JP2004274329A - Passive optical network, serial number acquiring method, and terminal device used in passive optical network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passive optical network in which an OLT (optical line terminal) can more quickly receive a reply signal from all ONUs (optical network units) and a time for shifting each ONU to an operating state can be shortened more and to provide a serial number acquiring method. <P>SOLUTION: When a station device (1) acquires the serial numbers of respective terminal devices (3-1 to 3-n) the station device itself houses, the station device (1) transmits a request signal (serial number request) to the respective terminal devices (3-1 to 3-n), and the respective terminal devices which have received the request signal transmit the reply signal (SN window) including self-serial number information to the station device a plurality of times, respectively. Each terminal device transmits the reply signal a plurality of times in this way and consequently, the number of times for transmitting the request signal transmitted by the OLT can be drastically reduced from the view point of a probability and all the ONUs can be more quickly shifted into an operating state. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a passive optical network (PON) in which a plurality of terminal devices and a station device that accommodates these terminal devices are connected via an optical branch circuit and an optical line.
Furthermore, the present invention provides a method for acquiring a serial number when acquiring a serial number signal from an ONU (Optical Network Unit; terminal device) in which an OLT (Optical Line Terminal; station device) is not in operation in a passive optical network. Particularly, the present invention relates to a serial number obtaining method suitable for obtaining a serial number in a GPON (Gigabit-Capable Passive Optical Network).
Furthermore, the present invention relates to a terminal device used in a passive optical network.
[0002]
[Prior art]
The PON is a technology for connecting a plurality of ONUs and an OLT accommodating these ONUs using an optical fiber and an optical splitter (optical branching circuit), and transmitting a signal transmitted from each ONU via a station device. For example, ITU-T recommendation G. 983.1 "Broadband optical access systems based on Passive Optical Networks (PON)". GPON is a technology that connects an OLT and an ONU with an optical fiber and an optical splitter to transmit a signal at 1.244416 Gbit / s or 2.48832 Gbit / s, and is currently specified by ITU-T and the like (International Telecommunication Union). Is being considered.
[0003]
In the GPON, the OLT needs to acquire the serial number of an ONU that is not in operation in order to bring the ONU into operation. For this purpose, the OLT transmits a request signal called Serial-Number request to all the ONUs that are accommodated. When receiving the Serial-Number request, the ONU that is not in the operation state transmits a response signal called SN window to the OLT after a random delay time. Since the SN window contains the serial number information, if the OLT receives the SN window, the serial number of the ONU can be obtained. Since there are a plurality of ONUs connected to the OLT, it is possible that an SN window transmitted by a certain ONU collides with an SN window transmitted by another ONU on a transmission path to the OLT. That is, since the OLT cannot grasp the distance to each ONU, it is not possible to set a delay time for each terminal device so that the SN window signal does not collide, and a problem that response signals collide occurs. On the other hand, if the SN windows collide with each other, the OLT cannot correctly receive the SN window, and thus the OLT cannot acquire the serial number of the ONU that transmitted the collided SN window. Therefore, in order to obtain the serial number of the ONU, it is necessary to transmit the Serial-Number request again.
[0004]
The present inventor has conducted a search on the related prior art documents regarding the method of obtaining the serial number of the passive optical network under the following search conditions, but could not find any patent document to be disclosed as the prior art.
Search target: Application publication gazette after 1993 and patent gazette after 1994 Retrieval method: Full-text search was performed by the following logical formula.
(PON + PDS + GPON + passive optical network) x (serial number) x (plural)
[0005]
[Problems to be solved by the invention]
Now, when a plurality of ONUs are connected to the OLT, if a temporary failure occurs in the optical fiber between the OLT and the optical splitter, all the ONUs are out of operation and the communication service is interrupted. Alternatively, if all ONUs are installed in one building and a failure occurs in the power supply equipment for those ONUs, all the ONUs are out of operation and the communication service is interrupted. After the failure of the optical fiber or the power supply equipment is restored, the OLT needs to acquire the serial numbers of all ONUs in order to put all ONUs into operation again. On the other hand, when the OLT transmits the Serial-Number request, all ONUs transmit the SN window at the same time, so that a state in which the SN window easily collides on the transmission path occurs. That is, since the delay time from the reception of the request signal to the transmission of the response signal cannot be set for each ONU so that the SN windows do not collide with each other, a problem occurs in that the response signals collide. For this reason, there is a problem that it takes time until all the ONUs are brought into the operation state again, and the service interruption time becomes long. In particular, in a GPON in which data transmission is performed at a higher speed, it takes a long time to transition an ONU to an operation state, which is a serious problem.
