CN1152488C - Realization Method of Ranging in ATM Passive Optical Network - Google Patents

Abstract

The present invention discloses a method for realizing the distance measurement in ATM passive optical networks. The present invention has the key that the method at least comprises the following steps: a, an optical line terminal (OLT) sends a configuring message of distance measurement to an optical network unit (ONU); b, the OLT opens distance measurement windows, waits for trapping distance measurement physical layer operation maintenance management (PLOAM) sent by an optical network unit and begins timing; c, when the PLOAM is trapped, timing is stopped, and the validity of the distance measurement result is judged; d, if three times of distance measurement fail, distance measurement is finished, and failure reasons are informed to network management; otherwise, the method returns to the step b; if three times of distance measurement succeed, equivalent delaying values are calculated and adjusted according to the distance measurement results, the OLT sends a configuring message of distance measurement finish to the ONU, and the ONU sends a response message after the ONU receives the message; if ONU sends no response message, distance measurement is considered to fail, distance measurement is finished, and failure reasons are informed to network management; otherwise, the method returns to the step b.

Description

Realization Method of Ranging in ATM Passive Optical Network

technical field

The present invention relates to the distance measuring technology in ATM passive optical network, especially a kind of distance measurement can be realized between optical line terminal (OLT) and optical network unit (ONU) in ATM passive optical network, and the maximum degree A ranging method to ensure service quality.

Background technique

Due to the advent of the network era, communication networks with increasingly powerful functions are developing rapidly to meet people's ever-increasing needs. ATM Passive Optical Network (APON) is one of them. It combines the ATM broadband service based on cell transmission with the passive optical network (PON) technology, and uses optical fiber as the transmission medium to provide high-speed data and broadband services. The processing communication network has a wide frequency band and a large capacity. The so-called PON is an optical access network without any active electronic equipment between the optical line terminal (OLT) and the optical network unit (ONU), that is, between the central office and the remote user. In APON, an OLT can connect multiple ONUs at the same time. Therefore, APON can not only provide broadband multimedia services more flexibly, but also allow multiple users in the access network to share the entire bandwidth.

In the APON system, the central OLT and each remote ONU are connected through optical fibers and optical splitters. Due to the different logical distances from each ONU to the OLT, the phases of data arriving at the OLT from different ONUs are different, resulting in different ONUs arriving at the OLT. Data conflicts, causing data loss. In order to ensure that each ONU maintains the same logical distance, so that each ONU can transmit data to the central office according to a certain phase without conflict, the method of distance measurement is used to solve this problem and realize the measurement of the distance between OLT and ONU.

At present, ITU-T has released standards G.983.1 and G.983.2 for APON, which respectively define the specification of the transmission medium layer and the specification of the high-level management entity interface. Among them, the transmission medium layer is further divided into two parts: the transmission convergence sublayer (TC layer) and the physical medium layer, and ranging is a part of the G.983.1 specification for the TC layer.

According to the definition of ranging in G.983.1, the specific ranging process and the relationship between the phase specification points between the OLT and ONU related to ranging are shown in Figure 1. In Figure 1, TiS1 and TiS2 represent the electrical/optical conversion delay at the central office; Tpd represents the transmission delay of the signal on the optical fiber; TiO1 and TiO2 represent the remote electrical/optical conversion delay; Ts is the basic cell transmission delay , generated by PON signal processing in the ONU; Td is the equivalent delay value obtained through ranging and conversion, and 0≤Td≤32000bit in the 155Mbps system. Tconst is the same logical distance to be achieved by each ONU, and generally has two specifications: 4T (50 kilometers) and 2T (25 kilometers); T _response is the response time of the ONU. According to the above parameters, Tconst and T _response value of each ONU should be:

Tconst＝TiS1+Tpd+TiO1+Ts+Td+TiO2+Tpd+TiS2

T _response <ONU>=TiO1+Ts+Td+TiO2

When Td=0, that is, when there is no ranging,

T _response <ONU>=TiO1+Ts+TiO2

In a normal operating state, that is, for ONUs after successful ranging, the equalized round-trip delays of all ONUs should have the same constant Tconst. That is to say, for all ONUs in normal operation state, they have the same logical distance, so that each ONU in normal operation can access data without conflict at the OLT side.

