WO2016173265A1 - 一种时间同步的方法及系统、网络设备 - Google Patents

一种时间同步的方法及系统、网络设备 Download PDF

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Publication number
WO2016173265A1
WO2016173265A1 PCT/CN2015/097462 CN2015097462W WO2016173265A1 WO 2016173265 A1 WO2016173265 A1 WO 2016173265A1 CN 2015097462 W CN2015097462 W CN 2015097462W WO 2016173265 A1 WO2016173265 A1 WO 2016173265A1
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Prior art keywords
network device
service frame
rec
system clock
data packet
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PCT/CN2015/097462
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English (en)
French (fr)
Inventor
陈聪
徐川
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华为技术有限公司
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Publication date
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to JP2017556141A priority Critical patent/JP6505255B2/ja
Priority to KR1020177033300A priority patent/KR102009588B1/ko
Priority to EP15890640.4A priority patent/EP3277034B1/en
Publication of WO2016173265A1 publication Critical patent/WO2016173265A1/zh
Priority to US15/794,904 priority patent/US10412697B2/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/001—Synchronization between nodes
    • H04W56/0015—Synchronization between nodes one node acting as a reference for the others
    • 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
    • H04J3/0644—External master-clock
    • 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
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices
    • H04W88/085—Access point devices with remote components
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0658—Clock or time synchronisation among packet nodes
    • H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/20—Control channels or signalling for resource management
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices

Definitions

  • the present invention relates to the field of communications technologies, and in particular, to a method and system for time synchronization, and a network device.
  • the distributed base station is characterized in that the radio equipment (English: Radio Equipment, RE: RE) and the radio equipment controller (English: Radio Equipment Control, REC) are separated, and then the connection between the two is realized through the optical fiber.
  • the radio equipment English: Radio Equipment, RE: RE
  • the radio equipment controller English: Radio Equipment Control, REC
  • the RECs can be deployed in the equipment room to form a baseband pool, and then connected to the REs deployed on the planning site through optical fibers to complete network coverage.
  • the REC and the RE, and the RE and the RE may be connected by using a common public radio interface (English: Common Public Radio Interface, CPRI for short).
  • CPRI itself has strict clock synchronization plane requirements and time synchronization plane requirements.
  • the clock synchronization plane requirement can be understood as the deviation between the frequency at which the REC sends the CPRI service frame and the frequency at which the RE sends the CPRI service frame, and the deviation between the frequency and the frequency at which the RE sends the CPRI service frame should be controlled to ensure the accuracy of the air interface frequency.
  • the time synchronization plane requirement can be understood as ensuring that the communication delay between the REC and the RE is fixed.
  • the communication delay between the REC and the RE may be calculated, and based on the communication delay, the downlink signal transmission time of the REC is controlled in the downlink direction, and the uplink signal transmission delay of the RE is compensated in the uplink direction. In order to ensure that the communication delay between the REC and the RE is fixed.
  • T communication T a + T b + T c + T d
  • T a is the delay between the REC sending the transmission time stamp to the REC transmission sampling signal (English: Radio Sample Signal)
  • T b is the transmission delay of the sampled signal on the fiber link
  • T c is the delay between the RE receiving the sampled signal and the RE receiving the receiving time stamp
  • T d is the RE setting the receiving time stamp to the sampling signal transmission to the delay Test the delay between reference points.
  • the signal transmission point of the RE that is, the antenna port, can be defined as a delay test reference point.
  • the method and system for time synchronization of the embodiment of the present invention and the network device help to ensure the relationship between REC and RE The delay remains unchanged.
  • a method for time synchronization where a first network device is connected to a wireless device controller REC, a second network device is connected to a radio frequency device RE, and the first network device and the second network device maintain a system Time synchronization, the method includes:
  • the first network device keeps a system clock synchronization with the second network device, and the first network device receives the service sent by the REC After the frame, the method further includes:
  • the first network device calculates a frequency offset by using a system clock of the first network device and a system clock of the REC;
  • the data packet sent by the first network device to the second network device includes the service frame, the first timestamp, and the frequency offset.
  • a method for time synchronization where a first network device is connected to a wireless device controller REC, a second network device is connected to a radio frequency device RE, and the first network device and the second network device maintain a system Time synchronization, the method includes:
  • the first data packet sent by the first network device where the first data packet includes a first service frame and a first timestamp T1, where the first service frame is sent by the REC to The first network device, where the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame;
  • the second network device records the second timestamp T2 of the first service frame by using the system time of the second network device;
  • the first data packet further includes a frequency deviation
  • the frequency deviation is obtained by the system clock of the first network device and the system clock of the REC
  • the second network device obtains the system clock of the REC by using the first data packet, including:
  • the second network device extracts the frequency offset from the first data packet
  • the second network device calculates a system clock of the REC by using a system clock of the second network device and the frequency deviation.
  • the second network device sends, by using the system clock of the REC, the The first service frame extracted in a data packet includes:
  • the second network device buffers the first service frame extracted from the first data packet to a memory
  • the second network device reads the first service frame from the memory by using a system clock of the REC as a read clock, and sends the first service frame to the RE, where the first service frame is cached in the memory.
  • the duration is zero.
  • the methods include:
  • the second network device buffers the second service frame to the memory, and sets a buffer duration of the second service frame to a fixed delay minus the transmission delay;
  • the second network device If it is determined that the buffer duration arrives, the second network device reads the second service frame from the memory with the system clock of the REC as a read clock, and sends the second service frame to the RE .
  • a network device is provided, where the network device is a first network device, the first network device is connected to a wireless device controller REC, and the first network device and the second network device maintain system time synchronization.
  • the second network device is connected to the radio device RE, and the first network device includes:
  • a receiving unit configured to receive a service frame sent by the REC, where the service frame carries a system clock of the REC;
  • a recording unit configured to record, by using the system time of the first network device, a first timestamp T1 for receiving the service frame when the receiving unit receives the service frame;
  • a sending unit configured to send a data packet to the second network device, where the data packet includes the service frame and The first timestamp, the data packet is used to advertise the system clock of the REC and the first timestamp to the second network device.
  • the first network device and the second network device are kept in a system clock, the first network device further includes:
  • An extracting unit configured to extract, after the receiving unit receives the service frame, a system clock of the REC from the service frame;
  • a calculating unit configured to calculate a frequency deviation by using a system clock of the first network device and a system clock of the REC;
  • the data packet sent by the sending unit to the second network device includes the service frame, the first timestamp, and the frequency offset.
  • a fourth aspect provides a network device, where the network device is a second network device, the second network device is connected to a radio frequency device RE, and the second network device maintains system time synchronization with the first network device.
  • the first network device is connected to the wireless device controller REC, and the second network device includes:
  • a receiving unit configured to receive a first data packet sent by the first network device, where the first data packet includes a first service frame and a first timestamp T1, where the first service frame is sent by the REC to the a first network device, where the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame;
  • an obtaining unit configured to obtain, by using the first data packet, a system clock of the REC;
  • a sending unit configured to send, by using a system clock of the REC obtained by the obtaining unit, the first service frame extracted from the first data packet to the RE;
  • a recording unit configured to record, by using a system time of the second network device, a second timestamp T2 that the sending unit sends the first service frame;
  • the first network device keeps a system clock synchronization with the second network device
  • the first data packet further includes a frequency deviation
  • the frequency deviation is obtained by calculating the system clock of the first network device and the system clock of the REC, and the obtaining unit includes:
  • An extracting unit configured to extract the frequency deviation from the first data packet received by the receiving unit
  • a calculating unit configured to calculate a system clock of the REC by using a system clock of the second network device and the frequency deviation.
  • the sending unit includes:
  • a buffering unit configured to cache the first service frame extracted from the first data packet to a memory
  • a sending subunit configured to read, by the system clock of the REC, a first service frame from the memory, and send the first service frame to the RE, where the first service frame is cached in the memory
  • the duration is zero.
  • the receiving unit is further configured to: After calculating the transmission delay, receiving a second data packet sent by the first network device, where the second data packet includes a second service frame;
  • a setting unit configured to cache the second service frame to the memory, and set a buffer duration of the second service frame to a fixed delay minus the transmission delay;
  • a duration determining unit configured to determine whether the cache duration is reached
  • a reading unit configured to: when the duration determining unit determines that the buffer duration arrives, read the second service frame from the memory, and send the second service frame to the RE by using a system clock of the REC as a read clock The second service frame.
  • a fifth aspect a time synchronization system is provided, the system comprising: the first network device according to the third aspect or the first possible implementation manner of the third aspect, such as the fourth aspect or the fourth aspect Any one of the first to third possible implementation manners, the second network device, the wireless device controller REC, and the radio frequency device RE,
  • the first network device is connected to the REC, and the second network device is connected to the RE, and the first network device and the second network device maintain system time synchronization.
  • a network device is provided, where the network device is a first network device, the first network device is connected to a wireless device controller REC, and the first network device and the second network device maintain system time synchronization.
  • the second network device is connected to the radio frequency device RE, where the first network device includes: a processor and a memory;
  • the memory for storing program instructions and data
  • the processor is configured to read program instructions and data stored in the memory, and perform the following operations:
  • the first network device The second network device keeps the system clock synchronized. After the processor receives the service frame sent by the REC, the processor further performs the following operations:
  • the processor extracts a system clock of the REC from the service frame
  • the processor calculates a frequency offset by using a system clock of the first network device and a system clock of the REC;
  • the data packet sent by the processor to the second network device includes the service frame, the first timestamp, and the frequency offset.
  • a network device is provided, where the network device is a second network device, the second network device is connected to a radio frequency device RE, and the second network device maintains system time synchronization with the first network device.
