OLT and PON systems

Abstract

To provide an OLT and the like that achieve low delay guarantee.SOLUTION: An OLT used in a PON using an optical splitter has a collection unit and a processing unit. The collection unit collects time information of arrival of packets from an ONU and data volume information of the packets. The processing unit determines transmission timing of the ONU on the basis of transmission timing information assigned to the ONU, the time information, and the data volume information.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical line terminal (OLT) and a PON system. [Background technology]

[0002] Key requirements for 5G include new concepts such as high capacity, low latency, and multiple connections, which are becoming increasingly important for B5G (Beyond 5G) and 6G. Low latency in particular is a concept that has not been given much consideration in the past, and even with existing networks, there are many cases where low latency data transmission cannot be guaranteed.

[0003] An example of a network that cannot guarantee low data latency is a PON (Passive Optical Network). Here, the mechanism of a TDM (Time Division Multiplexing)-PON will be explained. Fig. 9A is an explanatory diagram showing an example of downstream traffic in a PON system 100, and Fig. 9B is an explanatory diagram showing an example of upstream traffic in the PON system 100.

[0004] The PON system 100 includes a plurality of subscriber terminals 110, a plurality of ONUs (Optical Network Units) 120, an optical splitter 130, and an OLT (Optical Line Terminal) 140.

[0005] The ONU 120 is a subscriber-side optical terminal device that connects to the subscriber terminal 110 that it accommodates. The ONU 120 optically converts packets from the subscriber terminal 110 that it accommodates, and outputs the optically converted packets to the optical splitter 130. The ONU 120 also converts packets from the optical splitter 130 into electrical signals, refers to the headers of the electrically converted packets, discards packets not addressed to itself, and receives arriving packets addressed to itself.

[0006] The optical splitter 130 multiplexes the packets from the ONUs 120 and outputs the multiplexed packet to the OLT 140. The optical splitter 130 also copies the packets from the OLT 140 and splits and outputs the copied packets to the ONUs 120.

[0007] The OLT 140 is an optical terminal device on the central office side of a telecommunications carrier, which connects to a core network (not shown). The OLT 140 outputs packets from the optical splitter 130 to the core network, and also outputs packets from the core network to the optical splitter 130.

[0008] 9A, for downstream traffic from OLT 140 to ONU 120, optical splitter 130 copies packets from OLT 140 and outputs the copied packets to all ONUs 120. Each ONU 120 has a filtering function, refers to the packet header, discards all arriving packets other than those addressed to itself, and receives arriving packets addressed to itself.

[0009] 9B, each ONU 120 outputs packets in a time-division manner. That is, each ONU 120 can output packets in the bandwidth allocated to it, thereby avoiding packet collisions between ONUs 120.

[0010] Furthermore, TDM-PON employs a fixed bandwidth allocation (FBA) scheme in which a fixed bandwidth is allocated to each ONU 120 in advance. Fig. 10 is an explanatory diagram showing an example of the bandwidth allocated to each ONU 120 using the FBA scheme. Assume that the ONUs 120 include, for example, four ONUs 120 numbered #1 to #4. Assume that the OLT 140 allocates a first bandwidth to the ONU 120 numbered #1, a second bandwidth to the ONU 120 numbered #2, a third bandwidth to the ONU 120 numbered #3, and a fourth bandwidth to the ONU 120 numbered #4. Assume that, during a first time period, for example, the ONUs 120 numbered #1, #2, and #3 have output packets, and during a second time period, the ONUs 120 numbered #1 and #2 have output packets, and the ONUs 120 numbered #1, #2, #3, and #4 have output packets. That is, it is assumed that there are no output packets from ONU 120 #4 during the first time period, and there are no output packets from ONUs 120 #3 and #4 during the second time period.

[0011] In the FBA method, although a fixed bandwidth is allocated to each ONU 120, there are no output packets from ONU 120 #4 during the first time period, and there are no output packets from ONU 120 #3 and #4 during the second time period, resulting in unused and wasted bandwidth.

[0012] To avoid unused and wasted bandwidth, a known method is the Dynamic Bandwidth Allocation (DBA) method, which dynamically changes the bandwidth allocated to each ONU 120. In DBA, each ONU 120 notifies the OLT 140 of the amount of data awaiting transmission, which is packets stored in its own buffer. The OLT 140 then adjusts the bandwidth allocated to each ONU 120 based on the amount of data awaiting transmission for each ONU 120. Figure 11 is an explanatory diagram showing an example of the bandwidth allocated to each ONU 120 using the DBA method. Assume that ONUs 120 #1, #2, and #3 have output packets in a first time slot, ONUs 120 #1 and #2 have output packets in a second time slot, and ONUs 120 #1, #2, #3, and #4 have output packets in a third time slot.

[0013] The OLT 140 receives a transmission request (REPORT) including the amount of data waiting to be transmitted from each ONU 120, and acquires the amount of data waiting to be transmitted from each ONU 120 from the received transmission request. The OLT 140 calculates an allocation bandwidth to be allocated to each ONU 120 based on the amount of data waiting to be transmitted from each ONU 120. The OLT 140 then dynamically allocates an allocation bandwidth for each time period to each ONU 120 based on the calculated allocation bandwidth.

[0014] That is, the OLT 140 allocates available bandwidth to the ONUs 120 #1, #2, and #3 in the first time period, allocates available bandwidth to the ONUs 120 #1 and #2 in the second time period, and allocates available bandwidth to the ONUs 120 #1, #2, #3, and #4 in the third time period. As a result, it is possible to suppress the generation of unused bandwidth in the PON system 100. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] US Patent Application Publication No. 2020 / 0092622 [Patent Document 2] Japanese Patent Application Publication No. 2019-149738 [Patent Document 3] Japanese Patent Application Publication No. 2018-74513 [Patent Document 4] US Patent Application Publication No. 2022 / 0123837 Summary of the Invention [Problem to be solved by the invention]

[0016] However, in a PON system 100 that employs the DBA method, it takes time for communications such as transmission requests (REPORT) and responses (GATE) between the ONUs 120 and the OLT 140, and for calculations of allocated bandwidth in the OLT 140. Therefore, because of this time required, the PON system is not suitable for low-latency use cases that require low latency without using wireless, such as remote medical care and autonomous driving.

