CN1507206A - Method for Transmission of Circuit Service on Ethernet-based Passive Optical Network - Google Patents

Abstract

The invention relates to a method for transmitting circuit services on an Ethernet-based passive optical network, which realizes integrated transmission of circuit services and Ethernet data services, and can reduce construction and operation and maintenance costs of access networks. At the sending end, write the incoming circuit service data into the buffer circuit, and periodically adapt the circuit service data to the data area of the Ethernet MAC frame; After that, it is sent through the transmission line. At the receiving end, the optical network unit uses the independent service time label method to realize synchronization with the circuit service clock of the optical fiber line terminal; the corresponding processing unit performs the decapsulation process to extract the circuit service data encapsulated in the Ethernet MAC frame , write into the buffer processing circuit to smooth the jitter introduced in the data transmission process; finally, according to the circuit service clock synchronized with the sending end, and continuously output the data according to the corresponding circuit service specifications and standards.

Description

Method for Transmission of Circuit Service on Ethernet-based Passive Optical Network

technical field

The invention relates to the technical field of communication, in particular to a method for effectively transmitting circuit services in an Ethernet-based passive optical network (Ethernet Passive Optical Network, abbreviated as EPON). It is mainly used in EPON system and other integrated transmission systems of Ethernet data service and circuit service.

Background technique

Circuit services include primary, secondary, and tertiary services, such as E1/T1 for primary. Circuit switching services are sensitive to transmission delay and delay jitter, and the existing packet switching network cannot meet the requirements of traditional circuit services on delay and jitter. How to efficiently transmit circuit services in the packet network, especially in the EPON system, is an urgent problem to be solved.

Since the EPON system carries Ethernet services, it is very difficult to realize the transmission of circuit services in the EPON system. The actual situation is that in the existing EPON technical solutions, there is no access problem involving circuit services, and there is no corresponding equipment is put into use.

In terms of providing circuit services in packet-switched networks, current research in the world is to realize circuit service transmission at the third layer (IP layer) of the ISO model. The efficiency is not high, and the fatal weakness is that the quality of service (Quality of Service, QoS for short) of the circuit business cannot be fully guaranteed at this stage.

EPON can carry circuit services such as E1/T1 by directly mapping the circuit services to the physical layer transmission scheme, but in this way, the physical layer is no longer a pure Ethernet frame, which is incompatible with the traditional Ethernet environment. It is bound to affect the application range of Ethernet.

Contents of the invention

The purpose of the present invention is to design a method for transmitting circuit services on an Ethernet-based passive optical network, to realize the access of circuit services (such as E1/T1) on the Ethernet-based passive optical network, and effectively The transmission circuit service provides carrier-class service quality circuit service while providing Ethernet data service, realizes the integrated transmission and access of Ethernet data service and circuit service, and reduces the construction and operation and maintenance costs of the access network.

The technical solution for realizing the object of the present invention is as follows: a method for transmitting circuit services on an Ethernet-based passive optical network is to transmit the circuit services on an Ethernet wireless network composed of an optical fiber line terminal, an optical distribution network, and a plurality of optical network units. The access circuit service data on the source optical network includes signal transmission in the downstream direction from the optical fiber line terminal to the optical network unit, and signal transmission in the upstream direction from the optical network unit to the optical network unit, and is characterized in that:

The signal transmission in the downlink direction includes the following processing steps:

A1. The optical fiber line terminal uses the service clock _fs to encapsulate the circuit service data into the data area of the Ethernet MAC frame, and at the same time encapsulates the Ethernet source address, destination address and time label value 1 in the Ethernet MAC data frame;

A2. The optical fiber line terminal sends the MAC frame of the circuit service data according to the bandwidth allocated to the circuit service data and the sending time slot;

A3. The optical network unit extracts the circuit service data from the circuit service data MAC frame through decapsulation processing;

A4. Optical network unit independent service time labeling method, the clock used has nothing to do with the system clock, use the time label value 1 to generate a service clock f _s2 synchronized with the service clock f _s of the optical fiber line terminal, and output the extracted circuit service data;

The signal transmission in the downlink direction includes the following processing steps:

B1. The optical network unit utilizes the service clock f _s2 to encapsulate the circuit data into the data area of the Ethernet MAC frame, and simultaneously encapsulates the source address and the destination address in the Ethernet MAC data frame;

B2. The optical network unit sends the circuit service data MAC frame according to the bandwidth allocated to the circuit service and the sending time slot;

B3. The optical fiber line terminal extracts the circuit service data from the circuit service data MAC frame through decapsulation processing;

B4. The optical fiber line terminal uses the service clock f _s to output the extracted circuit service data.

