OLT and bandwidth allocation method

Abstract

To enable PONs with different transmission speeds to coexist at low cost.SOLUTION: An apparatus according to an embodiment of the present disclosure is an optical line terminal (OLT) for a PON capable of optical communication at multiple upstream transmission speeds, and includes a first signal processor that executes the first DBA described below, a second signal processor that executes the second DBA described below, and a DBA linking unit that executes processing to exclusively link the allocable period of the first DBA with the allocable period of the second DBA. First DBA: A DBA that includes a first ONU whose upstream transmission speed is a first speed. Second DBA: A DBA that includes a second ONU whose upstream transmission speed is a second speed different from the first speed.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an OLT and a bandwidth allocation method. [Background technology]

[0002] Coexistence of GE-PON (Gigabit Ethernet Passive Optical Network: "Ethernet" is a registered trademark) and 10G-EPON has already been achieved by using wavelength multiplexing for downstream communications and time division multiplexing for upstream communications. Patent Document 1 also describes a migration method for an OLT (Optical Line Terminal) that enables the coexistence of multiple types of PONs with overlapping wavelength bands, such as three types of GE-PON, 10G-EPON, and 25G-EPON. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2018 / 179497 [Non-patent literature]

[0004] [Non-Patent Document 1] Fabienne Saliou, “Triple Coexistance of G-PON, XGS-PON and 50G-PON Systems with Extended Reach”, ECOC 2023, paper Tu.A.5.3. [Non-patent document 2] D. Umeda, "25G NRZ Transmission", IEEE P802.3ca Task Force, May 2016, contribution. [Non-patent document 3] Hongseok Shin, “Optical Pluggables for Mobile Fronthaul in SKT”, ECOC2023, workshop MOPA Optics for Wireless. Summary of the Invention [Problem to be solved by the invention]

[0005] For example, GE-PON, 10G-EPON, and 25G-EPON have different communication frame structures, which means that the forward error correction (FEC) methods are also different. Therefore, adopting a media access control (MAC) chip capable of comprehensive dynamic bandwidth allocation (DBA) for the ONUs of the three types of PONs would pose a problem of high development costs. An object of the present disclosure is to provide an OLT that can realize the coexistence of PONs with different transmission speeds at low cost. [Means for solving the problem]

[0006] An apparatus according to one embodiment of the present disclosure is an OLT of a PON capable of optical communication at multiple upstream transmission speeds, and includes a first signal processing unit that executes a first DBA described below, a second signal processing unit that executes a second DBA described below, and a DBA linkage unit that executes processing to exclusively link the allocatable period of the first DBA and the allocatable period of the second DBA. First DBA: DBA that includes the first ONU whose upstream transmission speed is the first speed Second DBA: A DBA including a second ONU whose upstream transmission speed is a second speed different from the first speed.

[0007] The present disclosure can be realized not only as a system and device having the above-described characteristic configuration, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the system and device. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to realize the coexistence of PONs with different transmission speeds at low cost. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a network connection diagram showing an example of the overall configuration of a PON system. [Figure 2] FIG. 2 is an explanatory diagram showing wavelength allocations according to the IEEE standard for GE-PON, 10G-EPON, and 25G-EPON. [Figure 3] FIG. 3 is an explanatory diagram showing recommended wavelength allocations for GE-PON, 10G-EPON, and 25G-EPON. [Figure 4] FIG. 4 is a block diagram showing an example of the internal configuration of an OLT. [Figure 5] FIG. 5 is a time chart showing the correspondence between the operation timing of the first signal processing unit and the operation timing of the second signal processing unit. [Figure 6] FIG. 6 is a timing chart showing an example of allocation of DBA allocable periods. [Figure 7] FIG. 7 is an explanatory diagram showing variations in the discovery operation method. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Summary of Embodiments of the Present Disclosure> The following provides an outline of embodiments of the present disclosure. (1) The device of this embodiment is an OLT of a PON capable of optical communication at multiple types of upstream transmission speeds, and is equipped with a first signal processing unit that executes the first DBA described below, a second signal processing unit that executes the second DBA described below, and a DBA linkage unit that executes processing to exclusively link the allocable period of the first DBA and the allocable period of the second DBA. First DBA: DBA that includes the first ONU whose upstream transmission speed is the first speed Second DBA: A DBA including a second ONU whose upstream transmission speed is a second speed different from the first speed.

[0011] According to the OLT of this embodiment, the DBA linking unit executes a process of exclusively linking the allocatable period of the first DBA with the allocatable period of the second DBA, so that time division multiplexing in the upstream direction can be achieved without performing a comprehensive DBA targeting the first ONU and the second ONU. This eliminates the need to develop a new MAC chip for comprehensive DBA, and enables PONs with different transmission speeds to coexist at low cost.

[0012] (2) In the OLT of (1) above, the first ONU may be an ONU of a GE-PON or an ONU of a 10G-EPON. In this case, the target of the first DBA is a GE-PON ONU or a 10G-EPON ONU, so a PON system can be constructed in which a GE-PON or 10G-EPON selected as the first speed and a PON of the second speed coexist for one ODN.

