PXML No. 65
APPROVAL No: NS/1412/2/3/D/022046

Click for Mitel Web Site

Introduced in 9183, the Mitel SX2000SG (SG = Single Group) is a dual processor digital PABX with provision for up to a maximum of 2500 extensions plus 625 trunks. This does not include the additional use of ports for data, Supersets etc. For maximum hardware and software configurations see SX2000. Consideration must also be given to traffic requirements when deciding on overall system configurations. Redundant processors are provided in Digital Service Unit areas, peripheral shelves and main control. Each cabinet has it's own DC/DC converters requiring 50 volt DC input. These can be supplied from either AC rectifiers, also located in each cabinet or from an external DC supply, which may be provided from an approved power system such as a Power System 2008J.

Superset 7 Used for operator consoles. Sometimes used as separate administration terminal or Message Centre.
DEC VT 102, 220 or 320 maintenance terminal, may also be used as an administration terminal.
DEC LA 50 or LA 75 Printer - minimum 2. 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 store medium for system and customer data.
Floppy disc unit. Used for data, program loading and customer data back up.
Superset 4 (known as TX14 if BT provided). Special feature phones.

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

Distributed and installed by BT, Mitel Telecom Limited and their sub-contractors.

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 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 Section: MITL9120-100-351).

SX2000SG WITHOUT DDI NS/1412/123/D/022046
SX2000SG WITH DDI NS/1412/123/F/451637

Dangerous voltages exist on the rectifiers, mains input terminal, PDU and backplane. These items are protected and highlighted in the site documentation.

Do not attempt to fault on the CRT area of the operators console VDU (Superset 7) as dangerous voltages exist in this area.

There are two specific safety problems that exist at present:-
1. SSM LED/fuse indicator reversal.
2. SSM hinge stay can buckle and earth the power bus.
The resolution to these problems are outstanding. The problem where the TBO tool insulating sleeve was missing has been resolved. Heat shrink insulators have been issued by Mitel for the local maintenance engineer to fit.

Taken from BT information



  • System Description
  • Hardware Description
  • Environmental and Electrical Requirements
  • Redundancy
  • System Dimensions

System Description
The SX-2000SG system is divided into two major control groups: the peripheral subsystem, and the main control subsystem. The peripheral subsystem contains peripheral interface cards and peripheral control cards both located on a peripheral shelf.

The main control subsystem contains control and DSU cards located on control shelves.

Peripheral Subsystem
The peripheral interface cards are the interfaces between the out de world and the SX-2000. The SX-2000 handles information in the form of 8-bit words. The peripheral cards for analogue terminations convert the analogue signals to PCM signals for use within the SX-2000 and also convert the PCM signals back to analogue.

Data terminal equipment provide signals already in digital form. The interface cards for such terminations convert the incoming data streams into 8-bit words, for transmission through the SX-2000. At the outgoing interface, the peripheral card converts the 8-bit words back into a data format suitable for the particular type of data terminal equipment. In the case of data equipment communicating by modems, the interface card converts the, incoming tones into 8-bit words, and then converts the 8-bit words back to tones at the outgoing side.

Each pair of peripheral shelves can serve up to 768 On Premise (ONS) lines (analogue extns). The SX-2000 system can provide up to 16 circuit switch link s for each pair of peripheral shelves. With 32 channels per link, this represents 512 channels. Thus there is a degree of concentration, and the system is not completely non-blocking. However, with the norm 1 mix of lines and trunks, the system is virtually non-blocking. Analogue lines terminate on a peripheral card which contains the circuitry for available number of lines, depending on the line type. The largest number is 16, which applies to ONS lines. The circuitry for each line contains 1 a MITEL Filter/Codec Type MT8960 integrated circuit This performs the analogue/PCM and PCM/analogue conversions for the speech circuits.

The peripheral switch consists of a micro processor (68000) and its associated memory plus digital switching matrices. Under control of messages received from the message processor (but originating in the main control complex), the peripheral switch acts as an interface between termination of the SX-2000 and the, rest of the system. It has numerous tasks, such as concentrating the PCM links arriving from the peripheral cards, deconcentrating them in the case of outgoing PCM, collecting signalling data from the peripheral cards for transmission upward to the main control complex; and distributing control data to the peripheral circuits in the opposite direction.