The present invention comprehensively considers the following two situations: the purpose of the EPON bearing circuit service is to realize the transparent transmission of the circuit service between the remote optical network unit (Optical Net Unit, ONU for short) and the local optical line terminal (OpticalLine Terminal OLT) , does not require circuit services to penetrate the metropolitan area network; accessing circuit services at the physical layer has poor compatibility, and accessing circuit services at the IP layer cannot guarantee the QoS of circuit services (as explained in the background technology). Transport circuit services at Layer 2.

The method for transmitting circuit services on the second layer of the present invention is to encapsulate the circuit service data into a standard Ethernet frame (circuit data MAC frame) at the sending end, and transmit them in unison with other Ethernet frames carrying data services, and then rely on distinguishing services The priority dynamic bandwidth allocation algorithm, or the static bandwidth allocation algorithm that guarantees the bandwidth according to the connection configuration, guarantees the circuit quality of service (QoS); at the receiving end, decapsulates the circuit data MAC frame to restore the circuit data. The method of the present invention adopts the independent service time label method to realize the synchronization of the circuit service, in the OLT side equipment, by encapsulating the time label value 1 in the circuit data MAC frame at the same time, and using the time label value 1 in the ONU side equipment to generate and OLT The service clock f _s2 synchronized with the service clock f _s of the side equipment solves the synchronization and timing of the transmission circuit data MAC frame between the two ends.

The method adopted in the invention can ensure the service quality of the circuit service, and the technical performance index of the circuit service interface can meet the requirements of relevant norms at home and abroad. The bandwidth allocation control part of the Ethernet-based passive optical network allocates bandwidth to ensure that circuit services are not affected by other Ethernet data frames during transmission. The method of the present invention can be applied in EPON system and other Ethernet data services and the integrated transmission system of circuit service, moreover, in any Ethernet-based network that can provide the synchronous method of the present invention, also can apply the technology of the present invention plan.

Description of drawings

Fig. 1 is a schematic diagram of the location of the circuit service access part at the central office (OLT side) in the EPON;

Fig. 2 is a schematic diagram of the location of the remote (ONU side) circuit service access part in EPON;

Fig. 3 is a schematic diagram of an implementation process of circuit service access in EPON;

Fig. 4 is a schematic diagram of the mechanism and principle of realizing timing synchronization of circuit services between endpoints by adopting the independent service time label method in the present invention.

Detailed ways

The circuit service access is completed by the service access port of the user end and the service port of the central office. There is a corresponding relationship between these two ports, and different corresponding relationships correspond to different connections. In this way, the central office can be configured conveniently. connected. For circuit services, Ethernet source addresses and destination addresses can be assigned according to the correspondence between the two service endpoints.

At the sending end, the circuit service data entering the EPON is written into the cache circuit, and the circuit data is encapsulated by Ethernet MAC at a fixed cycle, and the circuit service data is adapted to the Ethernet MAC (Media Access Control, Media Access Control) through the encapsulation process. Control layer, which is a sublayer of the Ethernet data link layer) in the data area of the frame; the Ethernet MAC frame containing the circuit data reaches the sending port through the switching process of the switching chip, and obtains the sending bandwidth (or time slot) of this cycle After that, it is sent to the receiving end through the transmission line.

At the receiving end, through the exchange chip or through the search of the destination address, determine the processing unit corresponding to the MAC frame encapsulated with circuit data, and send it to the processing unit; The circuit service data in the circuit is extracted, written into the buffer processing circuit, and the jitter introduced in the data transmission process is smoothed; finally, according to the circuit service clock synchronized with the sending end, the data is continuously output according to the corresponding circuit service specifications and standards. Through these processes, the transparent transmission of circuit services in EPON is realized.

