WO1999018687A1

WO1999018687A1 - Distributed communications system

Info

Publication number: WO1999018687A1
Application number: PCT/AU1998/000816
Authority: WO
Inventors: David Jenkinson
Original assignee: Telspec Pty. Ltd.
Priority date: 1997-10-06
Filing date: 1998-10-06
Publication date: 1999-04-15
Also published as: AUPO959397A0

Abstract

The invention concerns a distributed communications system. In particular it concerns a modular system which includes one or more exchange units for installation in a rack at a telephone exchange. Each exchange unit has an exchange line interface, one or more optical fibre bearer cards and one or more service cards to support services to one or more remote units. The system also includes one or more remote units. Each remote unit is enclosed in a sealed housing for installation in a pit or manhole, and has an optical bearer card and remote service cards to provide customer services. The exchange unit is connected to a series of the remote units by a series of optical fibre links which extend between an optical fibre bearer card in each unit. The service cards associated with each optical fibre bearer card in the exchange unit are matched to the service cards of the remote units which are connected in the series to that optical fibre bearer card in the exchange unit.

Description

DISTRIBUTED COMMUNICATIONS SYSTEM Technical field

The invention concerns a distributed communications system. In particular it concerns a modular system based around an optical fibre digital loop carrier, and is designed for the customer access network and has small capacity.

Summary of the invention

The invention is a modular distributed communications system, including: one or more exchange units for installation in a rack at a telephone exchange, each exchange unit having an exchange line interface, one or more optical fibre bearer cards and one or more service cards to support services to one or more remote units; one or more remote units, each of which is enclosed in a sealed housing for installation in a pit or manhole, and has an optical bearer card and remote service cards to provide customer services; where the exchange unit is connected to a series of remote units by a series of optical fibre links which extend between an optical fibre bearer card in each unit, and the service cards associated with each optical fibre bearer card in the exchange unit are matched to the service cards of the remote units which are connected in the series to that optical fibre bearer card in the exchange unit.

Plain ordinary telephone services (POTS), or Integrated Services Digital Network services (ISDN), or both, may be provided. The system may provide an analogue telephone service with high performance for facsimile and VF data.

The cards in the exchange and remote units may be of plug-in design so that the system is reconfigurable by plugging cards in and out of the units. The remote unit housing can be opened in the field and the remote unit configuration changed, by inserting or removing plug-in line cards before being resealed. This allows customers to be added or removed from a remote unit. Once configured the remote unit must be resealed. The modular approach allows a very cost effective solution to the provision of services, in the range five to thirty customer lines per system. The operating software may automatically configure the system for POTS or ISDN operation depending on which line cards are inserted. The system detects the insertion of a new line card and automatically allocates spare capacity on the optical fibre to that line card. Other products need to be manually set up or pre-configured using either a terminal or man-machine interface to provide the customer with a service. The small capacity distributed system needs no human intervention to provide either plain ordinary telephone services or integrated services digital network service to the end customer apart from the insertion of a line card. Regenerating optical cards in the remote units utilise a custom designed fibre signal framer which operates in conjunction with a switching element to allow multiple time division multiplexed signals from local or remote POTS or ISDN services to be transmitted upstream. The framer and switching element also allow downstream services to be delivered to the correct distributed remote. Terminating optical cards may be placed in the last remote unit of a series.

The system may use a single optical fibre bearer to distribute up to say thirty plain ordinary telephone services at one or more geographically remote sites. It uses fibre to access sites that lack the population density to support the traditional multiplexer systems, and provides a low cost connection for between five and thirty customers in isolated areas of the urban fringe or in rural locations.

A comprehensive operation, administration and maintenance facility may also be incorporated on an operations, administration and maintenance card in the exchange unit. The operations, administration and maintenance facility may provide software download to all plain ordinary telephone services and optical bearer cards in the system, alarm management and customer line testing. All external interfaces may be of robust design and fully protected against the adverse lightning and surge conditions present in the network.

Power requirements for the exchange unit may be provided from the local exchange.