[0017] Therefore, there is a demand for a PON system that can ensure low latency even in general-purpose low-latency use cases, without requiring special interfaces or protocols, while still using the mechanisms of existing PON systems.

[0018] One aspect of the present invention is to provide an OLT or the like that can ensure low latency in a PON system. [Means for solving the problem]

[0019] An OLT according to one embodiment is used in a PON using an optical splitter. The OLT includes a collection unit and a processing unit. The collection unit collects time information of arrival of packets from ONUs and data volume information of the packets. The processing unit determines the transmission timing of the ONUs based on the transmission timing information assigned to the ONUs, the time information, and the data volume information. [Effects of the Invention]

[0020] According to one aspect, it is possible to ensure low latency in a PON system. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an explanatory diagram showing an example of a PON system according to this embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of an OLT. [Figure 3] FIG. 3 is an explanatory diagram showing an example of a group of intermediate packets and a group of leading packets. [Figure 4]FIG. 4 is an explanatory diagram showing an example of allocation timing before allocation of an ONU requiring low delay. [Figure 5] FIG. 5 is an explanatory diagram showing an example of allocation timing before and after allocation of an ONU requiring low delay. [Figure 6] FIG. 6 is a flow diagram showing an example of the processing operation of the OLT related to the allocation process. [Figure 7] FIG. 7 is a flow diagram showing an example of the processing operation of the OLT related to the determination processing. [Figure 8] FIG. 8 is an explanatory diagram showing an example of the results of comparison of delay, jitter, and the presence or absence of unused bandwidth in this embodiment, the DBA method, and the FBA method. [Figure 9A] FIG. 9A is an explanatory diagram showing an example of downstream traffic in a PON system. [Figure 9B] FIG. 9B is an explanatory diagram showing an example of upstream traffic in a PON system. [Figure 10] FIG. 10 is an explanatory diagram showing an example of the bandwidth allocated to each ONU in the FBA system. [Figure 11] FIG. 11 is an explanatory diagram showing an example of the bandwidth allocated to each ONU in the DBA system. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the OLT and the like disclosed in the present application will be described in detail with reference to the drawings. Note that the disclosed technology is not limited to each embodiment. Furthermore, the embodiments shown below may be combined as appropriate within the scope that does not cause contradictions. [Example]

[0023] 1 is an explanatory diagram showing an example of a PON system 1 according to this embodiment. The PON system 1 shown in FIG. 1 includes a plurality of first terminals 2, a plurality of ONUs (Optical Network Units) 3, an optical splitter 4, an OLT (Optical Line Terminal) 5, a core network 6, and a plurality of second terminals 7.

[0024] The first terminal 2 is a subscriber-side terminal device that is communicatively connected to the ONU 3. The ONU 3 is a subscriber-side optical terminal device that is communicatively connected to the first terminal 2. For ease of explanation, it is assumed that there are, for example, N ONUs 3, such as ONU 3 #1, ONU 3 #2, ONU 3 #3, and ONU 3 #N.

[0025] The ONU 3 optically converts packets received from the first terminal 2 it accommodates, and outputs the optically converted packets to the optical splitter 4. The ONU 3 also electrically converts the packets received from the optical splitter 4, refers to the headers of the electrically converted arriving packets, discards arriving packets not addressed to itself, and receives arriving packets addressed to itself.

[0026] Furthermore, when ONU3 receives a packet from the first terminal 2 within the allocation timing assigned to it by OLT 5, it outputs the received packet to OLT 5 via the optical splitter 4. On the other hand, when ONU3 receives a packet from the first terminal 2 outside its allocation timing, it buffers the received packet. Then, when its allocation timing arrives, ONU3 outputs the buffered packet from the first terminal 2 to OLT 5 via the optical splitter 4.

[0027] The optical splitter 4 is placed between N ONUs 3 and the OLT 5, combines optical packet signals from each ONU 3, and outputs the combined optical packet signal to the OLT 5. The optical splitter 4 copies the optical signal from the OLT 5, and demultiplexes and outputs the copied optical signal to each ONU 3.

[0028] The OLT 5 is disposed between the core network 6 and the optical splitter 4, and is an optical terminal device on the carrier side of the core network 6. The OLT 5 outputs packets from the optical splitter 4 to the core network 6, and also outputs packets from the core network 6 to the optical splitter 4.

[0029] Note that traffic from ONU 3 to OLT 5 is referred to as upstream traffic, and traffic from OLT 5 to ONU 3 is referred to as downstream traffic. The PON system 1 of this embodiment has a mechanism for achieving low packet latency for upstream traffic on an ONU 3 basis. Packets requiring low latency include, for example, periodic communication packets that flow between a first terminal 2, such as an operation terminal that remotely controls a medical device, and a second terminal 7, such as a medical device. For example, the first terminal 2 remotely controls the second terminal 7 via ONU 3 → optical splitter 4 → OLT 5 → core network 6.

[0030] Fig. 2 is a block diagram showing an example of the OLT 5. The OLT 5 shown in Fig. 2 includes an opto-electrical conversion unit 11, a PON physical layer 12, a PON MAC 13, a NW interface 14, a collection unit 15, and a CPU (Central Processing Unit) 16.

