Title of Invention	"OPTICAL NETWORK UNIT FOR USE IN A FIBER ACCESS SYSTEM"
Abstract	An optical network unite (ONU) for use in communication system also referenced as fiber access system (FAS). It provides the interface between the optical distribution network and the subscribers. The FAS finds different uses and applications.

Full Text

The present invention relates to an optical network unit for use in a fiber access system and generally in communication system. The communication system of the present invention is an optical network based system referred to as fiber access system (FAS). The novel 'optical network unit (ONU) of the present invention provides the interface between the optical distribution network (ODN) and the subscribers. Each ONU is connected to the end of a branch fiber pair near the subscriber that it serves. The fiber access system comprising the optical network unit also comprises host digital terminal as a main station. The host digital terminal (HDT) of the fiber access system interfaces with one or more optical distribution network (ODNs), and a number of optical network units (ONUs), typically located in a building or street locations. This main station, i.e., the host digital terminal has a capacity of operating at least 4 ODNs, each ODN being preferably supported by a separate ODN interface. HDT-ODN interface is capable of supporting at least 32 ONUs. The present invention can be understood clearly and explicitly from the accompanying drawings which define the features of the invention. These drawings, however, do not restrict the broad scope of the invention. The present invention relates to an optical network unit for use in a communication system, i.e., fiber access system , providing interface between the ODN and the subscribers. The optical network unit comprises means for communication between the ODN and the subscriber. STATEMENT OF THE INVENTION According to the present invention there is provided an optical network unit for use in a fiber access system providing interface between the optical distribution network and the subscribers comprising: an optical receiver receiving input data; a clock recovery module for receiving outputs from the said receiver to generate clock and a retimed data; a synchronous digital hierarchy (SDH) termination chip for separating lower order tributaries, actual data bytes and control signals; an optical network unit (ONU) controller card (OCC) receiving lower order tributaries, data and control signals; a phase locked loop; and a remote test card for testing and maintaining the subscriber interface cards. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 defines the architecture of the fiber access system of the present invention. Figure 2 shows direct interface of the fiber access system of the present invention with exchange. Figure 3 shows FAS in SDH network. Figure 4 gives the block diagram of TDMA port card. Figure 5 gives the block diagram of ONU controller card. Figure 6 gives a block diagram of remote test card. DETAILED DESCRIPTION OF INVENTION Figure 1 as accompanied with the present invention defines an outline of the fiber access system of the present invention. This defines the basic architecture of the fiber access system. The Fiber Access system of the present invention finds different uses and applications. Of the various uses and applications of the FAS of the present invention, two major applications are : 1. Direct interface with exchange: This is applicable when HOT and exchange are in the same building or very close to each other. Minimum 32 numbers of 2Mb interfaces exist between HDT and exchange. The direct interface with exchange is clearly brought out and can be understood in a better manner with the help of the accompanying figure 2. 2. Interface via SDH ring: This application is most suitable when a large size exchange is deployed and is extended to FAS subscriber via SDH ring. The SDH/ADM ring network provides transparent transport of the HDTV through 2 Mb interface. An explicit description can be referred to in the accompanying figure 3. The fiber access system of the present invention is capable of supporting many devices such as analog telephony (POTS), analog leased lines, ISDN-BA, ISDN-BRA and the like, and also of upgrading the present system to BISDN. Further, digital video interactive and distributive is done by reconfiguring the prevalent system in a cost effective and practical manner while causing a minimum disturbance to existing customers. The fiber access system employing optical network units of the present invention can be provided in various configurations, e.g., FTTC (fiber to the curb), FTTB (fiber to the building) and FTTO (fiber to the office) based on passive optical network (PON). These configurations define only a few configurations and are not defined to restrict the scope of the present invention. The communication mechanism between the optical network unit and the host digital terminal (HOT) employs use of time division multiplex/time division multiple access (TDM/TDMA) transport protocol over an optical distribution network. The subscriber interfaces are provided at the ONU. Services available to the subscriber are either POTs or ISDN-BA or ISDN-PRA. The TDM/TDMA protocol is well known in passive optical networks wherein it is employed to permit transactions between a single base station and a plurality of base stations. The transmission technique employed in the fiber access system allows the HDT-ONU connection to be point to multipoint as well as allows point to point transmission. The multiple access is based on TDMA transmission method whereas bi-directional transmission scheme is based on space division multiplexing (SDM). Further, to allow sharing of optoelectronics among many ONU's TDM downward/TDMA upward technique is