JP2015154211A - Master station device, communication system, communication control method and control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a master station device which does not generate a frame loss at a wavelength changeover.SOLUTION: The master station device, which constitutes a communications system together with one or more slave station devices capable of changing a reception wavelength, can simultaneously transmit a plurality of optical signals of different wavelengths. At the changeover of a downlink wavelength to be received by the slave station device, before the start of the downlink wavelength changeover at the slave station device, the master station device halts data transmission destined to the slave station device and starts buffering data destined to the slave station device. After the completion of the wavelength changeover at the slave station device, the master station device transmits the buffered data destined to the slave station device, using a new wavelength after the changeover.

Description

  The present invention relates to a master station device, a communication system, a communication control method, and a control device of an optical communication system.

  With the spread of FTTH (Fiber To The Home), optical subscriber termination devices such as G-EPON (Gigabit Ethernet Passive Optical Network) have been introduced. The PON system is an optical communication system in which a plurality of subscriber devices (ONU: Optical Network Unit) as slave station devices are connected to a station side device (OLT: Optical Line Terminal) as a master station device via a star coupler. In the currently introduced PON system, an OLT and a plurality of ONUs connected by a single optical fiber and a star coupler communicate with each other by using different wavelengths for upstream and downstream. That is, downstream communication is transmitted by broadcast communication from the OLT to each ONU, and upstream communication is performed in bursts by time division multiplexing toward each OLT according to an instruction from the OLT. In upstream communication, control is performed so that signals from each ONU on the transmission line do not collide. Even with 10G-EPON, the next-generation model of G-EPON, the transmission speed has been increased from 1 Gbps to 10 Gbps, but the transmission control is the same as G-EPON. Has been.

  As a next-generation PON system, a PON system using both TDM (Time Division Multiplexing) / WDM (Wavelength Division Multiplexing) has been studied. The OLT of a PON system using both TDM / WDM includes a plurality of OSUs (Optical Subscriber Units), and each OSU transmits and receives optical signals having different wavelengths. The wavelength transmitted and received by each OSU is fixed. On the other hand, the ONU is colorless, and the wavelength transmitted and received by each ONU is dynamically changed according to an instruction from the OLT.

  In a conventional PON system using TDM / WDM, a method has been proposed in which a downstream signal is once separated into signals for each ONU, dynamically cross-connected, and distributed to a plurality of wavelength tunable lasers (see Patent Document 1). The dynamic downlink wavelength allocation, which is a feature of this system, differs by monitoring the traffic volume in the downlink signal to each ONU and dynamically assigning the downlink wavelength according to the traffic volume of each downlink signal. Perform optimal bandwidth allocation across wavelengths.

JP 2011-82908 A

  In the conventional system described above, the downstream signal is transmitted from the OLT even while the ONU is switching the wavelength, and the downstream signal that arrives at the ONU while the ONU is switching the wavelength (used before the start of wavelength switching). There is a problem that the downstream signal (arriving at the wavelength) cannot be received by the ONU.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a master station device, a communication system, a communication control method, and a control device in which no frame loss occurs when switching wavelengths.

  In order to solve the above-described problems and achieve the object, the present invention forms a communication system together with one or more slave station devices capable of switching the wavelength to be received, and simultaneously transmits a plurality of optical signals having different wavelengths. When switching the downlink wavelength received by the slave station device, which is a master station device capable of transmission, the transmission of the data addressed to the slave station device is stopped before the downlink wavelength switching in the slave station device is started. In addition, buffering of the data addressed to the slave station device is started, and after the switching of the wavelength in the slave station device is completed, the buffered data addressed to the slave station device is transmitted at the new wavelength after switching. It is characterized by.

  According to the present invention, it is possible to prevent occurrence of frame loss during wavelength switching.

FIG. 1 is a diagram illustrating a configuration example of a communication system including a master station device according to the present invention. FIG. 2 is a diagram showing a conventional PON system using both TDM / WDM. FIG. 3 is a diagram illustrating an example of a functional configuration block of the OLT. FIG. 4 is a sequence diagram illustrating an example of the downstream wavelength switching operation.

