PON system and communication control method

Abstract

To provide a PON (Passive Optical Network) system that ensures fairness between upper-stage ONUs (Optical Network Units) and lower-stage ONUs.SOLUTION: A multi-stage PON system includes an upper stage OLT (Optical Line Terminal) that performs upper stage DBA (Dynamic Bandwidth Allocation) for multiple upper stage ONUs and a lower stage OLT that performs lower stage DBA for lower stage ONUs, in which the upper stage ONUs include a relay ONU connected to the lower stage OLT. The lower stage OLT stores lower stage QoS (Quality of Service) information and notifies the upper stage OLT of the information. The upper stage OLT stores upper stage QoS information and the notified lower stage QoS information, and performs priority control of user frames in an uplink direction based on the upper stage QoS information and the lower stage QoS information.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a PON system and a communication control method.

Background Art

[0002] Patent Document 1 describes a PON system in which an upper-stage PON (Passive Optical Network) and a lower-stage PON are configured in multiple stages in order to extend the service area of FTTH (Fiber To The Home). Specifically, the upper-stage PON and the lower-stage PON are multi-stage connected (cascaded) by a relay device that performs upstream multiple access control on the lower-stage ONU (Optical Network Unit) according to the upstream multiple access control performed by the upper-stage OLT (Optical Line Terminal).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, a relay node adds tag information to an upstream frame, and an upper-stage OLT aggregates the upstream traffic volume for each lower-stage ONU based on the tag information, thereby achieving the SLA (Service Level Agreement) of the lower-stage ONUs under the relay node. However, in Patent Document 1, the relay node does not add tag information to the upstream frames of the upper-stage ONUs under the upper-stage OLT. It does not disclose a means for ensuring fairness between the upper-stage ONUs and the lower-stage ONUs.

[0005] The present disclosure aims to provide a multi-stage PON system that can ensure fairness between upper-stage ONUs and lower-stage ONUs, exceeding such conventional disclosures.

Means for Solving the Problem

[0006] A system according to one aspect of the present disclosure includes an upper OLT that performs upper DBA targeting a plurality of upper ONUs, and at least one lower OLT that performs lower DBA targeting at least one lower ONU, and the plurality of upper ONUs include relay ONUs connected to the lower OLT, which is a multi-stage PON system.

[0007] The lower OLT has a memory for storing the following lower QoS information and a controller for notifying the upper OLT of the lower QoS information, and the upper OLT has a memory for storing the following upper QoS information and the notified lower QoS information, and a controller for performing priority control of uplink user frames based on the upper QoS information and the lower QoS information.

[0008] Upper QoS information: Information including the priority order for each upper LLID, which is the LLID of an upper ONU other than the relay ONU, and identification information for substituting the lower LLID Lower QoS information: Information including the priority order for each lower LLID, which is the LLID of a lower ONU, and identification information for substituting the lower LLID

[0009] The present disclosure can be realized not only as a system and apparatus having the above-described characteristic configuration, but also as a program for causing a computer to execute such a characteristic configuration. Further, the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the system and apparatus.

Advantages of the Invention

[0010] According to the present disclosure, a multi-stage PON system capable of ensuring fairness between the upper ONU and the lower ONU can be realized.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0012] <**Overview of Embodiments of the Present Disclosure**> The overview of the embodiments of the present disclosure will be listed and described below. (1) A system according to an aspect of the present embodiment includes an upper-stage OLT that performs upper-stage DBA targeting a plurality of upper-stage ONUs, and at least one lower-stage OLT that performs lower-stage DBA targeting at least one lower-stage ONU, and is a multi-stage PON system in which the plurality of upper-stage ONUs include relay ONUs connected to the lower-stage OLT.

[0013] The lower-stage OLT has a memory that stores the following lower-stage QoS information, and a controller that notifies the upper-stage OLT of the lower-stage QoS information. The upper-stage OLT has a memory that stores the following upper-stage QoS information and the notified lower-stage QoS information, and a controller that executes priority control of an upstream user frame based on the upper-stage QoS information and the lower-stage QoS information.

[0014] Upper-stage QoS information: Information including the priority order for each upper-stage LLID, which is the LLID of an upper-stage ONU other than the relay ONU, and identification information that replaces the lower-stage LLID Lower-stage QoS information: Information including the priority order for each lower-stage LLID, which is the LLID of a lower-stage ONU, and identification information that replaces the lower-stage LLID

[0015] According to the PON system of this embodiment, since the upper OLT executes priority control of the upstream user frame based on the upper QoS information and the lower QoS information notified from the lower OLT, fair priority control is performed on the upstream user frame whose source is the upper ONU or the lower ONU. Therefore, a multi-stage PON system that can ensure fairness between the upper ONU and the lower ONU can be obtained.

[0016] (2) In the PON system of (1) above, the controller of the lower OLT may add identification information that substitutes for the lower LLID to the user frame transmitted to the relay ONU. The reason is that in order to ensure the fairness of the priority control by the upper OLT, the upper OLT needs to detect the identification information that substitutes for the lower LLID from the user frame received from the lower side.

