JP5056909B2 - Receiving device, PON system, and receiving method - Google Patents

Description

  The present invention relates to a receiving apparatus and a receiving method for receiving a burst signal transmitted in time division, and a PON (Passive Optical Network) system to which the receiving apparatus and the receiving method are applied.

  The PON system uses an optical fiber network that branches a station side device as an aggregation station and a home side device installed in a plurality of subscriber homes into a plurality of optical fibers via an optical coupler from a single optical fiber. Are connected (for example, see Patent Document 1). When transmission is performed from a plurality of home-side devices to the station-side device at the same time, transmission data collides, and therefore the station-side device gives the home-side device permission regarding the transmission timing and the amount of transmission data. Upon receiving this permission, the home side apparatus transmits the permitted amount to the station side apparatus at a timing permitted from the station side apparatus.

  A signal (optical signal) transmitted from the home side device is a burst signal composed of binary signals of 0 or 1. Since the distance and route between the station-side device and the home-side device differ depending on the installation location of the home-side device, the intensity of the upstream burst signal that reaches the station-side device from the home-side device is not constant. That is, the burst signal is intermittently received from the plurality of home-side devices with various strengths (amplitudes) to the station-side device. In the station side device, a photodiode that receives an optical burst signal and converts it into an electrical burst signal, an amplifier that amplifies the burst signal output from the photodiode, and compares the amplified burst signal with a threshold value Thus, a receiving device including a comparator that outputs a binary signal (digital signal) is provided (for example, see Patent Document 2). The burst signal is configured to include a leading preamble and subsequent data.

  Since the burst signal is composed of binary signals of 0 or 1 as described above, the receiving device, for example, calculates the center (average value) of the signal amplitude in the burst signal transmitted for each home device. Search is performed, and this is used as a threshold value, and a determination of 0 or 1 is sequentially made according to the signal change in the burst signal. A time constant circuit can be used to determine the center of the signal amplitude. In addition, the receiving apparatus changes the threshold according to burst signals transmitted with different signal amplitudes.

Japanese Patent Laying-Open No. 2004-64749 (FIG. 4) Japanese Patent Laying-Open No. 2010-4228 (FIG. 3)

  In the conventional receiving apparatus as described above, it is ideal that the threshold value, that is, the baseline, does not move once converged to the center of the signal amplitude, but in practice, the sign of 0 or 1 in the burst signal is If it continues, it will shift from the center value. This is a phenomenon called Baseline Wander. In particular, if 0 or 1 continues for a long time in the burst signal, the threshold value may be shifted from the central value of 0/1 due to being dragged by a continuous code. In this case, there is a possibility that the 0/1 determination is erroneous. Becomes larger. Such a baseline wander can be suppressed by increasing the time constant (in other words, lowering the low-frequency cutoff frequency).

  However, since the response to the burst signal is delayed when the time constant is increased, it is necessary to increase the preamble length (preamble section) for reliable reception. When the preamble length is increased, a limited transmission band is used accordingly, which is not preferable from the viewpoint of effective band utilization for data transmission.

  In GE-PON (Gigabit Ethernet PON (Ethernet is a registered trademark)) based on IEEE802.3ah, 8B / 10B codes are used. Specifically, an encoded signal (10-bit signal) obtained by adding 2 bits to an 8-bit signal is generated. At this time, two types of encoded signals are assigned, and the code to be used By selecting the digitized signal, a balance of 0/1 can be maintained. Therefore, even if the time constant is set relatively short, a large baseline wander does not occur. However, in 10G-EPON (10 Gigabit Ethernet PON) based on IEEE802.3av, the encoding method is different, and a balance of 0/1 cannot be obtained by selecting an encoded signal as in the 8B / 10B code. Therefore, 10G-EPON requires a new countermeasure against baseline wander.

  In view of such a problem, an object of the present invention is to provide a receiving device, a PON system, and a receiving method that contribute to effective use of a transmission band while reliably receiving a burst signal.

(1) The present invention is a receiving device capable of receiving, in a time division manner, a burst signal having a level difference in encryption processing including the presence / absence of encryption from a plurality of transmission devices, wherein the burst signal is processed by the encryption processing. The preamble length differs according to the level difference,
A storage unit that stores information related to encryption processing of each transmission device, a burst reception unit that follows a burst signal including a predetermined preamble length with a predetermined time constant, and a reception timing of the burst signal from each transmission device And a control unit that operates the burst reception unit with a time constant corresponding to the preamble length specified for each transmission source from the information on the encryption process stored in the storage unit .

In the reception apparatus configured as described above, the control unit sets the preamble length specified for each transmission source from the information related to the encryption processing stored in the storage unit in accordance with the reception timing of the burst signal from each transmission apparatus. Since the burst receiver is operated with the corresponding time constant, the burst signal can be received with an appropriate time constant and preamble length corresponding to the relative level of the randomness of the transmission signal depending on encryption. .
That is, when the randomness is low, there is a possibility that 0 or 1 may continue. Therefore, the generation of a large baseline wander may be suppressed by relatively increasing the time constant.
On the other hand, if the randomness is high, it does not shift to either 0 or 1, so that a large baseline wander does not occur. Therefore, it is only necessary to relatively shorten the time constant. If the time constant is shortened, the preamble length can also be shortened. Shortening the time constant contributes to ensuring responsiveness to burst signals, and shortening the preamble length contributes to effective use of bandwidth.

(2) In the receiver of (1) above, the control unit shortens the time constant and the preamble length as the randomness of the transmission signal depending on encryption is higher, and conversely, as the randomness is lower, The preamble length may be determined to be increased.
In this case, if the encryption process is performed, the time constant and the preamble length can be relatively shortened. Conversely, if the encryption process is not performed, the time constant and the preamble length are relatively set. Can be long. Furthermore, when the encryption process is performed, the time constant and the preamble length are relatively short if the encryption process is highly encrypted, and the encryption process is low encryption. Therefore, various settings such as slightly shortening the time constant and the preamble length are possible.

(3) On the other hand, according to the present invention, a plurality of types of station-side devices connected to a plurality of home-side devices via optical fibers have a level difference in encryption processing including the presence / absence of encryption from the plurality of home-side devices. PON system capable of receiving uplink burst signals in a time-division manner, wherein the home-side device gives a preamble having a preamble length determined based on the relative level of randomness of a transmission signal depending on encryption And transmitting a burst signal, and the station side device stores a storage unit that stores information related to the encryption processing of each home side device, and a burst signal including a predetermined preamble length includes a predetermined time constant. a burst receiver configured to follow with a, in accordance with the reception timing of the burst signal from each optical network unit, corresponding to the identified preamble length for each source from the information on the encryption process stored in said storage unit Is obtained and a control unit for operating said burst receiver at a time constant that.

