" direction.  On the A-pair, either a tip-to-ground or ring-to-ground measurement can be made in the "E" direction.  The expected voltage on the E-lead or B-pair is about -34 VDC for a D1 or D4 channel bank and -9 VDC for a D3 channel bank.

Signaling Tests

Tandem channel units are rich in options.  The methods given assume that the tandem channel units are correctly optioned.  While incorrectly optioned channel units may work on an end-to-end basis, they will not work properly during these tests.

The signaling states for correctly wired FX circuits as seen at an access point between tandem channel units are listed in Table 1.

Towards Switch

These methods are designed to draw dial tone and outpulse towards the switch as a way of testing a FX circuit.  Methods are given for loop-start and ground-start circuits.

Loop-Start

For loop-start circuits, the steps to draw dial tone and outpulse are given in Chart 1.  Chart 2 lists the steps required to draw dial tone and Touch-Tone address on a loop-start circuit.

Ground-Start

The steps to draw dial tone and dial pulse on a ground-start circuit are given in Chart 3.  Chart 4 gives the procedure to draw dial tone and Touch-Tone address on a ground-start circuit.

Towards Station

Procedures for ringing the station-end of a FX circuit are given in Charts 5 and Chart 6.  Chart 5 is for use with loop-start circuits and Chart 6 covers ground-start circuits.  When ringing a station using these methods, the tester should remember that continuous ringing is supplied to the station.  The ringing continues until either the customer answers or the tester removes the ground from the simplex circuit by use of the L0I/LP/CLSD/RL/B/ command.



Transmission Tests

To perform transmission tests on FX circuits, the circuit must be put in the off-hook state.  For measurements between a tandem channel unit and the office-end of a circuit, the E-lead must be grounded in the direction towards the office-end channel unit.  This will give a "loop closed" signal to the office-end channel unit.  To make measurements towards the station-end, the M-lead must be grounded in the direction towards the station.  This will be recognized by the station-end channel unit as a tip-ground signal, which will cause the station-end channel unit to close the tip lead, thus providing continuity on the transmission leads.


Figure 1: Back-to-Back Tandem Channel Unit Connection









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Table 1:
Foreign Exchange Signaling States at Access Points Between Back-to-Back Tandem Channel Units

Signaling Towards Switch-End (E Direction)

Circuit Condition      E-Lead         A-Pair Simplex     Circuit Type
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Loop Closed            Ground         Open               Loop-Start
Loop Open              Open           Open               Loop-Start
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Loop Closed            Ground         -                  Ground-Start
Loop Open              Open           -                  Ground-Start
Ring Grounded          -              Ground             Ground-Start
Ring Not Grounded      -              Open               Ground-Start
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Signaling Towards Station-End (F Direction)

Circuit Condition      M-Lead         B-Pair Simplex     Circuit Type
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Ringing                Ground         Ground             Loop-Start
Not Ringing            Open           Open               Loop-Start
-----------------------------------------------------------------------------------------
Tip Grounded           Ground         -                  Ground-Start
Tip Not Grounded       Open           -                  Ground-Start
Ringing                -              Ground             Ground-Start
Not Ringing            -              Open               Ground-Start
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-End-

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Chart 1: Dial Pulse to Switch (Loop-Start)

SARTS Command            Result
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G01/E/A&B/               Establish test direction towards switch.

L01/LP/OPN/RL/A/         Split voice frequency circuit.

G07/TLK/                 Establish talk line.

H12/                     Set up talk and listen paths.

E01/E/E/GRD/             Grounds E-lead towards switch causing loop closure to the switch and
                         drawing dial tone.  Tester should hear dial tone.

E03/E/S/tel#/10/58/      Puts circuit on-hook follwed by off-hook, dial tone detection,
                         and outpulsing.  Test should hear ringback followed by answer.

E07/E/                   Office-end channel unit opens loop to office to put circuit in an 
                         on-hook state.
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-End-






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Chart 2: Touch-Tone to Switch (Loop-Start)

SARTS Command            Result
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G01/E/A&B/               Establish test direction towards switch.

L01/LP/OPN/RL/A/         Split voice frequency circuit.

G07/TLK/                 Establish talk line.

H12/                     Set up talk and listen paths.

E01/E/E/GRD/             Grounds E-lead towards switch causing loop closure to the switch and
                         drawing dial tone.  Tester should hear dial tone.

E04/S/tel#/SUPVN E/      Puts circuit on-hook followed by off-hook, dial tone detection, and
                         Touch-Tone addressing towards the switch.  Tester should hear ringback
		         followed by answer.