[0006]
An object of the present invention is to solve the above-mentioned drawbacks, and when transmitting a request signal to each ONU, the OLT can more quickly receive response signals from all ONUs, and transition each ONU to the operation state. It is an object of the present invention to provide a passive optical network that can further reduce the time required for the operation.
Still another object of the present invention is to realize a serial number obtaining method capable of obtaining a response signal transmitted from each ONU more quickly in a passive optical network.
Another object of the present invention is to provide a terminal device suitable for high-speed data transmission.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a passive optical network according to the present invention is a passive optical network in which a plurality of terminal devices and a station device that accommodates these terminal devices are connected via an optical branch circuit and an optical line,
The station device transmits a request signal requesting transmission of serial number information to all the accommodated terminal devices at the same time, in order to transition the accommodated terminal device to the operation state,
Each terminal device, when receiving the request signal, transmits a response signal including its own serial number information to the station device a plurality of times,
When the station device receives a response signal transmitted from each terminal device, the station device transitions the terminal device to an operation state.
[0008]
[Action]
Consider a GPON in which an OLT and an ONU are connected by an optical fiber and an optical splitter.
The time from when the OLT transmits a Serial-Number request (request signal) to when an SN window (response signal), which is a response to the signal, arrives at the OLT is the time during which the Serial-Number request is transmitted from the OLT to the ONU ( t1), the time (t2) until the SN window is transmitted corresponding to the Serial-Number request in the ONU, and the time (t3) during which the SN window is transmitted from the ONU to the OLT. The upper limit of t1 + t2 + t3 is L. As a specific value of L, for example, when the maximum length of the reciprocation of the optical fiber between the OLT and the ONU is 40 km, the reciprocation time of the laser beam is 200 μs, and the Serial-Number request in the ONU corresponds to There is a total of 220 μs, which is the sum of 20 μs when the upper limit of the time until the transmission of the SN window is 20 μs. The lower limit of t1 + t2 + t3 is 0.
[0009]
Let T be the time length of the SN window. A specific value of T is, for example, about 0.3 μs when the length of the SN window is 50 bytes and the transmission bit rate is 1.244 Gbit / s.
Calculate the probability that SN window will collide. It is assumed that two ONUs are accommodated, and the locations where the ONUs are installed are random, that is, the distance between the OLT and the ONU is random. If the time until the SN window is transmitted corresponding to the Serial-Number request in the ONU is also random, the time from when the OLT transmits the Serial-Number request to when the corresponding SN window arrives at the OLT. Is random. SN windows collide with each other when the SN window from one ONU and a part of the SN window from another ONU overlap. Therefore, when the ONU transmits the SN window once, the probability that the SN windows do not collide with each other is approximately 1-2 T / L. A specific value of this probability is 0.997 when L = 220 μs and T = 0.3 μs.
[0010]
Next, when the ONU transmits the SN window twice with a time interval, the probability that the SN windows will not collide with each other twice is approximately 1- (2T / L) ² . A specific value of this probability is 0.999993 when L = 220 μs and T = 0.3 μs. It can be seen that transmitting the SN window twice increases the probability of receiving the SN window in which the OLT does not collide. This means that since T is considerably smaller than L, the collision probability of the SN window when the SN window is transmitted only once is significantly smaller than 1, and the collision probability is further reduced by transmitting the SN window twice. Because it can be.
[0011]
As described above, by transmitting the SN window a plurality of times, it is possible to reduce the probability that all SN windows collide, and thus increase the probability that the OLT receives at least one non-colliding SN window. Therefore, the service interruption time can be statistically reduced.
[0012]
Based on the above recognition, the serial number obtaining method according to the present invention operates a terminal device in a passive optical network in which a plurality of terminal devices and a station device accommodating these terminal devices are connected via an optical branch circuit and an optical line. A method in which a station device acquires a serial number of a terminal device to transition to a state,
A step of simultaneously transmitting a request signal requesting transmission of serial number information from the station apparatus to all terminal apparatuses;
A step in which each terminal device that has received the request signal transmits a response signal including its own serial number information to the station device,
A station device, receiving a response signal transmitted from each terminal device and causing each terminal device to transition to an operation state,
Each terminal device transmits a response signal to the station device a plurality of times.