In the PON system configured as described above, the control unit of the station-side device matches the reception timing of the burst signal from each home-side device for each transmission source from the information related to the encryption processing stored in the storage unit. Since the burst receiver is operated with the time constant corresponding to the specified preamble length, the burst signal is set with an appropriate time constant and preamble length corresponding to the relative level of the randomness of the transmission signal depending on encryption. Can be received .
That is, when the randomness is low, there is a possibility that 0 or 1 may continue. Therefore, the generation of a large baseline wander may be suppressed by relatively increasing the time constant.
On the other hand, if the randomness is high, it does not shift to either 0 or 1, so that a large baseline wander does not occur. Therefore, it is only necessary to relatively shorten the time constant. If the time constant is shortened, the preamble length can also be shortened. Shortening the time constant contributes to ensuring responsiveness to burst signals, and shortening the preamble length contributes to effective use of bandwidth.

(4) In the PON system, the control unit may determine that the time constant and the preamble length are shorter as the randomness is higher, and conversely, the time constant and the preamble length are longer as the randomness is lower. Good.
In this case, if the encryption process is performed, the time constant and the preamble length can be relatively shortened. Conversely, if the encryption process is not performed, the time constant and the preamble length are relatively set. Can be long. Furthermore, when the encryption process is performed, the time constant and the preamble length are relatively short if the encryption process is highly encrypted, and the encryption process is low encryption. Therefore, various settings such as slightly shortening the time constant and the preamble length are possible.

(5) Also, in the PON system of (3) or (4) above, the home side apparatus performs 64B / 66B encoding including an exclusive OR operation between the feedback signal of the linear feedback shift register and the input signal. You may have an encoding part to perform.
In this case, if 0 continues for a long time in the input signal, the output signal also tends to be set and output easily, and a large baseline wander is likely to occur. However, such a problem does not occur if the input signal is encrypted, and the station side device can receive with a short time constant. Thus, by determining the time constant according to the encryption, this problem, that is, the problem caused by the 64B / 66B encoding can be alleviated.

(6) On the other hand, according to the present invention, burst signals having a level difference in encryption processing including the presence / absence of encryption can be received from a plurality of transmission devices in a time division manner. The predetermined preamble length and the time constant are determined in advance based on the relative level of the randomness of the transmission signal depending on the encryption of each transmitting apparatus. a step, the transmission device, the steps of imparting a predetermined preamble length defined for transmitting the burst signal, the receiving apparatus, in accordance with the reception timing of the burst signal from each transmitting device, the burst signal sender and having a step for receiving that follows to the burst signal at a time constant corresponding to the preamble length which is granted in accordance with the encryption process.

In the reception method as described above, the reception device uses a time constant corresponding to the preamble length given by the transmission source of the burst signal according to the encryption process in accordance with the reception timing of the burst signal from each transmission device. since the received that follows to the burst signal, corresponding to the relative level of randomness of the transmit signal dependent on the encryption, it is possible to receive a burst signal in an appropriate time constant and the preamble length.
That is, when the randomness is low, there is a possibility that 0 or 1 may continue. Therefore, the generation of a large baseline wander may be suppressed by relatively increasing the time constant.
On the other hand, if the randomness is high, it does not shift to either 0 or 1, so that a large baseline wander does not occur. Therefore, it is only necessary to relatively shorten the time constant. If the time constant is shortened, the preamble length can also be shortened. Shortening the time constant contributes to ensuring responsiveness to burst signals, and shortening the preamble length contributes to effective use of bandwidth.

(7) In the reception method of (6) above, the predetermined preamble length is determined by the receiving device, and a step of instructing each transmitting device may be further included.
In this case, the receiving apparatus can independently manage the preamble length transmitted from each transmitting apparatus.

  According to the receiving apparatus, the PON system, and the receiving method of the present invention, it is possible to effectively use the transmission band while reliably receiving the burst signal.

1 is a connection diagram of a PON system according to an embodiment of the present invention. It is a block diagram which shows the outline of the internal structure of the station side apparatus in FIG. FIG. 3 is a circuit diagram illustrating an example of a circuit configuration of an optical receiving unit in FIG. 2. FIG. 4 is a circuit diagram illustrating another example of the circuit configuration of the optical receiver in FIG. 2. It is a block diagram which shows the outline of the internal structure of the home side apparatus in FIG. It is a sequence diagram showing exchange of control frames between a station side device and a home side device. It is a sequence diagram which shows the upstream communication in a PON system, and has shown an example of the distributed allocation system. It is a sequence diagram which shows the general discovery process performed between a station side apparatus and an unregistered home side apparatus. FIG. 2 is a connection diagram of a PON system that is slightly different from FIG. 1 in terms of encryption. It is a flowchart which shows the procedure (including a human process) of the process which memorize | stores the information regarding encryption about the home side apparatus registered for the first time. It is a logic diagram of the scrambler and descrambler used for 64B / 66B encoding. It is a figure which shows the structure for the simulation regarding a baseline wander. It is a graph which shows a simulation result, (a) shows a baseline wander from 0 to 100,000 bits in time when Seed = A and all inputs are 0, and (b) shows Seed = A, The baseline wander from 0 to 100,000 bits in time is shown under the condition that the input is PRBS2 ⁷ -1. It is a graph which shows a simulation result, (a) shows a baseline wander from 0 to 3 million bits under conditions where Seed = A and all inputs are 0, and (b) shows Seed = A, The baseline wander from 0 to 3 million bits in time under the condition that the input is PRBS2 ⁷ -1. It is a graph showing a simulation result, (a) shows a baseline wander from 0 to 100,000 bits in time when Seed = B and all inputs are 0, and (b) shows Seed = B, The baseline wander from 0 to 100,000 bits in time is shown under the condition that the input is PRBS2 ⁷ -1. It is a graph which shows a simulation result, (a) shows a baseline wander from 0 to 3 million bits under conditions where Seed = B and all inputs are 0, and (b) shows Seed = B, The baseline wander from 0 to 3 million bits in time under the condition that the input is PRBS2 ⁷ -1.

  Hereinafter, a PON system as a typical example including a receiving apparatus (or receiving method) according to an embodiment of the present invention will be described with reference to the drawings.

<< Baseline wander in 10G-EPON >>
The PON system of this embodiment is applied to 10G-EPON based on IEEE802.3av. In 10G-EPON, 64B / 66B codes are used. For the 64B / 66B code, a 58-stage linear feedback shift register (LFSR) composed of a generator polynomial of (1 + X ³⁹ + X ⁵⁸ ) is used. Here, the linear feedback shift register is a shift register having an exclusive OR of a part of a bit string constituting the value as an input bit.