Referring to Figure 1 and Figure 2, the position of the circuit service access part in EPON is explained. The OLT side adopts the structure shown in Figure 1, and the OLT side of the EPON mainly includes a CPU module 11, a switch module 12, a PON interface module between an optical signal (PON interface) and an Ethernet signal (Ethernet interface) and a system control module 13, and Ethernet interface module (Gigabit/100M Ethernet interface and Ethernet interface) 14, the circuit service access part 15 of the present invention transmits multi-channel circuit data to the switching module 12, and the circuit service access part 15 mainly It includes functional modules such as a circuit interface module, a circuit service adaptation module, and an Ethernet interface module, and obtains circuit service synchronization with the module 13 through the circuit service synchronization module. The design of the circuit service access part on the ONU side can be completely the same as that on the OLT side, that is, the structure shown in FIG. 1 is adopted. However, in the specific implementation process, in order to reduce the cost on the ONU side, the structure shown in FIG. 2 can be adopted, and there is no switching module 12 in the ONU side structure shown in FIG. 2 .

The circuit service access part 15 is directly mapped to the Ethernet physical (MAC) layer, sends circuit service data, and extracts valid data in the MAC frame containing the circuit service data and sends it to the circuit interface module. The PON interface module is responsible for sending and receiving Ethernet MAC frames between optical fibers; the circuit service synchronization module realizes the synchronization of the circuit service clock on the ONU side and the OLT side.

Referring to FIG. 3 , the figure shows the main functional modules involved in the method of the present invention and the specific flow for their realization. The EPON system includes an OLT-side device 18 , an Optical Distribution Network (ODN) 10 and a plurality of ONU-side devices 20 .

The structure shared by the OLT side 18 and the ONU side 20 includes circuit service interface processing modules 1, 14, adaptation packaging processing parts 2, 17, synchronization and clock processing circuits 3, 12, circuit service control and OAM (operation and management) Modules 4, 16, sending control circuits 5, 15, sending related processing circuits 6, 19, decapsulation processing parts 7, 13, Ethernet receiving processing circuits 9, 11, wherein the OLT side 18 also includes a switching processing part 8.

After the system is initialized, the circuit service control and OAM module 4 on the OLT side, and the ONU side circuit service control and OAM module 16 are responsible for communication and message processing with the system network management, and configure the adaptation encapsulation processing parts 2 and 17 according to the requirements of the system network management. Connect the ports of OLT and ONU that have opened circuit services through the form of Ethernet source address and destination address, and process other OAM information such as alarms. In this way, the adaptive encapsulation processing part 2, 17 can encapsulate the circuit data into the Ethernet MAC frame according to the obtained source Ethernet address and destination address.

The encapsulated Ethernet source address and destination address are assigned by the system network management through the system software according to the correspondence between the circuit services between the optical fiber line terminal and the two ends of the optical network unit when the system is initialized, and are stored in the optical fiber line terminal and the optical network unit. in local storage in . In the normal operation stage of the system, the network management can also adjust or reconfigure the corresponding relationship between the optical fiber line terminal and the circuit service between the two ends of the optical network unit through the same method.

As shown in the figure, the signal transmission in the downstream direction is completed by the OLT downstream sending circuit (part of the circuit in device 18), the ONU downstream receiving circuit (part of the circuit in device 20) and the optical distribution network (ODN) 10, that is, the OLT side to Signal transmission in the direction of the ONU side.

The signal transmission process is: the circuit data enters the OLT side equipment 18 of the EPON through the circuit service interface processing module 1;

Adapt package processing part 2 to obtain circuit data from 1, 1->2;

In the adaptive encapsulation processing part 2, under the control of the circuit service control and the OAM module service clock _fs , the circuit data is first buffered for a time T of the encapsulation cycle, and then these data are encapsulated into the data area of the Ethernet MAC frame. During the encapsulation process, the address mapping information written during initialization is read from the local memory, and the source address and destination address are written into the MAC frame; the length value of the MAC data area is written to the length/type byte of the Ethernet MAC frame; Encapsulate the time tag value 1 generated by the synchronization and clock processing circuit 3 into the MAC frame; calculate and insert the frame check sequence (FCS); finally send the MAC data frame encapsulated in the defined form of the Ethernet MAC frame to the switching processing part 8, 2 -> 8.

