JP5364857B1 - Ranging method - Google Patents

Abstract

Even when the path length from an ONU to each OSU is different, it is not necessary to redo the discovery process accompanying a change in the ONU-OSU connection, and a guard interval having a sufficient time is provided between upstream signal lights. It is an object of the present invention to provide a ranging method that is unnecessary and can prevent a decrease in band use efficiency.
The present invention measures the RTT of one child node with only one wavelength combination at the time of ranging, and for RTTs of other child nodes or other wavelength combinations, the RTT already registered in the table is also stored. It was decided to calculate it.
[Selection] Figure 3

Description

  The present invention relates to a ranging method.

  Due to the increasing needs for high-speed access services, FTTH (Fiber To The Home) is spreading worldwide. Most of the FTTH services accommodate a plurality of subscriber side devices (ONU: Optical Network Unit) by means of time division multiplexing (TDM: Time Division Multiplexing), where one accommodation station side device (OSU: Optical Subscriber Unit). It is provided by a PON (Passive Optical Network) system which is excellent in economy. In uplink communication of TDM-PON, as in the optical communication system 300 of FIG. 1, the system band is shared between the ONUs 200 based on the dynamic band allocation calculation in the OSU 51, and each ONU 200 is notified of the transmission notified from the OSU 51. Intermittent transmission of signal light is prevented by transmitting the signal light intermittently only during the allowable time. The current main systems are GE-PON (Gigabit Ethernet (registered trademark) PON) and G-PON (Gigabit-capable PON) whose transmission speed is gigabit class. Due to the appearance of applications for uploading / downloading, etc., there is a demand for further increasing the capacity of the PON system. However, in TDM-PON, because the system bandwidth is expanded by increasing the line rate, the reception characteristics are significantly deteriorated due to the effects of speeding up and chromatic dispersion, and the economics of the burst transmitter / receiver becomes a problem. Large capacity exceeding 10 giga is difficult.

  Application of wavelength division multiplexing (WDM) technology is being studied toward a capacity increase of more than 10 Giga. The optical communication system in FIG. 2 is an example of WDM / TDM-PON in which WDM technology is combined with TDM-PON. Each ONU 200a is assigned with a downstream wavelength and an upstream wavelength, and the time overlap of signals between the ONUs 200a is allowed up to the number M of OSUs 51 in the OLT 100a (M is an integer of 1 or more). Therefore, the system bandwidth can be expanded without increasing the line rate per wavelength by adding the OSU 51.

  Each ONU assigned the same upstream wavelength is logically connected to the same OSU and shares a band. When the wavelength assigned to each ONU is fixed, the logical connection between each ONU and the OSU is invariable, and the bandwidth cannot be shared between ONUs connected to different OSUs, and the bandwidth fairness is not ensured. .

  On the other hand, Non-Patent Document 1 proposes a wavelength tunable WDM / TDM-PON in which an ONU has a wavelength tunable function (FIG. 3). In this method, since the OSU 51 that is logically connected in units of ONUs can be changed by changing the wavelength allocated to the ONU 200a, the system band can be shared among all the ONUs 200a. Therefore, the tunable burst transmitters in each ONU 200a intermittently transmit signal light at the transmission wavelength notified based on the dynamic allocation calculation in the OLT 100a during the notified transmission allowable time. Bandwidth fairness can be ensured.

  Further, in Non-Patent Document 1 and Non-Patent Document 2, in the wavelength variable WDM / TDM-PON, in addition to the expansion of the system band using wavelength multiplexing, the load distribution between OSUs using the wavelength variable function allows users to It is described that efficient capital investment can be made according to fluctuations in the required bandwidth and user capacity. When the user capacity increases and the bandwidth demand expands, the system bandwidth can be expanded by adding an OSU as shown in FIG. 4 to FIG. 5. Therefore, as shown in FIG. When the user accommodation rate is low, the initial capital investment can be minimized by operating with the number of OSUs that meet the bandwidth demand without installing all the OSUs. In addition, when the requested bandwidth per user is expanded, as shown in FIG. 6, the system bandwidth is expanded to meet the importance of the bandwidth by adding the OSU, and then accommodated in the existing OSU using the wavelength variable function of the ONU. The allocated bandwidth per user can be expanded by reducing the load on the OSU by changing the accommodation of the ONU.

S. Kimura, “WDM / TDM-PON Technologies for Future Flexible Optical Access Networks”, OECC 2010, 6A1-1, 2010 Kaneko et al., “Proposal of Wide-area Optical Concentration NW Using Wavelength Tunable WDM / TDM-PON”, 2012 Society Conference, B-8-25, 2012

  In TDM-PON, since signal light is broadcast to all ONUs in downstream communication, each ONU uses an ONU identifier such as LLID (Logical Link ID) to determine whether the received frame is addressed to itself. The received frame is selected. In upstream communication, the ONU transmits a transmission frame including the ONU identifier assigned to itself, and the OSU determines which ONU the frame is transmitted from based on the ONU identifier in the reception frame. The OSU manages the ONU identifiers of all ONUs under its control, and assigns ONU identifiers to newly connected ONUs so that they do not overlap with registered ONUs through the discovery process. In the discovery process, ranging for measuring a round trip time (RTT) between the OSU and the ONU is also performed, and the OSU stores RTT information with all of the ONUs under its control. The OSU determines the allowable transmission time of the upstream signal light of each ONU in consideration of the RTT, thereby avoiding the collision of the upstream signal light.

  Also in the wavelength variable WDM / TDM-PON, similarly to the TDM-PON, it is necessary for each OSU to grasp ONU identifiers and RTT information of all ONUs logically connected to itself. Further, the ONU needs to recognize the ONU identifier assigned to itself. Here, in the wavelength tunable WDM / TDM-PON, the OSU to be logically connected in units of ONUs is changed. Therefore, when managing the ONU identifier and RTT information for each OSU, the discovery process is performed every time the ONU-OSU connection is changed. It is necessary to start over. However, since the transmission of the data signal is not permitted during the discovery process, the bandwidth utilization efficiency decreases.