Control Subsystem
The main control complex contains NMOS dynamic RAM and hard disk storage which hold all the program s and data. The' hard disk provides non volatile storage for the system programs and customer data. A small EPROM containing the system bootstrap is associated with the main processor which is a 68000. The main control comp ex communicates with the rest of the system using serial message links. Each message consists of 32 bytes, for which the time scale is the same as the circuit switch links. The main control complex governs, the setting up of all calls and produces the orders to set up the paths through the circuit switch. In a redundant system, a link continuously updates the duplicate controller through, the Bulk Data transfer subsystem. The data transferred allows warm standby operation. This implies that the system operation is not disturbed during a fault condition, apart from calls in the process of being established, which may be lost. The message switch is a microprocessor controlled switching matrix which establishes the message paths in the system, under the direction of the main processor. The main processor transmits orders to the message processor via, a two-port communication RAM. The message processor communicates with the remainder of the system by message links. The message, switch has, links which carry messages reporting to a grid carrying commands from the main, controller to all intelligent portions of the system.

The messages include the off-hook, dial pulse, DTMF and other signalling, information which is collected by the peripheral switch and fed to the main control through the message switch. The main complex decides which circuit path to connect and transmits messages down to the peripheral switch which decodes them into commands issued to the peripheral cards. The circuit switch microprocessor, controlled and like the message switch is based on the MITEL Type MT8980 digital crosspoint (DX) integrated circuit.  Data is transferred uni-directionaly through the matrices. The digital switching matrix establishes paths between parties or between digital processing equipment under control of messages received from the main control via the communication RAM. The information which it switches consists of words of 8-bit length.

The tone generator unit provides call progress tones over two 32-channel circuit switch links which can be connected to the circuit switch. Each channel effectively represents one output of a particular tone generator. Normally, one unit is fitted in each half of a duplicated system. Other types of digital service cards which can be used in the control shelves are the conference card, the data transceiver, and the tone detector.

The SX-2000 control and memory cards can be duplicated for additional reliability. A mate bus between the two sets of assemblies enables the active set to continually update the other set (plane) with working data. The other plane contains duplicates known as mates. In the event of failure, the system automatically bypasses the fault by switching to the mate plane. The only connections lost are those in the process of being established.

System Software
The SX-2000 hardware and applications software is managed by a process-based operating system. The operating system is written primarily in Pascal with additional routines using Assembler languages related to the particular microprocessor involved. Each process is independent of the others, however communication does occur between processes in order to keep the system operating as efficiently as possible. Three 68000 microprocessors are used for executing the processes and they are controlled by the main system processor. Each one is event driven according to a simple prioritising algorithm. The operating system which controls the processes and their interaction has eight main areas of control. It is responsible for scheduling the processes to the appropriate processor, it controls any message communication between processors for multi-processor tasks and it controls shared use of system resources and files. In addition to these functions the operating system also controls the system clock, the prioritising and/or deletion of processes, the queuing of low priority tasks and it maintains control of the memory management system. Finally after all of the above tasks are handled the operating system is responsible for performing audits on itself for system sanity and, for system usage and performance. The SX-2000 has a number of software facilities that are used continuously for task completion. These include: a file system used for creating, deleting, reading and writing files, a directory system which is used to keep track of files, commands, and digit strings; a command interpreter which performs the man-machine interface at the data terminals; a debug system for detecting any faults in process execution; a log system for reporting any errors, and finally a performance system for measuring system activity and usage.

The last aspect of the SX-2000 software is the layering of routines in order to obtain maximum efficiency and speed of the many microprocessors in use. This layering consists of assigning certain routines to different levels of system access. For example, there are software routines that are used only by one processor for very specialised tasks. On the other hand there are routines that are globally accessible by almost all of the processors. This layering allows the software to be very modular and thus well suited to expansion or enhancement.

Call Progression
SX-2000 system software is message driven. The message switch matrix is used to pass status information from the peripheral processor to the main processor and commands from the main processor to the peripheral processor.

Recall button scanning occurs at 100m sec intervals. When an extension goes off hook, the peripheral processor mutes the line and sends a message to the main processor.