[0013]
Further, a terminal device according to the present invention is a terminal device used in a passive optical network in which a plurality of terminal devices and a station device that accommodates these terminal devices are connected via an optical branch circuit and an optical line,
When receiving a request signal transmitted from the station apparatus for acquiring the serial number of the terminal apparatus, the apparatus has a function of transmitting a response signal including its own serial number information to the station apparatus a plurality of times. . As described above, since each terminal device has a function of transmitting the response signal a plurality of times, all the terminal devices can be shifted to the operation state more quickly, and the terminal device useful for the GPON performing high-speed data transmission. Can be realized.
[0014]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an example of a passive optical network according to the present invention. An OLT 1 that accommodates a plurality of ONUs is connected to a passive optical network (subscriber user branch network). An optical splitter 2 is connected to the OLT 1 via an optical line, and a plurality of (n in the drawing) ONUs 3-1 to 3-n are connected to the optical splitter 2 via an optical line.
[0015]
When the OLT 1 causes all the terminal devices 3-1 to 3-n to transition to the operation state, the OLT 1 simultaneously transmits a request signal to all the ONUs. Each terminal device has a function of transmitting a response signal to the OLT 1 a plurality of times when receiving the request signal. Then, after receiving the request signal, after a predetermined delay time (time period) defined by a predetermined probability distribution has elapsed, a response signal is transmitted to the OLT 1. As the probability distribution, for example, a uniform distribution can be used. This response signal is transmitted a plurality of times, such as two, three, or four times. However, the same number of transmissions is set for all ONUs. Note that the number of transmissions does not necessarily need to be set to the same value, and may be different. In addition, the delay time between the transmission of the first response signal and the transmission of the second response signal is set to follow a predetermined probability distribution, for example, a uniform distribution. The OLT receives the response signal sent from each ONU, acquires the serial number of each terminal device from the received response signal, and transitions each terminal device to the operation state.
[0016]
Next, an operation when the OLT 1 acquires a serial number from each ONU in order to bring the ONU into an operation state will be described. In this example, an example in which a serial number is obtained from two ONUs 3-1 and 3-2 will be described for the sake of clarity. FIG. 2 is a diagram illustrating a time relationship between signals when the OLT 1 acquires the serial numbers of the two ONUs 3-1 and ONU 3-2 almost at the same time. Upon obtaining the serial number of the ONU, the OLT 1 transmits a Serial-Number request (request signal) to all the ONUs 3-1 to 3-n accommodated at the same time. In this example, it is assumed that each ONU transmits a response signal twice to the OLT 1 in response to the Serial-Number request. In response to the Serial-Number request transmitted by the OLT 1, the ONU 3-1 transmits SN window 3-1a and 3-1b including its own serial number information as a response signal, and the ONU 3-2 transmits the SN window 3-2a with the SN window 3-2a. Send 3-2b. In the example illustrated in FIG. 2, the first SN window 3-1a transmitted from the ONU 3-1 and the first SN window 3-2a transmitted from the ONU 3-2 collide, and the second SN window transmitted from the ONU 3-1. 3-1b and SN window 3-2b illustrate a state in which the OLT 1 satisfactorily receives the signal without collision.
[0017]
When each ONU transmits the SN window only once, the first SN window transmitted by each ONU collides with each other, so that the OLT 1 cannot acquire the serial number of the ONU without transmitting the Serial-Number request again. FIG. 3 shows the time relationship between the signals in this case. In FIG. 3, after receiving the first Serial-Number request from the OLT 1, two ONUs transmit a response signal. As a result, the SN window 3-1 and the SN window 3-2 collide, and the OLT 1 receives a response from each ONU. This indicates a state in which a response signal has not been received. Since the OLT 1 has not received the response signal from each ONU, it transmits a Serial-Number request again to each ONU after a considerable time has elapsed. In response to the second reception of the Serial-Number request, ONUs 3-1 and 3-2 transmit SN windows 3-1b and 3-2b, respectively, and since these response signals do not collide with any SN window, the OLT is These response signals are correctly received. As is clear from the comparison result between FIG. 2 and FIG. 3, each ONU for one Serial-Number request is different from the case where the Serial-Number request is transmitted twice and the serial number of each ONU is obtained for the first time. The process can be completed in a shorter time by transmitting the response signal twice and acquiring the serial number of each ONU.
[0018]
Next, simulation results will be described. The number of Serial-Number requests transmitted by the OLT until the OLT acquired the serial numbers of all ONUs was evaluated by numerical simulation. The parameters used in the simulation were set as follows.