To realize the access of circuit services in EPON, it is necessary to ensure the timing synchronization of the circuit services at both receiving and sending ends. The basic method to achieve timing synchronization is the time tag value method, which can be implemented in two different application forms: one is to directly provide time tag values for single-channel circuit services, and synchronize each channel of business separately; the other One is to multiplex the accessed multiple circuit services into high-order group services (for example, multiplex 4 E1 channels into 8Mbit/s secondary groups), and use the time tag value method for high-order groups to realize timing synchronization. Timing synchronization is realized between the multiplexed circuit service and the circuit service recovered by the peer tap;

In the switching processing part 8, under the control of the circuit service control and the OAM module 4, different Ethernet data are switched to different ports according to the destination MAC address (the MAC frame that has encapsulated the circuit data is switched to a certain port to Differentiate other MAC frames without encapsulating circuit data), and send the MAC frame encapsulating circuit data to the sending control circuit 5, 8->5;

The sending control circuit 5 sends the data to the sending related processing circuit 6 according to the bandwidth allocated to the circuit data and the sending time slot, 5->6. The QoS of the circuit service is mainly realized through bandwidth guarantee and other auxiliary measures. For the bandwidth guarantee, in the EPON system using the dynamic bandwidth allocation mechanism, among all the downlink data on the OLT side, the Ethernet MAC frame (referred to as the circuit service data MAC frame) that encapsulates the circuit service has the highest priority, and the priority of transmission is also the highest. Highest, when the transmission control circuit 5 detects that there is a circuit service data MAC frame, check whether there is data being sent in the sending buffer, if there is no data to send, then start to send the circuit service data MAC frame; if there is data being sent, the current transmission The frame is not truncated, and after the frame is sent, the circuit service data MAC frame is sent.

Send related processing circuit 6, after performing parallel/serial conversion, 8B/10B encoding processing and electrical/optical conversion, send to optical distribution network (ODN) 10, 6->10, and finally transmit to the Ethernet reception of ONU side equipment 20 In the processing circuit 11, 10->11;

Ethernet reception processing circuit 11, under the control of the circuit service control and OAM module, forwards data of different service types to different modules (used to distinguish other MAC frames without encapsulating circuit data and MAC frames encapsulating circuit data) , transfer the MAC frame encapsulated with the circuit data to the decapsulation processing part 13, 11->13, and extract the time tag value 1 of the OLT example and send it to the synchronization and clock processing circuit 12;

The decapsulation processing part 13, under the control of the circuit service control and OAM module, extracts valid circuit data from the MAC frame, first sends this part of data to the local memory for buffering, and smoothes the data by buffering data belonging to adjacent cycles Jitter; then utilize the circuit service clock (f _s2 ) synchronous with the OLT side provided by the synchronization and clock processing circuit 12 to sequentially read from the local memory, and output to the circuit service interface processing module 14, 13->14;

The circuit service interface processing module 14 outputs the circuit data through the corresponding port, so as to complete the downlink transparent transmission of the circuit data in the EPON system.

As shown in Figure 3, the signal transmission in the upstream direction is completed by the ONU upstream sending circuit (part of the circuit in the device 20), the OLT upstream receiving circuit (part of the circuit in the device 18) and the optical distribution network (ODN) 10, that is, the ONU Signal transmission to the OLT direction.

The circuit data enters the ONU side device 20 of EPON through the circuit service interface processing module 14, and the adaptation encapsulation processing part 17 obtains the circuit service data from 14, 14->17;

In the adaptive encapsulation processing part 17, under the control of the circuit service control and OAM module, the circuit data is cached for a time T of an encapsulation cycle, and then these data are encapsulated into the data area of the Ethernet MAC frame. In the encapsulation process, the address mapping information written during initialization will be read from the local memory, and the source address and the destination address are written in the MAC frame; calculate and insert the frame check sequence (FCS); utilize the synchronization and clock processing circuit 13 to generate The service clock (f _s2 ), the circuit data MAC frame encapsulated according to the defined form of the Ethernet MAC frame is sent to the transmission control circuit 15, 17->15 by the adaptation encapsulation part 17;

The transmission control circuit 15 transmits the MAC frame containing the circuit data to the transmission-related processing circuit 19 according to the bandwidth allocated to the circuit data and the transmission time slot, 15->19. During the ONU upstream transmission process, the transmission bandwidth of the circuit data MAC frame is guaranteed through the bandwidth allocation mechanism, and the circuit data MAC frame is sent to the OLT after obtaining the allocated bandwidth. In EPON that adopts static bandwidth allocation, the circuit service is processed according to the connection configuration, that is, the bandwidth of the circuit service is fixed. After the system is synchronized, the sending time of the OLT and the ONU circuit data MAC frame is fixed. In this way, the circuit data MAC frame can be periodically This is a strong QoS guarantee measure. Other measures for QoS guarantee include: the circuit data MAC frame has the highest priority at the switch chip, and the priority is achieved by inserting the virtual local area network (VLAN) priority. After the circuit data MAC frame arrives at the receiving end and is decapsulated, it is cached in the memory For a certain period of time, smooth the jitter caused by the Ethernet packet transmission method, and completely smooth out the delay jitter;

