CN101431385A - Frequency and time synchronization method for passive optical network - Google Patents

Frequency and time synchronization method for passive optical network Download PDF

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Publication number
CN101431385A
CN101431385A CN 200810142096 CN200810142096A CN101431385A CN 101431385 A CN101431385 A CN 101431385A CN 200810142096 CN200810142096 CN 200810142096 CN 200810142096 A CN200810142096 A CN 200810142096A CN 101431385 A CN101431385 A CN 101431385A
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time
optical network
described optical
network unit
line terminal
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CN101431385B (en
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李明生
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ZTE Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0658—Clock or time synchronisation among packet nodes
    • H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
    • H04J3/0667—Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q2011/0088—Signalling aspects

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Small-Scale Networks (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Optical Communication System (AREA)

Abstract

The invention discloses a method for synchronizing frequency and time of a passive optical network. The method comprises the following steps: an optical line terminal periodically transmits a protocol message with a time stamp to an optical network unit, dynamically measures range information used for maintaining the passive optical network, and acquires time deviation between the optical line terminal and the optical network unit in real time; real-time and dynamic compensation for the time deviation is carried out on the optical network unit, so that the frequency and the time of the optical network unit is synchronized to the optical line terminal. As the range information of the passive optical network is utilized, IEEE1588 protocol is combined, synchronous transfer of time and frequency between devices on the passive optical network can be realized so as to ensure that the optical network unit is accurately synchronized to the optical light terminal on frequency and time, and each optical network unit has the same frequency and time.

Description

A kind of EPON medium frequency and the method for synchronous of time
Technical field
The present invention relates to a kind of EPON method for synchronous in the field of wireless communications, relate in particular to a kind of EPON medium frequency and the method for synchronous of time.
Background technology
Passive optical network PON (Passive Optical Network) technology is the optical fiber access technology of a kind of point to multiple spot, it is by optical line terminal OLT (the Optical Line Terminal of office's net side, optical line terminal), the optical network unit ONU of user side (Optical Network Unit, optical network unit) and Optical Distribution Network ODN (Optical Distribution Network, Optical Distribution Network) form.
EPON has polytype, roughly can be divided into wavelength-division PON, power P ON and these the two kinds mixing PON that mutually combine, and wherein power P ON because of the agreement difference of link layer, is divided into APON, GPON and EPON again.
With power P ON is example, its descending general employing time division multiplexing and multiplexer TDM (TimeDivision Multiplex and Multiplexer) broadcast mode, and up general employing time division multiple access TDMA (Time Division Multiple Access) access way, and can form various topological structures such as tree type, star-like and bus-type neatly, most typical structure is a tree structure.
The so-called PON that mixes be meant in an Optical Distribution Network ODN to have a plurality of power P ON simultaneously, and the wavelength that these power P ON is adopted is all inequality.
Passive optical network PON also can be used as the bearer network that inserts section, and Fig. 1 is exactly the typical networking of passive optical network PON in mobile communication, and passive optical network PON need be finished the transmission of two tasks: the transmission of Business Stream; The transmission of clock synchronization gives the transmission and the method for salary distribution of clock stream among Fig. 1.
Yet, itself has only realized Frequency Synchronization the passive optical network PON procotol, the optical network unit ONU that is user side is synchronized with innings optical line terminal OLT of net side, but because the phase difference of the optical network unit ONU of each user side is arbitrarily, be that the passive optical network PON procotol can't be supported time synchronized between the two, so also just can't satisfy mobile communication or the free network that requires synchronously.
The simultaneous techniques of EPON includes two aspect implications in the communication system this moment, i.e. frequency and time two parts:
A, frequency: when Frequency Synchronization is meant in the EPON processing signals such as transmission, exchange for avoiding slip required Frequency Synchronization separately.So-called slip refers to, when the clock rate difference of two digital local exchange installations surpasses certain numerical value in the digital network, make when the buffer storage reading and writing clock generating speed difference of received signal switch, this difference surpass a certain set point, will cause the error code or the step-out that receive digital stream;
B, time: time synchronized is meant that the clock of equipment in the EPON and World clock are harmonious, also claims Phase synchronization.
