CN113922869B - EPON network protection switching quick ranging system - Google Patents

EPON network protection switching quick ranging system Download PDF

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CN113922869B
CN113922869B CN202111183736.3A CN202111183736A CN113922869B CN 113922869 B CN113922869 B CN 113922869B CN 202111183736 A CN202111183736 A CN 202111183736A CN 113922869 B CN113922869 B CN 113922869B
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pon port
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message
onu
onus
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CN113922869A (en
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龙光平
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Xinhe Semiconductor Technology Wuxi Co Ltd
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Xinhe Semiconductor Technology Wuxi Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/03—Arrangements for fault recovery
    • H04B10/032—Arrangements for fault recovery using working and protection systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/03—Arrangements for fault recovery
    • H04B10/038—Arrangements for fault recovery using bypasses
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q2011/0079—Operation or maintenance aspects
    • H04Q2011/0081—Fault tolerance; Redundancy; Recovery; Reconfigurability
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Signal Processing (AREA)
  • Small-Scale Networks (AREA)

Abstract

The invention relates to the technical field of EPON networks, in particular to a system for quick ranging of EPON network protection switching, which comprises a main OLT PON port, a standby OLT PON port, an ODN and N ONUs, wherein the main OLT PON port and the N ONUs complete registration activation and perform network service interaction, the standby OLT PON port synchronizes service configuration of the main OLT PON port in real time, the standby OLT PON port can quickly complete ranging calculation of all ONUs by issuing special Discover messages, and then the messages of the ONUs can be received according to designated time slots by using new RTT information. The invention can reduce the service interruption time of the switching under the condition that the number of ONU and the trunk distance are dynamically changed, improve the user experience and improve the system stability.

Description

EPON network protection switching quick ranging system
Technical Field
The invention relates to the technical field of EPON networks, in particular to a system for quick ranging of EPON network protection switching.
Background
With the development of network technology, the demand for users to transmit a large amount of voice, data, video and other services by using a network is continuously increasing, and passive optical networks (Passive Optical Network, PON) are generated;
as shown in fig. 2, the PON system generally comprises an OLT (Optical Line Terminal ), an ODN (Optical Distribution Network, optical distribution network), and an ONU (Optical Network Unit ), and adopts a P2MP (Point to More Point, point-to-multipoint) network structure; in the current PON technology, a TDM (Time Division Multiplexing ) mode and a WDM (Wavelength Division Multiplexing, wavelength division multiplexing) mode are mainly adopted, in the TDM PON system, an EPON (Ethernet Passive Optical Network ) system adopts a broadcasting mode in the downlink direction (from an OLT to an ONU), each ONU receives all data frames, and then obtains own data frames according to own LLID (Logical Link identity, logic link identification) information;
PON technology can be subdivided into a plurality of types, and the main differences are represented by differences between a data link layer and a physical layer, and APON, EPON, GPON is commonly used.
