Control method for station-side equipment and line unit

Abstract

This invention provides a control method for station-side equipment and line units that suspend some of the frame buffers of multiple aggregation nodes. [Solution] A central office device comprising a plurality of line units connected to a home-side device in a P2MP configuration, a central unit that aggregates them, and a control unit that controls the communication operation of the plurality of line units and the central unit, wherein the plurality of line units and the central unit each have a frame buffer for temporarily holding up uplink frames, and the control of the communication operation includes the process of instructing at least one of the plurality of line units to execute the next relay mode and instructing at least one of the remaining line units to execute the next relayed mode. The relay mode is an operating mode in which the device functions as a relay node for uplink frames received from a line unit in relayed mode, and the relayed mode is an operating mode in which the transmission and reception of uplink frames with the central unit is entrusted to the line unit in relay mode.

Description

Technical Field

[0005] ,

[0001] The present disclosure relates to a method for controlling a local device and a line unit.

Background Art

[0002] Patent Document 1 describes an OLT (Optical Line Terminal) including a plurality of OSU (Optical Subscriber Unit) that perform optical communication with an ONU (Optical Network Unit) via a PON (Passive Optical Network) line, a concentration unit that aggregates the plurality of OSU, and an overall control unit that controls the communication operations of the plurality of OSU and the concentration unit.

[0003] In the OLT of Patent Document 1, an upstream frame with the ONU as the transmission source is aggregated in the OSU and output to the concentration unit inside the OLT. Further, the upstream frame output from the OSU to the concentration unit is aggregated by the concentration unit and sent to the upper level.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Communication nodes (hereinafter referred to as "aggregation nodes") that aggregate upstream frames with different transmission sources, such as the OSU and the concentration unit of Patent Document 1, may have a frame buffer that temporarily stores upstream frames during upstream congestion. In this case, if an operation method of always operating the frame buffer is adopted, even when there is a margin in the upstream bandwidth of a specific PON line, the frame buffers of all aggregation nodes will operate, resulting in a problem that power saving is inhibited.

[0006] In light of the aforementioned conventional problems, this disclosure aims to enable the suspension of some of the frame buffers among multiple aggregation nodes. [Means for solving the problem]

[0007] An apparatus according to one aspect of the present disclosure is a central office apparatus comprising: a plurality of line units connected to a home-side apparatus in a P2MP configuration; a central office unit for converging the plurality of line units; and a control unit for controlling the communication operations of the plurality of line units and the central office unit, wherein the plurality of line units and the central office unit each have a frame buffer for temporarily holding up uplink frames. Furthermore, the control of the communication operation includes the process of instructing at least one of the plurality of line units to execute the relay mode described below, and instructing at least one of the remaining line units to execute the relayed mode described below.

[0008] Relay Mode: An operating mode in which the unit functions as a relay node for uplink frames received from a line unit in relay mode. Relay Mode: An operating mode in which the transmission and reception of upstream frames with the concentrator unit are entrusted to a line unit in relay mode.

[0009] This disclosure can be implemented not only as a system and apparatus having the characteristic configuration described above, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, this disclosure can be implemented as a semiconductor integrated circuit that implements part or all of the system and apparatus. [Effects of the Invention]

[0010] According to this disclosure, some of the framebuffers among multiple aggregation nodes can be paused. [Brief explanation of the drawing]

[0011] [Figure 1]Figure 1 is a network connection diagram showing an example of a communication system configuration. [Figure 2] Figure 2 is a block diagram showing an example of the internal configuration of a line unit and a concentrator unit. [Figure 3] Figure 3 is an explanatory diagram illustrating an example of a method for determining the operating state of a frame buffer in a line unit. [Figure 4] Figure 4 is an explanatory diagram illustrating an example of a method for determining the operating state of the frame buffer in a concentrator unit. [Figure 5] Figure 5 is an explanatory diagram showing frame buffer operation pattern 1. [Figure 6] Figure 6 is an explanatory diagram showing frame buffer operation pattern 2. [Modes for carrying out the invention]