Communication network is to all having requirement synchronously between the communication system generally speaking, and particularly between the wireless device, the wireless technology that following table has been listed various wireless devices is to clock frequency and synchronous specific requirement of time:
Wireless technology The Clock Frequency Accuracy requirement The time synchronized requirement
GSM 0.05ppm NA
WCDMA 0.05ppm NA
CDMA2000 0.05ppm 3us
TD-SCDMA 0.05ppm 1.5us
WiMax 0.05ppm 1us
LTE 0.05ppm Tend to adopt time synchronized
How to guarantee in EPON that frequency and time between the various wireless devices are synchronous,, just become to press at present the problem of solution to satisfy the network that mobile communication or free synchronous condition require.
Therefore, prior art still haves much room for improvement and develops.
Summary of the invention
The problem to be solved in the present invention is, a kind of EPON medium frequency and the method for synchronous of time are provided, with solve in EPON, can not guarantee ONU frequency and on the time precise synchronization in the problem of OLT.
Technical scheme of the present invention is as follows:
A kind of EPON medium frequency and the method for synchronous of time may further comprise the steps:
A, optical line terminal periodically send ranging information between that the protocol massages that has timestamp and optical line terminal kinetic measurement obtain and the optical network unit to optical network unit, obtain time deviation between described optical line terminal and the described optical network unit in real time by the Time Calculation to described protocol massages;
B, the enterprising line time deviation of described optical network unit in real time, dynamic compensation, make the frequency of described optical network unit and time be synchronized with optical line terminal.
Described method for synchronous, wherein, described steps A specifically also comprises:
Local T1 constantly when A1, described optical line terminal will send protocol massages first bit is inserted in the timestamp territory of the protocol massages that sends;
Local T2 constantly when A2, last bit of the described protocol massages of described optical network unit recorder;
A3, described optical line terminal are calculated in real time and are worth two-way time between itself and the described optical network unit RTT as described ranging information and send to described optical network unit;
A4, described optical network unit calculate the time deviation value Offset between described optical line terminal and the described optical network unit:
Offset＝T2-T1-RTT/2。
Described method for synchronous, wherein, described steps A 3 specifically also comprises:
A31, the described optical line terminal local echoing time T of measurement ResponseT when sending distance measuring signal this locality for it 0T during to its receiving feedback signals this locality 2Time difference (t 2-t 0);
A32, the local stand-by period T of the described optical network unit of measurement WaitT during local when receiving the distance measuring signal that described optical line terminal sends for it 0T during local when sending the feedback signal of described distance measuring signal to it 1Time difference (t 1-t 0);
Be worth RTT the two-way time between A33, the described optical line terminal of definition and the described optical network unit is up time T UpstreamWith downgoing time T DownstreamSum equals described optical line terminal local echoing time T ResponseWith the local stand-by period T of described optical network unit WaitPoor:
RTT＝T downstream+T upstream
＝T response-T wait
＝(t 2-t 0)-(t 1-t 0)
＝t 2-t 1。
Described method for synchronous, wherein, further comprising the steps of:
Before C, the described steps A, the IEEE1588 clock synchronization protocol of operation standard makes the frequency of described optical line terminal and time be synchronized with described higher level equipment between described optical line terminal and higher level equipment that it is connected; And/or after the described step B, IEEE1588 clock synchronization protocol of operation standard between the following attached device that described optical network unit is connected with it makes the described frequency and the time of attached device down be synchronized with described optical network unit.
