JP7768430B2 - Scheduler, optical TDM transmission system, scheduling method, and scheduling program - Google Patents

Description

The present invention relates to a scheduler, an optical TDM transmission system, a scheduling method, and a scheduling program.

In order to increase the number of optical paths in optical signal transmission networks, it is effective to combine existing WDM (Wavelength Division Multiplexing) with optical TDM (Time Division Multiplexing), which can make effective use of wavelengths. By applying multiplexing/demultiplexing (optical TDM) at a finer granularity in time axis units to a transmission network composed only of WDM, it becomes possible to connect multiple locations with a single wavelength, thereby increasing the number of optical paths in wide-area optical transmission networks.

Patent document 1 describes that a scheduler that schedules TSs (Time Slots), which are units for allocating optical TDM signals on one wavelength, allocates an allocation amount of TSs according to the traffic volume of each route.

JP 2017-73812 A

FIG. 19 is an explanatory diagram showing the difference between a continuous signal and an optical burst signal.
A time series graph 501 shows a continuous signal P0 in which a single signal occupies a transmission path of the same line and the same wavelength.
The time series graph 502 shows burst signals P1-P3, which are multiple signals divided into TSs on the time axis over the same line and transmission path of the same wavelength. The burst signals P1-P3 are intermittent optical signals on the time axis, and in optical TDM transmission, data is superimposed on these burst signals for transmission. Between the burst signals, there are signal-free intervals (GT: Guard Time) where the optical power is almost zero.

FIG. 20 is an explanatory diagram showing the relationship between TS and TDM frame length.
The time slots (TS) to which burst signals P1-P3 are assigned are divided into periods T and assigned to each node. This period is called the TDM frame length. The guard time (GT) provided between TSs serves to absorb signal misalignment (synchronization error, described later).

FIG. 21 is an explanatory diagram showing TS synchronization.
In the optical TDM transmission data transfer method, multiple nodes (TRXs 601-603) connected on the same line by couplers 611 and 612 transmit burst signals on the same wavelength with a time difference, thereby avoiding collisions between signals. For example, a burst signal 621 transmitted from TRX 601 and a burst signal 622 transmitted from TRX 602 have a time difference (different TSs), so both signals 623 reach TRX 603 without collisions between the signals.
This state in which burst signals can arrive at the receiving end of the destination without colliding with each other is called a "synchronized state." Therefore, in optical TDM transmission, by synchronizing each node and determining the transmission timing (TS allocation) in advance, optical devices such as couplers 611 and 612 can multiplex signals without collisions.

In optical TDM transmission, burst signal transmission nodes synchronize their timing to prevent collisions between signals. To achieve this, each node must subtract the propagation delay time of the signal between nodes before transmitting and switching the direction of the burst signal. Furthermore, the optical fiber that transmits the signal fluctuates over time due to temperature changes. Therefore, to achieve high-precision synchronization for optical TDM transmission, each node must synchronize its timing with high precision while also taking into account discrepancies in signal propagation delay time caused by fluctuations in optical distance over time.

FIG. 22 is an explanatory diagram showing a state in which TS synchronization is not achieved.
The burst signals P1, P2, and P3 are superimposed onto the optical fiber in this order. If there is a large synchronization error between the nodes, the burst signals P2 and P3 may partially overlap, resulting in a signal collision.

FIG. 23 is an explanatory diagram showing a state in which TS synchronization is achieved.
The burst signals P1, P2, and P3 are superimposed onto the optical fiber in this order, just as in Fig. 22. Here, since the synchronization error between the nodes is small, the burst signals P2 and P3 can be correctly superimposed onto the optical fiber without overlapping.

In other words, to achieve the synchronized state shown in Figure 23, it is necessary to suppress the synchronization error between nodes to an order that can be compensated for by GT. Here, assuming that the delay and reduction in transmission efficiency caused by optical TDM transmission are suppressed to an order that can be ignored, and assuming that the number of optical paths is expanded 100 times using optical TDM technology, the GT required in a wide area network is estimated using the following (GT estimation procedure 1) and (GT estimation procedure 2).

(GT Estimation Procedure 1) considers the delay aspect. Optical TDM transmission is characterized by the fact that in addition to the transmission delay of signals propagating through optical fiber, the TDM signal waiting time, which corresponds to the TDM frame length, determines the total delay experienced by the user. In order to minimize the impact of this waiting time, which is specific to TDM transmission, the TDM frame length is set to 1% (T = 100 μs) of the optical fiber propagation delay (the maximum transmission distance assumed in this study, several tens of ms when propagating several thousand km). In this case, since it is assumed that 100 multiplexing will be performed using optical TDM technology, TS is set to 1 μs.

