KR20040063453A - The method for RTT estimation in EPON system - Google Patents

Abstract

PURPOSE: A method for measuring an RTT(Round Trip Time) of an EPON(Ethernet Passive Optical Network) system is provided to minimize error generation of RTT by omitting a time set process. CONSTITUTION: A clock timer of an OLT(Optical Line Termination) is set to measure time of OLT(S1). A timer operating in synchronization with the OLT with respect to an ONU(Optical Network Unit)/ONT(Optical Network Termination) is driven(S2). A test pattern for starting RTT is delivered from the OLT to each ONU/ONT, and corresponding time is recorded in a time stamp(S3). The ONU/ONT records a point of time when the test pattern is received from the OLT in the time stamp(S4) and then records transmission time in the time stamp(S5). The ONU/ONT sends an absolute value of a time stamp difference between a point of time when the test pattern has been received and a point of time when the test pattern has been transmitted(S6). An OLT detects a return value, that is, the absolute value of the transmission/reception time stamp difference of the test pattern which is transmitted to the ONU/ONT(S8).

Description

Altitimetry Method of EPIO System {The method for RTT estimation in EPON system}

The present invention relates to a ranging technology of an EPON (Ethernet Passive Optical Network) system, in particular, when the distance between each optical network unit (ONU) / optical network termination (ONT) in the optical line termination (OLT) The present invention relates to a round trip time (RTT) measurement method for determining a distance of an ONU / ONT.

EPON (Ethernet Passive Optical Network) is the most active standardization standard in the IEEE802 standardization organization, and operates in a point-to-multipoint optical communication network unlike an existing Ethernet network. EPON has economic advantages over point-to-point methods.

EPON passive devices include single mode fiber (SMF), passive optical splitters, couplers and connectors, which are placed in the optical distribution network. Active network elements such as OLT and ONU are located at the end points of the PON. Optical signals transmitted through the PON are separated into multiple optical fibers or combined into a single optical fiber by optical splitters / couplers depending on the transmission direction. In general, the PON structure has a point-to-multipoint tree structure or branch structure when applied to a residential environment, a bus structure when used in a campus environment, and a protection ring structure when applied to a business area. The main difference between EPON and APON is that EPON data is delivered in variable-length packets, while APON data is delivered in fixed-length cells of 53 bytes. This means that APON is inefficient for carrying IP traffic.

ONU (Optical Network Unit) is an end device of an optical network that provides a service interface to end users. ONU is implemented to be accessible to users by accommodating fiber to the curb (FTTC), fiber to the building (FTTB), fiber to the floor (FTTF), and fiber to the office (FTTO). ONU is a device that connects cables and optical facilities that transmit analog signals of customers, so optical and electrical signals are exchanged here.

FTTC can be thought of as a term used to replace the ordinary telephone service, removing all the telephone lines that appear to be related to installing and using optical cables to roads near homes or businesses, and replacing them with optical cable lines. Recognizing that optical fiber is already used for this purpose. However, it is very expensive for the last step, FTTC. For this reason, FTTC is advancing at a very slow pace, while other low-cost alternatives, such as ADSL over ordinary telephone lines or satellite communications, are moving faster. The FTTC implies that signals are routed from the road in front of the house to each home using coaxial cable or other media, while the FTTB (Fiber to the building) is a specific building from a telephone company such as a company or apartment That means installing fiber optics up.

1 is a block diagram showing the basic structure of an EPON system. As shown, in the EPON system, the OLT transmits an optical signal, that is, data, transmitted through an optical coupler to ONU / ONT, which is a subscriber part of the EPON system. In this case, the downstream data is bridged, and the same data is transmitted to each subscriber (ONU / ONT) at the same time. Upstream data lines are bridged, but are sequentially raised to avoid collisions of data transmitted from each subscriber (ONU / ONT).

At this time, the subscriber part of the Ethernet Passive Optical Network (EPON) system must be enabled in order to avoid data collision during upstream data transmission as described above. In this case, the distance between each ONU / ONT in the OLT may be different. In this case, there is a need for a ranging technique for identifying each distance and giving a time delay to virtually the same distance. For example, if the downlink data transfer time for ONU / ONT 1 to ONU / ONT 3 is 4 seconds, the distance to ONU / ONT 4 is further assuming that the downlink data transfer time for ONU / ONT 4 is 6 seconds. It can be seen that. In this case, in order to set the virtual same distance for sequential enable during uplink data transmission, the downlink data transmission time for the individual subscriber units ONU / ONT 1 to ONU / ONT 3 is 2 seconds for the actual time of 4 seconds. By delaying, in OLT, the downlink data transfer time for all individual subscribers is 6 seconds. As a result, in the OLT, the distances to all individual subscribers are recognized as the same.