[0017] (3) In the PON system of (2) above, the controller of the upper OLT may delete the identification information that substitutes for the upper LLID and the identification information that substitutes for the lower LLID from the user frame transmitted to the upper device. The reason is that outside the PON system, the identification information that substitutes for the upper LLID and the identification information that substitutes for the lower LLID are not required.

[0018] (4) In the PON system of (1) to (3) above, the controller of the lower OLT may update the lower QoS information according to the change in the link state of the lower ONU, and notify the upper OLT of the lower QoS information every time such an update is made. In this way, the latest lower QoS information after the link state of the lower ONU changes can be notified to the upper OLT.

[0019] (5) In the PON system of (1) to (4) above, the relay ONU may have a controller that determines its own upper-level LLID for each priority corresponding to the identification information that replaces the lower-level LLID, and requests the upper-level OLT for the transmission data amount based on the determined upper-level LLID. In this way, the relay ONU can execute a bandwidth request to the upper-level OLT based on the upper-level LLID that inherits the priority of the lower-level LLID.

[0020] (6) The method according to one aspect of the present embodiment is a communication control method executed in the PON system of (1) to (5) above. Therefore, the communication control method of the present embodiment has the same operational effects as the PON system of (1) to (5) above.

[0021] <Details of Embodiments of the Present Disclosure> Hereinafter, details of embodiments of the present disclosure will be described with reference to the drawings. Note that at least a part of the embodiments described below may be arbitrarily combined.

[0022] 〔Definition of Terms, etc.〕 Generally, the layer 2 PDU (Protocol Data Unit) may be called a "frame", and the layer 3 PDU may be called a "packet". However, in the present embodiment, the names of the PDUs of these layers are unified as "communication frames".

[0023] In the present embodiment, the direction from the lower side to the upper side is referred to as the "upward direction", and the direction from the upper side to the lower side is referred to as the "downward direction". Also, a communication frame including user data related to a communication service (also referred to as the "main signal") is referred to as a "user frame", and a communication frame including control information exchanged between communication nodes for setting communication parameters and communication control is referred to as a "control frame".

[0024] In this embodiment, each communication node constituting the PON system executes Ethernet-based (Ethernet is a registered trademark) communication, and the PON is assumed to be Ethernet-based EPON (for example, 10G-EPON). For example, in EPON, registration and disconnection of ONUs, bandwidth requests from ONUs, and bandwidth grants based on bandwidth requests are executed by MPCP (Multi-Point Control Protocol) frames, which are control frames defined in IEEE802.3ah. The upstream transmission amount of user data permitted to the ONU is determined by DBA (Dynamic Bandwidth Allocation) performed by the OLT.

[0025] 〔Physical Configuration of PON System〕 FIG. 1 is a block diagram showing an example of the physical configuration of the PON system 100. As shown in FIG. 1, the PON system 100 of this embodiment is a multi-stage PON system in which an upper-stage PON 200 located on the upper side (left side in FIG. 1) and a lower-stage PON 300 located on the lower side (right side in FIG. 1) are multi-stage connected (cascaded) by a relay ONU 20R, which is a kind of upper-stage ONU 20.

[0026] An upper device 50 communicating with an upper network (not shown) such as a core network and a management terminal 60 of a communication carrier are connected to the upper-stage PON 200 (specifically, the upper-stage concentrator card 11). The connection form between the concentrator card 11 and the upper device 50 and the connection form between the concentrator card 11 and the management terminal 60 may be a direct connection using a metal line or an optical line as a medium, or an indirect connection via a LAN.

[0027] The upper-stage PON 200 includes an upper-stage OLT 10 and a plurality of upper-stage ONUs 20. The upper-stage OLT 10 is configured by, for example, a chassis-type OLT having slots capable of accommodating a concentration card 11 and at least one PON card 12 respectively. In FIG. 1, the case where one concentration card 11 and two PON cards 12, 12 are accommodated in the chassis of the upper-stage OLT 10 is illustrated.

[0028] The concentration card 11 is a card-type communication module including a circuit board on which at least one communication IC (Integrated Circuit) is mounted. The communication IC of the concentration card 11 includes a frame processing unit 11U that performs Ethernet-based relay processing. The PON card 12 is a card-type communication module on which at least one communication IC is mounted. The communication IC of the PON card 12 includes an OLT MAC (Media Access Controller) 12A capable of communicating according to the PON protocol.

[0029] The PON card 12 has a memory 12B that stores "management information" with the management terminal 60 as the transmission source. The management information includes, for example, QoS (Quality of Service) management information regarding the upper-stage OLT 10 (hereinafter also referred to as "upper-stage QoS information"). The upper-stage QoS information includes, for example, the LLID (Logical Link ID) of the upper-stage ONU 20, the priority for each LLID, and identification information for replacing the LLID. The identification information can adopt, for example, VLAN (Virtual LAN) identification information (hereinafter referred to as "VID").

