JP2011015278A - Communication system, optical line terminal and optical network unit, and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system and the like for reducing receiving-side power consumption by stopping an FEC (Forward Error Collection) decoder not to be used in accordance with information from an optical line terminal (OLT) that transmits information.SOLUTION: The optical line terminal (OLT) transmits to an optical network unit (ONU) information designating an error-correcting code decoder D0, D1 to be operated by the ONU to the ONU. The ONU operates the designated error-correcting code decoder D0, D1. The OLT transmits data to the ONU while placing the data on a frame CW0, CW1 with an error-correcting code of a time slot corresponding to the FEC decoder D0, D1 being operated by the ONU.

Description

  The present invention relates to a communication system capable of transmitting data from a station side device to a home side device using a frame with an error correction code.

Two-way communication between the station side equipment (Optical Line Terminal: optical subscriber line terminal equipment) and multiple home side equipment (Optical Network Unit: optical subscriber line termination equipment) using the optical data communication network An optical communication system is known.
In this optical communication system, an optical signal transmitted between a station side device and a home side device is configured by an FEC (Forward Error Collection) frame including a parity for error correction.

  The home-side apparatus performs error correction / decoding of the data of the FEC frame in units of FEC frames using the error correction parity included in the received optical signal. The FEC decoder that performs error correction / decoding of this data is referred to as an error correction code decoder (also referred to as FEC decoder). In order to perform processing at high speed, a plurality of FEC decoders are used in parallel on the home side apparatus side.

JP 2007-104571 A

However, since the FEC decoder has a large circuit scale, it consumes a lot of power. Even though the data transmission speed on the transmission line varies depending on the communication contents (telephone, image data, etc.), it is a waste of power consumption to always keep all the FEC decoders operable in the receiving side.
In addition, before the communication is established, the home side device may process a short management packet, but if all the FEC decoders are turned on, power is wasted for a long time. .

Therefore, an object of the present invention is to provide a communication system and the like that can reduce power consumption by stopping an FEC decoder that is not used for error correction in a home device.
Further, the present invention does not move all the FEC decoders of the home side device that consumes a large amount of power during the idling operation, but stops only the remaining FEC decoders by the cooperative operation of the home side device and the station side device. An object of the present invention is to provide a communication system or the like that reduces power consumption.

  (1) The communication system according to the present invention includes a transmission unit that divides a plurality of frames with error correction codes into time slots and transmits the frames to the home side device in the station side device. A time slot setting means for setting a time slot for operating the station, and the station side device includes, for the home side device, an error correction code of a time slot corresponding to the error correction code decoder operated by the home side device. Data is transmitted in a frame.

In this communication system, the home side device has an error correction code decoder that performs processing on each frame that is divided in time, but the operation of the unnecessary error correction code decoder may be stopped. This can reduce power consumption on the home device side.
The home-side device can also fix the physical position of the error correction code decoder operated by the home-side device.

In addition, since the home side device cyclically distributes a plurality of frames with error correction codes sent in time for each time slot, the physical position of the error correction code decoder operated by the home side device is fixed. Instead, it may be set at any number of the predetermined period L of the time slot.
In the home-side apparatus, the time slot setting means includes a switching means for distributing the plurality of transmitted error correction code-added frames for each time slot, and a plurality of operable error correction code-added frames. If each error correction code decoder is configured to include an error correction code decoder and a decoding control unit that can set whether each error correction code decoder performs an error correction operation or stops an error correction operation, each error A time slot for operating the error correction code decoder can be set by operating a predetermined one of the correction code decoders and stopping the remaining ones.

If the home side device sets an error correction code decoder to be operated by the home side device according to the communication content or data transmission rate transmitted from the station side device, according to the capacity to be processed, Only a minimal error correction code decoder can always be operated.
By the way, before establishing the communication between the station side device and the home side device, the station side device must know the number of error correction code decoders installed in the home side device if the number of error correction code decoders installed in the home side device is not known. The position cannot be specified. In this case, the station side device further includes storage means for storing the number m of error correction code decoders provided in the home side device, and before establishing communication between the station side device and the home side device, the home side device Operates a part of predetermined error correction code decoders, and the station side device transmits a frame with an error correction code (referred to as a discovery frame) including data for establishing communication with the home side device in the first time slot. To the m-th time slot, and communication may be performed using the time slot in which the home side apparatus responds.

  By transmitting from the first time slot to the mth time slot, the home side apparatus can receive the discovery frame, correct the error, and decode it. In this system, the home-side apparatus only needs to move some predetermined error correction code decoders when idling before communication is established. Therefore, in the idle state, power consumption can be suppressed by stopping the FEC decoder other than the error correction code decoder that can pass some predetermined frames necessary for establishing communication. The number of “some predetermined error correction code decoders” to be operated by the home side apparatus is sufficient if the data of the discovery frame can be processed. Therefore, the home side apparatus moves only one error correction code decoder, for example. It is enough to be there.