  FIG. 11A is a logic diagram of a scrambler used for 64B / 66B encoding. The scrambler Sc is a linear feedback shift composed of a shift register composed of 58 stages of flip-flops S0 to S57 and an operator Sc1 that takes the exclusive OR (also referred to as XOR) of the outputs of S38 and S57. The register Sc2 is provided as a basic configuration. The scrambler Sc further includes an operator Sc3 that performs an exclusive OR of the input signal and the feedback signal of the linear feedback shift register Sc2.

  On the other hand, FIG. 11B is a logic diagram of the descrambler De used for 64B / 66B decoding. This descrambler De has, as a basic configuration, a linear feedback shift register De2 composed of a shift register composed of 58-stage flip-flops S0 to S57 and an operator De1 that performs exclusive OR of outputs of S38 and S57. is doing. The descrambler De further includes an operator De3 that performs an exclusive OR of the input signal and the feedback signal of the linear feedback shift register De2.

  In FIG. 11A, an input signal (serial data) is scrambled by a scrambler Sc mounted on a transmitting device (home device) and output as scrambled data. The descrambler De mounted on the receiving device (station side device) can perform descrambling to restore the original scrambled data input and output the original signal (serial data).

  The scrambler Sc shown in FIG. 11A further takes an exclusive OR with the input signal (Input) for the exclusive OR of the outputs of S57 and S38. That is, the scrambled data output is expressed as XOR (S57, S38, Input). Such a scrambler Sc basically has the effect that the input signal itself contributes to the scramble, and the balance (mark rate) of the 0/1 signal is made uniform and outputted.

However, if Input is fixed at 0 (continuously 0),
XOR (S57, S38, Input) = XOR (S57, S38) (1)
It becomes. When Input is fixed to 1 (continuously 1),
XOR (S57, S38, Input) = ˜XOR (S57, S38) (2)
("~" Represents an inversion value).
As shown in the above formulas (1) and (2), there is no “Input” term on the right side of each formula. That is, when Input is fixed to 0 or 1, Input does not contribute to scramble, and it can be seen that the output of scrambler Sc is determined by the state of the shift register by 58-stage flip-flops S0 to S57.

  In an Ethernet frame (Ethernet is a registered trademark) that is an actual input signal, 0/1 signals are arranged in a balanced manner in the header portion and the like, and are not fixed to 0 or 1. Thereby, a certain amount of scrambling can be performed. However, in the case of a long frame in which the data payload is fixed to 0 or 1 (for example, a 1518 byte frame), most of the input signal is this long frame, so that most of the input signal is fixed to 0 or 1. . The state in which the data payload is fixed to 0 or 1 is, for example, pure black or pure white image data, which is sufficient.

Next, the occurrence of baseline wander when Input is fixed to 0 or 1 will be considered. The linear feedback shift register composed of 58 stages of flip-flops S0 to S57 maintains 0/1 balance in the cycle (2 ^ 58-1 bits), but temporarily 0/1 balance is poor. And there is a baseline wander.
First, consider a case where Input = 0 is fixed. Table 1 shows a truth table of exclusive OR.

  From Table 1 above, when there are many 0s in the 58-stage flip-flops S0 to S57, the scrambled data output has a higher probability of XOR (S57, S38, Input) = XOR (0, 0) = 0. That is, when a large number of 0s begins to be output from the scrambler Sc, the feedback signal is not inverted and becomes 0, and thus a state in which 0 is easily output continues. In this case, a large base run wander occurs temporarily. On the other hand, when 1 is increased in S0 to S57, the probability that the scrambled data output becomes XOR (S57, S38, Input) = XOR (1, 1) = 0 increases. In this case, even if a large amount of 1 starts to be output from the scrambler Sc, the feedback signal is inverted and becomes 0, so that the state where 1 is likely to be output does not continue.

  Next, consider a case where Input is fixed to 1. In this case, if 0 is increased in S0 to S57, the probability that the scrambled data output becomes XOR (S57, S38) = ˜XOR (0, 0) = 1 increases. For this reason, even if many 0s start to be output from the scrambler Sc, the feedback signal is inverted and becomes 1, so that the state in which 0 is likely to be output does not continue. When 1 is increased in S0 to S57, the probability that the scrambled data output becomes XOR (S57, S38) = to XOR (1, 1) = 1 increases. For this reason, when a large amount of 1 starts to be output from the scrambler Sc, the feedback signal is not inverted and becomes 1, so that a state where 1 is likely to be temporarily output continues. In this case, a large base run wander occurs.

《Baseline wander simulation》
Next, in the 64B / 66B code, how the baseline wander appears when the input signal is fixed to 0 is verified by simulation.
FIG. 12 is a diagram showing a configuration for simulation. When the input signal (serial data) passes through the 64B / 66B encoder (including the scrambler Sc), it becomes an NRZ (Non Return Zero) signal having an amplitude of 1. In this case, the code 1 corresponds to +0.5, and the code 0 corresponds to −0.5. This NRZ signal passes through a low-pass filter (LPF) having a cutoff frequency fc = 2 MHz.

The output of the low-pass filter, that is, the detected value of the baseline is ideally 0, which is an intermediate value of the amplitude of the NRZ signal.
The simulation conditions are as follows. First, as an initial state (Seed) of a 58-bit shift register,
“Seed = A”: the worst case where bit 0 is 1 and all others are 0, and
“Seed = B”: all bits are 1
2 types are prepared.

As the input signal (serial data), all 0 (fixed to 0) and PRBS2 ⁷ −1 are prepared. PRBS2 ⁷ -1 is a pseudo-random bit sequence (Pseudo Random Bit Sequence) corresponding to seven stages. A pseudo-random bit sequence is a test sequence that exhibits specific randomness and autocorrelation. This can be used to evaluate the performance of the system under random data conditions. In this way, there are two types of input signals: all zero signals with low (no) randomness, and high randomness signals with a balance of 0/1.

13 to 16 are graphs showing simulation results, in which the horizontal axis represents time (bits) and the vertical axis represents baseline wander (BLW) corresponding to the detected values in FIG.
FIG. 13A shows a baseline wander from time 0 to 100,000 bits under conditions where Seed = A and all inputs are zero. In this case, a large baseline wander (about 0.3) is generated on the sign 0 side (minus side). FIG. 13B shows a baseline wander from 0 to 100,000 bits in time under the condition that Seed = A and the input is PRBS2 ⁷ -1. In this case, a large baseline wander does not occur.

FIG. 14 shows the baseline wander when the time scale is made larger (30 times) than in the case of FIG. That is, FIG. 14A shows a baseline wander from 0 to 3 million bits in time under conditions where Seed = A and all inputs are zero. In this case, in addition to the first large baseline wander shown in FIG. 13A, a baseline wander of about 0.1 appears on the reference numeral 0 side at the location indicated by the following two arrows. FIG. 14B shows a baseline wander from 0 to 3 million bits in time under the condition that Seed = A and the input is PRBS2 ⁷ -1. In this case, a large baseline wander does not occur.