[0012] <Summary of the embodiments of this disclosure> The embodiments of this disclosure are outlined below. (1) An apparatus according to one aspect of this embodiment is a central office apparatus comprising: a plurality of line units connected to a home-side apparatus in a P2MP configuration; a central office unit that concentrates the plurality of line units; and a control unit that controls the communication operation of the plurality of line units and the central office unit, wherein the plurality of line units and the central office unit each have a frame buffer for temporarily holding up uplink frames, and the control of the communication operation includes the process of instructing at least one of the plurality of line units to execute the relay mode described below, and instructing at least one of the remaining line units to execute the relayed mode described below.

[0013] Relay Mode: An operating mode in which the unit functions as a relay node for uplink frames received from a line unit in relay mode. Relay Mode: An operating mode in which the transmission and reception of upstream frames with the concentrator unit are entrusted to a line unit in relay mode.

[0014] According to the local device of the present embodiment, by instructing the execution of the above relay mode and the relayed mode, the number of communication lines between the line unit and the concentration unit can be reduced, so the possibility of pausing the frame buffer of the concentration unit can be increased. Therefore, it becomes possible to pause the frame buffers of some of the plurality of aggregation nodes (line unit and concentration unit), and power saving of the local device can be achieved.

[0015] (2) In the local device of (1) above, the control unit may instruct the operation of the frame buffer when N×Bc < ΣBk + Bc for the line unit in the relay mode, and may instruct the pause of the frame buffer when N×Bc ≧ ΣBk + Bc.

[0016] However, N: Number of lines of backplane communication with the concentration unit Bc: Maximum upstream bandwidth per line of backplane communication ΣBk: Total value of the maximum upstream bandwidth of the communication lines with the home devices connected to the line unit In this way, the frame buffer of the line unit in the relay mode can be appropriately operated or paused.

[0017] (3) In the local device of (1) and (2) above, the control unit may instruct the operation of the frame buffer when Bc < ΣBk for the line unit in the relayed mode, and may instruct the pause of the frame buffer when Bc ≧ ΣBk. In this way, the frame buffer of the line unit in the relayed mode can be appropriately operated or paused.

[0018] (4) In the local device of (1) to (3) above, the control unit may instruct the operation of the frame buffer when Bu < J×Bc for the concentration unit, and may instruct the pause of the frame buffer when Bu ≧ J×Bc.

[0019] however, J: Number of backplane communication lines with line units Bu: Maximum uplink bandwidth for communication with higher-level devices This allows the frame buffer of the concentrator unit to be properly activated or deactivated.

[0020] (5) In the station-side equipment described in (1) to (4) above, if the control unit detects a communication interruption in the line unit in relay mode, it may instruct the line unit being relayed to either perform a standalone mode, which transmits uplink frames to the concentrator unit independently, or the relay mode. In this way, even if the line unit in relay mode loses communication, the transmission of uplink frames can be properly continued.

[0021] (6) In the station-side equipment described in (1) to (5) above, the concentrator unit may be made redundant by at least two identical units for load balancing. In this way, by shutting down one of the concentrating units, for example, which is set up as a standby system, it is possible to achieve both improved reliability and power savings for the station-side equipment.

[0022] (7) The method according to this embodiment is a method for controlling a line unit that is executed in the station-side equipment described in (1) to (6) above. Therefore, the control method according to this embodiment has the same effects as the station-side equipment described in (1) to (6) above.

[0023] <Details of the embodiments of this disclosure> The embodiments of this disclosure will be described in detail below with reference to the drawings. At least some of the embodiments described below may be combined in any way.

[0024] [Overall configuration of the communication system] Figure 1 is a network connection diagram showing an example configuration of the communication system 100. As shown in Figure 1, the communication system 100 of this embodiment is a P2MP (Point to Multi Point) network in which a central office device 1 and a plurality of home devices 2 are connected by a tree-structured communication line 3.