[0013] (3) In the OLT of (2) above, the target of the first DBA may include other ONUs having an upstream transmission rate different from that of the first ONU. In this case, the first DBA targets two types of ONUs, so a triple coexistence PON system can be constructed in which three types of PONs coexist with one ODN.

[0014] (4) In the OLT of (3) above, the first ONU may be an ONU of GE-PON, the other ONU may be an ONU of 10G-EPON, and the second ONU may be an ONU of 25G-EPON. In this case, the first DBA targets two types of ONUs, so a triple-coexistence PON system can be constructed in which GE-PON, 10G-EPON, and 25G-EPON coexist for one ODN.

[0015] (5) In the OLTs described in (1) to (4) above, the linking process may be a process of setting the following conditions in the first signal processing unit and the second signal processing unit: Condition 1: The length of the allocation cycle for both DBAs must be the same. Condition 2: The sum of the allocation periods of both DBAs is equal to or less than the length of the allocation cycle. Condition 3: The assignment periods of both DBAs must be allocated without overlapping.

[0016] In this case, the process of setting the above conditions allows the allocation periods of both DBAs to be exclusively linked, so there is no need to synchronize the local times of the first and second signal processors for this linkage, which simplifies the process of exclusively linking the allocation periods.

[0017] (6) In the OLTs described in (1) to (4) above, the DBA control unit may execute a process of updating the ratio between the allocable period of the first DBA and the allocable period of the second DBA according to a ratio representing the uplink communication status. In this way, the ratio of the allocable period is updated in accordance with the ratio representing the uplink communication status, so that the uplink communication band can be changed appropriately.

[0018] (7) In the OLT of (6) above, the ratio representing the communication status may be the ratio between the number of ONUs to be allocated by the first DBA and the number of ONUs to be allocated by the second DBA. In this way, the ratio of the allocable periods is updated according to the number of installed ONUs, thereby ensuring equality of the upstream communication bands.

[0019] (8) In the OLT of (6) above, the ratio representing the communication status may be a ratio between a statistical value of an upstream transmission volume per unit time in the first signal processing unit and a statistical value of an upstream transmission volume per unit time in the second signal processing unit. In this way, the ratio of the allocable period is updated in accordance with the statistical value of the upstream transmission amount per unit time, thereby ensuring equality of the upstream communication band.

[0020] (9) A method according to one aspect of this embodiment is a bandwidth allocation method executed in the OLTs described above in (1) to (8). Therefore, the bandwidth allocation method of this embodiment has the same effects as the OLTs described above in (1) to (8).

[0021] <Details of the embodiment of the present disclosure> Hereinafter, details of embodiments of the present disclosure will be described with reference to the drawings. Note that at least some of the embodiments described below may be combined in any manner.

[0022] [Overall configuration of PON system] FIG. 1 is a network connection diagram showing an example of the overall configuration of a PON system 100. As shown in FIG. As shown in FIG. 1, the PON system 100 of this embodiment is a triple coexistence PON system in which three types of ONUs 20, 30, and 40 with different transmission speeds are connected to one OLT 10 via an ODN (Optical Distribution Network) 50.

[0023] Specifically, the ODN 50 includes a plurality of branch fibers 53 branched from a trunk fiber 51 via an optical splitter 52, the trunk fiber 51 is connected to the OLT 10, and the branch fibers 53 are connected to the ONUs 20, 30, and 40, respectively. 1 shows only one ONU 20, but multiple ONUs 20 may be connected. The same applies to ONUs 30 and 40 with other transmission speeds.

[0024] In the PON system 100 of this embodiment, for example, the ONU 20 is an ONU of GE-PON, the ONU 30 is an ONU of 10G-EPON, and the ONU 40 is an ONU of 25G-EPON. In the following description, among the upstream and downstream optical signals transmitted to the ODN 50 of the PON system 100, the upstream may be abbreviated as "US" and the downstream may be abbreviated as "DS".

[0025] [Wavelength allocation in case of triple coexistence] Incidentally, standardization of 25G-EPON has been completed by IEEE, and standardization of 50G-PON has been completed by ITU-T. It has been reported that triple PONs consisting of G-PON, XGS-PON, and 50G-PON will coexist among ITU-T PONs (Non-Patent Document 1). On the other hand, the coexistence of GE-PON, 10G-EPON, and 25G-EPON has not yet been reported for IEEE-based PONs, because GE-PONs use Fabry-Perot Laser Diodes (FP-LDs) for US and occupy the entire O-band.

[0026] GE-PON has become widespread in Japan, and 10G-EPON has recently been introduced. One OLT serves both 10G-EPON and GE-PON, and by using wavelength division multiplexing (WDM) for downstream transmission and time division multiplexing (TDM) for upstream transmission for 10G-EPON, it is possible for GE-PON and 10G-EPON to coexist on the same ODN. In contrast, 25G-EPON uses the O band for both upstream and downstream transmissions, making coexistence with GE-PON an issue.