Described method for synchronous, wherein, described step C specifically also comprises:
C1, described higher level equipment send the protocol massages that has timestamp to described optical line terminal constantly at the T1` of local zone time, and described optical line terminal receives this protocol massages constantly at the T2` of local zone time; And/or described optical network unit sends the protocol massages that has timestamp to described attached device down constantly at the T1` of local zone time, and described attached device down receives this protocol massages constantly at the T2` of local zone time;
C2, described higher level equipment send tracking message to described optical line terminal; And/or described attached device down sends tracking message to described optical network unit;
Constantly to described higher level equipment transmission lag request message, described higher level equipment is answered message to described optical line terminal feedback delay constantly at the T4` of local zone time at the T3` of local zone time for C3, described optical line terminal; And/or described down attached device at the T3` of local zone time constantly to described optical network unit transmission lag request message, described optical network unit is answered message to described attached device feedback delay down constantly at the T4` of local zone time;
C4, calculate between described optical line terminal and its higher level equipment and/or described optical network unit and its time deviation value Offset` between attached device down:
Offset`＝(T2`-T1`+T3`-T4`)/2。
Described method for synchronous, wherein, step C specifically also comprises:
C5, periodically sending protocol massages message down between the attached device between described optical line terminal and its higher level equipment and/or at described optical network unit and its, dynamically, the real-time update time deviation;
C6, described optical line terminal and/or the described down enterprising line time deviation of attached device dynamically, real-Time Compensation.
Described method for synchronous wherein, uses hardware to receive and dispatch when transmitting described protocol massages that has a timestamp or described ranging information.
Described method for synchronous, wherein, in following style interface, use field programmable gate array hardware or application-specific integrated circuit (ASIC) hardware to carry out extraction, insertion, transmission or the reception of described protocol massages: the first line of a couplet Uplink interface of optical line terminal or the uni interface of optical network unit.
Described method for synchronous wherein, adopts the phase locked algorithm of CPU, according to the output of corresponding time deviation control figure phase-locked loop, and needed system clock of generation system and control signal.
Described method for synchronous, wherein, described optical line terminal sends described ranging information for described optical network unit by the physical layer operations management maintenance PLOAM message of gigabit passive optical network or the ethernet operation management maintenance Ethernet OAM message of Ethernet passive optical network.
A kind of EPON medium frequency provided by the present invention and the method for synchronous of time, owing to utilized the distinctive ranging information of passive optical network PON network, the IEEE1588 clock synchronization protocol of combined standard, avoided the asymmetric property of passive optical network PON network, realized in the synchronous transmission of time and frequency between the equipment at different levels on the passive optical network PON network, precise synchronization is in optical line terminal OLT in frequency with on the time to have guaranteed optical network unit ONU, and each optical network unit ONU has identical frequency and time; And, the IEEE1588 clock synchronization protocol of operation standard between optical network unit ONU and its subordinate equipment, optical network unit ONU can also pass to subordinate equipment to frequency and time accurately, between the equipment that has guaranteed to connect under each optical network unit ONU identical frequency and time is arranged also.
Description of drawings
Fig. 1 is networking and the clock transitive graph of the PON of the inventive method at moving communicating field;
Fig. 2 is the IEEE1588 agreement realization mechanism figure of the inventive method;
Fig. 3 is the mechanism figure that realizes frequency and time precise synchronization between the PON network OLT of the inventive method and the ONU;
Fig. 4 is the range finding mechanism figure of the OLT of EPON system of the inventive method to ONU;
Fig. 5 is that a specific embodiment of the inventive method is realized schematic diagram.
Embodiment
Below with reference to shown in accompanying drawing, the embodiment of EPON medium frequency of the present invention and the method for synchronous of time is described in detail.
EPON medium frequency of the present invention and the method for synchronous of time, main core point is embodied in the method that the ranging information that adopted IEEE1588 clock synchronization protocol and PON EPON combines, known by prior art as for technology such as IEEE1588 protocol contents, do not repeated them here.
The specific embodiment of the present invention is based on mobile communications network or frequency is arranged and the synchronous network that requires of time, adopts IEEE1588 agreement realization frequency and time synchronous between the peer-to-peer network internal unit wherein:
1) hypothesis of characteristic symmetry Network Based adopts master-slave mode, stabs mark at the enterprising line time of sync packet Packet, the cycle clock issue, and the recipient carries out clock skew and measures and delay measurements;
2) point-to-point link can provide the highest precision, introduces boundary clock, and is irrelevant with delay and jitter as shown in Figure 1, reaches every jumping 10ns level time accuracy.