Transmit related processing circuit 19, after performing parallel/serial conversion, 8B/10B encoding processing and electrical/optical conversion, send to optical distribution network (ODN) 10, 19->10, and finally transmit to OLT side equipment 18 upstream receiving circuit Ethernet receiving processing circuit 9, 10->9;

The Ethernet receiving processing circuit 9 realizes Ethernet physical layer processing, and then sends the processed data to the switching processing part 8, 9->8;

Through the switching processing part 8, under the control of the circuit service control and OAM module, the MAC frame encapsulated with circuit data is switched to the decapsulating processing part 7, 8->7;

The decapsulation processing part 7, under the control of the circuit service control and OAM module, extracts valid circuit data from the MAC data frame, and sends this part of the data to the local memory cache, and smooths the time delay by caching data of different cycles Jitter; then use the service clock (f _s ) provided by the synchronization and clock processing circuit 3 to sequentially read data from the memory, and output to the circuit service interface processing module 18, 7->18;

The circuit service interface processing module 18 outputs the circuit data through the corresponding port, so as to complete the uplink transparent transmission of the circuit data in the EPON system.

Fig. 4 shows the principle that the present invention realizes synchronization of circuit services between two endpoints (OLT and OUN) by utilizing the independent service time label method. The clock used in the independent service time labeling method has nothing to do with the system clock. In EPON, the circuit service clock of each ONU should be synchronized with the circuit service clock of the OLT side.

The structure of the synchronization and clock processing circuit 3 of the OLT side equipment includes an OLT circuit service clock (f _s ) generating circuit 41, a frequency multiplier (a clock that generates a time stamp value of 1) 42, a counter 43, and a time stamp value of 1 is read and sent The circuit 45 and the time stamp value 1 transmission control circuit 44; the structure of the synchronization and clock processing circuit of the ONU side equipment, including the ONU circuit service clock (f _s2 ) generation circuit 51, the local clock (f _ts2 ) generation circuit 52, and a controllable counter 53 (generating time stamp value 2), frequency division controller 54, difference calculation circuit 55 between time stamp value 1 and time stamp value 2 and receiving processing circuit 56 of time stamp value 1.

The time stamp value 1 is obtained by reading the output value of the counter 43. The driving clock of this counter 43 is a positive integer multiple (f _ts ) of the service clock frequency (f _s ), and the counter 43 counts once per clock cycle to form a time Tag value 1 (OLT timestamp timestamp)).

The basic principle of realizing synchronization is: the OLT side utilizes the service clock f _s to perform frequency multiplication to obtain the time stamp clock f _ts ; a certain 8-bit counter 43 calculates the number of cycles passed by the f _ts clock to generate a time stamp value of 1. 1 Under the control of the sending control circuit 44, the read sending circuit 45 sends the time stamp value 1 to the ONU side. The transmission of the time stamp value 1 can be transmitted through a special MAC frame, or can be transmitted together with a MAC frame containing circuit data or other network management MAC frames;

There is f _ts2 local clock on the ONU side device circuit board, and the nominal frequency of f _ts2 and time label 1 clock f _ts is the same, and the frequency division number when f _ts2 is controlled by a frequency division controller 54 to obtain the service clock f _s2 ; there is an 8-bit controllable counter 53 at the same time, driven by the local clock f _ts2 , this controllable counter 53, the output generates the time stamp value 2 of the ONU side; when the ONU side equipment receives the time of the OLT side by the receiving processing circuit 56 When the tag value is 1, read the local time tag value 2, and the time tag difference calculation circuit 55 compares these two values to obtain a difference, and utilizes the difference to set the value of the ONU controllable counter 53 to be equal to the time tag value 1 Same; at the same time, the difference after comparison is sent to the frequency division controller 54, and the frequency division controller 54 obtains the specific parameters for adjusting the frequency division of the frequency division controller 54 according to the difference, controls the frequency division number, obtains the service clock f _s2 , and realizes Synchronization of circuit service clocks f _s and f _s2 on the ONU and OLT sides.