The entire registration activation process for EPON is shown in fig. 3:
1. the OLT broadcasts and issues a Discovery message with a structure shown in fig. 4, and marks a local Timestamp T on a Timestamp field of the message 0 ；
2. After ONU receives Discovery message, it updates time stamp T in message 0 To the local site; after a certain random time delay T random After that, a register_req message with the structure shown in fig. 6 is fed back, and the Timestamp field in the message is filled with the local Timestamp T of the ONU 1 ；
3. OLT (optical line terminal) local T 2 The register_req message of the ONU is received at any time, and the timestamp T in the message is extracted 1 Calculating the loop delay RTT (RoundTrip Time) =t according to the method shown in fig. 7 2 -T 1 Thus, the loop time of the ONU is obtained;
4. the OLT issues a Register message and follows a Gate2 bandwidth to the ONU; the Gate2 bandwidth at this time is to allocate an uplink transmission time slot according to the RTT information obtained previously, so that the packet of the ONU may not be affected by the data of other ONUs and reach the OLT;
5. after receiving the Register and the Gate2 message, the ONU feeds back a register_ack message;
6. after the OLT receives a register_ack message fed back by the ONU, the registration activation is completed;
7. the OLT intermittently transmits normal_gate messages to the ONU;
8. the ONU receives the normal_gate message, and sends a service data message according to the bandwidth of the message, and feeds back a Report message;
9. the OLT receives Report messages of the ONU, extracts time stamps in the messages, calculates new RTT information, compares the new RTT information with the previous RTT information, and updates the RTT information if the difference value is within a reasonable range required by the standard; the RTT information is the ranging information, and the service interaction flow is completed at the moment;
in deployment applications of passive optical networks, some users need higher security, and it is desirable that operators provide a guarantee mechanism to ensure that their service paths are not interrupted, or that the next level of requirements is to be able to quickly recover after a service path is interrupted. The requirements of a protection path and a fast switching path are provided for the passive optical network carrying the operation of the user service;
fig. 5 shows a typical network architecture diagram in EPON network protection mode;
when the OLT has network failure abnormality, the service needs to be quickly switched from a main working PON (Passive Optical Network ) port to a backup PON port, in which the EPON service undergoes a process from interruption to recovery, and the time consumed in this process is called protection switching time; the protection switching of the OLT needs to re-range the ONU under the EPON port, so that the situation that the time slot conflict does not exist when the service of each ONU arrives at the OLT can be ensured, and the time of the re-ranging also determines the time of the protection switching;
there are two common techniques available:
firstly, after a network failure occurs in a main PON port, switching to a standby PON port, then carrying out ranging again on all ONU, and then recovering the service;
secondly, usually before the distribution of the ONUs, the main PON port and the standby PON port perform ranging on the ONUs under the PON in advance and store ranging values locally, and when the main PON port has network faults, the main PON port is directly switched to the standby PON port, and the re-ranging is not performed any more;
the technical method of the first method is limited in that: the distance measurement needs to be re-measured, the consumed time is at least more than 100 milliseconds, the service interruption time is too long, and the user experience is affected;
the technical method of the second method is limited in that: the whole main-standby PON port network cannot change in the use process, if an additional ONU user event occurs or the trunk optical fiber distance of the standby PON port changes, the standby OLT PON port needs to update RTT information of all ONUs under the ODN in time, then the current main PON port network service needs to be stopped, the standby PON port is switched to perform ranging record ranging information again, and then the main PON port network is switched back; if the switching is started once without timely updating, if the distance between the main optical fiber and the standby optical fiber is poor or the ONU is newly added, ONU data under the PON port of the standby OLT misses a transmission time slot allocated to the ONU by the OLT, so that the uplink service of the whole system is seriously lost; the protection switching may be two OLT PON ports of the same OLT line card, or may be OLT PON ports on different line cards, so that uncertainty of a system environment is very common, once such a situation occurs, a hidden danger of service interruption is easily caused, and maintenance is very inconvenient.
Disclosure of Invention
The invention provides a system for quick ranging of EPON network protection switching, which can reduce the service interruption time of switching, improve the user experience and improve the system stability under the condition that the number of ONU and the trunk distance are dynamically changed.
In order to achieve the purpose of the invention, the system for quick ranging of EPON network protection switching comprises a main OLT PON port, a standby OLT PON port, an ODN and N ONUs, wherein the main OLT PON port and the N ONUs complete registration activation and perform interaction of network services, the standby OLT PON port synchronizes the service configuration of the main OLT PON port in real time, and a standby OLT PON port transmitting end is closed; when the protection switching is started, a sending end of a PON port of the standby OLT is opened, a Discovery2 message is sent to the ONU of the corresponding LLID, and the ONU of the corresponding LLID feeds back a Report message; the PON port of the standby OLT receives the Report message, extracts the time stamp information therein and calculates a new loop delay time RTT new According to the new loop delay time RTT new With the old loop delay time RTT old And determining final RTT information.
As an optimization scheme of the invention, the ODN is a 2:N optical splitter, wherein N is the number of ONU.