(GT estimation procedure 2) We will look at transmission efficiency. Guard times (GT) are provided between TSs to absorb synchronization errors. Here, the ratio of TS to GT determines the transmission efficiency in TDM, so it becomes necessary to set GT to 1% of TS (GT = 10 ns) to prevent a decrease in transmission efficiency.

As mentioned above, in order to ensure the number of multiplexes while taking into account the delay and transmission efficiency caused by optical TDM transmission, it is necessary to compensate for synchronization errors with a narrow GT of 10 ns. However, when TDM signals are sent and received at this GT interval, overlapping of TDM signals occurs due to the effects of chromatic dispersion in wide area networks of several thousand km. This creates a problem when attempting to separate signals using an optical switch (optical SW) along the transmission path, as the signals cannot be separated due to the overlapping signals.

Therefore, the main objective of this invention is to realize optical TDM transmission that enables path switching/separation using optical SW while suppressing increases in delay and decreases in transmission efficiency, even when optical SW-based optical TDM transmission technology is applied to wide-area optical transmission networks.

In order to solve the above problems, the scheduler of the present invention has the following features.
The present invention provides a scheduler for use in an optical TDM transmission system in which a plurality of metro planes accommodating metro nodes are connected via a core plane accommodating core nodes and having a transmission distance longer than that of the metro planes, the scheduler comprising:
The scheduler
creating first scheduling information for assigning signals to first TSs at intervals of a first GT with respect to signals transmitted within the metro plane without passing through the core plane, and controlling the metro node to perform optical TDM transmission based on the first scheduling information;
For signals transmitted between different metro planes via the core plane, the present invention is characterized in that it has a time slot allocation unit that creates second scheduling information to allocate multiple first TSs having the same combination of the metro plane of the source and the metro plane of the destination to second TSs at intervals of a second GT longer than the first GT, and controls the core node to perform optical TDM transmission based on the second scheduling information.

According to the present invention, even when optical SW-based optical TDM transmission technology is applied to a wide-area optical transmission network, it is possible to realize optical TDM transmission that enables path switching/separation using optical SW while suppressing increases in delay and decreases in transmission efficiency.

1 is a configuration diagram of an optical TDM transmission system according to an embodiment of the present invention. 1 is a flowchart showing a process of the optical TDM transmission system according to the present embodiment. 1 is a network diagram of an optical TDM transmission system according to an embodiment of the present invention. FIG. 4 is an explanatory diagram of a TS (first TS) transmitted on the metro plane of FIG. 3 according to this embodiment. FIG. 4 is an explanatory diagram of a TSB (second TS) transmitted on the core plane of FIG. 3 according to the present embodiment. FIG. 10 is an explanatory diagram showing an example of a schedule table for signals transmitted between different metro planes via a core plane according to the present embodiment. FIG. 7 is an explanatory diagram showing an example of the TSB of FIG. 6 according to the present embodiment. 1 is a configuration diagram of an optical TDM transmission system according to an embodiment of the present invention. 9 is an explanatory diagram showing a first example of an optical path set in the optical TDM transmission system of FIG. 8 according to the present embodiment. 10 is an explanatory diagram showing a second example of an optical path set in the optical TDM transmission system of FIG. 8 according to the present embodiment. FIG. 10 is an explanatory diagram showing a third example of an optical path set in the optical TDM transmission system of FIG. 8 according to the present embodiment. FIG. 10 is an explanatory diagram showing a fourth example of an optical path set in the optical TDM transmission system of FIG. 8 according to the present embodiment. FIG. 2 is a configuration diagram of a core node according to the present embodiment. FIG. 2 is a configuration diagram of a metro node according to the present embodiment. 1 is a hardware configuration diagram of each device of an optical TDM transmission system according to an embodiment of the present invention. FIG. 1 is an explanatory diagram showing a dispersion compensating fiber (DCF) system as a comparative example. FIG. 10 is an explanatory diagram showing a chirped fiber Bragg grating (CFBG) system as a comparative example. FIG. 10 is an explanatory diagram showing a dispersion compensation method for time-domain demultiplexing by a DSP as a comparative example. FIG. 2 is an explanatory diagram showing the difference between a continuous signal and an optical burst signal. FIG. 1 is an explanatory diagram showing the relationship between TS and TDM frame length. FIG. 10 is an explanatory diagram showing TS synchronization. FIG. 10 is an explanatory diagram showing a state in which TS synchronization is not achieved. FIG. 10 is an explanatory diagram showing a state in which TS synchronization is achieved.