used. The interactive services provided by the fiber access system employs use of 1260nm-1360nm for both upstream and downstream transmission on separate fibers for both simplex and duplex transmission system. The system also uses 1475nm-1565nm wavelength for analog CATV distribution and B-ISDN services. On the optical distribution network side, one HDT interfaces with upto four passive optical networks (PONs) each containing upto 32 optical network units (ONUs) located near the customer premises. Each ODN interface uses separate fibers for upstream (ONU-HDT) and downstream (HDT-ONU) transport. The ODN interface provides a set of optical physical interface functions terminating the relevant set of optical fibers of the ODN. On the receive side of the optical network unit, STM-1 data at the rate of 155.52 Mbps is accepted. The output of the receiver is given to a clock recovery module to generate the 155.52 Mhz clock and retimed data. The retimed data and clock is given to a SDH termination chip which separates out lower order tributaries, actual data bytes and control signals. The lower order tributaries, data and control signals are given out to OCC for further processing. The 155.52 Mhz output of the clock recovery module is also given to a Phase locked loop to generate a 8.192 Mhz clock. This clock is given out to Optical network unit controller card (OCC). Moreover a microcontroller also sits on the TPC to monitor the operations of the optical transmitter, optical receiver and SDH termination chip. It also has an ACIA link which it communicates with OCC. Figure 4 shows a block diagram of TDMA port card. The functions of the TPC are divided into four major areas 1. Transmit portion 2. Receive portion 3. Phase locked loop 4. Microcontroller Transmit Portion: On the transmit side the TPC accepts TTL accepts TTL byte data at the rate of 19.44 Mbps from the OCC. It converts the TTL byte data into PECL byte data. Thereafter it converts the byte data into serial data using a parallel to serial converter. The output of the P/S converter is a burst data at the rate of 155.52 Mbps. The serial data burst is reshaped and given to the optical transmitter in differential form for further transmission. Receive Portion: On the receive side the TPC accepts STM-1 optical input at the rate of 155.52 Mbps. The differential output of the receiver is given to a clock recovery module (SCRM-155) to recover the 155.52 Mhz differential clock and retimed differential data. The 155.52 Mhz differential clock and retimed differential are given to a SDH transmission chip to generate the lower order tributaries and their respective clocks, actual data bytes and control signals. The lower order tributaries, actual data bytes and control signals are given to the OCC for further processing. A holdover circuit is also present on the receive side. Phase locked loop: The differential clock output of the clock recovery module is also given to a 1:4 clock distribution chip. One of the output of the clock distribution chip is given to the PLL to generate a stable 8.192 Mhz clock. This TTL clock is given out to OCC. Microcontroller: Microcontroller sits on the TPC to initialize the SDH termination chip. It also monitors the performance of optical transmitter, optical receiver and SDH termination chip. Moreover it has an ACIA link through which it communicates with OCC. ONU controller card (OCC) Figure 5 shows the block diagram of ONU controller card. This is the primary controller card in ONU that controls the operation of all other cards in ONU. The functionality of this card can be broadly classified into the categories of subscriber interface function; TDM/TDMA port control function, PSTN signal processing function; packet handling function; communication function and OAM function. 1. Subscriber interface function: This card provides bi-directional IOM-2 (GCI) interface to "basic access" and "analog" subscriber interface cards. It also sends SMPS clock and metering clock to analog line cards and demultiplexed microprocessor bus to basic access cards in order to access the D channel data and control the D channel handling devices. ISDN-PRA subscriber interface consists of 4 bi-directional 2.048 Mb.s digital NRZ (Non Return to Zero) data interface and 2 bi directional HDLC links to the ISDN-PRA subscriber interface cards. 2. TDM A/TDM port control function : It extracts the required time slot data from the 19.44 Mb/s data coming from STM-1 termination device. It converts transmit data to the TDMA format and generates the required control signal. It also performs useful roles during automatic ranging. 3. PSTN Signal processing function: It performs functions like on hook off hook detection, ring trip detection and digit detection through register signaling using IOM-2 command/ indication (C/I) channels. It also controls the ring feed relay and test access relay at the analog line cards. All these information are converted to PSTN protocol messages and passed on to the packet handling entity. On the receive side the PSTN protocol messages coming from HOT are translated and passed to the front end devices through C/I channel. 4. Packet handling function: It generates/terminates PSTN message packets from/to C/I channel signals. This card receives/sends signaling, performance and configuration information from/to primary access cards through HDLC links. Messages from these three sources and local OAM entity are multiplexed over a single HDLC link and sent through EOC (Embedded operational channel). In the reverse direction messages are demultiplexed and sent to these entities. 