Abstract:
A method, device and system for implementing a long reach passive optical network (LR-PON) are provided, which solve the problem that the cost for establishing an LR-PON system is high. The method includes: receiving an uplink burst packet transmitted by an optical network unit (ONU) in a burst manner ( 101 ), converting a burst optical signal of the uplink burst packet into a continuous optical signal, and transmitting the continuous optical signal to a receiving device ( 105 ). The present invention is applicable to an LR-PON.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2009/072054, filed on May 31, 2009, which claims priority to Chinese Patent Application No. 200810226005.0, filed on Nov. 3, 2008, both of which are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD 
     The present invention relates to the communication field, and more particularly to a method, device and system for implementing a long reach passive optical network (LR-PON). 
     BACKGROUND 
     The PON technology is a broadband optical access technology most widely applied at present. The conventional PON system includes an optical line terminal (OLT), a passive optical splitter, an optical network unit (ONU), a trunk fiber, and the like. The trunk fiber, the optical splitter, and a branch fiber between the OLT and the ONU are together called an optical distribution network (ODN). In the uplink direction, the ONU transmits uplink data in a burst mode and the OLT receives the uplink data in the burst mode. In the downlink direction, the OLT transmits downlink data in a continuous mode, and the ONU receives the downlink data in the continuous mode. 
     The conventional PON system covers a small range, so that a great number of OLTs are required to expand the coverage. Therefore, a solution of implementing LR-PON by using regenerator remote connection in an electrical relay manner is proposed in the prior art. 
       FIG. 1  illustrates basic architecture of a system for implementing LR-PON by using an optical-electrical-optical (OEO) relay device. A reamplifying, reshaping, retiming ( 3 R) relay device is disposed between the optical splitter and the OLT to serve as a remote connection relay device between the OLT and the ONU for accomplishing reamplifying, reshaping, and retiming functions. The  3 R device receives an uplink burst packet transmitted by the ONU in a burst manner, and transmits the uplink burst packet with aligned phases to the OLT in a “burst transmission” manner. Further, with the increase of the distance, a plurality of  3 R relay devices may be disposed between the optical splitter and the OLT. 
     Because the  3 R relay device transmits uplink data in the “burst transmission” mode, a receiving device has to receive the uplink data forwarded by the  3 R relay device in a “burst reception” mode. 
     During the implementation of the present invention, the inventor finds that the prior art at least has the following problems. 
     The cost for the receiving device adopting the “burst reception” mode is high, which leads to the problem that the cost for establishing an LR-PON system is too high. 
     SUMMARY 
     In one aspect, an embodiment of the present invention provides a method for implementing LR-PON, so as to reduce the cost for establishing an LR-PON system. 
     To achieve the objective, the embodiment of the present invention adopts the following technical solution: 
     A method for implementing LR-PON includes: 
     receiving an uplink burst packet transmitted by an ONU in a burst manner; 
     converting a burst optical signal of the uplink burst packet into a continuous optical signal; and 
     transmitting the continuous optical signal to a receiving device. 
     In another aspect, an embodiment of the present invention provides a device for implementing LR-PON, so as to reduce the cost for establishing an LR-PON system. 
     In order to achieve the objective, the embodiment of the present invention adopts the following technical solution: 
     A device for implementing LR-PON includes: 
     a receiving unit, configured to receive an uplink burst packet transmitted by an ONU in a burst manner; 
     a conversion unit, configured to convert a burst optical signal of the uplink burst packet into a continuous optical signal; and 
     a transmission unit, configured to transmit the continuous optical signal to a receiving device. 
     In another aspect, an embodiment of the present invention provides a system for implementing LR-PON, so as to reduce the cost for establishing an LR-PON system. 
     To achieve the objective, the embodiment of the present invention adopts the following technical solution: 
     A system for implementing LR-PON includes: 
     an ONU, configured to transmit an uplink burst packet in a burst manner; 
     a relay device, configured to receive the uplink burst packet transmitted by the ONU in a burst manner, convert a burst optical signal of the uplink burst packet into a continuous optical signal, and transmit the continuous optical signal to a receiving device; and 
     the receiving device, configured to receive the continuous optical signal forwarded by the relay device. 