Next, FIG. 15A shows a baseline wander from 0 to 100,000 bits in time under the condition that Seed = B and all inputs are zero. In this case, although not as high as Seed = A (FIG. 13A), a baseline wander exceeding 0.1 is generated on the code 0 side. FIG. 15B shows a baseline wander from time 0 to 100,000 bits under the condition that Seed = B and the input is PRBS2 ⁷ -1. In this case, a large baseline wander does not occur.

FIG. 16 shows the baseline wander when the time scale is made larger (30 times) than in the case of FIG. That is, (a) of FIG. 16 shows the baseline wander from 0 to 3 million bits under the condition that Seed = B and all inputs are 0. In this case, in addition to the first baseline wander shown in FIG. 15A, a slightly conspicuous baseline wander appears on the code 0 side at a plurality of subsequent locations. FIG. 16B shows a baseline wander from time 0 to 3 million bits under the condition that Seed = B and the input is PRBS2 ⁷ -1. In this case, a large baseline wander does not occur.

From the above, if the input signal is highly random PRBS2 ⁷ -1, a large baseline wander does not occur, but if the input signal is fixed at 0, a relatively large baseline wander occurs. Was verified.

Here, attention can be paid to encryption as an actual operation status of the PON system similar to the situation where the input signal is PRBS2 ⁷ -1 with high randomness. That is, the encrypted input signal has high randomness, and 0 or 1 cannot continue for a long time. Therefore, when an encrypted upstream burst signal is sent from the home side device, a large baseline wander does not occur. Conversely, when an unencrypted upstream burst signal is sent. Large baseline wander can occur. Therefore, it is conceivable to change the reception method of the station side device according to the encryption processing. Hereinafter, an embodiment of a PON system including such a receiving apparatus (receiving method) will be described.

<< Overall system configuration >>
FIG. 1 is a connection diagram of a PON system according to an embodiment of the present invention.
In FIG. 1, a station-side device 1 is installed as a central station for a plurality of home-side devices 2, 3, and 4, and each home-side device 2, 3, and 4 is installed at a subscriber home of a PON system. .
One optical fiber (trunk line) 5 connected to the station side device 1 is branched into a plurality of optical fibers (branch lines) 7 via an optical coupler 6, thereby forming an optical fiber network. Home devices 2, 3, and 4 are connected to the ends of the optical fibers 7 branched from the optical coupler 6, respectively.

The station side device 1 is connected to the host network 8, and the home side devices 2, 3, 4 are connected to the respective user networks 9.
Although FIG. 1 shows a total of three home-side devices 2, 3, and 4, it is possible to connect 32 home-side devices by branching, for example, 32 from one optical coupler 6. In FIG. 1, only one optical coupler 6 is used. However, more home-side devices can be connected to the station-side device 1 by providing a plurality of optical couplers in a column.

In FIG. 1, data based on an optical signal having a wavelength λ1 is transmitted in the upward direction from each home-side device 2, 3, 4 to the station-side device 1. Conversely, in the downstream direction from the station-side device 1 to each of the home-side devices 2, 3, and 4, data using an optical signal having a wavelength λ2 is transmitted.
These wavelengths λ1 and λ2 are assumed to have values in the following range, for example, in a 10 Gbps signal of IEEE 802.3av.
1260nm ≦ λ1 ≦ 1280nm
1575 nm ≦ λ2 ≦ 1580 nm

  In the present embodiment, out of the upstream burst signals B2, B3, B4 from the home side devices 2, 3, 4, the upstream burst signals B3, B4 from the home side devices 3, 4 are encrypted, It is assumed that the upstream burst signal B2 from the side device 2 is not encrypted. In addition to the level difference of encryption processing such as the presence / absence of encryption, there is also a level difference in the encryption processing for the upstream burst signals B3 and B4 from the home side devices 3 and 4 that are encrypted. is there. That is, the home side device 4 performs high encryption processing with higher randomness than the home side device 3, and conversely, the home side device 3 is slightly less random than the home side device 4 ( However, it is clearly higher than without encryption.) Low encryption processing is performed.

Further, the distances from the station-side device 1 to the home-side devices 2 to 4 (lengths of the optical fibers 5 + 7) are different from each other, and therefore the strength of the upstream burst signal is also different from each other. In the example shown in the figure, the distances are increased in the order of the home devices 2, 3, and 4.
Note that error correction (FEC) capability (FEC encoding / decoding) can be provided as necessary according to the distance.

In the example shown in the figure, there are three home side devices 2, 3 and 4 that perform three different types of encryption processing (including no encryption). There may be other various patterns in the difference in the number of the devices and the level of the encryption processing.
Since the station side device 1 functions as a central station for each of the home side devices 2, 3, and 4 as described above, information on encryption processing in the home side devices 2, 3, and 4 (encryption / non-encryption, encryption) , Content of decryption, encryption level, etc.). That is, the station-side device 1 grasps information related to the encryption processing of all the home-side devices 2, 3, and 4 that it manages.

Further, as shown in FIG. 1, the station side device 1 includes the level of encryption processing (including no encryption) of the home side devices 2, 3, and 4 and the time constant of its own receiving circuit suitable for it. And the reference table Ta which prescribed | regulated the information regarding the preamble length of upstream burst signal B2-B4 is memorize | stored in the memory | storage part 10 (refer FIG. 2).
As is clear from this reference table Ta, in the present embodiment, it is defined that both the time constant and the preamble length become shorter as the level of encryption processing (randomness) of the upstream burst signals B2 to B4 is higher. .

<< Configuration of station side equipment >>
FIG. 2 is a block diagram illustrating an outline of the internal configuration of the station-side device 1. Each part of the station side apparatus 1 of this embodiment is connected as shown in FIG.
In FIG. 2, a frame from the upper network 8 is received by the upper network side receiving unit 101 and sent to the data relay processing unit 103. The data relay processing unit 103 passes the frame to the PON side transmission unit 105. This frame is converted into an optical signal having a wavelength λ 2 and a predetermined transmission rate (10.3125 Gbps) by the optical transmission unit 108, and is transmitted to each of the home devices 2 to 4 through the multiplexing / demultiplexing unit 110.

On the other hand, the optical signal having the wavelength λ 1 transmitted from the home devices 2, 3, 4 in the upstream direction passes through the multiplexing / demultiplexing unit 110 and is received by the optical receiving unit (burst receiving unit) 109.
The optical receiving unit 109 includes a photoelectric conversion element 111, an amplifier 112, a time constant circuit 113, and a comparator 114 inside.
The photoelectric conversion element 111 is a semiconductor light receiving element such as a photodiode or an avalanche photodiode, and outputs a burst electric signal at a level corresponding to the received light amount of the upstream burst signals B2 to B4. The amplifier 112 amplifies the electric signal. Output.