5. Communication function: It provides communication links to TPC, RTC and PACs. It also provides an ACIA link to the video distribution unit and an ACIA port for testing purpose. The electrical interface for these ACIA links are RS-232C. It provides an ACIA link with TPC for control and monitoring purpose. The communication link with RTC is synchronous in nature. OAM function: In coordination with OAM unit present in host digital terminal (HOT), this card performs operations and management function at ONU. It carries out these maintenance functions either through microprocessor bus or maintenance commands passed through IOM-2 or serial interfaces. The reports are then either passed to OAM at HDT through EOC or HHT. The subscriber interface function is achieved through EPIC (Enhanced peripheral interface controller) in case of analog PSTN and basic access subscribers. The NRZ (Non Return to Zero) ISDN-PRA subscriber interface comprises of a time switch and two HDLC link controller. REMOTE TEST CARD Figure 6 shows a block diagram of remote test card. In fiber access system the subscriber interfaces are provided through different line cards located at ONU, the remote unit. RTC is responsible for testing and maintenance of this subscriber interface cards. RTC interfaces with OCC and the line cards. The functionality of these cards can be classified as 1. Line testing: Subscriber lines are tested for both open loop as well as closed loop condition to identify short circuits, open circuits etc. and to measure parameters like loop resistance, capacitance, etc. 2. Subscriber interface circuit testing: It basically tests the analog subscriber interface circuits for BORHT functions excluding the speech testing. 3. Communication function: It provides an RS-232 ACIA interface to the HHT. It has a synchronous peripheral interface with the OCC. This card houses the drivers for both this ports. 4. Monitoring function: This card monitors power supply, battery backup condition and an array of sensors like door open close sensor, temperature sensor, water sensor and the like. ONU has a 4 layer PCB as a back plane. The optical termination has a front end accessibility. Routing of the optical cable avoids sharp bends. For line termination small MDF may be used. They are all placed on top of subrack inside the box. The top half of the portion is used for line termination and other half is used for interconnection between the primary and secondary units. A battery back up is provided which allows ONU to continue to function in the event of the failure of the main supply . During change over to backup batteries, ONU configuration is retained. Status of battery back up is constantly monitored and recorded at the host digital terminal. The ONU has four modules where the administration module acts on commands from the host digital terminal to provision ONU or a subscriber. The maintenance module interfaces with the remote maintenance software in the host digital terminal for carrying out remote diagnostics. It also interfaces with administration module for inventory management the host digital terminal to reporting errors or performance logs. The transport module is in the form of firmware to control the devices at ONU end for transporting the signal between OCC and TCC. In addition it reports the transport path performance to the host digital terminal over the HOC link. The signalling software interfaces with the customer equipment for generation and interpretation of line signals and with the host digital terminal signalling software for mapping/relay of these signals according to the V5.2 interface specifications towards the exchange. The administration module on the ONU performs the functions of provisioning the ONU which involves bringing the ONU into service by configuring it into a particular slot of the TDMA burst on provisioning commands received from the HDT. It further performs provisioning particular subscribers on the ONU based on remote commands from the host digital terminal for provisioning a particular subscribes an ISDN or a PSTN subscriber as per its terminal number. It also performs management of code download on the ONU and configuration of subscriber time slots. The maintenance module performs initiliasiation if all the ONU cards, subscriber line test, performance and status monitoring, alarm supervision, ISDN and PSTN port maintenance and graceful degradation if so desired in case of power failure at the ONU. The transport module at the ONU performs the functions of ranging delay control based on the ranging data received from the HDT transport module, security by private key generation for the ONU and monitoring HDT to ONU transport path performance measurement and reporting to the administration module in the HDT. The signal processing functions are performed by POTS line card, ISDN-BA line card, ISDN PRI line card and ONU controller card. The embedded channel management function accepts all the HDLC messages generated or received from the ISDN line cards. It also performs link access management for packets of exchange with HDT over EOC. Here three type of messages are handled which includes PSTN signalling from POTS line cards, ISDN D channel packets and OAM messages which is responsible for transmission, reception and distribution of operations messages over the EOC channel of the TDM/TDMA transport mechanism. At the user terminal there mainly are four blocks relating to administration module, maintenance module and graphical user interface. The administration module provides administration and operations commands to operator. The module receives system configuration, provisioning, report control and traffic monitoring commands from operator. It maintains object models for the whole fiber access system. The development of object models are according to CCITTs proposed model for information modelling. The maintenance module provides diagnostic, alarm reporting, remote line testing services to operator. The Graphical user interface is a windows based interface provided to