Its mechanism is as shown in Figure 2:
A) time deviation between supposition Master (main equipment) and the Slave (slave unit) is Offset`;
B) Master equipment sends the sync packet Packet that is with timestamp to Slave equipment constantly at its local T1`, and Slave equipment receives sync message constantly at its local T2`, sets up following equation thus:
T2`＝T1`+Delay`+Offset`-------------------(1)，
Wherein Delay` is the propagation delay time of sync message from Master to Slave equipment;
C) Master equipment sends to Slave equipment and follows the tracks of Follow_up message;
D) Slave equipment at local T3` constantly to Master equipment transmission lag request Delay_Req message;
E) Master equipment is answered Delay_Resp message to Slave equipment transmission lag constantly at its local T4`,
Set up following equation thus:
T4`＝T3`+Delay`-Offset`-------------------(2)；
F) associating equation (1) and (2) can be obtained the Offset` value:
Offset`＝(T2`-T1`+T3`-T4`)/2------------------(3)；
G) periodically between Master equipment and Slave equipment, send: sync message Sync, tracking Follow_up, delay request Delay_Req and delayed response Delay_Resp message,, real-time update Offset` value dynamic with regard to energy, thus keep Slave equipment on time and frequency, to be synchronized with Master equipment;
H), obtain the time accuracy of 10ns level between Master equipment and the Slave equipment in dynamic, the real-Time Compensation of the enterprising line time deviation of Slave equipment Offset`.
From the description of front as can be known, the IEEE1588 agreement is based on the hypothesis of network characteristic symmetry, promptly supposes the delay and jitter from Master equipment to Salve equipment, and is identical with delay and jitter from Slave equipment to Master equipment.Yet the PON network is not owing to following reason is not a peer-to-peer network, and at up direction big jittering component arranged, and the cycle that for example new ONU finds and registration is introduced windows, and causes the ONU upstream data to send and is delayed; And for example roll off the production line on the ONU and introduce the change of ONU uplink time slot position.At this moment, just can not be between the OLT and ONU of PON network, by operation IEEE1588 agreement guarantee ONU frequency and on the time precise synchronization in OLT.
General introduction in theory, the inventive method comprises following three big steps:
One, the IEEE1588 agreement of operation standard between the optical line terminal OLT (being called for short OLT herein) of office's net side and its higher level equipment guarantees the OLT frequency and is synchronized with higher level's network equipment on the time;
Two, operation core methed of the present invention between OLT and ONU, promptly OLT sends synchronization message to ONU, utilizes the ranging information of the ONU of PON network operation, just can obtain ONU with the time deviation Offset between the OLT; OLT periodically sends synchronization message to ONU, and cooperation OLT dynamically measures the distance of ONU, just can obtain the time deviation Offset of ONU and OLT dynamically, in real time; If in dynamic, the real-time compensation of the enterprising line time deviation of ONU Offset, just can realize that ONU frequency and time precise synchronization are in OLT;
Three, in the optical network unit ONU (being called for short ONU herein) of user side and its IEEE1588 agreement of operation standard between attached device down, just can guarantee down that precise synchronization is in ONU on attached device frequency and time.
By three above big steps, can and and be synchronized with a source synchronously accurately on the time in frequency between ONU and the following attached device, promptly OLT can track the most top time source.