There are a plurality of home-side devices in the communication system, and the slot positions of the error correction code decoders operated by the home-side devices as seen from the station-side devices are not uniform for each home-side device and are distributed. preferable. As a result, it is possible to prevent a decrease in the downlink transmission rate as compared to “when all home-side devices move only the FEC decoder at the same timing”.
In addition, even if the station-side device does not know the number of error correction code decoders installed in the home-side device, the home-side device does not set a predetermined time slot before establishing communication between the station-side device and the home-side device. A part of the error correction code decoder included in the period is operated, and the station side apparatus transmits the frame with the error correction code including the data for establishing communication with the home side apparatus for the first time in the predetermined period. If transmission is performed over the time slot from the slot to the Lth time slot, communication can be performed using the time slot in which the home side apparatus responds. This makes it possible to save the power of the home device.

(2) The station-side device of the present invention is used for communication with the home-side device and divides a plurality of frames with error correction codes into time slots and transmits the frames to the home-side device. On the other hand, data transmitting means for transmitting data in a frame with an error correction code in a time slot corresponding to the error correction code decoder operated by the home side apparatus is provided.
This station side device can transmit data on the frame with the error correction code of the time slot corresponding to the error correction code decoder operated by the home side device to the home side device. Thus, the home-side apparatus having a plurality of error correction code decoders that perform parallel processing can stop the operation of the unnecessary error correction code decoder, and can suppress power consumption in the home-side apparatus.

  (3) The home-side apparatus of the present invention is used for communication with the station-side apparatus and receives a plurality of error correction code-added frames transmitted from the station-side apparatus for each time slot. A switching means capable of distributing a plurality of frames with error correction codes sent for each time slot; a plurality of error correction code decoders operable in parallel with each distributed error correction code-added frame; Communication control or data transmitted from the station-side device, comprising a decoding control means capable of individually setting whether each error correction code decoder performs an error correction operation or stops an error correction operation According to the transmission speed, the error correction code decoder operated by the home side apparatus can be limited.

This home-side device can stop the operation of unnecessary error-correcting code decoders among a plurality of error-correcting code decoders that perform parallel processing on each frame, and suppresses power consumption on the home-side device side Can do.
(4) The communication method of the present invention is a communication method for dividing a plurality of error correction code-added frames into time slots from a station side device and transmitting the frames to the home side device. It is a communication method according to substantially the same invention.

As described above, according to the present invention, the home side device can operate a number of FEC decoders according to the transmitted communication content or data transmission speed during communication, so that power consumption is reduced in the home side device. Can be suppressed.
Further, in the idle state where communication is not established, the station side device finds a timing at which a short management packet can be processed using only some predetermined FEC decoders of the home side device, and Packets can be sent. Since the home side apparatus can always process only one FEC decoder in the idling state to process a packet, power consumption can be suppressed.

It is the schematic which shows the structural example of the optical communication system which connected between the station side apparatus OLT and several home side apparatus ONU with the optical fiber via the optical coupler. It is a frame block diagram of the optical signal transmitted from the station side apparatus OLT to the home side apparatus ONU. It is a figure which shows the internal structure of one FEC frame. It is a block diagram showing the structure of the optical communication system from the station side apparatus OLT to the home side apparatus ONU. It is a block diagram which shows an example of an internal structure of the FEC encoding part 14 of the station side apparatus OLT. It is a block diagram which shows an example of an internal structure of the FEC decoding part 22 of the home side apparatus ONU. It is a transition diagram between each state when the state of the user data sent from the station side apparatus OLT to the home side apparatus ONU is defined according to the communication content or the data transmission speed. It is a figure which shows the arrangement | sequence of the FEC decoder corresponding to each CW of the row | line | column of the FEC frame (it displays with "CW" in a figure) which the station side apparatus OLT transmits, and the FEC frame row | line | column which ONU received. CW1 and CW2 are FEC decoders that operate during low-rate communication. An example is shown in which the station side device OLT transmits a control frame once in “cycle L” regardless of the physical number M of the FEC decoders of the home side device ONU.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a configuration example of an optical communication system to which the present invention is applied.
This optical communication system is a PON (Passive Optical Network) communication system in which one optical fiber drawn from a station-side apparatus OLT is shared by a plurality of home-side apparatuses ONU. In the PON optical communication system, one station side device OLT is connected via a passive optical branching device (optical coupler) that passively branches and multiplexes a signal from an input signal without requiring an external power supply. A plurality of home-side devices ONU are connected by an optical transmission line. The station-side apparatus OLT and the N-station home-side apparatus ONU are based on 1-to-N transmission connected via an optical fiber SMF and an optical coupler OC.