Below, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an optical TDM transmission system 100.
2 is a flowchart showing the processing of the optical TDM transmission system 100. Below, each component of the optical TDM transmission system 100 in FIG. 1 will be described with reference to FIG.
The optical TDM transmission system 100 is configured by connecting a scheduler 10, a management terminal 20, a core node 30, and a metro node 40 via a network. As will be described later in Fig. 3, the core node 30 and the metro node 40 form the transmission plane of the optical transmission network, and are either a passive type that utilizes couplers or an active type that utilizes high-speed optical SW.
The management terminal 20 is a terminal operated by an administrator and is used to input information to the scheduler 10. The scheduler 10 sets paths between nodes on the transmission side of the optical TDM transmission network.

The management terminal 20 includes a node information setting unit 21 and a synchronization information setting unit 22 .
The node information setting unit 21 sets physical topology information such as transmission distances between nodes in an optical transmission network and connection relationships between nodes as node information in the scheduler 10 (S11 in FIG. 2).
The synchronization information setting unit 22 sets the number of multiplexes by TDM (number of multiplexes M=number of TSs that can be assigned to one wavelength), TDM delay, and transmission efficiency in the scheduler 10 as synchronization setting information (S12 in FIG. 2).

The scheduler 10 is used in an optical TDM transmission system 100 in which multiple metro planes 140 (Figure 3) accommodating metro nodes 40 are connected via a core plane 130 (Figure 3) accommodating core nodes 30 and having a longer transmission distance than the metro planes 140.
The scheduler 10 has a node information holding unit 11, a synchronization information holding unit 12, a wavelength allocation unit 13, a route information holding unit 14, a time slot allocation unit 15, a schedule table 16, a timer 17, a node control signal generation unit 18, and a control signal output unit 19.

The node information holding unit 11 holds the node information input from the node information setting unit 21. Every time a data overwrite command is issued from the node information setting unit 21, the information in the node information holding unit 11 is also overwritten.
The synchronization information holding unit 12 holds, as synchronization information, the synchronization setting information input from the synchronization information setting unit 22 and information on time slots determined from the synchronization setting information (TS width, GTS, TSB width, and GTB, which will be described later). Every time the synchronization information setting unit 22 issues a data overwrite command, the information in the synchronization information holding unit 12 is also overwritten.

The wavelength assignment unit 13 performs path design for each wavelength by wavelength assignment (S13 in FIG. 2), and stores the result as wavelength path information (route information) in the route information storage unit 14. If the wavelength path is interrupted for some reason, the wavelength assignment unit 13 again identifies the wavelength path and overwrites the information in the route information storage unit 14.
The time slot allocation unit 15 allocates time slots within one wavelength for each node based on the route information in the route information storage unit 14 (S14 in FIG. 2), and stores the results as scheduling information in the schedule table 16. The data stored in the schedule table 16 is overwritten and updated every time data is input from the time slot allocation unit 15.

FIG. 3 is a network diagram of the optical TDM transmission system 100.
3, the core nodes 30 in FIG. 1 are indicated by devices "C," and the metro nodes 40 are indicated by devices "M." The scheduler 10 is connected to each core node 30 and each metro node 40 via a network for transmitting and receiving control signals.
The optical TDM transmission system 100 in Figure 3 shows an example in which two metro planes 140 connecting multiple metro nodes 40 are connected to one core plane 130 connecting multiple core nodes 30. Each metro plane 140 is a small-scale transmission network with a transmission distance of 100 km or less. The core plane 130 is a large-scale transmission network with a transmission distance of several thousand km.
Two types of "time slots" are defined below.

FIG. 4 is an explanatory diagram of a TS (first TS) transmitted on the metro plane 140 of FIG.
"TS" refers to a time slot assigned to each metro node 40, such as the time slots assigned to burst signals P1-P3 in Fig. 20. The length of a TS is referred to as the "TS width," and the guard time between adjacent TSs is referred to as the "GTS" (first GT).