[0027] That is, the DS wavelength band of 25G-EPON is 1356 to 1360 nm in the O band, which may interfere with the US wavelength band (1260 to 1360 nm) of GE-PON. Therefore, simply adopting WDM or TDM will not allow the two to coexist. It is possible to allocate 25G-EPON wavelengths to the C and L bands, but 25G transmission in the C / L bands has a large dispersion penalty.

[0028] For example, when NRZ (Non Return to Zero) modulation is used using a distributed feedback (DFB) laser integrated with an electroabsorption (EA) modulator, the dispersion penalty in 20 km transmission in the C band can be 5 dB or more (Non-Patent Document 2). However, if electrical dispersion compensation (EDC) is adopted, it is possible to transmit 25.78 Gbit / s over 30 km even in the C band (Non-Patent Document 3).

[0029] Therefore, if the DS wavelengths of 25G-EPON are allocated to the C / L band and WDM is used for downstream transmission and TDM is used for upstream transmission, it is thought that 25G-EPON can also coexist in an ODN where GE-PON and 10G-EPON coexist. Below, an example of wavelength allocation based on the above considerations will be explained with reference to Figures 2 and 3.

[0030] FIG. 2 is an explanatory diagram showing wavelength allocations according to the IEEE standard for GE-PON, 10G-EPON, and 25G-EPON. FIG. 3 is an explanatory diagram showing recommended wavelength allocations for GE-PON, 10G-EPON, and 25G-EPON.

[0031] As shown in Figure 2, the US wavelength band of GE-PON can vary between 1260 and 1360 nm depending on the operating temperature. This range interferes with the standard DS wavelength band of 25G-EPON. It is possible to narrow the US wavelength range of GE-PON and allocate the 25G DS wavelengths as per the standard, but narrowing the wavelength range requires narrowing the temperature range or using distributed feedback (DFB) lasers. Therefore, as shown in FIG. 3, in the PON system 100 of this embodiment, the DS wavelength band of 25G-EPON is changed to the C / L band.

[0032] However, it is necessary to avoid the 10G-EPON DS wavelength band (1575-1580nm) and the RF (Radio frequency) video wavelength band (1550-1560nm), with a guard band of approximately 15nm between the two. Therefore, the DS wavelength band for 25G-EPON is preferably either 1530 to 1535 nm or 1595 to 1625 nm. In this band, as mentioned above, a power budget that meets the specified requirements can be secured by electronic dispersion compensation (EDC).

[0033] From the above, in this embodiment, the US wavelength and DS wavelength of the PON system 100 are set, for example, as follows: Of course, the wavelengths below are just examples, and the DS wavelength of the ONU 40 may be any wavelength included in the C / L band. ONU20 US wavelength = 1310 nm DS wavelength=1490nm ONU30:US wavelength=1270nm DS wavelength=1577nm ONU40: US wavelength = 1270 or 1300 nm DS wavelength=1530nm

[0034] On the other hand, the communication frame structures of 1G / 10G-EPON and 25G-EPON are different, so the FEC methods are also different. For this reason, it is difficult to economically support three generations of PON communication frames with a single type of MAC chip. Therefore, in this embodiment, the coexistence of three generations of PON is enabled by controlling the DBA by a 1G / 10G-EPON MAC chip, which can synchronize the dynamic bandwidth allocation (DBA) cycle, and the DBA by a 25G-EPON MAC chip so that they are time-shared.

[0035] [OLT configuration example] FIG. 4 is a block diagram showing an example of the internal configuration of the OLT 10. As shown in FIG. In FIG. 4, solid arrows indicate "communication frames" (US or DS) exchanged within the OLT 10, and dashed arrows indicate "control signals" exchanged within the OLT 10. As shown in FIG. 4, the OLT 10 of this embodiment includes an optical transceiver 11, a first signal processing unit 12, a second signal processing unit 13, a DBA link unit 14, and a switch unit 15.

[0036] The optical transceiver 11 is a multi-rate optical transceiver capable of electrical-to-optical conversion and optical-to-electrical conversion at three or more transmission speeds. That is, the optical transceiver 11 has a transmitter 11T that converts 1G / 10G / 25G electrical signals into optical signals of the specified wavelengths shown in the figure, and a receiver 11R that converts optical signals of the specified wavelengths shown in the figure into 1G / 10G / 25G electrical signals.

[0037] Specifically, the transmitter 11T of the optical transceiver 11 converts the 1.25 Gbit / s electrical signal (downstream frame) input from the first signal processor 12 into a 1490 nm downstream optical signal, and sends this downstream optical signal to the ODN . Similarly, the transmitter 11T of the optical transceiver 11 converts the 10.31 Gbit / s electrical signal (downstream frame) input from the first signal processor 12 into a 1577 nm downstream optical signal, and sends this downstream optical signal to the ODN .

[0038] Furthermore, the transmitting unit 11T of the optical transceiver 11 converts the 25.78 Gbit / s electrical signal (downstream frame) input from the second signal processing unit 13 into a 15XX nm downstream optical signal, and sends this downstream optical signal to the ODN 50. The above "15XX nm" is set to any value included in the numerical range of the DS wavelength of 25G-EPON shown in FIG.