The time constant circuit 113 follows the amplitude of the amplified signal of the amplifier 112 with a variable time constant, and the comparator 114 outputs a comparison result with the output signal of the time constant circuit 113. The output signal of the comparator 114 is input to the PON side receiving unit 107.
A more detailed circuit configuration of the optical receiver 109 will be described later.

The PON side receiving unit 107 includes a clock / data reproducing unit 115, an FEC decoding unit 116, a physical layer decoding unit 117, an encryption / decryption unit 118, and a frame reproduction unit 119.
The clock / data recovery unit 115 recovers the timing component (clock) and data in synchronization with the binary output signal received from the comparator 114 of the optical reception unit 109.
The FEC decoding unit 116 performs predetermined error correction decoding on the reproduced data, and the physical layer decoding unit 117 decodes a predetermined code applied to the reproduced data.

Note that the error correction decoding performed by the FEC decoding unit 116 is a decoding process for the error correction code generated by the FEC encoding unit 212 of the home-side apparatuses 2, 3, and 4 to be described later.
Also, the decoding performed by the physical layer decoding unit 117 is a decoding process for a code generated by the physical layer encoding unit 211 of the home-side devices 2, 3, and 4 described later, that is, a 64B / 66B decoding process (descrambling process). Is included.)

  The encryption / decryption unit 118 performs decryption processing corresponding to the encryption of the home side apparatuses 3 and 4 on the data input from the physical layer decryption unit 117. Note that this processing can be omitted for unencrypted data. The encryption processing in the home side devices 3 and 4 will be described later.

The frame reproduction unit 119 detects a frame boundary from the decoded data and restores, for example, an Ethernet (registered trademark) frame. The frame playback unit 119 reads the header portion of the frame and determines whether the received frame is a data frame or a frame of control information for media access control.
An example of the control information is MPCP (Multi-point Control Protocol) PDU (Protocol Data Unit) assumed in IEEE 802.3av.

The station side device 1 controls the “grant” which is control information for instructing the home side devices 2, 3, 4 to transmit the upstream burst signals B 2 to B 4 and the transmission permission amount, and the home side devices 2, 3, 4. “Report”, which is control information for notifying the station-side device 1 of a value related to the amount of accumulated uplink data, is a kind of MPCP PDU.
As a result of the frame type determination, if the frame is a data frame, the frame playback unit 119 sends this to the data relay processing unit 103.

The data relay processing unit 103 performs predetermined relay processing such as change of header information of the data frame and transmission control for the upper network side transmission unit 102, and the processed frame is transmitted from the upper network side transmission unit 102 to the upper network 8. Is sent to.
On the other hand, if the frame type is a report frame as a result of the frame type determination, the frame reproduction unit 119 sends it to the station-side signal processing unit 104. The station-side signal processing unit 104 generates a grant frame as control information based on this report, and causes the PON-side transmission unit 105 and the optical transmission unit 108 to transmit this grant frame in the downlink direction.

  The station-side signal processing unit (station-side control unit) 104 also includes the level of encryption processing of each home device 2, 3, 4 and the time constant and upstream burst signal of the time constant circuit 113 suitable for this level. Based on the reference table Ta stored in the storage unit 10 as information on the preamble lengths B2 to B4, the preamble length corresponding to the level of the encryption process can be determined. Information on the determined preamble length is included in the grant frame and notified from the station-side signal processing unit 104 to the home-side devices 2 to 4.

On the other hand, the station-side signal processing unit 104 specifies the next time to receive the upstream burst signals B2 to B4 from the home-side devices 2, 3, and 4 based on the grant distributed to the home-side devices 2, 3, and 4. Then, the encryption processing corresponding to the home devices 2, 3, and 4 and the time constant suitable for the level of the encryption processing are determined with reference to the reference table Ta.
Then, the station-side signal processing unit 104 notifies the PON-side receiving unit 107 of the encryption / decryption processing corresponding to the encryption processing of the home-side device that receives the next upstream burst signal, and also sets the time constant to the optical receiving unit. 109 is notified.

The optical receiving unit 109 and the PON side receiving unit 107 adapt their reception functions in accordance with the reception timing of the upstream burst signals B2 to B4 received from the home side devices 2, 3, and 4.
Specifically, the optical receiving unit 109 switches the internal parameter of the time constant circuit 113 to the time constant notified from the station side signal processing unit 104, and the preamble length notified to the home side devices 2, 3, and 4 with the same grant. Within a period of time, the gain of the amplifier 112 is switched to a predetermined value, and the time constant circuit 113 is converged.

Further, the encryption / decryption unit 118 of the PON side receiving unit 107 performs encryption / decryption processing based on the notification from the station side signal processing unit 104. In the case of the upstream burst signal B2 without encryption (in the case of the home device 2 in FIG. 1), the encryption / decryption unit 118 does not perform encryption / decryption processing.
As for FEC decoding, information is stored in the storage unit 10 and decoding is performed in accordance with FEC encoding of the home side apparatus that sends the upstream burst signal, but detailed description thereof will be omitted.

<Configuration of optical receiver>
FIG. 3 is a circuit diagram illustrating an example of a circuit configuration of the optical receiver 109.
In FIG. 3, a photodiode 111 as a light receiving element receives upstream burst signals B2 to B4 made of optical signals based on binary signals (digital signals), converts them into upstream burst signals of electrical signals, and outputs them. .
The output signal of the photodiode 111 is amplified by the amplifier 112 having a feedback resistor 124 connected between the input and output.

The amplified burst signal (amplified signal) output from the amplifier 112 is directly input to one input terminal (−) of the comparator 114 as a signal voltage. Further, a voltage at which the burst signal is output via the time constant circuit 113 is input to the other input terminal (+) of the comparator 114 as a threshold voltage.
The time constant circuit 113 shown in FIG. 3 includes a resistor 120 whose resistance value is variable by an external control signal, and a capacitor 121 having one end connected to the variable resistor 120 and the other end being a ground potential. It consists of a low-pass filter. That is, this is a real machine corresponding to the low-pass filter (LPF / FIG. 12) in the above-described simulation.

In this case, when the resistance value of the variable resistor 120 is R and the capacitance of the capacitor 121 is C, the time constant τ of the time constant circuit 113 is τ = R · C.
The comparator 114 compares the signal voltage with the threshold voltage, and outputs the comparison result Dout, which is a binary signal (digital signal) of 0 or 1, and its logical inversion signal.
The resistance value R of the variable resistor 120 changes according to the control signal from the station-side signal processing unit 104, whereby the time constant τ of the time constant circuit 113 is changed in three stages from τ1 to τ3 (τ1 <τ2 <τ3). Can be switched. The three stages are examples in which three types of time constants are required, and it is needless to say that the number of stages can be provided according to the types of required time constants.

