WO2012065402A1

WO2012065402A1 - Ethernet passive optical network system and method for implementing end-to-end transparent clock in such system

Info

Publication number: WO2012065402A1
Application number: PCT/CN2011/072872
Authority: WO
Inventors: 王伟
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-11-17
Filing date: 2011-04-15
Publication date: 2012-05-24
Also published as: CN102469377A

Abstract

A method for implementing an End-to-End Transparent Clock (E2ETC) in an Ethernet Passive Optical Network (EPON) system is disclosed by the present invention. The method includes: when receiving a Precision Time Protocol (PTP) message, a first network element records a first time when receiving the PTP message, sets the recorded first time in the PTP message and transmits the PTP message to a second network element; and the second network element receives the PTP message, and the PTP message, which will be transmitted to a lower device or an upper device, carries the residence time of the PTP message which is calculated according to the first time and the current time. The EPON system is also disclosed by the present invention. With the present invention, the E2ETC function in the IEEE1588-2008 protocol can be implemented in the condition of without extra hardware assistance.

Description

Method for implementing end-to-end transparent clock in EPON system and system

TECHNICAL FIELD The present invention relates to the field of Ethernet network synchronous clocks, and proposes an Ethernet Passive Optical Network (EPON) system and a method for implementing an end-to-end transparent clock in the system.

Background technique

IEEE1588-2008 Clock Synchronization Protocol, also known as Precision Time Synchronization Protocol (PTP), is a more accurate clock synchronization scheme in Ethernet. By transmitting IEEE1588 messages between master and slave devices, the time and frequency offset is calculated. The master-slave frequency and time are synchronized, which solves the bottleneck of long delay time and poor synchronization capability of the general Ethernet.

IEEE 1588-2008 defines two types of PTP messages: an Event message and a General message. An Event message is a message containing time information, which requires accurate timestamp information to be received and sent. The General message does not require accurate timestamp information. The End-to-End Transparent Clock (E2ETC) is a working model defined in the IEEE1588-2008 protocol. The end-to-end transparent clock forwards various messages like ordinary bridges, switches, and routers. However, for IEEE1588-2008 Event messages, E2ETC needs to calculate the event time in the device's internal dwell time for time delay correction, which will be corrected. Afterwards, the Event ^ message is forwarded to the next-level network to implement the IEEE-2008 protocol step by step, thereby maintaining the time synchronization of the entire network.

The main application scenario of the IEEE1588-2008 protocol in the EPON system is to keep the base station (NodeB) device connected to the Optical Network Unit (ONU) and the clock of the primary clock server synchronized. At present, most of the solutions are implemented by a mature time processing chip or a field-programmable gate array (FPGA) device, which is used as a boundary clock by an optical line terminal (OLT) and an ONU. The IEEE1588-2008 master clock is implemented on the ONU side, and the PTP message is transmitted to the lower-level NodeB device to keep the time between the NodeB device and the master clock server synchronized. However, this solution generally requires hardware device assistance. The cost of the EPON system has been increased.

SUMMARY OF THE INVENTION The technical problem to be solved by the present invention is to provide an EPON system and a method for implementing an end-to-end transparent clock in a system, which effectively reduces the cost of the EPON system. To solve the above technical problem, the present invention provides an Ethernet passive optical network (EPON) system for implementing an end-to-end transparent clock, the method comprising: when a first network element receives a precise time synchronization protocol (PTP) message Recording a first time when the PTP message is received, and placing the first time of the record in the PTP message and sending the message to the second network element; and the second network element receiving the PTP message, in the subordinate device The PTP message sent by the upper-level device carries the retention time of the PTP message calculated according to the first time and the current time. among them:

The first network element is an optical line terminal (OLT), and the second network element is an optical network unit (ONU); or the first network element is an ONU, and the second network element is an OLT. among them:

The time between the OLT and the ONU is synchronized. among them:

The PTP message is a PTP event message. among them:

The carrying the retention time in the PTP message includes adding the retention time and the time in the PTP message header correction field to the correction field in the PTP message header. The method further includes: deleting, by the second network element, the PTP before sending the PTP message to the lower-level device or the upper-level device The first time in the message.