  • the first network device is connected to the wireless device controller REC, and the second network device includes: a processor and a memory;
  • the memory for storing program instructions and data
  • the processor is configured to read program instructions and data stored in the memory, and perform the following operations:
  • the processor Receiving, by the processor, the first data packet sent by the first network device, where the first data packet includes a first service frame and a first timestamp T1, where the first service frame is sent by the REC to the a first network device, where the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame;
  • the processor obtains a system clock of the REC by using the first data packet
  • the processor sends, by using a system clock of the REC, the first service frame extracted from the first data packet to the RE;
  • the processor records the second timestamp T2 of the first service frame by using the system time of the second network device;
  • the first data packet further includes a frequency deviation
  • the frequency deviation is obtained by the system clock of the first network device and the system clock of the REC
  • the processor obtains the system clock of the REC by using the first data packet, including:
  • the processor extracting the frequency offset from the first data packet
  • the processor calculates a system clock of the REC by using a system clock of the second network device and the frequency deviation.
  • the processor sends, by using a system clock of the REC, the first data from the RE Extracted from the package
  • the first service frame includes:
  • the processor buffers the first service frame extracted from the first data packet to a memory
  • the processor reads the first service frame from the memory by using the system clock of the REC as a read clock, and sends the first service frame to the RE, where the cache time of the first service frame in the memory is zero.
  • the processor after the second network device calculates the transmission delay, the processor also performs the following operations:
  • the processor receives a second data packet sent by the first network device, where the second data packet includes a second service frame;
  • the processor caches the second service frame to the memory, and sets a buffer duration of the second service frame to a fixed delay minus the transmission delay;
  • the processor determines whether the cache duration is reached
  • the processor If it is determined that the buffer duration arrives, the processor reads the second service frame from the memory with the system clock of the REC as a read clock, and sends the second service frame to the RE.
  • the eighth aspect provides a system for time synchronization, the system comprising: the first network device according to the first aspect or the first possible implementation manner of the sixth aspect, such as the seventh aspect or the seventh aspect Any one of the first to third possible implementation manners, the second network device, the wireless device controller REC, and the radio frequency device RE,
  • the first network device is connected to the REC, and the second network device is connected to the RE, and the first network device and the second network device maintain system time synchronization.
  • the network device the first network device records the first timestamp T1 of the first service frame sent by the REC, and generates the data packet by using the first timestamp and the first service frame. And sending to the second network device, and thus providing technical support for the second network device to calculate the transmission delay T between the first network device and the second network device.
  • the second network device first obtains the system clock of the REC through the data packet, and then uses the system clock of the REC to forward the first service frame extracted from the data packet to the RE, and records the forwarding to the RE.
  • a second time stamp T2 of a service frame, from which a transmission delay T T2-T1 is obtained. In this way, by using the fixed delay between the REC and the RE, technical support is provided for delay compensation of the transmission delay, which helps to ensure that the delay between the REC and the RE remains unchanged.
  • 1 is a schematic diagram of calculating a communication delay between a REC and an RE in the prior art
  • FIG. 2 is a schematic diagram of a novel network architecture according to an embodiment of the present invention.
  • FIG. 3 is a schematic diagram of a system for time synchronization according to an embodiment of the present invention.
  • FIG. 4 is a flowchart of a method for time synchronization on a first network device side according to an embodiment of the present invention
  • Embodiment 1 is a flowchart of Embodiment 1 of a method for time synchronization on a second network device side according to an embodiment of the present invention
  • Embodiment 6 is a flowchart of Embodiment 2 of a method for time synchronization on a second network device side according to an embodiment of the present invention
  • FIG. 7 is a schematic diagram of a first network device according to an embodiment of the present invention.
  • FIG. 8 is a schematic diagram of a second network device according to an embodiment of the present invention.
  • FIG. 9 is a schematic structural diagram of hardware of a first network device according to an embodiment of the present invention.
  • FIG. 10 is a schematic diagram showing the hardware configuration of a second network device according to an embodiment of the present invention.
  • the REC and the RE are directly connected through the optical fiber.
  • the new network architecture sets a forward backhaul network between the REC and the RE (English: Fronthaul Network), thereby replacing the direct-connected fiber between the REC and the RE, and the forward-backed fiber
  • the network device in the transmission network implements packet aggregation transmission between the REC and the RE.
  • the forward backhaul network may include at least a network device 1 connected to the REC and a network device 2 connected to the RE.
  • the REC can also communicate with the core network (English: Core) through the backhaul line (English: Backhual).
  • the network device in the embodiment of the present invention may be an independent device; or, the network device It is also possible to split a plurality of devices that jointly implement the functions of the network device, that is, to split the functions of the network device into the plurality of devices; or the network device may also be a packet transmission network that integrates the functions of the network device (English: Packet Transport Network (referred to as: PTN) equipment, routers, switches, microwave equipment, optical transport network (English: Optical Transport Network, referred to as: OTN) equipment, synchronous digital system (English: Synchronous Digital Hierarchy, referred to as: SDH) equipment can be realized
  • PTN Packet Transport Network
  • OTN Optical Transport Network
  • SDH Synchronous Digital Hierarchy
  • the embodiment of the present invention may not specifically limit the existence form of the network device in the network.
  • a flowchart of a method for time synchronization on a first network device side may be included, which may include:
  • the first network device receives the service frame sent by the REC, and records the first timestamp T1 of the service frame by using the system time of the first network device, where the service frame carries the system clock of the REC. .
  • the first network device may be connected to the REC, the second network device may be connected to the RE, and the first network device and the second network device may be directly connected; or the first network device and The second network device may be indirectly connected through an optical fiber or other network device.
  • the connection relationship between the two may not be specifically limited in the embodiment of the present invention.
  • the first network device may be embodied as the network device 1, and the second network device may be embodied as the network device 2, and the two are indirectly connected through other network devices.
  • the system time synchronization should be maintained between the first network device and the second network device.
  • the system time synchronization between the first network device and the second network device may be implemented by using the 1588 V2 time synchronization technology, which may not be specifically limited in this embodiment of the present invention.
  • the REC may send a service frame to the first network device according to the local system clock of the REC, and accordingly, the first network device receives the service frame, and records the reception by using the local system time of the first network device.
  • the first timestamp T1 of the service frame For example, the first network device can receive the service frame sent by the REC through the first user network interface (English: User Networks Interface, UNI for short).
  • the first network device sends a data packet to a second network device, where the data packet includes the service frame and the first timestamp, and the data packet is used to notify the second network device of the The system clock of the REC and the first timestamp.
  • the first network device sends a data packet to the second network device by using a first network node interface (English: Network to Network Interface, NNI for short), and the second network device receives the data from the first network device by using the second NNI. Packet.
  • a first network node interface English: Network to Network Interface, NNI for short
  • NNI Network to Network Interface
  • the first network device may group the service frames, perform rate adaptation on each packet, and add a frame header or a packet header to generate the data packet, so that the data packet may be scheduled to
  • the first NNI interface transmits.
  • the first network device is a transmission device such as a microwave device, an OTN device, or an SDH device integrated with the network device function
  • the data packet may be generated by adding a frame header manner; if the first network device is an integrated network device
  • a packet switching device such as a PTN device, a router, or a switch can generate the packet by adding a packet header.
  • the first network device can generate a data packet in at least two ways.
  • the first network device performs packet mapping on the first timestamp and the service frame to generate the data packet.
  • the second network device can obtain the system clock of the REC through the data packet by using a system clock adaptive adjustment manner.
  • the first timestamp may be carried in the header of the data packet, and the service frame may be carried in the payload of the data packet; or the first timestamp and the service frame may be carried in the payload of the data packet, which is used by the embodiment of the present invention. Can not be specifically limited.
  • the first network device may also generate a data packet by the first network device extracting the REC from the service frame. a system clock; the first network device calculates a frequency offset by using a system clock of the first network device and a system clock of the REC; the first network device pairs the frequency offset, the first timestamp, and The service frame is packaged and mapped to generate the data packet.
  • the first timestamp and the frequency deviation may be carried in a header of the data packet, and the service frame may be carried in a payload of the data packet; or the first timestamp, the frequency deviation, and the service frame may be carried in the payload of the data packet.
  • This embodiment of the present invention does not specifically limit this.
  • system clock synchronization can be understood as frequency synchronization and phase synchronization of the system clock between the first network device and the second network device.
  • a physical layer synchronization technology such as synchronous Ethernet may be used, or a precise time protocol (English: Precision Time Protocol, PTP) message frequency synchronization technology may be used to implement a system between the first network device and the second network device.
  • PTP Precision Time Protocol
  • the clock synchronization is not specifically limited in this embodiment of the present invention.
  • the first network device calculates the transmission delay between the two network devices, and provides technical support.
  • the second network device can combine the fixed delay T b with the actual The delay of the transmission delay is used to ensure that the delay between the REC and the RE is fixed.
  • Embodiment 1 of a method for time synchronization on a second network device side according to an embodiment of the present invention, which may include:
  • the second network device receives the first data packet sent by the first network device, where the first data packet includes a first service frame and a first timestamp T1, and the first service frame is used by the REC.
  • the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame.
  • the first network device After the first network device sends the first data packet to the second network device according to the solution shown in FIG. 4, if the first network device is directly connected to the second network device, the second network device may directly receive the first data packet. And obtaining the transmission delay by using the solution of the embodiment of the present invention; if the first network device and the second network device are indirectly connected by other network devices, the first data packet may be forwarded between the other network devices until the confirmation When a data packet is transmitted to the second network device in communication with the RE, the transmission delay is obtained according to the solution of the embodiment of the present invention.
  • the second network device obtains a system clock of the REC by using the first data packet.
  • the second network device In order for the second network device to correctly forward the first traffic frame from the REC to the RE, the second network device should be aware of the system clock of the REC. Corresponding to the two ways of generating a data packet introduced in FIG. 4 above, the second network device can obtain the system clock of the REC in the following two ways.