[0030] A PON line L1 composed of a tree-structured optical fiber network is connected to the PON card 12. The upper-stage ONU 20 is connected to the lower end of the PON line L1. The upper-stage ONU 20 includes the following two types of ONUs. Normal ONU 20N: The upper-stage ONU 20 not connected to the lower-stage OLT 30 Relay ONU 20R: The upper-stage ONU 20 connected to the lower-stage OLT 30 by a predetermined communication line

[0031] Generally, the ordinary ONU 20N is installed at the subscriber's home of the PON that uses the communication service, etc. Note that different LLIDs can be assigned to one ordinary ONU 20N for each type of communication service (for example, optical TV and Internet communication).

[0032] The relay ONU 20R is a communication node for multi-staging the PON system 100, and is installed, for example, in a fixed facility (such as a building or an outdoor pole) under the management of a communication carrier. The fixed facility of the relay ONU 20R may be a remote or neighboring facility different from the fixed facility of the lower-stage OLT 30, or may be the same as the fixed facility of the lower-stage OLT 30.

[0033] The connection form between the relay ONU 20R and the concentration card 31 of the lower-stage OLT 30 described later may be a direct connection using a metal line or an optical line as a medium, or an indirect connection via a LAN (Local Area Network). The relay ONU 20R has a communication board on which at least one communication IC is mounted. The communication IC of the relay ONU 20R includes a MAC 20A that functions as an ONU on the upper-stage side and performs Ethernet-based communication on the lower-stage side. The relay ONU 20R also has a memory 20B that stores the lower-stage QoS information and the like described later.

[0034] The lower-stage PON 300 includes a lower-stage OLT 30 and at least one lower-stage ONU 40. The lower-stage OLT 30 is configured by, for example, a chassis-type OLT having slots capable of accommodating a concentration card 31 and at least one PON card 32 respectively. In FIG. 1, the case where one concentration card 31 and two PON cards 32, 32 are accommodated in the chassis of the lower-stage OLT 30 is illustrated.

[0035] The concentration card 31 is a card-type communication module including a circuit board on which at least one communication IC is mounted. The communication IC of the concentration card 31 includes a frame processing unit 31D that performs Ethernet-based relay processing and the like. The PON card 32 is a card-type communication module on which at least one communication IC is mounted. The communication IC of the PON card 32 includes, for example, a MAC 32A for OLT capable of communicating in accordance with the PON protocol.

[0036] The PON card 32 has a memory 32B that stores "management information" whose source is the management terminal 60. The management information includes, for example, QoS setting information regarding the lower-stage OLT 30 (hereinafter also referred to as "lower-stage QoS information"). The lower-stage QoS information includes, for example, the LLID of the lower-stage ONU 40, the priority for each LLID, and identification information (for example, VID) that replaces the LLID.

[0037] A PON line L2 composed of a tree-structured optical fiber network is connected to the PON card 32. The lower-stage ONU 40 is connected to the lower end of the L2 of the PON line. The lower-stage ONU 40 is installed in each of the subscriber homes of PON that use communication services. Note that different LLIDs can be assigned to one lower-stage ONU 40 for each type of communication service (for example, optical TV and Internet communication).

[0038] As described above, the PON system 100 of the present embodiment is a multi-stage PON system in which the upper-stage PON 200 and the lower-stage PON 300 are multi-stage connected by connecting a part (relay ONU 20R) of the plurality of upper-stage ONUs 20 to the lower-stage OLT 30.

[0039] In this way, by connecting the upper-stage OLT 10 and the lower-stage OLT 30 in multiple stages, for example, by installing the lower-stage OLT 30 in a predetermined facility located 20 km or more away from the office building, the FTTH service area can be expanded. Also, by connecting the upper-stage OLT 10 and the lower-stage OLT 30 in multiple stages, there is an advantage that more than 128 ONUs 20, 40 (the number of ONUs that can be accommodated in a one-stage configuration) can be accommodated when viewed from the upper-stage OLT 10.

[0040] 〔Management communication using a management terminal〕 The management terminal 60 is, for example, a management computer operated by a communication administrator and can communicate with the concentrator card 11 in accordance with a predetermined communication protocol. The management terminal 60 generates management information regarding the PON system 100 in response to an operation input by the communication administrator using a command line or the like, and transmits the generated management information to the concentrator card 11. The concentrator card 11 transfers the received management information to the PON card 12. This management information may include upper-stage information and lower-stage information.

[0041] When the MAC 12A of the PON card 12 determines that the received management information is for the upper stage and for itself, it stores the management information for itself in the memory 12B. When the MAC 12A of the PON card 12 determines that the received management information is for the upper stage but not for itself, it discards the management information that is not for itself. When the MAC 12A of the PON card 12 determines that the received management information is for the lower stage, it transmits the management information for the lower stage to the relay ONU 20R.

[0042] When the concentrator card 11 of the upper-stage OLT 10 receives management information from the relay ONU 20R for the lower-stage OLT 30, it transfers the received management information to the PON card 32. When the MAC 32A of the PON card 32 determines that the received management information is for the lower stage and for itself, it stores the management information for itself in the memory 32B. When the MAC 32A of the PON card 32 determines that the received management information is for the lower stage but not for itself, it discards the management information that is not for itself.