  Hereinafter, embodiments of a master station device, a communication system, a communication control method, and a control device according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of a communication system including a master station device according to the present invention. FIG. 1 shows a PON (Passive Optical Network) system as an example of a communication system. As shown in FIG. 1, this communication system is connected to a station side device (also referred to as “Optical Line Terminal”, hereinafter referred to as “OLT”) 1 operating as a master station device, and to an OLT 1 via an optical fiber and a splitter. And a user side device (also referred to as “Optical Network Unit”, hereinafter referred to as “ONU”) 2 that operates as a slave station device. Although not shown, each ONU 2 is connected to one or a plurality of terminal devices (hereinafter referred to as “terminals”), and each terminal is connected via the ONU 2, OLT 1, and upper network. Sends / receives data to / from the communication partner terminal.

  FIG. 1 also shows the hardware configuration of the OLT 1. The OLT 1 stores a PON control unit (control device) 101 that performs processing on the OLT side based on the PON protocol, a reception buffer 102 for storing upstream data received from the ONU 2, and downstream data to be transmitted to the ONU 2. NNI (Network Node Interface) between a transmission buffer 103 for transmission, an optical transceiver 104 that performs transmission / reception processing of an optical signal, a WDM coupler (WDM) 105 that multiplexes a plurality of optical signals having different wavelengths, and an upper network And a physical layer processing unit (PHY) 106 that realizes the physical interface function. The optical transceiver 104 can transmit and receive a plurality of optical signals having different wavelengths. Note that the PON control unit 101 assigns a band to each ONU 2 for transmission permission so that transmission time zones do not overlap each other for each ONU 2 group having the same wavelength to be used, as in the conventional PON system. The transmission data from the ONU 2 is prevented from colliding.

  The communication system shown in FIG. 1 is a PON system using both TDM (Time Division Multiplexing) / WDM (Wavelength Division Multiplexing).

  Here, a conventional general TDM / WDM combined PON system will be described with reference to FIG.

  As shown in FIG. 2, in the PON system using both TDM / WDM, the OLT includes a plurality of OSUs (Optical Subscriber Units) as optical transceivers, and each OSU transmits and receives optical signals having different wavelengths. The wavelength transmitted and received by each OSU is fixed. In the PON system shown in FIG. 2, OSU # n (n = 1, 2, 3) transmits the downstream wavelength λdn and receives the upstream wavelength λun. Each ONU is connected to the OLT via a star coupler. In the example of FIG. 2, ONUs # 1, # 4, and # 7 use upstream wavelength λu1 and downstream wavelength λd1, ONUs # 2, # 5, and # 8 use upstream wavelength λu2 and downstream wavelength λd2, and ONU # 3, # 6 and # 9 use upstream wavelength λu3 and downstream wavelength λd3. Each ONU is a colorless ONU, and the wavelength transmitted and received by each ONU can be dynamically changed, for example, according to an instruction from the OLT. When receiving the downstream frame addressed to each ONU, the I / F unit distributes it to any one OSU (an OSU corresponding to the wavelength used by the destination ONU). The setting of the downstream frame distribution destination is changed in accordance with the change of the reception wavelength on the ONU side. As described above, in the conventional TDM / WDM combined PON system, if a downstream frame arrives while switching the wavelength received by the ONU, a frame loss occurs. In FIG. 2, wavelengths (λd1 to λd3, λu1 to λu3) described between the OLT and the ONU indicate wavelengths transmitted and received by each ONU. As for the downstream wavelengths, in practice, all wavelengths (λd1 to λd3) are transmitted from the OLT to each ONU, and each ONU is assigned to one of the downstream wavelengths transmitted from the OLT. Receive wavelength.

  Next, the OLT 1 of the present embodiment shown in FIG. 1, specifically, the OLT 1 capable of preventing the occurrence of frame loss when the reception wavelength is switched on the ONU side will be described.