The remote unit may also have a battery management card which automatically switches in a battery backup in the event of local power failure. The battery is maintained in a charged state by a local mains powered plug pack or solar power source. A typical system may involve:

System capacity up to thirty Plain Ordinary Telephone Services (POTS), subrack capacity maximum one hundred and twenty plain ordinary telephone services; System capacity up to twelve Integrated Services Digital Network

(ISDN), subrack capacity forty eight ISDN basic rate services;

POTS and ISDN services in the same system is possible provided the correct cards are installed at the exchange and remote units;

Plain ordinary telephone services, normal, and leased line are supported as well as ISDN (2B1Q);

Bearer - single mode fibre (bi-directional on one fibre);

All VF POTS timeslots 64 Kbit/s (no compression is used);

Sultan like test head access to all customer services;

Operations, administration and maintenance card capable of interfacing to telstra's operation, administration and maintenance infrastructure;

Up to six distributed remote units per system; and

Up to one hundred and twenty customers per exchange unit subrack without concentration. The system, in summary, is an optical fibre based digital loop carrier designed for the customer access network providing thirty POTS or twelve ISDN basic rate access services at one or more geographically distributed points along a single fibre.

No other customer access network equipment has the feature to insert customer services onto a single optical fibre from geographically distributed points. Other customer access equipment provides point to point multiplexing from one remote location. Inter-exchange and main trunking multiplexers provide drop-and-insert features but these are not specifically designed for direct customer access using plain ordinary telephone services or integrated services digital network services.

The invention has implemented this feature using a regenerating optical fibre bearer card in conjunction with plain ordinary telephone services or integrated services digital network line cards. The regenerating bearer card may utilise a custom designed fibre signal framer which in conjunction with a switching element allows multiple time division multiplexed signals from local or remote plain ordinary telephone services or integrated services digital network services to be transmitted upstream. The framer and switching element also allows downstream services to be delivered to the correct distributed remote.

Brief description of the drawings

An example of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of the distributed system;

Figure 2 is a schematic diagram showing an exchange unit subrack layout;

Figure 3 is a block diagram of an operations, administration and maintenance unit for use with the system;

Figure 4 is a block diagram of an exchange unit for providing plain ordinary telephone services; Figure 5 is a block diagram of an exchange unit for providing ISDN services;

Figure 6 is a block diagram of an exchange unit for providing connection to optical fibre;

Figure 7a is a pictorial diagram of a remote unit housing, and Figure 7b is a pictorial diagram of the remote unit without its housing;

Figure 8 is a block diagram of a remote unit power management card;

Figure 9 is a block diagram showing the internal structure of a main card in a remote unit providing POTS;

Figure 10 is a block diagram showing the internal structure of an expansion card in a remote unit providing POTS;

Figure 11 is a block diagram showing the interconnection between the main card and the expansion card in the remote unit of Figures 9 and 10;

Figure 12 is a block diagram showing the internal structure of a main card in a remote unit providing ISDN services; Figure 13 is a block diagram showing the internal structure of a main card with an expansion card in a remote unit providing ISDN services;

Figure 14 is a block diagram showing the structure of a regenerating optical card in a remote unit;

Figure 15 is a block diagram showing the structure of a terminating optical card in a remote unit; Figure 16 is a pictorial diagram of a system having a regenerating and a terminating optical cards in remote units; and

Figure 17 is a pictorial diagram of a system having three remote units providing respectively POTS services, ISDN services, and a mixture of services.

Best modes for carrying out the invention

Referring first to figure 1, the system 1 is designed around an exchange subrack 2 with front access to the 'krone' insulation displacement connector termination area for the connection of customers to the main distribution frame. An optical fibre bearer is connected to the subrack via an exchange unit optical bearer card, using an angled SC connector.

The remote units 3 are enclosed in a sealed optical housing and installed in a pit or manhole. The housing can be opened in the field and the remote unit configuration changed, before being resealed in the pit. The remote units 3 have an integral 'krone' insulation displacement connector termination with over voltage protection and fibre cassette. Remote unit cards are enclosed in the internal card cage.

