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PXML No. 65
APPROVAL No's. NS/1412/123/D/022046 & NS/1412/123/F/451637

Introduced in 1988, the Mitel SX2000S (S for small) is a digital PABX with either single or dual processors for up to a maximum of 1536 extension ports and 420 Digital Service ports (4 cabinet system). The switch combines voice and data transmission using the same software structure and principles as the SX2000SG.

Most of the features and facilities are common between the SX2000SG and the SX2000S, the only difference being size and software feature dimension packages.

The system can either be AC powered from a 13 Amp AC supply per cabinet or DC powered from a 50v DC source supplied from an approved power supply, such as the Powersystem 2008S.

In addition to the major system features the following special application options are available:- Message Centre, DPNSS, Hotel Motel, DASS II, Digital Data Sets (Voice/Data), VHOC, and centralised attendant.

Superset 7DN - Used for operator consoles. Sometimes used as separate administration terminal or Message Centre.

Superset 7 with VHOC

Superset 6DN - Used as a low cost alternative to the Superset7DN, in low traffic environments. The set has a LCD display and is similar to the TSX50 console.


DEC VT220 or VT320. VDU maintenance terminal, may also be used as administration terminal.

DEC LA50 or LA75 Printer - minimum 1. Used for maintenance logs, screen printer and administration work including SMDR (call logging).

Winchester disc units (one per CPU). Mass storage device used as a permanent storage medium for system and customer data.

Floppy disc unit (1). Used for data, program loading and customer data back up.

Superset 4 (known as TX14 if BT provided). Special feature phones.

Superset 3DN and 4DN. Digital sets used for voice and data over a twisted pair. They have similar voice features to a Superset 4.

Made by Mitel Telecom Limited
Portskewett, Gwent. NP6 4YR

Distributed and installed by BT, Mitel Telecom Limited and others.

Fully Approved. PXML 65 gives all levels of approved software, hardware etc. The distributor is responsible for ensuring that a PXML is provided to each site either at the time of upgrade or before connection to BT network.

The hardware can be identified by the numbering of each item e.g. MC302AB where M=Mitel, Type C=Card, Identifier=302, A=Issue and B=Variant. There is a separate label showing the revision. The software revision of the system can be identified by the use of the "Version" command (see the Maintenance Manual).

SX2000S WITHOUT DDI - NS/1412/123/D/022046
SX2000S WITH DDI - NS/1412/123/F/451637
The latest revision of software is MS2004 Rev0l K stream.

1. Filter cleaning or replacement must take place at least once every six months. A more frequent routine will be necessary if local conditions dictate.

2. The frequency and separate charge for the back-up of customer data to floppy disc is under review. A policy CSI will be issued on the subject. The frequency to perform data back-ups will depend on regularity and extent of customer changes and terms agreed with the customer.

Regular "Data Saves" must be performed in preference to a "DBMS backups", as this will protect the data in the situation where the SYS ID fails. 3. An annual check should be made to ensure that generated alarms appear on Remote Alarm Unit (if fitted) or Superset 7.

Exchange Line:
Normal - Capacitor 'A' to 'B'
Seize - Dis 'A', earth 'B'
Hold - Loop
Loop seize is also available but less common.

1. Warning: The SX 2000SG Superset 7 are not directly interchangeable with SX2000S Superset 7DN's.

2. Always use Mitel recommended Floppy Discs i.e. Maxell MD 2-HD.

3. SYSTEM ID MODULES - Failure of the module or the maintenance panel will result in a loss of facilities after 5 days.


4. All switches are tested prior to leaving the factory and loaded with the system software. There is still a need to load the system software on site from floppy disk to validate the disks, cable connections and associated hardware.

The Mitel SX2000S is superseded by the Mitel SX2000 Light and SX2000 Ultra Light

Link to Console description (PDF)

Link to Supersets

For more up to date information - Click here for Mitel Web Site

Taken from BT information.

The SX2000S is not supported by Mitel after July 2002.

The SX-2000S system uses one type of cabinet, with two identical shelves in each. Each equipment shelf is functionally divided into two sections: a Control section and a Peripheral section. The Control section holds the cards which govern the overall operation of the system. The Peripheral section holds the cards used to interface the system to various telephony and data devices. In addition to these two sections, space is also allotted for in-shelf Power Converters. The Power Converters supply all the voltages required for each slot in the shelf.