During the ranging process, the OLT needs to open the ranging window in addition to sending configuration messages to the ONU. This ranging window is actually to shield a certain section of bandwidth of the line, so that the ranging physical layer operation, management and maintenance (PLOAM) cells sent by the ONU under test to the OLT can appear in this section of the shielded section without being affected by other data. Then the TC layer of the OLT ends the ranging timing according to the captured cells, thereby obtaining the delay of the line and processing, and finally calculates the required Td according to the delay, and sends it to the ONU.

However, the current ranging process only measures the delay value of each ONU without giving an exact judgment condition for the validity of the delay value. It is proposed in G.983.1 that in the three-time ranging process, only two If the difference from the delay value is less than a certain range, it is considered successful. But in fact, if the delay value obtained by ranging exceeds 4T, and the three delay values are the same, it seems that the ranging is successful, but in fact the delay value is already illegal at this time. If the delay value is illegal, it will cause an error in the phase of data access from the ONU to the OLT, which will seriously affect the data access of other ONUs. In addition, there is no judgment on the running status of the ONU in the existing ranging process, so that the OLT may cause wrong operations on the ONU. Because the OLT needs the ONU to respond to the message configured by the central office after the ranging is successful. If the ONU does not respond, although the ONU ranging is successful, the OLT still thinks that the ONU is in an abnormal state. Then, in order to ensure the operation of the system, the OLT , it is necessary to deal with the ONU that is not working normally, so that mishandling will occur.

In addition, a part of the fixed bandwidth will be occupied more or less during the ranging process, thereby affecting services that are sensitive to delay and jitter. And if the fixed bandwidth of an ONU is larger, the fixed bandwidth loss caused by ranging will be more. Then in the case of frequent ranging, it will have a certain impact on the service and damage the quality of service (QOS).

Contents of the invention

In view of this, the main purpose of the present invention is to provide a method for realizing ranging in an ATM passive optical network, so that the reliability and accuracy of ranging are higher, and ONU can quickly enter the normal working state after ranging , so as to ensure the normal operation of the system.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

A method for realizing ranging in an ATM passive optical network, at least comprising the following steps:

a. The optical line terminal (OLT) sends a ranging configuration message to the optical network unit (ONU);

b. The optical line terminal (OLT) opens the ranging window, waits to capture the ranging physical layer operation and maintenance management (PLOAM) sent by the optical network unit (ONU), and starts timing;

c. The optical line terminal (OLT) captures the ranging physical layer operation and maintenance management (PLOAM) sent by the optical network unit (ONU), and stops timing;

d. Judging whether the delay value is obtained within the specified time, if the delay value is not obtained within the specified time, then end the ranging; if the delay value is obtained within the specified time, then judge whether the delay value is within the specified time In the opened ranging window, if the delay value is not in the opened ranging window, the ranging will be ended; if the delay value is in the opened ranging window, then judge the delay value of two adjacent times Whether the difference is within the fixed range, if not within the fixed range, then add one to the number of ranging failures, and then judge whether the ranging has failed three times, and enter step e; if the difference between two adjacent delay values is within the fixed range, Then add one to the number of times of successful distance measurement, then judge whether the distance measurement has been successful three times, and enter step f;

e. If the distance measurement fails three times, then end the distance measurement and notify the network management of the failure reason; otherwise, return to step b;

f. If the three distance measurements are successful, proceed to step g; otherwise, return to step b;

g. The optical line terminal (OLT) calculates and adjusts the equivalent delay value according to the ranging result, the optical line terminal (OLT) sends a configuration message to end the ranging to the optical network unit (ONU), and the optical network unit (ONU) receives After receiving the message, send a response message;

h. The optical line terminal (OLT) receives the response message from the optical network unit (ONU), notifies the network management that the distance measurement is successful, and sets the operation state of the ONU to normal operation; otherwise, the optical line terminal (OLT) issues an abnormal operation message to notify the NMS of the cause of the failure and end the distance measurement.

The method further includes the following steps: if the first ranging is successful, the optical line terminal (OLT) reopens the ranging window according to the first ranging result.

The specified time described in step d is 300ms. The fixed range described in step d is 2 bits. The ranging result described in step g is the average value of three successful ranging results.