[0031] The photoelectric conversion unit 11 is connected to the optical fiber of the PON that is connected to the optical splitter 4, and performs electrical conversion of packets from the ONU 3 and optical conversion of packets to be sent to the ONU 3. The PON physical layer 12 performs physical layer processing on packets received from the ONU 3 and also performs physical layer processing on packets to be sent to the ONU 3. The physical layer processing is based on a PON standard such as IEEE802.3ah.

[0032] The PONMAC 13 performs MAC layer processing on packets from the ONUs 3, and also performs MAC layer processing on packets to the ONUs 3. The MAC layer processing is based on a PON standard such as IEEE802.3ah. The MAC layer processing is, for example, processing that executes instructions for allocation timing such as a transmission start time, a transmission amount, an allocated bandwidth, and an allocated time for each ONU 3. The NW interface 14 is a communication interface that connects to the core network 6.

[0033] When an ONU 3 is a target for which low delay is required, the collection unit 15 monitors the upstream traffic from the ONU 3 to the OLT 5, and collects packet information of packets arriving from each ONU 3, such as the arrival time and data amount.

[0034] The CPU 16 is an example of a processing unit, and includes a discrimination unit 16A, an estimation unit 16B, a calculation unit 16C, and a control unit 16D. The discrimination unit 16A executes a discrimination process to determine whether an arriving packet is a first packet group or an intermediate packet group based on the allocation timing of the ONU 3 requiring low latency and the arrival time and data amount of the arriving packet from the ONU 3 requiring low latency collected by the collection unit 15. The allocation timing is, for example, an allocation time and a transmission start time. The allocation time is a time period that can be used for packet communication of the ONU 3 in upstream traffic. The transmission start time is the time at which packet communication of the ONU 3 in upstream traffic starts.

[0035] Here, the head packet group and the midway packet group will be explained. Fig. 3 is an explanatory diagram showing an example of the midway packet group and the head packet group. In the example shown in Fig. 3, for example, the allocation time of the allocation timing of ONU3 #3 is followed by the allocation time of the allocation timing of ONU3 #1, and then the allocation time of the allocation timing of ONU3 #2. The allocation time is a period allocated to ONU3 itself, during which arriving packets arriving at ONU3 can be preferentially output to OLT5.

[0036] When focusing on the allocated time of ONU3 #1, the group of arriving packets that arrive in a burst immediately after the start of the allocated time is considered to be the first group of packets. In contrast, the group of arriving packets that arrive discretely during the allocated time, excluding immediately after the start of the allocated time, is considered to be the intermediate group of packets.

[0037] The first group of packets that arrive in a burst immediately after the start of the allocation time of ONU3 #1 can be said to be arriving packets that arrived at ONU3 #1 from the first terminal 2 #1 during the allocation time of other ONU3 #2 and #3, and were buffered at ONU3 #1. In other words, the first group of packets can be assumed to be arriving packets that are buffered and are output preferentially from ONU3 #1 to OLT5 as their allocation time arrives. Therefore, the first group of packets can be said to be arriving packets that have a large delay and are not guaranteed to have low delay.

[0038] Furthermore, the group of intermediate packets that arrive discretely during the allocated time can be estimated as packets arriving from the first terminal 2 of #1, which are not buffered at the ONU 3 of #1 and arrive directly from the ONU 3 of #1 to the OLT 5. Therefore, the group of intermediate packets can be said to be a group of arriving packets with small delays and with guaranteed low delays.

[0039] Furthermore, from the perspective of low latency, the arrival timing of the group of packets that arrive discretely during the allocated time, i.e., the arrival timing of the packets that arrive directly from ONU3 to OLT5 without being buffered at ONU3, can be said to be the optimal timing for ensuring low latency.

[0040] Based on the results of collection by the collection unit 15, the determination unit 16A determines that an arriving packet is a first packet if the arrival time of the arriving packet is the beginning of the allocation timing of an ONU 3 that requires low latency. Furthermore, if there is a next arriving packet within the allocation timing, the determination unit 16A determines whether the interval between the immediately preceding arriving packet and the next arriving packet is 0. If the interval is 0, the determination unit 16A determines that the arriving packet is a first packet, and determines that it is part of a first packet group, just like the immediately preceding first packet. Furthermore, the first packet is a packet that is transmitted at the allocation start time within one allocation timing assigned to the ONU 3, based on the transmission timing information and time information.

[0041] Furthermore, if the arrival time of the arriving packet is not the beginning of the allocation timing of the ONU 3 that requires low delay, i.e., if it is in the middle of the allocation timing, the discrimination unit 16A determines that the arriving packet is an intermediate packet and determines whether there is a next arriving packet within the allocation timing. Then, the discrimination unit 16A determines that the next arriving packet within the allocation timing is an intermediate packet and determines that it is part of the intermediate packet group, just like the immediately preceding intermediate packet.

[0042] The estimation unit 16B acquires the start time T1 of the first midstream packet group and the start time T2 of the second midstream packet group based on the determination result of the determination unit 16 A. Furthermore, the estimation unit 16B acquires the data amount b of the head packet group between the first midstream packet group and the second midstream packet group, and the data amount a of the first midstream packet group.

[0043] The estimation unit 16B obtains an integer value c that is an approximation of (data amount b of the first packet group ÷ data amount a of the first intermediate packet group). Then, the estimation unit 16B estimates the output period Tc of packets from the first terminal 2 that requires low latency based on (T2-T1) / (c+1). Note that the output period Tc can be said to be the output period of packets output by the first terminal 2 that requires low latency. The output period Tc can also be said to be the transmission allocation period of the ONU 3 connected to the first terminal 2 that requires low latency. Furthermore, the data amount a of the first intermediate packet group used to obtain the integer value c may be the data amount of the second intermediate packet group, and can be changed as appropriate.