To solve the above technical problem, the present invention further provides an Ethernet Passive Optical Network (EPON) system, including a first network element and a second network element, where: the first network element is set to: The time synchronization protocol (PTP) message records the first time when the PTP message is received, and the first time of the record is placed in the PTP message and sent to the second network element;

The second network element is configured to: receive the PTP message, and carry the PTP message sent by the lower-level device or the upper-level device with the retention time of the PTP message calculated according to the first time and the current time.

The first network element is an optical network terminal (OLT), and the second network element is an optical network unit (ONU); or the first network element is an ONU, and the second network element is an OLT. among them:

The time between the OLT and the ONU is synchronized. among them:

The PTP message is a PTP event message. among them:

The second network element includes a first unit and a second unit, where: the first unit is configured to: receive the PTP message; the second unit is configured to: use the retention time and the PTP message header The time in the partial correction field is added to the correction field in the header of the PTP message. among them:

The second network element further includes a third unit, where the third unit is configured to: the second unit deletes the first time in the PTP message before sending the PTP message to the lower-level device or the upper-level device. Since the uplink interface of the OLT and the downlink interface of the ONU are both Ethernet interfaces, refer to Figure 1. Using the ranging mechanism of the PON, the OLT and ONU can be conveniently implemented by extending the Operation Administration and Maintenance (OAM) message. Time synchronization. The solution of the invention fully utilizes the existing EPON system equipment, realizes the E2ETC function in the IEEE1588-2008 protocol without additional hardware assistance, satisfies the application scenario of the EPON system, effectively and effectively reduces the cost of the EPON system, and brings certain economy. benefit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a system structure according to an embodiment of the present invention; FIG. 2 is a flowchart of processing a downlink PTP Event message; and FIG. 3 is a flowchart of processing an uplink PTP Event message.

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the features in the embodiments and the embodiments in the present application may be arbitrarily combined with each other. The method for implementing the E2ETC in the IEEE1588-2008 protocol in the embodiment of the present invention includes: the first network element records the first time of receiving the message when receiving the precise time synchronization protocol (PTP) message, and the first time of the record The time is placed in the PTP message and sent to the second network element; and the second network element receives the PTP message, and the PTP message sent by the lower-level device or the upper-level device is calculated according to the first time and the current time. The retention time of the PTP message. Specifically, in the downlink, the retention time is a time when the PTP message is received by the ONU from the OLT to the ONU subordinate device; in the uplink, the retention time is that the PTP message is received from the ONU and sent by the OLT to the OLT upper-level device. Time to go out. In the above solution, the OLT and the ONU are regarded as a whole in the EPON system. The schematic diagram of the system structure is shown in Figure 1. Under the premise that the time between the OLT and the ONU is synchronized, the uplink interface of the OLT and The ONU's downlink interfaces form a transparent clock to jointly complete the E2ETC function in the IEEE1588-2008 protocol. In the figure, the 1588 master clock can be a clock server, and the 1588 slave clock can be a base station or the like that needs to be synchronized. The OAM-1 frame is used to send the ranging information to the corresponding ONU in the unicast message. The OAM 2 frame is used to periodically send the time synchronization information to all ONUs in the broadcast message. . When the first network element is an OLT, the second network element is an ONU; or, when the first network element is an ONU, the second network element is an OLT. Specifically, when the PTP message is transmitted in the downlink, the OLT records the time when the OLT Ethernet uplink interface receives the PTP Event message, and adds the time to the PTP message. When the message passes through the Ethernet downlink interface of the ONU, the ONU calculates the The retention time experienced by the message traversing the OLT and the ONU is added to the correction field in the header of the PTP Event message and forwarded to the next-level NodeB device. See Table 1 for the format of the PTP message header. When the PTP message is transmitted in the uplink, the ONU records the time of the PTP Event message received by the ONU Ethernet downlink interface, and adds the time to the PTP message. When the message passes through the Ethernet uplink interface of the OLT, the message is calculated to traverse the OLT and The residence time experienced by the two ONU devices is added to the CorrectionField in the header of the PTP Event message and forwarded to the higher-level device. The above addition to the CorrectionField in the header of the PTP Event message means that the calculated residence time and the time in the correction field are accumulated and added to the correction field. Table 1

Through the above processing, the delay and jitter caused by the transmission and processing of the PTP message in the EPON system can be removed, and the accuracy of the time synchronization is ensured.