FIG. 5 is an explanatory diagram of the TSB (second TS) transmitted on the core plane 130 of FIG.
A "TSB" is a time slot for superimposing signals superimposed on multiple TSs together. Each TS included in the same TSB has the same combination of transmission and reception between the source (from) metro plane 140 and the destination (to) metro plane 140 in units of metro plane 140. Like TSs, TSBs are assigned to one time slot per TSB. The length of a TSB is called the "TSB width," and the guard time between adjacent TSBs is called the "GTB" (second GT).
When transmitting over distances of several thousand kilometers, such as from the metro plane 140 to the core plane 130 and back again to the metro plane 140, optical TDM multiplexing and demultiplexing of paths is performed in TS units on the metro plane 140 and in TSB units on the core plane 130. The GTB is made at least 10 times longer than the GTS to prevent interference between TSs even if the signal waveforms of the TSs are spread due to chromatic dispersion. In other words, multiple TSs are considered to be one TSB, and by making the GTB wider than the GTS, the TSB signal is not clipped even when it is separated from the core plane 130 to the metro plane 140.

The intervals between TSs within a TSB are the same as those for the GTS in Fig. 4. If signal waveform interference occurs between TSs within a TSB, this can be compensated for by a dispersion compensation circuit in a DSP (Digital Signal Processor) provided in the receiving node (the optical SW functional unit 43 of the metro node 40). In other words, the metro node 40 has a dispersion compensation circuit that compensates for signal waveform interference between multiple first TSs within a second TS.
In addition, the wavelength allocation unit 13 estimates the GT and TDM frame lengths required in the wide area network from the transmission distance of the node information, taking into consideration the delay due to TDM transmission and transmission efficiency, using the following (GT estimation procedure 1) and (GT estimation procedure 2).

In (GT estimation procedure 1), the wavelength allocation unit 13 takes delay into consideration. Optical TDM transmission is characterized by the fact that in addition to the transmission delay of signals propagating through optical fiber, the TDM signal waiting time, which corresponds to the TDM frame length, determines the total delay experienced by the user. To minimize the impact of this waiting time, which is unique to TDM transmission, the wavelength allocation unit 13 sets the TDM frame length to 1% (T = 100 μs) of the optical fiber propagation delay (the maximum transmission distance assumed in this study, several tens of ms when propagating several thousand km). Since it is assumed that 100 multiplexing is performed using optical TDM technology, TS is set to 1 μs.

In (GT estimation procedure 2), the wavelength allocation unit 13 focuses on the perspective of transmission efficiency. A guard time (GT) is provided between TSs to absorb synchronization errors. Here, the ratio of TS to GT determines the transmission efficiency in TDM, so the wavelength allocation unit 13 needs to set the GT to 1% of TS (GT = 10 ns) to prevent a decrease in transmission efficiency.
In other words, if the transmission distance of the node information input from the node information setting unit 21 is several thousand km, the propagation delay during transmission is 10 ms, and the wavelength allocation unit 13 sets 1/100 of that 10 ms as the TDM frame length (T = 100 μs or less).The wavelength allocation unit 13 also determines the metro node 40 (metro plane) to which TS is applied and the core node 30 (core plane) to which TSB is applied, based on the transmission distance of the node information.

FIG. 6 is an explanatory diagram showing an example of a schedule table 16 for signals transmitted between different metro planes via a core plane.
The schedule table 16 is a diagram assuming that the horizontal axis represents the time width of the TDM frame length and the vertical axis represents the number of wavelengths allocated by the wavelength allocation unit 13, which is 20 (λ1 to λ20). In the schedule table 16, TSBs 101, 102, 111, 112, etc. are allocated as time slots on the wavelength and time axes. For example, the TSB width is less than 10 μs, and the GTB is less than 100 ns.
TSB101 assigned to wavelength λ1 has "metro plane 1→2" written on it, and contains a set of TSs whose source is the first metro plane and whose destination is the second metro plane. Similarly, TSB111 assigned to wavelength λ20 has "metro plane 1→20" written on it, and contains a set of TSs whose source is the first metro plane and whose destination is the 20th metro plane.

FIG. 7 is an explanatory diagram showing an example of the TSB 111 of FIG.
A plurality of TSs are accommodated at GTS intervals in one TSB 111. For example, the TS width is less than 1 μs, and the GTS is less than 10 ns.
For example, the TS "node 1-1 → node 20-1" is a TS whose source is the first node belonging to the first metro plane and whose destination is the first node belonging to the 20th metro plane. Similarly, the TS "node 1-1 → node 20-2" is a TS whose source is the first node belonging to the first metro plane and whose destination is the second node belonging to the 20th metro plane.