[0025] Hereafter, the direction from the central office device 1 to the home device 2 will be referred to as the "downlink direction," and the opposite direction as the "uplink direction." Furthermore, communication frames transmitted in the downlink direction will be called "downlink frames," and communication frames transmitted in the uplink direction will be called "uplink frames." In this embodiment, a PON system is assumed as an example of a P2MP communication system 100. When the communication system 100 is a PON system, the "central office equipment," "home equipment," and "communication line" can be expressed as follows.

[0026] Station side equipment → “OLT” (Optical Line Terminal) Home device → “ONU” (Optical Network Unit) Communication line → "PON line"

[0027] PON line 3 is configured using an ODN (Optical Distribution Network) with bidirectional transmission, for example, where both the downlink and uplink optical signals are transmitted through a single optical fiber. Specifically, the PON line 3 includes a trunk line 4 extending upstream and multiple branch lines 6 branching off from trunk line 4 and extending downstream. Both trunk line 4 and branch lines 6 are single-core (single optical fiber) optical transmission paths through which both upstream and downstream optical signals are transmitted.

[0028] The main line 4 and branch lines 6 are connected by an optical coupler 5 that splits the optical power. The optical coupler 5 is a type of passive optical component that does not have wavelength selection capabilities. An OLT 1 ​​is connected to the upper end of the main line 4, and an ONU 2 is connected to the lower end of each branch line 6. In the example shown in Figure 1, the PON line 3 contains only one optical coupler 5, but multiple optical couplers 5 can be arranged in a vertical column to create a multi-tiered tree structure.

[0029] OLT1 is installed in a central office building, such as a telephone exchange, and is connected to a higher-level device 8 that leads to a higher-level network 7, such as a core network. Multiple ONUs 2 are installed in the homes of subscribers using communication services, for example, and are connected to lower-level networks 9, such as user networks. Therefore, OLT1 is an upper-level relay node of the PON system 100 and functions as a device that aggregates communication between multiple ONUs 2 and the upper-level device 8.

[0030] [OLT Hardware Configuration] As shown in Figure 1, OLT1 is, for example, a chassis-type OLT, and has a housing 12 with a structure in which vertically elongated slots 11 of the same shape are arranged side by side in the width direction. The enclosure 12 includes a backplane (for example, the BP in Figure 2) to which the connector terminals (not shown) of each of the units 20, 30, and 40, which will be described later, can be connected.

[0031] The illustrated OLT1 includes, as an example, two line units 20, two concentrator units 30, and one control unit 40. These units 20, 30, and 40 are made up of circuit boards of roughly the same shape that can be inserted into and removed from any slot 11. Both the line unit 20 and the concentrator unit 30 are types of "aggregation nodes," that is, communication nodes that aggregate uplink frames from different sources.

[0032] The line unit 20 is an OSU capable of connecting multiple PON lines 3. Therefore, the line unit 20 communicates with at least one ONU 2, which is connected to at least one of the multiple PON lines 3, using the PON protocol. In the example shown in Figure 1, three ONUs 2 are connected to the upper PON line 3A in the upper line unit 20, and two ONUs 2 are connected to the lower PON line 3B. Each PON line 3A and 3B can accommodate up to 64 ONUs 2.

[0033] An uplink optical signal with wavelength λ1 is transmitted from ONU2 to line unit 20. A downlink optical signal with wavelength λ2 is transmitted from line unit 20 to ONU2. For example, in the case of the 10G-EPON standard (IEEE 802.3av), the wavelengths λ1 for the uplink optical signal and λ2 for the downlink optical signal are set to the following numerical ranges. 1260nm ≤ λ1 ≤ 1280nm 1575nm ≤ λ² ≤ 1580nm

[0034] The line unit 20 is equipped with multiple optical transceivers 21, and each optical transceiver 21 is connected to the trunk line 4 of the PON line 3. The optical transceiver 21 sends the time-division multiplexed downlink optical signal DO to the trunk line 4. The downlink optical signal DO is decoupled by the optical coupler 5 and transmitted to each branch line 6, reaching the optical transceiver (not shown) of each ONU2. The ONU2 receives and processes the downlink frames addressed to itself included in the downlink optical signal DO, and discards downlink frames not addressed to itself.

