CN102480415B - A kind of method and device being recovered optical transport network clock by reference clock - Google Patents

A kind of method and device being recovered optical transport network clock by reference clock Download PDF

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CN102480415B
CN102480415B CN201010561244.9A CN201010561244A CN102480415B CN 102480415 B CN102480415 B CN 102480415B CN 201010561244 A CN201010561244 A CN 201010561244A CN 102480415 B CN102480415 B CN 102480415B
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packet
oduk
clock
nms
length
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CN102480415A (en
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苑岩
宋晓鹏
韦玉线
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ZTE Corp
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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
    • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
    • H04J3/1605—Fixed allocated frame structures
    • H04J3/1652—Optical Transport Network [OTN]
    • 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
    • H04J3/0685—Clock or time synchronisation in a node; Intranode synchronisation
    • H04J3/0691—Synchronisation in a TDM node

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

The invention discloses a kind of method being recovered optical transport network clock by reference clock, the method comprises: the frequency information measuring ODUk clock with reference measurement clock, is encapsulated into by the frequency information measured in the expense of bag or grouping; Going out in the decapsulation process of ODUk from bag or packet recovery, recovering the ODUk clock of same frequency according to the reference measurement clock of same frequency, the frequency information parsed from the expense of bag or grouping and bag or the length of dividing into groups.The invention also discloses and a kind ofly recover the device of optical transport network clock by reference clock, the processing module wherein wrapping or be grouped into ODUk recovers the ODUk clock of same frequency for the reference measurement clock according to same frequency, the frequency information parsed from the expense of bag or grouping and bag or the length of dividing into groups.Adopt method of the present invention and device, make ODUk still can recover good clock after postponing indefinite bag or packet switching process.

Description

Method and device for recovering optical transport network clock through reference clock
Technical Field
The present invention relates to the field of optical transport networks, and in particular, to a method and an apparatus for recovering an optical transport network clock using a reference clock.
Background
The optical transport network standard is made by international telecommunication union (ITU-T), the basic contents are defined in g.709 and g.798, the standard requires that cross-scheduling at ODUk (k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex, etc.) level is realized, and ODUk clock transparent transmission is required to be realized at the same time of scheduling. Here, the ODUk refers to an optical channel data unit in an optical transport network. The ODUk generally cannot implement cross-scheduling directly, but needs to be converted into another signal format, for example, into a Synchronous Digital Hierarchy (SDH) signal, or into a packet or packet signal, and then implement cross-scheduling. The way of implementing ODUk cross-scheduling based on packet or packet switching has great technical advantages, and users can implement the functions of data equipment and transmission equipment on one physical platform at the same time. However, due to the way of implementing ODUk cross-scheduling based on packet or packet switching, delay is not fixed during processing and the variation range is large, resulting in the following problems: it is very difficult to recover the high quality ODUk clock after packet or packet switching. If the problem cannot be solved according to the existing method of generating the recovery clock according to the First-in First-out (FIFO) or the buffer depth, a solution is urgently needed so that the ODUk clock with sufficient quality and performance can still be recovered after the packet or packet switching processing with variable delay.
Disclosure of Invention
In view of the above, the main objective of the present invention is to provide a method and an apparatus for recovering an optical transport network clock by using a reference clock, so that an ODUk can still recover a clock with sufficient quality and performance after undergoing packet or packet switching processing with variable delay.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a method of recovering an optical transport network clock from a reference clock, the method comprising:
in the encapsulation processing of converting an ODUk into a packet or a packet in an optical transport network, measuring frequency information of an ODUk clock by using a reference measurement clock, and encapsulating the measured frequency information into an overhead of the packet or the packet; in the decapsulation processing for recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered according to the reference measurement clock of the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet.
Wherein, the ODUk is specifically an ODUk (k ═ 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex); the frequency of the ODUk is Ck specifically; the frequency of the reference measurement clock is Cm; the frequency of the recovered ODUk clock is specifically Cj, and Cj is Ck; the length of the packet or the packet is a fixed value, the payload length of the fixed-length packet or the fixed-length packet is a byte B, the fixed-length packet or the fixed-length packet contains ODUk information of the byte B, and overhead of the fixed-length packet or the fixed-length packet at least contains 2 bits of the measured frequency information;
in the encapsulation process of converting from an ODUk to a packet or a packet, each time the ODUk information of B bytes is encapsulated into the packet or the packet of a fixed length, the method further includes: counting the number Nm of cycles passed by the reference measurement clock in the process of receiving the B byte ODUk information; nm is the frequency information of the ODUk clock measured by the reference measurement clock;
on the premise that the frequency deviation of the ODUk is less than plus or minus 150ppm, the Nm value is specifically Nms, Nms-1 or Nms +1, wherein Nms adopts a formula 1:calculating to obtain; wherein, Cks is the standard rate of the ODUk.
Wherein, the method also comprises: and packaging the measured frequency information which is represented by 2 bits, namely Nms, Nms-1 or Nms +1, into the fixed-length overhead of the packet or the packet for transmission.