Taking the transmission of E1 circuit signals as an example, the process of encapsulating circuit data in MAC frames to form circuit data MAC frames in the technical solution of the present invention will be further described. There are two implementations:

The first way: at the sending end, carry out Ethernet MAC encapsulation for each E1 respectively; The E1 data frame after the encapsulation (Ethernet MAC frame encapsulating E1 data) passes through the exchanging process of exchanging processing part (8) exchanging chip and After the line (10) between the OLT and the ONU, it arrives at the receiving end; at the receiving end, the E1 data frame after the encapsulation is decapsulated, extracts the E1 valid data, and performs buffer processing; then utilizes the service clock synchronous with the sending end to send the E1 send it out. In this way, a synchronous service clock must be provided for each E1 channel separately, and the time tag value method is used to realize synchronization; if the data of some E1 channels come from the same switch, then these E1 data channels can share one synchronous service clock.

The second method: this method uses the secondary group processing chip to multiplex 4 channels of E1 into a secondary group data stream of 8.448Mbit/s, and then perform Ethernet encapsulation on the secondary group data stream (hereinafter referred to as this MAC frame is E1 data frame). This method only requires synchronization on the 8.448Mbit/s signal, which can ensure that each E1 is synchronized on the OLT side and the ONU side of the EPON, and the 8.448Mbit/s secondary transmission between the OLT and the ONU is realized by using the time tag value method. Group data synchronization. When processing according to the connection configuration, after the bandwidth is allocated, the sending position is fixed. The E1 data frame has the highest priority at the switch chip, and the priority is realized by inserting the virtual local area network (VLAN) priority at the port of the switch chip. After the OLT or ONU receives the E1 data frame of the opposite end, it performs decapsulation processing, extracts the secondary group data, writes it into the memory cache, and caches it for a certain period of time to smooth the delay and jitter; use the 8.448MHz clock synchronized with the sending side , Write the data of 8.448Mbit/s from the cache area into the secondary group processing circuit, and then restore the 4-way E1 data by the secondary group processing circuit.

At this time, the source address and destination address used by the secondary group for MAC encapsulation are obtained by the network management through system software configuration. The network management configures the corresponding relationship between the circuit service ports at both ends of the OLT and the ONU. After the configuration, the source MAC address and the corresponding destination MAC address of the port are sent to the corresponding processing circuit.

The method of the present invention realizes the access technology of the circuit service at the Ethernet MAC layer, is an important part of the multi-service access of the EPON system, technically realizes the transmission problem of the circuit switching service in the packet network in the EPON system, and satisfies The time delay and time delay jitter requirements of the circuit service solve the problem of synchronous timing, and provide the circuit service of the quality of telecommunication service in the connectionless packet network. The scheme design and its main modules in the present invention have reusability, compatible with OLT and ONU both sides, EPON system compatible with static bandwidth allocation algorithm (SBA) and dynamic bandwidth allocation algorithm (DBA), compatible with EPON system and other Ethernet, circuit A system for integrated business transmission.

The method of the invention can ensure the quality of service (QoS) of the circuit service, and the technical performance index of the circuit service interface can meet the requirements of relevant specifications at home and abroad, and the synchronization method in the method of the invention can be applied to any network based on Ethernet.

Claims (16)