FIG. 4 is a circuit diagram illustrating another example of the circuit configuration of the optical receiver 109.
As shown in FIG. 4, the time constant circuit 113 in this case includes a resistor R0 (resistance value R0) and a series body of a capacitor 121 provided between the output terminal of the amplifier 112 and the ground potential, and a resistor R0. A series body of a resistor R1 (resistance value R1) and a switching element (for example, a MOS-FET) 122 connected in parallel to each other, and a resistor R2 (resistance value R2) and a switching element 123 similarly connected in parallel to the resistor R0. And a serial body.

Each control terminal of the switching elements 122 and 123 (for example, the gate of the MOS-FET) is connected to the station side signal processing unit (station side control unit) 104, and the switching elements 122 and 123 are turned on / off by the processing unit 104. Be controlled.
Here, assuming that the on-resistance of the switching element 122 is Rs1 and the on-resistance of the switching element 123 is Rs2, and assuming that the relationship of (R2 + Rs2) <(R1 + Rs1) is satisfied, the switching elements 122 and 123 are switched on and off, The following three time constants τ1 to τ3 can be obtained.

(1) In the case of element 122 → off, element 123 → on τ1 = {R0 · (R2 + Rs2) / (R0 + R2 + Rs2)} · C
(2) In the case of element 122 → on, element 123 → off τ2 = {R0 · (R1 + Rs1) / (R0 + R1 + Rs1)} · C
(3) In the case of element 122 → off, element 123 → off τ3 = R0 · C

In this case, since there is a relationship of (R2 + Rs2) <(R1 + Rs1), τ1 <τ2 <τ3.
Therefore, also in the case of the optical receiver 109 shown in FIG. 4, the time constant τ of the time constant circuit 113 is set to τ1 by the control signal generated based on the grant from the station side signal processor (station side controller) 104. ˜τ3 (τ1 <τ2 <τ3).

<Configuration of home side device>
Next, the configuration of the home device will be described.
FIG. 5 is a block diagram showing an outline of the internal configuration of the home device 3.
Each part of the home side apparatus 3 of this embodiment is connected as shown in FIG. The configuration of the home device 4 is the same. The home-side device 2 is different only in that the encryption unit 310 is not provided, but is otherwise the same.
In FIG. 5, the optical signal transmitted from the station side device 1 in the downstream direction passes through the multiplexing / demultiplexing unit 301 and is converted into an electric signal by the optical receiving unit 302, and this electric signal is further received by the PON side. Received by the unit 304.

The optical receiving unit 302 has an RSSI (Received Signal Strength Indicator) function, monitors the strength of the downlink received signal, and sends the detection information from the PON side receiving unit 304 to a home side signal processing unit (home side control) to be described later. Part) 306.
The PON side receiving unit 304 reads the header portion (including the preamble portion) of the received frame, and the frame is addressed to itself (in this case, to the device in the user network 9 under its control or the user's own control). .) Is determined.

As a result of the determination, if it is addressed to itself, the frame is taken in. If not, the frame is discarded. For example, as an example of header information for performing the above destination determination, a logical link identifier (LLID) assumed in IEEE 802.3av can be cited.
Further, the PON side receiving unit 304 determines whether the received frame is a data frame or a grant frame by reading the header portion of the frame.

As a result of the determination, if it is a data frame, the PON side receiving unit 304 sends this to the data relay processing unit 307. The data relay processing unit 307 performs predetermined relay processing such as transmission control for the user network side transmission unit 308, and the processed frame is transmitted from the user network side transmission unit 308 to the user network 9.
As a result of the determination, if the frame is a grant frame, the PON side receiving unit 304 transfers this to the home side signal processing unit 306. The home-side signal processing unit 306 instructs the data relay processing unit 307 to perform uplink transmission based on the grant frame.

On the other hand, the frame from the user network 9 is received by the user network side receiving unit 309 and transferred to the data relay processing unit 307. The transferred frame is temporarily stored in the buffer memory in the data relay processing unit 307, and the data amount is notified to the home signal processing unit 306.
The home-side signal processing unit 306 performs transmission control on the PON-side transmission unit 305, causes the frame stored in the buffer memory to be output to the PON-side transmission unit 305 at a predetermined timing, and notifies the notified buffer memory A report frame is created on the basis of the amount of data stored therein, and is output to the PON side transmission unit 305.

  The output of the PON side transmission unit 303 is converted into an optical signal by the optical transmission unit 303 and transmitted in the upstream direction through the multiplexing / demultiplexing unit 301 as an optical signal having a wavelength λ1 and a predetermined transmission rate (10.3125 Gbps). Is done. The PON side transmission unit 303 includes an encryption unit 310, a physical layer encoding unit 311, and an FEC encoding unit 312 inside.

  The encryption unit 310 performs encryption processing on the transmission data transmitted from the data relay processing unit 307. The encryption of 10G-EPON is performed in accordance with IEEE802.1AE that defines Ethernet (registered trademark) security, and GCM-AES-128 is defined as a default algorithm. GCM-AES-128 is one mode of operation of AES (Advanced Encryption Standard) defined by NIST (The National Institute of Standards and Technology) and is suitable for hardware and high speed. Encryption is possible. Note that 128 means that the key length is 128 bits.

  The physical layer encoding unit 311 performs predetermined encoding, that is, 64B / 66B encoding processing (including scrambling) on the data transmitted from the data relay processing unit 307. Further, the FEC encoding unit 312 adds a redundant bit to the encoded data to generate a predetermined error correction code.

In addition, the physical layer encoding unit 311 adds a preamble length including a predetermined pattern (repeating a 66-bit synchronization pattern in IEEE 802.3av) to the data simultaneously with encoding. This preamble length can be changed according to the notification from the home-side signal processing unit 306.
When information regarding the preamble length is described in the grant frame, the home-side signal processing unit 306 sets the preamble length of the code generated by the physical layer encoding unit 311 based on the information.

<Control frame exchange>
FIG. 6 is a sequence diagram showing exchange of control frames between the station-side device 1 and, for example, the home-side device 3 (the same applies to the home-side devices 2 and 4). As shown in the figure, first, the station side device 1 has already calculated an RTT (Round Trip Time) related to the home side device 3 at the operation time start time T0. At time Ta1, the station apparatus 1 transmits a grant (grant frame) G1 including the report transmission start time Tb2 to the home apparatus 3 in order to notify the transmission request amount.

  This report transmission start time Tb2 is calculated so as not to collide with reports transmitted from other home-side devices 2 and 4. When receiving the grant G1 for the home side device 3, the home side device 3 refers to the amount of data stored in the buffer memory of the data relay processing unit 307 to calculate the transmission request amount, and at the report transmission start time Tb2 included in the grant G1. Then, a report (report frame) R1 including the transmission request amount is transmitted to the station side device 1.

