CN102684806A - High-accuracy self-adaptive clock recovery method of packet transport network (PTN) simulation service - Google Patents

Abstract

The invention discloses a high-accuracy self-adaptive clock recovery method of a packet transport network (PTN) simulation service. A basic clock information extraction module, a first-in first-out (FIFO) fine adjustment information extraction module and a clock generation module are arranged on a receiving side of PTN simulation service equipment and used for recovering a system clock, wherein the basic clock information extraction module acquires data flow speed by channel associated detection of a data flow and then computes basic clock information; the FIFO fine adjustment information extraction module self-adaptively detects an FIFO buffer on the receiving side, acquires buffer jitter information and extracts the fine adjustment information of the basic clock information; and the clock generation module inputs the basic clock information which is extracted by the basic clock information extraction module to corresponding clock recovery factors, performs fine adjustment on the basic clock information according to the fine adjustment information which is extracted by the FIFO fine adjustment information extraction module, and recovers an accurate clock. The method is high in clock accuracy and high in clock recovery speed.

Description

A kind of high-accuracy self-adaptation clock recovery method of PTN artificial service

Technical field

The invention belongs to technical field of telecommunications, relate in particular to the clock recovery method of Packet Transport Network artificial service.

Background technology

PTN equipment is Metro Ethernet access of the 4th generation and the delivery platform of using towards looped network, supports to carry the value-added service of high added value from having SDH/SONET framework smooth evolution now to packet-optimized transmission network.PTN equipment is integrated into ether divide into groups ring and cut-in convergent function in elastomeric metropolitan area in the unified SDH/SONET platform of future generation, the transmission of can implementation efficiency high Metro Ethernet grouping data services such as (or other data services) and converging.

According to the metropolitan area network present situation of China operator, core layer mainly is the coarsegrain flow after converging, and transmitting is main with OTN/ROADM mainly, and the PTN technology should be used to solve the transmission problem of access/convergence-level.Telecommunication service and network progressively are being evolved to towards the business and the network that divide into groups, and the traditional TDM business has been occupied considerable market.This trend is particularly outstanding in the IPization developing progress in the mobile phone users upstream device, and simultaneously, network element device also progressively uses Ethernet as business interface, and the traditional TDM interface also still coexists as in the mobile device in each aspect with packet interface.

Packet Service can reduce this viewpoint of return network cost greatly and extensively received by industry, yet traditional T1/E1 interface of widespread deployment and basic network will continue and the new equipment long-term co-existence towards grouping.The mixed transmission equipment that can serve conventional requirement has great demand, like T1/E1, MLPPP and ATM/IMA towards circuit, and the IP/Ethernet hybrid interface.PTN equipment can be applied to any traditional TDM and Ethernet service environment.And mixed light/Packet Transport Network also not only is confined to mobile operator.In fact, it can be applied to the operator that all provide mixed service.

In the artificial service of E1/T1; Data are that the form according to bag carries out alternately in packet switching network PSN, need from packet, recover clock information at receiver side, just will make the clock of receiver side can follow the tracks of the clock of transmitter side; It is congested to consider that simultaneously the PSN network may exist; Out of order, fortuitous events such as packet loss need carry out a certain amount of caching process to packet at receiver side.

Publication number is that the invention application of CN101640578A discloses a kind of TDM service clock recovery method that is used for grouping conveying network; Through gathering the interval time of advent of the grouping that arrives in the clock recovery cycle; Utilize filter that packet arrives time interval sequence is carried out preliminary treatment; Estimate source end TDM business clock frequency then, and through in each business clock frequency trim cycle, the detection of buffering area filling level in time being made adjustment to unconformable business clock frequency.This method is based on Kalman filtering and prediction algorithm for estimating; Generate a reference clock earlier; And make compensation on this basis; The practical application more complicated of getting up, taking resource may be bigger, and the method clock recovered precision can be subject to filter and the naturally occurring error of prediction algorithm.

Summary of the invention

The objective of the invention is to solve prior art exist for the PSN network congested, out of order, the coarse problem of clock tracing under the fortuitous events such as packet loss, it is fast to propose a kind of resume speed, the clock recovery method that precision is high.