  The ONU identifier assigned through the discovery process at the time of new registration of the ONU is fixedly assigned even after the change of the assigned wavelength, and the management table as shown in FIG. By sharing the network, it becomes unnecessary to redo the discovery process accompanying the change of the ONU-OSU connection.

  However, when the path length from the ONU to each OSU is different, an error occurs between the actual RTT and the RTT described in the management table when logically connected to an OSU different from the OSU that measured the RTT. For example, in FIG. 2, when the path length from the optical multiplexing / demultiplexing means in the OLT to each OSU is different, the path length from the ONU to each OSU is different. Since the allowable transmission time of the uplink signal light is determined in consideration of the RTT, there is a possibility that the uplink signal light collides due to an RTT error. On the other hand, it is possible to prevent collision of signal light by providing a guard interval having a sufficient time between the upstream signal lights, but there is a problem that band utilization efficiency is lowered.

  Therefore, in order to solve the above-described problem, the present invention eliminates the need to redo the discovery process associated with a change in the ONU-OSU connection even when the path length from the ONU to each OSU is different, and between upstream signal lights. It is an object of the present invention to provide a ranging method that does not require a sufficient guard interval and can prevent a reduction in bandwidth utilization efficiency.

  In order to achieve the above object, the present invention measures the RTT of one child node with only one wavelength combination during ranging, and the RTTs of other child nodes or other wavelength combinations are already registered in the table. It was decided to calculate based on the RTT.

Specifically, in the ranging method according to the present invention, a parent node and a plurality of child nodes are connected by an optical fiber transmission line, and a frame round-trip propagation time (RTT) between the parent node and at least one of the child nodes. ： Round Trip Time (WDM: Wavelength Division Multiplexing, TDM: Time Divide Multiplexing, PON: Passive NP) in which all the combinations of downstream signal wavelength and upstream signal wavelength are stored. A ranging method for obtaining an RTT,
An RTT measurement procedure for measuring an RTT for the child node to be ranged using at least one of the wavelength combinations;
Based on the RTT of the child node to be measured measured by the RTT measurement procedure and the RTT of the other child node stored by the parent node, the children of the ranging target other than the wavelength combinations used in the RTT measurement procedure An RTT calculation procedure for calculating the RTT of the node;
I do.

In the RTT calculation procedure of the ranging method according to the present invention,
In the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node to be ranged and the RTT of another child node is calculated,
The difference can be added to each RTT of the other child nodes other than the wavelength combination used in the RTT measurement procedure.

In the RTT calculation procedure of the ranging method according to the present invention,
For the other child nodes, calculate the difference between the RTT in the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
Each difference may be added to the RTT of the child node to be measured measured by the RTT measurement procedure.

  This ranging method measures the RTT of one child node with only one wavelength combination during ranging, and calculates the RTT of another child node based on the RTT already registered in the table.

  Therefore, according to the present invention, even when the path length from the ONU to each OSU is different, it is not necessary to redo the discovery process accompanying the change of the ONU-OSU connection, and a guard interval having a sufficient time is provided between the upstream signal lights. It is possible to provide a ranging method that does not need to be provided and that can prevent a decrease in band use efficiency.

Specifically, in the ranging method according to the present invention, a parent node and a plurality of child nodes are connected by an optical fiber transmission line, and the RTT between the parent node and at least one child node is defined as a downstream signal wavelength. In a wavelength tunable WDM / TDM-PON storing all wavelength combinations of upstream signal wavelengths, a ranging method for acquiring an RTT,
An RTT measurement procedure for measuring an RTT for one of the child nodes with the wavelength combination to be ranging;
The child measured in the RTT measurement procedure for the wavelength combination used in the RTT measurement procedure based on the RTT of the child node measured in the RTT measurement procedure and the RTT in the other wavelength combination stored in the parent node An RTT calculation procedure for calculating an RTT other than a node;
I do.

In the RTT calculation procedure of the ranging method according to the present invention,
In addition to the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node measured in the RTT measurement procedure and each RTT of the other child node is calculated,
Each difference can be added to the RTT of the child node measured by the RTT measurement procedure.

In the RTT calculation procedure of the ranging method according to the present invention,
For the child node measured in the RTT measurement procedure, calculate the difference between the RTT of the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
The difference may be added to each RTT of another child node other than the wavelength combination used in the RTT measurement procedure.

  This ranging method measures RTT of one child node with only one wavelength combination at the time of ranging, and calculates RTTs of other wavelength combinations based on RTTs already registered in the table.

  Therefore, according to the present invention, even when the path length from the ONU to each OSU is different, it is not necessary to redo the discovery process accompanying the change of the ONU-OSU connection, and a guard interval having a sufficient time is provided between the upstream signal lights. It is possible to provide a ranging method that does not need to be provided and that can prevent a decrease in band use efficiency.

  According to the present invention, even when the path length from the ONU to each OSU is different, it is not necessary to redo the discovery process accompanying the change of the ONU-OSU connection, and a guard interval having a sufficient time is provided between the upstream signal lights. Can be provided, and it is possible to provide a ranging method that can prevent a decrease in bandwidth utilization efficiency.

It is a figure explaining the uplink communication of TDM-PON. It is a figure explaining WDM / TDM-PON which combined WDM technology with TDM-PON. It is a figure explaining the wavelength variable type WDM / TDM-PON which employs the ranging method according to the present invention. It is a figure explaining the expansion of the system band using wavelength multiplexing, and the load distribution between OSUs using a wavelength variable function in wavelength variable type WDM / TDM-PON. It is a figure explaining the expansion of the system band using wavelength multiplexing, and the load distribution between OSUs using a wavelength variable function in wavelength variable type WDM / TDM-PON. It is a figure explaining the expansion of the system band using wavelength multiplexing, and the load distribution between OSUs using a wavelength variable function in wavelength variable type WDM / TDM-PON. It is an example of the management table which described LLID and RTT for every ONU. It is a figure explaining the wavelength variable type WDM / TDM-PON which employs the ranging method according to the present invention. It is a figure explaining the wavelength variable type WDM / TDM-PON which employs the ranging method according to the present invention. It is a figure explaining the wavelength variable type WDM / TDM-PON which employs the ranging method according to the present invention. In addition to the correspondence between each registered ONU and LLID, RTT between each ONU is described for all combinations of optical transmitters that transmit downstream signal light and optical receivers that receive upstream signal light It is a figure explaining the management table which was done. It is a figure explaining the wavelength variable type WDM / TDM-PON which employs the ranging method according to the present invention. It is a figure of the management table explaining the ranging method which concerns on this invention. It is a figure of the management table explaining the ranging method which concerns on this invention. It is a figure of the management table explaining the ranging method which concerns on this invention. It is a figure of the management table explaining the ranging method which concerns on this invention. It is an example (M> = H) of the input / output relationship of the downstream signal light in a wavelength routing means. It is an example (M> = H) of the input / output relationship of the upstream signal light in the wavelength routing means.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