[0035] The optical transceiver of ONU2 sends uplink optical signals UO to each of the branch lines 6 of the PON line 3. The transmitted uplink optical signals UO are combined by the optical coupler 5 and transmitted to the main line 4, where they reach the optical transceiver 21 of the line unit 20. The line unit 20 uses time-division multiplexing to control the transmission timing of each ONU 2 so that the uplink optical signals UO do not collide on the main line 4. Therefore, the uplink optical signals UO transmitted by each ONU 2 are aligned on the time axis with a guard time in between.

[0036] The concentrator unit 30 is a device that concentrates all line units 20 within the OLT 1 ​​at the upper end. The concentrator unit 30 communicates with the upper end device 8 via an optical transceiver 31 and communicates with each line unit 20 via a backplane (for example, BP in Figure 2). The two concentrator units 30, 30 are made redundant for load balancing. Specifically, the physical links (optical fibers) connecting each concentrator unit 30, 30 to the higher-level device 8 are logically combined into one to form a multi-chassis link aggregation (MC-LAG).

[0037] The control unit 40 is a control device that controls the communication operations of each unit mounted in the slot 11 of the housing 12, such as the line unit 20 and the concentrator unit 30. The control unit 40 is connected to the management terminal 10 via a control line such as a LAN (Local Area Network) cable. A LAN (Local Area Network) may also be interposed between the OLT1 and the management terminal 10.

[0038] The management terminal 10 is, for example, a management computer operated by a communications administrator, and is capable of communicating with the control unit 40 using a predetermined management communication protocol. The management terminal 10 transmits configuration information regarding OLT1 communication to the control unit 40 in response to operation input obtained, for example, via the command line. The control unit 40 performs various settings related to the communication operation of OLT1 based on the configuration information received from the management terminal 10.

[0039] Specifically, the control unit 40 performs serial communication (for example, I2C communication) with itself as the master and the other units 20 and 30 as slaves, and performs various settings by causing the other units 20 and 30 to execute predetermined slave processing. Various settings include, for example, setting the maximum bandwidth for the uplink and downlink directions, setting the wavelengths for optical transceivers 21 and 31, setting QoS (Quality of Service) policies for each LLID (Logical Link ID), and setting VLAN (Virtual LAN) settings.

[0040] [Internal configuration of line unit and concentrator unit] Figure 2 is a block diagram showing an example of the internal configuration of the line unit 20 and the concentrator unit 30. Below, we will explain the definitions of the reference numerals and parameters in Figure 2, and then describe the internal configuration of each unit 20 and 30.

[0041] The reference signs and parameter definitions in Figure 2 are as follows: m: This is the identification number of line unit 20. LN1: This is line unit 20 with m=1. LN2: This is line unit 20 with m=2.

[0042] n: This is the identification number of the wire collection unit 30. This is a concentrating unit 30 with LC1:n=1. LC1 is redundant with LC2. This is a concentrating unit 30 with LC2:n=2. LC2 is redundant with LC1.

[0043] k: This is the identification number for optical transceiver 21 or PON line 3. TRx1: This is optical transceiver 21 with k=1. This is an optical transceiver 21 with TRx2:k=2. This is optical transceiver 21 with TRx3:k=3. This is an optical transceiver 21 with TRx4:k=4.

[0044] PON1: This is PON line 3 connected to TRx1. PON2: This is PON line 3 connected to TRx2. PON3: This is PON line 3 connected to TRx3. PON4: This is PON line 3 connected to TRx4.

[0045] Pi: A port on line unit 20 (LN1 or LN2) that sends and receives communication frames in backplane communication. "i" is the identification number of port Pi. P1: This is the port for sending and receiving communication frames for LC1. P2: This is the port for sending and receiving communication frames for LC2.

[0046] Pr: This is the port for sending and receiving communication frames for other line units 20. Hereinafter, port Pr of line unit 20 will be referred to as the "relay port Pr".