Referring now to Figure 2, the exchange subrack 4 is 19 inches wide, 10U high and is designed for installation into a telstra type 92 or type 84 rack. The exchange subrack contains up to 17 cards. One slot 5 is an operations, administration and maintenance card, the remaining 16 card slots are divided into 4 independent systems. Each system comprises 3 exchange plain ordinary telephone services cards 6 and one exchange unit optical bearer card 7. The exchange unit plain ordinary telephone services line cards 6 each supports ten customer lines, thus each system distributes up to thirty customer lines.

Alternatively, exchange unit ISDN cards may be installed , and each card may support 4 IDSN basic rate customers. Each system can distribute a maximum of 12 ISDN customer services.

The exchange unit optical bearer card 7 provides power and clock signals for the 3 exchange unit line cards. The operations, administration and maintenance and exchange unit optical bearer cards derive their own power directly from the exchange 50v battery source. The 4 exchange unit subrack systems continue to operate if the operations, administration and maintenance card is removed which also greatly enhances the reliability of the system.

A comprehensive operation, administration and maintenance facility 5 is incorporated in the exchange subrack, providing alarm management, fault analysis, performance recording, system configuration and customer line testing; the arrangement of the operations, administration and maintenance is shown in Figure 3.

A female DB9 serial communication port (RS232) labelled terminal 8 is provided on the exchange subrack, this allows operations, administration and maintenance facilities to be accessed via datagate modems or directly using a laptop.

The second (male DB9) serial port 9 labelled operations, administration and maintenance is intended for communication with a centralised management system. All system set-up parameters are stored in non-volatile memory so that the system remembers these parameters in the event of power failure. At installation the system will power up to a default configuration, suitable for immediate customer connection.

The addition of new remote units to an existing system will not effect the configuration of existing remote units or customers. A unique remote unit identifier stored in non-volatile memory in the remote unit makes this possible.

A software download is available to all customer cards within the system. The memory configuration allows uninterrupted system operation while a new software version is being downloaded. Once the new software version has been downloaded, the system implements a fail-safe procedure while the new software version is being executed for the first time. If any problems are encountered during start up of the new software version, automatic restoration of the previous software version will be executed. As a further precaution the production release of the software is stored in nonerasable memory and can be restored at any time if required, thus providing a guaranteed working release of software at all times.

Local alarm facilities are provided using urgent, non-urgent and alarm receiving attention relay contacts and indicators, located on the operations, administration and maintenance card. An exchange plain ordinary telephone services unit 6 provides interfacing for ten plain ordinary telephone services customer lines. The configuration of the card is shown in Figure 4. Input impedance and hybrid balance networks are selected on a per channel basis as either TN6 or TN12 to match customers to different exchange types. Power requirements and synchronisation clocks for the exchange unit plain ordinary telephone services line card are provided by the exchange unit optical bearer unit.

Key parameters of this card are:

1. 50 Hz and 12 KHz meter detection; 2. Ring detect 14 - 52 Hz;

3. Break detect;

4. Reversal detect;

5. Input impedance selectable as TN6 or TN12 (default TN12);

6. Balance network selectable BN6 or BN12 (default BN12); 7. On hook VF transmission (class compatible);

8. VF coded as 64 Kbits PCM (A-law); and

9. Downloadable software.

An exchange unit ISDN line card may alternatively be used to provide four ISDN basic rate connections; see Figure 5. The system is designed to act as an ISDN regenerator and fully complies with all relevant ETSI specifications.

The line code utilised is 2B1Q with each ISDN service occupying 3x64 Kbit/s timeslots. Each exchange interface incorporates a resistive load to mimic an NTl so that the exchange line cards see appropriate loading of their power feed circuits. System synchronisation is derived from a 2M/b/s clock cabled from the exchange clock distribution point meeting G703 section 10.

An exchange optical bearer unit 7, as shown in Figure 6, performs electrical to optical interface for up to thirty plain ordinary telephone services lines, connection to the optical bearer is provided by angled SC optical connectors.