FIG. 3 is a diagram illustrating an example of a functional configuration block of the OLT 1. The OLT 1 includes a wavelength demultiplexing unit 10, a plurality of OSUs 20 (OSUs 20 ₁ , 20 ₂ ,..., 20 _m ), a downlink allocating unit 30, a destination information table 31, a downlink wavelength assigning unit 40, a statistical information managing unit 41, and a read control. Unit 50, a plurality of queues 51 (queues 51 ₁ , 51 ₂ ,..., 51 _n ), a queue distribution unit 60, a MAC address learning table 61, and a multiplexing unit 70. Each OSU 20 includes an LD (Laser Diode) 21 (21 ₁ , 21 ₂ ,..., 21 _m ) as an optical transmitter and a PD (Photodiode) 22 (22 ₁ , 22 ₂ ,..., 22 _m as an optical receiver. ), And a frame demultiplexing unit 23 (23 ₁ , 23 ₂ ,..., 23 _m ) that demultiplexes a PON control frame and a user frame (a frame for transmitting / receiving user data and the like). In each OSU 20, the downstream wavelength transmitted by the LD 21 and the upstream wavelength received by the PD 22 are fixed and are set when the apparatus is activated. Each component illustrated in FIG. 3 is realized by the PON control unit 101, the reception buffer 102, the transmission buffer 103, the optical transceiver 104, and the like illustrated in FIG. The ONU 2 can switch the wavelength to be transmitted / received. When receiving a wavelength change instruction from the OLT 1, the ONU 2 switches to transmit / receive the instructed wavelength.

  The wavelength demultiplexing unit 10 multiplexes the wavelength (optical signal) output from the LD 21 of each OSU 20 and outputs the multiplexed signal to each ONU 2 and is transmitted from each ONU 2 and arrives in a state where a plurality of wavelengths are multiplexed. Each wavelength is separated from the optical signal and output to the PD 22 of the OSU 20. The OSU 20 multiplexes the user frame input from the downlink allocating unit 30 and the control frame input from the downlink wavelength allocating unit 40 and transmits to the ONU 2 as a transmission operation of the wavelength allocated to itself. Also, as a reception operation of the wavelength allocated to itself, the frame received from each ONU 2 is confirmed, and if it is a control frame, it is output to the downlink wavelength allocation unit 40, and if it is a user frame, it is output to the multiplexing unit 70. .

  When a downlink frame (downlink user frame) is input from the read control unit 50, the downlink distribution unit 30 outputs the frame to the OSU 20 associated with the destination (ONU ID) of the input frame. The destination information table 31 manages the correspondence between the destination of the downstream frame and the output destination OSU (OSU ID). The destination information table 31 is updated when wavelength switching occurs in the ONU 2. The downlink wavelength allocation unit 40 determines the wavelength that each ONU 2 should receive from the statistical information of the downlink frame to each ONU 2 by an arbitrary algorithm. The statistical information management unit 41 collects and manages statistical information regarding the frames put into each of the plurality of queues 51. The statistical information is, for example, the amount of data (downstream frame) held by each queue 51 (the amount of data stored in the queue 51). The read control unit 50 stops and restarts frame output from each queue 51 for each queue in accordance with an instruction from the downstream wavelength assignment unit 40. Each of the plurality of queues 51 is associated with any one of the ONUs 2 and receives and holds a downstream frame addressed to the associated ONU 2. The queue distribution unit 60 receives the downstream frame from the upper network, identifies the ONU 2 (ONU ID) of the downstream frame destination based on the destination MAC address and the MAC address learning table 61, and associates it with the identified ONU 2. To the queue 51. The MAC address learning table 61 is a table that is referred to when the queue distribution unit 60 determines the output destination of the downstream frame, and manages the correspondence between the downstream MAC destination MAC address and the ONU ID. For example, the MAC address learning table 61 is updated when an uplink frame (uplink user frame) is transferred. That is, when an upstream frame is received, the transmission source MAC address stored in the received frame is registered in the MAC address learning table 61 in a state where the ONU ID is associated. The multiplexing unit 70 receives, multiplexes and outputs the upstream frame received by each OSU 20.

  Next, the overall operation of the OLT 1 will be described. First, the downlink frame transfer operation will be described. When a downstream frame arrives at the OLT 1 from a host network (not shown), the downstream frame is input to the queue distribution unit 60. When a downstream frame is input, the queue distribution unit 60 refers to the MAC address learning table 61 and searches for an ONU ID corresponding to the input MAC address of the downstream frame. When the search for the ONU ID is completed, the searched ONU ID is assigned to the input downstream frame and put into the queue 51 corresponding to the assigned ONU ID.