1. A method for transmitting circuit services on an Ethernet-based passive optical network is to insert circuit service data on an Ethernet passive optical network composed of an optical fiber line terminal, an optical distribution network and a plurality of optical network units , including signal transmission in the downstream direction from the optical fiber line terminal to the optical network unit, and signal transmission in the upstream direction from the optical network unit to the optical network unit, characterized in that: The signal transmission in the downlink direction includes the following processing steps: A1. The optical fiber line terminal uses the service clock _fs to encapsulate the circuit service data into the data area of the Ethernet MAC frame, and at the same time encapsulates the Ethernet source address, destination address and time label value 1 in the Ethernet MAC data frame; A2. The optical fiber line terminal sends the MAC frame of the circuit service data according to the bandwidth allocated to the circuit service data and the sending time slot; A3. The optical network unit extracts the circuit service data from the circuit service data MAC frame through decapsulation processing; A4. The optical network unit adopts the independent service time label method, and the clock used has nothing to do with the system clock. The time label value 1 is used to generate the service clock f _s2 synchronized with the service clock f _s of the optical fiber line terminal, and output the extracted circuit service data; The signal transmission in the uplink direction includes the following processing steps: B1. The technical network unit utilizes the service clock f _s2 to encapsulate the circuit data into the data area of the Ethernet MAC frame, and simultaneously encapsulates the source address and the destination address in the Ethernet MAC data frame; B2. The optical network unit sends the circuit service data MAC frame according to the bandwidth allocated to the circuit service and the sending time slot; B3. The optical fiber line terminal extracts the circuit service data from the circuit service data MAC frame through decapsulation processing; B4. The optical fiber line terminal uses the service clock f _s to output the extracted circuit service data. 2. a kind of circuit service according to claim 1 transmits the method on the passive optical network based on Ethernet, it is characterized in that: in described step A1, B1, the Ethernet source address and destination address of encapsulation, are When the system is initialized or the system is running normally, the system network management will allocate or adjust and reconfigure through the system software according to the corresponding relationship between the circuit services between the optical fiber line terminal and the two ends of the optical network unit, and save it in the optical fiber line terminal and the optical network unit in local storage. 3. a kind of circuit service according to claim 2 transmits the method on the passive optical network based on Ethernet, it is characterized in that: be by the circuit service control and OAM module in the optical fiber line terminal and the optical network unit, by and For the communication and message processing of the system network management, the adaptive encapsulation processing part is configured according to the requirements of the system network management, and the ports of the optical fiber line terminal and the two ends of the optical network unit that open the circuit service are connected through the Ethernet source address and the destination address. 4. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that in said steps A1 and B1, the circuit service data is first buffered for one encapsulation cycle time , and then periodically encapsulate the circuit service data according to the encapsulation cycle. 5. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that in said steps A1, B1, said encapsulation also includes inserting a frame check sequence and Length/type bytes. 6. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that in said step A1, the encapsulation time tag value 1 is to provide time for a single circuit service tag value 1. 7. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that in said step A1, the encapsulation time stamp value 1 is for circuit services after multiplexing Higher order group circuit services provide a time stamp value of 1. 8. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in the step A2, the sent time stamp value 1 is transmitted through a special MAC frame , or transmitted together with the MAC frame containing the circuit service data, or transmitted together with other network management MAC frames. 9. a kind of circuit service according to claim 1 transmits the method on the passive optical network based on Ethernet, it is characterized in that: the time stamp value 1 in the described step A1 is multiplied by the service clock f _s The time stamp clock f _ts is generated frequently, and then the counter calculates the number of cycles passed by the time stamp clock f _ts to obtain the time stamp value 1. 10. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in the steps A1 and B3, the switching processing part is based on the destination MAC address The encapsulated circuit service data MAC frame is switched to a predetermined port, and the port does not transmit the Ethernet frame carrying the data service. 11. The method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in the steps A2 and B2, the circuit service data MAC frame is the same as The Ethernet frame carrying the data service is uniformly transmitted under the control of the system. 12. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in said steps A2 and B2, a dynamic bandwidth allocation mechanism is used to allocate bandwidth to circuit services, Ethernet MAC frames encapsulating circuit service data have the highest sending priority. 13. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in said steps A2 and B2, a static bandwidth allocation mechanism is used to allocate a fixed bandwidth to the circuit services. Bandwidth, the Ethernet MAC frame encapsulating circuit service data is sent periodically at a fixed time. 14. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in the step A3, the encapsulated circuit service data MAC frame is searched for the purpose The address is used to determine the processing unit corresponding to the optical network unit for sending. 15. A method for transmitting circuit services on an Ethernet-based passive optical network according to claim 1, characterized in that: in the steps A3 and B3, the extracted circuit service data is first sent to a local memory Cache for smoothing delay jitter. 16. the method for a kind of circuit business according to claim 1 is transmitted on the passive optical network based on Ethernet, it is characterized in that: in the described step A4, adopt the independent time stamp method to generate the service clock _f synchronous with f _s2 further includes: generating a local clock f _ts2 with the same nominal frequency as the time stamp clock f _ts ; driving a controllable counter by the local clock f _ts2 to generate time stamp value 2; calculating the time stamp value 1 and time stamp value 2 Use this difference to set the time stamp value 2 output by the controllable counter to be the same as time stamp value 1, and use this difference to adjust the frequency division number of f _ts2 by the frequency division controller to obtain the service clock f _s2 .

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