WO2008098450A1 - Procédé, système et dispositif pour la mise en oeuvre de synchronisation temporelle dans un réseau de communications - Google Patents

Procédé, système et dispositif pour la mise en oeuvre de synchronisation temporelle dans un réseau de communications Download PDF

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Publication number
WO2008098450A1
WO2008098450A1 PCT/CN2007/070705 CN2007070705W WO2008098450A1 WO 2008098450 A1 WO2008098450 A1 WO 2008098450A1 CN 2007070705 W CN2007070705 W CN 2007070705W WO 2008098450 A1 WO2008098450 A1 WO 2008098450A1
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WO
WIPO (PCT)
Prior art keywords
network element
time
information
absolute
absolute time
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PCT/CN2007/070705
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English (en)
Chinese (zh)
Inventor
Kuiwen Ji
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Huawei Technologies Co., Ltd.
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Publication of WO2008098450A1 publication Critical patent/WO2008098450A1/fr

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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
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
    • 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
    • H04J3/0647—Synchronisation among TDM nodes
    • H04J3/065—Synchronisation among TDM nodes using timestamps

Definitions

  • the present invention relates to communication technologies, and in particular, to a method, system and device for implementing time synchronization in a communication network. Background of the invention
  • the traditional Synchronous Digital hierarchy (SDH) network can only achieve frequency synchronization, but not time synchronization.
  • 3G third-generation network
  • CDMA Code Division Multiple Access
  • TD-SCDMA Time Division Synchronous Code Division Multiple Access
  • WIMAX World Interoperability for Microwave Access, etc.
  • CDAM2000 requires the pilot time error between base stations to be within 3 us.
  • the time synchronization method commonly used in the prior art is a positioning method using a satellite source such as a Global Positioning System (GPS) as a time source.
  • GPS Global Positioning System
  • FIG. 1 shows a network that realizes time synchronization through GPS. Schematic.
  • Each base station is provided with a GPS receiving card for receiving GPS time information to achieve time synchronization of each base station.
  • the construction and maintenance costs required for this method are too high.
  • time synchronization is implemented between the base stations through a precision clock synchronization protocol standard (IEEE 1588) of the network measurement and control system.
  • IEEE 1588 protocol is a general specification for improving the network timing synchronization capability.
  • the basic idea is to synchronize the internal clock of the network device with the master clock of the master computer through hardware and software.
  • FIG. 2 is a schematic diagram of a network structure for implementing time synchronization through IEEE 1588.
  • Each network element completes 1588 through an SDH-based packet (POS, Packet Over SDH).
  • POS Packet Over SDH
  • This method has problems such as asynchronous mapping and pointer adjustment in the SDH branch, which causes jitter of up to several tens of US, so it is difficult to ensure the accuracy of time synchronization. Summary of the invention
  • Embodiments of the present invention provide a method for implementing time synchronization in a communication network, which can implement more accurate time synchronization.
  • Embodiments of the present invention provide a system for implementing time synchronization in a communication network, which can implement more accurate time synchronization.
  • the embodiments of the present invention provide a network element device that implements time synchronization in a communication network, which can implement relatively accurate time synchronization.
  • a method for implementing time synchronization in a communication network comprising:
  • the absolute time difference between the downstream network element and the upstream network element and the length of the line delay are calculated.
  • the absolute time is adjusted according to the absolute time difference and the line delay time to synchronize time with the upstream network element.
  • a system for implementing time synchronization in a communication network comprising an upstream network element and a downstream network element;
  • the upstream network element is configured to send time information to the downstream network element.
  • the downstream network element is configured to receive time information from the upstream network element, calculate an absolute time difference from the upstream network element, and a line delay duration according to the time information, and according to the absolute time difference and the line The delay time adjusts its absolute time to achieve time synchronization with the upstream network element.
  • a network element device for implementing time synchronization in a communication network, where the network element includes a central time generating unit and a time stamp processing unit;
  • the timestamp processing unit is configured to receive time information from an upstream network element, and according to the Calculating the absolute time difference between the time information and the upstream network element and the line delay duration, and transmitting the calculated absolute time difference and the line delay duration to the central time generating unit;
