WO2012022163A1 - Method and system for implementing time stamp synchronization between main and standby optical line terminals - Google Patents

Abstract

The present invention discloses a method for implementing time stamp synchronization between main and standby Optical Line Terminals (OLTs), which includes: a main OLT and/or a standby OLT selects a reference Optical Network Unit (ONU) (200); the main OLT synchronously sends the standby OLT the Round Trip Time (RTT) values between itself and all the on-line ONUs or the RTT value between itself and the reference ONU (201); after receiving a Multiple Point Control Protocol (MPCP) frame from the reference ONU, the backup OLT sets the value of a local time stamp timer according to the time stamp in the MPCP frame and the RTT value between the main OLT and the reference ONU (202). The present invention also discloses a system for implementing time stamp synchronization between main and standby OLTs. The solutions of the present invention can effectively synchronize the time stamp timers of the main and standby OLTs in the trunk fiber protection system of the Ethernet Passive Optical Network (EPON), avoid that the ONU becomes offline due to time stamp drift during switching, thus ensuring the switching to be implemented quickly.

Description

 Method and system for realizing time stamp synchronization of active and standby optical line terminals

 The present invention relates to an optical link protection technology, and in particular, to a method and system for realizing time stamp synchronization of a primary and backup optical line terminal. Background technique

 EPON (Ethernet Passive Optical Network) is a new generation broadband passive optical access technology based on IEEE802.3-2005 Section 5 standard. The system usually consists of optical line terminals (OLT, Optical Line). Terminal), the optical network unit (0NU, Optical Network Unit) / optical network termination (0NT, Optical Network Termination) and optical distribution network (ODN, Optical Distribution Network) on the user side. The ODN consists of passive optical components such as single-mode fiber and optical splitters and optical connectors, providing an optical transmission medium for the physical connection between the OLT and the ONU. ODN is usually a point-to-multipoint structure, that is, one OLT connects multiple ONUs. In the EPON system, the service traffic is divided into two directions: uplink and downlink: The uplink refers to the direction from the ONU to the OLT, and the downlink refers to the OLT sends the direction to the ONU. EPON uses the Multipoint Control Protocol (MPCP, Multipoint Control Prototol) as the Medium Access Control (MAC) sublayer.

Both the OLT and the ONU have their own 32-bit counters, incrementing every 16 ns, acting as a local timestamp. When the OLT or ONU device sends an MPCP protocol frame, the local counter value is mapped to the timestamp field in the MPCP protocol frame. When receiving the MPCP protocol frame, the ONU sets the timestamp in the MPCP protocol frame to the local counter, and when the ONU receives the MPCP protocol frame, it also calculates the difference between the local counter and the timestamp in the frame. If the difference is greater than the threshold, a timestamp drift alarm will be generated and the MPCP status opportunity will be deregistered. When the OLT receives the MPCP protocol frame, it uses the timestamp field in the MPCP protocol frame to calculate the OLT and A round trip time (RTT, Round Trip Time) value between ONUs, the RTT value being equal to the difference between the local counter and the timestamp received in the MPCP protocol frame.

 In order to improve network reliability and survivability, an optical link protection switching mechanism can be used in an EPON system. Type b protection is shown in Figure 1: The two PON ports of the OLT use separate PON MAC chips and optical modules to protect the two PON ports. The OLT PON port as the standby is in the cold standby state and is detected by the OLT. The link protection and the status of the primary OLT PON port control the switching between the primary OLT PON port and the standby OLT PON port.

 There is such a problem in the type b protection system: Before the switchover, the ONU timestamp counter is synchronized with the timestamp counter on the OLT main OLT PON port; when switching, the ONU starts to receive the MPCP protocol frame of the standby OLT PON port, if the MPCP protocol If the timestamp between the frame and the local timestamp counter are too large, the timestamp will drift, causing the ONU to drop. Since the timestamp counters of the OLT's active and standby PON ports are not synchronized, the timestamp drift is easy to occur in the type b switching.