Power to the exchange unit plain ordinary telephone services cards is provided by the switch mode power supply located on this card. All system clocking is provided from the exchange unit optical bearer unit from either a crystal oscillator or from the external 2Mb/s clock input on the backplane, since external clocking is required for the ISDN channel cards. The remote unit 3, shown in Figure 7, is enclosed in an optical housing 10. The remote unit incorporates a metal frame to which is attached a 3 x 10 way krone block and a fibre cassette 11. Above this area is a card cage 12 with an 8-slot mother board for one remote unit optical bearer assembly, three remote unit main and three remote unit expansion plain ordinary telephone services cards.

The remote unit fibre bearer card consists of two printed circuit boards, main and sub which are bolted together to form one assembly which is inserted into two card slots. There are two versions of the remote unit optical bearer card, regenerating and terminating. Normally a regenerating remote unit optical bearer card is installed but if the remote unit is at the end of the line, a terminating remote unit optical bearer card may be installed.

The remote unit services cards functions consist of two discrete units, main and expansion, both handling five customer lines for POTS and two customer lines for ISDN. The card slots for main and expansion cards are off-set to prevent insertion of cards into the wrong card slot. The main card can be used without the expansion card to distribute five POTS or two ISDN subscriber lines, the expansion card must be used in conjunction with a main card. The main card will operate as a stand alone card, the expansion card will not operate as a stand alone card and receives timing and control from its main card.

A cavity between the krone block and fibre cassette accommodates the power supply and battery management unit.

The remote unit power supply and power management card is located behind the remote unit terminal bracket, dip switches are located on the card, accessible through the side bracket. The dip switches are required to set the card for the type of power supply (power pack or solar panel) and to turn the remote unit power on and off.

The external power supply to the remote unit can be a solar panel or a mains powered plug pack. Alternatively an external 15.5 - 70 v dc supply can be used.

The battery management card incorporates all the circuitry necessary to charge an external 12 v battery, as well as providing low voltage monitoring, battery disconnect and a load; see Figure 8. A switchmode power supply unit on the card provides +5v and -5v supplies for the remote unit fibre bearer cards. A second power supply unit provides rails for the ringer and power to the remote unit plain ordinary telephone services cards.

The card has three LEDs visible through the left hand side of the termination field, a red alarm led to indicate that one or more of the output voltage rails is out of spec (±5v, -36v, -50v or ringer).

Two green LEDs indicate the input voltage (mains or solar) and batteiy voltages are OK.

The remote unit plain ordinary telephone services main unit provides plain ordinary telephone services interfacing for up to five customers over maximum 700 Ω tails. Adjustable gain settings allow end to end loss to be varied. The loss can be programmed remotely via the operations, administration and maintenance interface. Input impedances and balance networks are selectable on a per customer basis. Power supplies for the cards is derived from the remote unit power supply and battery management unit. The main plain ordinary telephone services card is a stand alone unit, it has its own timing and control circuitry.

Key parameters are:

12khz meter generation;

Ring generation 25 Hz @ 55 v RMS (ringer equivalence number = 5); Break generation;

Reversal generation;

Impedance selectable as (TN6, TN12) (default TN12);

Hybrid balance network selectable as (BN6 and BN12) (default BN12);

Exchange unit - remote unit and remote unit - exchange unit loss selectable 0 - 6dB (default 3 dB);

Feed current > 21 mA;

On hook VF transmission (class compatible);

VF coded as 64 Kbit/s PCM (A-law);

Test access per line to test head on remote unit optical bearer unit; and Total customer loop 700Ω (tail) + 500Ω (telephone).

The arrangement is shown in Figure 9.

The remote unit plain ordinary telephone services expansion unit contains line interface circuitry for five line circuits. It is inserted to expand the capacity of the remote unit plain ordinary telephone services main unit to ten subscriber lines. The expansion card is not a stand alone card and receives timing and control from its associated main card. The arrangement of the expansion card is shown in figure 10, and the arrangement of the main and expansion cards is shown in figure 11.