  • the central time generating unit is configured to receive an absolute time difference from the timestamp processing unit and a line delay duration, and adjust an absolute time of the line according to the absolute time difference and the line delay duration to implement the upstream network element. Time synchronization.
  • the downstream network element in the network adjusts its absolute time to be consistent with the upstream network element according to the calculated absolute time difference between the upstream network element and the line delay duration.
  • the difference of absolute time and the influence of line delay time synchronization is realized more accurately.
  • FIG. 1 is a schematic diagram of a network structure in which time synchronization is implemented by using GPS
  • FIG. 2 is a schematic diagram of a network structure for implementing time synchronization through IEEE 1588;
  • FIG. 3 is a schematic structural diagram of a system embodiment of the present invention.
  • FIG. 4 is a schematic structural diagram of a network element device in an embodiment of the present invention.
  • FIG. 5 is a schematic structural diagram of a time stamp processing unit according to an embodiment of the present invention
  • FIG. 8 is a schematic structural diagram of a central time generating unit according to a preferred embodiment of the present invention
  • FIG. 8 is a schematic diagram of a network element including more than one in the embodiment of the present invention
  • Schematic diagram of the time stamp processing unit
  • Figure 9 is a general flow chart of an embodiment of a method of the present invention.
  • Figure 10 is a flow chart of a preferred embodiment of the method of the present invention.
  • FIG. 11 is a schematic structural diagram of a network for implementing time synchronization of each base station according to an embodiment of the present invention. Mode for carrying out the invention
  • the downstream network element calculates the absolute time difference between the upstream network element and the line delay time; and adjusts the absolute time according to the calculated absolute time difference and the line delay time to achieve time synchronization with the upstream network element.
  • FIG. 3 is a schematic structural diagram of a system embodiment of the present invention. As shown in FIG. 3, the system includes an upstream network element 301 and a downstream network element 302;
  • the upstream network element 301 is configured to send time information to the downstream network element 302, and the downstream network element 302 is configured to receive time information from the upstream network element 301, and calculate an absolute relationship with the upstream network element 301 according to the time information.
  • the time difference and the delay time of the line are adjusted, and the absolute time of the line is adjusted according to the absolute time difference and the line delay time to realize time synchronization with the upstream network element 301.
  • the system further includes a base station 303 for receiving synchronized time information from the upstream network element 301 and the downstream network element 302.
  • FIG. 4 is a schematic structural diagram of a network element device according to an embodiment of the present invention.
  • the network element mainly includes a timestamp processing unit 401 and a central time generating unit 402.
  • the timestamp processing unit 401 is configured to receive time information from the upstream network element, calculate an absolute time difference from the upstream network element and a line delay duration according to the time information, and send the calculated absolute time difference and the line delay duration. Giving a central time generating unit 402;
  • a central time generating unit 402 configured to receive an absolute time difference from the timestamp processing unit 401 and a line delay duration, according to the absolute time difference and the line delay duration The absolute time of the body is synchronized with the time of the upstream network element.
  • the time stamp processing unit 401 further includes: a time receiving unit 4011, a time sending unit 4012, and a time comparing unit 4013. As shown in FIG. 5, FIG. 5 is a schematic structural diagram of a time stamp processing unit 401 according to an embodiment of the present invention.
  • the time receiving unit 4011 is configured to receive the time information t1 sent by the upstream network element at the time of the absolute time t1 and after the line delay, send the time information t1 to the time comparing unit 4013, and receive the time of the upstream network element returning. Information t3, the time information t3 is sent to the time comparison unit 4013;
  • the time sending unit 4012 is configured to send time information t3 to the upstream network element at the time of its absolute time t3;
  • the time comparison unit 4013 is configured to receive the time information t1 from the time receiving unit 4011, calculate a difference between the absolute time and the time information t1, and obtain an absolute time difference; and receive the time information t3 from the time receiving unit 4011, and calculate the received time.
  • the time difference between the time t4 and the time t3 of the time information t3 is 1/2, and the line delay time length is obtained; and the calculated absolute time difference and the line delay time length are transmitted to the central time generating unit 402.