[0039] Meanwhile, the receiver 11R of the optical transceiver 11 converts the upstream optical signal of 1260 to 1360 nm into an electrical signal of each rate and outputs it. In this case, only the electrical signal corresponding to the rate of the upstream optical signal is meaningful, and electrical signals corresponding to other rates become noise or are masked. Note that "12YYnm" in FIG. 4 means any value included in the numerical range of the US wavelength of 25G-EPON shown in FIG.

[0040] The first signal processing unit 12 includes a MAC chip capable of frame processing in accordance with GE-PON and 10G-EPON. The MAC chip is configured by, for example, an SoC (System on a Chip) including at least one CPU (Central Processing Unit) and memory. The MAC chip of the first signal processing unit 12 may include an integrated circuit such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) in addition to or instead of a CPU.

[0041] The second signal processing unit 13 includes a MAC chip capable of frame processing in accordance with 25G-EPON. This MAC chip is also configured, for example, by an SoC including at least one CPU and memory. The MAC chip of the second signal processing unit 13 may include an integrated circuit such as an FPGA or an ASIC in addition to or instead of a CPU.

[0042] The DBA linking unit 14 is a controller that controls the operations of the first signal processing unit 12, the second signal processing unit 13, etc. The DBA linking unit 14 may be configured, for example, with at least one CPU and memory, but may also include an integrated circuit such as an FPGA or ASIC in addition to or instead of the CPU. The DBA linking unit 14 can exchange control signals with the optical transceiver 11, the first signal processing unit 12, and the second signal processing unit 13 by serial communication such as I2C (Inter-Integrated Circuit).

[0043] The switch unit 15 is an integrated circuit such as an LSI (Large Scale Integration) that has a relay function for the L2 layer and the L3 layer. The switch unit 15 has a plurality of Ethernet ports ("Ethernet" is a registered trademark). The first signal processing unit 12 is connected to a predetermined port among the plurality of Ethernet ports, and the second signal processing unit 13 is connected to another predetermined port. The switch unit 15 and the DBA link unit 14 may be implemented in a single integrated circuit such as an SoC.

[0044] Each of the signal processing units 12 and 13 can independently measure local time, and the first signal processing unit 12 can execute DBA (hereinafter referred to as "first DBA") for the ONUs 20 and 30 under its control at predetermined cycles. The second signal processing unit 13 can also perform DBA (hereinafter referred to as "second DBA") for the ONUs 40 under its control at predetermined cycles. Performing DBA at predetermined cycles (periods) facilitates bandwidth control based on QoS (Quality of Service), including fixed bandwidth.

[0045] The DBA performed by each of the signal processors 12 and 13 includes, for example, the following processes. Process 1: Wait for a bandwidth request (report) from the ONU. Process 2: After receiving the report, the ONU starts the process of allocating upstream transmission time. Process 3: In the allocation process, the upstream transmission time (bandwidth) to be allocated to each ONU is calculated based on the report and QoS information. Process 4: A transmission permission including the upstream transmission time calculated by the allocation process (a downstream gate including a transmission permission for a report) is transmitted to each ONU.

[0046] In the DBA described above, the data reception in the previous cycle and the allocation process in the current cycle overlap, so the upstream transmission bandwidth can be used efficiently. However, the transmission permission (downstream gate) must be transmitted at least the RTT (Round Trip Time) before the transmission time of the transmission permission. Hereinafter, the time period during which each signal processor 12, 13 of the OLT can detect an upstream frame transmitted by each ONU in accordance with the transmission permission (downstream gate) of the OLT will be referred to as an "allocatable period."

[0047] However, if the allocable period of the first DBA and the allocable period of the second DBA overlap, the US transmission time of ONUs 20 and 30 and the US transmission time of ONU 4 may overlap, and upstream optical signals may collide in the trunk fiber 51. In the OLT 10 of this embodiment, the DBA linking unit 14 transmits control signals S1 and S2 to the signal processing units 12 and 13, respectively, to set predetermined parameters, and performs processing to exclusively link the allocable period of the first DBA and the allocable period of the second DBA. Such parameter setting will be described below.

[0048] [Allocation period coordination processing by DBA coordination unit] FIG. 5 is a time chart showing the operation timing of the first signal processing unit 12 and the operation timing of the second signal processing unit 13 in correspondence with each other. Below, the definitions of the parameters in FIG. 5 will be explained, followed by an example of processing for exclusively linking the allocatable periods of both DBAs (hereinafter referred to as "linking processing").

[0049] (Parameter definition) “tn”: local time kept by the first signal processing unit 12. “tm”: local time measured by the second signal processing unit 13. “n”: An identification value of the allocation cycle that the first signal processing unit 12 counts independently. “m”: An identification value of the allocation cycle that the second signal processing unit 13 counts independently. “Tn”: the start time of the allocation cycle m determined by the first signal processing unit 12. “Tm”: the start time of the allocation cycle n determined by the second signal processing unit 13.