Upon receiving the report R1, the station side device 1 calculates a value that is less than the fixed or variable maximum transmission allowable amount and can send as much data as possible in the buffer memory included in the report R1, and calculates the calculation result. It is inserted into the grant G2 as a transmission permission amount.
When the transmission request amount included in the report R1 is zero, the calculation result by the station side device 1 is zero, so no band is allocated, but the home side device 3 needs to send the report R2, The side device 1 always sends a grant G2 to the home side device 3.

The transmission start time Tb4 included in the grant G2 is the scheduled reception time of the previous home-side device data that has been calculated, the previous permitted amount of transmission of the home-side device 3, the RTT related to the current home-side device 3, and the fixed time. Using the guard time, the data and the report are calculated so as not to collide with the data or reports from the other home side apparatuses 2 and 4.
The station-side device 1 calculates a time Ta3 for sending the grant G2 including the sending permission amount and the sending start time Tb4 so that the grant G2 arrives at the home device 3 by the sending start time Tb4.

When receiving the grant G2 for itself, the home side device 3 sends the data D for the transmission permission amount to the station side device 1 together with the report R2 including the next transmission request amount at the transmission start time Tb4 included in the grant G2. Send it out.
The report R2 is sent immediately before or after the data D. When the report R2 is sent immediately before the data D, the value to be reported to the station side device 1 as the send request amount is the data stored in the buffer memory. This is the difference between the amount and the data amount of data D.

  Upon receiving the data D and the report R2, the station side device 1 sends the data D to the upper network 8, and the report R2 performs the same process as the process for the report R1. The sequence processing described above is performed independently for all the home side devices 2 to 4, and the processing from time Ta <b> 3 to time Ta <b> 4 is repeated until the operation time ends.

<< Upstream communication sequence >>
FIG. 7 is a sequence diagram showing uplink communication in the PON system, and shows an example of a distributed allocation method. Hereinafter, the operation of the PON system mainly including the station side apparatus 1 will be described on the assumption that time advances from the left side to the right side in FIG.
First, the station-side device 1 sequentially sends grants G41, G31, and G21 to the home-side devices 4, 3, and 2, respectively.

Next, when the station side device 1 receives the reports R41, R31, and R21 from the home side devices 4, 3, and 2, respectively, it first sends a grant G42 to the home side device 4 that is permitted to send data.
And the station side apparatus 1 will transmit the grant G32 with respect to the home side apparatus 3 in parallel with this, if the data D41 sent from the home side apparatus 4 and the following report R42 are received.

Upon receiving the data D31 sent from the home side device 3 and the next report R32, the station side device 1 sends a grant G22 to the home side device 2 in parallel therewith. Subsequently, the grant G43 for the home device 4 is also sent out.
The station side apparatus 1 receives the data D21 and the next report R22 transmitted from the home side apparatus 2.

The station side device 1 receives the data D42 sent from the home side device 4 and the next report R43, and sends a grant G33 to the home side device 3 in parallel therewith.
Further, the station side device 1 receives the data D32 sent from the home side device 3 and the next report R33, and sends a grant G23 to the home side device 2 in parallel therewith.
Here, if there is no data transmitted from the home side apparatus 2, the station side apparatus 1 receives only the next report R23.

  Thereafter, the same processing is repeated, and the station side apparatus 1 dynamically allocates bands to the home side apparatuses 2, 3, and 4 in sequence and repeats data reception.

<< Relationship between encryption and reception >>
By the sequence as described above, the station side device 1 can receive the uplink burst signals from the home side devices 2 to 4 in a time division manner. The station-side device 1 manages and grasps all schedules for receiving signals from which home-side devices at which time. Further, the station side device 1 stores information related to the encryption processing of the home side devices 2 to 4 in the storage unit 10. Therefore, the station-side device 1 determines the time constant and the preamble length based on the relative level of the randomness of the transmission signal that depends on the encryption.

  As described above, the randomness of the transmission signal depends on encryption, and a large baseline wander may occur without encryption, so the time constant τ needs to be set relatively long. Correspondingly, the preamble length of the transmission signal needs to be relatively long. On the other hand, even in the case of encryption, there is a difference in randomness due to the level difference of the encryption processing. Therefore, in the case of high encryption, the time constant is relatively short and the preamble length is also relatively short. In the case of low encryption, both the time constant and the preamble length are set as medium as an intermediate setting between high encryption and no encryption (reference table Ta in FIG. 1).

Therefore, as shown in the reference table Ta in FIG. 1, the control unit (station side signal processing unit 104) of the station side device 1 responds to encryption with the time constant and the preamble length “long”, “medium”, “ “Short” is determined, and the preamble length is notified to the other party's home-side device when the grant is transmitted. Further, in accordance with the reception timing of the burst signal from each of the home side devices 2, 3 and 4, the optical receiver 109 has a time constant (τ ₃ , τ ₂ , τ ₁ ) corresponding to the preamble length of the burst signal. The time constant circuit 113 is operated. Note that the actual length of the preamble length “long”, “medium”, and “short” varies depending on the time constant. That is, the preamble length is set so that the threshold value converges to an intermediate amplitude value within the preamble interval with respect to the set time constant, and 0/1 of the input signal can be read reliably. It is necessary and sufficient length.

  In the PON system configured as described above, it is possible to focus on the randomness of the transmission signal depending on the encryption, and to determine a suitable time constant and preamble length based on the relative level of the randomness. . That is, when randomness is low, there is a possibility that 0 or 1 continues, so that the occurrence of a large baseline wander can be suppressed by relatively increasing the time constant. On the other hand, if the randomness is high, it does not shift to either 0 or 1, so that a large baseline wander does not occur. Therefore, it is only necessary to relatively shorten the time constant. If the time constant is shortened, the preamble length can also be shortened. Shortening the time constant contributes to ensuring responsiveness to burst signals, and shortening the preamble length contributes to effective use of bandwidth. Therefore, effective use of the transmission band can be realized while reliably receiving the burst signal.

  In addition to the presence or absence of encryption, the case where encryption processing is performed is divided in stages, and if the encryption processing is high encryption, the time constant and preamble length are particularly short, If the encryption process is low encryption, various settings such as slightly shortening the time constant and the preamble length are possible.

  Also, when 64B / 66B encoding is performed using a linear feedback shift register that includes an exclusive OR operation between an input signal and a feedback signal, if the input signal continues for a long period of time, the output signal is also fixed and output. This is likely to cause a large baseline wander. However, if the input signal is encrypted, such a problem does not occur, and the station apparatus 1 can receive with a short time constant. Thus, by determining the time constant according to the encryption, this problem, that is, the problem caused by the 64B / 66B encoding can be alleviated.

<< Discovery Process >>
In the above description, it is assumed that all the home side devices 2, 3, and 4 have already joined the PON system.
However, in practice, for example, there is a procedure in which the home-side devices 2, 3, and 4 are recognized by the station-side device 1 when the power is turned on from the power-off state and joins the PON system, and this procedure is called a discovery process.