[0044] 4 is an explanatory diagram showing an example of allocation timing before allocation of an ONU3 requiring low latency. ONU3 receives packets from the first terminal 2 it accommodates. ONU3 outputs packets from the first terminal 2 to OLT5 at each allocation timing. If the timing at which ONU3 receives packets from the first terminal 2 is not its own allocation timing, ONU3 buffers the received packets and, when the next allocation timing arrives, preferentially outputs the buffered packets to OLT5.

[0045] Therefore, when OLT 5 detects a low-latency request from ONU 3, it sequentially receives arriving packets at each allocation timing of ONU 3 requesting low latency. In this case, OLT 5 shown in Fig. 4 receives the first intermediate packet group at the first allocation timing, receives the first leading packet group at the second allocation timing, and receives the second leading packet group at the third allocation timing. Furthermore, OLT 5 receives the third leading packet group at the fourth allocation timing, and receives the second intermediate packet group at the fifth allocation timing.

[0046] The estimation unit 16B acquires the start time T1 of the first intermediate packet group and the start time T2 of the second intermediate packet group. Furthermore, the estimation unit 16B acquires the data amount a of the first intermediate packet group and the data amount b of the three first packet groups between the first intermediate packet group and the second intermediate packet group. The data amount a of the first intermediate packet group is 1 packet, and the data amount b of the three first packet groups is 3 packets. The integer value c is b / a = 3 / 1 = 3. In other words, the output period Tc of the first terminal 2 requiring low latency is (T2 - T1) / (3 + 1).

[0047] The calculation unit 16C calculates the allocated bandwidth, transmission start time, and allocated time as allocation timing for the ONU3 with a low latency request, based on the output cycle Tc of the first terminal 2 with a low latency request estimated by the estimation unit 16B. Specifically, the calculation unit 16C calculates the allocation timing for the ONU3 with a low latency request after the current time, based on (T2 + Tc × X > current time). The allocation timing can be said to be the transmission allocation phase of the ONU3. The allocation timing can also be said to be the transmission timing at which all arriving packets at each allocation timing from the ONU3 with a low latency request become an in-progress packet group.

[0048] 5 is an explanatory diagram showing an example of allocation timing before and after allocation to an ONU3 requiring low latency. The calculation unit 16C calculates allocation timing for an ONU3 requiring low latency after the current time based on (T2+Tc×X>current time). In the example shown in FIG. 5, X is 4. Furthermore, for an ONU3 requiring low latency, allocation timing is allocated at intervals of Tc thereafter.

[0049] If the allocation timing of the allocation process is successful, the OLT 5 allocates the allocation timing to the ONU 3 that requires low latency. The ONU 3 that requires low latency outputs the packets from the first terminal 2 that requires low latency to the OLT 5 in sequence based on the allocation timing without buffering the packets from the first terminal 2 that requires low latency. As a result, the OLT 5 receives all arriving packets from the first terminal 2 that requires low latency as en route packets, thereby ensuring low latency packet communication with the first terminal 2.

[0050] If the allocation timing of the allocation process fails, the OLT 5 determines that low delay cannot be guaranteed, and terminates the allocation process.

[0051] The control unit 16D notifies the ONU 3 requiring low latency of the calculated allocation timing using the PONMAC 13. The ONU 3 outputs the arriving packets from the first terminal 2 to the OLT 5 based on the allocated allocation timing. As a result, the ONU 3 requiring low latency can output the arriving packets from the first terminal 2 to the OLT 5 without buffering the arriving packets, thereby ensuring low latency for packets from the ONU 3 requiring low latency.

[0052] The control unit 16D uses the DBA method based on the transmission start time, transmission volume, etc. in the information from the PONMAC 13 to allocate allocation timings for the ONUs 3 other than the ONUs 3 requiring low delay from the remaining timings other than the allocation timings for the ONUs 3 requiring low delay.

[0053] The control unit 16D notifies the ONUs 3 other than the ONUs 3 requiring low latency of the allocation timing using the PONMAC 13. Each ONU 3 outputs the arriving packets from the first terminal 2 it accommodates to the OLT 5 based on the received allocation timing. As a result, each ONU 3 other than the ONU 3 requiring low latency outputs the arriving packets from the first terminal 2 it accommodates to the OLT 5 based on the allocation timing assigned by the DBA method.

[0054] In packet communication with an ONU 3 that does not require low latency among a plurality of ONUs 3, the OLT 5 receives arriving packets from the first terminal 2 at the allocation timing of the ONU 3 that uses the existing DBA method. On the other hand, in packet communication with an ONU 3 that requires low latency among a plurality of ONUs 3, the OLT 5 receives arriving packets from the first terminal 2 that requires low latency at the allocation timing of the ONU 3 that uses the method of this embodiment.

[0055] Next, the operation of the PON system 1 of this embodiment will be described. First, it is assumed that, in the PON system 1, among a plurality of ONUs 3, for example, ONU 3 #1 accommodates a first terminal 2, and a second terminal 7, and packet communication requiring low latency is performed at a predetermined cycle.

[0056] First, it is assumed that the OLT 5, like the FBA method, allocates fixed and equal bandwidths to each ONU 3. In this case, the period and phase of the allocated bandwidth allocated in the FBA method may be any appropriate value.

[0057] 6 is a flow diagram showing an example of the processing operation of the OLT 5 related to the allocation process. In FIG. 6, the OLT 5 determines whether or not a low-latency request has been detected from an ONU 3 that requires low latency (step S11). The ONU 3 that requires low latency is an ONU 3 that accommodates a first terminal 2 that requires low-latency packet communication.

[0058] When the collection unit 15 in the OLT 5 detects a low-delay request (step S11: Yes), it collects the arrival time and data amount of each packet arriving from the ONU 3 within the allocation timing of the ONU 3 requesting low delay (step S12).