  • the first data packet includes a first timestamp and a first service frame.
  • the obtaining, by the second network device, the system clock of the REC by using the first data packet that: the second network device caches the first service frame that is to be extracted from the first data packet And the second network device obtains the system clock of the REC by using a system clock adaptive adjustment manner based on a system clock of the second network device.
  • the second network device after receiving the first data packet sent by the first network device, the second network device first obtains, from the first data packet, a high frequency clock used by the first network device to send the first data packet, such that The second network device can read the first service frame from the first data packet and cache it to the first buffer.
  • the first buffer may be an asynchronous buffer, such as an asynchronous first in first out (FIFO) buffer.
  • the system clock can be adaptively adjusted based on the local system clock of the second network device.
  • the second network device can determine whether a clock adjustment is needed according to whether the first service frame can be read. If the system clock of the second network device is the read clock, the first service frame in the first buffer is not read, indicating that the system clock of the second network device is different from the system clock of the REC, and clock adjustment is required.
  • the second network device may further determine whether clock adjustment is needed according to the quantity of the first service frame in the first buffer. If the inventory of the first service frame in the first buffer changes, the system clock of the second network device is different from the system clock of the REC, and clock adjustment is required.
  • the quantity of the first service frame in the first buffer refers to the number of the first service frame that the REC sends to the second network device and writes to the first buffer, minus the second network device from the first buffer.
  • the number of first service frames read and forwarded to the RE.
  • the inventory change is specifically more and more inventory, that is, the number of first service frames sent by the REC to the second network device is greater than the first service frame forwarded by the second network device to the RE.
  • the number of the second network device can determine that the system clock of the second network device is slower than the system clock of the REC, so that the system clock of the second network device can be adjusted faster.
  • the adjusted system clock can be determined as the system clock of the REC: the second network device can read from the first buffer. A service frame, and the inventory of the first service frame in the first buffer remains unchanged or the inventory varies within a preset allowable range.
  • the first data packet includes a first timestamp, a frequency offset, and a first service frame.
  • the obtaining, by the second network device, the system clock of the REC by using the first data packet that: the second network device extracts the frequency offset from the first data packet;
  • the second network device sends, by using a system clock of the REC, the first service frame extracted from the first data packet to the RE.
  • the first service frame can be sent to the RE in the following four manners.
  • the sending, by the second network device, the first service frame extracted from the first data packet to the RE includes: the second network device with the REC
  • the system clock is a read clock
  • the first service frame is read from the first buffer
  • the first service frame is sent to the RE.
  • the sending, by the second network device, the first service frame extracted from the first data packet to the RE includes: the second network device The first service frame extracted in the first data packet is buffered to the first buffer; the second network device reads the first clock from the first buffer by using a system clock of the REC as a read clock. The first service frame is sent to the RE, and the first service frame has a cache duration of zero in the first buffer.
  • the second network device may further set a second buffer, where the second buffer buffers the service frame for delay compensation.
  • the second buffer can be a synchronous buffer, such as a synchronous FIFO buffer.
  • the delay compensation process using the second buffer may be simulated as much as possible.
  • the embodiment of the present invention further provides the third mode and the fourth mode of sending the first service frame to the RE as follows.
  • the sending, by the second network device, the first service frame extracted from the first data packet to the RE includes: the second network device with the REC
  • the system clock is a read clock
  • the first service frame is read from the first buffer and buffered to the second buffer; and the second network device uses the system clock of the REC as a read clock.
  • the sending, by the second network device, the first service frame extracted from the first data packet to the RE includes: the second network device The first service frame extracted in the first data packet is buffered to the first buffer; the second network device reads the system from the first buffer by using a system clock of the REC as a read clock. Decoding a first service frame to the second buffer; the second network device reads the first service frame from the second buffer by using a system clock of the REC as a read clock. Sending the first service frame to the RE, where the first service frame has a buffer duration of zero in the second buffer.
  • the second network device records, by using a system time of the second network device, a second timestamp T2 that sends the first service frame.
  • the second network device obtains the system clock of the REC, and when the first service frame is forwarded to the RE, the second network device may also record the second timestamp T2 of the first service frame sent to the RE by using the local system time. For example, the second network device may send the first service frame to the RE through the second UNI.
  • the second network device can obtain the second timestamp T2 of the first service frame sent to the RE in combination with the local system time.
  • the second network device can obtain the first network device to receive the REC and send the first service by using the first data packet.
  • the delay compensation value for the transmission delay T can be obtained.
  • This solution helps to ensure that the delay between the REC and the RE is fixed.
  • the fixed delay may be represented as T b ; or the fixed delay may also be embodied as other preset delay values. The embodiment of the present invention does not specifically limit this.
  • Embodiment 2 of a method for time synchronization on a second network device side according to an embodiment of the present invention is shown.
  • the method may further include:
  • the second network device receives a second data packet sent by the first network device, where the second data packet includes a second service frame.
  • the second network device buffers the second service frame to the memory, and sets a buffer duration of the second service frame to a fixed delay minus the transmission delay.
  • the second network device determines whether the buffer duration is reached.
  • the second network device If it is determined that the buffer duration arrives, the second network device reads the second service frame from the memory, and sends the second to the RE, using a system clock of the REC as a read clock. Business frame.
  • the second network device may perform delay compensation on the transmission delay in the subsequent interaction process in combination with the fixed delay to ensure the packet.
  • the delay on the network device meets the requirements of the fixed delay, thereby ensuring that the communication delay between the REC and the RE remains unchanged.
  • the REC may send the second service frame to the first network device according to the local system clock, the first network device receives the second service frame, and performs packet mapping processing on the second service frame to obtain the first Two data packets, the second data packet is sent to the second network device.
  • the second network device receives the second data packet, and caches the second service frame to the memory, and calculates the buffer duration of the second service frame by using the fixed delay and the transmission delay.
  • the buffer duration can be understood as that the transmission delay is compensated to the fixed delay, and the second service frame needs to wait in the memory.
  • the system clock of the REC obtained by the scheme shown in FIG. 5 is the read clock, and the second service frame is read from the memory and forwarded to the RE.
  • the second network device uses the buffer duration to perform delay compensation, which can be reflected in at least two ways.
  • delay compensation is performed by timing. After the second service frame is written into the memory, the timing can be started, and when the timing reaches the buffer duration, the second service frame is read from the memory.
  • the memory is a FIFO memory
  • delay compensation can be performed by adjusting the FIFO water line, and after the second service frame is written into the memory, the height of the water line is adjusted according to the buffer duration, thereby implementing delay compensation.
  • the second network device can cache the second service frame to the memory by using at least the following two manners.
  • the second network device has a first buffer
  • the memory in this embodiment refers to the first buffer
  • the second network device buffering the second service frame to the memory comprises: the second network device extracting a second service frame from the second data packet and buffering to the first buffer;
  • the buffer duration of the second service frame includes: setting a buffer duration of the second service frame in the first buffer.
  • the delay compensation value may not always be fixed.
  • a change in the fixed delay and/or a change in the transmission delay may cause the delay compensation value to change. Therefore, in the embodiment of the present invention, the second network device can query and maintain the delay compensation value in addition to the delay compensation value.
  • the first buffer acts as an asynchronous FIFO, and the FIFO water line may change due to delay jitter in the message forwarding process. Therefore, the first buffer is used once. After the delay compensation, it is impossible to accurately know the previous compensation value, that is, the query and maintenance of the delay compensation value cannot be accurately realized.
  • the embodiment of the present invention further provides a method 2 of buffering the second service frame to the memory as follows.
  • the second network device has a first buffer and a second buffer
  • the memory in this embodiment specifically refers to the second buffer.
  • the buffering, by the second network device, the second service frame to the memory comprises: the second network device extracting the second service frame from the second data packet and buffering to the first buffer, the second service frame The buffer length of the first buffer is zero; the second network device reads the second service frame from the first buffer with the system clock of the REC as the read clock, and caches the buffer to the second buffer;
  • the buffer duration of the second service frame includes: setting a buffer duration of the second service frame in the second buffer.
  • the delay compensation by adjusting the FIFO water line method is taken as an example.
  • the second buffer is used as the synchronous FIFO, and the FIFO water line is stable, which is helpful for accurate query of the delay compensation value.
  • the second network device may also send the first service frame to the RE by using the mode 1 and the mode 2. This is not specifically limited.
  • the first network device and the second network device may be integrated into one device, or the first network device and the second network device may be embodied as two independent devices. This is not specifically limited.
  • the embodiment of the present invention further provides a network device.
  • the network device is specifically a first network device, and the first network device and the wireless device are controlled.
  • the first network device is in synchronization with the second network device, and the second network device is connected to the radio device RE.
  • the first network device includes:
  • the receiving unit 401 is configured to receive a service frame sent by the REC, where the service frame carries a system clock of the REC;
  • the recording unit 402 is configured to record, by using the system time of the first network device, a first timestamp T1 for receiving the service frame when the receiving unit receives the service frame;
  • a sending unit 403 configured to send, to the second network device, a data packet, where the data packet includes the service frame and the first timestamp, where the data packet is used to notify the second network device of the The system clock of the REC and the first timestamp.
  • the first network device keeps a system clock synchronization with the second network device, where the first network device further includes:
  • An extracting unit configured to extract, after the receiving unit receives the service frame, a system clock of the REC from the service frame;
  • a calculating unit configured to calculate a frequency deviation by using a system clock of the first network device and a system clock of the REC;
  • the data packet sent by the sending unit to the second network device includes the service frame, the first timestamp, and the frequency offset.
  • the network device provided by the foregoing embodiment is only illustrated by the division of the foregoing functional modules when performing time synchronization.