[0050] "TR1": A period that can be allocated by the first signal processing unit 12 to receive reports from the ONUs 20 and 30. Hereinafter, this will be referred to as "report allocation period TR1." "TD1": A period that can be allocated by the first signal processing unit 12 to receive upstream data from the ONUs 20 and 30. Hereinafter, this will be referred to as "data allocation period TD1."

[0051] "TE1": The processing period of the first DBA. Specifically, the processing period TE1 of the first DBA is the period from a predetermined start point after all report frames arrive, through bandwidth allocation processing for each ONU 20, 30, to transmitting a transmission permission (downstream gate) to each ONU 20, 30.

[0052] "O1": the interval (offset) between the time of transmission permission (downstream gate) to the ONUs 20 and 30 and the time of permission for upstream transmission to the ONUs 20 and 30. The offset O1 must have a time length equal to or greater than the RTT. Therefore, when the offset O1 becomes equal to or less than the RTT, the first signal processing unit 12 can delay the permitted time for uplink transmission so as to prevent this from happening.

[0053] "TR2": a period that can be allocated by the second signal processing unit 13 to receive a report from the ONU 40. Hereinafter, this will be referred to as "report allocation period TR2." "TD2": A period that can be allocated by the second signal processing unit 13 to receive upstream data from the ONU 40. Hereinafter, this will be referred to as "data allocation period TD2."

[0054] "TE2": The processing period of the second DBA. Specifically, the second data processing period TE2 is the period from a predetermined start point after all report frames have arrived, through bandwidth allocation processing for each ONU 40, to sending a transmission permission (downstream gate) to each ONU 40.

[0055] "O2": the interval (offset) between the time of transmission permission (downstream gate) to the ONU 40 and the time of permission for upstream transmission to the ONU 40. The offset O2 must have a time length equal to or greater than the RTT. Therefore, when the offset O2 becomes equal to or less than the RTT, the second signal processing unit 13 delays the permitted time for uplink transmission so as to prevent this from happening.

[0056] In addition, when the second signal processing unit 13 receives a command to shift the allocation cycle from the DBA linkage unit 14 prior to the processing period TE2 of the allocation cycle m-1, it can also delay the start time Tm-1 of the allocation cycle m-1 by the amount of time specified in the command. This allows the allocation periods TR2 and TD2 of allocation cycle m-1 to be positioned after the time specified by the command.

[0057] (Conditions for collaboration processing) The above-described cooperation process is a process that prevents overlap between the allocatable periods TR1, TD1 of the first DBA and the allocatable periods TR2, TD2 of the second DBA, assuming that the time lengths of the two allocation cycles m, n match. Alternatively, the cooperative process is a process that makes each of the allocable periods TR1, TD1, TR2, and TD2 available for dense allocation even when the bandwidth request is sufficiently large.

[0058] To achieve such an allocation state without temporal overlap (hereinafter referred to as a "cooperative state"), the sum of the allocable times TR1, TD1, TR2, TD2 of both DBAs is made equal to or less than the cycle length of allocation cycle m, n, and the arrangement within allocation cycle m, n is adjusted so that the allocable periods TR1, TD1, TR2, TD2 do not overlap. In other words, the cooperation state can be said to be a state that satisfies the following "cooperation conditions."

[0059] Partnership conditions: Condition 1: The length of the allocation cycles m and n of both DBAs must match. Condition 2: The sum of the allocation times TR1, TD1, TR2, and TD2 of both DBAs is equal to or less than the time length of allocation cycle m and n. Condition 3: The allocation periods TR1, TD1, TR2, and TD2 of both DBAs must be arranged without overlapping (specifically, the phases of allocation cycles m and n must be adjusted so that there is no overlap).

[0060] Therefore, the operations required to satisfy the coordination conditions (such as parameter setting and command transmission to each of the signal processing units 12 and 13: hereinafter referred to as "coordinated operations") can be organized for each of the signal processing units 12 and 13 as follows:

[0061] (Cooperative operation for first signal processing unit) The cooperative operation for the first signal processing unit 12 includes the following parameter settings. 1) Setting the cycle length of allocation cycle n The cycle length can be set by a control signal S1 from the DBA linking unit 14, but may also be set by a command input from the communications manager.

[0062] 2) Setting the allocation period In this embodiment, the first signal processing unit 12 is an existing chip and therefore does not have the function of directly defining the allocable periods TR1 and TD1 in the allocation cycle n. However, if the fixed bandwidth of the dummy ONU is set in the first signal processing unit 12, the allocable periods TR1 and TD1 can be indirectly set in the first signal processing unit 12.

[0063] That is, since the fixed bandwidth of the dummy ONU defines the "allocation prohibition time" in the allocation cycle n, the value obtained by subtracting the allocation prohibition time from the cycle length is equivalent to the allocation period TR1, TD1. The setting of the fixed bandwidth can also be executed by the control signal S1 from the DBA linking unit 14, but may also be executed by command input by the communications manager.