[0047] Qj: This is a port on the concentrator unit 30 (LC1 or LC2) that transmits and receives communication frames in backplane communication. "j" is the identification number of port Qj. Q1: This is the port for sending and receiving communication frames for LN1. Q2: This is the port for sending and receiving communication frames for LN2.

[0048] BP: This is the backplane of the chassis 12, which includes the transmission lines L1, L2, L3, L4, and L5 of the following communication frames. L1: This is a transmission line connecting port P1 of LN1 and port Q1 of LC1. L2: This is a transmission line connecting port P2 of LN2 and port Q1 of LC2. This is a transmission line connecting port P1 of L3:LN2 and port Q2 of LC1. L4: This is a transmission line connecting port P2 of LN2 and port Q2 of LC2. L5: This is a transmission line connecting the relay port Pr of LN1 and the relay port Pr of LN2.

[0049] [Internal configuration of the line unit] Since LN1 and LN2 have the same internal configuration, the following explanation will mainly focus on the configuration of LN1. In other words, redundant explanations regarding devices with the same reference numeral in LN1 and LN2 will be omitted. As shown in Figure 2, the LN1 comprises multiple optical transceivers 21 (TR1 and TR2 in the example), multiple PON processing units 22, a control unit 23, a frame buffer 24, and a switch unit 25.

[0050] The optical transceiver 21 is an optical module that converts optical signals and electrical signals for PON communication into and out of each other. For example, an SFP (Small Form Factor Pluggable) type can be used as the optical transceiver 21. SFP type refers to a general term for SFP, SFP+, SFP28, QSFP, QSFP28, and their backward-compatible pluggable optical modules.

[0051] The PON processing unit 22 is a frame processing unit for PON communication, provided in one-to-one correspondence with the optical transceiver 21. The PON processing unit 22 is electrically connected to the corresponding optical transceiver 21 and is also electrically connected to a predetermined port of the switch unit 25. The PON processing unit 22 includes an LSI (Large Scale Integration) that performs the aforementioned upstream time-division multiplexing in accordance with the PON standard (e.g., IEEE 802.3av).

[0052] The PON processing unit 22 may be composed of, for example, a System on a Chip (SoC) that includes at least one CPU (Central Processing Unit). The PON processing unit 22 may include an integrated circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) in addition to or as a substitute for the CPU.

[0053] The switch unit 25 is an integrated circuit such as an LSI having a Layer 2 relay function, and may consist of a MAC chip including at least one of FPGA and ASIC. The switch unit 25 performs relay processing to determine the output port according to the destination MAC address of the received communication frame. When traffic congestion occurs during the relaying of a communication frame, the switch unit 25 temporarily saves the communication frame to the frame buffer 24.

[0054] The frame buffer 24 is a volatile memory that operates at a predetermined data transfer rate. As the volatile memory, SDR (Single Data Rate) memory or DDR (Double Data Rate) memory may be used. The control unit 23 is, for example, an arithmetic processing unit including a CPU and memory. The control unit 23 may include an FPGA, ASIC, or ASSP (Application Specific Standard Product), or it may consist of at least one of FPGA, ASIC, and ASSP.

[0055] The control unit 23 operates as a slave for serial communication such as I2C, and can perform the following settings on itself according to instructions from the control unit 40. Setting 1: Setting the operating status of frame buffer 24 (e.g., "Running" or "Hibernating"). Setting 2: Setting the operating status of the relay port Pr (e.g., "Enabled" or "Disabled"). Setting 3: Setting the operating mode of the line unit 20 ("standalone mode", "relay mode", or "relayed mode")

[0056] Standalone mode is an operating mode in which the unit independently transmits and receives uplink frames with the concentrator unit 30, without the need for relaying through other line units 20. The relay mode is an operating mode in which the unit functions as a relay node for uplink frames received from other line units 20. The relay mode is an operating mode in which the transmission and reception of uplink frames with the concentrator unit 30 is not performed directly by the unit itself, but is entrusted to the relay mode line unit 20.