The combination of main and expansion remote unit plain ordinary telephone services cards allows the connection of ten customers to the remote unit. If up to five customers is required the use of only a main card is required. Systems requiring more than five customers at a remote unit may require main and expansion plain ordinary telephone services cards. For instance, thirty plain ordinary telephone services at a remote unit require three main and three expansions units, or fifteen plain ordinary telephone services at the remote unit maybe supplied with two main and one expansion unit, or three main plain ordinary telephone services units.

The remote unit ISDN main line card provides two ISDN basic rate connections fro two customer pairs. The card is an alternative to the POTS line cards and when used is inserted into the main line card slot. The card supplies a 100 V power feed, current limited to 30 mA, to each customer pair.

This is sufficient to meet all NTl powering requirements over a 700 Ω tail length. The main card is a stand-alone card and has its own timing and control circuitry; see Figure 12.

The expansion card provides two ISDN customer interface, as does the main ISDN card. The expansion card requires the main card for control and timing circuitry; see Figure 13.

The remote unit optical regenerating unit is an assembly made up of two cards, main and sub, which are bolted together to form one assembly. This whole assembly plugs into two card slots on the remote unit mother board; see Figure 14.

The two framers, microprocessor and clocking are incorporated on the main card.

The receive and transmit optical interface, fibre modules and a line tester module are located on the sub card. Two fibre interfaces are provided to allow drop and insert mode of operation. The arrangement is shown in figure 10.

The remote unit optical terminating unit fibre card assembly is similar to the regenerating fibre unit. The main card uses only one PCM framer and the sub card one optical module. The terminating optical unit provides a cost effective solution when a system requires only one remote unit, or is used in the last remote unit in system. The arrangement is shown in figure 15.

Figure 16 shows a configuration with two remote units. The first remote unit 13 requires the regenerating optical bearer unit and the second 14 requires the terminating unit.

Figure 17 shows a mixed configuration having a first system 15 having thirty POTS, a second system 16 having twelve ISDN customers, and a third system 17 having twenty POTS and 4 ISDN services.

Advanced man to machine maintenance and operational facilities are available to the operator via the RS232 serial terminal interface, provided on the exchange subrack. A local terminal or datagate modem connection is achieved using the female sub miniature D connector marked terminal.

The operations, administration and maintenance male sub miniature D connector is for future connection into telstras operation, administration and maintenance facilities and is not currently used.

The communication configurations for the terminal d connector are:

Baud rage: (9600), 1200, 4800, 19200 bps

Start bit: 1 bit

Data word length: 8 bits Stop bit: 1 bit

Parity: none

Software flow control: XON/XOFF

The serial terminal, or laptop computer communication software terminal emulation must be set to VT100. The default speed of the system is set to 9600 b/s.

When the terminal with the correct comms setting is plugged into the system via the RS232 port marked terminal, the operator will be presented the main menu screen. Navigation through the screens can be achieved using the keyboard or mouse. The system status screen gives the user an overview of the installed systems. A system is considered to be installed if the exchange unit bearer is present in the subrack. The derived cable information is displayed for each installed system. The type each card installed in the subrack is also displayed, as well as the remote unit identification number for each remote unit which is connected. Subrack cards and remote units which are unable to be communicated with correctly will not be displayed.

Visual alarm LEDs on the operations, administration and maintenance card will indicate if the alarm is urgent or non-urgent and indicate if the alarm is receiving attention. A flashing alarm led indicates a current active alarm condition, a continuous alarm led with a continuous alarm receiving attention led indicates the alarm is receiving attention. Three relay contacts extend the alarms to the station alarm system.

To view the alarm the operator must log in to the active alarm screen. The alarm surveillance system allows the operator to monitor any alarms which are occurring or may have occurred. If one or more alarms are currently occurring a text description of the most recent of these alarms appears in the box at the bottom of the display. For more detailed examination of alarms select the alarms option from the main menu. Three further options are available which function as follows:

Active alarms - to view a list of alarms which are currently occurring, and to clear them if possible.