  • the time sending unit 4012 is further configured to: send the absolute time information of the local network element to the downstream network element, and invert the time information received from the downstream network element. It is passed back to the downstream network element.
  • the specific working mode of the timestamp processing unit 401 shown in FIG. 5 is: a clock packet defined by a protocol (NTP, Network Time Protocol), or a data packet of other formats, such as mapping time information with a general frame processing program (GFP-F). ) Encapsulate and put this Ethernet packet into the SDH line overhead information.
  • the specific method may be that one byte after the segment overhead S1 byte is defined as S2 for transmitting time information; or an existing overhead such as a byte in D1 ⁇ D12, or a certain number of bytes may be used to transmit time. information. Assume this embodiment The time information is transmitted by using the D4 byte. Then, the Ethernet packet is 64 bytes long and sent once every second.
  • the time transmitting unit 4012 puts 64 bytes into the continuous 64 frames of D4 and transmits it to the downstream.
  • the time sending unit 4012 is further configured to receive the time packet sent by the downstream network element, put it into the D4 of the continuous 64 frames, and transmit the packet to the downstream network element. .
  • the time receiving unit 4011 receives the time packet in the SDH line overhead information. If the network element shown in FIG. 4 is the downstream network element, the time receiving unit 4011 sends the time packet to the time comparing unit 4013. If the network element shown in FIG. 4 is The upstream receiving unit 4011 sends the time packet to the time sending unit 4012 for reverse phase return.
  • the time comparison unit 4013 receives the time packet from the time receiving unit 4011, determines the time information of the time, and compares it with the absolute time of the network element.
  • the absolute time difference is obtained by comparing the absolute time of the network element with the time information actively sent by the upstream network element, and the time delay of the line is obtained by comparing the absolute time of the network element with the time information of the inverted backhaul, and the absolute time difference and the line are obtained.
  • the delay time is transmitted to the central time generating unit 402.
  • the time receiving unit 4011 and the time transmitting unit 4012 receive and transmit time packets from the Ethernet accordingly, and the processing is similar.
  • the central time generating unit 402 further includes: a filtering unit 4021 and an adjusting unit 4022. As shown in FIG. 6, FIG. 6 is a schematic structural diagram of the central time generating unit 402 in the embodiment of the present invention.
  • the filtering unit 4021 is configured to receive an absolute time difference from the time comparing unit 4013 and a line delay duration, perform a pass-through filtering on the absolute time difference and the line delay duration, and send the filtered absolute time difference and the line delay duration to the The adjusting unit 4022; the filtering unit 4021 may further include a first filtering unit and a second filtering unit: The first filtering unit is configured to receive an absolute time difference from the time comparing unit 4013, perform low-pass filtering on the absolute time difference, and send the filtered absolute time difference to the adjusting unit 4022.
  • the second filtering unit is configured to receive the The time delay unit 4013, the line delay duration, the line delay time is low-pass filtered, and the filtered line delay time is sent to the adjustment unit 4022;
  • the adjusting unit 4022 is configured to receive the filtered absolute time difference from the filtering unit 4021 and the line delay duration, calculate the sum of the absolute time and the filtered absolute time difference, and the line delay duration, and adjust the current absolute time of the line. For the calculation of the results.
  • FIG. 7 is a schematic structural diagram of a central processing unit in a preferred embodiment of the present invention. As shown in FIG. 7, the adjusting unit in this embodiment is an adder, and the two filtering units are low pass filters (LE) 1 and LF2, respectively.
  • LE low pass filters
  • the network element in this embodiment may be located in an SDH network or an Optical Transport Network (OTN).
  • OTN Optical Transport Network
  • FIG. 8 is a schematic structural diagram of a network element including more than one timestamp processing unit according to an embodiment of the present invention. The time information for which the timestamp processing unit is selected to receive the upstream network element needs to be selected by the downstream network element.
  • the working mode of the network element shown in Figure 8 is as follows: First, the network element shown in Figure 8 (hereinafter referred to as the local network element) selects one of the plurality of timestamp processing units as the upstream network element information receiving port, and the specific selection manner may be The network element is configured according to the network configuration. For example, each timestamp processing unit corresponds to a network element in a network, that is, network element A, network element B, ... network element N, if the network element A is the current upstream network element of the network element, and the local network element selects a timestamp processing unit corresponding to the network element A, and the instant stamp processing unit A receives the information sent by the upstream network element;