The call process routine is allocated to the caller. It instructs the caller interface to set codec gain, remove the muting and connect the caller to the circuit switch matrix.

Meanwhile, a DTMF receiver is found and connected in the forward path to the caller. A dial tone generator is connected to the caller in the reverse path. Both connections are through the circuit switch matrix.

The line is then scanned every 10m sec for rotary dial pulses or DTMF tones. This scanning rate is changed to 30m sec if a DTMF digit is received.

In this manner both DTMF and rotary sets are supported. Once enough digits for call processing and routing have been received, the DTMF receiver and the "associated" circuit switch link are released.

The main processor performs required translations and, after identifying the called device, creates a terminating call process. This routine checks to see if the extension is on hook and connects it to the circuit switch matrix. The peripheral processor rings the extension and monitors its switchhook for an answer. At the same time, the ringback is connected to the originator. Both connections are through the circuit switch matrix.

Once the called extension is answered, ringing and ringback are removed and bothway communication is enabled between the two parties. The mate plane in the main processor is updated with the details of the call so that the call is not lost in the event of plane switching. During the conversation, recall buttons of both extensions are scanned every 100m sec for hang up or hook flash. When a party hangs up, a call processing routine is invoked. This routine will release the circuit switch link and connection, inform the other call process and ask the main processor for termination. The other call process releases the circuit switch link and asks the main processor for termination.

Hardware Description

The SX-2000SG consists of two cabinets and a System Support Module. The first cabinet, containing both Control Shelves and Peripheral Shelves is called the Control Cabinet. The second cabinet, called the Peripheral Cabinet, contains only Peripheral Shelves. The Control and Peripheral Cabinets and the System Support Module are the same size.

Front View
Control Cabinet Configuration

The cabinets contain up to four standard size shelves, a Power Converter for each shelf, an optional mains rectifier, a Maintenance Unit, and Cooling Fans. Doors front and rear provide access to the field-replaceable units and the cabling. All line and trunk connections are made directly by cabling from the backplane connectors, to the Test Jack Frame (TJF), using standard 25-pair plug-ended cables.

Peripheral Cabinet
Each Peripheral Cabinet contains from two or four Peripheral Shelves. Two peripheral shelves that are driven by the same Peripheral Switch are installed in adjacent shelves, and are termed a "Peripheral Shelf Pair".  The Cabinet Maintenance Unit for the Peripheral Cabinet contains circuitry to monitor its own cabinet and report the data to the System Maintenance Unit.

Control Cabinet Configuration
Peripheral Cabinet Configuration

The shelves in the SX-2000SG are field replaceable units which bolt onto the cabinet's frame. They are 762mm (30in) long, 305mm (12in) high, and 380mm (15in) deep, and contain up to 32 cards, located on 21.6mm (0.85in) centres. Card slot 33 is always occupied by a filler plate. Shelves consist of sheet metal side plates connected by horizontal extruded rails at the front and back. At the back of the shelves there is a 4-layer printed circuit board backplane, with buried power and earth layers. It includes shrouds on the card side of the backplane to guide the cards onto the connectors. On the other side of the backplane, shrouds are mounted at any location where a cable connector might be connected. On the top and bottom of the shelf are moulded plastic card guides.

The Control Shelf contains the Main Control Complex, the Message Switch, the Circuit Switch and one zone of up to six Digital Service Units. The Peripheral Shelf contains the Peripheral Switch and up to 24 Peripheral Interface cards.

Control Cards
Control cards are all cards other than the Peripheral Interface cards. They plug into either the Control Shelf or the Peripheral Switch section of the Peripheral Shelf. They are 375mm (14.75in) deep by 279mm (11 in) high. Generally, they are 4-layer printed circuit boards, with two buried power layers, one for earth and one for +5 volts. This allows a higher packing density on the board and improves the noise performance. All signals are tracked on the outer two layers. Along the rear edge of the card are four connectors: two 20-pin (2 x 1 0) connectors at the top and bottom of the board for power connection, including advanced power and earth signals, and two 96-pin (3 x 32) DIN connectors for signal interconnection. Along the front of the card is a translucent faceplate, which allows status LEDs (and on some Control cards a hexadecimal display), to be viewed. Each card has an extractor/lock latch located at the top and the bottom of the faceplate, which allows the card to be extracted easily or seated securely in place. The marketing code and name of the card is engraved on the top lock latch.