[0059] The determination unit 16A in the OLT 5 acquires the allocation timing of the ONU 3 requiring low latency, and the arrival time and data amount of the arriving packets collected within the allocation timing. Based on the acquired results, the determination unit 16A executes the determination process shown in Fig. 7 to determine, for each arriving packet, whether the arriving packet is a leading packet group or an intermediate packet group (step S13).

[0060] The estimation unit 16B in the OLT 5 determines whether or not the intermediate packet groups for two allocation timings of the ONU 3 requiring low latency have been collected (step S14). If the intermediate packet groups for two allocation timings have been collected (step S14: Yes), the CPU 16 determines whether or not the data amounts of the first intermediate packet group and the second intermediate packet group are constant (step S15).

[0061] If the data amounts of the first and second intermediate packet groups are constant (step S15: Yes), CPU 16 acquires information to be used in calculating the output period of first terminal 2 that requires low latency (step S16). The information to be used in calculating the output period includes the start time T1 of the first intermediate packet group and the start time T2 of the second intermediate packet group. Furthermore, the information to be used in calculating the output period includes the data amount a of the first intermediate packet group and the data amount b of the first packet group between the first intermediate packet group and the second intermediate packet group. The integer value c is an integer value that is an approximation of b / a.

[0062] The estimation unit 16B estimates the output period Tc of the first terminal 2 that requires low delay based on (T2-T1) / (c+1) (step S17).

[0063] The calculation unit 16C calculates the allocation timing for the ONU 3 requiring low delay after the current time based on (T2-Tc×X>current time) (step S18).

[0064] The calculation unit 16C reflects the pre- and post-margins in the calculated allocation timing for the ONUs 3 requiring low delay after the current time, and allocates the allocation timing reflecting the pre- and post-margins to the ONUs 3 requiring low delay (step S19).

[0065] After allocating the allocation timing, the control unit 16D monitors packets arriving at the allocation timing of the ONU 3 that requires low delay (step S20). Based on the result of monitoring the arriving packets, the control unit 16D determines whether the arriving packet at the allocation timing is the first packet (step S20A).

[0066] If the arriving packet at the allocation timing is not the first packet (step S20A: No), the control unit 16D determines that the arriving packet is an intermediate packet and determines whether a group of intermediate packets for M periods of the allocation timing has been continuously observed (step S21).

[0067] When the control unit 16D continuously observes a group of packets during M cycles of the allocation timing (step S21: Yes), it determines that the allocation is successful and ends the processing operation shown in FIG.

[0068] If the control unit 16D has not continuously observed a group of intermediate packets for M cycles of allocation timing (step S21: No), it sets the allocation timing to Tc after the most recent allocation timing (step S21A) and then proceeds to processing of step S20 to determine whether the arriving packet at the allocation timing is the first packet or not.

[0069] If the packet arriving at the allocation timing is the first packet (step S20A: Yes), control unit 16D determines that the allocation timing has failed (step S22), and increments the number of failures by +1 (step S23).

[0070] The control unit 16D determines whether the number of failures is L (step S24). If the number of failures is L (step S24: Yes), the control unit 16D determines that low latency cannot be guaranteed (step S25) and ends the processing operation shown in Fig. 6. Furthermore, if the OLT 5 does not detect a low latency request (step S11: No), it ends the processing operation shown in Fig. 6.

[0071] Furthermore, if the number of failures is not L (step S24: No), the control unit 16D returns to the process of step S12 to collect information about arriving packets within the allocation timing. Furthermore, if the estimation unit 16B has not collected intermediate packet groups for two allocation timings (step S14: No), the estimation unit 16B returns to the process of step S12 to collect information about arriving packets within the allocation timing. Furthermore, if the data amount between the intermediate packet group of the first allocation timing and the intermediate packet group of the second allocation timing is not constant (step S15: No), the estimation unit 16B returns to the process of step S12 to collect information about arriving packets within the allocation timing.

[0072] 7 is a flow diagram showing an example of the processing operation of the OLT 5 related to the determination process. In FIG. 7, the determination unit 16A in the OLT 5 determines whether the arrival time of the arriving packet is the head of the transmission start times within the allocated timing (step S31). If the arrival time is the head of the transmission start times (step S31: Yes), the determination unit 16A determines that the arriving packet is the head packet (step S32).

[0073] The determination unit 16A determines whether or not there is a next arriving packet within the allocated timing (step S33). If there is a next arriving packet (step S33: Yes), the determination unit 16A determines whether or not the interval between the immediately preceding arriving packet and the next arriving packet is 0 (step S34).

[0074] If the interval between the immediately preceding arriving packet and the next arriving packet is 0 (step S34: Yes), the determining unit 16A determines that the arriving packet is the first packet of the series and determines that the arriving packet is part of a first packet group (step S35).Then, the determining unit 16A returns to the process of step S33 to determine whether or not there is a next arriving packet.

[0075] If the interval between the immediately preceding arriving packet and the next arriving packet is not 0 (step S34: No), the determining unit 16A determines that the arriving packet is an en route packet (step S36). The determining unit 16A determines whether or not there is a next arriving packet within the allocated timing (step S37).

[0076] If there is a next arriving packet within the allocation timing (step S37: Yes), the determination unit 16A determines that the next arriving packet is a continuous intermediate packet and determines that the next arriving packet is an intermediate packet group (step S38). Then, the determination unit 16A returns to the process of step S37 to determine whether there is a next arriving packet within the allocation timing.

[0077] If the arrival time is not the beginning of the transmission start time (step S31: No), the determination unit 16A proceeds to the process of step S36 to determine that the arriving packet is an en route packet. If there is no next arriving packet (step S33: No), the determination unit 16A ends the processing operation shown in Fig. 7. If there is no next arriving packet within the allocated timing (step S37: No), the determination unit 16A ends the processing operation shown in Fig. 7.