The peripheral section of each shelf can hold a maximum of 12 Peripheral Interface Cards. Special-purpose cards called Digital Service Units (DSUs) can also be used. One DSU per shelf can be installed, up to a maximum of 6, for a 3 cabinet SX-2000S system.

Each cabinet has a Fan Unit, which is used to cool the system. Each Unit has three fans mounted in it. The fans draw cool air from the lower front of the cabinet through an air filter mounted in the front door. The air leaves the system at the upper rear, through vents in the rear door.

SX2000S Shelf

The Maintenance Panel of cabinet 1 provides switches and indications for system restart, system load and activity switching. Additionally, the maintenance panel also provides temperature sensing, power alarm monitoring, master and system fail transfer, music-on-hold audio input, two paging zones and a software option module interface.

Space is also provided for the installation of one or two Hard Disk Modules (HDMs). The HDMs are only installed in Cabinet 1. In the second and third cabinets filler plates are used in place of the Maintenance Panel and the Hard Disk Modules. The HDMs store all operating system software, customer data, logs, etc.

SX2000S Rear View

Main Control Hardware
The system hardware varies depending on the system configuration. In single cabinet, non-redundant, 384-port systems, the Main Control consists of the Main Controller II card and one Hard Disk Module. In multi-cabinet, non-redundant configurations, the Main Control consists of the Main Controller II card, the Circuit Switch Matrix II card and the Hard Disk Module.

Control Section Components Main Controller II Card:
The Main Controller is a six-layer card which controls the operation of the SX-2000S. Circuits on the card include:

  • The master processor. This is a 68020 device with 8 Mbytes of RAM and error detection and correction. The processor operates at a clock rate of 12 MHz.
  • The master system clock generator;
  • A Small Computer Systems Interface (SCSI) circuit to provide access to the system Winchester and cartridge tape drive;
  • A 24 x 24 circuit switching matrix which uses digital crosspoint (DX) chips;
  • A 16 link message switch which uses DX chips;
  • The system tone generator;
  • A tone detector which can detect DTMF on ten channels simultaneously.
  • Conference facilities which can provide a maximum of five simultaneous conferences or 15 simultaneous 3 party conferences.
  • Circuits which control activity switching on systems with the redundancy option.
  • Circuits which provide data in RS-232 format for the maintenance terminal and the Station Message Detail Recording feature.
  • 2 HDLC's (High Level Data Link Controller).

Circuit Switch Matrix II Card:
When a second cabinet is installed, the Circuit Switch Matrix II (CSM-II) card is inserted in Slot 18 of the first cabinet. This increases the circuit switch matrix size from the 24 x 24 circuit-switched links of the base system to a 56 x 56 2 Mb/s non-blocking link matrix. The links are provided in groups of four and are distributed to the Peripheral Switch Controller in the first cabinet directly. All other links are distributed to the additional Peripheral Switch Controllers in the system and the DSUs as differential signals via the Control and Peripheral Balance Transceiver pairs.

Control Balanced Transceiver:
The addition of a second cabinet requires the installation of a Control Balanced Transceiver module. This module is mounted on the side of the cabinet behind the shelf in Cabinet 1. It takes the single-ended control signals and converts them to balanced signals before they leave Cabinet 1, and converts balanced signals coming from other cabinets back into single-ended signals.

Maintenance Panel:
The Maintenance Panel resides in the Control Cabinet, above Shelf 2. The panel provides the following features:

  • Faceplate pushbutton switches and LED indicators for:
    - system restart (Planes A and B)
    - system load (Planes A and B)
    - activity switch
    - activity freeze enable/disable
    - alarm indicators (critical, major, and minor)
    - remote alarms enable/disable
    - panel enable/disable
  • Temperature sensor monitors
  • Power Converter alarm monitors
  • Master Fail Transfer/System Fail Transfer contact closures
  • Music On Hold audio input
  • Two DNIC interface ports
  • Battery backed-up real-time clock
  • System ID and Options Modules interface
  • Card ID and Revision straps

System ID Module:
Each system comes equipped with a System Identity Module, which installs in the faceplate of the Maintenance Panel. This module contains a unique identifier which is read by the system on start-up, and compared to an identifier stored on the system's Hard Disk Module(s). When an Optional Feature Package is purchased (e.g., Message Centre), the SYSID module is temporarily removed, and an Options Module inserted in its place. This permits the purchased option to be enabled on the system.


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Last revised: October 30, 2022