PLESSEY CDSS No. 1


Customer Digital Switching System No.1

The Customer Digital Switching System No. 1 is highly advanced in concept, using single channel codecs and Pulse Code Modulation (PCM) techniques for the transmission of speech and microprocessor control for calls and facilities. Reliability is ensured by the use of solid state devices. The equipment is mounted on easily-changed, plug-in units and maintenance, on a ‘service-by-substitution’ basis, is reduced to a minimum.

For the user
CDSS1 is a small PABX switching system providing service for up to 120 extensions, modern in appearance, and capable of providing a large range of operational features as an aid to business efficiency. It is quiet and can live happily in an office environment if need be - no need to banish it to the cellar. The operator console combines efficiency with absolute simplicity and its operation requires minimal training. For the smaller systems the console can be dispensed with and call supervision carried Out on a master extension.
CDSS1 marks a radical departure from existing electromechanical systems, offering a whole new range of capabilities with greater reliability, and improved maintenance and installation techniques.

System variants
CDSS1 has been conceived as one system with several variants. All variants use the same basic hardware parts but with modified software or optional plug-in cards to give the required range of facilities. In this way maximum flexibility has been achieved whilst keeping equipment varieties to an absolute minimum.

The facilities include:
Three party conference on enquiry call
Transfer on exchange or inter-PBX calls
Dial answer night service
Designated extension night service
Metering - on selected calls by the operator
Metering - exchange line totals
Metering - individual extension
Emergency switching of exchange lines (manual or automatic)
Night busying of I/C exchange lines
Manager/Secretary
Class of Service change at console
Multi-party conference (8 party and 4 party)
Camp on - call waiting
Call back - extension to extension
Extension group hunting
Dial call pick up
CCITT MF and Dial telephones-mixed on same line
Auto extension-extension calls
Immediate ring-all calls
Executive intrusion (extension to extension)
Distinctive ring - internal calls
Discriminatory call barring
Exchange line access via operator’s console
Single digit access to exchange/inter-PBX group
Inter-PBX line access via console
Level ‘9’ access barred
Incoming calls via console
Direct dialling in on inter-PBX circuits
Automatic call diversion after no reply
Absent extension diversion (extension control)
Operator call-in on exchange and inter-PBX calls
Level ‘0’ operator access
Enquiry calls

Other variants under consideration and planned for ongoing development once the basic system has been established include:
Designated extension in place of console
Direct dialling in on exchange lines
Auto/manual tandem switching of inter-PBX circuits
Special hotel/motel option with facilities such as:
Message waiting
Unoccupied room restriction
Emergency fire alarm system
Wake up service
Call charging- with or without printer
Room number translation
Seminar/Conference lines
Lecture call
Paging

Additional optional facilities
In addition to the basic types, the flexibility inherent in
the microprocessor control makes possible the
adoption of further facilities in the future, often
without the need for additional equipment. Such
facilities as:
Multi-tenant working
Mixed digit length extension numbering
Music on hold
General access to attachments (single digit)
Diary service
Simple computing
Automatic alarm call
Automatic call recording
Data transmission
Contact operate
Data collection
Contact sensing
Key call-automatic
Do-not-disturb
Small business system telephone (SBS)
Time of day display
Digital telephone instruments
Night Watchman reporting
Long line extension working
MF5(R2) Inter PABX signalling
Fast FAX (64kbit/sec)
Standby power supply - in event of mains failure
Double sized unit 240/40

Equipment Summary
The Central Equipment Unit (CEU)
The switching equipment, line cards, power unit and ringing and tone supply units are housed in a cabinet approximately 1600mm (l62in) high, 550mm (22in) wide and 600mm (24in) deep. The Cabinet houses IEC standard 482.6mm (l9in) shelves which accommodate Printed Wiring Boards (PWB’s) with dimensions 200.66mm (7.9in) high and 323.2mm (12.72in) deep. PWB’s are connected by high density connector to an auto-wire wrapped metal backplane mounted on the rear of each shelf.

The equipment, which is silent in operation, may be sited either adjacent to or remote from the operator’s console. Cooling is provided by natural convection - no cooling fans are normally necessary.