As an optimization scheme of the invention, the force_report is set to 1 and the Discovery flag is set to 0 in the flag field of the Discovery2 message; and the ONU with the corresponding LLID receives the Discovery2 message for analysis and sends a Report message.
As an optimization scheme of the invention, a new loop delay time RTT new With the old loop delay time RTT old Comparing and calculating a difference RTT delta ：
1) If RTT new ≥RTT old Indicating that the trunk fiber distance of the PON port of the standby OLT is equal to or greater than the trunk fiber distance of the PON port of the main OLT, reading out the RTT information of all the ONUs stored in the PON port of the standby OLT one by one at the moment, and adding the difference RTT delta As final RTT information;
2) If RTT new ＜RTT old Indicating that the trunk fiber distance of the PON port of the standby OLT is less than the trunk fiber distance of the PON port of the main OLT, at this time, the RTT information of all ONUs stored in the PON port of the standby OLT needs to be read one by one, and the difference RTT is subtracted delta As the final RTT information.
The invention has the positive effects that: the invention can complete the switching from the main OLT PON port to the standby OLT PON port within 5 milliseconds, and can accept the situation that the ONU number dynamic change and the main and standby optical fiber distances are inconsistent before the switching; compared with the prior two implementation modes, the protection switching time is saved, the stability of the system is improved, the maintenance is convenient, the service can be quickly recovered after the service path is interrupted, and the network experience of a user is improved.
Drawings
The invention will be described in further detail with reference to the drawings and the detailed description.
FIG. 1 is a diagram illustrating a data structure of a Discovery2 message according to the present invention;
fig. 2 is a schematic diagram of the topology of a PON system;
fig. 3 is a schematic diagram of an ONU registration activation procedure for EPON;
FIG. 4 is a diagram of a standard Discovery message data structure;
fig. 5 is a schematic diagram of a typical network architecture in PON network protection mode;
FIG. 6 is a diagram of a register_req message data structure;
fig. 7 is a schematic diagram of RTT calculation.
Detailed Description
The implementation of the invention is described in further detail below with reference to the accompanying drawings:
the invention discloses a system for quick ranging of EPON network protection switching, which comprises a main OLT PON port, a standby OLT PON port, an ODN and N ONUs, wherein the main OLT PON port and the N ONUs complete registration activation and perform interaction of network services, the standby OLT PON port synchronizes service configuration of the main OLT PON port in real time, and a standby OLT PON port transmitting end is closed; when the protection switching is started, a sending end of the PON port of the standby OLT is opened, a Discovery2 message is sent to the ONU of the corresponding LLID, and the ONU of the corresponding LLID feeds back a Report messageA text; the PON port of the standby OLT receives the Report message, extracts the time stamp information therein and calculates a new loop delay time RTT new According to the new loop delay time RTT new With the old loop delay time RTT old And determining final RTT information.
Discovery2 is a special message, is a modification of the standard Discovery message structure, is not within the standard specification, but the ONU on the market is identifiable:
for the initiator (spare OLT PON port), the OLT designer may let the receiving side of the OLT consider this to be a normal Discovery message; the OLT opens a Discovery window on the receiving side according to the processing flow of Discovery messages, where the Discovery window is sufficient to cover the furthest logical distance that its PON can support; in this way, the OLT can receive the effective message fed back by the ONU in the discovery window time slot no matter how much the optical fiber distance of the ONU is changed after the main/standby switching;
for the ONU under the PON port of the OLT, because the Discovery flag is set to 0, the force_report flag is set to 1, the ONU recognizes a normal gate message according to the standard rule, and the ONU must feed back a Report message carrying the timestamp information to the OLT according to the standard rule.
Wherein: the main OLT PON port and the standby OLT PON port are connected with the ONU through a 2:N optical splitter, and N is the maximum number of the ONU.