Peripheral Interface Cards
Peripheral Interface cards are similar to Control cards except for the connector arrangement. They contain two 60-pin (2 x 30) connectors which handle both power and signal interconnection. Also the Peripheral Interface cards tend to be 2-layer. On many of the Peripheral Interface cards are field-replaceable hybrid modules. These hybrids consist of active and passive components on a ceramic substrate and have C-clips or pins on two edges which mate with sockets on the cards. A typical hybrid module, such as found on the On Premises Line card, is approximately 32mm (1.25in) by 51mm (2in) in size. The socketed hybrid module approach allows the replacement of most of the circuitry associated with a given line or trunk circuit without replacing the whole card. This simplifies and reduces the cost of spares.

Power System
The SX-2000SG is powered externally from 240V ac or 48V dc. An internal circuit senses the loss of 240V ac on power failure, and automatically switches to the 48V dc input connected to the Reserve Power Supply unit in the System Support Module. A holdover battery situated in the mains rectifier maintains the power supply during the momentary interval between power loss and reserve power supply cut in. The power system within each cabinet consists of a mains rectifier unit, one control converter unit per Control Shelf, and one peripheral converter per Peripheral Shelf. The rectifier is mounted in the base of the cabinet,  and the converters are mounted on the rear door. A cabinet may be equipped without the rectifier, and powered from an external source of 48V dc.

System Support Module (SSM)
The System Support Module is contained in a standard cabinet casing, and contains the following units:

Test Jack Frame
The Test Jack Frame consists of up to four modules and occupies the front of the cabinet. The Test Jack Frame modules carry the interconnections between the SX2000SG and the Building Distribution.

Reserve Power Supply
The Reserve Power supply consists of a battery pack and rectifier which trickle-charges the batteries. The batteries are located behind the rectifier which is in the base of the cabinet.

Alarm Panels
There are two alarm panels that are located outside of the SSM cabinet. The System Alarm Panel can be mounted at any convenient location in the PABX room. It contains all the alarm indicators for the SX-2000SG system, and includes a control for removal or return of alarm conditions to the Remote Alarm Panel.

The Remote Alarm Panel also contains alarm indicators for the SX-2000SG system.

Combiner Unit 
This is located at the front of the SSM, above the Requirements Test Jack Frame Modules. The Combined Unit provides a central location for all system alarm circuits, remote alarm circuits, Automatic  Emergency Switching control functions and the  2 and 4-wire test circuits from the SX-2000SG cabinets. 

Automatic Emergency Switching Unit
This unit occupies the upper portion of the SSM. In the event of a critical failure the  Automatic Emergency Switching Unit connects predetermined extensions directly to outside exchange lines. 

Power Distribution Unit
This unit is located in the centre of the rear of the cabinet. It provided a centralised source of AC and DC power distribution and control for connection to the two SX-2000SG cabinets, ancillary equipment and Telecommunications company equipment. Fault diagnostic indicators are also located in the Power Distribution Unit. 

Environmental and Electrical Requirements
The Environmental and Electrical requirements for the SX-2000SG System are shown in Tables 1 and 2. Note that the SX-200OSG does not need a specialised, air-conditioned "computer room" environment.

Table 1
SX-2000SG Environmental requirements

Dimensions        Metric Imperial
Height                            1753mm    69in
Width                             864mm     34in
Depth                             736mm     29in
Weight (fully loaded)       385kg      850lb
Weight (SSM)                500kg      1100lb
Floor Loading                 621 kg/sq m 1271b/sq ft
Floor Loading (SSM)      800kg/sq m 1641b/sq ft
Temperature                    0-50C    32 - 122F
Relative Humidity (non-condensing) 5 - 95%

Table 2
SX-2000SG Electrical Requirements

Primary Voltage 240Vac + 10% Single phase, or 440Vac Three phase, or 48Vdc.
Primary Frequency 50Hz + or - 3%.
Primary Power 2.5kW typical DC input, or 3.0kW AC input, per cabinet with full peripheral shelf pair occupancy and typical line/trunk mix and traffic loading.
Reserve Power Battery Backup included in System Support Module, giving between 1.5 to 2hrs reserve capacity.