[0057] [Internal configuration of the wire collection unit] Since LC1 and LC2 have the same internal configuration, the following explanation will mainly focus on the configuration of LC1. In other words, redundant explanations regarding devices with the same reference numeral in LC1 and LC2 will be omitted. As shown in Figure 2, LC1 comprises an optical transceiver 31, a switch unit 32, a control unit 33, and a frame buffer 34.

[0058] The optical transceiver 31 is an optical module that converts optical signals and electrical signals for optical communication with the host device 8. Similar to the case of the optical transceiver 21, an SFP type may be used for the optical transceiver 31. The optical transceiver 21 and each port Qj (ports Q1 and Q2 in the diagram) are electrically connected to predetermined ports of the switch unit 32.

[0059] The switch unit 32 is an integrated circuit such as an LSI having a Layer 2 relay function, and may be composed of a MAC chip including at least one of FPGA and ASIC. The switch unit 32 performs relay processing to determine the output port according to the destination MAC address of the received communication frame. If traffic congestion occurs during the relaying of the communication frame, the switch unit 32 temporarily saves the communication frame to the frame buffer 24.

[0060] The frame buffer 34 is a volatile memory that operates at a predetermined data transfer rate. SDR memory or DDR memory can be used as the volatile memory. The control unit 33 is, for example, an arithmetic processing unit including a CPU and memory. The control unit 33 may include an FPGA, ASIC, or ASSP, or may consist of at least one of FPGA, ASIC, and ASSP.

[0061] The control unit 33 operates as a slave for serial communication such as I2C, and can set the operating status of the frame buffer 34 related to its own unit (for example, "operating" or "hibernating") according to instructions from the control unit 40.

[0062] [Method for determining the operating state of the frame buffer in a line unit] Figure 3 is an explanatory diagram illustrating an example of how the operating state of the frame buffer 24 in the line unit 20 is determined. The meanings of the reference numerals and parameters in Figure 3 are as follows:

[0063] LNm: This is line unit 20 with identification number m. N: This is the number of backplane communication lines. Specifically, it is the number of LNm ports connected to the backplane BP. In the example diagram, the number of ports N is "2" (ports P1 and P2). Bc: Maximum uplink bandwidth per backplane communication line (e.g., 10 Gbps) ΣBk: This is the total maximum uplink bandwidth of the three PON lines connected to LNm.

[0064] As shown in Figure 3, the operating state of the LNm's frame buffer 24 is determined as follows, depending on the type of operating mode. When LNm is in "standalone mode": When N×Bc < ΣBk, frame buffer 24 is activated (turned on). When N×Bc ≥ ΣBk, frame buffer 24 is paused (turned off).

[0065] If LNm is in "relay mode": When N×Bc < ΣBk+Bc, frame buffer 24 is activated (turned on). When N×Bc ≥ ΣBk+Bc, framebuffer 24 is paused (turned off).

[0066] When LNm is in "relay mode": When Bc < ΣBk, frame buffer 24 is activated (turned on). When Bc ≥ ΣBk, frame buffer 24 is paused (turned off).

[0067] The switching of the operating state of the frame buffer 24 may be determined manually by the communications administrator, or it may be determined autonomously by the control unit 40. When the control unit 40 makes a decision, the management terminal 10 should notify the control unit 40 of the type of operating mode to be set in LNm and the parameters N, Bc, and ΣBk. In this case, the control unit 40 should activate or deactivate the frame buffer 24 of the line unit 20 by determining which inequality the notified parameters correspond to for each type of operating mode.

[0068] [Method for Determining the Operating State of the Frame Buffer in the集线Unit] FIG. 4 is an explanatory diagram showing an example of a method for determining the operating state of the frame buffer 34 in the集线 unit 30. The meanings of the reference numerals and parameters in FIG. 4 are as follows.