[0064] Since the report allocation period TR1 can be calculated from the number of ONUs 20 and 30, the DBA linking unit 14 can estimate the report allocation period TR1 based on the number of ONUs 20 and 30 currently connected. However, since the time value of TR1 is relatively short, the maximum length may be secured from the maximum number of connections of the ONUs 20 and 30. Therefore, it is not necessary to set the report allocatable period TR1 as a parameter.

[0065] 3) Allocation of allocation period In the first DBA, the first signal processing unit 12 performs bandwidth allocation (allocation in which the transmission time of the dummy ONU is set first) to give priority to transmission of a fixed bandwidth to the dummy ONU. As a result, in allocation cycle n, the report allocation period TR1, allocation prohibition period, and data allocation period TD1 are arranged in this order.

[0066] As will be described later, in this embodiment, the second signal processing unit 13 has a function of adjusting the phase of allocation cycle m. Therefore, the first signal processing unit 12 does not need to adjust the phase of allocation cycle n. However, allocation cycle n may also be delayed for the first DBA. For example, if the first signal processing unit 12 can set the RTT with the ONUs 20 and 30, it is possible to set a larger RTT and shift the allocation cycle n. In this case, in the first DBA, the allocation permission time is delayed by an offset O1 that is larger than the RTT.

[0067] (Cooperative operation for second signal processing unit) The linked operation for the second signal processing unit 13 includes the following parameter settings. 4) Setting the cycle length of the allocation cycle m The cycle length can be set by a control signal S2 from the DBA linking unit 14, but may also be set by a command input from the communications manager.

[0068] 5) Setting the allocation period In this embodiment, the second signal processing unit 13 is a new chip, and therefore has the function of directly defining the allocable periods TR2 and TD2 in the allocation cycle m (setting the allocation prohibited period). The setting of the allocable periods TR2 and TD2 can be performed by a control signal S2 from the DBA linking unit 14, but may also be performed by a command input by the communications manager.

[0069] Here, if the report allocation period TR2 and data allocation period TD2 in one allocation cycle m are a continuous time range, the second signal processing unit 13 only needs to determine the classification of reports and data in each allocation period TR2, TD2, and the DBA linking unit 14 does not need to be involved. Therefore, as in the case of the first DBA, there is no need to set the report allocation period TR2 as a parameter.

[0070] 6) Adjustment of allocation period As mentioned above in 5), if the allocation periods TR2 and TD2 are a series of time ranges in one allocation cycle m, then the time ranges can be adjusted to match the allocation prohibition period of the first DBA (time periods other than TR1 and TD1 in allocation cycle n). The operation of shifting the allocation cycle m of the second DBA can be performed by adjusting the RTT as described above, but it is preferable that the second signal processing unit 13 receives and executes a command to shift the allocation cycle m. Such a command can be executed by a control signal S2 from the DBA linking unit 14.

[0071] Normally, the second signal processing unit 13 sets the end time of a given allocation cycle m-1 as the start time of the next allocation cycle m, but upon receiving the above command, the second signal processing unit 13 delays the start time Tm of the next allocation cycle m by the amount of time specified in the command. For example, the DBA cooperation unit 14 deductively calculates the designated time to be instructed to the second signal processing unit 13 based on the phase difference between the allocation cycles m and n obtained by snooping the operations of both signal processing units 12 and 13.

[0072] The above-mentioned designated time may be calculated by trial and error. Specifically, the DBA linking unit 14 may acquire the PON reception error frequency at each designated time from the second signal processing unit 13 while gradually changing the designated time to shift the phase. In this case, the DBA linking unit 14 determines whether the state is approaching or moving away from a state where appropriate PON reception is possible (optimum point), and adjusts the specified time accordingly.

[0073] [Adjusting the optical transceiver's reception status] As shown in FIG. 4, the DBA linking unit 14 can transmit the next control signal R1 to the optical transceiver 11, and the first signal processing unit 12 can transmit the next control signal R2 to the optical transceiver 11. R1: Control signal to select 25G R2: A control signal that indicates the selection of either 1G or 10G.

[0074] Specifically, the DBA linking unit 14 transmits the control signal R1 to the optical transceiver 11 in accordance with the start of the allocable period of the second DBA. Upon receiving the control signal R1, the optical transceiver 11 switches the receiving configuration of the receiver 11R (e.g., amplifier gain according to the transmission speed, clock recovery operation, decoding operation, etc.) to 25G, thereby ensuring reliable reception of 25G upstream optical signals.

[0075] Furthermore, the first signal processing unit 12 transmits a control signal R2 to the optical transceiver 11 in synchronization with the reception timing of an upstream optical signal (1G or 10G) whose transmission is permitted by the first DBA. Upon receiving the control signal R2, the optical transceiver 11 switches the receiving state of the receiver 11R to either 1G or 10G as instructed by the control signal R2, thereby ensuring reliable reception of 1G or 10G upstream optical signals.