  • the foregoing function allocation may be completed by different functional modules according to requirements, that is, the network device is
  • the internal structure is divided into different functional modules to perform all or part of the functions described above.
  • the embodiment of the present invention further provides a network device, as shown in FIG.
  • the network device is specifically a second network device, the second network device is connected to the radio frequency device RE, and the second network device maintains system time synchronization with the first network device, where the first network device and the wireless device are The controller REC is connected, and the second network device includes:
  • the receiving unit 501 is configured to receive the first data packet sent by the first network device, where the first data packet includes a first service frame and a first timestamp T1, where the first service frame is sent by the REC to The first network device, where the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame;
  • the obtaining unit 502 is configured to obtain, by using the first data packet, a system clock of the REC;
  • the sending unit 503 is configured to send, by using the system clock of the REC obtained by the obtaining unit, the first service frame extracted from the first data packet to the RE;
  • the recording unit 504 is configured to record, by using a system time of the second network device, a second timestamp T2 that the sending unit sends the first service frame;
  • the first data packet further includes a frequency deviation, where the frequency deviation is determined by a system clock and a location of the first network device
  • the system clock calculation of the REC is obtained, and the obtaining unit includes:
  • An extracting unit configured to extract the frequency deviation from the first data packet received by the receiving unit
  • a calculating unit configured to calculate a system clock of the REC by using a system clock of the second network device and the frequency deviation.
  • the sending unit includes:
  • a buffering unit configured to cache the first service frame extracted from the first data packet to a memory
  • a sending subunit configured to read, by the system clock of the REC, a first service frame from the memory, and send the first service frame to the RE, where the first service frame is cached in the memory
  • the duration is zero.
  • the receiving unit is further configured to: after the time delay determining unit calculates the transmission delay, receive a second data packet sent by the first network device, where the second data packet includes a second Business frame
  • a setting unit configured to cache the second service frame to the memory, and set a buffer duration of the second service frame to a fixed delay minus the transmission delay;
  • a duration determining unit configured to determine whether the cache duration is reached
  • a reading unit configured to: when the duration determining unit determines that the buffer duration arrives, read the second service frame from the memory, and send the second service frame to the RE by using a system clock of the REC as a read clock The second service frame.
  • the network device provided by the foregoing embodiment is only illustrated by the division of the foregoing functional modules when performing time synchronization.
  • the foregoing function allocation may be completed by different functional modules according to requirements, that is, the network device is
  • the internal structure is divided into different functional modules to perform all or part of the functions described above.
  • the embodiment of the present invention further provides a time synchronization system.
  • the system may include: the first network device shown in FIG. 7 and the second network device shown in FIG. REC and RE.
  • the first network device is connected to the REC, and the second network device is connected to the RE, and the first network device and the second network device maintain system time synchronization.
  • the embodiment of the present invention further provides a first network device 500.
  • the first network device may include: a processor 501, a memory 502, and a network interface. 503. Bus system 504.
  • the bus system 504 is configured to connect the processor 501, the memory 502, and the network interface 503.
  • the network interface 503 is configured to implement a communication connection between the device and other network devices.
  • the network interface 503 can be implemented by an optical transceiver, an electrical transceiver, a wireless transceiver, or any combination thereof.
  • the optical transceiver can be a small form-factor pluggable transceiver (sFP) transceiver (English: transceiver), and the enhanced small form-factor pluggable (English: enhanced small form-factor pluggable, Abbreviation: SFP+) Transceiver or 10 Gigabit small form-factor pluggable (XFP) transceiver.
  • the electrical transceiver can be an Ethernet (Ethernet) network interface controller (English: network interface controller, abbreviation: NIC).
  • the wireless transceiver can be a wireless network interface controller (English: wireless network interface controller, abbreviation: WNIC).
  • the memory 502 is configured to store program instructions and data.
  • the memory 502 may include a volatile memory (English: volatile memory), such as a random access memory (English: random-access memory, abbreviation: RAM); the memory may also include a non-volatile memory (English: non-volatile) Memory), such as flash memory (English: flash memory), hard disk (English: hard disk drive, abbreviated: HDD) or solid state drive (English: solid-state drive, abbreviation: SSD); memory can also include the above types of memory The combination.
  • a volatile memory such as a random access memory (English: random-access memory, abbreviation: RAM)
  • non-volatile memory English: non-volatile) Memory
  • flash memory English: flash memory
  • hard disk English: hard disk drive, abbreviated: HDD
  • SSD solid state drive
  • the processor 501 is a central processing unit (English: central processing unit, abbreviated as CPU), and may also be a combination of a CPU and a hardware chip.