     In the method, device, and system for implementing LR-PON according to embodiments of the present invention, an uplink burst packet transmitted by an ONU is received in a burst manner, a burst optical signal of the uplink burst packet is converted into a continuous optical signal, and the continuous optical signal is transmitted to a receiving device. In this way, the receiving device can receive the optical signal in a “continuous reception” mode that requires a low cost and is simple for implement, so as to reduce the cost for establishing an LR-PON system and simplify the implementation of the LR-PON system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To illustrate the technical solutions according to the embodiments of the present invention more clearly, the accompanying drawings for describing the embodiments are introduced briefly in the following. Apparently, the accompanying drawings in the following description are only some embodiments of the present invention, and persons of ordinary skill in the art can derive other drawings from the accompanying drawings without creative efforts. 
         FIG. 1  is a basic architecture diagram of an LR-PON system according to the prior art; 
         FIG. 2  is a schematic diagram of a method for implementing LR-PON according to an embodiment of the present invention; 
         FIG. 3  is a structure diagram of a device for implementing LR-PON according to an embodiment of the present invention; 
         FIG. 4  is a structure diagram of a system for implementing LR-PON according to an embodiment of the present invention; 
         FIG. 5  is a schematic diagram of a method for implementing LR-PON according to an embodiment of the present invention; and 
         FIG. 6  is a structure diagram of a device for implementing LR-PON according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions of the present invention will be clearly and completely described in the following with reference to the accompanying drawings. It is obvious that the embodiments to be described are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     An embodiment of the present invention provides a method for implementing LR-PON. As shown in  FIG. 5 , the method for implementing LR-PON according to the embodiment of the present invention includes the following steps: 
       401 : A  3 R relay device receives an uplink burst packet transmitted by an ONU in a burst manner. 
       402 : The  3 R relay device converts a burst optical signal of the uplink burst packet into a continuous optical signal. 
     Specifically, the  3 R relay device may adjust optical power of the burst optical signal of the uplink burst packet, convert the adjusted optical signal into an electrical signal, amplify and shape the electrical signal, perform clock data recovery on the amplified and shaped electrical signal, convert the electrical signal after the clock data recovery into the continuous optical signal, and amplify the continuous optical signal. 
       403 : The  3 R relay device transmits the continuous optical signal to a receiving device. 
     In the method for implementing LR-PON according to the embodiment of the present invention, an uplink burst packet transmitted by an ONU is received in a burst manner, a burst optical signal of the uplink burst packet is converted into a continuous optical signal, and the continuous optical signal is transmitted to a receiving device. In this way, the receiving device can receive the optical signal in a “continuous reception” mode that requires a low cost and is simple to implement, so as to reduce the cost for establishing an LR-PON system and simplify the implementation of the LR-PON system. 
     To reduce the cost for establishing an LR-PON system, an embodiment of the present invention provides a method for implementing LR-PON. As shown in  FIG. 2 , the method for implementing LR-PON according to the embodiment of the present invention includes the following steps: 
       101 : A  3 R relay device receives an uplink burst packet transmitted by an ONU in a burst manner. 
     During the specific application, the  3 R relay device may receive the uplink burst packet transmitted by the ONU in a burst manner after receiving a reset signal. 
       102 : The  3 R relay device adjusts optical power of a burst optical signal of the received uplink burst packet, converts the adjusted optical signal into an electrical signal, and amplifies and shapes the electrical signal. 
       103 : The  3 R relay device performs clock data recovery on the amplified and shaped electrical signal. 
     A reference clock used in the clock data recovery is a downlink retiming clock generated by the  3 R relay device, and the  3 R relay device converts a continuous downlink optical signal received from a receiving device into an electrical signal, amplifies and shapes the electrical signal, so the downlink retiming clock is recovered from the amplified and shaped electrical signal. The downlink retiming clock is used to perform clock data recovery on the uplink signals, so that clock phases become more stable and phases of the uplink burst packets are uniform after the uplink signals pass through the  3 R device, so that the receiving device can better receive the uplink signals. 
       104 : The  3 R relay device converts the electrical signal after the clock data recovery into a continuous optical signal, and amplifies the continuous optical signal. 