Returning to FIG. 1, the timer 17 is synchronized between the core node 30 and the metro node 40 and provides information on each time used in the schedule table 16 .
The node control signal generator 18 generates a control signal for notifying each node of the timing for transmitting a TDM signal based on the information in the schedule table 16 (S15 in FIG. 2).
- The control signal (TSB control signal) generated from the scheduling information (second scheduling information) for TSB allocation includes the allocation area (wavelength, time), information indicating the metro plane 140 of the sender, and information indicating the metro plane 140 of the receiver.
- The control signal (TS control signal) generated from the TS allocation scheduling information (first scheduling information) includes the allocation area (wavelength, time), information indicating the metro node 40 within the metro plane 140 of the sender, and information indicating the metro node 40 within the metro plane 140 of the receiver.

The control signal output unit 19 notifies each node of the control signal generated by the node control signal generation unit 18. The control signal output unit 19, for example, notifies the core node 30 of the TSB control signal and notifies the metro node 40 of the TS control signal (S16 in Figure 2).

In S13 of FIG. 2, it is desirable that the wavelength allocation unit 13 performs wavelength path design in accordance with at least one of the following guidelines.
- Design the shortest route.
Wavelength paths are set up so that the number of paths is equal to or less than the number of multiplexing M, and if the number of paths is greater than the number of multiplexing M, a different wavelength is used. Note that the number of TSs indicates the number of paths that can connect a transmitting node and a receiving node with one wavelength, and the number of paths = number of transmitting nodes × number of receiving nodes.
- TSs whose source is a node within the same metropolitan area and TSs whose destination is a node within the same metropolitan area are assigned the same wavelength as much as possible.
- TSB is applied to optical paths that use optical TDM technology in wide area networks (core plane, etc.).
- Change the GTB between TSBs to an order that can accommodate chromatic dispersion so that path switching/separation on the core side can be performed on a TSB basis.

In addition, in S14 of FIG. 2, the time slot allocation unit 15 determines the following information (1) to (4) about each time slot based on the information in the synchronization information storage unit 12 and the route information storage unit 14.
(1) The TS width is the TDM frame length (T = 100 μs) divided by the number of multiplexes M. For example, if the number of multiplexes M = 100, the TS width = 1 μs.
(2) For GTS, if you want to keep the decrease in transmission efficiency to 1%, the GTS width is 1/100 of the TS width, or 10 ns. Note that errors smaller than the GTS width can be absorbed by the GTS, so a synchronization accuracy on the order of that which can be corrected by the GTS is required. In other words, the synchronization accuracy required for 100 multiplexing is 10 ns or less (on the order of a few ns).

(3) The TSB width is determined by the number of TSs included in the TSB. For example, if one TSB includes 10 TSs, then the TSB width = TS width x 10 = 10 μs.
(4) The GTB is set to a length longer than the GTS, which is long enough to accommodate the effects of chromatic dispersion. For example, the GTB is also set to 1/100 of the TSB width, or 100 ns. In other words, the synchronization accuracy required for the TSB is relaxed to 100 ns or less (on the order of several tens of ns).
Therefore, the time slot allocation unit 15 determines the synchronization accuracy required for the transmission plane (metro plane 140, core plane 130) from the synchronization setting information (number of multiplexing M, TDM delay, and transmission efficiency) held by the synchronization information holding unit 12. Then, the time slot allocation unit 15 determines information (1) to (4) about each time slot so as to satisfy the determined synchronization accuracy.

The time slot allocation unit 15 then performs the following control.
- For signals transmitted within the metro plane 140 without passing through the core plane 130, the time slot allocation unit 15 creates first scheduling information that allocates signals to the first TS at intervals of the first GT, and controls the metro node 40 to perform optical TDM transmission based on the first scheduling information.
- For signals transmitted between different metro planes 140 via the core plane 130, the time slot allocation unit 15 creates second scheduling information that allocates multiple first TSs with the same combination of source metro plane and destination metro plane to the second TS at intervals of a second GT that are longer than the first GT, and controls the core node 30 to perform optical TDM transmission based on the second scheduling information.

Hereinafter, with reference to FIGS. 8 to 12, specific examples of optical paths will be shown and a description will be given of the situations in which the time slot allocation unit 15 sets TS and TSB.
FIG. 8 is a diagram showing the configuration of an optical TDM transmission system 200.
1 shows a configuration in which two metro planes 140 are connected at a core plane 130. On the other hand, the optical TDM transmission system 200 in FIG. 8 shows a configuration in which four metro planes 210-240 are connected at a core plane 250.