In a decapsulation process of recovering an ODUk from a packet or a packet, the method further includes:
analyzing the measured frequency information of 2 bits from the fixed-length overhead of the packet or the packet;
nm is obtained according to the measured frequency information of 2 bits and the Nms obtained by calculation of the formula 1, and the value of the Nm is specifically Nms, Nms-1 or Nms + 1;
calculating the Cj according to the Nm, another reference measurement clock with the same frequency as the reference measurement clock and the B, wherein the formula adopted by the calculation is formula 2:
after the Cj is obtained through calculation, the method further comprises the following steps: inputting Cj into a desynchronizer designed according to the formula 2, and obtaining a clock with the frequency of Cj according to the formula 2; the clock with the frequency Cj is as follows: and recovering the ODUk clock with the same frequency after the ODUk is subjected to encapsulation processing and decapsulation processing.
Wherein, the method also comprises: according toAnd calculating Cjk, and inputting the Cjk into the desynchronizer to obtain a recovered OTUk clock with the frequency Cjk, wherein the OTUk is specifically OTUk (k is 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6).
An apparatus for recovering an optical transport network clock from a reference clock, the apparatus comprising: an ODUk to packet or packet processing module and a packet or packet to ODUk processing module; wherein,
the ODUk to packet or packet processing module is configured to measure frequency information of an ODUk clock by using a reference measurement clock in an encapsulation process for converting an ODUk into a packet or packet in an optical transport network, and encapsulate the measured frequency information into an overhead of the packet or packet;
and the processing module of the packet or the packet to the ODUk is configured to, in decapsulation processing for recovering the ODUk from the packet or the packet, recover an ODUk clock of the same frequency according to a reference measurement clock of the same frequency, the frequency information parsed from overhead of the packet or the packet, and a length of the packet or the packet.
Wherein, the ODUk is specifically an ODUk (k ═ 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex); the frequency of the ODUk is Ck specifically; the frequency of the reference measurement clock is Cm; the frequency of the recovered ODUk clock is specifically Cj, and Cj is Ck; the length of the packet or the packet is a fixed value, the payload length of the fixed-length packet or the fixed-length packet is a byte B, the fixed-length packet or the fixed-length packet contains ODUk information of the byte B, and the overhead of the fixed-length packet or the fixed-length packet at least contains measured frequency information of 2 bits;
the ODUk to packet or packet processing module further includes: the device comprises a first counter, a second counter, a first calculation module and a packet or grouping generation module; wherein,
the first counter is used for counting the number of bytes of the received ODUk information, and the maximum value is B;
the second counter is configured to count a number Nm of cycles that the reference measurement clock passes through in each process of receiving a byte B of ODUk information; nm is the frequency information of the ODUk clock measured by the reference measurement clock; on the premise that the frequency deviation of the ODUk is less than plus or minus 150ppm, the value of Nm is specifically Nms, Nms-1 or Nms +1, where Nms adopts formula 1:calculating to obtain; wherein, Cks is the standard rate of the ODUk;
the first calculating module is configured to receive a B byte count end indication signal of the first counter and an Nm obtained by counting by the second counter, where a value of the Nm is specifically Nms, Nms-1, or Nms +1, and Nms, Nms-1, or Nms +1 indicated by 2 bits is used as measured frequency information;
and the packet or packet generating module is used for generating the fixed-length packet or packet with the payload length of B bytes, and simultaneously packaging the measured frequency information of 2 bits into the overhead of the fixed-length packet or packet for transmission.
Wherein, the processing module of the packet or the packet to ODUk further includes: the system comprises an analysis module, a second calculation module and a desynchronizer; wherein,
the analysis module is used for analyzing the measured frequency information of 2 bits from the received packets or packets with fixed length;
the second calculation module is configured to obtain Nm according to the measured frequency information of 2 bits and Nms obtained through calculation in the formula 1, where a value of Nm is specifically Nms, Nms-1, or Nms + 1; calculating the Cj according to the Nm, another reference measurement clock with the same frequency as the reference measurement clock and the B, wherein the formula adopted by the calculation is formula 2:
the desynchronizer is used for obtaining a clock with the frequency of Cj according to the input Cj and the formula 2; the clock with the frequency Cj is as follows: and recovering the ODUk clock with the same frequency after the ODUk is subjected to encapsulation processing and decapsulation processing.
In the encapsulation processing of switching from an ODUk to a packet or a packet in an optical transport network, frequency information of an ODUk clock is measured by using a reference measurement clock, and the measured frequency information is encapsulated into the overhead of the packet or the packet; in the decapsulation processing for recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered according to the reference measurement clock of the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet.
The invention is suitable for the occasion that the ODUk realizes cross scheduling through packet or packet switching, in the encapsulation processing of switching from the ODUk to the packet or packet, the frequency information of the ODUk clock is measured by a reference measurement clock, and when the ODUk is encapsulated into the packet or packet, the measured frequency information is put into the overhead of the packet or packet; in the decapsulation process for recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered according to the reference measurement clock of the same frequency, frequency information in the overhead of the packet or the packet, and the length of the packet or the packet. By adopting the invention, the influence of the delay non-fixity generated by packet or packet switching on the recovered clock can be ignored, and the ODUk clock with good enough quality and performance can be recovered.