However, the present invention can also be applied to an optical communication system that is not a PON. For example, a network configuration in which the station side device OLT and each home side device ONU are radially connected by a single optical fiber (Single Star) may be used.
Hereinafter, the description will be given by taking the PON optical communication system as an example.
In this PON optical communication system, a station side device OLT provided in a station building and a home side device ONU provided in a plurality of subscribers are connected via an optical fiber SMF and an optical coupler OC.

The home-side apparatus ONU includes a network interface for connecting a terminal for enjoying an optical network service, such as a personal computer installed in a subscriber's home.
The optical coupler OC is composed of a star coupler that passively branches and multiplexes a signal from an input signal without requiring an external power supply.

  The optical fibers connected to the station side device OLT, the optical coupler OC, the optical coupler OC, and the home side device ONU are single state fibers each composed of one optical fiber SMF. That is, one station side device OLT is connected to one optical coupler OC through one trunk optical fiber SMF. One optical coupler OC is connected to M home-side devices ONU via branch optical fibers SMF. Therefore, a signal transmitted and received by one station-side device OLT is distributed to M home-side devices ONU by the optical coupler OC. Note that the numbers of the optical couplers OC and the home-side devices ONU are merely examples.

  A communication system according to an embodiment of the present invention incorporates 10 Gigabit Ethernet (Ethernet is a registered trademark) technology into the PON optical communication system, and an optical fiber at a baseband speed of 10 Gbps. The 10GE-PON (10 Gigabit Ethernet-Passive Optical Network) method is used to realize the access section communication.

According to the 10GE-PON system, the communication between the station side device OLT and the home side device ONU is performed in units of variable length packets.
First, a downlink frame that enters the station side apparatus OLT from the higher level network is subjected to a predetermined bridge process in the station side apparatus OLT, and a logical link to be relayed is specified. Then, it is transmitted to the optical fiber SMF as an optical signal through the station side device OLT. The optical signal transmitted to the optical fiber SMF is branched by the optical coupler OC and transmitted to the home-side apparatus ONU connected to the optical coupler OC. However, only the home-side apparatus ONU constituting the logical link receives a predetermined downlink frame. Capture and relay frame to home network interface.

  On the other hand, the upstream optical signal includes an upstream frame from each home-side apparatus ONU. The upstream optical signal needs to be transmitted so that the optical signals from the respective home devices ONU do not compete with each other in time. For this purpose, the station side device OLT allocates a window (hereinafter simply referred to as a window) during which an upstream optical signal may be transmitted to each home side device ONU, and notifies it as a control frame. The home apparatus ONU to which the window is assigned transmits an upstream optical signal to the assigned window. This upstream optical signal is referred to as a “burst optical signal”. The burst optical signal is a finite-time optical signal sequence that is transmitted from each home-side apparatus ONU and whose light emission state is changed by a baseband signal of 10 Gbps.

Therefore, the competition of the upstream optical signal between each home-side apparatus ONU is avoided. Each home-side apparatus ONU, when given a certain window, may transmit frames continuously as long as it fits in that window.
The station apparatus OLT can receive a burst optical signal including a series of frame signals from each home apparatus ONU.

  The optical signal waveform and the optical signal intensity received by the station side device OLT and the home side device ONU are, for example, the characteristics of the light emitting elements of the station side device OLT and the home side device ONU, the length of the optical fiber SMF, It depends on the characteristics of the optical transmission line. Therefore, the station side device OLT and the home side device ONU perform a predetermined waveform shaping process on the received optical signal, and then transmit the restored significant frame sequence to the network.

FIG. 2 is a diagram illustrating a format of a downstream optical signal. FIG. 3 is a diagram illustrating the structure of the FEC frame.
This optical signal is composed of continuous FEC (with error correction code) frames. The FEC frame is configured by adding FEC parity data to a certain length of FEC data to be sent. The FEC frame is a unit of error correction code encoding processing and decoding processing. The period during which this FEC frame is sent is called a “time slot”.

  The FEC frame is composed of an FEC data part and an FEC parity part, scrambled data is stored in the FEC data part, and parity data for error correction calculated from the FEC data part is stored in the FEC parity part. Stored. A unit of data included in the FEC data part and the FEC parity part is referred to as “block” or “word”. In the embodiment of the present invention, the 64B / 66B code is used for data transmission, and hence it is referred to as a “66B block”. The 66B block consists of 66 bits, of which 64 bits (8 bytes) are transmission data, and 2 bits are a synchronization header SH for synchronization.

The synchronization header SH of the FEC data part is composed of a code “01” or “10”, and the synchronization header SH of the FEC parity part is composed of a code “11” or “00”. The FEC frame is synchronized by searching for a location where these synchronization header patterns match.
In the FEC data part, a plurality of, for example, 27 66B blocks sent from the 64B / 66B converter 12 (see FIG. 4) are stored. The FEC parity part is composed of a plurality of 66B blocks for storing packet data, and this also has a structure in which 2 bits of the synchronization header SH are added, like the FEC data part. In this FEC parity part, a plurality of, for example, four 66B blocks are stored.