A kind of high-accuracy self-adaptation clock recovery method of PTN artificial service; Be used for surveying the clock of following the tracks of transmitter side in the reception of PTN artificial service; The receiver side of described PTN artificial service comprises the fundamental clock information extraction modules; First in first out buffer memory FIFO refinement information extraction module and clock generating module, described clock recovery method comprises step:

Step 1, at the receiver side of artificial service, through detecting data flow, extract fundamental clock information with the road;

Step 2, the buffer memory FIFO of receiver side is carried out self-adapting detecting, obtain the buffer memory wobble information, extract FIFO refinement information fundamental clock information;

Step 3, fundamental clock information is corresponded to corresponding clock recover on the factor;

Step 4, based on the refinement information that the clock recovery factor that obtains and buffer memory FIFO provide, obtain accurate recovered clock.

Further, said step 1 comprises:

Step 1.1, the payload number that receives in the receiver side statistics are in a period of time of M, and the count cycle number of local sampling clock is added up N time, and the assembly average of count periodicity;

Step 1.2, to send the payload number according to transmitter side be that the count cycle number of M should equate calculating transmitter side fundamental clock information with the assembly average that step 1.1 is calculated.

The data flow of considering the transmitter side of artificial service bag is continuously, on Ethernet, sends behind these data packets, statistically says, the payload user data number that transmitter side sends in a period of time should be consistent with the payload number that receiver side is received.Equally, if the service rate of transmitter side accelerates, the payload number that receiver side is received should increase equally, and rate of change is consistent.Therefore add up receiver side counting and transmitter side counting, just can calculate transmitter side fundamental clock information.

Further, said step 2 comprises:

Step 2.1, in FIFO, data being flow to the line data Flow Control and detect, whether have packet loss alarm indication, if metadata cache surplus statistics is then carried out in not alarm, do low-pass filtering treatment again if detecting;

If step 2.2 has packet loss alarm indication, then directly carry out LPF;

Step 2.3, result and waterline after low pass handled compare, if be lower than the waterline that is provided with in advance, then generate the negative justification indication and give FIFO information extraction modules, if be higher than waterline, then generate positive justification and indicate and give FIFO information extraction modules.

Further, said waterline is under the situation of PTN artificial service operate as normal, and the metadata cache surplus of extracting current FIFO is carried out the value behind the LPF.

Said clock generating module is according to the address of a look-up table of fundamental clock information generating; And according to this allocation index to the relevant clock recovery factor, the data in the said look-up table corresponding under fundamental clock information, recover the clock recovery factor that needs to follow the tracks of clock.

Further, if buffer memory FIFO provides positive justification indication, show that then data residual in the FIFO increase, this moment, recovered clock was slow partially, needed to start fine setting clock recovery function, and the clock recovery factor is carried out the fine setting of add operation, obtained accurate recovered clock; If FIFO provides the negative justification indication, show that then data residual in the FIFO reduce, this moment, recovered clock was fast, needed to start fine setting clock recovery function, and the clock recovery factor is carried out the fine setting of subtraction, obtained accurate recovered clock.

The metadata cache surplus of FIFO is carried out LPF generation waterline during with operate as normal; Then current data buffer memory surplus is carried out comparing with waterline behind the LPF; If being higher than waterline, to show that the metadata cache data read the side clock rate slow partially; Positive justification takes place, and the clock that recovers to come out need accelerate; Otherwise, need negative justification if be lower than waterline, promptly reduce the frequency of the clock that generates.

The wherein operation of addition or subtraction; All calculate based on least unit Δ t, Δ t representes the base unit of the amplitude of at every turn finely tuning, and causes that the shake of clock is bigger than normal if Δ t crosses conference; But this value dynamic-configuration in the practice is according to the size of real-time clock tracing state adjustment Δ t.The accuracy standard measurement bit-width that the clock recovery factor adopts shows that more greatly the clock recovery precision is high more, but resource cost is big more, therefore in product is used, can adjust in real time according to actual conditions.High-order overflow position after the clock recovery factor adds up is the precision clock of final recovery.

The high-accuracy self-adaptation clock recovery method of PTN artificial service disclosed by the invention; Through detecting data flow with the road, obtain fundamental clock information, and according to the refinement information of FIFO; Recover accurate clock fast; The constraint that can break away from first in first out buffer memory FIFO fully, and resume speed is fast, and precision is high.