The main OLT PON port completes the registration activation of the ONU and performs the interaction of the network service through the flow shown in figure 3; the process is implemented as follows:
1) The OLT issues a Discovery message with the structure shown in fig. 4 in a broadcast mode, and marks a local Timestamp T on a Timestamp field of the message 0 Filling random time delay upper limit value T in Grant field of message max_random (i.e. ONU generated random delay T) random Cannot exceed the value), the purpose of random time delay is to prevent the data sent by the ONU under the PON port of the OLT for the first time from generating time slot conflict as far as possible; at the same time, the OLT opens a discovery window with a window length T as shown in the right side of fig. 3 at the receiving side max_random +T logic_distance ，T logic_distance A common default value is 20KM, which is converted into a time unit of about 200us; therefore, all the data sent by the ONU within the optical fiber distance of 20KM below the PON port can reach the OLT within the range of the discovery window, and then the data can be analyzed;
2) After ONU receives Discovery message, it updates time stamp T in message 0 To the local site; after a certain random time delay T random After that, a register_req message with the structure shown in fig. 6 is fed back, and the Timestamp field in the message is filled with the local Timestamp T of the ONU 1 ；
3) OLT (optical line terminal) local T 2 The register_req message of the ONU is received at any time, and the timestamp T in the message is extracted 1 Calculate the delay RTT (RoundTrip Time) =t of the loop 2 -T 1 Thus, the loop time of the ONU is obtained, and fig. 7 is a schematic diagram of RTT calculation;
4) The OLT issues a Register message, and generates a Gate2 bandwidth to the ONU according to the RTT information;
5) After receiving the Register and the Gate2 message, the ONU transmits the register_ack message to the OLT according to an uplink transmission time slot designated in the Gate 2;
6) After the OLT receives a register_ack message fed back by the ONU, the registration activation is completed;
7) The OLT intermittently transmits normal_gate messages to the ONU;
8) The ONU receives the normal_gate message, and sends a service data message according to the bandwidth of the message, and feeds back a Report message;
9) The OLT receives Report messages of the ONU, extracts time stamps in the messages, calculates new RTT information, compares the new RTT information with the previous RTT information, and updates the RTT information if the difference value is within a reasonable range required by the standard; RTT is the information of ranging, and the business interaction flow is finished at the moment;
after the registration and activation of all ONUs are completed, the standby OLT PON port synchronizes the service configuration of the main OLT PON port in real time, where the service configuration includes RTT information values of all ONUs under the main OLT PON port, but the transmitting end is closed.
When the PON port of the main OLT fails (normally, the receiving side of the PON port of the main OLT has a certain time periodThe optical signal sent by the upstream ONU cannot be received), the sending end of the main OLT PON port needs to be immediately closed, and the sending end of the spare OLT PON port needs to be opened; because the PON port of the main OLT is closed in the downstream direction, the ONU of the EPON system enters a Hold_over state, and the time T for staying in the state hold The PON port of the main OLT is sent to the ONU when the registration is activated; the OLT needs to complete the switching process from the main OLT PON to the standby OLT PON in this time; if the distances between the main optical fibers of the main OLT PON port and the standby OLT PON port are not consistent, then an important thing that the OLT needs to complete in this process is to re-range all ONUs under the ODN connection, and the time consumed for this ranging is T hold Is a minimum time of (2).
In order to prevent the occurrence of events such as a change in the distance of a trunk optical fiber of a PON port of a standby OLT or the addition of a new ONU under an ODN connection before starting protection switching, the technical solution provided by the present invention is to issue a special Discovery message, i.e. Discovery2 message, when the PON port of the standby OLT is opened. The force_report is set to 1 and the Discovery flag is set to 0 in the flag field of the Discovery2 message; the message is issued to the ONU through the unicast LLID, and only the ONU of the corresponding LLID can analyze and respond, so that a certain ONU in the Hold_over state responds and feeds back a Report message. For the spare OLT PON port, the message is a Discovery message, so a Discovery window capable of covering the farthest logical distance is opened to receive the message, so that the spare OLT PON port can receive the message even if the distance between the backbone fiber of the spare OLT PON port and the main OLT PON port is greatly different; after receiving Report message sent by specific ONU, the back-up OLT PON port can extract time stamp information in the message and calculate new RTT new Then the old loop delay time RTT of the ONU under the PON port of the main OLT is connected with old Comparing and calculating a difference RTT delta ：
1) If RTT new ≥RTT old Indicating that the trunk fiber distance of the PON port of the standby OLT is equal to or greater than the trunk fiber distance of the PON port of the main OLT, reading out the RTT information of all the ONUs stored in the PON port of the standby OLT one by one at the moment, and adding the difference RTT delta As final RTT information;
2) If RTT new ＜RTT old Indicating that the trunk fiber distance of the PON port of the standby OLT is less than the trunk fiber distance of the PON port of the main OLT, at this time, the RTT information of all ONUs stored in the PON port of the standby OLT needs to be read one by one, and the difference RTT is subtracted delta As the final RTT information.