  • the network element A sends the time information t1 to the timestamp processing unit A at its own absolute time t1. Since there is a line delay, the time information reaches the timestamp processing unit A at the absolute time t2 of the network element A; the timestamp processing The unit A compares the absolute time of the local network element with the received time information t1 to obtain an absolute time difference between the local network element and the network element A, and sends the absolute time difference to the central time generating unit; the timestamp processing unit A The time information t3 is sent to the network element A at the time t3 of the absolute time of the network element. After receiving the time information t3, the network element A immediately returns the time information t3 to the local network element.
  • the time stamp processing unit is present due to the line delay.
  • A receives the time information t3 at the absolute time t4 of the network element, and obtains a value of 1/2 of the difference between t4 and t3 as the line delay duration, and sends the line delay time to the central time generating unit;
  • the time generating unit performs low-pass filtering on the received absolute time difference and the line delay duration, and calculates the filtered absolute time difference and the line delay duration and the network element. The time and, as a result of the calculated absolute time of the current network element to achieve synchronization with the travel time of the NE.
  • time processing units other than the time processing unit A can be used as the downstream time output port.
  • FIG. 9 is a general flowchart of an embodiment of a method according to the present invention. As shown in FIG. 9, the method includes the following steps:
  • Step 901 The downstream network element calculates an absolute time difference between the upstream network element and the line delay time.
  • the upstream network element sends time information t1 to the downstream network element at its own absolute time t1; the downstream network element compares its absolute time with the time information tl received from the upstream network element and after the line delay. Get the difference between the two, that is, the absolute time difference.
  • the downstream network element sends time information t3 to the upstream network element;
  • the network element returns the received time information t3 to the downstream network element;
  • the downstream network element receives the time information t3 at its own absolute time t4, and obtains a value of 1/2 of the difference between t4 and t3, and obtains the result. This is the line delay time.
  • Step 902 The downstream network element adjusts its absolute time according to the absolute time difference and the line delay duration to synchronize time with the upstream network element.
  • the downstream network element performs low-pass filtering on the received absolute time difference and the line delay duration. Then, the downstream network element calculates the sum of its absolute time and the filtered absolute time difference and the line delay duration, which will be calculated. The result is its own current absolute time.
  • the time information sent by the upstream network element to the downstream network element may be carried in the overhead information, and the time information sent by the downstream network element to the upstream network element may be carried in the inverted overhead information.
  • the specific carrying mode may be: The upstream network element/downstream network element defines a new field in the overhead information/inversion overhead information to carry the time information; or the upstream network element/downstream network element uses the overhead information/inversion overhead information.
  • the existing field carries the time information.
  • the upstream network element/downstream network element can carry the time information by using the existing fields D1 ⁇ D12 in the overhead information/inversion overhead information.
  • the D4 ⁇ D12 carries the time information. Time information.
  • the upstream network element and the downstream network element are only a relative concept, it is possible that a downstream network element itself is the most upstream network element in the network, so that the upstream network element corresponding to the downstream network element changes. It is a base station controller or a time integrated server (BITS), and the downstream network element receives time information from the base station controller or the BITS, and performs subsequent operations according to the time information, and details are not described herein.
  • a downstream network element itself is the most upstream network element in the network, so that the upstream network element corresponding to the downstream network element changes. It is a base station controller or a time integrated server (BITS), and the downstream network element receives time information from the base station controller or the BITS, and performs subsequent operations according to the time information, and details are not described herein.
  • BIOS time integrated server
  • the upstream network element/downstream network shown in Figure 9 may be an SDH network element or an OTN network.
  • the SDH network is taken as an example to further illustrate the method of the present invention.