  • the above hardware chip may be a combination of one or more of the following: dedicated integration Circuit (English: application-specific integrated circuit, abbreviation: ASIC), field-programmable gate array (English: field-programmable gate array, abbreviation: FPGA), complex programmable logic device (English: complex programmable logic device, abbreviation: CPLD) and network processor (English: network processor, abbreviation: NP).
  • the processor 501 is configured to read program instructions and data stored in the memory 502, and perform the following operations:
  • the embodiment of the present invention further provides a second network device 600.
  • the second network device may include: a processor 601, a memory 602, and a network interface. 603. Bus system 604.
  • the bus system 604 is configured to connect the processor 601, the memory 602, and the network interface 603.
  • the network interface 603 is configured to implement a communication connection between the device and other network devices.
  • the memory 602 is configured to store program instructions and data.
  • the processor 601 is configured to read program instructions and data stored in the memory 602, and perform the following operations:
  • the processor Receiving, by the processor, the first data packet sent by the first network device by using the network interface, where the first data packet includes a first service frame and a first timestamp T1, where the first service frame is The REC is sent to the first network device, where the first service frame carries a system clock of the REC, and the first timestamp is a timestamp of the first network device receiving the first service frame;
  • the processor obtains a system clock of the REC by using the first data packet
  • the processor sends, by using a system clock of the REC, the first service frame extracted from the first data packet to the RE;
  • the processor records the second timestamp T2 of the first service frame by using the system time of the second network device;

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Abstract

本发明实施例提供一种时间同步的方法及系统、网络设备，所述方法包括：第二网络设备接收第一网络设备发送的第一数据包，第一数据包包括第一业务帧和第一时间戳T1，第一业务帧由REC发送至第一网络设备，第一业务帧携带有REC的系统时钟，第一时间戳为第一网络设备接收第一业务帧的时间戳；第二网络设备通过第一数据包获得REC的系统时钟；第二网络设备利用REC的系统时钟，向RE发送从第一数据包中提取出的第一业务帧；第二网络设备利用第二网络设备的系统时间，记录发送第一业务帧的第二时间戳T2；第二网络设备确定第一网络设备与第二网络设备之间的传输时延T＝T2-T1。如此方案，有助于保证REC与RE之间的时延维持不变。

Description

一种时间同步的方法及系统、网络设备
本申请要求于2015年4月27日提交中国专利局、申请号为201510204323.7、发明名称为“一种时间同步的方法及系统、网络设备”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及通信技术领域，具体涉及一种时间同步的方法及系统、网络设备。
背景技术
目前，分布式基站在现网中被广泛使用。分布式基站的特点是，将射频设备(英文：Radio Equipment，简称：RE)和无线设备控制器(英文：Radio Equipment Control，简称：REC)分离，再通过光纤实现二者之间的连接。
在进行网络部署时，可以将REC集中部署在机房，形成基带池，再通过光纤与规划站点上部署的RE相连，完成网络覆盖。具体地，REC与RE之间、RE与RE之间，可以使用通用公共无线接口(英文：Common Public Radio Interface，简称：CPRI)连接。
通常，CPRI自身有着严格的时钟同步面要求和时间同步面要求。具体地，时钟同步面要求可以理解为，REC发送CPRI业务帧的频率与RE发送CPRI业务帧的频率，之间的偏差应控制在一定范围内，以此来保证空口频率的准确度。时间同步面要求可以理解为，应保证REC与RE之间的通信时延固定不变。
为了满足时间同步面要求，可计算REC与RE之间的通信时延，并基于所述通信时延，在下行方向上控制REC的下行信号发送时刻，在上行方向上补偿RE的上行信号传输时延，以此来保证REC与RE之间的通信时延固定不变。参见图1，通信时延T通信＝Ta+Tb+Tc+Td，其中，Ta为REC打下发送时间戳到REC发送采样信号(英文：Radio Sample Signal)之间的时延，Tb为采样信号在光纤链路上的传输时延，Tc为RE接收到采样信号到RE打下接收时间戳之间的时延，Td为RE打下接收时间戳到采样信号传输至时延测试参考点之间的时延。举例来说，可以将RE的信号发射点，即天线口定义为时延测试参考点。
发明内容
本发明实施例的时间同步的方法及系统、网络设备，有助于保证REC与RE之间 的时延维持不变。
为此，本发明实施例提供如下技术方案：
第一方面，提供了一种时间同步的方法，第一网络设备与无线设备控制器REC相连，第二网络设备与射频设备RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步，所述方法包括：
所述第一网络设备接收所述REC发送的业务帧，并利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1，所述业务帧携带有所述REC的系统时钟；
所述第一网络设备向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
结合第一方面，在第一方面的第一种可能的实现方式中，所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一网络设备接收所述REC发送的业务帧之后，所述方法还包括：
所述第一网络设备从所述业务帧中提取所述REC的系统时钟；
所述第一网络设备利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
相应地，所述第一网络设备向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
第二方面，提供了一种时间同步的方法，第一网络设备与无线设备控制器REC相连，第二网络设备与射频设备RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步，所述方法包括：
所述第二网络设备接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟；
所述第二网络设备利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
所述第二网络设备利用所述第二网络设备的系统时间，记录发送所述第一业务帧的第二时间戳T2；
所述第二网络设备确定所述第一网络设备与所述第二网络设备之间的传输时延 T＝T2-T1。
结合第二方面，在第二方面的第一种可能的实现方式中，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟包括：
所述第二网络设备从所述第一数据包中提取所述频率偏差；
所述第二网络设备利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
结合第二方面的第一种可能的实现方式，在第二方面的第二种可能的实现方式中，所述第二网络设备利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：
所述第二网络设备将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
所述第二网络设备以所述REC的系统时钟为读时钟，从所述存储器中读取所述第一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
结合第二方面或者第二方面的第一种或第二种可能的实现方式，在第二方面的第三种可能的实现方式中，所述第二网络设备计算所述传输时延之后，所述方法包括：
所述第二网络设备接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
所述第二网络设备将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
所述第二网络设备确定所述缓存时长是否到达；
如果确定所述缓存时长到达，所述第二网络设备以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
第三方面，提供了一种网络设备，所述网络设备为第一网络设备，所述第一网络设备与无线设备控制器REC相连，所述第一网络设备与第二网络设备保持系统时间同步，所述第二网络设备与射频设备RE相连，所述第一网络设备包括：
接收单元，用于接收所述REC发送的业务帧，所述业务帧携带有所述REC的系统时钟；
记录单元，用于在所述接收单元接收到所述业务帧时，利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1；
发送单元，用于向所述第二网络设备发送数据包，所述数据包包括所述业务帧和 所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
结合第三方面，在第三方面的第一种可能的实现方式中，所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一网络设备还包括：
提取单元，用于在所述接收单元接收到所述业务帧后，从所述业务帧中提取所述REC的系统时钟；
计算单元，用于利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
相应地，所述发送单元向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
第四方面，提供了一种网络设备，所述网络设备为第二网络设备，所述第二网络设备与射频设备RE相连，所述第二网络设备与第一网络设备保持系统时间同步，所述第一网络设备与无线设备控制器REC相连，所述第二网络设备包括：
接收单元，用于接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
获得单元，用于通过所述第一数据包，获得所述REC的系统时钟；
发送单元，用于利用所述获得单元获得的所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
记录单元，用于利用所述第二网络设备的系统时间，记录所述发送单元发送所述第一业务帧的第二时间戳T2；
时延确定单元，用于确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
结合第四方面，在第四方面的第一种可能的实现方式中，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述获得单元包括：
提取单元，用于从所述接收单元接收到的所述第一数据包中提取所述频率偏差；
计算单元，用于利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
结合第四方面的第一种可能的实现方式，在第四方面的第二种可能的实现方式中，所述发送单元包括：
缓存单元，用于将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
发送子单元，用于以所述REC的系统时钟为读时钟，从所述存储器中读取所述第一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
结合第四方面或者第四方面的第一种或第二种可能的实现方式，在第四方面的第三种可能的实现方式中，所述接收单元，还用于在所述时延确定单元计算所述传输时延之后，接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