Specifically, referring to Fig. 3, the performing step of PON network medium frequency of the present invention and time synchronization mechanism is as follows:
1, the clock synchronization IEEE1588 agreement of operation standard between OLT and coupled higher level's network equipment 301, higher level's network equipment 301 operates in the Master pattern, OLT operates in the Slave pattern, guarantee OLT frequency and on the time precise synchronization in higher level equipment:
A) time difference between supposition " higher level equipment " and the OLT is Offset`;
B) " higher level equipment " sends the sync message of being with timestamp to OLT constantly at its local T1`, and OLT receives sync message constantly at its local T2`, sets up following equation:
T2`＝T1`+Delay`+Offset`-------------------(1)，
Wherein Delay` is that the propagation delay time of sync message from " higher level equipment " to OLT is slow;
C) " higher level equipment " sends to OLT and follows the tracks of Follow_up message;
D) OLT at local T3` constantly to " higher level equipment " transmission lag request Delay_Req message;
E) " higher level equipment " answers Delay_Resp message to the OLT transmission lag constantly at its local T4`, sets up following equation:
T4`＝T3`+Delay`-Offset`-----------------(2)；
F) associating equation (1) and (2) is obtained the Offset` value:
Offset`＝(T2`-T1`+T3`-T4`)/2------------------(3)；
G) periodically between " higher level equipment " and OLT, send: sync message Sync, tracking Follow_up, delay request Delay_Req and delayed response Delay_Resp message, just dynamic, the real-time update Offset` value of energy;
H) OLT carry out time deviation Offset` dynamically, real-Time Compensation, just can realize that OLT is synchronized with " higher level equipment " in frequency and on the time.
At this moment, if OLT connects two " higher level equipments " simultaneously, just can realize the active and standby of clock source, the reliability of network is provided, the selection in master/backup clock source realizes according to the IEEE15888 agreement.
2, belong to asymmetrical network between OLT and the ONU, do not move the IEEE1588 agreement of standard, OLT is operated in the Master pattern of clock, and ONU operates in the Slave pattern, guarantee by the following method ONU frequency and on the time precise synchronization in OLT:
A) time difference of OLT and ONU is defined as Offset;
B) OLT sends the sync message Sync that is with timestamp to ONU constantly at its local T1, and ONU receives sync message Sync constantly at its local T2, sets up following equation:
T2＝T1+Delay+Offset------------------(1)，
Wherein Delay is that the propagation delay time of sync message Sync from OLT to ONU is slow;
C) OLT dynamically finds range to ONU, obtains the round distance R TT value between ONU and the OLT:
Delay＝RTT/2--------------------------(2)；
In the EPON system OLT and ONU distance R TT value test process and mechanism as shown in Figure 4, the computational process of RTT value just:
Set OLT response time T ResponseT when sending distance measuring signal for it is local 0T during to receiving feedback signals 2Time difference (t 2-t 0), ONU stand-by period T WaitT during local when receiving the distance measuring signal that OLT sends for it 0T during local when sending feedback signal to distance measuring signal to it 1Time difference (t 1-t 0), both local zone time t when wherein OLT dynamically finds range to ONU 0Be made as identically, also be t during local when promptly ONU is provided with it and receives distance measuring signal that OLT sends 0Hence one can see that, and OLT is to the downgoing time T of ONU DownstreamWith the up time T of ONU to OLT UpstreamSum is OLT response time T for coming and going distance R TT value ResponseWith ONU stand-by period T WaitPoor:
RTT＝T downstream+T upstream
＝T response-T wait
＝(t 2-t 0)-(t 1-t 0)
＝t 2-t 1
In addition, the round distance R TT value between ONU and the OLT also can adopt identical range measurement principle in the GPON system;
D) associating equation (1) and (2) can be obtained the Offset value:
Offset＝T2-T1-Rtt/2-----------------------(3)；
E) OLT periodically sends sync message Sync message to ONU, the RTT value between itself and ONU of OLT real time dynamic measurement simultaneously, and issue ONU, and ONU just can dynamic, real-time update Offset value;
F) in dynamic, the real-Time Compensation of the enterprising line time deviation of ONU Offset, just can realize that ONU is synchronized with OLT in frequency and on the time;
G) each ONU is synchronized with OLT, has just realized the precise synchronization of frequency and time between each ONU.
3, operation standard IEEE 1588 agreements between ONU and coupled " following attached device ", " following attached device " can frequency and on the time precise synchronization in ONU, at moving communicating field " following attached device " is exactly base station 302 among Fig. 3, step process between the identical OLT of the process of this step and the coupled higher level's network equipment 301 no longer repeats herein.