[0076] In switching the receiving mode as described above, the optical transceiver 11 first determines whether to switch the receiving mode to 25G based on the control signal R1, and if the determination result is negative, selects whether to switch to a 1G or 10G receiving mode based on the control signal R2. Note that the control signals R1 and R2 may be omitted from the configuration example in Fig. 4. In a modified example in which the control signals R1 and R2 are omitted, the optical transceiver 11 is configured to output electrical signals corresponding to the received optical signals to the 1G, 10G, and 25G signal lines, and the receiving side of the electrical signals determines whether or not to demodulate the signals.

[0077] [Example of DBA allocation period] FIG. 6 is a timing chart showing an example of allocation of DBA allocable periods. In Fig. 6, the horizontal axis represents time. Fig. 6 illustrates a case where the start time of the allocatable period TD2 of the second DBA is T3 and the end time is T4. In this case, the second signal processing unit 13 (specifically, the 25G MAC chip) is only capable of PON data communication with the ONU 40 during the allocable period TD2 (=T4-T3), and does not perform PON data communication with the ONU 40 during other time periods.

[0078] Similarly, FIG. 6 illustrates a case where the start time of the allocable period TD1 of the first DBA is T1 and the end time is T2. The first signal processing unit 12 (specifically, a 1G / 10G MAC chip) is capable of PON data communication with ONUs 20 and 30 only during the allocable period TD1 (=T2-T1), and does not perform PON data communication with ONUs 20 and 30 during other time periods.

[0079] As shown in Figure 6, the status of the control signal R1 is synchronized with the allocation period TD1 and the allocation period TD2, so the optical transceiver 11 prepares for reception at 1G / 10G during the allocation period TD1 and prepares for reception at 25G during the allocation period TD2. The switching between the 1G and 10G reception modes is performed by the control signal R2, so that the optical transceiver 11 can receive upstream optical signals with appropriate gain and bandwidth.

[0080] 6, the first signal processing unit 12 may perform discovery on the ONUs 20 and 30 (the hatched area in FIG. 6) during an allocable period TD1 of the first DBA assigned to the first signal processing unit 12. Similarly, the second signal processing unit 13 may perform discovery on the ONU 40 during an allocable period TD2 of the second DBA assigned to the second signal processing unit 13. The above discovery is performed by transmitting a gate that permits registration requests during the allocation periods TD1 and TD2 to the ONUs 20, 30, and 40 in advance.

[0081] [Allocation period update process] In the OLT 10 of this embodiment, the DBA collaborating unit 14 may update the ratio RT (=TD1 / TD2) between the allocable period TD1 and the allocable period TD2 according to the ratio representing the communication status of the US. For example, the ratio RT representing the communication status can be defined by the following formula (1).

[0082] RT=NC1 / NC2 ……(1) NC1: Number of ONUs (20, 30) connected to ODN (50) NC2: Number of ONU40 connections connected to ODN50 The connection numbers NC1 and NC2 may be either declared values ​​notified to the DBA linkage unit 14 by each signal processing unit 12 and 13 via serial communication, or set values ​​transmitted to the DBA linkage unit 14 from the telecommunications carrier's management terminal (not shown).

[0083] If formula (1) is employed, when the number of connections NC2 of ONUs 40 is small, the allocable period TD1 becomes long, and sufficient upstream bandwidth is secured for 1G / 10G-EPON ONUs 20 and 30. Thereafter, when the number of connections NC2 of ONUs 40 increases, the allocable period TD1 decreases and the allocable period TD2 becomes longer, so that an upstream bandwidth is secured for the 25G-EPON ONUs 50 as well.

[0084] Furthermore, the ratio RT representing the communication situation may be defined by the following equation (2). RT=VC1 / VC2 ……(2) VC1: Statistical value of the upstream transmission amount per unit time in the first signal processing unit 12 VC2: Statistical value of the upstream transmission amount per unit time in the second signal processing unit 13

[0085] The upstream transmission volume may be, for example, the number of frames or the amount of data passing through the switch unit 15 in a predetermined unit time (for example, one day). The statistical values ​​VC1 and VC2 are statistical representative values ​​of the upstream transmission volume in a unit time, and may be, for example, the average value, moving average value, or median value of the upstream transmission volume.

[0086] By employing formula (2), when the statistical value VC1 of the upstream transmission amount of ONU 40 is low, the allocable period TD1 becomes longer, and a sufficient upstream bandwidth is secured for 1G / 10G-EPON ONUs 20 and 30. Thereafter, when the statistical value VC2 of the upstream transmission amount of ONU 40 increases, the allocable period TD1 decreases and the allocable period TD2 becomes longer, so that an upstream bandwidth is secured for ONU 50 of 25G-EPON as well.

[0087] [Discovery operation method] FIG. 7 is an explanatory diagram showing variations in the discovery operation method. The parameters in Figure 7 have the following meanings: C: Common cycle time D: Discovery Period C0: Data cycle C1: Discovery cycle for ONU20,30 of 1G / 10G-EPON C2: Discovery cycle for ONU40 of 25G-EPON

[0088] Pattern 1 in FIG. 7 is an operation method in which discovery period D is included in allocation periods TD1 and TD2. In this case, each of the signal processors 12 and 13 allocates a discovery period D within the allocable periods TD1 and TD2. Such a short discovery period D is suitable when the distances between the OLT 10 and the ONUs 20, 30, and 40 are known in advance.