If the distance to all individual subscribers from the OLT is the same, data transmission from the individual subscribers should not occur in the same transmission line at the same time for data transmission in the upward direction. To this end, the individual subscribers are allowed to perform sequential upward data transmission, and data transmission by time division method is possible due to the same time according to the same distance. That is, by sequentially allocating a predetermined time to individual subscribers, the uplink data transmission from individual subscribers is performed sequentially.

Looking at the RTT measuring method according to the prior art with reference to Figure 2 as follows.

First, OLT and ONU / ONT operate with their clocks synchronized according to their respective clocks. When the test pattern (Start Time) is given at the time "2" in the OLT, the received ONU / ONT 1 clock sets its own time equal to the time of the OLT, that is, 2 at the time of reception. In this case, the test pattern refers to specific data for RTT measurement and refers to data used only for RTT.

On the other hand, ONU / ONT 1 goes through the processing to match the time of the OLT and transmits its own time of 6 to the OLT. The OLT calculates the time taken over the line, that is, 4 minus 6, the time at the time of transmission, from the reception time 10. The value at this time is called RTT (Round Trip Time). By calculating ONU / ONT 2 in the same way, we can see that RTT is 12-6 = 6. OLT looks at the RTT value of each ONU / ONT and finds out how long each ONU / ONT is at a time delay, and sets the delay so that each ONU / ONT is located at the same distance.

3 is a diagram illustrating an error occurrence in the RTT measurement according to the prior art. As shown in the figure, when the time of the ONU / ONT is corrected according to the OLT time sent by the OLT, the ONU / ONT must extract the time of the OLT from the test pattern of the OLT and analyze the time. In this process, a time delay occurs and thus the OLT time cannot be set to the correct reception time.

As shown in the figure, an error occurring during time setting is overlapped with a delay according to a reception process and a delay according to an actual time setting. In other words, during the process of receiving and recognizing the time and actually setting the recognized time, a delay occurs and an error occurs. For example, when the time received from the OLT is 2, a time delay for recognizing and processing the delay and the actual time, which is a time for actually setting the processing, may be different from the actual time 3. In addition, the same error occurs in the time transmission from the ONU / ONT to the OLT.

As a result, the time setting and the actual time setting according to the occurrence of the delay are different from the actual time required when calculating the RTT, and thus there is a problem in that the actual RTT and the error are shown as much as the delay time.

The present invention is to solve the above-mentioned problems, and to provide a method of minimizing the error of the RTT by immediately reflecting without delay from the received time by omitting the reception time setting process of the ONU / OLT.

1 is a block diagram showing the basic structure of an EPON system

2 is a diagram illustrating a RTT measurement method according to the prior art.

3 is a view showing the occurrence of the RTT measurement error according to the prior art

4 is a diagram illustrating a RTT measuring method according to the present invention;

5 is a flowchart illustrating a RTT measurement method according to the present invention.

In order to achieve the above object, the present invention includes the steps of dropping a test pattern (Start time) capable of starting RTT from each OLT to each ONU / ONT; Recording the reception time in a time stamp as an OLT time; Recording the transmission time of the ONU / ONT in a time stamp; Sending an absolute value of the time stamp difference; and calculating an RTT by detecting an absolute value of a return of the ONU / ONT; Is made of.

As described above, the downlink data is bridged, and the same data is delivered to each subscriber (ONU / ONT) at the same time, and the uplink data is bridged but transmitted from each subscriber (ONU / ONT). It is configured to come up sequentially to avoid data collisions.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention. 4 is a diagram illustrating a RTT measuring method according to the present invention.

First, a test pattern (Start time) which is specific data for RTT measurement is transmitted from the OLT to the subscriber station (ONU / ONT). When the subscriber station (ONU / ONT) receives the test pattern of the OLT, as described above, the subscriber station (ONU / ONT) checks the time of the OLT, or 2, and adjusts the time of the subscriber station (ONU / ONT) to the same time, that is, 2, as described above. This was done. However, the present invention allows the count to continue according to the time originally set regardless of the OLT time. In other words, it records the time 7 when the test pattern is received in the time stamp and then proceeds with the internal processing of the subscriber station from 7. That is, the internal processing start time of the subscriber end is 7. The subscriber's internal processing starting at 7 continues the internal count until it returns a result to the OLT. At this time, it can be seen that a time is required.