Description of drawings

Fig. 1 surveys module diagram for PTN artificial service of the present invention receives;

Fig. 2 is a PTN artificial service clock recovery method flow chart of the present invention.

Embodiment

Below in conjunction with accompanying drawing and embodiment technical scheme of the present invention is explained further details, following examples do not constitute qualification of the present invention.

As shown in Figure 1, in the E1/T1 of PTN artificial service, data are that the form according to bag carries out need from packet, recovering clock information at receiver side alternately in PSN, just will make the clock of receiver side can follow the tracks of the clock of transmitter side.

The reception of PTN artificial service equipment of the present invention is surveyed and is provided with the fundamental clock information extraction modules, and FIFO refinement information extraction module, and clock generating module are used for the recovery system clock.Wherein the fundamental clock information extraction modules is obtained data rate, and then is calculated fundamental clock information through detecting data flow with the road; FIFO refinement information extraction module carries out self-adapting detecting to the buffer memory FIFO of receiver side, obtains the buffer memory wobble information, extracts the refinement information to fundamental clock information; The fundamental clock information that clock generating module is extracted the fundamental clock information extraction modules corresponds to corresponding clock and recovers on the factor, and according to the refinement information that FIFO refinement information extraction module extracts fundamental clock information is finely tuned, and recovers precision clock.

The high-accuracy self-adaptation clock recovery method flow process of Packet Transport Network artificial service of the present invention is as shown in Figure 2, comprises the steps:

Step 201, at the receiver side of artificial service, through detecting data flow, and then extract fundamental clock information with the road.

The data flow of considering the transmitter side of artificial service bag is continuously, on Ethernet, sends behind these data packets, statistically says, the payload user data number that transmitter side sends in a period of time should be consistent with the payload number that receiver side is received.Equally, if the service rate of transmitter side accelerates, the payload number that receiver side is received should increase equally, and rate of change is consistent.

Suppose, utilize the local clock statistics to receive number and be D at payload _Trans(t) in a period of time, the count cycle number of local sampling clock is Cnt _Osc, f _OscBe data sampling clock, f _TransBe data clock, the fundamental clock information that promptly need follow the tracks of.

Assembly average should be: $\stackrel{\‾}{{\mathrm{Cnt}}_{\mathrm{Osc}}\left(t\right)}=\frac{1}{n}\underset{i=t}{\overset{i=t+n}{\mathrm{\Σ}}}{\mathrm{Cnt}}_{\mathrm{Osc}}\left(i\right);$

And transmitter side clock count Cnt0 is: $\mathrm{Cnt}0=\frac{D_{\mathrm{Trans}}\left(t\right)\×f_{\mathrm{Osc}}}{f_{\mathrm{Trans}}};$

Under the situation of packet network operate as normal, the receiver side counting should equal the transmitter side counting, has:

$f_{\mathrm{Trans}}=D_{\mathrm{Trans}}\left(t\right)\×f_{\mathrm{osc}}/\left(\frac{1}{n}\underset{i=1}{\overset{i=n}{\mathrm{\Σ}}}{\mathrm{Cnt}}_{\mathrm{osc}}\left(i\right)\right)$

Cnt wherein _OSC(i) be the count cycle number of the i time sampling, carried out counting altogether n time.

Payload for confirming is counted D _Trans(t), can guarantee under the situation of precision, configuration arbitrarily, the configuration precision is according to formula: the message disturbance is counted * (message time/timing statistics) and is confirmed.Wherein, message disturbance number comprises interim packet loss by the network state decision, and the number of out of order grade under the normal condition, is considered the realization resource needed, and this number should be controlled within the smaller scope.

Step 202, the buffer memory FIFO of receiver side is carried out self-adapting detecting, obtain the buffer memory wobble information, extract the FIFO refinement information to fundamental clock information, this refinement information can be used for accurately following the trail of clock jitter by a small margin.

At first data stream is carried out packet loss detection; Detect whether unusual packet loss is arranged, consider the naturally occurring packet delay of packet network, the congested defective mode that waits; Need carry out metadata cache (Jitter buffer) at the receiver side of artificial service, in order to eliminate these to the professional influence of data.Under normal circumstances, the data volume of metadata cache the inside should fluctuate near predefined FIFO waterline among a small circle, and the statistical value in the short time need maintain on the FIFO waterline; When because the data rate of PTN artificial service transmitter side when changing, what show at receiver side is that the data volume of metadata cache the inside can gradually change, and this variation is consistent with the changes in data rate direction of PTN artificial service transmitter side.