System redundancy is one of the main features of the SX-2000SG architecture. For reliability the control-level subsystems (Main Control Complex, Message Switch and Circuit Switch), and all Peripheral Switches and Digital Service Units are duplicated. The Peripheral Interface cards (ie. lines and trunks) and the Maintenance Units are the only non-redundant parts of the system. In the event of a major hardware or software fault activity will automatically switch from the active to the inactive mate, which immediately assumes the functions of the formerly active mate. This ensures continued service and integrity of all calls in progress. Two identical Control Shelves are equipped in adjacent positions in the Control Cabinet. The Main Control Complex, Circuit Switch and Message Switch are part of the same activity unit.

If a failure is detected in any of these subsystems, all three subsystems switchover to their redundant mates as one block. Switchover is automatic when the Main Control Complex discovers a non-recoverable problem. Sanity monitors ensure that a faulty Main Control Complex will surrender activity. In addition, control activity can be switched manually by maintenance personnel, by means of the Maintenance Unit or Maintenance Terminal. Peripheral Switches are also configured as redundant pairs. One Peripheral Switch controls two Peripheral Shelves. Depending on the Peripheral Switch activity signal gathered by the Main Control Complex, one or the other of the Peripheral Switches has control over the Peripheral Interface cards on both shelves. The power system also provides redundancy. Each Shelf has its own associated converter, each converter is wired to a pair of shelves and can power two shelves should an adjoining converter fail. Redundancy at the rectifier level is supplied by the back-up battery pack in the System Support Module.

Digital Service Units also have their own activity, which is controlled by the Main Control Complex. Each DSU can switch independently of any other in the system.

Each redundant element is switchable independently, so that a fault in one of them causes a plane switch of only that element. Peripheral cards are non-redundant items.

System Dimensions

Peripheral Shelves 6

Number of Attendant Consoles 16
ONS/OPS stations 1360
Trunks 256
Superset 4 telephones 300
Digital Service Units (DSU's) 6

Modems 20
Data Transceivers (DTRX's) 24
Data Stations 112
DTMF Receivers 96

Trunk Groups 64
Trunks per Trunk Group 256
Hunt Groups 64
Members per Hunt Group 32
Multi-Call Groups 300
Members per Multi-Call Group 32
Call Pickup Groups 100
Members Per Pickup Group 32

Data Station Groups 10
Data Stations per Group 50
Modem Groups (Pools) 10
Modems per Group 20

Number of Operator Groups 32
Operators per Group 15
Maximum Call Hold's (Operator) 8

Maximum Number of Conferences 21
Maximum Number of Conferees/Conference 8
Maximum Number of Conferees/System 63

Simultaneous Callbacks 128
Simultaneous Camp-Ons 64
Simultaneous Camp-Ons to a Group 30
Paging Zones 16
Number of COS 64
Number of COR 64
Device Interconnect Restriction Numbers 32
Maximum Digits - Internal Number 7
Maximum Digits - External Number 26
Maximum Number of Call Hold's 128

System Speed Call Numbers 500
Personal Speed Call Numbers 1500

Directory Numbers 1360
Maximum Number of Locations Names 50
Maximum Number of Department Names 50

Independent Account Codes 512
Default Account Codes 100
System Account Codes 16

Maximum Number of Digit Strings 600
Digit Modifications Tables 128
Route Plans 16
Route Lists 64
Routes 128
Day Zones 3
Time Zones 4

Digit Modification
- Maximum Number of Digits Add 36
- Maximum Number of Digits Delete 11


The SX-2000SG provides a wide selection of features and services to the customer. The features are divided into Telephony Features and Data Features. The Telephony Features are further divided into System Features, Extension Features and Operator Features, System features are inherent in the system. Features in the other groups, (Telephony, Operator and Data), are available according to the customer's requirements and the types of extensions and terminals connected to the SX-2000SG. The features and services required for each extension, Superset and Dataset are programmed into the system during the Customer Data Entry process. Subsequent additions and deletions are made simple by the use of Moves and Changes forms in the CDE process.