 The Technical Requirements for China Telecom EPON Equipment V2.1 stipulates that the ONU should support the "holdover" function. This function means that the ONU can be kept in the "registered" state within the state of the holdover time under the control of the OLT's OAM message (the HoldoverConfig attribute) without registering. This feature can solve the ONU offline problem caused by timestamp drift in type b switching. However, this feature reduces the sensitivity of the ONU to normal deregistration events. On the other hand, many ONU devices on the live network do not support the holdover function. When the type b is switched, the time stamp drift is likely to occur. Summary of the invention

In view of the above, the main purpose of the present invention is to implement a method and a system for realizing the timestamp synchronization of the active and standby optical line terminals, which can effectively synchronize the timestamp counters of the active and standby OLTs in the EPON backbone optical fiber protection system, and avoid the ONU time in the switching. The stamp drift occurs offline, ensuring that the switchover can be completed quickly. In order to achieve the above object, the technical solution of the present invention is achieved as follows:

 The invention provides a method for realizing time stamp synchronization of a master and backup optical line terminal, and the method comprises:

 The primary OLT and/or the standby OLT select the reference ONU;

 The primary OLT synchronously transmits the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT;

 After receiving the MPCP frame of the reference ONU, the standby OLT sets the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU.

 In the above solution, the synchronous transmission is: periodically transmitting, and/or transmitting when the RTT value of the primary OLT and any one of the online ONUs is changed, and/or when the RTT value of the primary OLT and the reference ONU is changed.

 In the above solution, the selection reference ONU is: when the reference ONU number is empty, an online ONU is selected as the reference ONU, the ONU number of the ONU is set as the reference ONU number, and the reference ONU number is synchronized to the standby OLT or The main OLT.

 In the above solution, the method further includes: when the primary OLT and/or the standby OLT are queried that the ONU has an offline event and the ONU number of the offline event is the reference ONU number, the ONU number of the online ONU is set as the reference again. The ONU number and synchronize the reference ONU number to the standby OLT or the primary OLT.

In the above solution, the local timestamp counter is set according to the timestamp in the MPCP protocol frame and the latest RTT value of the primary OLT and the reference ONU, and the timestamp is set to tl in the MPCP protocol frame. The latest RTT value of the OLT and the reference ONU is r, and the value t2 of the local timestamp counter is: t2 = (tl + r) %2 ³² , where % indicates the remainder operation.

The system provides a system for realizing time-synchronization of an active and standby OLT, and the system includes: a primary OLT and a standby OLT; The primary OLT and/or the standby OLT are used to select the reference ONU;

 The primary OLT is further configured to synchronously send the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT;

 The standby OLT is further configured to: after receiving the MPCP protocol frame of the reference ONU, set the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU.

 In the above solution, the standby OLT includes: a timestamp counter, a reference ONU setting module, an RTT value saving module, a frame receiving module, and an update module;

 a timestamp counter, which is used to start a timer with a period of 16 ns at the time of initialization, and accumulates its own count value each time the 16 ns timer expires;

 The reference ONU setting module is used to select the reference ONU, and notify the RTT value saving module when the reference ONU number is not empty;

 The RTT value saving module is configured to receive an RTT value sent by the primary OLT and all the online ONUs or an RTT value of the reference ONU, and save the information to the local;

 a frame receiving module, configured to: when the MPCP protocol frame of the reference ONU is received according to the reference ONU number, extract a timestamp in the MPCP protocol frame, and then notify the update module;

 An update module, configured to query an RTT value of the primary OLT and the reference ONU from the RTT value saved by the RTT value saving module, obtain a value of the timestamp counter according to the RTT value and a timestamp extracted by the frame receiving module, and update the timestamp counter. Value.

 In the above solution, the reference ONU setting module is specifically configured to set an ONU number of an online ONU as a reference ONU number when the reference ONU number is empty, and synchronize the reference ONU number to the active OLT.

In the above solution, the reference ONU setting module is further configured to re-set the ONU number of an online ONU as the reference ONU number when the ONU number of the ONU is detected as an offline event and the ONU number of the offline event is the reference ONU number, and Synchronize the reference ONU number to the standby OLT or The main OLT.