[0078] Next, we will explain the operation when requesting low latency in packet communication for #1 first terminal 2. Assume that OLT 5 detects a low latency request from #1 ONU 3 among multiple ONUs 3. When detecting a low latency request from #1 ONU 3, collection unit 15 of OLT 5 collects information on packets arriving from #1 ONU 3 at each allocation timing of #1 ONU 3.

[0079] Based on the results of collecting packets arriving from ONU 3 #1, the determination unit 16A of OLT 5 determines, for each arriving packet within the allocated timing of ONU 3 #1, whether the arriving packet is a leading packet group or an intermediate packet group.

[0080] The estimation unit 16B of the OLT 5 acquires the start time T1 of the first mid-transit packet group and the start time T2 of the second mid-transit packet group, which are related to the allocation timing of the ONU 3 #1. The estimation unit 16B acquires the data amount b of the first mid-transit packet group between the first mid-transit packet group and the second mid-transit packet group, and the data amount a of the first mid-transit packet group. Then, the estimation unit 16B estimates the output period Tc of the first terminal 2 #1, which has a low delay requirement, based on (T2-T1) / (c+1).

[0081] The calculation unit 16C in the OLT 5 calculates the allocation timing after the current time (T2 + Tc × X > current time) to the ONU 3 of #1 based on the start time T2 of the second intermediate packet group and the output period Tc of the first terminal 2 of #1.

[0082] Then, the control unit 16D in the OLT 5 notifies the calculated allocation timing to the #1 ONU 3 that requires low delay. Then, the #1 ONU 3 outputs the arriving packet from the first terminal 2 to the OLT 5 based on the allocation timing.

[0083] Then, when the control unit 16D observes that all packets arriving at the allocation timing from ONU3 #1 with a low delay request are mid-stream packets for M consecutive periods, it determines that the allocation of the allocation timing for ONU3 #1 has been successful.

[0084] However, if the control unit 16D does not observe a case where all arriving packets at the allocation timing from ONU3 #1 with a low latency request are mid-transit packets for M consecutive periods, the control unit 16D increments the failure count by +1. Then, after incrementing the failure count by +1, the estimation unit 16B again acquires the first mid-transit packet group and the second mid-transit packet group related to ONU#1 at the currently allocated allocation timing. Furthermore, the estimation unit 16B acquires the data amount b of the first packet between the first mid-transit packet group and the second mid-transit packet group, and the data amount a of the first mid-transit packet group. Then, the estimation unit 16B re-estimates the output period Tc of the first terminal 2 #1.

[0085] The calculation unit 16C then calculates the allocation timing for ONU3 #1 after the current time based on the output period of the first terminal 2 #1 and the start time of the second intermediate packet. The control unit 16D then notifies ONU3 #1 of the calculated allocation timing for ONU3 #1 after the current time. ONU3 #1 then outputs arriving packets from the first terminal 2 to the OLT 5 based on the allocation timing. The control unit 16D then determines whether or not it has observed for M consecutive periods that all arriving packets at the allocation timing from ONU3 #1 with a low latency request are intermediate packets. If it has observed for M consecutive periods that all arriving packets at the allocation timing from ONU3 #1 with a low latency request are intermediate packets, the control unit 16D determines that the allocation timing for ONU3 #1 was successful.

[0086] Then, if the control unit 16D has not observed that all packets arriving at the allocation timing from ONU3 #1 with a low delay request are mid-stream packets for M consecutive periods, the control unit 16D increments the number of failures by 1. After incrementing the number of failures by 1, the control unit 16D determines whether the number of failures is L.

[0087] If the number of failures is L, the control unit 16D determines that there is no periodicity in the packets arriving from ONU 3 #1, and terminates the process for calculating the allocation timing for ONU 3 #1. In other words, it determines that low delay for ONU 3 #1 cannot be guaranteed.

[0088] The OLT 5 of the first embodiment can achieve low delay guarantee in the PON system 1 by adjusting the allocation timing of the ONUs 3 requiring low delay so that all arriving packets output from the ONUs 3 requiring low delay are in the en route packet group.

[0089] The OLT 5 collects packet information on arriving packets from the ONU 3 that arrive within the allocation timing assigned to the ONU 3 requiring low latency. Based on the collected information, the OLT 5 determines whether the arriving packet is a first packet that arrives immediately after the start of the allocation timing or an intermediate packet that arrives during the allocation timing, excluding immediately after the start of the allocation timing. Based on the determination result, the OLT 5 acquires the start time T1 of the first intermediate packet group, the start time T2 of the second intermediate packet group, the data amount b of the first packet between the first intermediate packet group and the second intermediate packet group, and the data amount a of the intermediate packet. The OLT 5 estimates the output cycle Tc of the first terminal 2 requiring low latency based on (T2-T1) / (c+1). Then, the OLT 5 calculates the allocation timing to be assigned to the ONU 3 requiring low latency based on the estimated output cycle Tc. As a result, low latency can be guaranteed in the PON system 1.

[0090] Based on the output cycle Tc, the OLT 5 calculates the allocation timing at which all of the first packets between the first group of packets and the second group of packets become intermediate packets. As a result, the ONU 3 with a low latency requirement can output the arriving packets from the first terminal 2 to the OLT 5 without buffering them, because the allocation timing matches the output cycle of the packets from the first terminal 2 with a low latency requirement.

[0091] When the OLT 5 detects a low-latency request from any of the ONUs 3, it starts collecting packets that arrive within the allocation timing assigned to the ONU 3 requesting low latency. As a result, it can execute allocation processing only for the ONUs 3 that require low latency.