Telephony Features

a) System Features

Features which apply on a system basis, rather than those features which are peculiar to the peripheral equipment (eg. extension or Operator features), are termed System features.

System Features

  • Account Codes
  • Advanced Tone Detection
  • Automatic Emergency Service
  • Automatic Night Service
  • Automatic Route Selection (ARS)
  • Class of Restriction (COR)
  • Class-Of-Service (COS)
  • Dial Access to Operator
  • Dial Pulse Signalling
  • Dial Through Busy
  • Direct Dialling Inward (DDI)
  • Direct-in Lines
  • Direct Inward System Access (DISA)
  • Direct Outward Dialling (DOD)
  • Distinctive Dial Tone
  • Distinctive Ringing
  • DTMF to Rotary Dial Conversion
  • Exception Handling
  • Expensive Route Warning Tone
  • Flexible Extension Numbering Plan
  • Flexible Tone Plan
  • Group Hunting
  • Immediate Ringing
  • Interconnection Restrictions
  • Message Waiting
  • Mixed Extensions Dialling
  • Multiple Operator Consoles
  • Multiple Extensions
  • Music on Hold
  • Night Service Dial Answer (NSDA)
  • Paging
  • Priority Queuing
  • Recall Dial Tone
  • Redundant System Control
  • Second Dial Tone
  • Single Digit Dialling
  • Single Voice/Data Transmission Network
  • Station Message Detail Recording (SMDR)
  • System Rerouting
  • System Speed Call (Abbreviated Dialling)
  • Tandem Trunking
  • Tie Trunks (Private Lines)
  • Timed Recall
  • Toll Control (Discriminatory Barring)
  • Tone Demonstration
  • Traffic Measurement
  • Trunk Group Hunting
  • Uniform Numbering Network

b) Extension Features
These are features which can be activated for those users having industry-standard types of telephone sets and which are fitted with either a rotary dial or multifrequency (MF) keypad.

  • Automatic Callback (Extensions)
  • Automatic Callback (Groups)
  • Busy Override
  • Busy Override Security
  • Call Hold
  • Call Privacy
  • Call Transfer
  • Camp-on (Wait on Busy)
  • Camp-on Retrieve
  • Camp-on Tone Security
  • Conference
  • Dial Through Busy
  • Do Not Disturb
  • Extension Message Waiting

Extension to Extension Dialling

  • Forced Release
  • Forwarding - Accept
  • Forwarding - External Destination
  • Forwarding - Internal Destination
  • Forwarding on Busy (External Source)
  • Forwarding on Busy (internal Source)
  • Forwarding of All Calls
  • Forwarding From a Remote Extension
  • Forwarding on No Reply (External Source)
  • Forwarding on No Reply (internal Source)
  • Hot Line
  • Last Number Redial
  • Personal Speed Call
  • Pick-up
  • Pick-up - Accept
  • Pick-up Group
  • Pick-up Group - Accept
  • Recall Button
  • Shuttle
  • Transfer with Privacy

c) Operator Features
The operator console consists of a SUPERSET 7, which has been selected by system programming to perform Operator functions for the system. The system can support up to 16 Superset 7, Operator Consoles.

Operator Features are described in the Superset 7 booklet.

  • Alarms
  • Busy Override
  • Call Answer
  • Call Splitting
  • Call Transfer
  • Call Waiting Display
  • Camp-On
  • Connect Answered Call to Held Call
  • Controlled Conference
  • Dial by Name
  • Dial from Directory
  • End to End Signalling for Operator (DTMF)
  • Feature Cancel
  • Feature Set
  • Hold and Retrieve Calls
  • Individual Directory Numbers
  • Individual Trunk Access
  • Interposition Transfer
  • Message Waiting
  • Multiple Operator Consoles
  • Night Service Control
  • Paging
  • Position Busy Out
  • Recalls
  • Selective Answer
  • Serial Call
  • Source and Destination Display
  • Specialised Operator Service
  • Telephone Directory
  • Time and Date Display

Data Features

  • Data features are described in the Data Communications booklet.
  • Automatic Baud Recognition
  • Bit Transparency
  • Data Call by Name
  • Data Call Origination, Termination and Disconnection
  • Data Call Queuing
  • Data Help
  • Data Hot Lines
  • Data Line Loop back
  • Data System Speedcall
  • Dataset Hunt Group
  • Data Transceiver
  • Dedicated Modem Circuits
  • Modem Hunt Groups
  • Modem Pooling