Drawings
FIG. 1 is a schematic flow diagram of the process principle of the present invention;
fig. 2 is a schematic position diagram of the apparatus of the present invention in an existing system for implementing ODUk cross-dispatching based on packet or packet switching;
fig. 3 is a schematic diagram of an embodiment of the apparatus according to the present invention, which implements ODUk encapsulation processing to a packet or packet;
fig. 4 is a schematic diagram of an embodiment of the apparatus according to the present invention for implementing decapsulation processing of packets or packets to ODUk.
Detailed Description
The basic idea of the invention is: in the encapsulation processing of converting an ODUk into a packet or a packet in an optical transport network, measuring frequency information of an ODUk clock by using a reference measurement clock, and encapsulating the measured frequency information into an overhead of the packet or the packet; in the decapsulation processing for recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered according to the reference measurement clock of the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet.
The following describes the embodiments in further detail with reference to the accompanying drawings.
The invention can ignore the influence of delay non-fixity generated by packet or packet switching on the recovered clock, and recover the ODUk clock with good quality and performance. And the recovery effect of the ODUk clock is equivalent to the effect of the conventional fixed code Rate (CBR) signal recovered from the optical channel transport unit (OTUk) de-asynchronous mapping, so that the performance of the recovered ODUk or OTUk clock can meet the requirements of the relevant standards of the optical transport network.
Here, it should be noted that: originally, what needs to be transmitted is the frequency of the ODUk (the frequency of the ODUk is Ck), and since Ck is frequency, the invention actually needs to transmit Ck by measuring the frequency information of the ODUk clock (the measured frequency information is Nm) by using a reference measurement clock, and since the value of Nm may be more than one thousand, it cannot be represented by 2 bits, but since Nm can be represented by plus or minus an offset value of Nms, and since Nms is a fixed value, it can achieve the purpose of transmitting Nm only by using a 2-bit transmission offset value.
A method for recovering an optical transport network clock by using a reference clock is described by taking an ODUk (k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex) as an example, where the ODUk is at least an ODUk (k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex), and the method is not limited to the present example and mainly includes the following contents:
the flow diagram of the method principle shown in fig. 1 comprises the following steps:
step 101, in the encapsulation process of converting from ODUk to packet or packet, measuring frequency information of ODUk clock by using reference measurement clock, and encapsulating the measured frequency information into overhead of packet or packet.
Step 102, in the decapsulation process of recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered by using the reference measurement clock of the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet.
For convenience of description, the following parameter definitions are made:
a1, frequency information of the ODUk clock measured by the reference measurement clock, that is, the frequency of the ODUk to be transmitted is Ck.
a2, the clock frequency of the ODUk recovered after packet or packet switching is Cj, and Cj and Ck are very close and will change along with the change of Ck.
a3, where the frequency of the reference measurement clock is Cm, the number of the reference measurement clocks is multiple, and the same reference measurement clock exists in all the apparatuses for implementing ODUk to packet or packet encapsulation processing of the present invention, and also exists in all the apparatuses for implementing packet or packet to ODUk decapsulation processing of the present invention. All reference measurement clocks only need to be consistent in frequency, and do not need to be consistent in phase.
a4, forming a packet or packet after receiving the ODUk of B bytes, and sending out the packet or packet, where the length of the payload of the ODUk in the packet or packet is fixed to B bytes, and the length of the packet or packet is fixed and is fixed B + h bytes, where h is the byte occupied by the overhead of the packet or packet.
a5, and a proprietary field with 4 bits in packet or packet overhead, named CI0 (occupying 2 bits) and CI1 (occupying 2 bits), respectively, are used to transmit the measured frequency information of ODUk clock mentioned in a 1. Only 2 bits are actually needed for the frequency information, CI0 is used in a normal case, and the CI1 overhead is added to transmit the frequency information of the ODUk clock mentioned in a1, which has the advantage of ensuring that the frequency information is not lost after 1 packet or packet is lost, thereby ensuring that the ODUk clock with the same frequency can be recovered according to the frequency information in the overhead. If the frequency information is not lost after n packets are continuously lost, the overhead of 2 x (n +1) bits can be further used. That is to say, after obtaining the measured frequency information of the ODUk clock mentioned in a1 with 2 bits, in order to ensure that the frequency information of the ODUk clock is not lost after n consecutive packets or packets with the fixed length are lost in the switching process of the packets or packets with the fixed length, the frequency information of the ODUk clock with 2 bits above may be copied into n +1 (n is an integer greater than 1) consecutive packets or packets with the fixed length, and the overhead of 2 × (n +1) bits is occupied, thereby ensuring that the frequency information of the ODUk clock with 2 bits can still be obtained after n packets or packets with the fixed length are continuously lost.
a6, the standard rate of ODUk is Cks.
Here, it should be noted that: in view of the principle of implementation of packets and packets being substantially the same, the packets and packets will be referred to as packets hereinafter unless otherwise specified.
