Nortel DMS-100 Trunk Maintenance Overview

Functional Description

This document describes the DMS-100 family trunk maintenance subsystem.  The trunk maintenance subsystem shows how to test and monitor trunk operation.  The subsystem also shows how to detect, identify, and locate trunk problems.  In addition, the trunk maintenance subsystem performs tests and maintenance functions for several non-trunk circuits.  The circuits include the circuits associated with receivers and test equipment.  Figure 1 shows a block diagram of the trunk maintenance subsystem.


Figure 1 - Block Diagram of the Trunk Maintenance Subsystem

The trunk subsystem can transmit analog voice or digital voice signals.  Trunk Peripheral Modules (PM) transmit signals.  You cannot process analog and digital signals on the same trunk PM.  Each type of signal requires separate PMs.  You can also use trunk PMs for maintenance and service activities.

Three categories of trunks are:

Analog Voice Trunks

Analog voice trunks transmit voice signals.

Trunk Module

The Trunk Module (TM) is a subsystem that occupies a single shelf.  The TM provides an interface to analog trunks from the outside plant through a distributing frame.  Trunk modules can contain special service circuits and internal test equipment.  Use the test equipment to test both inside and outside plant facilities.

The trunk module consists of four common circuit packs (excluding power) with many trunk interfaces that you can change.

The primary functions and features of the TM are the following:

TM features include:

All trunk modules share the basic functions and features described above.  Several types of trunk modules are present for different types of trunk facilities.  A "TM2" is a TM cabled for 2-wire trunks.  In the same way, "TM4" and "TM8" are 4-wire and 8-wire trunk modules in the sequence given.  A "TM8A" is also a 8-wire trunk.

The Analog Interface Module (AIM) provides emulation of analog trunks.  This series-1 TM peripheral replaces the older version TM and Maintenance Trunk Modules (MTM) analog trunk cards and the Remote Maintenance Module (RMM) controller.  For call processing, trunk and TM maintenance, you manage all AIM trunks the same as previous generation analog trunks

In central offices, AIM consists of the AIM controller card (NTFX46AA) with an internal Integrated Service Module (ISM) controller to interface DS-30 trunks.  The AIM also consists of the DSP processor that controls the operation of six analog trunks and generates signaling tones.  The AIM card B (NTFX48AA) is an extension of the controller card.  When you use the AIM card B with the controller card, analog trunk emulation increases to 18.  You can use the controller card alone.  The card requires the AIM signal routing card (NTFX15AA) to replace AIM card B.


Remote AIM consists of the AIM-based RMM controller (NTFX14AA).  This card contains an internal RMM controller to interface DS-30A links.  This card also contains a DSP processor that operates a maximum of four NT2X90AD analog trunks.

Digital Voice Trunks

Digital voice trunks enter the DMS switch through a Digital Trunk Controller (DTC).  One 24 channel DS-1 carrier (also called T-span or T-1) transmits 24 digital voice trunks.

Each DTC can accommodate up to 20 DS-1 carriers, to a maximum of 480 (24 x 20 = 480) digital trunk circuits.  The capacity of the DTC is higher than the capacity of a TM.

Analog Test Equipment and Service Trunks

Maintenance Trunk Modules (MTM) control the analog test equipment and service trunks.  The structure of a MTM is the same as a modified TM.  MTMs use the same control cards as TMs.  MTMs have all the basic functions of a TM.  MTMs interface with all of the TM interface cards and special test and service circuits.

The maintenance trunk module is a peripheral module located in a TM equipment frame.  The primary functions and features of the MTM are the following:

MTM features include:

The Service Trunk Module (STM) is a peripheral module that consists of two compact MTMs.  The primary functions and features of the STM are the following:

STM features include:

The Office Alarm Unit (OAU) is a peripheral mode in a TM equipment frame.  The OAU is like the MTM.  The primary functions and features of the OAU are the following:

OAU features include:

The primary functions and features of the Digital Recorded Announcement Machine (DRAM) are the following:

DRAM features include:

TM/MTM/STM Configuration

The TM, MTM, and STM modules have a common configuration.  The modules provide an interface between network C-side and P-side links.  Other common characteristics include a shelf with a common control section that performs four functions.  The four functions are network interface, processor, control, and group CODEC (PCM/PAM coder/decoder).  The TM Interface card, the TM processor card, the TM control card, and the group CODEC card provide these functions.  Figure 2 shows an example of a shelf from this group of modules (the trunk module shelf).


Figure 2 - Trunk Module Shelf

Shelves with AIM conform to present ISM and RMM shelf designs.  Mount the AIM controller card (NTFX46AA) in any even-numbered slot (6 through 16) in MTM shelves.  If you use card B (NTFX48AA), the card occupies the odd-numbered slot to the left-side.