E07/E/                   Office-end channel unit opens loop to office to put circuit in an 
                         on-hook state.
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-End-


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Chart 3: Dial Pulse to Switch (Ground-Start)

SARTS Command            Result
-----------------------------------------------------------------------------------------
G01/E/A&B/               Establish test direction towards switch.

L01/LP/CLSD/RL/A/        Split voice frequency circuit.

G07/TLK/                 Establish talk line.


H12/                     Set up talk and listen paths.


E01/M/E/OPN/             Opens tip-ground signaling path to station-end channel unit.
                         Prevents PBX ringing for PBXs that ring on tip-ground with open-loop.

E01/E/E/GRD/             Grounds E-lead towards switch causing loop closure to the switch.

L01/LP/CLSD&GRD/RL/A/    Causes the office-end channel unit to give a ring-ground to the switch.
                         This will draw dial tone.

E03/E/S/tel#/10/58/      Opens loop then closes loop, detects dial tone, and outpulses.
                         The circuit will "pump" during the open-loop interval.  Tester should
		         hear ringback followed by answer.

L01/LP/CLSD/RL/A/        Removes ring-ground signal by putting an open on the Ex1 signaling path.
                         The office-end channel unit autonomously remove the ring-ground towards
		         the switch when tip-ground is detected.

E07/E&M/                 Returns the E&M-leads to normal, the office-end channel unit opens the
                         loop to the switch putting the circuit in the on-hook state.
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-End-
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Chart 4: Touch-Tone to Switch (Ground-Start)

SARTS Command            Result
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G01/E/A&B/               Establish test direction towards switch.

L01/LP/CLSD/RL/A/        Split voice frequency circuit.

G07/TLK/                 Establish talk line.

H12/                     Set up talk and listen paths.

E01/M/E/OPN/             Opens tip-ground signaling path to station-end channel unit.
                         Prevents PBX ringing for PBXs that ring on tip-ground with open-loop.

E01/E/E/OPN/             Sends open-loop signal to office-end channel unit to ensure that
                         the circuit is on-hook.

E01/E/E/GND/             Sends closed-loop signal to office-end channel unit.

L04/S/tel#/GST/SUPVN A/  After minimum of 4 seconds, applies ground to the simplex which
                         translates to ring-ground in the office-end channel unit.
			 This should draw dial tone, if dial tone is detected, then Touch-Tone
		         addressing is sent towards office-end channel unit.  Tester should
			 hear ringback followed by answer.

E07/E&M/                 Returns the E&M leads to normal, the office-end channel unit open the
                         loop to the swtich putting the circuit in the on-hook state.
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-End-


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Chart 5: Ring Towards Station (Loop-Start)

SARTS Command            Result
-----------------------------------------------------------------------------------------
G01/F/A&B/               Establish test direction towards station.

L01/LP/CLSD/RL/B/        Split voice frequency circuit.

G07/TLK/                 Establish talk line.

H12/                     Set up talk and listen paths.

E01/E/E/OPN/             Opens loop closure signaling path to keep an answer at the station
                         from drawing dial tone.

L01/LP/CLSD&GRD/RL/B/    Station-end channel unit sends continuous ringing to station.
                         When station goes off-hook and returns loop closure to the
                         station-end channel unit, the channel unit locally trips ringing.
			 However, if the station goes on-hook before the following command
			 is executed, ringing will resume.

L01/LP/CLSD/RL/B/        Removes ringing signal to station-end channel unit.  If this
                         command is not executed, ringing will resume when station is
			 put on-hook.

G09/                     Restores circuit to normal.
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-End-
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Chart 6: Ring Towards Station (Ground-Start)

SARTS Command            Result
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G01/F/A&B/               Establish test direction towards station.

L01/LP/CLSD/RL/B/        Split voice frequency circuit.

G07/TLK/                 Establish talk line.

H12/                     Set up talk and listen paths.

E01/M/F/GND/             Causes station-end channel unit to send tip-ground to 
                         station.  Note: Some PBXs recognize a tip-ground as a ringing
			 signal.
 
L01/LP/CLSD&GRD/RL/B/    Station-end channel unit sends continuous ringing to station.
                         When station goes off-hook and returns loop closure to the
			 station-end channel unit, the channel unit locally trips ringing.
			 However, if the station goes on-hook before the following command
			 is executed, ringing will resume.

L01/LP/CLSD/RL/B/        Removes ringing signal to station-end channel unit.  If this
                         command is not executed, ringing will resume when station is
			 put on-hook.

G09/                     Restores circuit to normal.
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-End-