The Console
The console is low-profile and compact. Its approximate dimensions are 130mm (5.lin) high (max), 470mm (18.5in) wide and 250mm (9.8in) deep. No moving parts whatever are used in operation of the console; Operator-to-machine communication is by means of touch sensitive keys and machine-to-operator communication is by way of a visual display unit (VDU) and a limited number of LED indicators. On the VDU is displayed such information as the calling circuit, extension number keyed, Class-of-Service of a called extension, extension status, etc.
Maximum use is made of advanced technology to achieve a highly functional unit and yet retain the flexibility necessary for efficient and speedy call handling in all types of customer environment. Typical examples of such flexibility are:
Customer Table Modification (CTM) - because the console has its own microprocessor and VDU it is possible to convert the console into a simple teletype for changes of extension, Class of Service, Extension numbering and receiving fault information etc. Key per facility - each major facility available from the console is provided with its own dedicated key. Speedy and accurate operation is thus literally at the operator’s fingertips.
Selective answering - each type of call has a dedicated answer key. This gives the operator considerable choice in assigning priorities when handling calls.

Technical details
Extension Lines Min: 4. Max: 120. Growth: 4.
Exchange Lines or PW Min: 0. Max: 40. Growth: 2.
Traffic Capacity Greater than 0.21 erlangs per extension (limited only by processor occupancy)
Time Slots 256 (equal to 128 bothway channels)
Coding ‘A’ - Law PCM as per CEPT.
Switching Time-switching with 256 ports or optionally 2 cabinets may be inter-connected Time - Space - Time with 512 ports.

Station instrument
Switching Speed 2,048 Mbits/sec.
Control Stored Programme Control using an 8 bit Microprocessor.
Extension Wiring 2 wires + earth (4 wires available for future developments).

Extension Instruments
Standard rotary dial or CCITT MF Keyphones or both. Future options for SBS telephone and digital instruments.

Exchange Lines
O/G Earth seizure (Other types available as options), I/C 25Hz, ringing. Private Wires E Et M, SCDC & IVF. Power 240V, 50HZ consumption approximately 0.5 Kilowatts.

Standby Power
Optional extra.

Construction
The system uses frameless printed wiring boards and wire strap metal backplanes.

Installation
Modern wiring techniques are used to reduce installation time. Cables are run from the test case or MDF in the usual way but are then terminated locally by an insulation displacement method on multiway connectors. No soldering or crimping operations are needed.


Technical description Outline of CDSS1
The CDSS1 is a digital PABX using single channel codecs incorporated in line circuits, such that the analogue/digital conversion occurs at the periphery of the PABX, and therefore only digital signals need to be switched.
There are 256 time interleaved digital channels available through the switch block and for normal calls, a single channel must be allocated to each direction of transmission for the duration of the call. Thus the switch itself is non-blocking which means that the total system traffic capacity is dependant primarily on processor loading.
Each of the 5 line unit shelves gains access to the switch block via a shelf multiplexer, each handling 32 ports.
The digital encoding is A-law PCM, with an 8kHz sampling rate, giving an architecture compatible with CEPT 30 channel recommendations.
The central control of the CDSS1 comprises a single microprocessor using an 8 bit word length. Stored programme control techniques are utilised with both the system operating programme and customers’ configuration protected in the event of any power failures.
Memory size would be 96 Kwords, but this is partially dependant on the system configuration. CDSS1 provides generous equipment flexibility such that, within certain limitation and with little formality, line, trunk and auxiliary cards are interchangeable. The absolute system size limit is governed by the total of 256 ports, and the maximum installed capacity of the system would normally be:
120 extension lines
40 trunks and auxiliary circuits (proportioned as required). Up to 30 trunks can be used as power fail transfer lines.
1 Conference Unit (with variable number of conferees) occupying 32 ports.
1 Tone Generator, occupying 32 ports.
1 Operator’s console, occupying 2 ports. The remaining ports are available for special purpose equipment or system expansion.

Conclusion
CDSS1 is an all-digital PABX with a large range of customer facilities. It is small in size - compatible with modern offices, flexible in configuration, easy to install and maintain. It is capable of operating both in the analogue environment met by existing PABX's - without extra penalties, and in a future digital environment. It is also compatible with existing types of telephone instrument and line signalling systems, but the possibility of inter-working with new developments in these areas is not precluded. In short CDSS1 offers the customer an advanced communication system fully compatible with modern business requirements.

Taken from Plessey Publication No. 7760/1 7/80

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Last revised February 25, 2007

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