In order to guarantee time precision, the protocol massages of passing time is is all received and dispatched with hardware, Fig. 5 gives specific implementation example of the present invention, the first line of a couplet Uplink interface from the OLT and the application of PON interface on PON interface and the ONU and the several different aspects of uni interface respectively below is according to down direction and up direction explanation PON network medium frequency and the method for synchronous of time.
One) realization of first line of a couplet Uplink interface on the OLT or PON interface:
1) realization of Uplink interface:
Between last connecting port physical layer PHY (Physical Layer) and MAC sublayer MAC (Media Access Control), insert application-specific integrated circuit (ASIC) (hereinafter to be referred as the ASIC) chip of a slice field programmable gate array (hereinafter to be referred as FPGA) or identical function, be used for the extraction and the insertion of IEEE1588 protocol massages, so-called physical layer refers to, the bottom of the interconnected OSI of open system (OpenSystem Interconnection) architecture;
Down direction: the message of receiving from the UP-link port, whether FPGA analyzes it is the IEEE1588 protocol package, if protocol massages then extracts the timestamp that comprises in this protocol massages, and write down the moment that last bit of this protocol massages BIT arrives and be the local moment of receiving this message; If not the IEEE1588 protocol massages, then the exchange chip of giving follow-up medium access control MAC (MediaAccess Control) or master control borad this message is done further processing;
Up direction: the IEEE1588 protocol package of sending here from CPU, write in the FPGA, send by FPGA, and the timestamp that protocol package is carried is inserted when sending this message by hardware, what insert is the local zone time of this message when sending, and sends promptly that the timestamp territory begins bit BIT local zone time constantly in the message; FPGA also is responsible for the transmission from the exchange chip packet of coupled ethernet mac or master control borad;
Time difference Offset between OLT and " higher level equipment " is realized by FPGA hardware, reads for CPU;
Adopt the phase locked algorithm of CPU, control the output of OLT system digits phase-locked loop, the system clock that the generation system needs, and control signals such as 8K and 1S pulse according to Offset;
Because cycle of IEEE1588 protocol massages sends and receives, the time difference Offset between OLT and " higher level equipment " also is in real time, dynamically updates, assurance OLT frequency and on the time precise synchronization in " higher level equipment ".
2) realization of PON interface:
PON MAC realize IEEE1588 protocol sync message Sync message transmission and with the kinetic measurement of ONU distance;
CPU writes PON MAC to the IEEE1588 protocol massages, and MAC is responsible for message is sent to ONU from the PON interface, when transmitting time is stabbed the territory first bit BIT, the OLT local zone time is inserted into sync message;
OLT according to the PON agreement to ONU carry out in real time, dynamic distance test, measure RTT two-way time between OLT and the ONU, and send to ONU in real time, at this moment, OLT sends the selection that the RTT value can have dual mode to ONU: a kind of mode is that GPON (gigabit passive optical network) sends to ONU to the RTT value in real time by PLOAM (physical layer operations management maintenance) message, and this PLOAM message can be defined as follows:
Figure A200810142096D00171
Figure A200810142096D00181
Another kind of mode is that EPON (Ethernet passive optical network) sends to ONU to the RTT value in real time by Ethernet OAM (ethernet operation management maintenance) message;
Two) realization of last PON interface of ONU or uni interface:
1) realization of PON interface:
PON MAC realizes the reception of IEEE1588 protocol sync message Sync message and the reception of RTT value message;
Down direction: the message of receiving from the PON interface, whether PON MAC analyzes it is the IEEE1588 protocol sync message, if sync message, then extract the timestamp that comprises in this agreement newspaper, and write down the moment that last bit of this protocol massages BIT arrives, the moment of receiving this message for this locality; If not the IEEE1588 protocol massages, then give follow-up functional module this message and further handle;
Down direction: the RTT value message from the PON mouth is received, be received, extract the RTT value;
According to the RTT value, the moment that the timestamp that sync message Sync carries and protocol massages arrive, calculate the time difference Offset between ONU and the OLT, and realize the calculating of Offset by hardware, read for CPU;
Adopt the phase locked algorithm of CPU, control the output of ONU system digits phase-locked loop according to Offset, the system clock that the generation system needs, and control signals such as 8K and 1S pulse, be used for ONU system use itself or give " following attached device " as the base station use, the base station just can obtain the pulse per second (PPS) from ONU; And this pulse per second (PPS) also may be modulated at certain overhead-bits BIT of time division multiplexing tdm (Time Division Multiplex) interface;
OLT periodically sends synchronization message and RTT value to ONU, comprises clock frequency and time, guarantees that the ONU precise synchronization is in OLT.