FIG. 9 is an explanatory diagram showing a first example of optical paths set in the optical TDM transmission system 200 of FIG.
In the optical TDM transmission system 200A, TS transmission, multiplexing, and reception are performed only at the metro nodes 40 within the metro plane 220A. On the other hand, no wavelength paths are set in the other metro planes 210A, 230A, and 240A, and no signals flow through the core plane 250A.

FIG. 10 is an explanatory diagram showing a second example of optical paths set in the optical TDM transmission system 200 of FIG.
In the optical TDM transmission system 200B, TS transmission and multiplexing is performed from a metro node 40 in a metro plane 220B, the core plane 250B passes the signal through, and the TS is received at a metro node 40 in a metro plane 240B. On the other hand, no wavelength paths are set in the other metro planes 210B and 230B.
9 and 10, when the wavelength path does not include separation on the core plane (in the case of local communication within the metro plane or through communication on the core plane), the time slot allocation unit 15 uses TS instead of TSB. In other words, the time slot allocation unit 15 generates scheduling information based on the number of multiplexes M determined by the synchronization information holding unit 12 and TS information (TS width and GTS).

FIG. 11 is an explanatory diagram showing a third example of optical paths set in the optical TDM transmission system 200 of FIG.
In the optical TDM transmission system 200C, TSs are transmitted and multiplexed from the metro node 40 in the metro plane 220C, the core plane 250C separates the signals into the metro planes 230C and 240C, and the TSs are received at the metro nodes 40 in the metro planes 230C and 240C. On the other hand, no wavelength paths are set in the other metro plane 210C.

FIG. 12 is an explanatory diagram showing a fourth example of optical paths set in the optical TDM transmission system 200 of FIG.
In the optical TDM transmission system 200D, TSs are transmitted and multiplexed from metro nodes 40 within metro planes 210D and 220D, and the core plane 250D multiplexes and demultiplexes the signals to metro planes 230D and 240D, and the TSs are received at metro nodes 40 within metro planes 230D and 240D.
11 and 12, when the wavelength path includes separation at the core plane (in the case of separation or multiplexing/separation at the core plane), the time slot allocation unit 15 uses both TSB and TS so that multiplexing/demultiplexing is performed in TS units in the metro plane and multiplexing/demultiplexing in TSB units in the core plane. That is, the time slot allocation unit 15 generates scheduling information based on the multiplexing number M determined by the synchronization information holding unit 12, TS information (TS width and GTS), and TSB information (TSB width and GTB). In this case, the schedule table 16 may be generated for each metro plane (metro planes 230C and 240C in FIG. 11, and metro planes 230D and 240D in FIG. 12) that is the receiving destination, or a single table may be generated.

FIG. 13 is a configuration diagram of the core node 30.
The core node 30 includes a control signal input unit 31 , a TS control unit 32 , an optical SW function unit 33 , an optical SW switching control unit 34 , and a synchronization timer 35 .
The control signal input unit 31 receives a control signal from the scheduler 10 and inputs the scheduling information read from the control signal to the TS control unit 32 .
The TS control unit 32 inputs the switching timing of the optical SW to the optical SW switching control unit 34 based on the scheduling information obtained from the control signal input unit 31. In this embodiment, the core node 30 is neither a node that transmits a TS nor a node that receives a TS, so the TS control unit 32 passes an optical signal through its own device in units of TSB, or notifies the optical SW switching control unit 34 of path switching in units of TSB.

The optical SW switching control unit 34 inputs a signal for switching the optical SW provided in the optical SW function unit 33 to the optical SW function unit 33 based on information from the TS control unit 32 .
The optical SW function unit 33 switches the optical SW based on the input optical SW switching timing.
The synchronization timer 35 synchronizes the TS between the nodes with high accuracy, and provides the TS control unit 32 and the optical SW switching control unit 34 with a reference time.