  The downlink frames stored in the queue 51 are read by the read control unit 50 at a predetermined timing and output to the downlink distribution unit 30. The read control unit 50 sequentially reads the stored downlink frames without stopping reading the frames stored in each queue 51 during normal times (that is, when the downlink wavelength assigned to a certain ONU 2 is not being switched). Output to the down-distribution unit 30. On the other hand, when the downlink wavelength assigned to a certain ONU 2 is being switched, the read control unit 50 stops reading from the queue 51 in which the downlink frame whose destination is the ONU 2 whose downlink wavelength is being switched is stored. Reading is stopped and restarted according to an instruction from the downstream wavelength allocation unit 40.

  When receiving a downstream frame from the read control unit 50, the downstream distribution unit 30 refers to the destination information table 31 and searches the OSU ID by using the ONU ID given to the downstream frame by the queue distribution unit 60 as a key. . When the search is completed, the downlink distribution unit 30 transfers the downlink frame to the OSU 20 indicated by the searched OSU ID. In the OSU 20 that has received the downlink frame, the frame demultiplexing unit 23 multiplexes the received downlink frame and the PON control frame input from the downlink wavelength allocation unit 40, and the LD 21 converts the multiplexed frame into an optical signal. And output to the wavelength multiplexing / demultiplexing unit 10. The wavelength demultiplexing unit 10 outputs the optical signal transmitted from each OSU 20 toward each ONU 2.

  Next, the operation of switching the downstream wavelength will be described with reference to FIG. FIG. 4 is a sequence diagram illustrating an example of the downstream wavelength switching operation. In FIG. 4, among the components of OLT 1, downlink wavelength allocation unit 40, destination information table 31 and read control unit 50 related to downlink wavelength switching, and ONU 2 (referred to as ONU # n) that is a downlink wavelength switching target, Between the OSU of the communication partner before ONU # n switches the downstream wavelength (referred to as OSU # m) and the OSU of the communication partner after ONU # n switches the downstream wavelength (referred to as OSU # k) A downlink communication state and a setting sequence are shown.

  FIG. 4 shows (1) a phase before switching the downstream wavelength, (2) a phase during switching the downstream wavelength, and (3) a phase after switching the downstream wavelength. Each of these phases will be described.

(1) Phase before switching the downstream wavelength In this phase, the downstream frame addressed to the terminal connected to the ONU #n input to the OLT 1 is transmitted from the MAC address to the ONU ID by the queue distribution unit 60 in FIG. And is put into the queue for ONU # n (any _{one of the} queues 51 ₁ to 51 _n ). Here, the description will be continued _assuming that the queue 51 _n is a queue for ONU #n (a queue for storing frames addressed to ONU #n). The downstream distribution unit 30 reads the downstream frame from the queue 51 _n via the readout control unit 50, searches the OSU ID from the ONU ID given to the readout downstream frame, and the OSU of the retrieved OSU ID (FIG. 4). The frame is transferred to OSU # m in the example shown in FIG. The OSU # m transfers the frame received from the downlink distribution unit 30 to the ONU # n.

(2) Phase during downlink wavelength switching In this phase, first, the downlink wavelength assigning unit 40 (see FIG. 3) determines ONU # n wavelength switching by an arbitrary algorithm (step S1), and the read control unit 50 Is instructed to output gate the queue 51 _n which is the queue of ONU #n (step S2). Receiving this instruction, the read control unit 50 does not perform the read operation from the queue 51 _n, and stops outputting the frame addressed to ONU # n to the downstream distribution unit 30. The downlink wavelength allocating unit 40 further transmits to OSU # m (an OSU that transmits / receives a wavelength being used by ONU # n) so as to transmit a Gate frame for instructing a change in downlink wavelength setting to ONU # n. An instruction (notification of downlink wavelength setting) is issued (step S3). For example, when the amount of data stored in the queue 51 _n exceeds a preset threshold value, the downlink wavelength assigning unit 40 determines to switch the downlink wavelength assigned to the ONU #n. Although a method for determining a wavelength to be newly assigned (wavelength after switching) is not particularly defined, for example, a wavelength assigned to an ONU having a small downlink data reception amount is determined as a wavelength after switching. The amount of downlink data received by each ONU can be known from, for example, statistical information managed by the statistical information management unit 41.