[0089] Pattern 2 in FIG. 7 is an operation method in which the common cycle time C is separated into a data cycle C0 and two types of discovery cycles C1 and C2. In pattern 2, the first signal processing unit 12 sets a predetermined common cycle C between multiple cycles C0 as cycle C1, and the second signal processing unit 13 sets cycle C2 to all or part of cycle C1. The part may be a partial section of cycle C1, or the entire cycle that occurs once every few cycles of cycle C1, or a combination of these.

[0090] Under the above operating conditions, in cycle C2, a collision may occur between the connection requests from ONUs 20 and 30 and ONU 40, but it is believed that a retry will eventually enable connection. Therefore, the DBA link unit 14 prepares for a connection request from the ONU 40 by setting the control signal R1 to true for the optical transceiver 11 during the period to which the cycle C2 is assigned.

[0091] [Other Modifications] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configurations described in the claims.

[0092] In the above-described embodiment, in addition to the two signal processing units 12 and 13, a signal processing unit including a MAC chip that performs DBA (hereinafter referred to as "third DBA") for ONUs with transmission speeds exceeding 25G may be provided. In this case, if the DBA linking unit 14 is provided with a function for allocating the allocable periods of the first DBA, second DBA, and third DBA in a time-division manner, a quattro-coexisting PON system in which four types of PONs coexist can be constructed.

[0093] In the above-described embodiment, the MAC chip of the first signal processing unit 12 may be a chip that supports only one of GE-PON and 10G-EPON. That is, the PON system 100 of this embodiment may be a dual coexistence PON system in which GE-PON and 25G-EPON coexist, or may be a dual coexistence PON system in which 10G-EPON and 25G-EPON coexist. [Explanation of symbols]

[0094] 10 OLT 11 Optical transceiver 11T transmitter 11R Receiver 12 First signal processing section 13 Second signal processing section 14 DBA Collaboration Department 15 Switch section 20 ONU (1st ONU: GE-PON ONU) 30 ONUs (other ONUs: 10G-EPON ONUs) 40 ONU (2nd ONU: 25G-EPON ONU) 50 ODN 51 Trunk Fiber 52 Optical Splitter 53 Branch Fiber 100 PON Systems

Claims

1. A PON OLT capable of optical communication at a plurality of upstream transmission speeds, a first signal processing unit that executes the following first DBA; a second signal processing unit that executes the second DBA described below; and a DBA linking unit that executes a process of exclusively linking the allocatable period of the first DBA and the allocatable period of the second DBA. First DBA: DBA in which the first ONU whose upstream transmission speed is the first speed is included as a target. Second DBA: A DBA including a second ONU whose upstream transmission speed is a second speed different from the first speed.

2. The OLT according to claim 1 , wherein the first ONU is an ONU of a GE-PON or an ONU of a 10G-EPON.

3. The subject of the first DBA is: The OLT according to claim 2 , further comprising another ONU having an upstream transmission rate different from that of the first ONU.

4. The first ONU is an ONU of a GE-PON; the other ONU is an ONU of 10G-EPON, The OLT according to claim 3 , wherein the second ONU is an ONU of 25G-EPON.

5. The linking process includes:

5. The OLT according to claim 1, wherein the processing is to apply settings to the first signal processing unit and the second signal processing unit that satisfy the following conditions: Condition 1: The length of the allocation cycles of both DBAs must be the same. Condition 2: The sum of the allocable periods of both DBAs is equal to or less than the length of the allocation cycle. Condition 3: The allocation periods of both DBAs must be arranged without overlapping.

6. The DBA linkage unit 5. The OLT according to claim 1, further comprising: a process for updating the ratio between the allocable period of the first DBA and the allocable period of the second DBA according to a ratio representing the upstream communication status.

7. The ratio representing the communication status is: The OLT according to claim 6 , wherein the ratio is a ratio between the number of ONUs to be allocated to the first DBA and the number of ONUs to be allocated to the second DBA.

8. The ratio representing the communication status is:

7. The OLT according to claim 6, wherein the ratio is a ratio between a statistical value of an upstream transmission amount per unit time in the first signal processing unit and a statistical value of an upstream transmission amount per unit time in the second signal processing unit.

9. A bandwidth allocation method in an OLT of a PON capable of optical communication at a plurality of types of upstream transmission speeds, comprising: A step of executing a process of exclusively linking the allocable period of the first DBA described below with the allocable period of the second DBA described below; performing the first DBA during an allocable period of the first DBA, and performing the second DBA during an allocable period of the second DBA. First DBA: DBA in which the first ONU whose upstream transmission speed is the first speed is included as a target. Second DBA: A DBA including a second ONU whose upstream transmission speed is a second speed different from the first speed.

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