[0043] 〔Sharing of DBA and QoS Information Executed Individually〕 In the PON system 100 of this embodiment, the upper-stage PON card 12 performs upper-stage DBA for the upper-stage ONU 20 (including the relay ONU 20R), and the lower-stage PON card 32 performs lower-stage DBA separately from the upper-stage DBA for the lower-stage ONU 40. That is, the upper-stage DBA and the lower-stage DBA are executed asynchronously and independently. Therefore, configuration changes of the PON system 100, such as the addition or deletion of the upper-stage ONU 20 or the lower-stage ONU 40, can be easily executed.

[0044] On the other hand, if DBA and upper-stage scheduling are executed regardless of changes in the status of the lower-stage ONU 40 (for example, changes in the number of connections or priorities), the priority regarding the relay ONU 20R will always be constant, and unfairness may occur where the upstream bandwidth of the lower-stage ONU 40 is unduly restricted. Therefore, in the present embodiment, the lower-stage PON card 32 notifies the upper-stage PON card 12 of the lower-stage QoS information being managed by itself (the "QoS information notification process" in FIG. 2).

[0045] Then, the upper-stage PON card 12 and the concentrator card 11 execute priority control based on the notified lower-stage QoS information and the upper-stage QoS information that they originally manage, thereby ensuring the fairness of the upstream communication between the upper-stage ONU 20 (specifically, the normal ONU 20N) and the lower-stage ONU 40 included in the PON system 100. Hereinafter, the QoS information notification process, the logical configuration of the PON system 100, and the content of the control performed on the upstream user frames in the PON system 100 will be described.

[0046] 〔QoS information notification process〕 FIG. 2 illustrates correspondence tables T1 and T2, which are examples of each QoS information. As shown in FIG. 2, a "correspondence table T1" is registered in the memory 12B of the upper-stage PON card 12 as an example of the upper-stage QoS information. Similarly, a "correspondence table T2" is registered in the memory 32B of the lower-stage PON card 32 as an example of the lower-stage QoS information.

[0047] These correspondence tables T1 and T2 are examples of tables that define the priority (PRI) for each LLID and the identification information (VID) that replaces the LLID, and the set values registered in each of the tables T1 and T2 can be set by management communication using the aforementioned management terminal 60. In addition, when the ONUs 20 and 40 notify their own priorities (PRI) to the OLTs 10 and 20 in discovery, the PON cards 12 and 32 may record the priorities (PRI) notified from the ONUs 20 and 40 in the corresponding tables T1 and T2.

[0048] The corresponding table T1 is data in a table format including columns of "upper LLID", "lower LLID", "PRI", "outer VID", and "inner VID". In the "upper LLID" of the corresponding table T1, the LLID value of the communication ONU 20N among the upper ONUs 20 is recorded. The "lower LLID" of the corresponding table T1 is a column for recording the LLID value of the lower ONU 40. However, since the lower ONU 40 is not the target of the upper DBA, a blank (Null) is recorded in the "lower LLID" of the corresponding table T1.

[0049] In the "outer VID" of the corresponding table T1, the VID value of the communication node on the upper side of the upper OLT 10 (the upper device 50 in this embodiment) is recorded. In the "inner VID" of the corresponding table T1, a VID value uniquely corresponding to the upper LLID value (the same value as the upper LLID value in the illustrated example) is recorded. In the "PRI" of the corresponding table T1, a PRI value (for example, A, B, C) corresponding to the upper LLID value is recorded. The PRI values are in descending order of A > B > C and are parameters representing, for example, the ratio of the transmission allowance.

[0050] The number of records in the corresponding table T1 is the same as the number of records of the LLIDs assigned to the normal ONUs 20N during link-up (two in the illustrated example). The MAC 12A of the PON card 12 updates the corresponding table T1 according to the change in the link state of the inner LLID assigned to the normal ONU 20N. Specifically, it adds the record of the inner LLID of the normal ONU 20N that has been link-up to the corresponding table T1 and deletes the record of the inner LLID of the normal ONU 20N that has been link-down from the corresponding table T1.

[0051] The correspondence table T2 is data in a table format including columns of "lower LLID", "PRI", "outer VID", and "inner VID". The "lower LLID" of the correspondence table T2 is a column corresponding to the lower LLID of the correspondence table T1. The LLID value of the lower ONU 40 is recorded in the "lower LLID" of the correspondence table T2. In FIG. 2, a case where two LLID values ("1" and "2") are assigned to one lower ONU 40 is illustrated.

[0052] The "outer VID" of the correspondence table T2 records the VID value of the communication node (relay ONU 20R in this embodiment) connected to the upper side of the lower OLT 30. The "inner VID" of the correspondence table T2 records a VID value that uniquely corresponds to the lower LLID value (the same value as the lower LLID value in the illustrated example). The "PRI" of the correspondence table T2 records a PRI value (for example, A, B, C) corresponding to the lower LLID value. Assume that the PRI value is a parameter representing the ratio of the transmission permission amount, similar to the correspondence table T1.