The subscriber end (ONU / ONT) transmits a return value as an internal processing value for the OLT. In other words, the absolute value 4 of the difference between the start time of receiving the OLT test pattern 7 and the return time 11 is transmitted to the OLT as a result value, that is, a return value. On the other hand, the OLT calculates the difference from the difference between the time 8 when the test pattern occurs and the time when the return value is received and the return value 4, thereby obtaining an RTT.

This will be described in more detail as follows. In FIG. 4, it can be seen that a is 4, which is the time required from the test pattern reception time to the return value transmission time at the subscriber end (ONU / ONT), and b is the time required from the test pattern transmission time to the return value reception time from the OLT. We can see that it is eight hours. In addition, it can be seen that b is a value obtained by adding a, which is the time required by the subscriber station (ONU / ONT), to the sum of x, which is the time required for data transmission and y, which is the time required for data reception. That is, b = x + a + y.

Eventually, x and y, which are the time required for data transmission and reception, are subtracted a from b, and the time required for transmission and reception, i.e., x and y, which are RTT, is assumed to be equal to the transmission and reception time, that is, when x = y, RTT = ( It can be seen that b-a) / 2 holds.

As described above, the present invention omits the time setting process according to the transmission and reception of the test pattern in this process, so that there is no room for delay due to time setting, thereby preventing the occurrence of the RTT measurement error.

5 is a flowchart illustrating a RTT measurement method according to the present invention.

First, the first step is to set the OLT clock timer to measure the time of the OLT (S1). The clock timer setting is for synchronization of the receiver. In the next step, the timer operating in synchronization with the OLT is driven for the subscriber end ONU / ONT (S2). Synchronization of timers is an important premise of the present invention.

The next step is to lower the test pattern for starting the RTT from the OLT to each subscriber end (ONU / ONT), and records the time in this time stamp (S3). The time at this time is the start time of the RTT measurement, the RTT measurement is performed by the time interval until the response value for the test pattern thereafter. The subscriber station (ONU / ONT) records the time at which the test pattern transmitted from the OLT is received in the stamp (S4), and then passes the internal processing from the subscriber station (ONU / ONT) to the time stamp again. Record (S5).

Next, the absolute value of the time stamp difference between the time point at which the test pattern is received at the subscriber end (ONU / ONT) and the transmission time point at the subscriber end (ONU / ONT) is transmitted (S6). At this time, the OLT detects a return value, which is an absolute value of the difference between the test pattern transmission and reception time stamps transmitted to the subscriber station ONU / ONT, in operation S7, so that the RTT can be calculated by the method described above (S8).

The technical spirit of the present invention has been described above with reference to the accompanying drawings, but this is by way of example only and not intended to limit the present invention. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

According to the present invention, the error setting of the RTT is minimized by omitting the time setting process for the RTT error generated by the subscriber station (ONU / ONT) to be delayed to set the same time as the OLT during the RTT measurement of the EPON system. Was made possible.

Claims (6)

In the RTT measurement method of determining the distance of the subscriber end when the distance between the subscriber end in the OLT, when measuring the RTT of the EPON system, Transmitting a test pattern from the OLT to the subscriber end and recording a transmission time point in a time stamp; Transmitting at the subscriber end an absolute value of a time stamp difference between a reception time and a transmission time of the test pattern; Calculating an RTT by detecting a return value in the OLT; RTT measurement method comprising a. The method as claimed in claim 1, wherein an OLT clock timer for measuring the time of the OLT is set to record the test pattern transmission time from the OLT in a time stamp. The method of claim 1, wherein a timer operating in synchronization with the OLT is driven for the subscriber station to record the test pattern transmission time from the OLT in a time stamp. The method of claim 1, wherein the subscriber station records a time stamp when the test pattern is received at the subscriber station in order to obtain a time stamp difference between the reception point and the transmission point of the test pattern. . The method of claim 1, wherein the subscriber station records the transmission time of the test pattern from the subscriber station in a time stamp to obtain a time stamp difference between the reception time and the transmission time of the test pattern. . The method of claim 1, wherein the RTT is calculated by subtracting the required time of the subscriber station from the required time of the OLT.