The solution of the invention is described below with reference to the above parameter definitions:
the first stage is as follows: in the encapsulation process of converting from an ODUk to a packet, when an ODUk of B bytes is received by a Ck clock, the number of cycles Nm, Nm which may also be referred to as the number of Cm clocks, that pass through a reference measurement clock having a frequency Cm during each reception of B byte ODUk information is counted. Frequency deviation of ODUk is less than plus or minus 150ppm and B is not more than BmaxOn the premise that Nm may only take the value of Nms, Nms-1 or Nms +1, the value of Nms may be calculated according to the following formula 1:
equation 1: <math> <mrow> <mi>Nms</mi> <mo>=</mo> <mi>round</mi> <mrow> <mo>(</mo> <mfrac> <mrow> <mi>Cm</mi> <mo>&times;</mo> <mi>B</mi> <mo>&times;</mo> <mn>8</mn> </mrow> <mi>Cks</mi> </mfrac> <mo>)</mo> </mrow> </mrow> </math>
in equation 1 above, round () is a rounded integer operation and Cks is the ODUk standard rate. Considering that Nms +1 and Nms-1 must have at least plus-minus 150ppm regulation capability, the Cm multiplied by B value is required not to be too large, and assuming that Cm is 350MHz, only the Nms is ensured to be less than (1000000/150) -0.5, and the regulation range which is more than plus-minus 150ppm can be ensured, so that the maximum B of B is obtainedmaxAs shown in Table 1 below, Table 1 shows B corresponding to each ODUk when Cm is 350MHzmaxList of maximum values.
ODUk type ODUk Rate (Mbps) Bmax
ODU0 1244.16 2962.064
ODU1 2498.775 5949.018
ODU2 10037.27 23896.48
ODU3 40319.22 95990.94
ODU4 104794.4 249491.9
TABLE 1
Considering the allowed B of ODU0maxThe value is minimal, so when Cm equals 350MHz, this scheme is guaranteed to have a frequency offset tolerance of at least plus or minus 150ppm to ODUk as long as B is kept less than 2962. If the frequency of Cm is reduced, BmaxThe value may also be increased.
And a second stage: the measured frequency information of the ODUk clock mentioned in a1 of 2 bits is converted from Nms, Nms-1 or Nms +1 calculated by using formula 1, that is, Nms-1 or Nms +1 is respectively corresponding to 2 bits bit00, bit01 and bit10, and the 2 bits bit is put into CI0 domain of overhead of a packet composed of next B byte ODUk, and the 2 bits bit is put into CI1 domain of overhead of a packet composed of next B byte ODUk, where the CI1 domain of overhead of a packet composed of next B byte ODUk is: it is ensured that 2bit frequency information is to be backed up in 2 consecutive packets.
And a third stage: in the decapsulation processing for recovering the ODUk from the packet, an offset value of 2bit frequency information corresponding to the previous packet is obtained from a CI0 domain of packet overhead under the condition of no packet loss, then the number Nm of clocks Cm corresponding to the previous packet of B bytes ODUk can be obtained according to the above calculated value Nms (the value of Nm may be Nms, Nms-1 or Nms +1), according to the following formula 2, the clock with the frequency Cj can be recovered by inputting Nm, Cm and B into a desynchronizer, and Cj will change along with Ck, and the clock with the frequency Cj is: and recovering the ODUk clock with the same frequency after the ODUk is subjected to packet or packet switching processing with indefinite delay.
Equation 2: <math> <mrow> <mi>Cj</mi> <mo>=</mo> <mfrac> <mrow> <mi>Cm</mi> <mo>&times;</mo> <mi>B</mi> <mo>&times;</mo> <mn>8</mn> </mrow> <mi>Nm</mi> </mfrac> </mrow> </math>
here, it should be noted that: the desynchronizer is designed in different ways, but the design principle and basis are derived from the above formula 2.
In the above processing, if 1 packet is lost, the number Nm of Cm clocks corresponding to the packet before the lost packet can be obtained by using the CI1 field of the packet next to the lost packet, and the byte with the value of 0 of B bytes is automatically filled, so that it is ensured that only some errors occur and no frame header shift occurs when 1 packet is lost, and the effect of clock recovery is not affected at the same time. If a plurality of packets are lost continuously, the number of Cm in the lost packet is considered to be Nms, and the number of bytes is automatically filled, wherein the number of the lost packets is multiplied by the number of bytes of B bytes, and the value of the bytes is 0, so that the number of the bytes in the recovered ODUk frame is completely normal and only a few bit errors, and a transient frame loss error is not generated due to frame header shift caused by a plurality of or a few of the bytes, and at this time, although some influence is also generated on the synchronization effect of the desynchronizer, only a transient poor clock following performance is caused as long as the number of the lost packets is not too many, the clock information is not lost completely, and the clock can recover synchronization quickly after no packet is lost.
A fourth stage: on the basis of the third stage, if it is desired to recover the clock of the OTUk (k is 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6), since the clock frequencies of the OTUk and the ODUk have a fixed proportional relationship, the recovered OTUk clock can be obtained by inputting the following formula 3 into the desynchronizer, and the frequency of the OTUk clock is Cjk. It can be seen that: after performing packet or packet switching processing with variable delay, the ODUk (k ═ 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex) still can recover OTUk (k ═ 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6) clocks with sufficient quality and performance. Among them, OTUk is at least OTUk (k ═ 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6), and is not limited to the present examples.