Unless you have an ISM shelf in a Cabinetized Integrated Services Module (CISM), you can install AIM card A.  You must install AIM card (NTFX46AA) in even-numbered slots from 6 through 16.  If you have an ISM shelf in a CISM cabinet, you can install the NTFX46AA.  You must install NTFX46AA in even-numbered slots from 10 through 16.  You must install AIM card B (NTFX48AA) to the left-side of card A, in an odd-numbered slot.  If you do not require card B, you must replace the card with an AIM signal routing card (NTFX15AA).

In RMM shelves, you must mount the remote AIM card (NTFX14AA) in slot 3, with slot 4 left empty.  You do not need NTFX15AA and NTFX48AA.  Figure 3 and Figure 4 show shelf locations for AIM cards in ISM and Trunk Module Equipment (TME) frames.


Figure 3 - AIM Shelf for Integrated Services Modules


Figure 4 - AIM Shelf for Trunk Module Equipment Frame

TM/MTM/STM Messages and Data Flow

The best method to describe the operation of these modules is to divide data flow into receive paths and transmit paths.

When the network or central control sends data, a network interface card in the trunk PM shelf receives the data.  The data passes through the receive path of the shelf to one of two points.  These points are a trunk interface, service circuit, or other personality card, or the peripheral processor.

When a personality card or peripheral processor sends data, the data passes through the transmit path of the trunk PM shelf.  The card or processor sends the data to the network or to central control.

Note:  Personality cards, which normally associate with XMS-based Peripheral Modules (XPM), give a trunk PM a different identity.  Trunk circuit cards are like personality cards.  Trunk circuit cards give a trunk module a personality or different identity.  Different trunk PMs have different personality cards.

The receive path in the TM, MTM, and STM shelves operates as follows:

The transmit path in the TM, MTM, and STM shelves operates as follows:

Problem Conditions

Focused Trunks Maintenance in feature package NTX272AA monitors trunk faults through the Trunks Trouble (TRKSTRBL) level of the MAP display.  When you access the TRKSTRBL through the Trunk Test Position (TTP) level, the TRKSTRBL identifies trunks and trunk groups that have faults and cause alarms.  TRKSTRBL alarms do not generate the same audible alarms as out-of-service alarms.  The Maintenance (MTC) and TRKSTRBL MAP levels indicate that TRKSTRBL alarms are present.  The TRKSTRBL level identifies trunks that have faults so that you can take maintenance action.  Do not perform maintenance action from the TRKSTRBL level.





Incrementing Buffer and Display of Alarms

The failure rate of a trunk group generates alarms when the failure rate exceeds acceptable limits.  Trunk faults cause the alarms.  A buffer records the rate of failure.  When a customer cannot complete a call because of a trunk fault, the failure count in the buffer increases by one.  The failure count decreases by one for a given quantity of successful attempts on the same trunk group.  For the failure count to decrease, the trunk group must accumulate the quantity of successful attempts defined by the operating company.  The quantity of failures generates an alarm when the quantity reaches the defined limits.

The different degrees of alarm codes displayed for the DMS trunks are:

Note:  If the failure rate on a trunk or trunk group rises quickly, the alarm degree increases from minor to critical.  The increase indicates the degree of the fault.

When the increase in failure rate generates a TRKSTRBL alarm, the trunk fault flags the alarm.  The alarm can be a Maintenance (M) or a Call Processing (CP) alarm.  When you access the TRKSTRBL MAP level, the level displays the alarm.  The LISTALM command displays and identifies the trunk group that causes the alarm.  The display helps you take the correct alarm clearing action.

If the command LISTALM does not display a trunk group, increase the threshold levels.  You can increase the threshold levels in field ATMPCNT of data table TRKMTCE.

The alarm display at the MTC MAP level updates to show the most important alarm generated by TRKSTRBL.  The alarm switches every 30 seconds with the current alarm to represent the percentage of out-of-service trunks.  The out-of-service alarm is more important than the TRKSTRBL alarm.  The alarm display shows the out-of-service alarm when no TRKSTRBL alarm is present.  When a TRKSTRBL alarm is present and there is no out-of-service alarm, the alarms switch every 30 seconds.  The difference between the two displays is that the alarm display does not show an out-of-service alarm.  If the alarm display shows the TRKSTRBL alarm, the alarm display will change if the out-of-service alarm changes.  The alarm display will change to show the out-of-service alarm.  After 30 seconds, the alarm display shows the TRKSTRBL alarm again.  The alarm codes MN, MJ, and CR show the degree of the TRKSTRBL.  The codes M or CP next to the alarm code indication show either it is a maintenance or call processing alarm.

A delay in the buffering of trunk troubles reduces CPU use during and immediately after a restart.  This delay occurs until two minutes after the restart is complete.