Under the situation of PTN artificial service operate as normal, extract the data volume of current FIFO, and these data are carried out LPF according to the statistics surplus in a period of time, filtered value Delt _FIFO(t), be exactly that normal working hours set FIFO waterline Level according to buffer memory _FIFO

If Delt _FIFO(t) be higher than Level _FIFOIt is slow partially to show that the metadata cache data read the side clock rate, and positive justification takes place, and the clock that recovers to come out need accelerate; Otherwise, if Delt _FIFO(t) be lower than Level _FIFONeed negative justification, promptly reduce the frequency of the clock that generates.

Data flow is carried out data-flow-control and is detected in buffer memory FIFO, whether detect has packet loss alarm indication, if metadata cache surplus statistics is then carried out in not alarm, does low-pass filtering treatment again, if packet loss alarm indication is arranged, then directly carries out LPF.Result after the low pass processing is carried out waterline relatively,, then generate the negative justification indication and give FIFO information extraction modules,, then generate the positive justification indication and give FIFO information extraction modules if be higher than waterline if be lower than the waterline that is provided with in advance.The FIFO information extraction modules can be made positive negative justification accordingly, and gives clock generating module with result.

Step 203, fundamental clock information is corresponded to corresponding clock recover on the factor.Clock generating module at first produces the address of a look-up table, and arrives relevant clock recovery parameter according to this allocation index, and generates final precision clock.

Fundamental clock information is corresponding to the address of the look-up table in the clock generating module, the data in the look-up table corresponding under fundamental clock information, recover the recovery parameter of the clock that needs to follow the tracks of.For fundamental clock information, the Cnt that receives at receiver side _OscThere is a corresponding relation with transmitter side.The Cnt of receiver side _OscWhen changing, the variation of the clock that corresponding is need recover out.For example, if Cnt _OscWhen value diminishes, show that the clock of transmitter side has sent the payload user data of equal number in the short period of time, just the data rate of transmitter side accelerates.Equally, if Cnt _OscWhen value becomes big, show that the clock of transmitter side has sent the payload user data of equal number in the long time, just the data rate of transmitter side is slack-off.Generally speaking, the Cnt that receives at receiver side _OscBe inversely proportional to the data rate of transmitter side.

The corresponding relation of the clock information and the clock recovery factor can be obtained by formula:

$\mathrm{lut}\_\mathrm{addr}=\frac{D_{\mathrm{Trans}}\left(t\right)\×f_{\mathrm{osc}}}{f_{\mathrm{Trans}}\×(1+\mathrm{ppm})}+\mathrm{\Δpsn}$

$\mathrm{clk}\_\mathrm{factor}=\frac{f_{\mathrm{Trans}}\×(1+\mathrm{ppm})}{f_{\mathrm{osc}}}$

Wherein, Δ psn is the packet jitter that network and entire equipment are introduced, and mainly is owing to network jitter, network delay, packet loss etc. cause; Can confirm through actual test; Its value can just can be born, the variation of the corresponding lut_addr of the adjustment of Δ psn, the adjustment of corresponding receiver side clock frequency.Lut_addr is the look-up table address that obtains the clock recovery factor of the clock information correspondence under the clock rates.Ppm is the variation of the clock rate of transmitter side, the corresponding different clock rate of recovery side just, if the clock jitter standard of definition is positive and negative 50ppm, and the degree of depth of look-up table is 1K, and then ppm=(50*2/1K) * 10 ^-6Clk_factor is illustrated in the clock recovery factor under the lut_addr.

Step 204, final based on the clock recovery factor of the top acquisition of tabling look-up and the positive negative justification indication information that buffer memory FIFO provides, is obtained accurate clock.If buffer memory FIFO provides the positive justification indication; Show that then data residual in the FIFO increase; This moment, recovered clock was slow partially, the current startup fine setting clock recovery function that needs, and the clk_factor value that clock recovery obtains to homophony is carried out the fine setting of add operation; Make the clock factor become big, the frequency of corresponding then raising clock recovery.In like manner; If FIFO provides the negative justification indication, show that then data residual in the FIFO reduce, this moment, recovered clock was fast; The current fine setting clock recovery function that also need start; The clk_factor value that clock recovery obtains to homophony makes the clock factor diminish, the frequency of corresponding then reduction clock recovery through the fine setting of row subtraction.