[0053] The number of records in the correspondence table T2 is the same as the number of records of the inner LLID assigned to the lower ONU 40 during link-up (4 in the illustrated example). The MAC 32A of the PON card 32 updates the correspondence table T2 according to the change in the link state of the inner LLID assigned to the lower ONU 40. Specifically, it adds the record of the inner LLID of the lower ONU 40 that has been link-up to the correspondence table T2, and deletes the record of the inner LLID of the lower ONU 40 that has been link-down from the correspondence table T2.

[0054] The "QoS information notification process" shown in FIG. 2 is a process in which the MAC 32A of the lower PON card 32 transmits the correspondence table T2 registered in the memory 32B to the MAC 12A of the upper PON card 12 via a predetermined control communication through the relay ONU 20R. The QoS information notification process is executed every time the corresponding table T2 is updated. Therefore, every time the MAC 20A of the relay ONU 20R receives the updated corresponding table T2, it stores the received corresponding table T2 in its own memory 20A.

[0055] In the QoS information notification process, when the relay ONU 20R receives the lower-layer QoS information (specifically, the corresponding table T2), the MAC 20A of the relay ONU 20R stores the received lower-layer QoS information in its own memory 20B. Therefore, based on the inner VID included in the user frame received from the lower-layer OLT 30 and the corresponding table T2, the MAC 20A of the relay ONU 20R can determine the priority (PRI) of the received user frame.

[0056] On the other hand, the MAC 12A of the PON card 12 stores the corresponding table T2 received from the relay ONU 20R in its own memory 12B together with the corresponding table T1. Specifically, the MAC 12A of the PON card 12 creates a comprehensive table T0 by merging the corresponding tables T1 and T2 and stores it in the memory 12B.

[0057] 〔Logical Configuration of PON System〕 FIG. 2 is a block diagram showing an example of the logical configuration of the PON system 100. As shown in FIG. 2, when the upper-layer OLT 10 relays the user frame received from the upper-layer ONU 20 (including the relay ONU 20R) to the upper-level device 50, it refers to the comprehensive table T0 and executes the following upper-layer processes P11, P12, P13, P14. In the following description, it is assumed that the PRI values of the corresponding tables T1 and T2, namely "A", "B", and "C", are "5", "3", and "1" respectively.

[0058] "Upper-layer DBA" (upper-layer process P11): The upper-layer DBA is a DBA targeting the upper-layer ONU 20 under the PON card 12 on the upper layer. The execution entity of the upper-layer DBA is the MAC 12A of the PON card 12. Specifically, the upper DBA is a DBA that allocates the bandwidth of the uplink user frame (hereinafter also referred to as the "uplink grant amount") that permits transmission to each upper ONU 20 in response to a request (bandwidth request), which is a type of MPCP frame notified from the upper ONU 20.

[0059] The uplink grant amount is determined according to a predetermined logic based on the PRI of the upper LLID. As the predetermined logic, a priority control logic such as H-WRR (Hierarchical Weighted Round Robin) can be adopted. In this case, the uplink grant amount in the DBA period is determined so that the ratio of the uplink grant amounts of the five upper LLIDs (= 1 to 5) is A:B:A:B:C = 5:3:5:3:1.

[0060] "First Scheduling" (upper processing P12): The first scheduling on the upper side is a process of scheduling the transmission order of the uplink user frames to the aggregation card 11 according to a predetermined logic based on the PRI of the inner VID. The execution entity of the first scheduling on the upper side is the MAC12A of the PON card 12.

[0061] As the predetermined logic, a priority control logic such as the above-mentioned H-WRR can be adopted. In this case, the order of the user frames to be put into the transmission queue is as follows. Note that after order 5, it is a repetition of order 1 to order 4. Order 1: Output "five" user frames with inner LLID = 1 Order 2: Output "three" user frames with inner LLID = 2 Order 3: Output "three" user frames with inner LLID = 3 Order 4: Output "one" user frame with inner LLID = 4

[0062] "Second Scheduling" (upper processing P13): The second scheduling on the upper stage is a process of scheduling the transmission order of the upstream user frames to the upper device 50 according to a predetermined logic based on the PRI of the inner VID. The execution entity of the second scheduling on the upper stage is the frame processing unit 11U of the concentrator card 11.

[0063] As the predetermined logic, the priority control logic such as the above-mentioned H-WRR can be adopted. In this case, the order of the user frames put into the transmission queue is the same as the order 1 to order 4 above. In addition to the first scheduling of the PON card 12, the reason for the concentrator card 11 to perform the second scheduling is to ensure the fairness of the upstream communication even when the concentrator card 11 receives user frames from a plurality of PON cards 12.