  The OSU # m receiving the instruction in step S3 transmits a Gate frame (downlink wavelength change Gate frame) instructing switching of the downlink wavelength to the ONU # n. At this time, in addition to the time stamp when the Gate frame is issued, the OSU # m takes a time required until the ONU # n returns a response (change response report frame) (after the ONU # n receives the Gate frame). A value obtained by adjusting the receiver so that a new wavelength can be received and returning a response) is added to the time stamp, and is stored in the Gate frame as a change response Report frame transmission start time. The value added to the time stamp (required time until the ONU # n returns a response) is specifically the reception processing time of the ONU # n downlink wavelength change Gate frame acquired in advance from the ONU # n, and the wavelength switching. Is a value obtained by adding the ONU # n downlink extraction clock recovery time, the code synchronization time, and the change response report frame generation processing time.

  When the ONU #n receives a downlink wavelength change Gate frame instructing a change of the downlink wavelength from the OSU #m, the ONU #n changes the setting of the receiver to receive the indicated downlink wavelength, and when the change is completed, the change response Report Return the frame. The change response report frame is transmitted at the time designated by the downlink wavelength change gate frame, that is, the change response report frame transmission start time.

When the OSU # m receives the change response report frame from the ONU # n, the OSU # m notifies the downstream wavelength allocation unit 40 of a setting response indicating that (step S4). When receiving the notification of the setting response, the downlink wavelength allocation unit 40 rewrites the destination of ONU # n set in the destination information table 31 (see FIG. 3) from OSU # m to OSU # k (step S5). It should be noted that the frame addressed to ONU # n is accumulated in the queue (queue 51 _n ) set for ONU # n after the process of step S2 until the process of step S5 ends. (Not read from queue 51 _n ).

(3) downstream wavelength switching after phase downstream wavelength assignment unit 40, when running the step S5 to update the destination information table 31 is terminated, to the read controller 50, releasing the gate of the queue 51 _n for ONU # n (Step S6). As a result, the frame addressed to ONU # n stored in the queue 51 _n is read out by the downstream distribution unit 30 and distributed to the OSU according to the information in the newly set destination information table 31. Specifically, the frame addressed to ONU # n is distributed from the downlink distribution unit 30 to OSU # k corresponding to the wavelength after switching, and transferred from OSU # k to ONU # n.

  As described above, in the communication system according to the present embodiment, when changing the downlink wavelength assigned to the ONU 2, the OLT 1 stops the transmission of the frame destined for the ONU 2 and then instructs the switching of the downlink wavelength. When the notification of completion is received from the ONU 2, transmission of a frame using the new downstream wavelength after switching is resumed.

That is, the downlink wavelength allocation unit 40 of the OLT 1 cooperates with each OSU 20, the read control unit 50, and the destination information table 31 to store the downlink frame addressed to this ONU 2 while switching the downlink wavelength allocated to a certain ONU 2. The operation of reading the downstream frame from the queue 51 (one of the queues 51 ₁ to 51 _n ) is stopped, and after confirming that the ONU 2 reception wavelength switching has been completed, the queue 51 in which the frame addressed to the ONU 2 is stored. Since the frame is transmitted from the OLT side to the ONU side during wavelength switching, frame loss can be prevented from occurring.

  The downlink wavelength change Gate frame transmitted by the OLT 1 includes a time stamp when the OLT issues the Gate frame and a change response report frame transmission start time (down wavelength change Gate processing time in the ONU 2 with respect to the time stamp, wavelength switching). Since the ONU 2 transmits the change response report frame according to the change response report frame transmission start time, the value obtained by adding the total value of the downlink extraction clock recovery time, the code synchronization time, and the change response report frame generation time) is stored. It is possible to shorten the downlink communication interruption time between the station side and the subscriber side. That is, the OLT 1 determines the change response report frame transmission start time in consideration of the time required for the wavelength switching process performed by the ONU 2 (performs band allocation), so that the ONU 2 can reliably transmit the change response report frame. So that the bandwidth can be allocated. As a result, the transmission of the change response report frame fails and the bandwidth for transmitting this frame is not requested again, and the down communication disconnection time can be prevented from becoming longer than necessary.