[0069] LCn:集线 unit 30 with identification number n. J: The number of ports of LCn used for backplane communication. In the illustrated example, the number of ports J is "2" (ports Q1 and Q2). Bu: Upstream maximum bandwidth for communication with the upper device 8 (e.g., 10 Gbps) Bc: Upstream maximum bandwidth in the backplane BP (e.g., 10 Gbps)

[0070] As shown in FIG. 4, the operating state of the frame buffer 34 of LCn is determined as follows. When Bu < J×Bc, the frame buffer 34 is activated (turned on). When Bu ≧ J×Bc, the frame buffer 34 is put into standby (turned off).

[0071] The switching of the operating state of the frame buffer 34 may be determined artificially by the communication administrator or autonomously by the control unit 40. When the control unit 40 makes the determination, the parameters J, Bu, and Bc may be notified from the management terminal 10 to the control unit 40. In this case, the control unit 40 may determine which inequality the notified parameters correspond to and operate or standby the frame buffer 34 of the集线 unit 30 accordingly.

[0072] [Operating Pattern 1 of the Frame Buffer] FIG. 5 is an explanatory diagram showing Operating Pattern 1 of the frame buffers 24 and 34. In Operating Pattern 1 of FIG. 5, the operating modes of LN1 and LN2 are both "standalone mode", and it is assumed that the upstream maximum bandwidth of the PON line 3 of each line unit 20 is as follows. LN1's ΣBk = 22Gbps LN2's ΣBk = 2Gbps

[0073] As shown in Figure 5, in standalone mode, LN1 has a frame buffer of 2 × 10 Gbps < 22 Gbps, so the frame buffer 24 of LN1 must be set to ON. However, in standalone mode, LN2 has a frame buffer of 2 × 10 Gbps ≥ 2 Gbps, so the frame buffer 24 of LN2 can be set to OFF. On the other hand, since 10Gbps < 20Gbps is the case for LC1 and LC2, the frame buffers 34 for LC1 and LC2 need to be set to ON.

[0074] [Framebuffer operation pattern 2] Figure 6 is an explanatory diagram showing operation pattern 2 of frame buffers 24 and 34. In operation pattern 2 of Figure 6, the operating mode of LN1 is "relay mode", the operating mode of LN2 is "received mode", and the maximum upstream bandwidth of the PON line 3 for each line unit 20 is as follows. LN1's ΣBk = 22Gbps LN2's ΣBk = 2Gbps

[0075] As shown in Figure 6, in relay mode LN1, 2 × 10Gbps < 32Gbps, so the frame buffer 24 of LN1 must be set to ON. However, in standalone mode LN2, 10Gbps ≥ 2Gbps, so the frame buffer 24 of LN2 can be set to OFF.

[0076] On the other hand, if LN1 is in relay mode and LN2 is in relay mode, LC1 and LC2 are connected to LN1 only via port Q1 in backplane communication. Therefore, for LC1 and LC2, 10Gbps ≥ 10Gbps is satisfied, and the frame buffers 34 of LC1 and LC2 can be set to OFF.

[0077] As is clear from comparing operation pattern 1 (Figure 5) and operation pattern 2 (Figure 6), by adopting a connection configuration in which LN1 is in relay mode and LN2 is in relay mode, the number of backplane communication lines J between LC1 and LC2 and the line unit 20 can be reduced to one. Therefore, compared to setting LN1 and LN2 to separate modes, the inequality Bu≧J×Bc is more likely to hold for LC1 and LC2, increasing the possibility of pausing the frame buffers 34 of LC1 and LC2.

[0078] [How to deal with communication interruptions] By the way, when LN2 is set to relay mode, LN1 takes over the uplink frames that LN2 should originally transmit and sends them to LC1 and LC2. Therefore, if LN1 is removed or malfunctions, uplink frames from PON line 3 connected to LN2 will no longer be transmitted. Therefore, it is preferable that the control unit 40, for example, by monitoring the status of serial communication, issues an instruction to switch LN2 to either standalone mode or relay mode when it detects a communication interruption in LN1, which is in relay mode.

[0079] [Other variations] The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments described above, and includes all modifications within the scope equivalent to the configurations described in the claims.