operator to access the features of OAM software. There are three types of message links between ONU and HDT. • Operations message link • PSTN message link • ISDN-D channel link Operations message link is a logical link for the remote operations messages from the OAM controller in HDT and TDMA port at ONU. The operations message packets are identified by the packet handling block in the HDT and sent to the testing block or the customer interface. The packets in the HDT are picked up by the packet handler. All operations messages are directed to the OAM controller. In PSTN message link all PSTN signalling messages generated by the user port in the customer interface units is handled by a network layer over shared HDLC k links between all the cards in ONU and the TDMA port. There packets are consolidated into a common message link. All packets are sent to the packet handler in HDT. The message flow between HDT V5 and LE V5 consists of five types of logical message links between HDT and LE. All these links are facilitated via a data link based on the LAPD. Layer two peer to peer messages are exchanged at the time of system initialization between LAPD processes at the two ends and multiple data links are established. There are separate data links for each protocol. The link control messages are between the link manager and the data link layer at the two sides that is HDT and LE. All control messages are multiplexed at layer 3 and carried over the control layer 2 data link over V5.1 interface. There are four type of messages flowing between AN protocol and LE control protocol in either direction over a control data link. They are port control messages, port control ack, common control and common control ack. The port control type of messages flow between individual port related control entities on either side by means of layer 3 address. The common control message is exchanged between two common control entities on either side of the V5.1 interface. The PSTN signalling messages from the ONUs are demultiplexed at the TDMA card in the HDT and sent to PSTN protocol in V5 processing block. The PSTN messages are exchanged between the HDT and the LE-PSTN protocols over one data link per V5.1 interface. The protocol is disconnected by disconnect request message. The ISDN D-channel data packets are multiplexed through a from envelope function in the V5 and are sent over a data link to the ISDN-D channel handling block in the LE. Further the bearer control message link applies only to V5.2 while protection protocol messages are as per V5.2. The invention hereby has been described in brief and is a mere statement of invention, which does not and shall not restrict the broad scope of the invention. WE CLAIM:- 1. An optical network unit for use in a fiber access system providing interface between the optical distribution network and the subscribers comprising: an optical receiver receiving input data; a clock recovery module for receiving outputs from the said receiver to generate clock and a retimed data; a synchronous digital hierarchy (SDH) termination chip for separating lower order tributaries, actual data bytes and control signals; an optical network unit (ONU) controller card (OCC) receiving lower order tributaries, data and control signals; a phase locked loop; and a remote test card for testing and maintaining the subscriber interface cards. 2. An optical network unit as claimed in claim 1, wherein the said OCC has a subscriber interface card; time division multiplex/time division multiple access (TDM/TDMA) port control card; PSTN signal processing card, packet handling card and communication card. 3. An optical network unit as claimed in claim 2, wherein the said subscriber interface card is configured to provide bi-directional interface to "basic access" and "analog" subscriber interface cards. 4. An optical network unit as claimed in claim 2, wherein the said TDM/TDMA port control card is configured to extract the required time slot data from coming from the termination device, convert transmit data to the TDMA format and generate the required control signal. 5. An optical network unit as claimed in claim 2, wherein the said PSTN signal processing card is configured to perform functions like on-hook and off- hook detection, ring trip detection and digit detection through register signaling and control the ring feed relay and test access relay at the analog line cards while converting the information to PSTN protocol messages and passed on to the packet handling entity. 6. An optical network unit as claimed in claim 2, wherein the said packet handling card is designed to generate/terminate PSTN message packets and receive/sends signalling, performance and configuration information from/to primary access cards through HDLC links. 7. An optical network unit as claimed in claim 2, wherein the said communication card is configured to provide an ACIA link to the video distribution unit and an ACIA port for testing purpose. 8. An optical network unit as claimed in claim 1, wherein the said Remote Test Card (RTC) responsible for testing and maintenance of the subscriber interface cards is configured to perform line testing, subscriber interface circuit testing as well as communication and monitoring. 9. An optical network unit for use in a fiber access system providing interface between the optical distribution network and the subscribers substantially as herein before described with reference to the accompanying drawings.

Documents:

321-del-1999-abstract.pdf

321-del-1999-claims.pdf

321-del-1999-correspondence-others.pdf

321-del-1999-correspondence-po.pdf

321-del-1999-description (complete).pdf

321-del-1999-drawings.pdf

321-del-1999-form-1.pdf

321-del-1999-form-19.pdf

321-del-1999-form-2.pdf

321-del-1999-form-4.pdf

321-del-1999-form-5.pdf

321-del-1999-gpa.pdf