Equation 3:
an apparatus for recovering an optical transport network clock from a reference clock, comprising: an ODUk to packet or packet processing module and a packet or packet to ODUk processing module. The ODUk-to-packet or packet processing module is used in an optical transport network to measure frequency information of an ODUk clock by using a reference measurement clock in an encapsulation process of converting an ODUk into a packet or packet, and encapsulate the measured frequency information into an overhead of the packet or packet. The processing module from the packet or the packet to the ODUk is configured to recover the ODUk clock having the same frequency according to the reference measurement clock having the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet in the decapsulation processing for recovering the ODUk from the packet or the packet.
Here, an example of the ODUk is an ODUk (k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex), but the ODUk is at least an ODUk (k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex), and is not limited to the example herein; the frequency of the ODUk is Ck specifically; the frequency of the reference measurement clock is Cm; the frequency of the recovered ODUk clock is specifically Cj, and Cj is Ck; the length of the packet or the packet is a fixed value, the payload length of the fixed-length packet or the fixed-length packet is a byte B, the fixed-length packet or the fixed-length packet contains ODUk information of the byte B, and overhead of the fixed-length packet or the fixed-length packet at least contains 2 bits of the measured frequency information;
the ODUk to packet or packet processing module further comprises: the device comprises a first counter, a second counter, a first calculation module and a packet or grouping generation module; wherein,
the first counter is used for counting the number of bytes of the received ODUk information, and the maximum value is B;
a second counter configured to count a number Nm of cycles that the reference measurement clock passes through every time a byte B ODUk information is received; nm is frequency information of the ODUk clock measured by the reference measurement clock; wherein, the frequency deviation of ODUk is less than plus or minus 150ppm and B is not more than BmaxOn the premise that the value of Nm may only be Nms, Nms-1 or Nms +1, where Nms adopts formula 1:calculating to obtain; wherein, Cks is the standard rate of the ODUk;
a first calculating module, configured to receive a B byte count end indication signal of the first counter and an Nm obtained by counting by the second counter, where a value of the Nm may only be Nms, Nms-1, or Nms +1, and Nms, Nms-1, or Nms +1 indicated by 2 bits is used as measured frequency information;
and the packet or packet generating module is used for generating the fixed-length packet or packet with the payload length of B bytes, and simultaneously packaging the measured frequency information of 2 bits into the overhead of the fixed-length packet or packet for transmission.
Here, the processing module of packet or packet to ODUk further includes: the system comprises an analysis module, a second calculation module and a desynchronizer; wherein,
the analysis module is used for analyzing the measured frequency information of 2 bits from the received packets or packets with fixed length;
the second calculation module is used for obtaining Nm according to the measured frequency information of 2 bits and the Nms obtained by calculation of the formula 1, and the value of the Nm can only be Nms, Nms-1 or Nms + 1; calculating the Cj according to the Nm, another reference measurement clock with the same frequency as the reference measurement clock and the B, wherein the formula adopted by the calculation is formula 2:
the desynchronizer is used for obtaining a clock with the frequency of Cj according to the input Cj and the formula 2; the clock with the frequency Cj is as follows: and recovering the ODUk clock with the same frequency after the ODUk is subjected to encapsulation processing and decapsulation processing.
In summary, compared with the prior art, the invention has the following beneficial effects:
1. the method and the device solve the problem that the ODUk clock is difficult to recover after the ODUk passes through the packet switching network, the ODUk clock recovery effect is irrelevant to the delay uncertainty of the packet switching, namely the influence of the delay instability generated by the packet or the packet switching on the recovery clock can be ignored, so that the ODUk clock with good quality and performance can be recovered.
2. The principle of clock recovery of the method and the device is similar to the existing principle of recovering the CBR from the OTUk by de-asynchronous mapping, and the clock recovery effect is consistent. Because the frequency of Cm and the length of B can be set, by adopting the method and the device of the invention, even better effect than that of recovering CBR from OTUk de-asynchronous mapping can be achieved by selecting proper Cm and proper B.
3. By adopting the method and the device, the packet obtained after the ODUk is encapsulated is a fixed-length packet with fixed length, the length of the packet can be set, the fixed-length packet has higher efficiency and smaller delay when passing through a packet switching system, and meanwhile, the optimization of a general packet switching system becomes possible, so that the ODUk cross can be greatly simplified when only the ODUk cross needs to be supported, and the realization cost of the packet switching system is reduced.
4. By adopting the method and the device, the packet obtained after the ODUk is encapsulated is the fixed-length packet, the length of the packet can be set, and the parallel processing when the ODUk is recovered from the fixed-length packet can be very simple by selecting the proper packet length, so that the complex operation of repeatedly adjusting the ODUk width for realizing the parallel processing of the ODUk when the ODUk is recovered from the variable-length packet is avoided.
5. The method and the device can better tolerate the packet loss phenomenon in the packet switching process, and can not generate the frame head dislocation phenomenon under the condition of losing one packet and only generate some error codes when using 4bit overhead, and simultaneously, the performance of recovering the clock is not influenced; frame head dislocation phenomenon can not appear under the condition of continuously losing a plurality of packets, only some error codes appear, the following performance of the recovered clock can be influenced temporarily, but jitter overproof phenomenon can not appear, the clock following performance can be recovered to be normal quickly after no packet loss occurs, and if the overhead of 2 x (n +1) bit is used, the performance of the recovered clock can be ensured not to be influenced when n packets are continuously lost.