  As described above, the master station device, the communication system, the communication control method, and the control device according to the present invention communicate with each other using a wavelength channel selected from a plurality of wavelengths by the slave station device and the master station device. Useful for systems.

1 station side device (OLT), 2 user side device (ONU), 10 wavelength demultiplexing unit, 20 ₁ , 20 ₂ , 20 _m OSU, 21 ₁ , 21 ₂ , 21 _m LD, 22 ₁ , 22 ₂ , 22 _m PD, 23 ₁ , 23 ₂ , 23 _m frame demultiplexing unit, 30 downlink allocation unit, 31 destination information table, 40 downlink wavelength allocation unit, 41 statistical information management unit, 50 readout control unit, 51 ₁ , 51 ₂ , 51 _n queue, 60 queue distribution unit, 61 MAC address learning table, 70 multiplexing unit, 101 PON control unit, 102 reception buffer, 103 transmission buffer, 104 optical transceiver, 105 WDM, 106 PHY.

Claims (6)

A master station device that constitutes a communication system together with one or more slave station devices capable of switching the wavelength to be received and can simultaneously transmit a plurality of optical signals having different wavelengths,
When switching the downlink wavelength received by the slave station device, before the downlink wavelength switch in the slave station device starts, the transmission of the data addressed to the slave station device is stopped and the buffering of the data addressed to the slave station device is started. Then, after the switching of the wavelength in the slave station device is completed, the buffered data addressed to the slave station device is transmitted at the new wavelength after switching.
A master station device characterized by that. A plurality of optical transmitters for transmitting optical signals of different wavelengths to the slave station devices;
A plurality of queues that are associated with any one slave station device of a communication partner and store frames addressed to the associated slave station device;
A frame reading unit that reads frames from the plurality of queues and distributes the frames to any one of the plurality of optical transmitters according to a destination of the read frames;
It is determined whether or not it is necessary to change the downlink wavelength received by the slave station device, and when the change is necessary, a downlink wavelength allocation unit that instructs switching of the downlink wavelength;
With
The frame reading unit stops reading from a queue in which frames addressed to the slave station device are stored while the slave station device is switching the received downstream wavelength.
The master station device according to claim 1. When the downlink wavelength assignment unit instructs the slave station device to switch the downlink wavelength, the downlink wavelength assignment unit determines a time at which the slave station device transmits a response frame in consideration of the time required for the downlink wavelength switching process on the slave station device side. And notify the slave station device of the determined time.
The master station device according to claim 2, wherein: A communication system comprising a master station device capable of simultaneously transmitting a plurality of optical signals having different wavelengths, and one or more slave station devices capable of switching received wavelengths,
The master station device is
When switching the downlink wavelength received by the slave station device, before the downlink wavelength switch in the slave station device starts, the transmission of the data addressed to the slave station device is stopped and the buffering of the data addressed to the slave station device is started. Then, after the switching of the wavelength in the slave station device is completed, the buffered data addressed to the slave station device is transmitted at the new wavelength after switching.
A communication system characterized by the above. A communication control method executed by a master station apparatus that forms a communication system together with one or more slave station apparatuses capable of switching the wavelength to be received and can simultaneously transmit a plurality of optical signals having different wavelengths. ,
A transmission stop step for determining that it is necessary to switch the downstream wavelength to be received by the slave station device, stopping transmission of the data addressed to the slave station device, and starting buffering of the data addressed to the slave station device;
A wavelength switching instruction step for instructing the slave station apparatus to switch the downlink wavelength to be received to switch the downlink wavelength;
A data transmission step of detecting that the downlink wavelength switching in the slave station device is completed, and transmitting the buffered data addressed to the slave station device at a new wavelength after switching,
The communication control method characterized by including. A control device in a master station device that constitutes a communication system with one or more slave station devices capable of switching the wavelength to be received and can simultaneously transmit a plurality of optical signals having different wavelengths,
When switching the downlink wavelength received by the slave station device, before the downlink wavelength switch in the slave station device starts, the transmission of the data addressed to the slave station device is stopped and the buffering of the data addressed to the slave station device is started. Then, after the switching of the wavelength in the slave station device is completed, the buffered data addressed to the slave station device is transmitted at the new wavelength after switching.
A control device characterized by that.

Images