[0092] After allocating the calculated allocation timing to the ONU 3, the OLT 5 determines that the allocation timing is successful if it observes M consecutive packets arriving at each allocation timing as intermediate packets. As a result, reliable allocation timing can be ensured.

[0093] After allocating the calculated allocation timing to the ONU 3, the OLT 5 determines that the allocation timing has failed if the arriving packet at each allocation timing is determined to be the first packet. As a result, reliable allocation timing can be ensured.

[0094] If the OLT 5 determines that the allocation timing has failed, it increments the number of failures by +1 and resumes collecting packet information on packets arriving from the ONU 3 within the allocation timing until the number of failures exceeds a predetermined number. As a result, it is possible to perform a retry operation to obtain the allocation timing.

[0095] Here, a comparison of the performance of the PON system 1 of this embodiment with that of a PON system using an FBA method and a PON system using a DBA method as comparative examples will be described. Fig. 8 is an explanatory diagram showing an example of the results of a comparison of delay, jitter, and the presence or absence of unused bands in this embodiment, the DBA method, and the FBA method. For ease of explanation, the processing delay within the ONU is set to 10 μs, the propagation delay of the optical fiber between the ONU and the OLT is set to 100 μs (20 km), and the processing delay within the OLT is set to 10 μs, with a total fixed delay of 120 μs.

[0096] In the DBA PON system of the comparative example, the period (DBA period) at which the OLT allocates bandwidth to each ONU is 1 ms. A REPORT arrives from an ONU at any time at the OLT. In this case, a delay of a minimum of 0 s, a maximum of 1 ms, and an average of 0.5 ms occurs in the REPORT.

[0097] In a DBA PON system, the OLT requests bandwidth via a report from each ONU, and after DBA calculation, the GATE notifies each ONU of the allocation timing within the next DBA cycle. As a result, in a DBA PON system, the system is forced to wait a fixed one DBA cycle (1 ms). Therefore, the DBA PON system depends on the DBA calculation and the level of congestion. In this case, the DBA calculation will cause a delay of a minimum of 0 seconds, a maximum of 1 ms, and an average of 0.5 ms.

[0098] Therefore, in a DBA PON system, as shown in FIG. 8, the total delay is, for example, 1.12 ms to 3.12 ms (jitter: 2 ms).

[0099] Furthermore, a fixed bandwidth is allocated to the ONUs in the comparative example of an FBA PON system. However, there is no guarantee that this matches the application cycle. Data packets arrive at any time within the DBA cycle (1 ms). At this time, a minimum delay of 0 ms, a maximum delay of 1 ms, and an average delay of 0.5 ms occurs. Therefore, in an FBA PON system, as shown in Figure 8, although the total delay is 0.12 ms to 1.12 ms (jitter: 1 ms), unused bandwidth is wasted.

[0100] In contrast, in the PON system 1 of this embodiment, the DBA period is also set to 1 ms. In the PON system 1, the allocation timing of the ONU 3 that requests low latency is adjusted within the range allocated using the FBA method at startup. Therefore, in the PON system 1 of this embodiment, the buffering delay in the ONU 3 is 0 ms, and communications such as REPORT and GATE for the ONU 3 that requests low latency are not required, so the total delay is 0.12 ms (jitter: 0 ms), as shown in Figure 8.

[0101] Therefore, the PON system 1 of this embodiment can guarantee lower delays at startup than the DBA PON system of the comparative example, and can also reduce unused and wasted bandwidth compared to the FBA PON system of the comparative example.

[0102] In the DBA PON system of the comparative example, the second terminal is controlled via the core network, and the packets transmitted by the first terminal are assumed to be in a fixed bandwidth with a fixed packet period and packet phase. In this case, factors that cause packets to accumulate in the ONU accommodating the first terminal include, in addition to the bandwidth, a discrepancy between the period and phase at which packets from the first terminal arrive at the ONU and the period and phase at which packets are transmitted by the ONU.

[0103] In the DBA PON system of the comparative example, even if the bandwidth is optimized, these period and phase shifts are not adjusted, so packet buffering due to period and phase shifts never becomes zero during operation. In other words, delays due to buffering must always be expected.

[0104] In contrast, in the PON system 1 of this embodiment, an allocation timing is set for the ONU 3 so that all arriving packets become en route packets, so that delays due to buffering by the ONU 3, which requires low latency, do not occur. As a result, in addition to the bandwidth, the difference between the period and phase at which packets from the first terminal 2 arrive at the ONU 3 and the period and phase at which packets are transmitted by the ONU 3 is eliminated, thereby realizing low latency guarantee.

[0105] Another example of a comparative example is a PON system specialized for MFH (Mobile Front Haul) to ensure low latency. However, this comparative PON system is specialized for MFH and cannot be applied to other low-latency use cases (e.g., telemedicine, autonomous driving, etc.) that do not use wireless technology. Furthermore, this comparative PON system requires a special interface called CTI in the OLT.

[0106] In contrast to this, the PON system 1 of this embodiment can ensure a general-purpose low delay guarantee without requiring a special interface or protocol, while still using the mechanisms of existing PON systems.

[0107] In this embodiment, the OLT 5 in the PON system 1 adjusts and allocates the allocation timing of the ONUs 3 that have requested low latency among multiple ONUs 3. The OLT 5 then adjusts the allocation timing of the ONUs 3 in the order in which they requested low latency. For example, if two ONUs 3 simultaneously request low latency, the OLT 5 adjusts the allocation timing of the ONUs 3 in random order, starting with the ONUs that requested low latency. In this case, the buffering delay of one ONU 3 is 0 ms, and the buffering delay of the other ONU 3 is 0.01 ms, resulting in a total delay of 0.13 ms (jitter: 0 ms). While there is a possibility of delay due to accidental timing overlap, it is significantly smaller than the DBA method of the comparative example, and jitter suppression effects can also be expected.

