CN102340396A

CN102340396A - Time synchronization method for Ethernet passive optical network (EPON)

Info

Publication number: CN102340396A
Application number: CN201010239739XA
Authority: CN
Inventors: 李旭光; 何运锋
Original assignee: Qualcomm Atheros International Shanghai Co Ltd
Current assignee: Qualcomm Atheros International Shanghai Co Ltd
Priority date: 2010-07-29
Filing date: 2010-07-29
Publication date: 2012-02-01

Abstract

The invention discloses a time synchronization method for an Ethernet passive optical network (EPON). A precision time protocol (PTP) slave clock is realized by an optical line terminal (OLT) side of the EPON. The method comprises the following steps that: 1) the OLT side writes a register by a central processing unit (CPU), and simultaneously locks a PTP timestamp counter and a multi-point control protocol (MPCP) timestamp counter; 2) the CPU reads a timestamp storage register; 3) the CPU calculates an MPCP timestamp counter value and time of data (ToD) information corresponding to the latest 1 pulse per second (1PPS) after a PTP timestamp counter value; 4) the CPU transmits the information to an optical network unit (ONU) by an operation and maintenance (OAM) message after a moment corresponding to the 1PPS; and 5) an ONU side realizes 1PPS and ToD information output. By the time synchronization method provided by the invention, a time synchronization technology can be realized simply and flexibly between the OLT supporting a PTP and the ONU not supporting the PTP protocol and only supporting an EPON OAM-based clock synchronization technology.

Description

The method of time synchronized in the EPON network

Technical field

The present invention relates to a kind of EPON network field, the method for time synchronized in particularly a kind of EPON network.

Background technology

EPON EPON (Ethernet Passive OpticalNetworks) based on Ethernet is a point-to-point configuration.Among the EPON EPON based on Ethernet, a local side apparatus OLT (Optical Line Terminal) connects a plurality of ustomer premises access equipment ONU (Optical Network Unit) through tree-structure mode.Local side apparatus is a down direction to the communication of ustomer premises access equipment, and ustomer premises access equipment is a up direction to the communication of local side apparatus.Fig. 1 is the network topology sketch map of EPON system, and when EPON network during as the transmission network of mobile communication, the ability of transmission time synchronizing information becomes needs, can for the mobile base station time source be provided cheaply like this.

The EPON system realizes the clock synchronization between ONU and the OLT through the transmission of MPCP bag.After compensation downlink transfer time delay, can realize the transmission of time synchronized.Shown in Figure 2, in the EPON 1PPS+ToD time synchronized scheme, after the clock source inputed to OLT with 1PPS+ToD information, the PON time stamp that OLT is corresponding with 1PPS was transferred to each ONU, and ONU delays when the compensation downlink transfer, output 1PPS+ToD information.In this scheme, needing a clock source is that OLT provides 1PPS+ToD information.

Summary of the invention

The technical problem that the present invention will solve provides method for synchronizing time in a kind of EPON network, is used in the Ethernet of supporting the PTP agreement.

For solving the problems of the technologies described above, the method for time synchronized in the EPON network of the present invention, the OLT side of this EPON network has realized PTP from clock, and realizes that in the ONU side based on the 1PPS+ToD output of the Clock Synchronization Technology of EPON OAM, this method comprises the steps:

1) the OLT side is write register through CPU, triggers a register signal PTP time stamp counter and MPCP time stamp counter are locked simultaneously, and be stored in respectively in the corresponding time stamp memory register;

2) CPU reads said time stamp memory register, obtains PTP time stamp Counter Value and MPCP time stamp Counter Value respectively;

3) CPU calculates the afterwards nearest 1PPS of said PTP time stamp Counter Value corresponding MPCP time stamp Counter Value and corresponding ToD information;

4) CPU sends to ONU with MPCP time stamp Counter Value that is calculated and ToD information through the OAM message after said 1PPS moment corresponding;

5) the ONU side realizes the output of 1PPS+ToD information.