Visible by above-mentioned scheme, the realization method of ranging in the ATM passive optical network provided by the present invention, has added the judgment to the delay value legitimacy that ranging obtains in ranging process, and to the judgment of ONU running state, In this way, the reliability and accuracy of the delay value obtained by ranging can be made higher, and the data access from the ONU to the OLT will not be wrongly caused by the invalid delay value. It can also enable the ONU to quickly enter the normal working state after ranging, and will not affect the normal processing of the OLT by the OLT due to the ONU's failure to respond in time after the ranging is completed, causing problems in system operation. In addition, the present invention can also add bandwidth compensation processing in the ranging process, so that the data submerged in the ranging window can be sent, so as to reduce the impact of the ranging process on the business, thereby achieving the purpose of improving business service quality.

Description of drawings

Figure 1 is a schematic diagram of the relationship between the phase specification points between the OLT and the ONU related to ranging as specified in G.983.1;

Fig. 2 is the schematic diagram of the configuration message issued by OLT to the ranged ONU when the present invention is preparing for ranging;

Fig. 3 is the schematic diagram of the configuration message issued by OLT to ONU after obtaining legal delay;

Fig. 4 is the schematic diagram of the response message of ONU to the configuration message sent by OLT after obtaining legal delay;

FIG. 5 is a flow chart of the implementation of the ranging method of the present invention.

Detailed ways

The detailed description and technical content of the present invention are as follows in conjunction with the accompanying drawings:

Please refer to shown in Figure 5, the ranging process of the present invention mainly includes the following stages:

(1) The OLT sends a configuration message to the ONU to be measured through a downlink PLOAM cell. As shown in FIG. 2 , the configuration message includes an uplink Rx control message Upstream_Rx_Control, an uplink overhead message Upstream_Overhead, a PON_ID assignment message Assign_Pon_ID, and an authorization allocation message Grant_Allocation. After the four messages are sent to the ONU, the ONU under test will change the state machine according to the received message, and configure the local uplink overhead, PON_ID, data authorization and PLOAM authorization according to the content of the message.

(2) Open the ranging window. The purpose of expanding the ranging window is to prevent the ONU from accessing data upwards in a certain segment of bandwidth on the line. Because the position of the ONU under test is uncertain, the ranging PLOAM cells it sends to the OLT may appear after the ranging starts. any position. If the OLT falls into a data cell, a common PLOAM cell, etc. in the opened ranging window when receiving, an inaccurate ranging result will be obtained. Therefore, the OLT does not issue any permission to the ONU within a certain bandwidth, so as to avoid the occurrence of the above situation. Generally, the first time to open the ranging window is to estimate the distance of the ONU and then open the window. For example, if the ONU is about 15 kilometers away, then you can open a window of 10-20 kilometers; but if you do not know the approximate location of the ONU, you can open a window of 0-50 The kilometer window is basically equal to Tconst. The fixed bandwidth lost at this time will be compensated in the steps of bandwidth compensation in Part 5.

(3) Judging the validity of the ranging delay value at the same time for multiple rangings. The first ranging is performed first, that is, the TC layer of the OLT captures the ranging PLOAM sent by the ONU, and ends the ranging timing after catching it, and judges whether the delay value is legal. Since G.983.1 stipulates that if three successful legal ranging delay values are obtained, the delay value is considered to be obtained successfully. Therefore, if the first ranging delay value is legal, the delay value obtained for the first time is used as the benchmark Open a smaller ranging window for the second and third ranging, because the position of the ONU has been roughly determined at this time, which can reduce the occupation of the fixed bandwidth, and judge its legitimacy after obtaining the delay value. Each time you judge whether the ranging delay value is legal, you need to confirm the following points:

a. Determine whether the delay value is obtained within the specified time? In G.983.1, it is suggested that 300ms is the maximum waiting time for the response. If not, the ranging must be stopped immediately.

b. Determine whether the obtained delay value is greater than the minimum value of the ranging window and less than the maximum value of the ranging window? Because if the measured delay value exceeds the range specified by the ranging window, the obtained delay value is illegal , which may lead to serious errors if they are still considered correct values. Therefore, if it does not meet, ranging must be stopped immediately.

c. Judging whether the difference between two adjacent delay values measured is within a certain range? The certain range is determined by bit. G.983.1 recommends that the delay value obtained for the first time be used as a standard, and the delay value obtained by subsequent ranging is generally not more than 2 bits different from it.

If the above conditions are not met, then it is considered that the acquisition of the delay value failed. If it fails three times, it is considered that the ranging of the ONU has failed.

(4) If a legal delay value is obtained, the OLT sends a series of configuration messages to the ONU to complete the entire ranging process.