[0064] "Upstream transmission on the upper stage" (upper stage process P14) The upstream transmission on the upper stage is a process of transmitting an upstream user frame to the upper device 50. The execution entity of the upstream transmission on the upper stage is the frame processing unit 11U of the concentrator card 11. In this case, the frame processing unit 11U of the concentrator card 11 executes a process of deleting the outer VID and the inner VID, which are identification information for replacing the LLID, from the user frame to the upper device 50 that is the transmission target.

[0065] On the other hand, when the lower OLT 30 relays the user frame received from the lower ONU 40 to the relay ONU 20R, the following lower stage processes P31, P32, P33, P34, P35 are executed with reference to the correspondence table T2.

[0066] "Lower stage DBA" (lower stage process P31): The lower stage DBA is a DBA targeting the lower ONU 40 under the PON card 32 on the lower stage. The execution entity of the lower stage DBA is the MAC 32A of the PON card 32. Specifically, the lower DBA is a DBA that allocates the bandwidth (upstream permission amount) of the user frame in the upstream direction that permits transmission to each lower ONU 40 in response to a request (bandwidth request), which is a type of MPCP frame notified from the lower ONU 40.

[0067] The upstream permission amount is determined according to a predetermined logic based on the PRI of the lower LLID. As the predetermined logic, a priority control logic such as the above-mentioned H-WRR can be adopted. In this case, the upstream permission amount in the DBA cycle is determined so that the ratio of the upstream permission amounts of the four lower LLIDs (= 1 to 4) is A:B:B:C = 5:3:3:1.

[0068] "VID Assignment" (Lower Processing P32) VID assignment is a process of assigning a VID (outer VID and inner VID), which is used as alternative information for the LLID, to the user frame received from the lower OLT 40 when the lower ONU 40 performs an upstream transmission in response to the bandwidth permission of the lower OLT 30. The entity that executes the VID assignment is the MAC32A of the PON card 32.

[0069] "First Scheduling" (Lower Processing P33): The first scheduling on the lower side is a process of scheduling the transmission order of the user frames in the upstream direction to the aggregation card 31 according to a predetermined logic based on the PRI for each inner VID. The entity that executes the first scheduling on the lower side is the MAC32A of the PON card 32.

[0070] As the predetermined logic, a priority control logic such as the above-mentioned H-WRR can be adopted. In this case, the order of the user frames to be put into the transmission queue is as follows. Note that after order 5, it is a repetition of orders 1 to 4. Order 1: Output "five" user frames with inner LLID = 1 Order 2: Output "three" user frames with inner LLID = 2 Order 3: Output "three" user frames with inner LLID = 3 Sequence 4: Output "one" user frame of the inner LLID = 4

[0071] "Second Scheduling" (upper process P34): The second scheduling on the lower side is a process of scheduling the transmission order of the upstream user frames for the relay ONU 20R according to a predetermined logic based on the PRI of the inner VID. The execution entity of the second scheduling on the lower side is the frame processing unit 31D of the concentrator card 31.

[0072] As the predetermined logic, a priority control logic such as the above-mentioned H-WRR can be adopted. In this case, the order of the user frames put into the transmission queue is the same as that from Sequence 1 to Sequence 4 above. In addition to the first scheduling of the PON card 32, the reason for the concentrator card 31 to perform the second scheduling is to ensure the fairness of the upstream communication even when the concentrator card 31 receives user frames from a plurality of PON cards 32.

[0073] "Lower Upstream Transmission" (lower process P35): The lower upstream transmission is a process of transmitting an upstream user frame to the relay ONU 20R. The execution entity of the lower upstream transmission is the frame processing unit 31D of the concentrator card 31. In this case, the frame processing unit 31D of the concentrator card 31 maintains the outer VID and the inner VID for the user frame to be transmitted. Therefore, the relay ONU 20R receives a user frame including the outer VID and the inner VID from the upper OLT 30.

[0074] 〔Control Executed on User Frame〕 FIG. 3 is a flowchart showing an example of the control executed on the upstream user frame in the PON system 100. As shown in FIG. 3, the lower-stage PON card 32 executes lower-stage DBA in units of lower-stage LLIDs (step ST11). Specifically, the lower-stage PON card 32 determines the upstream allowance of the subordinate lower-stage ONUs 40 based on the PRI of the lower-stage LLIDs.

[0075] Next, the lower-stage PON card 32 assigns an outer VID and an inner VID to the user frames received from the lower-stage ONUs 40 (step ST12). Specifically, the lower-stage PON card 32 performs the following assignments to the user frames. Assignment 1: For the user frame with LLID = 1, set the outer VID value to "1" and the inner VID value to "1".

[0076] Assignment 2: For the user frame with LLID = 2, set the outer VID value to "1" and the inner VID value to "2". Assignment 3: For the user frame with LLID = 3, set the outer VID value to "1" and the inner VID value to "3". Assignment 4: For the user frame with LLID = 4, set the outer VID value to "1" and the inner VID value to "4".

[0077] Next, the lower-stage PON card 32 performs lower-stage first scheduling on the user frames received from the lower-stage ONUs 40 (step ST13). Specifically, the lower-stage PON card 32 determines the order of the user frames to be put into the upstream transmission queue based on the PRI values (A, B, C) for each inner VID defined in the correspondence table T2.