(A) The transmission speed is set to 1.24416 Gbit / s for both downlink and uplink.
(B) The round trip transmission distance between the OLT and the ONU is a random variable that follows a uniform distribution with a minimum value of 0 km and a maximum value of 40 km.
(C) The delay time from when the ONU receives the Serial-Number request to when it transmits the SN window for the Serial-Number request is a random variable that follows a uniform distribution with a minimum value of 0 μs and a maximum value of 20 μs. However, the interval between the SN windows transmitted by one ONU is adjusted so that the SN windows do not collide with each other.
(D) The byte length of the SN window is 50 bytes.
The simulation was performed 100,000 times in each of the cases where the number of SN windows transmitted by the ONU was once, twice, three times, and four times. The simulation result is shown in the graph of FIG. In FIG. 4, the horizontal axis indicates the number of connected ONUs whose serial numbers are to be acquired, and the vertical axis indicates 100,000 times of the number of Serial-Number requests transmitted until the OLT acquires the serial numbers of those ONUs. The average is being taken. It is apparent from the graph that the number of times of transmitting the Serial-Number request is smaller when the SN window is transmitted twice or more than when the SN window is transmitted only once. Therefore, when the transmission is performed twice or more, the time required for the OLT to acquire the serial number is shorter.
[0019]
【The invention's effect】
As described above, according to the present invention, in the passive optical network, there is an effect that the probability that the OLT acquires the serial number of the ONU in a short time can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an example of a passive optical network according to the present invention.
FIG. 2 is a diagram showing a time relationship between signals related to the acquisition of a serial number of an ONU according to the present invention, showing a case where the ONU transmits an SN window twice to one OLT for one Serial-Number request.
FIG. 3 is a diagram illustrating a time relation between signals transmitted and received between the OLT and the ONU and related to the acquisition of a serial number of the ONU, wherein the ONU sends an SN window only once for one Serial-Number request to the OLT; This shows a case where no transmission is performed.
FIG. 4 is a graph of a simulation result showing an effect of the present invention.
[Explanation of symbols]
1 OLT
2 Optical splitter 3-1 to 3-n ONU

Claims (7)

A passive optical network in which a plurality of terminal devices and a station device that accommodates these terminal devices are connected via an optical branch circuit and an optical line,
The station device transmits a request signal requesting transmission of serial number information to all the accommodated terminal devices at the same time, in order to transition the accommodated terminal device to the operation state,
Each terminal device, when receiving the request signal, transmits a response signal including its own serial number information to the station device a plurality of times,
The passive optical network, wherein the station device transitions the terminal device to an operation state when receiving a response signal transmitted from each terminal device. In a passive optical network in which a plurality of terminal devices and a station device accommodating the terminal devices are connected via an optical branch circuit and an optical line, the station device changes the serial number of the terminal device in order to transition the terminal device to an operation state. How to get,
A step of transmitting simultaneously a request signal requesting transmission of serial number information from the station apparatus to all terminal apparatuses;
A step in which each terminal device that has received the request signal transmits a response signal including its own serial number information to the station device,
A station device, receiving a response signal transmitted from each terminal device and causing each terminal device to transition to an operation state,
A method for acquiring a serial number, wherein each terminal device transmits a response signal to the station device a plurality of times. 3. The serial number obtaining method according to claim 2, wherein each terminal device, upon receiving the request signal, transmits the response signal to the station device after a lapse of a delay time defined by a predetermined probability distribution. How to get the serial number. 4. The serial number acquiring method according to claim 2, wherein each terminal device transmits a response signal first, and then transmits a next response signal after a delay time defined by a predetermined probability distribution. Characteristic serial number acquisition method. In the serial number acquiring method according to any one of claims 2 to 4, each terminal device sends a response signal to the station device twice when receiving the request signal transmitted from the station device. A serial number obtaining method, wherein the serial number is transmitted three or four times. A terminal device used in a passive optical network in which a plurality of terminal devices and a station device that accommodates these terminal devices are connected via an optical branch circuit and an optical line,
It has a function of transmitting a response signal including its own serial number information to the station device a plurality of times when receiving a request signal transmitted from the station device for acquiring the serial number of the terminal device. Terminal device. 7. The terminal device according to claim 6, wherein a time period from when the request signal transmitted from the station device is received to when the first response signal is transmitted, and after the first response signal is transmitted, the next response signal is transmitted. A terminal device wherein the time period up to is a time period defined based on a predetermined probability distribution.

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