The time synchronization between the OLT and the ONU is based on the PON ranging mechanism. The extended OAM message transmission time synchronization information is used to implement the OLT and the EPON time synchronization mechanism according to the technical requirements of the China Telecom EPON equipment (V2.1 Revision 2). The time synchronization between the ONUs is not within the scope of the present invention. However, the implementation method of the present invention must be based on the synchronization of the OLT and ONU time.

The downlink PTP Event message is calculated by the ONU in the EPON system. The process flow is shown in Figure 2. The following steps are included: Step 201: The OLT uplink interface receives the PTP Event message sent from the upper-level network device or the master clock. , the PTP Event message processing flow is entered; the PTP General message that does not include the time information is not processed, and is directly forwarded; for the PTP Event message containing the time information, step 202 is performed; Step 202: The OLT records the current time of receiving the PTP Event message. The timestamp is Ta, and Ta is padded to the end of the PTP Event message according to the Timestamp format specified in IEEE1588-2008 to facilitate the ONU to calculate the residence time. In other embodiments, Ta may also be placed in the PTP Event message. Other locations, as long as the ONU can query it. Step 203: The OLT forwards the modified PTP Event message to the ONU. Step 204: The ONU downlink interface receives the modified PTP Event message forwarded from the OLT, and enters a PTP Event message processing flow. Step 205: The ONU records the current received PTP Event. The timestamp of the message is Tb, and the OLT receiving timestamp Ta is extracted from the modified PTP Event message; the ONU calculates the retention time of the current PTP Event message in the EPON system as ΔT:

△ T = Tb-Ta The Δ 填 is filled in the CorrectionField field in the PTP message header according to the requirements of IEEE1588-2008, and the timestamp Ta filled at the end of the PTP Event message is removed from the OLT; Step 206: The ONU forwards the correct PTP Event message to the next-level device.

The uplink PTP Event message is calculated by the OLT for the retention time in the EPON system. The process flow is shown in Figure 3. The following steps are included: Step 301: The ONU downlink interface receives the PTP Event message sent from the next-level network, and enters the PTP Event message. Process flow; for the PTP General message that does not contain the time information, it is not processed, and is directly forwarded; Step 302: The ONU records the current time of receiving the PTP Event message as Tc, and the Tc is followed.

The Timestamp format specified in IEEE1588-2008 is populated at the end of the PTP Event message to facilitate the OLT to calculate the residence time. Similarly, in other embodiments, the Tc can also be placed in other locations of the PTP Event message, as long as the OLT can query. Just go. Step 303: The ONU forwards the modified PTP Event message to the OLT. Step 304: The OLT uplink interface receives the modified PTP Event message forwarded from the ONU, and enters the PTP Event message processing flow. Step 305: The OLT records the current received PTP. The event message timestamp is Td, and the OLT receiving timestamp Tc is extracted from the received modified PTP Event message; the ONU calculates the retention time of the current PTP Event message in the EPON system as ΔT:

Δ T = Td-Tc The Δ T is filled in the CorrectionField in the PTP message header according to the requirements of IEEE1588-2008, and the timestamp Tc at which the ONU is filled at the end of the PTP Event message is removed; Step 306: The OLT forwards the correct PTP Event message to Upper level network or primary clock server. Through the above steps, the delay and jitter caused by the transmission and processing of the PTP message in the EPON system can be removed, and the accuracy of the time synchronization can be ensured, so that the transparent end-to-end clock of the IEEE1588-2008 protocol can be used to transmit the PTP message step by step.