设置单元，用于将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
时长确定单元，用于确定所述缓存时长是否到达；
读取单元，用于在所述时长确定单元确定所述缓存时长到达时，以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
第五方面，提供了一种时间同步的系统，所述系统包括：如第三方面或第三方面的第一种可能的实现方式所述的第一网络设备、如第四方面或者第四方面的第一种至第三种任一种可能的实现方式、所述的第二网络设备、无线设备控制器REC和射频设备RE，
所述第一网络设备与所述REC相连，所述第二网络设备与所述RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步。
第六方面，提供了一种网络设备，所述网络设备为第一网络设备，所述第一网络设备与无线设备控制器REC相连，所述第一网络设备与第二网络设备保持系统时间同步，所述第二网络设备与射频设备RE相连，所述第一网络设备包括：处理器和存储器；
所述存储器，用于存储程序指令和数据；
所述处理器，用于读取所述存储器中存储的程序指令和数据，执行以下操作：
所述处理器接收所述REC发送的业务帧，并利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1，所述业务帧携带有所述REC的系统时钟；
所述处理器向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
结合第六方面，在第六方面的第一种可能的实现方式中，所述第一网络设备与所 述第二网络设备保持系统时钟同步，所述处理器接收所述REC发送的业务帧之后，所述处理器还执行以下操作：
所述处理器从所述业务帧中提取所述REC的系统时钟；
所述处理器利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
相应地，所述处理器向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
第七方面，提供了一种网络设备，所述网络设备为第二网络设备，所述第二网络设备与射频设备RE相连，所述第二网络设备与第一网络设备保持系统时间同步，所述第一网络设备与无线设备控制器REC相连，所述第二网络设备包括：处理器和存储器；
所述存储器，用于存储程序指令和数据；
所述处理器，用于读取所述存储器中存储的程序指令和数据，执行以下操作：
所述处理器接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
所述处理器通过所述第一数据包，获得所述REC的系统时钟；
所述处理器利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
所述处理器利用所述第二网络设备的系统时间，记录发送所述第一业务帧的第二时间戳T2；
所述处理器确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
结合第七方面，在第七方面的第一种可能的实现方式中，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述处理器通过所述第一数据包，获得所述REC的系统时钟包括：
所述处理器从所述第一数据包中提取所述频率偏差；
所述处理器利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
结合第七方面的第一种可能的实现方式，在第七方面的第二种可能的实现方式中，所述处理器利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所 述第一业务帧包括：
所述处理器将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
所述处理器以所述REC的系统时钟为读时钟，从所述存储器中读取所述第一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
结合第七方面或者第七方面的第一种或第二种可能的实现方式，在第七方面的第三种可能的实现方式中，所述第二网络设备计算所述传输时延之后，所述处理器还执行以下操作：
所述处理器接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
所述处理器将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
所述处理器确定所述缓存时长是否到达；
如果确定所述缓存时长到达，所述处理器以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
第八方面，提供了一种时间同步的系统，所述系统包括：如第六方面或第六方面的第一种可能的实现方式所述的第一网络设备、如第七方面或者第七方面的第一种至第三种任一种可能的实现方式、所述的第二网络设备、无线设备控制器REC和射频设备RE，
所述第一网络设备与所述REC相连，所述第二网络设备与所述RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步。
本发明实施例的时间同步的方法及系统、网络设备，第一网络设备记录接收到REC发送的第一业务帧的第一时间戳T1，并利用第一时间戳和第一业务帧生成数据包，发送至第二网络设备，如此，便为第二网络设备计算第一网络设备与第二网络设备之间的传输时延T提供了技术支持。相应地，第二网络设备接收到数据包后，先通过数据包获得REC的系统时钟，再利用REC的系统时钟向RE转发从数据包中提取出的第一业务帧，并记录向RE转发第一业务帧的第二时间戳T2，据此获得传输时延T＝T2-T1。如此方案，便可为利用REC与RE之间的固定时延，对所述传输时延进行时延补偿提供了技术支持，有助于保证REC与RE之间的时延维持不变。
附图说明
为了更清楚地说明本申请实施例中的技术方案，下面将对实施例描述中所需要使用 的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请中记载的一些实施例，对于本领域普通技术人员来讲，还可以根据这些附图获得其它的附图。
图1是现有技术计算REC与RE之间通信时延的示意图；
图2是本发明实施例新型网络架构的示意图；
图3是本发明实施例时间同步的系统的示意图；
图4是本发明实施例第一网络设备侧的时间同步的方法的流程图；
图5是本发明实施例第二网络设备侧的时间同步的方法实施例1的流程图；
图6是本发明实施例第二网络设备侧的时间同步的方法实施例2的流程图；
图7是本发明实施例第一网络设备的示意图；
图8是本发明实施例第二网络设备的示意图；
图9是本发明实施例第一网络设备的硬件构成示意图；
图10是本发明实施例第二网络设备的硬件构成示意图。
具体实施方式
为了使本技术领域的人员更好地理解本发明方案，下面结合附图和实施方式对本发明实施例作进一步的详细说明。
在介绍本发明实施例方案之前，先对本发明实施例方案的应用场景做简单介绍。
通常，REC与RE之间通过光纤直连，为了尽量减少组网中光纤的使用量，降低组网成本以及网络维护成本，发明人结合实际组网经验，提出一种新型网络架构。参见图2，所述新型网络架构在REC与RE之间设置了前向回传网络(英文：Fronthaul Network)，以此替换掉REC与RE之间的直连光纤，并由所述前向回传网络中的网络设备实现REC与RE之间的报文汇聚传输。需要说明的是，由图3所示示意图可知，所述前向回传网络至少可以包括与REC相连的网络设备1以及与RE相连的网络设备2。另外，还需说明的是，REC除了可通过前向回传网络与RE通信之外，还可通过回程线路(英文：Backhual)与核心网(英文：Core)通信。
针对通过光纤直连实现REC与RE之间报文传输的方案，为了满足CPRI的时间同步面要求，需要使用收发等长的光纤，保证Tb保持不变，以此实现利用通信时延进行上下行补偿的目的。同样地，针对通过网络设备实现REC与RE之间报文传输的方案，亦要保证Tb固定不变，如此才可满足CPRI的时间同步面要求。本发明实施例方案即是为此而提出，下面结合具体示例，对本发明实施例方案的实现过程进行解释说明。
举例来说，本发明实施例中的网络设备可以为一台独立的设备；或者，网络设备 还可以为共同实现网络设备功能的多台设备，即，将网络设备的功能拆分到所述多台设备上；或者，网络设备还可以为集成了网络设备功能的分组传送网(英文：Packet Transport Network，简称：PTN)设备、路由器、交换机、微波设备、光传送网(英文：Optical Transport Network，简称：OTN)设备、同步数字体系(英文：Synchronous Digital Hierarchy，简称：SDH)设备等可实现报文转发的承载网设备。本发明实施例对网络设备在网络中的存在形式可不做具体限定。
参见图4，示出了本发明实施例第一网络设备侧的时间同步的方法的流程图，可包括：
101，第一网络设备接收REC发送的业务帧，并利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1，所述业务帧携带有所述REC的系统时钟。
举例来说，本发明实施例中，第一网络设备可与REC相连，第二网络设备可与RE相连，第一网络设备与第二网络设备之间可以直接连接；或者，第一网络设备与第二网络设备之间可以通过光纤或其他网络设备间接连接，本发明实施例对二者之间的连接关系可不做具体限定。参见图3所示示意图，第一网络设备可体现为网络设备1，第二网络设备可体现为网络设备2，二者之间通过其它网络设备间接连接。
为了正确计算第一网络设备与第二网络设备之间的传输时延，应使第一网络设备与第二网络设备之间保持系统时间同步。举例来说，可以采用1588V2时间同步技术，实现第一网络设备与第二网络设备间的系统时间同步，本发明实施例对此可不做具体限定。
需要进行同步时，REC可以按照REC的本地系统时钟，向第一网络设备发送业务帧，相应地，第一网络设备接收所述业务帧，并利用第一网络设备的本地系统时间，记录下接收所述业务帧的第一时间戳T1。举例来说，第一网络设备可以通过第一用户网络侧接口(英文：User Networks Interface，简称：UNI)接收REC发送的业务帧。
102，所述第一网络设备向第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
举例来说，第一网络设备通过第一网络结点接口(英文：Network to Network Interface，简称：NNI)向第二网络设备发送数据包，第二网络设备通过第二NNI接收来自第一网络设备的数据包。
举例来说，在将来自REC的CPRI业务复用到高速数据业务时，需要对业务帧进 行打包、映射处理，生成所述数据包。具体地，第一网络设备可以将所述业务帧分组，并对每个分组进行速率适配，再添加帧头或报文头生成所述数据包，如此，便可将所述数据包调度到第一NNI接口传输。举例来说，如果第一网络设备为集成了网络设备功能的微波设备、OTN设备、SDH设备等传输设备，可通过添加帧头方式生成所述数据包；如果第一网络设备为集成了网络设备功能的PTN设备、路由器、交换机等包交换设备，可通过添加报文头方式生成所述数据包。
举例来说，第一网络设备至少可通过以下两种方式生成数据包。
方式一
第一网络设备对第一时间戳和业务帧进行打包映射，生成所述数据包。对应于此，第二网络设备可利用系统时钟自适应调整方式，通过所述数据包获得REC的系统时钟。
可选地，第一时间戳可以携带于数据包的报头，业务帧可以携带于数据包的载荷；或者，第一时间戳和业务帧均可携带于数据包的载荷，本发明实施例对此可不做具体限定。
方式二
如果所述第一网络设备与所述第二网络设备还保持系统时钟同步，第一网络设备还可按如下方式生成数据包：所述第一网络设备从所述业务帧中提取所述REC的系统时钟；所述第一网络设备利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；所述第一网络设备对所述频率偏差、所述第一时间戳和所述业务帧进行打包映射，生成所述数据包。对应于此，因为第一网络设备与第二网络设备之间保持系统时钟同步，因此第二网络设备可以通过第二网络设备的系统时钟和数据包中的频率偏差，恢复出REC的业务时钟。举例来说，频率偏差△f＝f1-f2，其中，f1为通过第一网络设备的系统时钟获得的第一频率，f2为通过REC的系统时钟获得的第二频率。
可选地，第一时间戳和频率偏差可以携带于数据包的报头，业务帧可以携带于数据包的载荷；或者，第一时间戳、频率偏差和业务帧均可携带于数据包的载荷，本发明实施例对此可不做具体限定。
需要说明的是，系统时钟同步可以理解为，对第一网络设备和第二网络设备之间的系统时钟进行频率同步和相位同步。举例来说，可以采用同步以太等物理层同步技术，或者可以采用精密时间协议(英文：Precision Time Protocol，简称：PTP)报文频率同步技术，实现第一网络设备与第二网络设备间的系统时钟同步，本发明实施例对此可不做具体限定。
综上，第一网络设备即为第二网络设备计算二者之间的传输时延，提供了技术支 持，如此，第二网络设备便可结合固定时延Tb，对二者之间实际的传输时延进行时延补偿，有助于保证REC与RE之间的时延固定不变。
参见图5，示出了本发明实施例第二网络设备侧的时间同步的方法实施例1的流程图，可包括：
201，所述第二网络设备接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳。
第一网络设备按照图4所示方案，向第二网络设备发送第一数据包后，如果第一网络设备与第二网络设备直连，第二网络设备可直接接收所述第一数据包，并利用本发明实施例方案获得所述传输时延；如果第一网络设备与第二网络设备通过其它网络设备间接连接，第一数据包则可在所述其它网络设备之间转发，直至确认第一数据包被传输至与RE相通信的第二网络设备时，再按照本发明实施例方案获得所述传输时延。
202，所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟。
为了使第二网络设备可以正确向RE转发来自REC的第一业务帧，第二网络设备应知晓REC的系统时钟。对应于上文图4处介绍的生成数据包的两种方式，第二网络设备可通过以下两种方式获得REC的系统时钟。
方式一
对应于上文生成数据包的方式一，第一数据包中包括第一时间戳和第一业务帧。相应地，所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟包括：所述第二网络设备将从所述第一数据包中提取的所述第一业务帧缓存至第一缓存器；所述第二网络设备基于所述第二网络设备的系统时钟，通过系统时钟自适应调整方式获得所述REC的系统时钟。