Telephony Features
System features

Account Codes
Account codes identify the caller or called party on the Station Message Detail Recording (SMDR) record. This information can then be used for client billing. Account codes can be optional or forced depending on the customer's wishes. Account codes can be one to twelve digits long. There are three types of account code:

Extension (Default) Account codes. These are automatically recorded by the SMDR whenever a trunk, extension, or operator associated with that code is used. More than one trunk, extension, or operator can share the same account code; eg. all of the extensions in the Engineering department might share the same account code.

Independent (Forced) Account Codes are entered by the customer. They can be used for security reasons, customer charging, or to let an authorised user place a trunk call from an extension whose COS prevents trunk calls. For instance a manager, using his account code, could access a trunk on an extension which is denied trunk access. This feature is also known as Travelling Class of Service.

System (Specialised Common Carrier) Account Codes are used to access particular trunk(s). The Specialised Common Carrier (SCC) Account Code is used when an outgoing call on a specialised carrier trunk circuit is made. When an extension user makes an SCC Account call, the SCC Account code is also outpulsed and is used by the carrier to validate and record details of the call.


Technical Characteristics Typical Configurations

The SX-2000SG provides not only voice switching but also data switching. It provides a PACX type switch for local or remote data terminals and/or computers. Local terminals are connected to the system through Mitel's Datasets which are limited distance modems. Transmission is over a standard wire pair at a range of up to one kilometre. Remote terminals are connected to the system through a trunk with a modem at either end. The local modems can be dedicated to a trunk, or more often, used on a shared basis (modem pooling). 

The combination of shared resources (Dataset/ Modem Pooling), and data transmission over standard two wire pairs make the SX-200OSG Integrated Communications System uniquely cost effective for data switching. Frequently Datasets can be installed without any extra wiring, simply using an extra pair of wires in the industry standard BT Master Jack. The majority of data terminals are only used intermittently; for example a Stock Controller needs to interrogate the inventory database many times a day, but he does not need to be on-line to that database all day. Similarly a manager might only need to use his computer accounts once or twice a day. In these situations a dedicated modem, will lie idle most of the time; but Dataset/ Modem pooling makes efficient and cost effective use of resources.

The Dataset is designed to fit neatly under a Superset 4 or an industry standard telephone; no valuable desk space is wasted. Mitel realise that most terminal users are not computer experts and need simple, foolproof methods of setting up data calls. The Dataset is simple to use, there is only one switch and two indicator lamps. The switch, or Call Button, is used to signal the beginning or end of transmission. The Device indicator lamp shows when the user's data terminal (device) is ready for use, and the System indicator lamp shows when the requested link is ready for use.

There are two ways to set up a data call. The first, Associated Data Line (ADL), uses an extension to set up the data call. During Customer Data Entry an extension number is associated with a data terminal number. To make a data call the user dials the appropriate data terminal number, as soon as the data connection is made the user can replace his handset. The extension is then available for normal use. The second type of data call, Data Transceiver Call (DTRX), is set up directly form a terminal. At any stage during call set up if the user has a problem, or is unsure of the procedure, he can refer to Mitel's Data Help File upon request. Having found the relevant information the user can then resume the data call set up procedure.

The SX-2000SG handles data calls in the same way as voice calls so that the "System Features" are also available to data calls, including Hot Line and Call Queuing (Wait on Busy).

Data Features

  • Automatic Baud Recognition
  • Bit Transparency
  • Data Call by Name
  • Data Call Origination, Termination and Disconnection
  • Data Call Queuing
  • Data Help
  • Data Hot Lines
  • Data Line Loop back
  • Data System Speedcall
  • Dataset Hunt Group
  • Data Transceiver
  • Dedicated Modem Circuits
  • Inactivity Timer
  • Modem Hunt Groups
  • Modem Pooling

Automatic Baud Recognition
The Data Transceiver Card (DTRX) performs the auto-baud/auto-parity checking for the system. This automatically selects the proper speed and parity for the Data Terminal Equipment (DTE) used, saving the user from setting switches or entering parameters.