FIG. 14 is a diagram showing the configuration of the metro node 40.
The metro node 40 includes a control signal input unit 41 , a TS control unit 42 , an optical SW function unit 43 , an optical SW switching control unit 44 , a synchronization timer 45 , and a TRx 46 .
The control signal input unit 41 receives a control signal from the scheduler 10 and inputs the scheduling information read from the control signal to the TS control unit 42 .
Based on the scheduling information received from the control signal input unit 41 , the TS control unit 42 inputs the switching timing of the optical SW to the optical SW switching control unit 44 and also inputs the transmission and reception timing of the TDM signal to the TRx 46 .
In this embodiment, the metro node 40 corresponds to a node that transmits a TS or a node that receives a TS. Therefore, the TS control unit 42 notifies the optical SW switching control unit 44 of path switching on a TS basis.

The optical SW switching control unit 44 inputs a signal for switching the optical SW provided in the optical SW function unit 43 to the optical SW function unit 43 based on information from the TS control unit 42 .
The optical SW function unit 43 switches the optical SW based on the input optical SW switching timing, and when receiving a TDM signal, inputs the received signal to the TRx 46 .
The synchronization timer 45 synchronizes the TS between the nodes with high accuracy, and provides the TS control unit 42 and the optical SW switching control unit 44 with a reference time.
The TRx 46 determines the transmission and reception timing of the TDM signal based on the information from the TS control unit 42 and transmits the signal to the optical SW function unit 43 .

FIG. 15 is a diagram showing the hardware configuration of each device in the optical TDM transmission system 100.
Each device of the optical TDM transmission system 100 (scheduler 10, management terminal 20, core node 30, and metro node 40) is configured as a computer 900 having a CPU 901, RAM 902, ROM 903, HDD 904, communication I/F 905, input/output I/F 906, and media I/F 907.
The communication I/F 905 is connected to an external communication device 915. The input/output I/F 906 is connected to an input/output device 916. The media I/F 907 reads and writes data from a recording medium 917. Furthermore, the CPU 901 controls each unit by executing a program (also called an application, or an app for short) loaded into the RAM 902. This program can be distributed via a communication line or recorded on a recording medium 917 such as a CD-ROM and distributed.

Hereinafter, the switching/demultiplexing of optical TDM signals will be described with reference to this embodiment and a comparative example in which chromatic dispersion is compensated for.
FIG. 16 is an explanatory diagram showing a dispersion compensation fiber (DCF) system as a comparative example.
In SMF (Single Mode Fiber), pulses spread from optical signal 301 before passing through to optical signal 302 after passing through. Therefore, in DCF, a device with dispersion of the opposite sign to that of the transmission fiber is cascaded as the transmission fiber to make the total chromatic dispersion zero. In other words, in DCF, by passing optical signal 311 with spread pulses, compensation can be made to optical signal 312 before the pulse spread.
DCF is capable of dispersion compensation over a wide wavelength range, but requires a relatively long fiber length (approximately 10% of the total length of the transmission fiber), which increases insertion loss and delay.

FIG. 17 is an explanatory diagram showing a chirped optical fiber grating (CFBG) system as a comparative example.
The optical signal 321 with its pulse broadened is input to an optical circulator 323 from an input fiber 324, and is compensated as an optical signal 322 before the pulse broadens from an output fiber 326 via a CFBG 325. The CFBG 325 reflects light with shorter wavelengths earlier.
This method allows dispersion compensation over short fiber lengths (approximately 10 cm) and has low insertion loss and low latency, but the operating bandwidth is small (approximately 1 mm), making it difficult to achieve full compensation in WDM.

FIG. 18 is an explanatory diagram showing a dispersion compensation method for time-domain demultiplexing by a DSP as a comparative example.
18 shows a case where burst signals P1-P3 overlapping on the time axis are separated by the optical SW 430. In this case, after separation, the DSPs 411 and 421 are unable to restore the burst signals P1 and P2 that have collided.
As described above, the techniques for compensating for chromatic dispersion in the comparative examples of Figures 16 to 18 compensate for the broadening of optical pulses, but do not provide a method for enabling switching/separation of optical TDM signals while suppressing increases in delay and quality degradation while being used in combination with WDM.

[effect]
The present invention provides a scheduler 10 for use in an optical TDM transmission system 100 in which a plurality of metro planes 140 accommodating metro nodes 40 are connected via a core plane 130 accommodating core nodes 30 and having a longer transmission distance than the metro planes 140, the scheduler comprising:
The scheduler 10
For signals transmitted within the metro plane 140 without passing through the core plane 130, first scheduling information is created to assign the signals to the first TS at intervals of the first GT, and the metro node 40 is controlled to perform optical TDM transmission based on the first scheduling information;
For signals transmitted between different metro planes 140 via the core plane 130, the system is characterized by having a time slot allocation unit 15 that creates second scheduling information to allocate multiple first TSs having the same combination of source metro plane and destination metro plane to second TSs at intervals of a second GT longer than the first GT, and controls the core node 30 to perform optical TDM transmission based on the second scheduling information.