Here, the concept of the packet will be described. A packet is a unit of data contained in an optical signal. The length of one packet is variable from 64 bytes to 1522 bytes.
On the other hand, the FEC frame is obtained by dividing a byte string composed of packets into fixed bytes. In other words, the FEC frame is a frame in which the transmission data string is cut off at regular time slots without being aware of the beginning or end of the packet.

FIG. 4 illustrates the internal configuration of the optical transmission unit of the station side device OLT and the internal configuration of the optical reception unit of the home side device ONU from the station side device OLT to the home side device ONU using the 64B / 66B code. Is a simplified block diagram. Only one home device ONU is depicted.
The optical transmission unit of the station-side apparatus OLT includes a MAC transmission unit 11 that handles user data of an upper layer (MAC layer), and a 64B / 66B conversion unit 12 that receives 64-bit unit data from the MAC transmission unit 11. The 64B / 66B converter 12 attaches a 2-bit synchronization header SH to each 64-bit data, converts it to 66 bits (as described above, this is called a block or a word), and sends it to the scrambler unit 13. The scrambler unit 13 scrambles the 64-bit data portion. The scrambler unit 13 then sends scrambled 64-bit data and a 2-bit synchronization header SH to the FEC encoding unit 14. The 64-bit data and the synchronization header SH constitute the FEC data portion (FIG. 3). The FEC encoding unit 14 calculates the FEC parity, adds the FEC parity unit (FIG. 3) to the FEC data unit, generates an FEC frame, and sends it to the electrical / optical conversion unit 15 (E / O conversion). The electrical / optical converter 15 converts an electrical signal into an optical signal and sends it to an optical fiber.

Bit errors may occur in electrical signals due to attenuation of light or application of noise on this optical fiber transmission line.
The optical receiving unit of the home-side apparatus ONU converts an optical signal (which may include a bit error) from an optical fiber into an electric signal by an optical / electrical conversion unit 21 (O / E conversion), and performs FEC decoding. Send to part 22.

  The FEC decoding unit 22 detects the FEC data part of the FEC frame and the synchronization header SH of the parity part and performs processing for synchronizing the FEC frame. After synchronization, the received data is subjected to error correction using the FEC parity for each FEC frame. The contents of the error correction processing are calculation of an error position (in which position of a plurality of symbols there is an error) and size (correction value), and correction processing of an erroneous symbol. The error-corrected received data is descrambled by the descrambler unit 23. Thereafter, the 66B / 64B conversion unit 24 performs 64B / 66B decoding processing, removes the 2-bit synchronization header SH, and relays the data to the terminal device via the MAC reception unit 25 as an Ethernet frame.

Here, user data sent from the station-side device OLT to the home-side device ONU is defined according to communication contents or data transmission speed.
The “idle state” refers to a state where user data is not transmitted. In this state, the station side device OLT and the home side device ONU may or may not have the MPCP link up. In either case, the user data is not transmitted, so that the idle state is established.

The “low-rate communication state” refers to a state in which communication is established but voice information of a telephone with a small amount of information is transmitted.
The “normal state” refers to a state in which image information having a large amount of information is transmitted.
FIG. 5 is a block diagram illustrating an example of an internal configuration of the FEC encoding unit 14 of the station side apparatus OLT.

  The FEC encoding unit 14 includes a communication content determination unit 31 that determines the communication content of user data (specification of destination home device ONU, idle / low rate communication / normal distinction), control frame (frame including 64 bytes of MPCP) A control frame generating unit 32 that generates a counter, and a counter that registers information on the number of FEC decoders installed in each home-side apparatus ONU (when it is known from the beginning and when a notification is received from each home-side apparatus ONU) Management unit 33, data transmission scheduler 34 for determining the order of transmission to each home apparatus ONU, packet buffer 35 for temporarily storing user data, and distribution switch for cyclically distributing the incoming frames to each FEC encoder Circuit 36, n FEC encoders arranged in parallel, coupling switch circuit for coupling distributed frames 38.

For example, the control frame generation unit 32 sets an MPCP frame and a control frame in one FEC frame in an idle state. In the case of low-rate communication, two FEC frames are used to set an MPCP frame, a control frame, and a data frame. For normal communication, an MPCP frame, a control frame, and a data frame are set for all frames.
Further, the control frame generation unit 32 sets a “reference number” (described later) to the counter management unit 33.