[0078] Next, the lower-stage PON card 32 performs upstream transmission to the aggregation card 31 (step ST14), and the lower-stage aggregation card 31 performs lower-stage second scheduling on the user frames received from the PON card 12 (step ST15). Specifically, the lower-stage PON card 32 determines the order of the user frames to be put into the upstream transmission queue based on the PRI values (A, B, C) for each inner VID defined in the correspondence table T2

[0079] Next, the lower-stage concentrator card 31 transmits the user frame to the relay ONU 20R (step ST16). Specifically, the lower-stage concentrator card 31 transfers the user frame with the outer VID and the inner VID received from the PON card 32 to the relay ONU 20R of the upper-stage PON 200 while leaving the VID unchanged.

[0080] As shown in FIG. 3, the relay ONU 20R maintains the outer VID and the inner VID of the user frame received from the concentrator card 31 without deleting them (step ST17). Next, the relay ONU 20R specifies the PRI from the inner VID written in the received user frame, and determines its own upper-stage LLID corresponding to the PRI (step ST18). This determination is made with reference to the correspondence table T2.

[0081] Next, the relay ONU 20R requests the upper-stage OLT 10 for the upstream transmission data volume for each of its own upper-stage LLIDs corresponding to the determined PRI (step ST19). Specifically, the relay ONU 20R has a buffer (not shown) that accumulates user frames for each upper-stage LLID corresponding to the PRI, and requests the upper-stage OLT 10 for the data volume accumulated in each buffer at a predetermined period of the upper-stage DBA.

[0082] As shown in FIG. 3, the upper-stage PON card 12 executes the upper-stage DBA in units of upper-stage LLIDs (step ST20). Specifically, the upper-stage PON card 12 determines the upstream permission amount of the subordinate upper-stage ONUs 20 based on the PRI of the lower-stage LLID.

[0083] Next, the upper-stage PON card 12 executes the first scheduling on the lower stage for the user frame received from the upper-stage ONU 40 (step ST21). Specifically, the lower-stage PON card 32 determines the order of the user frames to be put into the upstream transmission queue based on the PRI values (A, B, C) for each inner VID defined in the comprehensive table T0.

[0084] Next, the upper-stage PON card 12 performs an upstream transmission to the concentration card 11 (step ST22), and the upper-stage concentration card 11 executes the second scheduling on the upper stage for the user frame received from the PON card 12 (step ST23). Specifically, the upper-stage concentration card 11 determines the order of the user frames to be put into the upstream transmission queue based on the PRI values (A, B, C) for each inner LLID defined in the comprehensive table T0.

[0085] Next, after the upper-stage concentration card 11 deletes the outer VID and the inner VID from the user frame (step ST24), it transmits the user frame to the upper device 50 (step ST25).

[0086] 〔Modification Example of QoS Information Notification Processing〕 FIG. 4 is a block diagram showing an example of QoS information notification processing in the PON system 100 having a plurality of lower-stage OLTs 30. In the PON system 100 of FIG. 4, two relay ONUs 20R, 20R are connected to the PON line L1 leading to the PON card 12 of the upper-stage OLT 10, and the lower-stage OLTs 30, 30 are respectively connected to these relay ONUs 20R, 20R.

[0087] In this case, the two lower-stage PON cards 32, 32 independently execute the QoS information notification processing. That is, the PON cards 32, 32 transmit the corresponding tables T2, T3 registered in the memories 32B to the MAC12A of the upper-stage PON card 12 respectively. The PON card 32 stores the received corresponding tables T2, T3 in its own memory 12B. Specifically, it saves the comprehensive table T0 obtained by merging the corresponding tables T1, T2, T3 in the memory 12B, and executes the upper-stage processes P11, P12 with reference to the comprehensive table T0.

[0088] Note that the corresponding table T2 on the lower stage side is stored in the relay ONU20R that relays the corresponding table T2. Also, the corresponding table T3 on the lower stage side is stored in the relay ONU20R that relays the corresponding table T3.

[0089] 〔Modification Example of Corresponding Table〕 FIG. 5 is an explanatory diagram showing a modification example of QoS information. In the modification example of FIG. 5, a column for the MAC address of the normal ONU20N among the upper-stage ONUs 20 is added to the corresponding table T1, which is an example of the upper-stage QoS information. Similarly, columns for the MAC addresses of the lower-stage ONUs 40 are added to the corresponding tables T12 and T3, which are examples of the lower-stage QoS information.

[0090] In this way, by adopting the corresponding tables T1, T2, and T3 including the MAC addresses of the ONUs 20 and 40, there is an advantage that it becomes easier for the OLTs 10 and 30 to execute Ethernet OAM or the like with the ONUs 20 and 40 as management targets.