 The method and system for realizing time stamp synchronization of the active and standby optical line terminals are provided by the present invention. The primary OLT and/or the standby OLT select the reference ONU; the primary OLT synchronously transmits the RTT value of itself and all the online ONUs or itself and the reference to the standby OLT. The RTT value of the ONU; after receiving the MPCP protocol frame of the reference ONU, the standby OLT sets the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU; Synchronize the timestamp counters of the active and standby OLTs in the EPON backbone fiber protection system to avoid the ONUs being offline due to timestamp drift during the switching, thus ensuring that the switching can be completed quickly. Moreover, the requirements for the ONU are lower, and the hold over function is not required. It is compatible with all ONU devices on the live network. DRAWINGS

 1 is a schematic structural view of a type b protection in the prior art;

 2 is a schematic flowchart of a method for implementing active/standby OLT timestamp synchronization according to the present invention; FIG. 3 is a schematic flowchart of a method for selecting a primary ONU OLT timestamp synchronization by using a standby OLT to select a reference ONU according to an embodiment of the present invention;

 FIG. 4 is a schematic structural diagram of a system for implementing active/standby 0 LT timestamp synchronization according to the present invention. Detailed ways

 The basic idea of the present invention is: the primary OLT and/or the standby OLT selects the reference ONU; the primary OLT synchronously transmits the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT; the standby OLT receives the reference After the MPCP protocol frame of the ONU, the value of the local timestamp counter is set according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU.

 The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The method for realizing the time synchronization of the active and standby OLTs is as shown in FIG. 2, and the method includes the following steps: Step 200: The primary OLT and/or the standby OLT select a reference ONU.

 Specifically, when the preset reference ONU number is empty, the primary OLT and/or the standby OLT selects an online ONU as the reference ONU, sets the ONU number of the ONU as the reference ONU number, and synchronizes the reference ONU number to the standby. OLT or primary OLT;

 The step further includes: when the primary OLT and/or the standby OLT query the ONU that the ONU has an offline event and the offline event occurs as the reference ONU number, set the reference ONU number to be empty, and re-set the ONU number of an online ONU. Set to the reference ONU number and synchronize the reference ONU number to the standby OLT or the primary OLT.

 Step 201: The primary OLT synchronously sends the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT.

 Specifically, the active OLT calculates an RTT value of itself and all online ONUs according to the received MPCP protocol frames of all online ONUs, and synchronously sends the RTT values to the standby OLT; or, the primary OLT is based on the received reference ONUs. The MPCP protocol frame, calculates the RTT value of itself and the reference ONU, and synchronously sends the RTT value to the standby OLT;

 The synchronous transmission is generally sent periodically, and/or when the RTT value of the primary OLT and any one of the online ONUs is changed, and/or when the RTT value of the primary OLT and the reference ONU is changed; the periodicity is generally Follow the set period.

 Step 202: The standby OLT starts a local timestamp counter. After receiving the MPCP protocol frame of the reference ONU, setting the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the latest RTT value of the primary OLT and the reference ONU. .

 Embodiment 1

 In this embodiment, the standby OLT selects the reference ONU to implement the method for timestamp synchronization of the active and standby OLTs. As shown in FIG. 3, the method includes the following steps:

Step 301: The standby OLT sets the value t2 of the local timestamp counter to 0, sets the reference ONU number to be empty, is generally represented by -1, and starts a timer with a period of 16 ns; Step 302: Determine whether the 16ns timer expires, if it times out, go to step 303, otherwise go to step 304;

 Step 303: The standby OLT accumulates the value t2 of the local timestamp counter according to the formula (1), and performs step 302;

T2 = (t2 + 1) % 2 ³² ( 1 )

 Where % indicates the remainder operation.

 Step 304: The standby OLT queries whether the RTT value sent by the active OLT and all the online ONUs is received. If yes, step 305 is performed; otherwise, step 306 is performed;

 Step 305: The standby OLT saves the received RTT value of the active OLT and all online ONUs to the local, and performs step 302;

 Step 306: The standby OLT queries whether there is an offline event of the ONU, and the ONU number of the offline event is the reference ONU number, if yes, step 307 is performed, otherwise step 310 is performed;

 In this step, when an ONU has an offline event, the active OLT sends a notification message that the ONU has an offline event to the standby OLT, and the standby OLT queries whether the notification message is present, and if so, further queries the offline event in the notification message. If the ONU number is the reference ONU number, if it is the reference ONU number, step 307 is performed, if the standby OLT queries that there is no notification message, or the ONU number of the offline event in the notification message is not the reference ONU number , step 310 is performed;

 Step 307: The standby OLT sets the reference ONU number to be empty.