[0108] As an application example of this embodiment, it is possible to apply it to various applications that require low delay under the premise of periodic traffic.

[0109] In the PON system 1 of this embodiment, an intermediate packet group including a plurality of intermediate packets or a leading packet group including a plurality of leading packets is exemplified, but the present invention can also be applied to an intermediate packet group including only a single intermediate packet or a leading packet group including a single leading packet.

[0110] Furthermore, the components of each unit shown in the figure do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each unit is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0111] Furthermore, the various processing functions performed by each device may be executed in whole or in part on a CPU (Central Processing Unit) (or a microcomputer such as an MPU (Micro Processing Unit), MCU (Micro Controller Unit), or DSP). Needless to say, the various processing functions may be executed in whole or in part on a program analyzed and executed by a CPU (or a microcomputer such as an MPU or MCU), or on hardware using wired logic. [Explanation of symbols]

[0112] 1 PON System 2. First terminal 3 ONU 4 Optical Splitter 5 OLT 6 Core Network 15 Collection Department 16 CPU 16A Discrimination part 16B Estimation part 16C calculation section 16D Control Unit

Claims

1. An OLT (Optical Line Terminal) used in a PON (Passive Optical Network) using an optical splitter, a collection unit that collects information on the time at which a packet arrives from an ONU (Optical Network Unit) and information on the amount of data in the packet; a processing unit that determines a transmission timing of the ONU based on the transmission timing information assigned to the ONU, the time information, and the data amount information; An OLT characterized by having:

2. The processing unit The OLT according to claim 1, characterized in that it has a determination unit that determines whether or not there is a packet being transmitted at the allocation start time within one of the timings assigned to the ONU from the transmission timing information and the time information.

3. The processing unit The OLT according to claim 2, further comprising an estimation unit that estimates a transmission allocation period of the ONU based on the determination result obtained by the determination unit, the time information, and the data amount information.

4. The processing unit The OLT of claim 3, further comprising a calculation unit that calculates the transmission allocation phase of the ONU from information on the time at which a packet that is determined to be transmitted at the allocation start time within one of the transmission timings assigned to the ONU arrives at the OLT in the determination unit.

5. the collection unit collecting packet information including the time information and the data amount information of packets arriving from the ONUs that arrive within allocation timings allocated to the ONUs connected to the terminal devices, The processing unit a determination unit that determines, based on the collection result, whether the arriving packet is a leading packet that arrives immediately after the start of the allocation timing or an intermediate packet that arrives during the allocation timing excluding immediately after the start of the allocation timing; an estimation unit that estimates an output period of the packets of the terminal device based on the determination result, the start time of a first midway packet, the start time of a second midway packet, the data amount of a head packet between the first midway packet and the second midway packet, and the data amount of the midway packets; a calculation unit that calculates allocation timings to be allocated to the ONUs based on the estimated output period; 2. The OLT according to claim 1, wherein:

6. The calculation unit 6. The OLT according to claim 5, wherein the allocation timing is calculated based on the output period such that all leading packets between the first intermediate packet and the second intermediate packet become intermediate packets.

7. The collecting unit The OLT described in claim 5, characterized in that when a low-latency request is detected from any ONU among multiple ONUs, it starts collecting arriving packets that arrive within the allocation timing assigned to the ONU requesting the low-latency.

8. The estimation unit The OLT according to claim 5, characterized in that the output period of the packets of the terminal device is estimated by substituting the first start time of the first intermediate packet, the second start time of the second intermediate packet, the data amount of the first packet between the first intermediate packet and the second intermediate packet, and the data amount of the first intermediate packet into a mathematical formula of {(second start time - first start time) / (an integer value approximating (data amount of the first packet / data amount of the first intermediate packet)) + 1}.

9. The estimation unit 9. The OLT according to claim 8, wherein the OLT starts estimating the output period when the data amount of the first midway packet and the data amount of the second midway packet are close to each other.

10. The OLT of claim 5, further comprising a control unit that determines that the allocation timing is successful if, after the allocation timing calculated by the calculation unit is assigned to the ONU, arriving packets at each allocation timing are identified as intermediate packets a predetermined number of times in succession.

11. The control unit The OLT of claim 10, characterized in that after the allocation timing calculated by the calculation unit is assigned to the ONU, if an arriving packet at each allocation timing is determined to be a first packet, the OLT determines that the allocation timing has failed.

12. The control unit The OLT of claim 11, characterized in that if it is determined that the allocation timing has failed, the number of failures is incremented by +1, and the collection operation of the collection unit is resumed to collect packet information of arriving packets from the ONU that arrive within the allocation timing until the number of failures exceeds a predetermined number.

13. The ONU comprises: The OLT according to claim 5, characterized in that it outputs arriving packets to the OLT when the current timing is within its own allocation timing, and buffers arriving packets when the current timing is outside its own allocation timing, and outputs the buffered arriving packets to the OLT in accordance with the start of the allocation timing.

14. A PON (Passive Optical Network) system includes an ONU (Optical Network Unit) connected to a terminal device and an OLT (Optical Line Terminal) connected to a core network, the OLT optically communicating packets from the terminal device with the ONU, The OLT comprises: a collection unit that collects time information of arrival of packets from the ONU and data amount information of the packets; a processing unit that determines a transmission timing of the ONU based on the transmission timing information assigned to the ONU, the time information, and the data amount information; The ONU comprises: Based on the transmission timing assigned to the OLT, when the current timing is within its own transmission timing, the OLT outputs the arriving packet from the terminal device to the OLT, and when the current timing is outside its own transmission timing, the OLT buffers the arriving packet from the terminal device and outputs the buffered arriving packet to the OLT in response to the start of the transmission timing. A PON system characterized by:

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