2) realization of uni interface:
Between the PHY of uni interface and the MAC of exchange chip, go up the Uplink interface as OLT, rely on the asic chip of a slice FPGA or identical function, realize that IEEE1588 synchronous protocol message receives and sends, realization and ONU " following attached device " are as operation IEEE1588 agreement between the base station;
Up direction: the message of receiving from uni port, whether FPGA analyzes it is the IEEE1588 protocol package, if protocol massages then extracts the timestamp that comprises in this protocol massages, and write down the moment that last bit of this protocol massages BIT arrives, the moment of receiving this message for this locality; If not the IEEE1588 protocol massages, then give follow-up MAC this message or the exchange chip on the ONU is done further processing;
Down direction: the IEEE1588 protocol package of sending here from CPU, write in the FPGA, and send by FPGA, and the timestamp that protocol package is carried is inserted when sending this message by hardware, what insert is the local zone time of this message when sending, and promptly sends first bit BIT local zone time constantly in timestamp territory in the message; FPGA also is responsible for sending from the packet of the exchange chip of coupled ethernet mac or master control borad;
By operation IEEE1588 agreement on the uni interface, ONU and its " following attached device " are as realizing frequency and the precise synchronization of time between the base station.
Above embodiment can adopt existing various possible schemes in the technology such as synchronous of APON, GPON and/or EPON system medium frequency and time according to practical application, is well known to those skilled in the art, and also repeats no more at this.
In the embodiment of EPON medium frequency of the present invention and the method for synchronous of time, owing to utilized the distinctive ranging information of PON network, the IEEE1588 agreement of combined standard, avoided the asymmetric property of PON network, realized having guaranteed that in the synchronous transmission of time and frequency between the equipment at different levels on the PON network each ONU has identical frequency and time; And, the IEEE1588 agreement of operation standard between ONU and its subordinate equipment, ONU can also pass to subordinate equipment to frequency and time accurately, between the equipment that has guaranteed to connect under each ONU identical frequency and time is arranged also.
Should be understood that; for those of ordinary skills; can be improved according to the explanation of such scheme or conversion; for example be used between other layer of OSI and APON, GPON and/or EPON system medium, and all these improve and conversion all should belong to the protection range of claims of the present invention.

Claims (10)

1, a kind of EPON medium frequency and the method for synchronous of time may further comprise the steps:
A, optical line terminal periodically send ranging information between that the protocol massages that has timestamp and optical line terminal kinetic measurement obtain and the optical network unit to optical network unit, obtain time deviation between described optical line terminal and the described optical network unit in real time by the Time Calculation to described protocol massages;
B, the enterprising line time deviation of described optical network unit in real time, dynamic compensation, make the frequency of described optical network unit and time be synchronized with optical line terminal.