 Step 308: The standby OLT determines whether there is an online ONU p, if yes, step 309 is performed, otherwise step 302 is performed;

 In this step, the selection of the online ONU p may be any one of all online ONUs, or may be selected according to the ONU number of the online ONU.

Step 309: The standby OLT sets the reference ONU number to p, and performs step 302; Step 310: The standby OLT determines whether the reference ONU number is empty. If yes, step 308 is performed; otherwise, step 311 is performed;

 Step 311: The standby OLT queries whether the MPCP protocol frame of the reference ONU is received according to the reference ONU number, if yes, step 312 is performed, otherwise step 302 is performed;

 Step 312: The backup OLT extracts the timestamp in the received MPCP protocol frame of the reference ONU, and the timestamp is set to tl. The primary OLT and the reference ONU are queried from the locally stored active OLT and the RTT values of all online ONUs. The latest RTT value, the RTT value is set to r;

 Step 313: The standby OLT updates the value t2 of the local timestamp counter according to formula (2), and performs step 302;

T2 = (tl + r) %2 ³² ( 2 )

 Where % indicates the remainder operation.

 In order to implement the foregoing method, the present invention further provides a system for implementing time-stamp synchronization of the active and standby OLTs. As shown in FIG. 4, the system includes: a primary OLT and a standby OLT;

 The primary OLT and/or the standby OLT select the reference ONU;

 The primary OLT is further configured to synchronously send the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT; wherein the synchronous transmission is generally sent periodically, and/or in the primary OLT. Transmitted when the RTT value of any one of the online ONUs is changed, and/or when the RTT value of the primary OLT and the reference ONU is changed;

 The standby OLT is further configured to start a local timestamp counter, and after receiving the MPCP protocol frame of the reference ONU, set a local timestamp according to the timestamp in the MPCP protocol frame and the latest RTT value of the primary OLT and the reference ONU. The value of the counter;

 Further, when the standby OLT is used to select the reference ONU, the standby OLT includes: a timestamp counter 41, a reference ONU setting module 42, an RTT value saving module 43, a frame receiving module 44, and an updating module 45;

The timestamp counter 41 includes a timer with a period of 16 ns, which is used to initialize The 16 ns timer is incremented, and each time the 16 ns timer expires, the count value of the timer is incremented. Specifically, the value of the time stamp counter 41 is set to t2, and each timeout of the 16 ns timer, the timestamp counter 41 Accumulate the count value of itself according to formula (1);

 The reference ONU setting module 42 is configured to select the reference ONU, and notify the RTT value saving module 43 when the reference ONU number is not empty;

 Specifically, the reference ONU setting module 42 sets the reference ONU number to be empty during initialization, and sets the ONU number of an online ONU as the reference ONU number when the reference ONU number is empty, and synchronizes the reference ONU number to the primary use. OLT, notify the RTT value saving module 43;

 The one ONRU may be arbitrarily selected in all online ONUs, or may be selected in the first ONU according to the ONU number of the online ONUs;

 Further, the reference ONU setting module 42 is further configured to: when the ONU number of the ONU occurs, and the ONU number of the offline event is the reference ONU number, set the reference ONU number to be empty, and re-set the ONU number of an online ONU. Set to the reference ONU number, and synchronize the reference ONU number to the standby OLT or the primary OLT;

 The RTT value saving module 43 is configured to receive the RTT value sent by the primary OLT and all the online ONUs or the RTT value of the reference ONU, and save the locality;

 The frame receiving module 44 is configured to extract, according to the reference ONU number set by the reference ONU setting module 42, the timestamp in the MPCP protocol frame when the MPCP protocol frame of the reference ONU is received, and the timestamp is set to tl. Then notify the update module 45;

 The update module 45 is configured to query the latest RTT value of the primary OLT and the reference ONU from the RTT values saved by the RTT value saving module 43, and obtain the value of the timestamp counter according to the RTT value and the timestamp extracted by the frame receiving module 44. Updating the value of the timestamp counter 41;

Specifically, the update module 45 queries the latest RTT value of the primary OLT and the reference ONU from the RTT value saved by the RTT value saving module 43, and the RTT value is set to r according to the RTT value r and the frame receiving module 44. The extracted timestamp tl gets the value of the timestamp counter t2, when updating The value of the stamp counter 41 is t2; the t2 is calculated according to the formula (2).