Recover accurate clock through following formula:

clk_factor=clk_factor±Δt

The wherein operation of addition or subtraction; All calculate based on least unit Δ t, Δ t representes the base unit of the amplitude of at every turn finely tuning, and causes that the shake of clock is bigger than normal if Δ t crosses conference; But this value dynamic-configuration in the practice is according to the size of real-time clock tracing state adjustment Δ t.The accuracy standard that clk_factor adopts is a 32bit carry pattern, and this measurement bit-width shows that more greatly the clock recovery precision is high more, but resource cost is big more, therefore in product is used, can adjust in real time according to actual conditions.High-order overflow position after clk_factor adds up is the precision clock of final recovery.

The above only is a preferred implementation of the present invention, should be pointed out that the those skilled in the art for the present technique field, and the present invention can also have various changes and variation.Under the prerequisite that does not break away from the principle of the invention, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (8)

1. the high-accuracy self-adaptation clock recovery method of a PTN artificial service; Be used for surveying the clock of following the tracks of transmitter side in the reception of PTN artificial service; The receiver side of described PTN artificial service comprises the fundamental clock information extraction modules; First in first out buffer memory FIFO refinement information extraction module and clock generating module is characterized in that, described clock recovery method comprises step:

Step 1, at the receiver side of artificial service, through detecting data flow, extract fundamental clock information with the road;

Step 2, the buffer memory FIFO of receiver side is carried out self-adapting detecting, obtain the buffer memory wobble information, extract FIFO refinement information fundamental clock information;

Step 3, fundamental clock information is corresponded to corresponding clock recover on the factor;

Step 4, based on the refinement information that the clock recovery factor that obtains and buffer memory FIFO provide, obtain accurate recovered clock.

2. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 1 is characterized in that, said step 1 comprises:

Step 1.1, the payload number that receives in the receiver side statistics are in a period of time of M, and the count cycle number of local sampling clock is added up N time, and the assembly average of count periodicity;

Step 1.2, to send the payload number according to transmitter side be that the count cycle number of M should equate calculating transmitter side fundamental clock information with the assembly average that step 1.1 is calculated.

3. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 1 is characterized in that, said step 2 comprises:

Step 2.1, in FIFO, data being flow to the line data Flow Control and detect, whether have packet loss alarm indication, if metadata cache surplus statistics is then carried out in not alarm, do low-pass filtering treatment again if detecting;

If step 2.2 has packet loss alarm indication, then directly carry out LPF;

Step 2.3, result after the low-pass filtering treatment and waterline are compared,, then generate the negative justification indication and give FIFO information extraction modules,, then generate the positive justification indication and give FIFO information extraction modules if be higher than waterline if be lower than the waterline that is provided with in advance.

4. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 3 is characterized in that, said waterline is under the situation of PTN artificial service operate as normal, and the metadata cache surplus of extracting current FIFO is carried out the value behind the LPF.

5. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 1; It is characterized in that; Said clock generating module is according to the address of a look-up table of fundamental clock information generating, and according to this allocation index to the relevant clock recovery factor.

6. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 5 is characterized in that, data in the said look-up table corresponding under fundamental clock information, recover the clock recovery factor that needs to follow the tracks of clock.

7. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 3; It is characterized in that,, show that then data residual in the FIFO increase if buffer memory FIFO provides the positive justification indication; This moment, recovered clock was slow partially; Need to start fine setting clock recovery function, the clock recovery factor is carried out the fine setting of add operation, obtain accurate recovered clock.

8. the high-accuracy self-adaptation clock recovery method of PTN artificial service according to claim 3; It is characterized in that,, show that then data residual in the FIFO reduce if FIFO provides the negative justification indication; This moment, recovered clock was fast; Need to start fine setting clock recovery function, the clock recovery factor is carried out the fine setting of subtraction, obtain accurate recovered clock.

Images