[First Embodiment]
In the first embodiment, in the wavelength tunable WDM / TDM-PON, through a discovery process, a parent node (OLT) in all combinations of an optical transmitter that transmits downstream signal light and an optical receiver that receives upstream signal light This is a ranging method in which RTT with a newly registered child node (ONU) is calculated from measurement time in one combination without measuring all combinations.

That is, in the first embodiment, a parent node and a plurality of child nodes are connected by an optical fiber transmission line, and a frame round-trip propagation time (RTT: Round Trip Time) between the parent node and at least one child node. ) Is stored for all wavelength combinations of downstream signal wavelengths and upstream signal wavelengths (WDM: Wavelength Division Multiplexing, TDM: Time Division Multiplexing, PON: Passive Optical Network) A ranging method to
An RTT measurement procedure for measuring an RTT for the child node to be ranged using at least one of the wavelength combinations;
Based on the RTT of the child node to be measured measured by the RTT measurement procedure and the RTT of the other child node stored by the parent node, the children of the ranging target other than the wavelength combinations used in the RTT measurement procedure An RTT calculation procedure for calculating the RTT of the node;
I do.

In particular, in the first embodiment, in the RTT calculation procedure,
In the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node to be ranged and the RTT of another child node is calculated,
The difference is added to each RTT of the other child nodes other than the wavelength combination used in the RTT measurement procedure.

  The ranging method in the present embodiment will be described by taking the optical communication system 301 having a wavelength variable WDM / TDM-PON configuration in FIG. 3 as an example. Note that the wavelength tunable WDM / TDM-PON configuration to which the ranging method in the present embodiment is applied is not limited to FIG. 3, and an optical communication system (302) that uses wavelength routing means 152 such as circular AWG (Arrayed Waveguide Grating). 302 ′) (FIGS. 8 and 9), and the optical communication system 303 (FIG. 10) having a configuration in which the wavelength multiplexing / demultiplexing means 153 and the optical multiplexing / demultiplexing means 151 such as AWG and thin film filter are combined. It is.

In the optical communication system (302, 302 ′), the downstream signal light from each of the wavelength tunable optical transmitters 18 is input to the wavelength routing unit 152 through separate optical transmitter / receiver side terminals, and different optical fibers according to the wavelengths. Output from the transmission line side terminal to the optical fiber transmission line 250. In the wavelength routing means 152, the number H of optical fiber transmission line side terminals (H is an integer of 1 or more) is equal to or less than the number M of optical transceiver side terminals, and the wavelengths λ _{D —} 1 to λ input from each optical transceiver side terminal _As shown in FIG. 17, an AWG (Arrayed Waveguide Grating) or the like that distributes the _{D_M} light to the optical fiber transmission line side terminals # 1 to _#H according to the wavelength is used.

On the other hand, the upstream signal light transmitted to the parent node 100c is distributed according to the wavelength by the wavelength routing means 152, and is input to the optical receiver 19 through a different optical transceiver side terminal. Wavelength routing means 152, the optical fiber transmission line side terminals # 1 through # optical transceiver terminal in accordance with the wavelength as represented in Figure 18 the light input wavelength lambda _{U_1} to [lambda] _{u_M} from H # 1 to # Sort to M.

The optical communication system 301 in FIG. 3 includes optical transmitters 11 (# 1 to #M) (M is an integer equal to or greater than 1) and optical receivers 15 (# 1 to #M), and have wavelengths λ _{D_1 to} λ _{D_M} . sends a certain downstream signal light, OLT100a the upstream signal light is the wavelength lambda _{U_1} to [lambda] _{u_M} is _{input, λ D_1 ~λ D_M, λ U_1} ~λ each downstream wavelength one by one of the wavelengths from _{u_M} and upstream wavelength Are connected to the plurality of ONUs 200a assigned from the OLT 100a via the optical fiber transmission line 250. Each optical transmitter 11 in the OLT 100 a transmits downstream signal light having a different wavelength for each optical transmitter 11, and the downstream signal light from each optical transmitter 11 is wavelength-multiplexed by the optical multiplexing / demultiplexing means 151. Thereafter, the data is output to the optical fiber transmission line 250. As the optical multiplexing / demultiplexing means 151, an optical coupler or the like produced by an optical fiber or PLC (Planar Lightwave Circuit) or the like corresponds to this.

  The ONU 200a selectively receives the downlink signal light, which is the downlink wavelength assigned from the OLT 100a, from the input wavelength multiplexed signal light. As shown in FIG. 3, a wavelength tunable filter 22 is arranged in front of a light receiver 21 such as PIN-PD (Photo-Diode) or APD (Avalanche Photo-Diode), and the transmission wavelength of the tunable filter 22 is assigned to the downstream. By changing according to the wavelength, it is possible to selectively receive the downlink signal light having a desired wavelength. Each ONU 200a determines whether the received frame is addressed to itself by using an ONU identifier such as LLID, and selects a received frame.