The design purpose is to let the OLT consider this message to be a Discovery message; however, let the ONU consider this not as a Discovery message, but as a NormalGate message; the normalGate message is unicast attribute and only belongs to an individual ONU; the Discovery message is broadcast, and the ONU in the Hold_over state does not respond to the Discovery broadcast message;
because the distance of the ONU changes greatly after the main/standby switching, the transmission delay of the message also changes; if the OLT also uses normal gate message to communicate with the ONU, the OLT cannot receive the message fed back by the ONU in the appointed allocation time slot; if the OLT side processes the Discovery message, a large time slot Discovery window is opened, and the OLT can receive the Discovery window no matter how much the ONU distance changes.
For accurate calculation of RTT delta The averaging may be performed several times more. Therefore, the PON port of the standby OLT can rapidly complete the ranging calculation of all the ONUs, and then the message of the ONUs can be received according to the designated time slot by using the new RTT information, the functions are completed by the chip logic, the consumed time is in the microsecond level, and compared with the time consumed by other technical implementation modes in the millisecond level, the time required by switching is greatly shortened.
The foregoing examples merely illustrate embodiments of the invention and are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that several variations and modifications can be made without departing from the inventive concept, which fall within the scope of the present invention.

Claims (2)

1. A system for quick ranging of EPON network protection switching is characterized in that: the system comprises a main OLT PON port, a standby OLT PON port, an ODN and N ONUs, wherein the main OLT PON port and the N ONUs complete registration activation and perform interaction of network services, the standby OLT PON port synchronizes service configuration of the main OLT PON port in real time, and a standby OLT PON port transmitting end is closed; when the protection switching is started, a sending end of a PON port of the standby OLT is opened, a Discovery2 message is sent to the ONU of the corresponding LLID, and the ONU of the corresponding LLID feeds back a Report message; the PON port of the standby OLT receives Report messages, extracts time stamp information in the Report messages, calculates new loop delay time RTTnew, and determines final RTT information according to a comparison result of the new loop delay time RTTnew and the old loop delay time RTTold; the force_report is set to 1 and the Discovery flag is set to 0 in the flag field of the Discovery2 message; an ONU with a corresponding LLID receives the Discovery2 message for analysis and sends a Report message;
the new loop delay time RTTnew is compared with the old loop delay time RTTold and a difference RTTdelta is calculated:
1) If RTTnew is more than or equal to RTTold, indicating that the trunk optical fiber distance of the PON port of the standby OLT is more than or equal to the trunk optical fiber distance of the PON port of the main OLT, reading RTT information of all ONUs stored in the PON port of the standby OLT one by one at the moment, and adding the difference RTTdelta as final RTT information;
2) If RTTnew is smaller than RTTold, it indicates that the trunk fiber distance of the PON port of the standby OLT is smaller than the trunk fiber distance of the PON port of the main OLT, at this time, RTT information of all ONUs stored in the PON port of the standby OLT needs to be read one by one, and the difference RTTdelta is subtracted as final RTT information.
2. The system for fast ranging of EPON network protection switching of claim 1, wherein: the ODN is a 2:N optical splitter, wherein N is the number of ONUs.
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