History - to view a list of all alarms which have occurred in the past, as well as those which are currently occurring. Test alarms - to test the alarm relay contacts connected to the exchange's alarm system.

Configuration of the systems and customers is generally carried out automatically by the operations, administration and maintenance card at the exchange on the initial power up of a new system. In many instances the default settings allow suitable operation of the system and customers, however operational requirements may require the changing of some configuration settings to match databases. For example on power up of a new system all remote units are given a unique remote unit identifier number, this can be changed to match the remote unit identifier number in the network plant assignment management system database. Default customer settings, such as termination and balance network impedances may require changing for PABX, modem and facsimile services.

To select the channel mapping, customer, exchange, remote, or operations, administration and maintenance screen from the configuration menu highlight the menu option, using either the tab key or hot keys, then select the option by pressing the enter key *, the combination of m+ * , will enter the mapping screen.

The configuration menu allows an operator to perform:

Mapping: allows mapping of remote unit channels to exchange unit channels in groups of five channels for plain ordinary telephone services, or mapping of remote unit channels to exchange unit channels in groups of two channels for ISDN.

Customer: change customer settings to allow optimum customer service performance. Exchange: reports the cards installed in given positions in subrack, the software version and electronic serial number of each card.

Remote: allows the entry of remote unit location, and reports the type of cards installed in the remote unit including software versions and electronic serial numbers. Operations, administration and maintenance: configuration of the operations, administration and maintenance card such as exchange subrack location, date and time etc.

When a new system is installed and the power up occurs the operations, administration and maintenance card allocates or maps remote unit channels to exchange unit channels in a way controlled by the auto mapping rules stored in memory.

The system automatically allocates or maps remote unit channels to exchange unit channels controlled by the following rules:

Detection of an remote unit (bearer synchronisation) causes mapping of currently unmapped remote unit channels to vacant exchange unit channels.

Remote units are mapped sequentially, remote unit 1, remote unit 2, remote unit 3, etc to remote unit 6 after power up and bearer synchronisation. Remote unit channels will be mapped to vacant exchange unit channels in groups of five channels sequentially ie channel 1-5, 6-10, 11-16 etc.

If remote units are added to a system at another time, new remote unit channels will be mapped in groups of five channels to remaining vacant exchange unit channels. If an remote unit is removed from a system the exchange unit channels remain mapped to that remote unit.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A modular distributed communications system, including: one or more exchange units for installation in a rack at a telephone exchange, each exchange unit having an exchange line interface, one or more optical fibre bearer cards and one or more service cards to support services to one or more remote units; one or more remote units, each of which is enclosed in a sealed housing for installation in a pit or manhole, and has an optical bearer card and remote service cards to provide customer services; where the exchange unit is connected to a series of remote units by a series of optical fibre links which extend between an optical fibre bearer card in each unit, and the service cards associated with each optical fibre bearer card in the exchange unit are matched to the service cards of the remote units which are connected in the series to that optical fibre bearer card in the exchange unit.

2. A system according to claim 1, where Plain ordinary telephone services (POTS), or Integrated Services Digital Network services (ISDN), or both, are provided.

3. A system according to claim 1, where the cards in the exchange and remote units are of plug-in design so that the system is reconfigurable by plugging cards in and out of the units.

4. A system according to claim 3, where operating software automatically configure the system for POTS or ISDN operation depending on which line cards are inserted.

5. A system according to claim 1, where regenerating optical cards in the remote units utilise a signal framer which operates in conjunction with a switching element to allow multiple time division multiplexed signals from local or remote POTS or ISDN services to be transmitted upstream.

6. A system according to claim 5, where the framer and switching element also allow downstream services to be delivered to the correct distributed remote.

7. A system according to claim 1, where a comprehensive operation, administration and maintenance facility card is including in the exchange unit.

8. A system according to claim 7, where the operations, administration and maintenance card provides software download to all cards in the system, alarm management and customer line testing.