也就是说，第二网络设备接收到第一网络设备发送的第一数据包后，先从第一数据包中，获得第一网络设备发送第一数据包时采用的高频时钟，这样，第二网络设备便可以该高频时钟为读时钟，从第一数据包中读取第一业务帧并缓存至第一缓存器。举例来说，第一缓存器可以为异步缓存器，如异步先进先出(英文：First In First Out，简称：FIFO)缓存器。
第二网络设备将第一业务帧写入第一缓存器后，便可在第二网络设备的本地系统时钟的基础上，进行系统时钟自适应调整。
举例来说，第二网络设备可根据能否读取到第一业务帧，判断是否需要进行时钟调整。如果以第二网络设备的系统时钟为读时钟，读取不到第一缓存器中的第一业务帧，说明第二网络设备的系统时钟不同于REC的系统时钟，需要进行时钟调整。
举例来说，第二网络设备还可根据第一缓存器中第一业务帧的存量，判断是否需要进行时钟调整。如果第一缓存器中第一业务帧的存量有变动，说明第二网络设备的系统时钟不同于REC的系统时钟，需要进行时钟调整。其中，第一缓存器中第一业务帧的存量指的是，REC发送至第二网络设备并写入第一缓存器的第一业务帧的数量减去第二网络设备从第一缓存器中读取并转发至RE的第一业务帧的数量。举例来说，存量变动具体为存量越来越多，也就是说，单位时间内，REC发送至第二网络设备的第一业务帧的数量多于第二网络设备转发至RE的第一业务帧的数量，第二网络设备便可据此判定第二网络设备的系统时钟与REC的系统时钟相比要慢一些，故可适当将第二网络设备的系统时钟调快些。
经过上述一系列的自适应调整，如果调整后的系统时钟满足如下条件，则可将该调整后的系统时钟确定为REC的系统时钟：第二网络设备能从第一缓存器中读取到第一业务帧，且第一缓存器中第一业务帧的存量保持不变或存量在预设允许范围内变动。
方式二
对应于上文生成数据包的方式二，第一数据包中包括第一时间戳、频率偏差和第一业务帧。相应地，所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟包括：所述第二网络设备从所述第一数据包中提取所述频率偏差；所述第二网络设备利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。举例来说，△f＝f1-f2，如果通过第二网络设备的系统时钟获得第三频率f3，且第一网络设备与第二网络设备之间保持系统时钟同步，则可得知f1＝f3，因此，f2＝f3-△f。
203，所述第二网络设备利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧。
举例来说，第二网络设备获得REC的系统时钟后，可通过以下四种方式向RE发送第一业务帧。
方式一
对应于上文获得REC系统时钟的方式一，第二网络设备向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：所述第二网络设备以所述REC的系统时钟为读时钟，从所述第一缓存器中读取所述第一业务帧，向所述RE发送所述第一业务帧。
方式二
对应于上文获得REC系统时钟的方式二，第二网络设备向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：所述第二网络设备将从所述第一数据包中提取的所述第一业务帧缓存至第一缓存器；所述第二网络设备以所述REC的系统时钟为读时钟，从所述第一缓存器中读取所述第一业务帧，向所述RE发送所述第一业务帧，所述第一业务帧在所述第一缓存器的缓存时长为零。
可选地，由下文图6所示实施例可知，为了实现时延补偿值的查询与维护，第二网络设备还可设置第二缓存器，由第二缓存器对时延补偿的业务帧进行缓存处理，举例来说，第二缓存器可以为同步缓存器，如同步FIFO缓存器。为了提高本发明实施例计算传输时延的准确性，可以尽量模拟利用第二缓存器进行时延补偿过程。基于此，本发明实施例还提供了如下向RE发送第一业务帧的方式三和方式四。
方式三
对应于上文获得REC系统时钟的方式一，第二网络设备向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：所述第二网络设备以所述REC的系统时钟为读时钟，从所述第一缓存器中读取所述第一业务帧，并缓存至所述第二缓存器；所述第二网络设备以所述REC的系统时钟为读时钟，从所述第二缓存器中读取所述第一业务帧，向所述RE发送所述第一业务帧，所述第一业务帧在所述第二缓存器的缓存时长为零。
方式四
对应于上文获得REC系统时钟的方式二，第二网络设备向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：所述第二网络设备将从所述第一数据包中提取的所述第一业务帧缓存至所述第一缓存器；所述第二网络设备以所述REC的系统时钟为读时钟，从所述第一缓存器中读取所述第一业务帧，并缓存至所述第二缓存器；所述第二网络设备以所述REC的系统时钟为读时钟，从所述第二缓存器中读取所述第一业务帧，向所述RE发送所述第一业务帧，所述第一业务帧在所述第二缓存器的缓存时长为零。
204，所述第二网络设备利用所述第二网络设备的系统时间，记录发送所述第一业务帧的第二时间戳T2。
第二网络设备获得REC的系统时钟，向RE转发第一业务帧时，第二网络设备还可利用本地的系统时间，记录下向RE发送第一业务帧的第二时间戳T2。举例来说，第二网络设备可以通过第二UNI向RE发送第一业务帧。
205，所述第二网络设备确定所述第一网络设备与所述第二网络设备之间的传输时 延T＝T2-T1。
综上，第二网络设备结合本地系统时间，可获得向RE发送第一业务帧的第二时间戳T2；第二网络设备通过第一数据包，可获得第一网络设备接收REC发送第一业务帧的第一时间戳T1，如此，第二网络设备便可计算知晓，第一业务帧在REC与RE之间的网络设备上的实际传输时延T＝T2-T1。再结合REC与RE之间的固定时延，便可获得针对传输时延T的时延补偿值，如此方案，有助于保证REC与RE之间的时延固定不变。举例来说，如果利用网络设备替换图1所示网络中的光纤，并保持T通信不变，则固定时延可以体现为Tb；或者，固定时延还可以体现为其它预设时延值，本发明实施例对此可不做具体限定。
参见图6，示出了本发明实施例第二网络设备侧的时间同步的方法实施例2的流程图。在第二网络设备计算传输时延T之后，所述方法还可包括：
301，所述第二网络设备接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
302，所述第二网络设备将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
303，所述第二网络设备确定所述缓存时长是否到达；
304，如果确定所述缓存时长到达，所述第二网络设备以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
第二网络设备获得第一网络设备与第二网络设备之间的传输时延后，即可在后续的交互过程中，结合固定时延，对所述传输时延进行时延补偿，确保报文在网络设备上的时延符合所述固定时延的要求，进而确保REC与RE之间的通信时延维持不变。
在后续交互过程中，REC可按照本地系统时钟向第一网络设备发送第二业务帧，第一网络设备接收所述第二业务帧，并对所述第二业务帧进行打包映射处理，获得第二数据包，将所述第二数据包发送至第二网络设备。
相应地，第二网络设备接收到第二数据包，可将第二业务帧缓存至存储器，便可利用固定时延和传输时延计算第二业务帧的缓存时长。本发明实施例中，缓存时长可以理解为，将所述传输时延补偿到所述固定时延，第二业务帧需要在存储器中的等待时长。如此，在缓存时长到达后，再以图5所示方案获得的REC的系统时钟为读时钟，从存储器中读取第二业务帧并转发至RE。
举例来说，第二网络设备利用缓存时长进行时延补偿，至少可体现为以下两种方 式：通过计时的方式进行时延补偿，将第二业务帧写入存储器后，便可启动计时，并在计时到达所述缓存时长时，再从存储器中读取第二业务帧。或者，如果存储器为FIFO存储器，还可通过调整FIFO水线的方式进行时延补偿，将第二业务帧写入存储器后，根据缓存时长调整水线的高低，以此实现时延补偿。
举例来说，结合上文图5处介绍的向RE发送第一业务帧的四种方式，第二网络设备至少可通过以下两种方式，将第二业务帧缓存至存储器。
方式一
对应于上文向RE发送第一业务帧的方式一和方式二，第二网络设备具有第一缓存器，本实施例中的存储器具体指第一缓存器。相应地，所述第二网络设备将所述第二业务帧缓存至所述存储器包括：第二网络设备从第二数据包中提取第二业务帧并缓存至第一缓存器；所述设置所述第二业务帧的缓存时长包括：设置第二业务帧在第一缓存器中的缓存时长。
可选地，在实际应用中，时延补偿值可能并非始终固定不变，例如，固定时延发生变化和/或传输时延发生变化，均可能导致时延补偿值发生变化。因此，本发明实施例中，第二网络设备除了可以设置时延补偿值之外，还可以查询并维护时延补偿值。以上述通过调整FIFO水线方式进行时延补偿为例，第一缓存器作为异步FIFO，FIFO水线可能会因报文转发过程中的时延抖动而变化，因此，利用第一缓存器进行一次时延补偿后，无法准确获知先前的补偿值为多少，即，无法准确实现时延补偿值的查询与维护。基于此，本发明实施例还提供了如下将第二业务帧缓存至存储器的方式二。
方式二
对应于上文向RE发送第一业务帧的方式三和方式四，第二网络设备具有第一缓存器和第二缓存器，本实施例中的存储器具体指第二缓存器。相应地，所述第二网络设备将所述第二业务帧缓存至所述存储器包括：第二网络设备从第二数据包中提取第二业务帧并缓存至第一缓存器，第二业务帧在第一缓存器的缓存时长为零；第二网络设备以REC的系统时钟为读时钟，从第一缓存器中读取第二业务帧，并缓存至第二缓存器；所述设置所述第二业务帧的缓存时长包括：设置第二业务帧在第二缓存器中的缓存时长。
仍以上述通过调整FIFO水线方式进行时延补偿为例，第二缓存器作为同步FIFO，FIFO水线平稳，有助于实现时延补偿值的准确查询。
可选地，在第二网络设备具有第一缓存器和第二缓存器的方案中，第二网络设备亦可根据需要，采用方式一和方式二向RE发送第一业务帧，本发明实施例对此可不做具体限定。
可选地，本发明实施例中，第一网络设备与第二网络设备可以集成为一台设备，或者，第一网络设备和第二网络设备可以体现为两台独立的设备，本发明实施例对此可不做具体限定。
与图4所示方法相对应地，本发明实施例还提供了一种网络设备，参见图7所示示意图，所述网络设备具体为第一网络设备，所述第一网络设备与无线设备控制器REC相连，所述第一网络设备与第二网络设备保持系统时间同步，所述第二网络设备与射频设备RE相连，所述第一网络设备包括：
接收单元401，用于接收所述REC发送的业务帧，所述业务帧携带有所述REC的系统时钟；
记录单元402，用于在所述接收单元接收到所述业务帧时，利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1；
发送单元403，用于向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
可选地，所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一网络设备还包括：
提取单元，用于在所述接收单元接收到所述业务帧后，从所述业务帧中提取所述REC的系统时钟；
计算单元，用于利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
相应地，所述发送单元向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
在上述可选方案中，本发明实施例网络设备可以实现的附加功能，请参照方法实施例中对第一网络设备附加功能的描述，这里不再赘述。
另外，上述实施例提供的网络设备在进行时间同步时，仅以上述各功能模块的划分进行举例说明，实际应用中，可以根据需要而将上述功能分配由不同的功能模块完成，即将网络设备的内部结构划分成不同的功能模块，以完成以上描述的全部或者部分功能。
与图5所示方法相对应地，本发明实施例还提供了一种网络设备，参见图8所示 示意图，所述网络设备具体为第二网络设备，所述第二网络设备与射频设备RE相连，所述第二网络设备与第一网络设备保持系统时间同步，所述第一网络设备与无线设备控制器REC相连，所述第二网络设备包括：
接收单元501，用于接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
获得单元502，用于通过所述第一数据包，获得所述REC的系统时钟；
发送单元503，用于利用所述获得单元获得的所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
记录单元504，用于利用所述第二网络设备的系统时间，记录所述发送单元发送所述第一业务帧的第二时间戳T2；
时延确定单元505，用于确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
可选地，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述获得单元包括：
提取单元，用于从所述接收单元接收到的所述第一数据包中提取所述频率偏差；
计算单元，用于利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
可选地，所述发送单元包括：
缓存单元，用于将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
发送子单元，用于以所述REC的系统时钟为读时钟，从所述存储器中读取所述第一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
可选地，所述接收单元，还用于在所述时延确定单元计算所述传输时延之后，接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
设置单元，用于将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
时长确定单元，用于确定所述缓存时长是否到达；
读取单元，用于在所述时长确定单元确定所述缓存时长到达时，以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务 帧。
在上述可选方案中，本发明实施例网络设备可以实现的附加功能，请参照方法实施例中对第二网络设备附加功能的描述，这里不再赘述。
另外，上述实施例提供的网络设备在进行时间同步时，仅以上述各功能模块的划分进行举例说明，实际应用中，可以根据需要而将上述功能分配由不同的功能模块完成，即将网络设备的内部结构划分成不同的功能模块，以完成以上描述的全部或者部分功能。