Bit Transparency
Once a data call has been established, the circuit switch of the SX-200OSG is transparent to any data or user protocols that pass through the system.

Data Call by Name
A user can call a data terminal by means of data name, (DTRX data call only), in the same way that an Operator can dial a number by name.

Data Call Origination, Termination, and Disconnection

Users can make data calls in two ways:

  • From a telephone associated with a Dataset (ADL)
  • From the terminal keyboard (DTRX)

These calls must terminate on one of the following:

  • A Dataset supporting a data terminal
  • A Dataset supporting a pooled modem
  • A Dataset supporting a dedicated modem

Disconnection occurs:

  • On receipt of a disconnect signal
  • When the user depresses the Dataset "Call" button
  • When the user goes on-hook in an incoming call using a modem.

Data Call Queuing
This feature is a form of Camp-on. If a user tries to make a DTRX call to a busy data terminal, he has the option of queuing or terminating the call.

Data Help
The DTRX also contains a "Help" file, which steps the user through the various commands available on the system. The responses are displayed in "plain" English, so that the average user can understand what actions he needs to take.

Data Hot Line
This feature provides for the connection of a device as soon as power is applied to the Dataset. Note that in this connection, system resources are only used when the power at the terminal device is on.

Data Line Loopback
Data users have the ability to dial a special code, and have their line looped back to their terminal. This lets them check the integrity of their physical path.

Data System Speedcall
This feature can be used for both ADL and DTRX data calls, and is especially useful for data calls to external data terminals which involve long and complex digit sequences.

Dataset Hunt Groups
Incoming data calls can hunt through a group of Datasets to get connection to digital equipment. Hunting is always circular.

Data Transceiver (DTRX)
The Data Transceiver, or DTRX, is a Digital Service Unit (DSU) which resides on the control shelf of the SX-200OSG. The DTRX interprets keystrokes from the data terminal, and sends the resulting commands to the SX-200OSG. For example, a user who has a terminal and Dataset can enter the data number of the system he wants connection to from his keyboard. The DTRX will receive that information, and pass it on to the Message Switch. Once the call is connected, the DTRX is dropped.

Dedicated Model Circuits
Customers can choose to have some modems permanently connected to some trunks. Such an arrangement is only valuable if the customer has enough external data traffic to justify a trunk dedicated to data only. See Figure 3.

Inactivity Timer
The System monitors activity during a data call, if the inactivity timeout period is exceeded the line is dropped. The timeout period is user programmable during CDE.

Modem Hunt Groups
Modems in a modem pool are configured as a circular hunt group.

Modem Pooling
The SX-2000SG can have modem pools for greater economy arid flexibility. A modem pool is a group of modems, usually in a Hunt Group, that any user can seize when he wishes to make an external data call. The modems connect to Datasets on one side, and to On-Premise extension (ONS) line cards at the other side. The ONS line gets connected to a trunk when a data call is made. Different classes of modem pools can be established for connections to different types of mainframes or networks. Connection to each class is governed by a code entered by the user at the time of connection.

Datasets 1 and 2 Technical

The Dataset 1 has these specifications:

  • Interface: V.24/RS-232C
  • Speed up to 9600 baud, asynchronous Data Communications Equipment (DCE) adaptor for modems 2-wire twisted pair, 22 to 26 gauge 1.0 km range
  • Power supply: Mains, 240 Vac 50 Hz Consumption: 3 watts
  • Controls: Call Button
  • Indicators: TX, RX/RDY LED's

The Dataset 2 has the following Specifications:

  • Interface: V.24/RS-232C
  • Speed up to 19,200 baud, synchronous 9600 baud, asynchronous DCE adaptor for modems 2-wire twisted pair, 22 to 26 gauge 1.0 km range
  • Power supply: Mains, 240 Vac 50 Hz Consumption: 3 watts
  • Controls: Call Button
  • Indicators: TX, RX/RDY LED's
  • DIP Switches for: sync/async, sync clocking source, sync speed, Answer/Originate

All take from Mitel documentation
Mitel SX2000 is superseded by the SX2000 light range

Link to Console description (PDF)

Link to Supersets


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Last revised: September 24, 2021