On the other hand, for uplink communications, ONU200a has a wavelength lambda _{U_1} to [lambda] _{u_M} wavelength tunable optical transmitter 24 capable of transmitting an uplink signal light, in upstream wavelength assigned from OLT100a, notified from OLT100a transmission The upstream signal light is transmitted within the allowable time. The permissible transmission time notified from the OLT 100a is determined in consideration of the RTT between each ONU 200a stored in the OLT 100a so that signal lights from different ONUs 200a to which the same upstream wavelength is assigned do not collide with each other. Is done. Here, in addition to the correspondence between each registered ONU 200a and an ONU identifier such as LLID, the OLT 100a performs RTT between each ONU 200a and the optical transmitter 11 that transmits the downstream signal light and the upstream signal light. The management table as shown in FIG. 11 describing all combinations of the optical receivers 15 that receive the signal is provided. As the tunable optical transmitter 24 mounted in the ONU 200a, a configuration in which the output light wavelength of a direct modulation laser such as a distributed feedback (DFB) laser is changed by temperature control, or a direct modulation laser having a different output light wavelength is used. This is an arrangement that can be arranged in an array and can perform high-speed wavelength switching for switching between lasers that emit light by switching bias currents. Further, a Mach-Zehnder type modulator using a continuous light from a wavelength tunable light source such as a distributed Bragg reflection type (DBR) laser or an external cavity type laser as a material, a semiconductor or lithium diobate (LiNbO ₃ ). Further, a configuration in which external modulation is performed using an electroabsorption (EA) modulator, a semiconductor optical amplifier (SOA) modulator, or the like is also possible.

  The upstream signal light transmitted to the OLT 100a is branched by the optical multiplexing / demultiplexing means 151, and then input to the optical receivers 15 (# 1 to #M) that selectively receive upstream signal lights having different wavelengths. As shown in FIG. 3, the wavelength filters 13 having different transmission wavelengths for the respective optical receivers 14 are arranged in front of the optical receivers 14 such as PIN-PD and APD. Signal light can be selectively received. Here, each ONU 200a transmits an upstream signal light including an ONU identifier such as LLID assigned to itself in the transmission frame, so that the OLT 100a can determine the transmission source of the frame based on the ONU identifier in the reception frame. .

FIG. 3 shows a configuration in which the wavelength tunable filter 22 and the wavelength filter 13 are respectively disposed in front of the light receivers (21, 14) in the ONU 200a and the OLT 100a to transmit only the wavelength of the desired signal light. As described above, it is also possible to use coherent receivers (27, 16) as optical receivers in the ONU 200b and the OLT 100b. In this case, the output light wavelength of the local light source 28 in the ONU 200b is set near the wavelength of the assigned downstream signal light. On the other hand, the output light wavelength of the local light source 17 in OLT100b the local light is so different phases for each coherent receiver 16 is inputted, it is set in the vicinity of one of the wavelengths λ _{U_1} ~λ _{U_M.} By applying coherent reception characterized by high reception sensitivity, the allowable loss in the optical fiber transmission line 250 or in the OLT 100b can be increased. By increasing the transmission loss and branching loss allowed in the optical fiber transmission line 250, the transmission distance can be lengthened and the number of ONUs 200b to be accommodated can be increased. Further, since the number of optical transceivers 51 can be increased by increasing the branching loss allowed in the OLT 100b, the total system bandwidth can be expanded. Furthermore, since the wavelength filter (13, 22) is not required by the application of coherent reception, it is possible to narrow the adjacent wavelength interval without being limited by the characteristics of the wavelength filter.

In the discovery process, the OLT 100a transmits, at a predetermined time, a search signal in which a command for returning a response signal as a registration request is returned to the unregistered ONU 200a. As a method by which the unregistered ONU 200a can reliably receive the search signal, for example, when the ONU 200a is not registered, the transmission wavelength of the wavelength variable filter 22 in the ONU 200a or the output light wavelength of the local light source 28 is searched. A wavelength control circuit (not shown) in the ONU 200a is set in advance so that the output light wavelength λ _{D_m of} the optical transmitter 11 # m (m = 1, 2,..., M) that transmits the signal is set. Can be considered. Further, by a method of periodically sweeping the output light wavelength of the transmission wavelength or the local light source 28 of the wavelength tunable filter 22 in ONU200a the range of lambda _{D_1} to [lambda] _{D_M,} reliably unregistered ONU200a the search signal Can be received. For specifying the wavelength of the response signal, an instruction to set the wavelength of the response signal to λ _{U —} n (n = 1, 2,..., M) may be included in the search signal, _or the search signal of λ _{D_m} is received. it may be previously set wavelength control circuit (not shown) in ONU200a so as to set the output light wavelength of the wavelength tunable optical transmitter 24 to the lambda _{U_n} the time. The response signal transmitted to the OLT 100a is branched by the optical multiplexing / demultiplexing means 151 and then received by the optical receiver 15 # n. m and n may be either m = n or m ≠ n.

と表わせる。 When the OLT 100a receives a response signal that is a registration request from the unregistered ONU 200a # k (k = 1, 2,..., K, K is an integer of 1 or more), the OLT 100a overlaps with the registered ONU 200a. An ONU identifier such as LLID is assigned to the transmission source ONU 200a # k so as not to occur. The once assigned ONU identifier is also changed when the optical transmitter 11 / optical receiver 15 that transmits / receives downstream / upstream signal light with the ONU 200a as a destination / transmission source is changed by changing the wavelength allocated to the ONU 200a. Continue to be granted fixedly. Also, the frame round-trip propagation time T when the optical transmitter 11 # m in the OLT 100a transmits the downstream signal light to the ONU 200a # k and the upstream signal light from the ONU 200a # k is received by the optical receiver 15 # n. Measure _k (m, n). The distance from the ONU 200a # k to the optical multiplexing / demultiplexing means 151 in the OLT 100a is L _k [km], the distance from the optical transmitter 11 # m in the OLT 100a, and the distance from the optical receiver 15 # n to the optical multiplexing / demultiplexing means 151, respectively. If l _m , l _n [km], the speed of light in vacuum is c [km / s], and the refractive index in the downstream signal wavelength band and upstream signal wavelength band in the optical fiber transmission line 250 is n _down , n _up ,

It can be expressed as

と表わせるため、式（１）、（２）より、各ＯＮＵ２００ａからＯＬＴ１００ａ内の光合分波手段１５１までの光路長の差Ｌ_ｋ−Ｌ_ｋ’は式（３）で表わされる。

The OLT 100a records the RTT with each registered ONU 200a for all combinations of the optical transmitter 11 that transmits the downstream signal light and the optical receiver 15 that receives the upstream signal light as shown in FIG. Has a table. The OLT 100a and the registered ONU 200a # k ′ (k ′ = 1, 2,...) In the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100a used when measuring T _k (m, n). K, k ≠ k ′) and the frame round-trip propagation time T _{k ′} (m, n) are described in the management table,

Therefore, from the equations (1) and (2), the optical path length difference L _k -L _{k ′} from each ONU 200a to the optical multiplexing / demultiplexing means 151 in the OLT 100a is represented by the equation (3).