The invention is illustrated below.
Fig. 2 is a schematic position diagram of the apparatus of the present invention in an existing system for implementing ODUk cross-dispatching based on packet or packet switching. An existing device for implementing ODUk cross-scheduling based on packet or packet switching is composed of n ODUk-to-packet or packet conversion units (as shown in 100-1 to 100-n in fig. 2), n packet or packet-to-switching network adaptation units (as shown in 101-1 to 101-n in fig. 2), and a switching network unit 103. The system firstly converts the ODUk into a packet or a packet, then converts the packet or the packet into a unified backplane signal, and then performs switching scheduling through a switching network, thereby realizing the cross scheduling of the ODUk. The reference measurement clocks (shown as 104-1 to 104-n in fig. 2) in fig. 2 are added to assist in clock recovery when the ODUk traverses the switching network, and require that the reference measurement clocks (shown as 104-1 to 104-n in fig. 2) must be the same frequency clock from the same high-precision reference clock source, and the phases of the n clocks may be different, the frequency is Cm, the frequency range is preferably 150M-350MHz, and other frequency values may be selected. The device of the present invention is located in an ODUk to packet or packet conversion unit (shown as 100-1 to 100-n in fig. 2) of the system shown in fig. 2.
The first embodiment of the device: in an embodiment of implementing the encapsulation processing from the ODUk to the packet or the packet by the apparatus of the present invention, considering that the implementation principle of the packet and the packet is basically the same, the packet and the packet are collectively referred to as the packet hereinafter if no specific description is made.
The ODUk to packet or packet processing module shown in fig. 3 includes: an ODUk clock 105 (the frequency of which is Ck), ODUk data 113, a first counter 106 (for calculating the number of received ODUk bytes, the maximum value is B), and a B byte count end indication signal 107 (an indication signal after the count value of the first counter 106 reaches B bytes); a reference measurement clock 109 (with a frequency Cm), a second counter 108 (for counting the number of reference measurement clocks 109), a count value 110 being the current count value of the second counter 108, a first calculation module 111 (for generating CI0 and CI1 overhead 112 based on the B-byte count end indicator signal 107 and the count value 110 of the first counter 106), CI0 and CI1 overhead 112 (i.e., CI0 and CI1 overheads generated by the first computing module 111), a packet generating module 114 (i.e., a module for generating a packet with a payload length of B bytes, which encapsulates an ODUk with B bytes into a payload portion of the packet according to the input ODUk clock 105 and ODUk data 113, so that the payload length is B bytes, and meanwhile, loads the CI0 and CI1 overhead 112 into the overhead of the packet), and a packet 115 (i.e., a packet with a payload length of B bytes generated by the packet generating module 114, and this packet finally enters the switching network unit 103 in fig. 2 for switching processing).
The second device embodiment: in view of the basic consistency of the implementation principle of the packet and the packet, the packet and the packet are collectively referred to as a packet hereinafter if no specific description is made.
After the packet 115 (a packet with a payload length of B bytes generated by the packet generation module 114 in fig. 3) is subjected to switching processing by the switching network unit 103 in fig. 2, the packet enters the processing module for sending the packet or packet to the ODUk as shown in fig. 4, which includes: a parsing module 120 (for parsing the overhead 121 of CI0 and CI1 from the packet 115 with a B byte length), a second calculating module 122 (for calculating Nm123 from these parsed overhead 121 of CI0 and CI 1), and a desynchronizer 125 (for recovering an ODUk clock 126 with a frequency Cj from Nm123 and a reference measurement clock 124, where the Cj will be consistent with the frequency Ck of the ODUk clock 105 in fig. 3).
With the above embodiment of the apparatus shown in fig. 3, the processing procedure of the corresponding method is as follows: in the ODUk-to-packet encapsulation process, an ODUk clock 105 (with a frequency Ck) enters a first counter 106, and generates 1B-byte count end indication signal 107 every time a B byte is counted; the second counter 108 counts the number of reference measurement clocks 109 (with a frequency Cm) which must be large enough to ensure that the count value does not overflow between the signal intervals of two adjacent B-byte count end indication signals 107; a first calculating module 111 calculates a difference value between signals of two adjacent B byte count end indication signals 107 and a count value output by a second counter 108, so as to obtain a clock number of a reference measurement clock 109 in each received B byte ODUk time, where the clock number may only be Nms, Nms +1 or Nms-1 on the premise that an ODUk clock frequency offset is less than plus or minus 100ppm, where Nms is a constant and can be calculated by the above formula 1; the first calculation module generates CI0 and CI1 overheads 112 according to the obtained Nms, Nms +1, or Nms-1, and at the same time, the packet generation module 114 puts the ODUk of the B byte into the payload of the packet and generates a packet 115 with a payload length of B byte every time the ODUk of the B byte is collected, and the packet generation module 114 simultaneously puts the CI0 and CI1 overheads 112 calculated by the first calculation module 111 into the overheads of the packet 115.