Adopt method for synchronizing time of the present invention; Can simple and flexible ground at the OLT that supports the PTP agreement with do not support the PTP agreement only to support between ONU based on the Time synchronization technique of EPON OAM; Realize Time synchronization technique, increase the flexibility of networking, reduce networking cost.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed explanation:

Fig. 1 is the network topology sketch map of EPON system;

Fig. 2 is the time synchronized scheme sketch map based on EPON OAM;

Fig. 3 is a method for synchronizing time flow chart of the present invention.

Embodiment

In Ethernet, support the product of PTP (Precision Time Protocal, precision time protocol) time host-host protocol to increase gradually.If realize PTP from clock, and be converted into the 1PPS+ToD message transmission, then can realize more flexibly networking plan more cheaply to ONU in the OLT side.

The method of time synchronized in the EPON network of the present invention, applied environment are that the OLT side of EPON has realized PTP from clock, and realize the 1PPS+ToD output based on the Clock Synchronization Technology of EPON OAM in the ONU side.The method of time synchronized of the present invention, concrete steps are:

1) the OLT side is write register through CPU (software); Trigger a register signal just PTP time stamp counter and MPCP (Mut i-Point Control Protocol; Multi-point Control Protocol) the time stamp counter locks simultaneously; And be stored in respectively in the corresponding time stamp memory register (wherein CPU is divided into read and write to operation registers, and reading is exactly the value that obtains in the register, and creating is to register assignment);

2) CPU (software) reads the time stamp memory register, obtains PTP time stamp Counter Value and MPCP time stamp Counter Value respectively;

3) CPU (software) calculates the afterwards nearest 1PPS of this PTP time stamp Counter Value corresponding MPCP time stamp Counter Value and corresponding ToD information;

4) CPU (software) sends to ONU with MPCP time stamp Counter Value that is calculated and corresponding ToD information through the OAM message after this 1PPS moment corresponding;

5) realize the output of 1PPS+ToD information in the ONU side.

In the OLT side of the EPON that supports the PTP agreement, realize that PTP can be described as simply from clock: OLT initiates path delay and measures, obtain path delay; OLT receives after the PTP Sync message, and recorded message time of advent, OLT calibrates local zone time after compensation transmission delay and asymmetry.

And realize 1PPS+ToD output based on the Clock Synchronization Technology of EPON OAM in the ONU side, and specifically can be ONU and receive the MPCP time stamp Counter Value and corresponding ToD information that is calculated, export 1PPS+ToD information constantly at next 1PPS after the delay compensation.More specifically can be: the MPCP Counter Value that ONU is corresponding constantly with next 1PPS is arranged in the register, and when the MPCP Counter Value equaled this register value, ONU output 1PPS pulse was risen and prolonged.After ONU output 1PPS pulse rising was prolonged, ONU hardware was changed to the corresponding MPCP Counter Value of next 1PPS with this register.ONU corresponding ToD information of (before 500ms) output in the stipulated time after output 1PPS rising edge of a pulse.After ONU receives through the next 1PPS information of OAM message transmission, behind the ONU compensation transmission delay, calculate the corresponding MPCP Counter Value of next 1PPS, and be placed in the above-mentioned register.

Adopt Time synchronization technique scheme of the present invention; Local side apparatus OLT need not the information such as GPS isochronon source input 1PPS+ToD; Only need realizing that PTP is from the basis of clock; With temporal information and the MPCP time stamp counter phase relation locking of PTP, and then calculate, produce, transmit corresponding 1PPS+ToD information by CPU (software) and give ONU from clock.Adopt method for synchronizing time of the present invention; Can simple and flexible ground at the Ethernet of supporting the PTP agreement with do not support the PTP agreement only to support to realize Time synchronization technique between ONU based on the Clock Synchronization Technology of EPON OAM; Increase the flexibility of networking, reduce networking cost.

Claims

1. the method for time synchronized in the EPON network; The OLT side of said EPON network has realized that PTP is from clock; And realize it is characterized in that based on the 1PPS+ToD output of the Clock Synchronization Technology of EPON OAM said method comprises the steps: in the ONU of EPON network side

5) the ONU side realizes the output of 1PPS+ToD information.

2. according to the described method of claim 1, it is characterized in that said step 5) is: the ONU side joint is received the information of sending in the step 4), after the delay compensation, exports 1PPS+ToD information constantly at next 1PPS.