When a downstream signal light addressed to the ONU 200a # k newly registered by an arbitrary optical transmitter 11 is transmitted using the expression (3) and an upstream signal light from the ONU 200a # k is received by an arbitrary optical receiver 15 The frame round-trip propagation time T _k (m ′, n ′) (m ′ = 1, 2,..., M, n ′ = 1, 2,..., M) with the ONU 200a # k of It can be expanded as follows.

Since T _{k ′} (m, n) and T _{k ′} (m ′, n ′) are described in the management table held by the OLT 100a, the frame round-trip propagation time measured with the newly registered ONU 200a # k. By referring to T _k (m, n) and the management table, as shown in FIG. 13, the OLT 100a and the ONU 200a # in all combinations of the optical transmitter that transmits the downstream signal light and the optical receiver that receives the upstream signal light. It can be seen that the RTT with k can be calculated. FIG. 13 shows a case where m = n = 1 and k ′ = K.

  In the present embodiment, the RTT between the OLT 100a and the newly registered ONU 200a in all the combinations of the optical transmitter 11 that transmits the downstream signal light and the optical receiver 15 that receives the upstream signal light is all combinations. Without measurement, it can be efficiently calculated from the measurement time in one combination. In addition, since the OLT 100a stores the RTTs for all combinations, even when the path lengths from the ONU 200a to the OSUs 51 are different, the allowable transmission time of the upstream signal light is set using a highly accurate RTT value in any combination. Therefore, it is possible to reduce the guard interval between the upstream signal lights from different ONUs 200a and improve the band utilization efficiency.

[Second Embodiment]
In the second embodiment, an optical transmitter for transmitting downstream signal light and an upstream signal light are transmitted through a discovery process in a wavelength tunable WDM / TDM-PON by a method different from the ranging method in the first embodiment. This is a ranging method in which the RTT between the OLT 100a and the newly registered ONU 200a in all combinations of receiving optical receivers is calculated from the measurement time in one combination without measuring all combinations.

That is, in the second embodiment, the RTT calculation procedure is as follows.
For the other child nodes, calculate the difference between the RTT in the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
The difference is added to the RTT of the child node to be measured measured by the RTT measurement procedure.

  The ranging method in the present embodiment will be described by taking the optical communication system 301 having the wavelength variable WDM / TDM-PON configuration of FIG. 3 as an example. The wavelength tunable WDM / TDM-PON configuration to which the ranging method according to the present embodiment is applied is not limited to FIG. 3, but an optical communication system (302, 302 ′) having a configuration using wavelength routing means 152 such as a recurring AWG. 8 and 9), and an optical communication system 303 (FIG. 10) having a configuration in which wavelength multiplexing / demultiplexing means such as AWG or thin film filter and optical multiplexing / demultiplexing means are combined.

Through the discovery process, the OLT 100a transmits the ONU 200a # k (k = 1, 2) in which the optical transmitter 11 # m (m = 1, 2,..., M, M is an integer of 1 or more) in the OLT 100a is unregistered. ,..., K, where K is an integer equal to or greater than 1) and the downstream signal light is transmitted to the upstream from the ONU 200a # k by the optical receiver 15 # n (n = 1, 2,..., M). The frame round-trip propagation time T _k (m, n) when receiving signal light is measured. m and n may be either m = n or m ≠ n. T _k (m, n) is represented by the formula (1) in the first embodiment.

The OLT 100a manages the RTT between each registered ONU 200a as shown in FIG. 11 in which all combinations of the optical transmitter 11 that transmits downstream signal light and the optical receiver 15 that receives upstream signal light are described. Has a table. The same combination as the combination of the optical transmitter and the optical receiver in the OLT 100a used when measuring T _k (m, n), and the OLT 100a and the registered OLT 100a # k ′ (k ′ = , 1,..., K, k ≠ k ′) and frame round-trip propagation times T _{k ′} (m, n), T _{k ′} (m ′, n ′) (m ′ = 1, 2, .., M, n ′ = 1, 2,..., M) are described in the management table, and Equation (5) is derived using both values.

Using Equation (1) and Equation (5), a downstream signal light addressed to ONU 200a # k newly registered by optical transmitter #m ′ is transmitted, and an upstream signal from ONU 200a # k is transmitted by optical receiver #n ′. The frame round-trip propagation time T _k (m ′, n ′) when receiving light can be developed as follows.

Since T _{k ′} (m, n) and T _{k ′} (m ′, n ′) are described in the management table held by the OLT 100a, the frame round-trip propagation time measured with the newly registered ONU 200a # k. By referring to T _k (m, n) and the management table, as shown in FIG. 14, the OLT 100a and the ONU 200a # in all combinations of the optical transmitter that transmits the downstream signal light and the optical receiver that receives the upstream signal light. It can be seen that the RTT with k can be calculated. FIG. 14 shows a case where m = n = 1 and k ′ = K.

  In this embodiment, the RTT between the OLT 100a and the newly registered ONU 200a in all combinations of optical transmitters that transmit downstream signal light and optical receivers that receive upstream signal light is measured in all combinations. Without being able to calculate efficiently from the measurement time in one combination. In addition, since the OLT 100a stores RTTs for all combinations, even when the path lengths from the ONU 200a to the OSUs are different, the allowable transmission time of the upstream signal light is set using a highly accurate RTT value in any combination. Therefore, it is possible to reduce the guard interval between the upstream signal lights from different ONUs 200a and improve the band utilization efficiency.

[Third Embodiment]
In the third embodiment, when an OSU is added in a wavelength tunable WDM / TDM-PON, the RTT between the added OSU and each registered ONU 200a is measured for all ONUs 200a. Rather, it is a ranging method calculated from the measurement time in one ONU 200a.