With the above embodiment of the apparatus shown in fig. 4, the processing procedure of the corresponding method is as follows: in the decapsulation processing of the packet to ODUk, the packet 115 in fig. 3 processed by the switching network unit 103 is subjected to decapsulation processing of an incoming packet to ODUk, the parsing module 120 parses CI0 and CI1 overhead 121 from the packet 115, the packet is sent to the second calculation module 122 to obtain Nm123, where a possible value of Nm123 may only be Nms, Nms +1, or Nms-1, the Nm123 and the reference measurement clock 124 (whose frequency is Cm) are sent to the desynchronizer 125, the desynchronizer 125 obtains Cj by calculation according to the above formula 2, and generates a recovered ODUk clock 126 (whose frequency is Cj) according to Cj, and the frequency of the recovered ODUk clock 126 is kept consistent with the frequency of the ODUk clock 105 in fig. 3. In addition, in the second calculation module 122, Nm is generated using the CI0 overhead when there is no packet loss, CI1 is used if 1 packet loss is detected, and Nm is forcibly output as Nms if continuous multiple packet loss is detected, so that the process of recovering the clock when there is a packet loss can still be performed correctly as much as possible. In addition, if it is desired to recover the clock of the OTUk, the clock of the OTUk (the frequency of which is Cjk) can be recovered by only letting the above desynchronizer operate according to the above formula 3.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims (9)

1. A method for recovering an optical transport network clock from a reference clock, the method comprising:
in the encapsulation processing of converting an ODUk into a packet or a packet in an optical transport network, measuring frequency information of an ODUk clock by using a reference measurement clock, and encapsulating the measured frequency information into an overhead of the packet or the packet; in the decapsulation processing for recovering the ODUk from the packet or the packet, the ODUk clock of the same frequency is recovered according to the reference measurement clock of the same frequency, the frequency information parsed from the overhead of the packet or the packet, and the length of the packet or the packet.
2. The method according to claim 1, wherein the ODUk is specifically an ODUk, where k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex; the frequency of the ODUk is Ck specifically; the frequency of the reference measurement clock is Cm; the frequency of the recovered ODUk clock is specifically Cj, and Cj is Ck; the length of the packet or the packet is a fixed value, the payload length of the fixed-length packet or the fixed-length packet is a byte B, the fixed-length packet or the fixed-length packet contains ODUk information of the byte B, and overhead of the fixed-length packet or the fixed-length packet at least contains 2 bits of the measured frequency information;
in the encapsulation process of converting from an ODUk to a packet or a packet, each time the ODUk information of B bytes is encapsulated into the packet or the packet of a fixed length, the method further includes: counting the number Nm of cycles passed by the reference measurement clock in the process of receiving the B byte ODUk information; nm is the frequency information of the ODUk clock measured by the reference measurement clock;
on the premise that the frequency deviation of the ODUk is less than plus or minus 150ppm, the Nm value is specifically Nms, Nms-1 or Nms +1, wherein Nms adopts a formula 1:calculating to obtain; wherein Cks is a standard rate of the ODUk, and the Nms is equal to a product of the Cm, the B byte, and the integer 8, divided by the Cks, and rounded.
3. The method of claim 2, further comprising: and packaging the measured frequency information which is represented by 2 bits, namely Nms, Nms-1 or Nms +1, into the fixed-length overhead of the packet or the packet for transmission.
4. The method of claim 3, wherein in a decapsulation process to recover the ODUk from the packet or packet, the method further comprises:
analyzing the measured frequency information of 2 bits from the fixed-length overhead of the packet or the packet;
nm is obtained according to the measured frequency information of 2 bits and the Nms obtained by calculation of the formula 1, and the value of the Nm is specifically Nms, Nms-1 or Nms + 1;
calculating the Cj according to the Nm, another reference measurement clock with the same frequency as the reference measurement clock and the B, wherein the formula adopted by the calculation is formula 2:
5. the method of claim 4, wherein after calculating Cj, the method further comprises: inputting Cj into a desynchronizer designed according to the formula 2, and obtaining a clock with the frequency of Cj according to the formula 2; the clock with the frequency Cj is as follows: and recovering the ODUk clock with the same frequency after the ODUk is subjected to encapsulation processing and decapsulation processing.
6. The method of claim 4, further comprising: according toAnd calculating Cjk, and inputting the Cjk into a desynchronizer to obtain a recovered OTUk clock with the frequency Cjk, wherein the OTUk is specifically OTUk, and k is 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6.
7. An apparatus for recovering an optical transport network clock from a reference clock, the apparatus comprising: an ODUk to packet or packet processing module and a packet or packet to ODUk processing module; wherein,
the ODUk to packet or packet processing module is configured to measure frequency information of an ODUk clock by using a reference measurement clock in an encapsulation process for converting an ODUk into a packet or packet in an optical transport network, and encapsulate the measured frequency information into an overhead of the packet or packet;
and the processing module of the packet or the packet to the ODUk is configured to, in decapsulation processing for recovering the ODUk from the packet or the packet, recover an ODUk clock of the same frequency according to a reference measurement clock of the same frequency, the frequency information parsed from overhead of the packet or the packet, and a length of the packet or the packet.