In the counter management unit 33, each counter value is incremented for each destination-side apparatus ONU by the count-up signal sent by the distribution switch circuit 36 for each FEC encoder switching process.
FIG. 6 is a block diagram illustrating an example of an internal configuration of the FEC decoding unit 22 of the home-side apparatus ONU.

The FEC decoding unit 22 is connected in parallel to a distribution switch circuit 41 that cyclically distributes FEC frames that are connected and input in a serial state for each FEC frame, and each of the FEC decoding units 22 performs error correction on each FEC frame. It has m FEC decoders 42 and a coupling switch circuit 43 for coupling the distributed frames.
The number of contacts of the switch circuit 41 matches the number of FEC decoders 42. For example, if eight FEC decoders 42 are prepared, the number of contacts of the switch circuit 41 is “8”. By this switching, FEC frames connected in a serial state and supplied one by one can be supplied to the FEC decoder 42 one by one to perform parallel processing.

Here is a numerical consideration. For example, as shown in FIG. 3, it is assumed that one FEC frame is composed of 27 words of data and 4 words of parity. As shown in FIG. 3, one word includes 8-byte data.
The capacity of the FEC decoder 42 is a capacity capable of storing one FEC frame. If one FEC frame includes 8 (bytes) * 27 (words) = 216 bytes of data, the capacity of the FEC decoder 42 is set to 216 bytes or more.

  Here, it is assumed that one word corresponds to one clock. Then, the home device ONU receives one FEC frame every 31 clocks. In this case, for example, when the time when data is input to the first FEC decoder is 0 (clk), the time when data is input to each FEC decoder is known as shown in Table 1.

  When the FEC decoder 42 operates with a clock of 156.25 MHz, since one word contains 8 bytes of data, the error correction processing capability of one FEC decoder 42 is 8 * 156.25 = 1.25 Gbps. Therefore, if eight FEC decoders 42 are operated in parallel, an error correction process of 8 * 1.25 = 10 Gbps can be realized. In other words, when transmitting data that can be stored in one FEC frame, that is, when transmitting data of 216 bytes or less in the numerical example described above, the home apparatus ONU only needs to operate one FEC decoder 42. Data can be decrypted. For example, in the idle state, the home device ONU is just waiting to receive a 64-byte MPCP frame, so it is sufficient to activate only one FEC decoder.

Returning to FIG. 6, the FEC decoding unit 22 further includes an FEC decoding control unit 44.
The FEC decode control unit 44 sends an error correction processing valid / stop setting switching signal to each FEC decoder 42 based on the determination result of idle / low rate communication / normal communication sent from the station side device OLT. Output.
Each FEC decoder 42, upon receiving the error correction processing valid / stop setting switching signal, performs error correction processing if the signal is a “valid” instruction, and the signal is a “stop” instruction. Error correction processing is not performed.

In order to instruct “stop”, the supply of the clock pulse signal supplied to the clock terminal of each FEC decoder 42 may be stopped, or the reset signal may be supplied to the reset terminal of each FEC decoder 42. As a result, only a limited decoder is operating from the entire FEC decoder 42, and power can be saved.
When the error correction processing is set to “stop” in response to the error correction processing valid / stop setting switching signal from the FEC decode control unit 44, the FEC decoder 42 stops the error correction processing operation, Only a delay process for a predetermined time is performed using a data holding circuit built in the FEC decoder.

In this way, since the FEC frame held for a predetermined time by the FEC decoder 42 set to “stop” is output from the FEC decoder 42, the arrangement, order, and order of each FEC frame in the serial data combined by the combination switch circuit 43 are output. The delay is preserved and the link state can be preserved.
In the embodiment of the present invention, since the station side apparatus OLT operates only a specific FEC decoder of the home side apparatus ONU, the station side apparatus OLT needs to know the number of FEC decoders of the home side apparatus ONU in advance. is there.

  For this purpose, (1) the number of FEC decoders of the home device ONU is predetermined in the system and the number is set in the memory of the station device OLT; and (2) the station side In some cases, the number of FEC decoders of the home device ONU is unknown to the device OLT. In the case of the latter (2), the station side device OLT needs to establish communication with the home side device ONU and report the number of FEC decoders to each home side device ONU.

First, a communication establishment procedure and a subsequent communication procedure when the number of FEC decoders of the home device ONU is predetermined on the system will be described.
In this procedure, the station-side apparatus OLT registers the number of FEC decoders m for each home-side apparatus ONU specified in the counter management unit 33 in advance.
The station side device OLT switches each encoder 37 by switching the distribution switch circuit 36 cyclically.

The station side apparatus OLT first sets the “reference number” to the counter management unit 33 as the a-th (for example, a = 1). The “reference number” refers to a number that determines the timing at which a discovery frame is loaded and transmitted to the home-side apparatus ONU when the encoder is switched to among the plurality of encoders.
The control frame generator 32 of the station apparatus OLT generates a discovery frame addressed to the home apparatus ONU and stores it in the packet buffer 35.