2, method for synchronous according to claim 1 is characterized in that, described steps A specifically also comprises:
Local T1 constantly when A1, described optical line terminal will send protocol massages first bit is inserted in the timestamp territory of the protocol massages that sends;
Local T2 constantly when A2, last bit of the described protocol massages of described optical network unit recorder;
A3, described optical line terminal are calculated in real time and are worth two-way time between itself and the described optical network unit RTT as described ranging information and send to described optical network unit;
A4, described optical network unit calculate the time deviation value Offset between described optical line terminal and the described optical network unit:
Offset＝T2-T1-RTT/2。
3, method for synchronous according to claim 2 is characterized in that, described steps A 3 specifically also comprises:
A31, the described optical line terminal local echoing time T of measurement ResponseT when sending distance measuring signal this locality for it 0T during to its receiving feedback signals this locality 2Time difference (t 0-t 0);
A32, the local stand-by period T of the described optical network unit of measurement WaitT during local when receiving the distance measuring signal that described optical line terminal sends for it 0T during local when sending the feedback signal of described distance measuring signal to it 1Time difference (t 1-t 0);
Be worth RTT the two-way time between A33, the described optical line terminal of definition and the described optical network unit is up time T UpstreamWith downgoing time T DownstreamSum equals described optical line terminal local echoing time T ResponseWith the local stand-by period T of described optical network unit WaitPoor:
RTT＝T downstream+T upstream
＝T response-T wait
＝(t 2-t 0)-(t 1-t 0)
＝t 2-t 1。
4, method for synchronous according to claim 1 is characterized in that, and is further comprising the steps of:
Before C, the described steps A, the IEEE1588 clock synchronization protocol of operation standard makes the frequency of described optical line terminal and time be synchronized with described higher level equipment between described optical line terminal and higher level equipment that it is connected; And/or after the described step B, IEEE1588 clock synchronization protocol of operation standard between the following attached device that described optical network unit is connected with it makes the described frequency and the time of attached device down be synchronized with described optical network unit.
5, method for synchronous according to claim 4 is characterized in that, described step C specifically also comprises:
C1, described higher level equipment send the protocol massages that has timestamp to described optical line terminal constantly at the T1` of local zone time, and described optical line terminal receives this protocol massages constantly at the T2` of local zone time; And/or described optical network unit sends the protocol massages that has timestamp to described attached device down constantly at the T1` of local zone time, and described attached device down receives this protocol massages constantly at the T2` of local zone time;
C2, described higher level equipment send tracking message to described optical line terminal; And/or described attached device down sends tracking message to described optical network unit;
Constantly to described higher level equipment transmission lag request message, described higher level equipment is answered message to described optical line terminal feedback delay constantly at the T4` of local zone time at the T3` of local zone time for C3, described optical line terminal; And/or described down attached device at the T3` of local zone time constantly to described optical network unit transmission lag request message, described optical network unit is answered message to described attached device feedback delay down constantly at the T4` of local zone time;
C4, calculate between described optical line terminal and its higher level equipment and/or described optical network unit and its time deviation value Offset` between attached device down:
Offset`＝(T2`-T1`+T3`-T4`)/2。
6, method for synchronous according to claim 4 is characterized in that, step C specifically also comprises:
C5, periodically sending protocol massages message down between the attached device between described optical line terminal and its higher level equipment and/or at described optical network unit and its, dynamically, the real-time update time deviation;
C6, described optical line terminal and/or the described down enterprising line time deviation of attached device dynamically, real-Time Compensation.
7, method for synchronous according to claim 1 or 5 is characterized in that, uses hardware to receive and dispatch when transmitting described protocol massages that has a timestamp or described ranging information.
8, method for synchronous according to claim 7, it is characterized in that, in following style interface, use field programmable gate array hardware or application-specific integrated circuit (ASIC) hardware to carry out extraction, insertion, transmission or the reception of described protocol massages: the first line of a couplet Uplink interface of optical line terminal or the uni interface of optical network unit.
9, according to each described method for synchronous in the claim 1 to 6, it is characterized in that, adopt the phase locked algorithm of CPU, according to the output of corresponding time deviation control figure phase-locked loop, needed system clock of generation system and control signal.
10, according to each described method for synchronous in the claim 1 to 3, it is characterized in that described optical line terminal sends described ranging information for described optical network unit by the physical layer operations management maintenance PLOAM message of gigabit passive optical network or the ethernet operation management maintenance Ethernet OAM message of Ethernet passive optical network.
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