可选地，本发明实施例还提供一种时间同步的系统，参见图3所示示意图，所述系统可包括：图7所示的第一网络设备、图8所示的第二网络设备、REC和RE。其中，所述第一网络设备与所述REC相连，所述第二网络设备与所述RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步。
与图4所示方法相对应地，本发明实施例还提供了一种第一网络设备500，参见图9所示示意图，所述第一网络设备可包括：处理器501、存储器502、网络接口503、总线系统504。
所述总线系统504，用于连接上述处理器501、存储器502和网络接口503。
所述网络接口503，用于实现设备与其它网络设备之间的通信连接。所述网络接口503可以由光收发器，电收发器，无线收发器或其任意组合实现。例如，光收发器可以是小封装可插拔(英文：small form-factor pluggable transceiver，缩写：SFP)收发器(英文：transceiver),增强小封装可插拔(英文：enhanced small form-factor pluggable，缩写：SFP+)收发器或10吉比特小封装可插拔(英文：10Gigabit small form-factor pluggable，缩写：XFP)收发器。电收发器可以是以太网(英文：Ethernet)网络接口控制器(英文：network interface controller，缩写：NIC)。无线收发器可以是无线网络接口控制器(英文：wireless network interface controller，缩写：WNIC)。
所述存储器502，用于存储程序指令和数据。所述存储器502可以包括易失性存储器(英文：volatile memory)，例如随机存取存储器(英文：random-access memory，缩写：RAM)；存储器也可以包括非易失性存储器(英文：non-volatile memory)，例如快闪存储器(英文：flash memory)，硬盘(英文：hard disk drive，缩写：HDD)或固态硬盘(英文：solid-state drive，缩写：SSD)；存储器还可以包括上述种类的存储器的组合。
所述处理器501是中央处理器(英文：central processing unit，缩写：CPU)，也可以是CPU和硬件芯片的组合。上述硬件芯片可以是以下一种或多种的组合：专用集成 电路(英文：application-specific integrated circuit，缩写：ASIC)，现场可编程逻辑门阵列(英文：field-programmable gate array，缩写：FPGA)，复杂可编程逻辑器件(英文：complex programmable logic device，缩写：CPLD)以及网络处理器(英文：network processor，缩写：NP)。所述处理器501，用于读取所述存储器502中存储的程序指令和数据，执行以下操作：
所述处理器通过所述网络接口接收所述REC发送的业务帧，并利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1，所述业务帧携带有所述REC的系统时钟；
所述处理器通过所述网络接口向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
附图9所示的第一网络设备的实现细节，请参考前面附图4所示的方法实施例中的描述，此处不再赘述。
与图5所示方法相对应地，本发明实施例还提供了一种第二网络设备600，参见图10所示示意图，所述第二网络设备可包括：处理器601、存储器602、网络接口603、总线系统604。
所述总线系统604，用于连接上述处理器601、存储器602和网络接口603。
所述网络接口603，用于实现设备与其它网络设备之间的通信连接。
所述存储器602，用于存储程序指令和数据。
所述处理器601，用于读取所述存储器602中存储的程序指令和数据，执行以下操作：
所述处理器通过所述网络接口接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
所述处理器通过所述第一数据包，获得所述REC的系统时钟；
所述处理器利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
所述处理器利用所述第二网络设备的系统时间，记录发送所述第一业务帧的第二时间戳T2；
所述处理器确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
需要说明的是，所述网络接口603、所述存储器602以及所述处理器601的具体表现形式，可参见上文针对图9所示第一网络设备所做的介绍，此处不再赘述。
附图10所示的第二网络设备的实现细节，请参考前面附图5所示的方法实施例中的描述，此处不再赘述。
通过以上的实施方式的描述可知，本领域的技术人员可以清楚地了解到上述实施例方法中的全部或部分步骤可借助软件加通用硬件平台的方式来实现。基于这样的理解，本发明的技术方案本质上或者说对现有技术做出贡献的部分可以以软件产品的形式体现出来，该计算机软件产品可以存储在存储介质中，如只读存储器(英文：read-only memory，简称：ROM)、RAM、磁碟、光盘等，包括若干指令用以使得一台计算机设备(可以是个人计算机，服务器，或者诸如媒体网关等网络通信设备)执行本发明各个实施例或者实施例的某些部分所述的方法。
需要说明的是，本说明书中的各个实施例均采用递进的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其他实施例的不同之处。尤其，对于网络设备及系统实施例而言，由于其基本相似于方法实施例，所以描述得比较简单，相关之处参见方法实施例的部分说明即可。以上所描述的网络设备实施例仅仅是示意性的，其中作为分离部件说明的单元可以是或者也可以不是物理上分开的，作为单元显示的部件可以是或者也可以不是物理单元，即可以位于一个地方，或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部模块来实现本实施例方案的目的。本领域普通技术人员在不付出创造性劳动的情况下，即可以理解并实施。
以上所述仅是本发明的可选实施方式，并非用于限定本发明的保护范围。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以作出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (13)

  1. 一种时间同步的方法，其特征在于，第一网络设备与无线设备控制器REC相连，第二网络设备与射频设备RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步，所述方法包括：
    所述第一网络设备接收所述REC发送的业务帧，并利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1，所述业务帧携带有所述REC的系统时钟；
    所述第一网络设备向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
  2. 根据权利要求1所述的方法，其特征在于，所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一网络设备接收所述REC发送的业务帧之后，所述方法还包括：
    所述第一网络设备从所述业务帧中提取所述REC的系统时钟；
    所述第一网络设备利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
    相应地，所述第一网络设备向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
  3. 一种时间同步的方法，其特征在于，第一网络设备与无线设备控制器REC相连，第二网络设备与射频设备RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步，所述方法包括：
    所述第二网络设备接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
    所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟；
    所述第二网络设备利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
    所述第二网络设备利用所述第二网络设备的系统时间，记录发送所述第一业务帧的第二时间戳T2；
    所述第二网络设备确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
  4. 根据权利要求3所述的方法，其特征在于，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述第二网络设备通过所述第一数据包，获得所述REC的系统时钟包括：
    所述第二网络设备从所述第一数据包中提取所述频率偏差；
    所述第二网络设备利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
  5. 根据权利要求4所述的方法，其特征在于，所述第二网络设备利用所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧包括：
    所述第二网络设备将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
    所述第二网络设备以所述REC的系统时钟为读时钟，从所述存储器中读取所述第一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
  6. 根据权利要求3至5任一项所述的方法，其特征在于，所述第二网络设备计算所述传输时延之后，所述方法包括：
    所述第二网络设备接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
    所述第二网络设备将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
    所述第二网络设备确定所述缓存时长是否到达；
    如果确定所述缓存时长到达，所述第二网络设备以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
  7. 一种网络设备，其特征在于，所述网络设备为第一网络设备，所述第一网络设备与无线设备控制器REC相连，所述第一网络设备与第二网络设备保持系统时间同步，所述第二网络设备与射频设备RE相连，所述第一网络设备包括：
    接收单元，用于接收所述REC发送的业务帧，所述业务帧携带有所述REC的系统时钟；
    记录单元，用于在所述接收单元接收到所述业务帧时，利用所述第一网络设备的系统时间，记录接收所述业务帧的第一时间戳T1；
    发送单元，用于向所述第二网络设备发送数据包，所述数据包包括所述业务帧和所述第一时间戳，所述数据包用于向所述第二网络设备通告所述REC的系统时钟和所述第一时间戳。
  8. 根据权利要求7所述的网络设备，其特征在于，所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一网络设备还包括：
    提取单元，用于在所述接收单元接收到所述业务帧后，从所述业务帧中提取所述REC的系统时钟；
    计算单元，用于利用所述第一网络设备的系统时钟和所述REC的系统时钟，计算频率偏差；
    相应地，所述发送单元向所述第二网络设备发送的数据包包括所述业务帧、所述第一时间戳和所述频率偏差。
  9. 一种网络设备，其特征在于，所述网络设备为第二网络设备，所述第二网络设备与射频设备RE相连，所述第二网络设备与第一网络设备保持系统时间同步，所述第一网络设备与无线设备控制器REC相连，所述第二网络设备包括：
    接收单元，用于接收所述第一网络设备发送的第一数据包，所述第一数据包包括第一业务帧和第一时间戳T1，所述第一业务帧由所述REC发送至所述第一网络设备，所述第一业务帧携带有所述REC的系统时钟，所述第一时间戳为所述第一网络设备接收所述第一业务帧的时间戳；
    获得单元，用于通过所述第一数据包，获得所述REC的系统时钟；
    发送单元，用于利用所述获得单元获得的所述REC的系统时钟，向所述RE发送从所述第一数据包中提取出的所述第一业务帧；
    记录单元，用于利用所述第二网络设备的系统时间，记录所述发送单元发送所述第一业务帧的第二时间戳T2；
    时延确定单元，用于确定所述第一网络设备与所述第二网络设备之间的传输时延T＝T2-T1。
  10. 根据权利要求9所述的网络设备，其特征在于，如果所述第一网络设备与所述第二网络设备保持系统时钟同步，所述第一数据包还包括频率偏差，所述频率偏差由所述第一网络设备的系统时钟和所述REC的系统时钟计算获得，所述获得单元包括：
    提取单元，用于从所述接收单元接收到的所述第一数据包中提取所述频率偏差；
    计算单元，用于利用所述第二网络设备的系统时钟与所述频率偏差，计算所述REC的系统时钟。
  11. 根据权利要求10所述的网络设备，其特征在于，所述发送单元包括：
    缓存单元，用于将从所述第一数据包中提取的所述第一业务帧缓存至存储器；
    发送子单元，用于以所述REC的系统时钟为读时钟，从所述存储器中读取所述第 一业务帧，并发送至所述RE，所述第一业务帧在所述存储器的缓存时长为零。
  12. 根据权利要求9至11任一项所述的网络设备，其特征在于，
    所述接收单元，还用于在所述时延确定单元计算所述传输时延之后，接收所述第一网络设备发送的第二数据包，所述第二数据包包括第二业务帧；
    设置单元，用于将所述第二业务帧缓存至所述存储器，并设置所述第二业务帧的缓存时长为固定时延减去所述传输时延；
    时长确定单元，用于确定所述缓存时长是否到达；
    读取单元，用于在所述时长确定单元确定所述缓存时长到达时，以所述REC的系统时钟为读时钟，从所述存储器中读取所述第二业务帧，向所述RE发送所述第二业务帧。
  13. 一种时间同步的系统，其特征在于，所述系统包括：如权利要求7或8所述的第一网络设备、如权利要求9至12任一项所述的第二网络设备、无线设备控制器REC和射频设备RE，
    所述第一网络设备与所述REC相连，所述第二网络设备与所述RE相连，所述第一网络设备与所述第二网络设备保持系统时间同步。
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