     In addition, in order to avoid the difficulty of the clock data recovery in the reception of the receiving device caused by long 0 and long 1 that appear in the continuous signal output by the  3 R relay device, the  3 R relay device, before converting the electrical signal after the clock data recovery into the continuous optical signal, may further determine an inter-packet gap between the uplink burst packet and a next adjacent burst packet and fill non-Consecutive Identical Digits (non-CID) bit information in the inter-packet gap, that is, the length of continuous 0 or 1 in the bit information does not exceed the clock data recovery capability of the receiving device, which can be implemented through the following process. 
     First, an end position of the uplink burst packet and a start position of the next adjacent burst packet are obtained respectively. For example, the end position of the uplink burst packet may be detected with a burst packet trailer detection technology, and the start position of the next adjacent burst packet may be found with a bit delimiter technology. Then, the inter-packet gap between the two adjacent burst packets is determined according to the end position of the uplink burst packet and the start position of the next adjacent burst packet. To achieve abutter filling effect, a byte rounding operation may be further performed on the inter-packet gap when the inter-packet gap between the two adjacent burst packets is determined. Finally, the inter-packet gap between the two adjacent burst packets is filled with effective non-CID bit information, for example, 0xCC. 
     When the  3 R relay device detects the end position of the uplink burst packet, a receiving unit and a clock data recovery unit of the  3 R relay device receive a reset signal respectively. The receiving unit continues to receive a next uplink burst packet transmitted by the ONU in a burst manner according to the received reset signal, and the clock data recovery unit performs clock data recovery on the amplified and shaped electrical signal according to the received reset signal. 
       105 : The  3 R relay device transmits the continuous optical signal to the receiving device. 
     The  3 R relay device transmits the continuous optical signal to the receiving device in a “continuous transmission” mode, and the receiving device also receives the continuous optical signal in a “continuous reception” mode. 
     The receiving device may be a  3 R relay device which adopts a “continuous reception” mode-“continuous transmission” mode, a  3 R relay device which adopts a “continuous reception” mode-“burst transmission” mode, or an OLT which adopts a “continuous reception” mode. 
     In the method for implementing LR-PON according to the embodiment of the present invention, an uplink signal is transmitted in a “continuous transmission” mode in the  3 R relay device, so that the receiving device can receive an optical signal in a “continuous reception” mode that requires a low cost and is simple to implement, which causes no damage to the uplink signal and helps to bear multiple PONs by using a wavelength division multiplexing (WDM) network, so as to save the fiber cost and reduce the cost of the LR-PON system, thereby simplifying the implementation of the LR-PON system. 
     An embodiment of the present invention further provides a device for implementing LR-PON. As shown in  FIG. 3 , the device for implementing LR-PON according to the embodiment of the present invention includes a receiving unit  201 , a conversion unit  202 , and a transmission unit  203 . 
     The receiving unit  201  is configured to receive an uplink burst packet transmitted by an ONU in a burst manner. 
     The conversion unit  202  is configured to convert a burst optical signal of the uplink burst packet into a continuous optical signal. 
     The transmission unit  203  is configured to transmit the continuous optical signal to a receiving device. 
     Further, as shown in  FIG. 6 , the conversion unit  202  specifically includes a burst optical signal processing subunit  2021 , a clock data recovery subunit  2022 , and a continuous optical signal conversion subunit  2023 . 
     The burst optical signal processing subunit  2021  is configured to adjust optical power of the burst optical signal of the uplink burst packet received by the receiving unit  201 , convert the adjusted optical signal into an electrical signal, and amplify and shape the electrical signal. 
     The clock data recovery subunit  2022  is configured to perform clock data recovery on the electrical signal output by the burst optical signal processing subunit  2021 . 
     The continuous optical signal conversion subunit  2023  is configured to convert the electrical signal output by the clock data recovery subunit  2022  into the continuous optical signal, and amplify the continuous optical signal. 
     In addition, the continuous optical signal conversion subunit  2023  further includes a conversion module  20234  and an amplification module  20235 . The conversion module  20234  is configured to convert the received electrical signal into the continuous optical signal. The amplification module  20235  is configured to amplify the continuous optical signal. 