The counter management unit 33 increments the counter value of the frame addressed to each home-side apparatus ONU by the count-up signal sent by the distribution switch circuit 36 at every switching. In this example, if the number of FEC decoders of a certain home-side apparatus ONU is m, time slots are counted from 1 to m.
When the counter value becomes the “reference number”, that is, the a-th, the scheduler unit 34 transmits a discovery frame addressed to the home device ONU1 of the packet buffer 35. Then, after transmitting the discovery frame, the FEC encoder 37 at the time of transmission, that is, in which time slot the FEC frame is transmitted to the home apparatus ONU is stored.

Since the home apparatus ONU is in a standby state for receiving a 64-byte MPCP frame in an idle state where communication has not been established, only one of the m FEC decoders 42 is activated. That is, error correction processing is enabled only for that one FEC decoder, and the error correction processing stop signal is sent to the other FEC decoders 42 to stop the error correction operation.
The home apparatus ONU does not fix which one of the m FEC decoders 42 is to be activated. Therefore, it is not necessarily the first (may be the first).

  The reason for “not fixed” is that if each home-side apparatus ONU operates only the same FEC decoder, for example, the first FEC decoder in the idle state, the timing that can be transmitted from the station-side apparatus OLT is limited to the first. It will be. Then, the timing that can be transmitted from the station side device OLT is 1 / (number of home side devices ONU * M), and the speed at which the MPCP frame, the control frame, and the data frame can be transmitted decreases accordingly. .

Therefore, it is preferable that each home-side apparatus ONU designates the FEC decoder operating for error correction processing using, for example, random numbers so that the numbers of FEC decoders to be operated are distributed.
The home apparatus ONU waits for reception of a discovery frame while switching the distribution switch circuit 41 from 1 to m for each frame period in the FEC decode control unit 44. The FEC decode control unit 44 of the home-side apparatus ONU has a counter that increments for each FEC frame.

When the operating FEC decoder 42 receives the discovery frame, the discovery frame is decoded. The home apparatus ONU receives this discovery frame in the FEC decoder 32 and responds using the uplink.
If there is a response from the home apparatus ONU, the station side apparatus OLT knows that the FEC frame of the time slot corresponding to the reference number is valid, so that the time slot of the FEC frame is determined as “a”, for example. And stored in the counter management unit 33.

If there is no response even if the discovery frame is transmitted, the process of transmitting the discovery frame in the time slot of the reference number “a + 1” and waiting for a response is repeated up to m times.
In this way, the station side device OLT can identify the FEC decoder operating in the home side device ONU and can transmit a discovery frame.

  Here, FIG. 7 shows a transition diagram between the states in the station-side apparatus OLT. The station apparatus OLT switches from the idle state to the low rate state when sending data with a small amount of information such as voice data (i). When sending data having a large amount of information such as image data, the idle state is switched to the normal state (ii). When data with a large amount of information such as image data is sent in the low rate state, the state is switched to the normal state (iii). When no data is transmitted for a certain period in the low rate state, the state is switched to the idle state (iv). When no data is transmitted for a certain period in the normal state, the state is switched to the idle state (v). When sending data with a small amount of information such as voice data in the normal state, the mode is switched to the low rate state (vi).

After receiving a response from the home apparatus ONU and establishing the control link, the station apparatus OLT determines low rate communication or normal communication according to the data transmission speed when transmitting user data. Then, the determined communication state is set in the counter management unit 33, and the state setting is also requested to the home device ONU.
The scheduler 34 of the station side apparatus OLT puts data only in a necessary frame and transmits it according to the state determined from the low rate / normal.

If the low-rate / normal state switching is designated in the control frame from the station-side device OLT, the control unit of the home-side device ONU switches the state of the own station accordingly.
(A) In the low rate state, the station side device OLT operates the encoder in a time slot in which the counter takes values of 1 and 2, for example. The first encoder is for processing control frames, and the second encoder is for data processing. For example, as shown in FIG. 8, the scheduler unit transmits a frame at the timing when the counter value is the first and the second timing after that. The home apparatus ONU does not operate FEC decoders (other than the first and second in the above example) that do not require error correction when receiving data. The FEC decoder in which the home apparatus ONU is not operating outputs data to the subsequent stage at the same timing as the error correction.

(B) If the state is a normal communication state, the home apparatus ONU operates all the FEC decoders.
In the state (a) or (b), the home device ONU determines that it can enter the idling state if it does not receive a downstream data frame for a certain period of time, and stops the FEC decoder other than the predetermined FEC decoder. , Notify the station side device OLT. As a result, the station side device OLT and the home side device ONU enter an idling state. When it is desired to newly establish communication, the station-side apparatus OLT performs the above-described process of transmitting a discovery frame while decrementing the reference number and waiting for a response.