Call Processing Error Threshold on Trunks

Call processing errors appear at a slower continuous rate.  Other types of error messages, like false seizures on trunks, occur quickly.

When messages from a trunk result in many call processing errors, a SWER log entry and additional log entries are output.  Additional log entries display the Call Condense Block (CCB), Call Data Block (CDB), and other extension blocks the call involves.  The call process terminates and diagnoses the trunk fault.  These actions cause loss of call processing time.  Switch performance degradation may result if a large number of call processing errors occur.

Call processing error thresholds and trunk handling procedures decrease large numbers of CP errors.

The operating company sets the CP error rate threshold for a trunk.  The operating company places the entry for the office parameter CPERRORTHRESHOLD in the table OFCENG.

A trunk exceeds the threshold if any of the following occurs:


Figure 5 - Threshold Limitations

The administration of trunks with many call processing errors causes the system to proceed as follows:

If the trunk fails the system diagnostic, or if the trunk exceeds the error threshold for a second time within 15 minutes:

Trunk Test Position

The Trunk Test Position (TTP) is a MAP level associated with hardware components used for trunk testing.  You may use any MAP display (including remote) for trunk testing.  The types of tests available depends on the hardware configuration of the trunks in the office.

Detached users can use all of the TTP abilities, except for the abilities that require dedicated hardware.

A TTP normally includes:

The VDU is the main Man-Machine Interface (MMI) device used to perform trunk tests.  You enter commands to test and monitor at the keyboard.  The screen displays and updates trunk status information and test results.

For voice communication, use:

The lines of the telephone set connect to the NE-1A2 KTS, which provides:

You can obtain a hardcopy of the status and test information from a printer accessed from a VDU.

A TTP contains two identical jack fields connected in parallel, one on each side of the VDU.  Each jack field has four configurations.  Each configuration has two jacks.  One jack transmits and one jack receives.  Three of the jack configurations connect to jack-ended trunks through the Main Distribution Frame (MDF).  Jack-ended trunks connect circuits under test to portable test equipment.  Use the portable test equipment when you require tests different from those provided by the internal equipment.  Functions determined by the operating company use the fourth jack configuration.  The fourth jack also connects to the MDF.  An example of a function defined by the operating company is connection to a voice frequency patch bay.  Circuit numbers of the jack-ended trunks are assigned in sequence according to the TTP number.  For example, circuits 0, 1, 2 are assigned to TTP 0, and circuits 3, 4, 5 to TTP 1.

Related to TTP Switch Hardware

The main test hardware for maintenance requests in the DMS switch is in a MTM.

The TTP switch hardware uses the following equipment:

All the connections between test equipment and a circuit under test are through the Network Module (NM).  The system selects an idle TTT, TTU, or milliwatt supply to use this test equipment.  The selection depends upon the test.  The system provides a connection with the circuit under test.  When the test is complete, the equipment becomes available to other users.

Trouble Tests

To locate faults, perform trouble tests manually.  The following reports identify faults:

You can perform most of the problem tests from the TTP level and from the following TTP sublevels:

The menus at each level include commands for most of the tests.  The menus also include commands for maintenance actions for the tests.

Maintenance Tests

Maintenance tests:

You can perform all trunk tests manually.  You can schedule the system to run some tests automatically.

Manual Testing

To perform a manual test, use commands at the MAP level.  The MAP level is the level that associates with the hardware and software that you test.  Command entry establishes, holds, and releases test connections.  Connected test equipment continuously transmits information until you stop the equipment.

For test functions not provided by the DMS switch, you can connect external testing equipment to the switch by the TTP jacks.  Tests run from external equipment include:

Note:  The term "manual testing" does not refer to the MANUAL level of the MAP display.

Automatic Maintenance

Automatic Trunk Testing (ATT) allows you to schedule the system to run trunk maintenance tests to be run by the system automatically.  The ATT is in feature package in NTX051AA.  You can schedule at the ATT level of the MAP, or in data table ATTSCHED.  Automatic tests do not occur as a result of a hardware or software failure.

You can schedule, initiate, monitor, or stop the tests at the ATT level.  You can run a maximum of 15 tests at the same time.

The ATT does not support all the tests scheduled at the ATT MAP level.  When a test the system does not support begins, the system generates an ATT log.  The system bypasses the test and the ATT log indicates the system cannot complete the test.

Escalation to Manual Maintenance

When automatic (system) maintenance fails to correct a fault in the subsystem of the trunks, the switch provides problem (fault) indicators.  The indicators identify the fault condition is present.  Alarms are examples of these fault indicators.  Operational Measurements (OM) and logs also indicate a failure of automatic maintenance.  When automatic maintenance fails to clear a fault, you must clear the fault manually.