     In order to avoid the difficulty of the clock data recovery in the reception of the receiving device caused by long 0 and long 1 that appear in the continuous signal output by the transmission unit  203 , a packet trailer detection module  20231 , an inter-packet gap delimitation module  20232 , and an inter-packet gap filling module  20233  may be added in the continuous optical signal conversion subunit  2023 . 
     The packet trailer detection module  20231  is configured to detect an end position of the uplink burst packet received by the receiving unit  201 , and transmit information about the end position of the uplink burst packet to the inter-packet gap delimitation module  20232  when detecting the end position of the uplink burst packet. 
     Moreover, the packet trailer detection module  20231  further transmits a reset signal to the receiving unit  201  and the clock data recovery subunit  2022  respectively when detecting the end position of the uplink burst packet. The receiving unit  201  continues to receive a next uplink burst packet transmitted by the ONU in a burst manner according to the received reset signal. The clock data recovery subunit  2022  performs clock data recovery on the electrical signal according to the received reset signal. 
     The inter-packet gap delimitation module  20232  is configured to determine an inter-packet gap between the uplink burst packet and a next adjacent burst packet and perform byte rounding on the inter-packet gap by receiving the information about the end position of the uplink burst packet transferred by the packet trailer detection module  20231  and obtaining the start position of the next adjacent burst packet. 
     The inter-packet gap filling module  20233  is configured to fill non-CID bit information in the inter-packet gap determined by the inter-packet gap delimitation module  20232  and transfer the optical signal having the packet gap filled with the non-long 0 long 1 bit information to the transmission unit  203 . The length of continuous 0 or 1 in the filled bit information does not exceed the clock data recovery capability of the receiving device. 
     In the device for implementing LR-PON according to the embodiment of the present invention, an optical signal of an uplink burst packet received in a burst manner is converted into a continuous electrical signal, and the continuous electrical signal is transmitted to a receiving device, so that the receiving device can receive the optical signal in a “continuous reception” mode that requires a low cost and is simple to implement, which causes no damage to the uplink signal and helps to bear multiple PONs by using a WDM network, so as to save the fiber cost and reduce the cost of the LR-PON system, thereby simplifying the implementation of the LR-PON system. 
     An embodiment of the present invention further provides a system for implementing LR-PON. As shown in  FIG. 4 , the device for implementing LR-PON according to the embodiment of the present invention includes an ONU  301 , a relay device  302 , and a receiving device  303 . 
     The ONU  301  is configured to transmit an uplink burst packet to a relay device in a burst manner. 
     The relay device  302  is configured to receive the uplink burst packet transmitted by the ONU  301  in a burst manner, convert a burst optical signal of the uplink burst packet into a continuous optical signal, and transmit the continuous optical signal to a receiving device  303 . 
     Further, the relay device  302  is specifically configured to receive the uplink burst packet transmitted by the ONU  301  in a burst manner, adjust optical power of a burst optical signal of the uplink burst packet, convert the adjusted optical signal into an electrical signal, amplify and shape the electrical signal, perform clock data recovery on the amplified and shaped electrical signal, convert the electrical signal after the clock data recovery into a continuous optical signal, amplify the continuous optical signal, and transmit the continuous optical signal. 
     The receiving device  303  is configured to receive the continuous optical signal forwarded by the relay device  302 . 
     The receiving device  303  is a  3 R relay device or an OLT. 
     In the system for implementing LR-PON according to the embodiment of the present invention, the  3 R relay device receives an uplink burst packet from an ONU in a burst manner, converts a burst optical signal of the uplink burst packet into a continuous optical signal, and transmits the continuous optical signal to a receiving device, so that the receiving device can receive the optical signal in a “continuous reception” mode that requires a low cost and is simple to implement, which causes no damage to the uplink signals and helps to bear multiple PONs by using a WDM network, so as to save the fiber cost and reduce the cost of the LR-PON system, thereby simplifying the implementation of the LR-PON system. 
     Persons of ordinary skill in the art should understand that all or a part of the procedures of the method according to the embodiments of the present invention may be implemented by a computer program instructing relevant hardware. The program may be stored in a computer readable storage medium. When the program is run, the procedures of the methods according to the embodiments of the present invention are performed. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), and the like. 
     The above are merely specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any variations or replacements that can be easily thought of by persons skilled in the art in the technical scope of the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be as defined by the claims.