That is, in the third embodiment, a parent node and a plurality of child nodes are connected by an optical fiber transmission line, and the parent node performs RTT between at least one of the child nodes with a downlink signal wavelength and an uplink signal wavelength. In a wavelength tunable WDM / TDM-PON stored for all wavelength combinations, a ranging method for acquiring an RTT,
An RTT measurement procedure for measuring an RTT for one of the child nodes with the wavelength combination to be ranging;
The child measured in the RTT measurement procedure for the wavelength combination used in the RTT measurement procedure based on the RTT of the child node measured in the RTT measurement procedure and the RTT in the other wavelength combination stored in the parent node An RTT calculation procedure for calculating an RTT other than a node;
I do.

In particular, in the third embodiment, in the RTT calculation procedure,
In addition to the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node measured in the RTT measurement procedure and each RTT of the other child node is calculated,
The difference is added to the RTT of the child node measured by the RTT measurement procedure.

  The ranging method in the present embodiment will be described by taking the optical communication system 301 having the wavelength variable WDM / TDM-PON configuration of FIG. 3 as an example. Note that the wavelength tunable WDM / TDM-PON configuration to which the ranging method in the present embodiment is applied is not limited to FIG. 3, but an optical communication system (302, 302 ′) having a configuration using wavelength routing means such as a recurring AWG (see FIG. 3). 8 and FIG. 9), and an optical communication system 303 (FIG. 10) having a configuration in which wavelength multiplexing / demultiplexing means such as AWG and thin film filter and optical multiplexing / demultiplexing means are combined.

と表わせる。 An _{OSU 51} # including an optical transmitter 11 # M + 1 (M is an integer of 1 or more) that transmits a downstream signal light having a wavelength _{λD_M + 1} and an optical receiver 15 # M + 1 that selectively receives an upstream signal light having a wavelength _{λU_M + 1.} When M + 1 is added, λ _{D_m} (m = 1, 2,..., M + 1) and λ _{U_M + 1} are assigned to _one of the _{ONUs 200a} as a downstream wavelength and an upstream wavelength, respectively. Thereafter, the optical transmitter 11 # m sends the downstream signal light to the ONU 200a # k (k = 1, 2,..., K, K is an integer equal to or greater than 1), and sends it to the optical receiver 15 # M + 1. Then, the frame round-trip propagation time T _k (m, M + 1) when receiving the upstream signal light from the ONU 200a # k is measured. The measured T _k (m, M + 1) is

It can be expressed as

The OLT 100a performs RTT between the existing OSU 51 and each ONU 200a, as shown in FIG. 11 for all combinations of the optical transmitter 11 that transmits downstream signal light and the optical receiver 15 that receives upstream signal light. A management table is provided. An ONU 200a # k in a combination different from the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100a used when measuring T _k (m, M + 1), and another ONU 200a # k ′ (k ′ = 1, 2,..., K, k ≠ k ′) frame round-trip propagation time T _k (m ′, n ′), T _{k ′} (m ′, n ′) (m ′ = 1, 2,. .., M, n ′ = 1, 2,..., M) are described in the management table, and using these values, the difference in optical path length from each ONU 200a to the optical multiplexing / demultiplexing means 151 in the OLT 100a L _{k ′} −L _k is expressed by Expression (8).

Frame round-trip propagation between the OLT 100a and the ONU 200a # k ′ in the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100a used when measuring T _k (m, M + 1) using the equation (8) The time T _{k ′} (m, M + 1) can be expanded as follows.

Since T _k (m ′, n ′) and T _{k ′} (m ′, n ′) are described in the management table held by the OLT 100a, the measured frame round-trip propagation time T _k (m, M + 1) and the management table 15, as shown in FIG. 15, between all the ONUs 200 a in the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100 a used when measuring T _k (m, M + 1). It can be seen that RTT can be calculated. FIG. 15 shows a case where m = 1 and m ′ = n ′ = M. Further, by sequentially changing the value of m, the RTT when the upstream signal light is received by the optical receiver 15 # M + 1 in the added OSU 51 # M + 1 is changed to the optical transmitter 11 that transmits the downstream signal light. Can be calculated for all combinations.

Next, λ _{D_M + 1} and λ _{U_m} are assigned to _{one of} the _{ONUs 200a} as a downstream wavelength and an upstream wavelength, respectively, and the optical transmitter 11 # M + 1 receives the ONU 200a # k ″ (k ″ = 1, 2,... K) Transmits the downstream signal light to address, and measures the frame round-trip propagation time T _{k ″} (M + 1, m) when the optical receiver 15 # m receives the upstream signal light from the ONU 200a # k ″. By referring to the measurement value T _{k ″} (M + 1, m) and the management table, similarly, the optical transmitter 11 and the optical receiver in the OLT 100a used when measuring T _{k ″} (M + 1, m). It can be seen that RTTs can be calculated with all ONUs 200a in 15 combinations. Further, by sequentially changing the value of m, the RTT when the downstream signal light is transmitted by the optical transmitter 11 # M + 1 in the added OSU 51 # M + 1 is changed to the optical receiver 15 that receives the upstream signal light. Can be calculated for all combinations.

  In this embodiment, when the OSU 51 is added, the RTT between the added OSU 51 and each registered ONU 200a is efficiently measured from the measurement time of one ONU 200a without measuring all the ONUs 200a. Can be calculated. In addition, since the OLT 100a stores the RTTs for all combinations, even when the path lengths from the ONU 200a to the OSUs 51 are different, the allowable transmission time of the upstream signal light is set using a highly accurate RTT value in any combination. Therefore, it is possible to reduce the guard interval between the upstream signal lights from different ONUs 200a and improve the band utilization efficiency.

[Fourth Embodiment]
In the fourth embodiment, when the OSU 51 is added in the wavelength tunable WDM / TDM-PON by a method different from the ranging method in the second embodiment, the added OSU 51 and each registered ONU 200a. Is a ranging method in which the RTT is calculated from the measurement time of one ONU 200a without measuring all the ONUs 200a.

That is, in the fourth embodiment, the RTT calculation procedure is as follows.
For the child node measured in the RTT measurement procedure, calculate the difference between the RTT of the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
The difference is added to each RTT of the other child nodes other than the wavelength combination used in the RTT measurement procedure.