In the operation examples so far, the station-side apparatus OLT has been operated to transmit a control frame once every m cycles, but can also be operated to transmit once every cycle other than m.
In the example of FIG. 8, the number m of the FEC decoders of the home-side apparatus ONU is 8, and the control frame is transmitted once every 8 times, but once every 16 times that is an integer multiple, once every 24 times, etc. A control frame may be transmitted.

  Further, the cycle for transmitting the control frame is not limited to an integer multiple of the number m of physical FEC decoders. FIG. 9 shows an example in which a control frame is transmitted once every “arbitrary period L” irrespective of the physical number m of the FEC decoder of the home-side apparatus ONU. However, both the station side device OLT and the home side device ONU need to know the “cycle L”. In the example of FIG. 9, the station side device OLT transmits a control frame once every five frames.

The FEC decode control unit 44 of the home-side apparatus ONU performs switching according to three types of state switching, i.e., idle / low rate / normal, specified in the control frame from the station-side apparatus OLT. In the scheduler unit of the station side device OLT, data is loaded and transmitted only in necessary frames in accordance with three types of states: idle / low rate / normal.
(C) If it is in the idle state, the station side device OLT causes the home side device ONU to consume power for FEC decoders other than L multiples (this is written as xL, where x is an integer of 1 or more). A control signal is transmitted so that correction is not performed. The FEC decoder corresponding to the xLth is not physically fixed except in the above-described embodiment where L = m. The home apparatus ONU does not perform error correction that consumes power to FEC decoders other than one FEC decoder that is operating. The FEC decoder that does not perform the decoding operation of the home-side apparatus ONU outputs data to the subsequent stage at the same timing as the error correction as described above.

Hereinafter, an example in which communication is established by transmitting a control frame in this idle state will be described. The station side device OLT sets the “reference number” to the counter management unit 33 from the beginning to the a-th out of L times at the time of idle. For example, a = 1.
The scheduler unit transmits data when the a-th time slot is reached in each L times. At the same time, the counter management unit 33 increments the counter value for each home-side apparatus ONU by the count-up signal sent by the distribution switch circuit 36 every time it is switched. In this way, time slots are counted in a cycle from 1 to L. Then, when transmitting the discovery frame, the FEC frame transmitted at that time is stored.

The home apparatus ONU divides the m FEC decoders 42 into L (see FIG. 9 when L = 5), and only one FEC decoder out of the L FEC decoders 42 is effective in error correction processing. To do. The home apparatus ONU waits for reception of a discovery frame while switching the distribution switch circuit 41 by the FEC decode control unit 44.
When the operating FEC decoder 42 receives the discovery frame, it performs a decoding process of the discovery frame and responds using the uplink.

If there is a home-side device ONU response, the station-side device OLT determines that the time slot of the FEC decoder of the home-side device ONU is hit and stores it because the corresponding FEC frame is valid. .
If there is no response even if the discovery frame is transmitted, the process of transmitting the discovery frame in the next time slot “a + 1” and waiting for a response is repeated until the Lth.

  (D) If the communication state is the low rate state, the station side device OLT causes the home side device ONU to operate the FEC decoder when the counter takes, for example, the xLth and (xL + 1) th values. For example, when L = 5, the fifth, sixth, tenth, eleventh, etc. (see FIG. 9). Also in this case, the FEC decoders corresponding to the xLth and (xL + 1) th times are not physically fixed in principle. The home apparatus ONU does not move the FEC decoder that does not require error correction when receiving data. The FEC decoder in which the home-side apparatus ONU is not operating outputs to the subsequent stage at the same timing as the error correction.

(E) In the normal communication state, the home apparatus ONU operates all the FEC decoders.
As described above, in this embodiment, the data transmission interval L can be increased / decreased regardless of the number of physical FEC decoders of the home device ONU. Therefore, different FEC decoders are provided for each home device ONU. It is also suitable for the system that has it.

  Next, the operation when the home apparatus ONU notifies the station apparatus OLT of the number of FEC decoders of its own station will be described. At the time of initial system startup or at a predetermined time, the home side apparatus ONU operates all the FEC decoders, and the station side apparatus OLT transmits a discovery frame to establish communication with the home side apparatus ONU. Thereafter, the home apparatus ONU notifies the station apparatus OLT of the number of FEC decoders of the own station. The station side device OLT registers the number of FEC decoders of the home side device ONU in the counter management unit 33 in response to the notification from the home side device ONU.

The scheduler 34 of the station side device OLT sets one of three types of states, low rate / normal according to the communication contents and data transmission speed, and designates the FEC decoder to be operated by the home device ONU according to the state. Then, the data is transmitted only on the necessary frames.
The subsequent procedure is the same as (a) and (b) described above.
In the operation examples (a) and (b), the station side device OLT receives the notification of the number m of FEC decoders of the home side device ONU and operates to transmit a control frame once every m cycles. However, an operation of transmitting a control frame once in L cycles, which is not necessarily m, is also possible. The subsequent procedure is the same as (c) to (e) described above.