8. The apparatus of claim 7, wherein the ODUk is specifically an ODUk, where k is 0, 1, 2, 2e, 3, 3e1, 3e2, 4, 5, 6, flex; the frequency of the ODUk is Ck specifically; the frequency of the reference measurement clock is Cm; the frequency of the recovered ODUk clock is specifically Cj, and Cj is Ck; the length of the packet or the packet is a fixed value, the payload length of the fixed-length packet or the fixed-length packet is a byte B, the fixed-length packet or the fixed-length packet contains ODUk information of the byte B, and the overhead of the fixed-length packet or the fixed-length packet at least contains measured frequency information of 2 bits;
the ODUk to packet or packet processing module further includes: the device comprises a first counter, a second counter, a first calculation module and a packet or grouping generation module; wherein,
the first counter is used for counting the number of bytes of the received ODUk information, and the maximum value is B;
the second counter is configured to count a number Nm of cycles that the reference measurement clock passes through in each process of receiving a byte B of ODUk information; nm is the frequency information of the ODUk clock measured by the reference measurement clock; on the premise that the frequency deviation of the ODUk is less than plus or minus 150ppm, the value of Nm is specifically Nms, Nms-1 or Nms +1, where Nms adopts formula 1:calculating to obtain; wherein Cks is a standard rate of the ODUk, and the Nms is equal to a product of the Cm, the B byte, and the integer 8 divided by the Cks, and rounded;
the first calculating module is configured to receive a B byte count end indication signal of the first counter and an Nm obtained by counting by the second counter, where a value of the Nm is specifically Nms, Nms-1, or Nms +1, and Nms, Nms-1, or Nms +1 indicated by 2 bits is used as measured frequency information;
and the packet or packet generating module is used for generating the fixed-length packet or packet with the payload length of B bytes, and simultaneously packaging the measured frequency information of 2 bits into the overhead of the fixed-length packet or packet for transmission.
9. The apparatus of claim 8, wherein the packet or packet to ODUk processing module further comprises: the system comprises an analysis module, a second calculation module and a desynchronizer; wherein,
the analysis module is used for analyzing the measured frequency information of 2 bits from the received packets or packets with fixed length;
the second calculation module is configured to obtain Nm according to the measured frequency information of 2 bits and Nms obtained through calculation in the formula 1, where a value of Nm is specifically Nms, Nms-1, or Nms + 1; calculating the Cj according to the Nm, another reference measurement clock with the same frequency as the reference measurement clock and the B, wherein the formula adopted by the calculation is formula 2:
the desynchronizer is used for obtaining a clock with the frequency of Cj according to the input Cj and the formula 2; the clock with the frequency Cj is as follows: and recovering the ODUk clock with the same frequency after the ODUk is subjected to encapsulation processing and decapsulation processing.
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Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103684651B (en) * 2012-09-13 2018-02-13 中兴通讯股份有限公司 The fixed bit rate interface data method of reseptance and device of optical transfer network mixed service
CN103841014A (en) * 2012-11-22 2014-06-04 西安邮电大学 Odu0 data packet circuit
CN105323053B (en) * 2014-06-23 2019-11-05 中兴通讯股份有限公司 The method and device of business clock transparent transmission
CN108242965B (en) * 2016-12-23 2019-07-19 华为技术有限公司 A kind of clock transfer method and relevant device
CN108880722B (en) * 2017-05-10 2021-04-23 深圳市中兴软件有限责任公司 Clock synchronization method, system and optical transmission equipment

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101232340A (en) * 2007-01-23 2008-07-30 华为技术有限公司 Communication system, method, transmission device as well as receiving apparatus
CN101834688A (en) * 2009-03-09 2010-09-15 华为技术有限公司 Method and device for mapping and demapping in optical transport network

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8699886B2 (en) * 2005-11-23 2014-04-15 Ciena Corporation Externally synchronized optical transport network systems and associated methods
CN101374030B (en) * 2007-08-24 2011-05-18 华为技术有限公司 Synchronizing system and method for virtual cascade of light transportation network
CN101150879B (en) * 2007-10-10 2010-08-04 中兴通讯股份有限公司 Intercrossed scheduling system and method based on optical transmission network
CN101170550B (en) * 2007-11-22 2010-05-26 中兴通讯股份有限公司 A transparent transmission method for 10000M Ethernet signals in optical transmission network
US8050567B2 (en) * 2008-09-12 2011-11-01 Applied Micro Circuits Corporation System and method for transporting asynchronous ODUk signals over a synchronous interface
US8081639B2 (en) * 2009-01-27 2011-12-20 Tellabs Operations, Inc. Method and apparatus for supporting client data transport with timing transparency

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101232340A (en) * 2007-01-23 2008-07-30 华为技术有限公司 Communication system, method, transmission device as well as receiving apparatus
CN101834688A (en) * 2009-03-09 2010-09-15 华为技术有限公司 Method and device for mapping and demapping in optical transport network

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Interface for the Optical Transport Network(OTN);International Telecommunication Union;《ITU-TG.709/Y.1331(03/03)》;20030316;正文第86页第一行至第90页最后一行，第16页最后一段，图7-1，图7-2，图19-1，图19-6，图19-8，图19-11 *

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