 In summary, the standby OLT updates the local timestamp counter according to the RRT value of the primary OLT and the reference ONU and the timestamp in the MPCP protocol frame of the reference ONU, so as to be synchronized with the timestamp of the primary OLT, which can be avoided in the switching. The ONU goes offline due to time stamp drift, thus ensuring that the switching can be completed quickly. In addition, the ONU requirement is low, and the hold over function is not required. It can be compatible with all ONU devices on the live network.

 The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included. Within the scope of protection of the present invention.

Claims

Claim  A method for realizing timestamp synchronization of an active/standby optical line terminal, the method comprising:  The primary optical line terminal (OLT) and/or the standby OLT selects the reference optical network unit (ONU); the primary OLT synchronously transmits the round trip time (RTT) value of itself and all online ONUs to the standby OLT or the RTT value of itself and the reference ONU. ;  After receiving the Multipoint Control Protocol (MPCP) frame of the reference ONU, the standby OLT sets the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU.  2. The method according to claim 1, wherein the synchronous transmission is: periodically transmitting, and/or transmitting when the RTT value of the primary OLT and any one of the online ONUs is changed, and/or in the primary OLT. Sent when the RTT value of the reference ONU changes.  The method according to claim 1, wherein the selection reference ONU is: when the reference ONU number is empty, an online ONU is selected as the reference ONU, and the ONU number of the ONU is set as the reference ONU number. , and synchronize the reference ONU number to the standby OLT or the primary OLT.  The method according to claim 3, wherein the method further comprises: when the primary OLT and/or the standby OLT are queried that the ONU number of the ONU occurs and the ONU number of the offline event is the reference ONU number, Re-set the ONU number of an online ONU to the reference ONU number, and synchronize the reference ONU number to the standby OLT or the active OLT. The method according to any one of claims 1 to 4, wherein the local timestamp counter is set according to a timestamp in the MPCP protocol frame and a latest RTT value of the primary OLT and the reference ONU, The timestamp in the MPCP protocol frame is tl, the latest RTT value of the primary OLT and the reference ONU is r, and the value t2 of the local timestamp counter is: t2 = (tl + r) %2 ³² , where % indicates the remainder operation. 6. A system for implementing time-stamp synchronization of an active and standby OLT, the system comprising: a primary OLT and a standby OLT;  The primary OLT and/or the standby OLT are used to select the reference ONU;  The primary OLT is further configured to synchronously send the RTT value of itself and all online ONUs or the RTT value of itself and the reference ONU to the standby OLT;  The standby OLT is further configured to: after receiving the MPCP protocol frame of the reference ONU, set the value of the local timestamp counter according to the timestamp in the MPCP protocol frame and the RTT value of the primary OLT and the reference ONU.  The system according to claim 6, wherein the backup OLT includes: a timestamp counter, a reference ONU setting module, an RTT value saving module, a frame receiving module, and an update module;  a timestamp counter, which is used to start a timer with a period of 16 ns at the time of initialization, and accumulates its own count value each time the 16 ns timer expires;  The reference ONU setting module is used to select the reference ONU, and notify the RTT value saving module when the reference ONU number is not empty;  The RTT value saving module is configured to receive an RTT value sent by the primary OLT and all the online ONUs or an RTT value of the reference ONU, and save the information to the local;  a frame receiving module, configured to: when the MPCP protocol frame of the reference ONU is received according to the reference ONU number, extract a timestamp in the MPCP protocol frame, and then notify the update module;  An update module, configured to query an RTT value of the primary OLT and the reference ONU from the RTT value saved by the RTT value saving module, obtain a value of the timestamp counter according to the RTT value and a timestamp extracted by the frame receiving module, and update the timestamp counter. Value. The system according to claim 7, wherein the reference ONU setting module is configured to set an ONU number of an online ONU as a reference ONU number when the reference ONU number is empty, and the reference ONU The number is synchronized to the primary OLT. The system according to claim 8, wherein the reference ONU setting module is further configured to: when an ONU number of an ONU occurs, and an ONU number of an offline event is a reference ONU number, re-establish an online The ONU's ONU number is set to the reference ONU number, and the reference ONU number is synchronized to the standby OLT or the primary OLT.