As described above, the home-side apparatus can operate a number of FEC decoders according to the content of communication to be transmitted or the data transmission speed to be transmitted, so that power consumption can be suppressed in the home-side apparatus.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, the station-side apparatus OLT sets one of three states, idle / low rate / normal, depending on the data transmission speed, but the number of states is not limited to three. Two types or more than four types may be defined. In addition, various modifications can be made within the scope of the present invention.

11 MAC transmitter 12 64B / 66B converter 13 Scrambler 14 FEC encoder 15 Electric / optical converter 21 Optical / electric converter 22 FEC decoder 23 Descrambler 24 66B / 64B converter 25 MAC receiver 31 Communication Content determination unit 32 Control frame generation unit 33 Counter management unit 34 Data transmission scheduler 35 Packet buffer 36 Distribution switch circuit 37 FEC encoder 38 Connection switch circuit 41 Distribution switch circuit 42 FEC decoder 43 Connection switch circuit 44 FEC decode control unit

Claims (13)

A communication system for performing communication between a station side device and a home side device,
The station-side device includes a transmission unit that divides a plurality of frames with error correction codes into time slots and transmits the frames to the home-side device,
The home-side apparatus comprises time slot setting means for setting a time slot for operating an error correction code decoder,
The transmission unit of the station side device transmits data to the home side device by placing data in a frame with an error correction code corresponding to a time slot in which the home side device operates the error correction code decoder. Communications system.   The communication system according to claim 1, wherein a physical position of an error correction code decoder operated by the home side apparatus is fixed.   The communication system according to claim 1, wherein the physical position of the error correction code decoder operated by the store-side apparatus is not fixed, and is set at a predetermined number of the predetermined period of the time slot.   The time slot setting means includes a switching means for distributing the transmitted plurality of error correction code-attached frames for each time slot, and a plurality of error correction codes operable for each assigned error correction code-added frame. The decoder according to any one of claims 1 to 3, further comprising: a decoder; and a decoding control unit that can set whether to perform an error correction operation or stop the error correction operation for each error correction code decoder. The communication system according to claim 1.   The said home side apparatus sets the error correction code | cord decoder which the said home side apparatus operates according to the communication content or data transmission rate transmitted from the said station side apparatus. The communication system according to 1. The station side device further comprises storage means for storing the number m of the error correction code decoders provided in the home side device,
Before establishing communication between the station side device and the home side device, the home side device operates some predetermined error correction code decoders, and the station side device establishes communication with the home side device. An error correction code-added frame including data to be transmitted is transmitted from the first time slot to the m-th time slot, and communication is performed using the time slot in which the home device responds. The communication system according to claim 1 or 2. A plurality of the home side devices exist in the communication system,
7. The communication system according to claim 6, wherein the positions of the slots of the error correction code decoder operated by the home side device as seen from the station side device are not unified for each home side device.   Before establishment of communication between the station side device and the home side device, the home side device operates a part of error correction code decoders included in a predetermined period of the time slot, and the station side device A frame with an error correction code including data for establishing communication with the side device is transmitted over the first time slot to the Lth time slot in the predetermined period, and a response is received from the home side device. 4. The communication system according to claim 3, wherein communication is performed using a predetermined time slot. A station-side device that is used for communication with a home-side device and divides a plurality of frames with error correction codes into time slots and transmits the frames to the home-side device,
A station-side apparatus comprising: data transmission means for transmitting data on a frame with an error correction code in a time slot corresponding to an error correction code decoder operated by the house-side apparatus. A home-side device that is used for communication with a station-side device and receives a plurality of error correction code-added frames sent from the station-side device for each time slot,
A home-side apparatus comprising time slot setting means for setting a time slot for operating an error correction code decoder.   The time slot setting means includes a switching means for distributing the transmitted plurality of error correction code-added frames for each time slot, and a plurality of error correction codes operable for each distributed error correction code-added frame. The home-side apparatus according to claim 10, further comprising: a decoder; and a decoding control unit that can set whether each error correction code decoder performs an error correction operation or stops an error correction operation.   12. The home side apparatus according to claim 10 or 11, wherein an error correction code decoder operated by the home side apparatus is limited according to a communication content or a data transmission rate transmitted from the station side apparatus. A communication method in which a plurality of frames with error correction codes are divided into time slots and transmitted to a home side device from a station side device,
The home device sets a time slot for operating the error correction code decoder,
A communication method in which the station side device transmits data to a frame with an error correction code corresponding to a time slot in which the home side device operates an error correction code decoder to the home side device.

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