  The ranging method in the present embodiment will be described by taking the optical communication system 301 having a wavelength variable WDM / TDM-PON configuration in FIG. 3 as an example. Note that the wavelength tunable WDM / TDM-PON configuration to which the ranging method in the present embodiment is applied is not limited to FIG. 3, but an optical communication system (302, 302 ′) having a configuration using wavelength routing means such as a recurring AWG (see FIG. 3). 8 and FIG. 9), and the optical communication system 303 (FIG. 10) having a configuration in which the wavelength multiplexing / demultiplexing means 153 and the optical multiplexing / demultiplexing means 151 such as AWG and thin film filter are combined.

An _{OSU 51} # including an optical transmitter 11 # M + 1 (M is an integer of 1 or more) that transmits a downstream signal light having a wavelength _{λD_M + 1} and an optical receiver 15 # M + 1 that selectively receives an upstream signal light having a wavelength _{λU_M + 1.} When M + 1 is added, λ _{D_m} (m = 1, 2,..., M + 1) and λ _{U_M + 1} are assigned to _one of the _{ONUs 200a} as a downstream wavelength and an upstream wavelength, respectively. Thereafter, the optical transmitter 11 # m sends the downstream signal light to the ONU 200a # k (k = 1, 2,..., K, K is an integer equal to or greater than 1), and sends it to the optical receiver 15 # M + 1. Then, the frame round-trip propagation time T _k (m, M + 1) when receiving the upstream signal light from the ONU 200a # k is measured. The measured T _k (m, M + 1) is expressed by Expression (7) in the third embodiment.

と表わせるため、式（７）、（１０）より、式（１１）が導かれる。

The OLT 100a records the RTT with each registered ONU 200a for all combinations of the optical transmitter 11 that transmits the downstream signal light and the optical receiver 15 that receives the upstream signal light as shown in FIG. Has a table. Frame round-trip propagation time T _k (m ′,) between ONU 200a # k in a combination different from the combination of optical transmitter 11 and optical receiver 15 in OLT 100a used when measuring T _k (m, M + 1) n ′) (m ′ = 1, 2,..., M, n ′ = 1, 2,..., M) are described in the management table,

Therefore, Expression (11) is derived from Expressions (7) and (10).

Using the expression (11), the OLLT and another ONU 200a # k ′ (k ′ = 1) in the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100a used when measuring T _k (m, M + 1). , 2,..., K, k ≠ k ′), the frame round-trip propagation time T _{k ′} (m, M + 1) can be expanded as follows.

Since T _k (m ′, n ′) and T _{k ′} (m ′, n ′) are described in the management table held by the OLT 100a, the measured frame round-trip propagation time T _k (m, M + 1) and the management table 16, as shown in FIG. 16, between all the ONUs 200 a in the combination of the optical transmitter 11 and the optical receiver 15 in the OLT 100 a used when measuring T _k (m, M + 1). It can be seen that RTT can be calculated. FIG. 16 shows a case where m = 1 and m ′ = n ′ = M. Further, by sequentially changing the value of m, the RTT when the upstream signal light is received by the optical receiver 15 # M + 1 in the added OSU 51 # M + 1 is changed to the optical transmitter 11 that transmits the downstream signal light. Can be calculated for all combinations.

Next, λ _{D_M + 1} and λ _{U_m} are assigned to _{one of} the _{ONUs 200a} as a downstream wavelength and an upstream wavelength, respectively, and the optical transmitter 11 # M + 1 receives the ONU 200a # k ″ (k ″ = 1, 2,... K) Transmits the downstream signal light to address, and measures the frame round-trip propagation time T _{k ″} (M + 1, m) when the optical receiver 15 # m receives the upstream signal light from the ONU 200a # k ″. By referring to the measurement value T _{k ″} (M + 1, m) and the management table, similarly, the optical transmitter 11 and the optical receiver in the OLT 100a used when measuring T _{k ″} (M + 1, m). It can be seen that RTTs can be calculated with all ONUs 200a in 15 combinations. Further, by sequentially changing the value of m, the RTT when the downstream signal light is transmitted by the optical transmitter 11 # M + 1 in the added OSU 51 # M + 1 is changed to the optical receiver 15 that receives the upstream signal light. Can be calculated for all combinations.

  In this embodiment, when the OSU 51 is added, the RTT between the added OSU 51 and each registered ONU 200a is efficiently measured from the measurement time of one ONU 200a without measuring all the ONUs 200a. Can be calculated. In addition, since the OLT 100a stores the RTTs for all combinations, even when the path lengths from the ONU 200a to the OSUs 51 are different, the allowable transmission time of the upstream signal light is set using a highly accurate RTT value in any combination. Therefore, it is possible to reduce the guard interval between the upstream signal lights from different ONUs 200a and improve the band utilization efficiency.

  The following describes the ranging method of the present embodiment.

<Issues>
In an optical access network based on TDM / WDM-PON, similarly to the conventional TDM-PON, each OSU needs to know the ONU identifier such as the LLID of the ONU and the RTT. However, every time the OSU logically connected in units of ONUs is changed due to the change of the allocated wavelength in TDM / WDM-PON, it is necessary to redo the discovery process.

<Problem solving means>
(1):
One parent node and multiple child nodes are connected via an optical fiber transmission line,
The parent node is provided with a plurality of optical transmitter and an optical receiver, the wavelength λ _{D_1} ~λ _{D_M} (M is an integer of 1 or more) sends a downstream signal light is a wavelength λ _{U_1} ~λ _{U_N} (N 1 Upstream signal light that is an integer above) is input,
Child _nodes, λ _{D_1} ~λ _{D_M,} λ _{U_1} wavelength from to [lambda] _{U_N} one is allocated from the parent node as the downstream wavelength and an upstream wavelength, respectively, wherein the same wavelength as the downstream wavelength assigned A ranging method for calculating a round-trip propagation time between the child node and the parent node in an optical communication system that receives downstream signal light and transmits the upstream signal light at the assigned upstream wavelength. ,
Measuring at least one of the combinations of the optical transmitter and the optical receiver, the frame round-trip propagation time between the child nodes to be ranged,
The parent node stores the frame round-trip propagation time between at least one of the child nodes not subject to ranging and the parent node for all the combinations,
From the measured frame round trip propagation time and the stored frame round trip propagation time,
A ranging method, comprising: calculating a frame round-trip propagation time between the child node and the parent node other than the combination when the frame round-trip propagation time is measured.