  • FIG 10 is a flow chart of a preferred embodiment of the method of the present invention. As shown in Figure 10, the following steps are included: Step 1001: The upstream network element sends time information t1 to the downstream network element at its own absolute time t1.
  • the time information sent by the upstream network element to the downstream network element is carried in the overhead information, and the specific carrying manner may be: the upstream network element defines a new field in the overhead information to carry the time information; or, the upstream network The time information is carried by the existing fields D4 ⁇ D12 in the element usage overhead information.
  • Step 1002 The downstream network element calculates an absolute time difference from the upstream network element according to the received time information t1.
  • the time information tl sent by the upstream network element in step 1001 can reach the downstream network element after a ⁇ time delay, that is, when the downstream network element receives the time information tl.
  • the downstream network element After receiving the time information t1, the downstream network element compares it with its absolute time to obtain the difference between the two, and the difference is the absolute time difference.
  • the absolute time difference includes both the original absolute time difference between the downstream network element and the upstream network element, and the time difference caused by the line delay time ⁇ .
  • Step 1003 The downstream network element sends time information t3 to the upstream network element at its own absolute time t3.
  • the time information that the downstream network element sends to the upstream network element may be carried in the reverse-cost information.
  • the specific carrying manner may be: The downstream network element defines a new field in the reverse-overload information to carry the time information. Or, the downstream network element carries the time information by using the existing fields D4-D12 in the reverse cost information.
  • Step 1004 The upstream network element returns the received time information t3 to the downstream network element.
  • Step 1005 The downstream network element calculates the length of the line delay between the upstream network element and the upstream network element.
  • Step 1006 The downstream network element performs a pass-through filtering on the calculated absolute time difference and the line delay duration.
  • the downstream network element Before proceeding to the next step, the downstream network element first low-pass filters the calculated absolute time difference and line delay duration to remove possible jitter.
  • Step 1007 The downstream network element adjusts its current absolute time to synchronize with the upstream network element time.
  • the downstream network element can adjust its absolute time according to the absolute time difference and the line delay duration.
  • the specific adjustment manner is as follows: adding the absolute time difference and the line delay duration to the original absolute time. After such processing, the downstream network element realizes time synchronization with the upstream network element.
  • FIG. 11 is a schematic structural diagram of a network for implementing time synchronization of each base station according to an embodiment of the present invention.
  • the network elements corresponding to the two base stations transmit time information to the corresponding base station. Since the time information received by the two base stations is synchronization information, the two base stations also implement time synchronization.
  • the upstream network element and the downstream network element mentioned in this embodiment are both SDH network elements.
  • the upstream network element and the downstream network element may also be network elements, that is, the same can be implemented in the network.
  • the specific implementation process of the time synchronization method of the present invention is the same as that of FIG. 10, and details are not described herein again. It can be seen that the time synchronization can be implemented more accurately by using the technical solution of the embodiment of the present invention.
  • the technical solution of implementing the embodiment of the present invention only needs to make minor changes to the network element on the basis of the original network, without adding any Equipment, economical and convenient.

Abstract

Procédé de mise en oeuvre de synchronisation temporelle dans un réseau de communications, selon les étapes suivantes: calcul par l'élément de réseau en aval de la différence de temps absolu et des retards pour les liaisons entre cet élément et l'élément de réseau en amont (901); sur la base de ces valeurs, l'élément de réseau en aval règle lui-même le temps absolu pour mettre en oeuvre la synchronisation temporelle avec l'élément de réseau en amont (902). On décrit également un système et un dispositif d'élément de réseau pour la mise en oeuvre d'une synchronisation temporelle dans un réseau de communications. Les procédé, système et dispositif en question permettent d'établir une synchronisation temporelle à faible coût et précision élevée.
PCT/CN2007/070705 2007-02-15 2007-09-17 Procédé, système et dispositif pour la mise en oeuvre de synchronisation temporelle dans un réseau de communications WO2008098450A1 (fr)

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CNA2007100848735A CN101247169A (zh) 2007-02-15 2007-02-15 一种在通信网络中实现时间同步的方法和系统以及设备

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