In this embodiment, the system for implementing the foregoing method includes a first network element and a second network element, where: the first network element is configured to: record and receive the message when receiving a precise time synchronization protocol (PTP) message The first time, and the first time of the record is placed in the PTP message and sent to the second network element; the second network element is set to: receive the PTP message, in a subordinate device or The PTP message sent by the upper-level device carries the retention time of the PTP message calculated according to the first time and the current time. When the first network element is an OLT, the second network element is an ONU; or, when the first network element is an ONU, the second network element is an OLT. Preferably, the second network element includes a first unit and a second unit, where: the first unit is configured to: receive the PTP message; the second unit is configured to: The time accumulation in the PTP message header correction field is added to the correction field in the PTP message header.

Preferably, the second network element further includes a third unit, where the third unit is configured to: the second unit deletes the first time in the PTP message before sending the PTP message to the lower-level device or the upper-level device.

One of ordinary skill in the art will appreciate that all or a portion of the above steps may be performed by a program to instruct the associated hardware, such as a read only memory, a magnetic disk, or an optical disk. Alternatively, all or part of the steps of the above embodiments may also be implemented using one or more integrated circuits. Correspondingly, each unit in the foregoing embodiment may be implemented in the form of hardware, or may be implemented in the form of a software function module. The invention is not limited to any specific form of combination of hardware and software. It is a matter of course that the invention may be embodied in various other forms and modifications without departing from the spirit and scope of the invention.

Industrial Applicability The solution of the present invention completely utilizes the existing EPON system equipment, realizes the E2ETC function in the IEEE1588-2008 protocol without additional hardware assistance, satisfies the application scenario of the EPON system, and effectively reduces the cost of the EPON system, bringing Certain economic benefits.

Claims

Claim

An Ethernet passive optical network (EPON) system for implementing an end-to-end transparent clock, the method comprising: recording, by a first network element, a PTP message received when receiving a precise time synchronization protocol (PTP) message The first time, the first time of the record is placed in the PTP message and sent to the second network element; and the second network element receives the PTP message, in the PTP message sent by the lower-level device or the superior device. Carrying a residence time of the PTP message calculated according to the first time and the current time.

2. The method according to claim 1, wherein: the first network element is an optical line terminal (OLT), and the second network element is an optical network unit.

(ONU); or, the first network element is an ONU, and the second network element is an OLT.

3. The method of claim 2, wherein the OLT and the ONU are time synchronized.

4. The method of claim 1 or 2 or 3, wherein: the PTP message is a PTP event message.

5. The method according to claim 1 or 2 or 3, wherein: the carrying the retention time in the PTP message comprises: adding the retention time and the time in the PTP message header correction field to the location In the correction field in the header of the PTP message.

The method according to claim 1 or 2 or 3, the method further comprising: deleting, by the second network element, the first time in the PTP message before sending the PTP message to the lower-level device or the upper-level device.

7. An Ethernet Passive Optical Network (EPON) system, comprising a first network element and a second network element, among them:

The first network element is configured to: record a first time of receiving the PTP message when receiving a precise time synchronization protocol (PTP) message, and place the first time of the record in the PTP message to send The second network element is configured to: receive the PTP message, and carry the PTP message sent by the lower-level device or the upper-level device according to the first time and the current time The retention time of the PTP message.

The system of claim 7, wherein: the first network element is an optical line terminal (OLT), and the second network element is an optical network unit (ONU); or the first network element is The ONU, the second network element is an OLT.

9. The system of claim 7 or 8, wherein the OLT and the ONU are time synchronized.

10. The system according to claim 7 or 8, wherein the PTP message is a PTP event message.

11. The system of claim 7 or 8, wherein:

The second network element includes a first unit and a second unit, where: the first unit is configured to: receive the PTP message; the second unit is configured to: use the retention time and the PTP message header The time in the partial correction field is added to the correction field in the header of the PTP message.

12. The system of claim 11 wherein:

The second network element further includes a third unit, where the third unit is configured to: the second unit deletes the first time in the PTP message before sending the PTP message to the lower-level device or the upper-level device.