After obtaining the legal delay value, the configuration message sent by the OLT to the ONU is shown in Figure 3, including: the ranging time message Ranging_Time, through which the measured delay value is sent to the ONU; configure VP/VC The message Config_VP/VC configures the VP/VC for in-band communication; the Churned_VP message of the Churned VP decides whether to encrypt the VP. The BER interval message Ber_interval determines how often the ONU reports a bit error to the OLT. The divided slot grant configuration message Divided_Slot_Grant_Config configures the divided slot grant value, mini-slot compliance length and offset of the ONU.

If the ranging fails, the PON_ID release message Deactive_Pon_ID is issued to deactivate the specified ONU so that the ONU can accept the next ranging.

It should be noted that the ONU must respond to Config_VP/VC, Churned_VP, and Ber_interval, that is, when the ONU receives these messages, it sends Acknowledge_Config_VP/VC, Acknowledge_Chumed_VP, and Acknowledge_Ber_interval to the OLT, as shown in Figure 4. If the ONU does not respond to any of them, it is considered that the ONU is in an abnormal operating state, and the OLT sends a Deactive_Pon_ID message to activate the specified ONU, and notifies the network management of the failure reason, and ends the ranging at the same time. If the OLT receives all the response messages from the ONU, it considers the operation state of the ONU to be in the normal working state, and the OLT notifies the network management that the ranging is successful, and sets the operating state of the ONU to the normal working state.

Calculate the average value of the ranging results based on the legal delay values measured three times successfully, and then calculate the Td value based on this value, and adjust Td with reference to the Tconst value that the ONU should have.

In addition, the bandwidth lost in the ranging process of the present invention can be compensated by a bandwidth compensation method. The specific method is: the ONU calculates the size of the fixed bandwidth lost, and adds this part of the bandwidth to the highest priority constant bit rate ( CBR) in the dynamic bandwidth request queue, and re-allocate bandwidth to it. In this way, the damage to the service QOS caused by ranging can be minimized, thereby ensuring the service QOS and protecting the interests of users. The method of bandwidth compensation has been filed separately.

Claims (5)

1, an implementation method of ranging in ATM passive optical network, it is characterized in that the method at least comprises the following steps: a. The optical line terminal (OLT) sends a ranging configuration message to the optical network unit (ONU); b. The optical line terminal (OLT) opens the ranging window, waits to capture the ranging physical layer operation and maintenance management (PLOAM) sent by the optical network unit (ONU), and starts timing; c. The optical line terminal (OLT) captures the ranging physical layer operation and maintenance management (PLOAM) sent by the optical network unit (ONU), and stops timing; d. Judging whether the delay value is obtained within the specified time, if the delay value is not obtained within the specified time, then end the ranging; if the delay value is obtained within the specified time, then judge whether the delay value is within the specified time In the opened ranging window, if the delay value is not in the opened ranging window, the ranging will be ended; if the delay value is in the opened ranging window, then judge the delay value of two adjacent times Whether the difference is within the fixed range, if not within the fixed range, then add one to the number of ranging failures, and then judge whether the ranging has failed three times, and enter step e; if the difference between two adjacent delay values is within the fixed range, Then add one to the number of times of successful distance measurement, then judge whether the distance measurement has been successful three times, and enter step f; e. If the distance measurement fails three times, then end the distance measurement and notify the network management of the failure reason; otherwise, return to step b; f. If the three distance measurements are successful, proceed to step g; otherwise, return to step b; g. The optical line terminal (OLT) calculates and adjusts the equivalent delay value according to the ranging result, the optical line terminal (OLT) sends a configuration message to end the ranging to the optical network unit (ONU), and the optical network unit (ONU) receives After receiving the message, send a response message; h. The optical line terminal (OLT) receives the response message from the optical network unit (ONU), notifies the network management that the distance measurement is successful, and sets the operation state of the ONU to normal operation; otherwise, the optical line terminal (OLT) issues an abnormal operation message to notify the NMS of the cause of the failure and end the distance measurement. 2. The implementation method according to claim 1, characterized in that: the method further includes the following steps: if the first distance measurement is successful, the optical line terminal (OLT) restarts the measurement according to the first distance measurement result from the window. 3. The implementation method according to claim 1, characterized in that the specified time in step d is 300ms. 4. The implementation method according to claim 1, characterized in that the fixed range described in step d is 2 bits. 5. The implementation method according to claim 1, characterized in that the ranging result in step g is the average value of three successful ranging results.

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