(2):
In the process of calculating the frame round-trip propagation time, the frame round-trip propagation between the child node other than the ranging target and the parent node in the combination when the frame round-trip propagation time is measured and the frame round-trip propagation time is measured. The ranging method according to (1), wherein a difference from time is derived.

(3):
In the process of calculating the frame round-trip propagation time, the combination when the frame round-trip propagation time is measured, and the frame round-trip propagation time between the child node that is not the ranging target in the other combination and the parent node, The ranging method according to (1), wherein the difference is derived.

(4):
One parent node and multiple child nodes are connected via an optical fiber transmission line,
The parent node is provided with a plurality of optical transmitter and an optical receiver, the wavelength λ _{D_1} ~λ _{D_M} (M is an integer of 1 or more) sends a downstream signal light is a wavelength λ _{U_1} ~λ _{U_N} (N 1 Upstream signal light that is an integer above) is input,
Child _nodes, λ _{D_1} ~λ _{D_M,} λ _{U_1} wavelength from to [lambda] _{U_N} one is allocated from the parent node as the downstream wavelength and an upstream wavelength, respectively, wherein the same wavelength as the downstream wavelength assigned A ranging method for calculating a round-trip propagation time between the child node and the parent node in an optical communication system that receives downstream signal light and transmits the upstream signal light at the assigned upstream wavelength. ,
Measuring a frame round-trip propagation time between at least one of the child nodes in one of the combinations of the optical transmitter and the optical receiver;
The parent node stores the frame round-trip propagation time with the parent node in the other combinations for all child nodes,
From the measured frame round trip propagation time and the stored frame round trip propagation time,
A ranging method for calculating a frame round-trip propagation time between the parent node and a child node other than the child node that measured the frame round-trip propagation time for the combination when the frame round-trip propagation time is measured .

(5):
The ranging method according to (4), wherein, in the process of calculating the frame round-trip propagation time, a time difference between child nodes in the combination different from the measurement of the frame round-trip propagation time is derived.

(6):
In the process of calculating the frame round-trip propagation time, between the measured frame round-trip propagation time and the child node and the parent node that measured the frame round-trip propagation time in another combination with the measured frame round-trip propagation time. The ranging method according to (4) above, wherein a difference from the frame round-trip propagation time is derived.

<Effect>
In the present invention, even when the wavelength between the ONU 200a and the OSU 51 changes, an unnecessary discovery process can be stopped by performing recalculation based on another RTT already registered in the table. .

11: Optical transmitter 12: Wavelength multiplexing / demultiplexing means 13: Wavelength filter 14: Light receiver 15: Optical receiver 16: Coherent receiver 17: Local light source 18: Wavelength variable optical transmitter 19: Optical receiver 19a: Wavelength Variable optical receiver 21: Light receiver 22: Wavelength variable filter 23: Wavelength variable optical receiver 24: Wavelength variable optical transmitter 26: Wavelength multiplexing / demultiplexing means 27: Coherent receiver 28: Local light source 51: OSU
100a, 100b, 100c: parent node 151: optical multiplexing / demultiplexing means 152: wavelength routing means 200, 200a, 200b, 200c: child node 250: optical fiber transmission lines 300, 300 ′, 301, 301 ″, 302, 302 ′, 303: Optical communication system

Claims (6)

A parent node and a plurality of child nodes are connected by an optical fiber transmission line, and a round trip propagation time (RTT: Round Trip Time) between the parent node and at least one child node is defined as a downstream signal wavelength and an upstream signal wavelength. A wavelength-tunable WDM / TDM-PON (WDM: Wavelength Division Multiplexing, TDM: Time Division Multiplexing, PON: Passive Optical Network), which stores all wavelength combinations of RTN, is a ranging method for obtaining RTT.
An RTT measurement procedure for measuring an RTT for the child node to be ranged using at least one of the wavelength combinations;
Based on the RTT of the child node to be measured measured by the RTT measurement procedure and the RTT of the other child node stored by the parent node, the children of the ranging target other than the wavelength combinations used in the RTT measurement procedure An RTT calculation procedure for calculating the RTT of the node;
A ranging method to do. In the RTT calculation procedure,
In the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node to be ranged and the RTT of another child node is calculated,
The ranging method according to claim 1, wherein the difference is added to each RTT of the other child nodes other than the wavelength combination used in the RTT measurement procedure. In the RTT calculation procedure,
For the other child nodes, calculate the difference between the RTT in the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
The ranging method according to claim 1, wherein the difference is added to the RTT of the child node to be ranging measured by the RTT measurement procedure. A parent node and a plurality of child nodes are connected by an optical fiber transmission line, and the parent node stores RTT between at least one child node for all wavelength combinations of downstream signal wavelengths and upstream signal wavelengths. In a wavelength tunable WDM / TDM-PON, a ranging method for acquiring an RTT,
An RTT measurement procedure for measuring an RTT for one of the child nodes with the wavelength combination to be ranging;
The child measured in the RTT measurement procedure for the wavelength combination used in the RTT measurement procedure based on the RTT of the child node measured in the RTT measurement procedure and the RTT in the other wavelength combination stored in the parent node An RTT calculation procedure for calculating an RTT other than a node;
A ranging method to do. In the RTT calculation procedure,
In addition to the wavelength combination used in the RTT measurement procedure, the difference between the RTT of the child node measured in the RTT measurement procedure and each RTT of the other child node is calculated,
The ranging method according to claim 4, wherein each difference is added to the RTT of the child node measured by the RTT measurement procedure. In the RTT calculation procedure,
For the child node measured in the RTT measurement procedure, calculate the difference between the RTT of the wavelength combination used in the RTT measurement procedure and the RTT other than the wavelength combination used in the RTT measurement procedure,
The ranging method according to claim 4, wherein the difference is added to each RTT of the other child nodes other than the wavelength combination used in the RTT measurement procedure.

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