[0080] In the above-described embodiment, the line unit 20 in relay mode is not limited to one but may be multiple. For example, in an OLT1 equipped with three line units 20, LN1, LN2, and LN3, LN1 may be set to relay mode and LN2 and LN3 to relay mode. In this case, LN2 and LN3 will be connected in a star configuration under LN1. Furthermore, the line unit 20 in relay mode is also not limited to one but may be multiple.

[0081] In the above-described embodiment, the central office device 1 and the home device 2 do not necessarily have to be devices that perform optical communication. In other words, the communication system 100 is not limited to PON and may be a system that employs a transmission path other than an optical line. [Explanation of symbols]

[0082] 1 Station side equipment (OLT) 2 Home unit (ONU) 3. Communication lines (PON lines) 3A PON line 3B PON line 5 Optical coupler 6 branch lines 7 Upper network 8. Higher-level equipment 9 Lower network 10 Management terminals 11 slots 12 cabinets 20 line units 21 Optical Transceiver 22 PON Processing Unit 23 Control Unit 24 frame buffers 25 Switch section 30 Concentration Units 31 Optical Transceiver 32 Switch section 33 Control Unit 34 Framebuffer 40 Control Units 100 Communication Systems (PON Systems) BP backplane Port for backplane communication on the Pi line unit Qj Port for backplane communication of the concentrator unit

Claims

1. Multiple line units connected to the home-side device in a P2MP configuration, A concentrating unit that brings together the aforementioned multiple line units, A station-side device comprising a control unit that performs control of the communication operation of the plurality of line units and the concentrator unit, The plurality of line units and the concentrating unit are, Each has a frame buffer to temporarily hold back incoming frames, The control of the aforementioned communication operation is as follows: A station-side device that includes a process of instructing at least one of the plurality of line units to perform the relay mode described below, and instructing at least one of the remaining line units to perform the relayed mode described below. Relay Mode: An operating mode in which the unit functions as a relay node for uplink frames received from a line unit in relay mode. Relay mode: An operating mode in which the transmission and reception of uplink frames with the concentrator unit is entrusted to a line unit in relay mode.

2. The control unit is For the line unit in relay mode, The operation of the frame buffer is instructed when N × Bc < ΣBk + Bc. The station-side device according to claim 1, which instructs the frame buffer to pause when N × Bc ≥ Σ Bk + Bc. however, N: Number of backplane communication lines with the concentrator unit Bc: Maximum uplink bandwidth per line for backplane communication ΣBk: The total maximum upstream bandwidth of the communication line between the line unit and the home-side equipment.

3. The control unit is For the line unit in relay mode, The operation of the frame buffer is instructed when Bc < ΣBk. The station-side device according to claim 2, which instructs the frame buffer to pause when Bc ≥ ΣBk.

4. The control unit is For the aforementioned concentrating unit, If Bu < J × Bc, the operation of the frame buffer is instructed. The station-side device according to claim 3, which instructs the frame buffer to pause when Bu ≥ J × Bc. however, J: Number of backplane communication lines with line units Bu: Maximum uplink bandwidth for communication with higher-level devices.

5. The control unit is If a communication interruption is detected in the line unit in relay mode, The station-side device according to any one of claims 1 to 4, which instructs the line unit in relay mode to perform either a standalone mode, in which it independently transmits uplink frames to the concentrator unit, or the relay mode.

6. The aforementioned wire collection unit is The station-side device according to any one of claims 1 to 4, which is redundant with at least two identical units for load balancing.

7. A method for controlling multiple line units connected to a home-side device in a P2MP configuration, The aforementioned multiple line units are, Each has a frame buffer to temporarily hold back incoming frames, The control method described above is The steps include instructing at least one of the plurality of line units to perform the relay mode described below, A method for controlling a line unit, comprising the step of instructing at least one of the remaining line units to perform the following relay mode. Relay Mode: An operating mode in which the unit functions as a relay node for uplink frames received from a line unit in relay mode. Relay mode: An operating mode in which the transmission and reception of uplink frames with the concentrator unit is entrusted to a line unit in relay mode.

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