[0091] 〔First Modification Example〕 In the above-described embodiment, the MACs 12A and 32A of the PON cards 12 and 32 may have a function of automatically generating VID values. In this case, the setting of the QoS information (corresponding tables T1, T2, and T3) using the management terminal 60 only needs to define the priority (PRI) for each LLID. Also, the identification information substituting for the LLID is not limited to the VID, and other information areas that can be defined by the vendor in the Ethernet frame may be used.

[0092] 〔Second Modification Example〕 In the above-described embodiment, when the PON cards 12 and 32 have a function of automatically assigning LLIDs and VIDs, in the discovery of PON communication, the ONUs 20 and 40 at the subscriber's home may report their own priorities (PRIs) to the PON cards 12 and 32. In this case, if the LLID and VID are assigned to the PON cards 12 and 32 according to the reported priority order, QoS information (corresponding tables T1, T2, and T3) can be automatically generated.

[0093] 〔Third Modification Example〕 In the above-described embodiment, the corresponding tables T1, T2, and T3 are exemplified as an example of the QoS information. However, the QoS information may be in a text-based data format instead of a table format. As the text-based data format, for example, CSV (Comma Separated Values), XML (Extensible Markup Language), and JSON (JavaScript Object Notation) can be adopted.

[0094] 〔Other Modification Examples〕 The embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the rights of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope equivalent to the configurations described in the claims.

[0095] In the above-described embodiment, the concentrator cards 11 and 31 and the PON cards 12 and 32 may be communication devices unitized by a housing, not just card types. Therefore, in the above-described embodiment, "concentrator card" and "PON card" can be read as "concentrator unit" and "PON unit", respectively.

Description of Reference Numerals

[0096] 10 Upper-stage OLT 11 Concentrator card (concentrator unit) 11U Frame processing unit (controller) 12 PON card (PON unit) 12A MAC (controller) 12B Memory 20 Upper-stage ONU 20N Normal ONU 20R Relay ONU 20A MAC (controller) 20B Memory 30 Lower OLT 31 Concentrator card (concentrator unit) 31D Frame processing section (controller) 32 PON card (PON unit) 32A MAC (controller) 32B memory 40 Lower ONU 50 Upper device 60 Management terminal 100 PON Systems 200 Upper PON 300 Lower PON T1 Supported Table (Upper QoS Information) T2 Corresponding table (lower row QoS information) T3 Supported Table (Lower QoS Information) P11 Upper DBA P12 First scheduling on the upper side P13 Second scheduling on the upper side P14 Upper level upstream transmission P31 Lower DBA P32 VID granted P33 First scheduling on the lower side P34 Second scheduling on the lower side P35 Lower row up transmission

Claims

1. An upstream OLT that performs upstream DBA for a plurality of upstream ONUs, At least one downstream OLT that performs downstream DBA for at least one downstream ONU, comprising: A multi-stage PON system in which the plurality of upstream ONUs include relay ONUs connected to the downstream OLT, The downstream OLT, A memory for storing the following downstream QoS information, A controller for notifying the upstream OLT of the downstream QoS information, The upstream OLT, A memory for storing the following upstream QoS information and the notified downstream QoS information, A PON system having a controller that performs priority control of an upstream user frame based on the upstream QoS information and the downstream QoS information. Upstream QoS information: Information including a priority order for each upstream LLID that is the LLID of an upstream ONU other than the relay ONU, and identification information that replaces the downstream LLID Downstream QoS information: Information including a priority order for each downstream LLID that is the LLID of a downstream ONU, and identification information that replaces the downstream LLID

2. The controller of the downstream OLT, Adds identification information that replaces the downstream LLID to a user frame transmitted to the relay ONU. The PON system according to claim 1.

3. The controller of the upstream OLT, Deletes the identification information that replaces the upstream LLID and the identification information that replaces the downstream LLID from a user frame transmitted to a higher-level device. The PON system according to claim 2.

4. The controller of the downstream OLT, Updates the downstream QoS information in response to a change in the link state of the downstream ONU, and notifies the upstream OLT of the downstream QoS information every time such an update is performed. The PON system according to any one of claims 1 to 3.

5. The relay ONU, Has a controller that determines its own LLID for each priority order corresponding to the identification information that replaces the downstream LLID, and requests the upstream OLT for the transmission data amount using the determined LLID. The PON system according to any one of claims 1 to 3.

6. An upstream OLT that performs upstream DBA for a plurality of upstream ONUs, At least one downstream OLT that performs downstream DBA for at least one downstream ONU, comprising: A communication control method executed in a multi-stage PON system including relay ONUs connected to the lower-stage OLT among the plurality of upper-stage ONUs, comprising: the lower-stage OLT: notifying the upper-stage OLT of the following lower-stage QoS information; the upper-stage OLT: performing priority control of an upstream user frame based on the following upper-stage QoS information and the notified lower-stage QoS information. Upper-stage QoS information: Information including a priority order for each upper-stage LLID, which is the LLID of an upper-stage ONU other than the relay ONU, and identification information for substituting the lower-stage LLID Lower-stage QoS information: Information including a priority order for each lower-stage LLID, which is the LLID of a lower-stage ONU, and identification information for substituting the lower-stage LLID

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