As a result, for optical paths on the core plane 130 that require optical TDM technology during long-distance transmission, the scheduler 10 devisees time slot scheduling and changes the time slot switching unit (TSB) and the GT (GTB) between time slots according to the transmission distance. Therefore, in a long-distance wide area network, optical TDM transmission can be realized that enables path switching/separation by optical SW while minimizing delay increases.
Furthermore, by introducing TSB and GTB, the scheduler 10 can significantly reduce the required synchronization accuracy while slightly suppressing the decrease in transmission efficiency. For example, in a comparative example in which TS is used without TSB even on the core plane 130, a strict synchronization accuracy (e.g., several ns) is required, but the propagation delay (e.g., 101 μs) and the decrease in transmission efficiency (e.g., less than 1%) are observed.
On the other hand, in the scheduler 10, by introducing TSB and GTB in the core plane 130, it is possible to obtain a relaxed required synchronization accuracy (e.g., several tens of nanoseconds) without reducing the number of multiplexes, and there are no significant disadvantages in terms of propagation delay (e.g., 102 μs) or reduction in transmission efficiency (e.g., less than 2%).

The optical TDM transmission system 100 of the present invention includes a scheduler 10 according to claim 1, a core node 30, and a metro node 40.
The metro node 40 is characterized by having a dispersion compensation circuit that compensates for interference of signal waveforms between a plurality of first TSs in the second TS.

This allows the metro node 40 to compensate for signals even when signal waveform interference occurs between TSs within a TSB.

DESCRIPTION OF SYMBOLS 10 Scheduler 11 Node information holding unit 12 Synchronization information holding unit 13 Wavelength allocation unit 14 Route information holding unit 15 Time slot allocation unit 16 Schedule table 17 Timer 18 Node control signal generation unit 19 Control signal output unit 20 Management terminal 21 Node information setting unit 22 Synchronization information setting unit 30 Core node 31 Control signal input unit 32 TS control unit 33 Optical SW function unit 34 Optical SW switching control unit 35 Synchronization timer 40 Metro node 41 Control signal input unit 42 TS control unit 43 Optical SW function unit 44 Optical SW switching control unit 45 Synchronization timer 46 TRx
100 Optical TDM transmission system 130 Core plane 140 Metro plane

Claims (4)

1. A scheduler for use in an optical TDM (Time Division Multiplexing) transmission system in which a plurality of metro planes accommodating metro nodes are connected via a core plane accommodating core nodes and having a transmission distance longer than that of the metro planes,
The scheduler
creating first scheduling information for allocating signals to first time slots (TSs) at intervals of a first guard time (GT) for signals transmitted within the metro plane without passing through the core plane, and controlling the metro node to perform optical TDM transmission based on the first scheduling information;
The scheduler is characterized in that, for signals transmitted between different metro planes via the core plane, it has a time slot allocation unit that creates second scheduling information to allocate multiple first TSs that have the same combination of the metro plane of the source and the metro plane of the destination to second TSs at intervals of a second GT that is longer than the first GT, and controls the core node to perform optical TDM transmission based on the second scheduling information. A system comprising the scheduler according to claim 1, the core node, and the metro node,
10. An optical TDM transmission system, wherein the metro node has a dispersion compensation circuit that compensates for interference of signal waveforms among a plurality of the first TSs in the second TS. A scheduling method by a scheduler used in an optical TDM (Time Division Multiplexing) transmission system in which a plurality of metro planes accommodating metro nodes are connected via core planes accommodating core nodes and having a transmission distance longer than that of the metro planes, comprising:
The time slot allocation unit of the scheduler
creating first scheduling information for allocating signals to first time slots (TSs) at intervals of a first guard time (GT) for signals transmitted within the metro plane without passing through the core plane, and controlling the metro node to perform optical TDM transmission based on the first scheduling information;
A scheduling method characterized in that, for signals transmitted between different metro planes via the core plane, second scheduling information is created to assign multiple first TSs having the same combination of the metro plane of the source and the metro plane of the destination to second TSs at intervals of a second GT longer than the first GT, and the core node is controlled to perform optical TDM transmission based on the second scheduling information. A scheduling program for causing a computer to function as the scheduler described in claim 1.