Since the unregistered home-side device before being recognized by the station-side device 1 has no opportunity to be granted a grant, all the home-side devices 2, 3, and 4 are explicitly granted a grant from the station-side device 1. Unless it is possible, uplink communication cannot be performed.
Therefore, the station-side device 1 is turned on from power-off (including unconnected), and home-side devices 2, 3, and 4 (hereinafter referred to as unregistered home-side devices) that are going to join the PON system. A discovery process for detection is periodically executed to give a response opportunity to an unregistered home device.

FIG. 8 is a sequence diagram showing a general discovery process performed between the station side device and the unregistered home side device.
In FIG. 8, the station side apparatus starts the discovery process at time T1, and broadcasts a discovery gate in the downstream direction.
This discovery gate includes information on the start time and the length of the discovery period during which a response to the discovery gate is allowed. This discovery period is called a discovery window and is, for example, a time ΔTd from time T2 to T4.

The unregistered home-side apparatus that has received the discovery gate waits for a random waiting time ΔTw having a random length from time T2 (synchronized with the station-side apparatus), and sends a registration request message to the station-side apparatus at time T3. Send to.
This random waiting time ΔTw is a random value within a range in which the registration request message fits in the discovery window. Therefore, even if there are a plurality of unregistered home devices that are going to join the PON system, the probability that registration request messages from a plurality of unregistered home devices collide with each other can be reduced.

The registration request message includes the MAC address as the individual identification number of the unregistered home device. The station side device that has successfully received the registration request message assigns a logical link number (LLID) on the PON system to the unregistered home side device, associates the MAC address with the LLID, and registers them in the PON system. To do.
Next, the station side device transmits a registration message to the newly registered home side device at time T5. The registration message includes the LLID of the home device and information on the synchronization time required when the station device receives the uplink burst communication.

Thereafter, at time T6, the station-side device transmits a grant (grant gate) that permits uplink communication to the home-side device.
The unregistered home device that has received the grant gate uses the grant to transmit a registration acknowledge to the station device at time T7, which is received by the station device, and the discovery process ends. Thereafter, normal PON system communication is started.

<< Other examples of encryption >>
FIG. 9 is a connection diagram of the PON system that is slightly different from FIG. The difference from FIG. 1 is that the level difference in the encryption process is simply two types, no encryption and encryption, and the time constant and preamble length are also two types, long and short. That is, the time constant is only a relatively long τ _L and a relatively short τ _S. Further, the preamble lengths in the upstream burst signals of the home side apparatuses 3 and 4 are the same as each other and are “short”.
In this way, it is possible to change the handling only by the presence or absence of encryption, and since there are only two types of time constants, it is simple. Rather, it may be better than FIG. 1 in terms of effective use of bandwidth.

<Obtaining initial information about encryption>
In addition, since the information about encryption is not memorize | stored in the station side apparatus 1 about the home side apparatus registered for the first time, the process which memorize | stores this is required.
FIG. 10 is a flowchart showing the procedure of such processing (including human processing). As the target PON system, FIG. 9 is considered in which only the presence or absence of encryption is considered.

  In FIG. 10, the station side device is represented as OLT and the home side device is represented as ONU. First, in step S1, a connection (discovery) between the OLT and the ONU is established with default settings of “encryption = none, time constant = length, preamble = length”. Next, the operator sets the upstream signal of the new ONU_n to “encryption = present” (step S2). Next, the OLT notifies the ONU_n of the transmission setting change (step S3). For example, the notification content should be changed to “encryption = present, preamble = short”.

Next, in step S4, if ONU_n supports encryption, the process proceeds to step S5, and if not, the process proceeds to step S8.
In step S5, the ONU_n changes the transmission setting and responds to the OLT that “encryption = present, preamble = short”. In response to this, the OLT changes the ONU_n reception setting to “encryption = present, time constant = short, preamble = short” (step S6). Thereafter, uplink transmission / reception from the ONU_n to the OLT is performed with “encryption = present, time constant = short, preamble = short”.

  On the other hand, when the process proceeds to step S8, a response “cannot be changed” is made from ONU_n to the OLT. In response to this, the OLT notifies the operator that "ONU_n does not support encryption" as a change failure (step S9). Thereafter, uplink transmission / reception from the ONU_n to the OLT is performed with the default of “encryption = none, time constant = length, preamble = length” (step S10).

<Others>
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
For example, in the above-described embodiment, the case where the receiving device that receives burst signals in a time division manner is the station side device of the PON system, but the receiving device of the present invention is adopted in other systems such as a wireless communication system. You can also.

1 Station side device (receiving device)
2-4 Home device (transmitter)
5, 7 Optical fiber 10 Storage unit 104 Station side signal processing unit (control unit)
109 Optical receiver (burst receiver)
311 Physical Layer Encoding Unit Sc2 Linear Feedback Shift Register

Claims (7)

A receiving device capable of receiving, in a time division manner, a burst signal having a level difference in encryption processing including the presence / absence of encryption from a plurality of transmitting devices, wherein the burst signal has a preamble length according to the level difference in the encryption processing Are different,
A storage unit for storing information regarding encryption processing of each transmission device;
A burst receiver that follows a burst signal including a predetermined preamble length with a predetermined time constant;
Control for operating the burst receiving unit with a time constant corresponding to the preamble length specified for each transmission source from the information regarding the encryption processing stored in the storage unit in accordance with the reception timing of the burst signal from each transmission device And a receiver. The control unit determines that the time constant and the preamble length are shorter as the randomness of the transmission signal depending on encryption is higher, and conversely, the time constant and the preamble length are longer as the randomness is lower. The receiving device according to 1. Station-side devices connected to multiple home-side devices via optical fiber receive multiple types of upstream burst signals with different levels of encryption processing including encryption / non-encryption from multiple home-side devices in a time-sharing manner A possible PON system,
The home-side apparatus has a transmission unit that transmits a burst signal with a preamble having a preamble length determined based on the relative level of randomness of a transmission signal depending on encryption,
The station side device
A storage unit for storing information related to encryption processing of each home-side device;
A burst receiver that follows a burst signal including a predetermined preamble length with a predetermined time constant;
The burst reception is performed with a time constant corresponding to the preamble length of the burst signal specified for each transmission source from the information related to the encryption processing stored in the storage unit in accordance with the reception timing of the burst signal from each home-side device. And a control unit for operating the unit.   The PON system according to claim 3, wherein the control unit determines that the time constant and the preamble length are shorter as the randomness is higher, and conversely, the time constant and the preamble length are longer as the randomness is lower.   5. The PON system according to claim 3, wherein the home-side apparatus includes an encoding unit that performs 64B / 66B encoding including an operation of exclusive OR of a feedback signal of a linear feedback shift register and an input signal. A receiving method that can receive burst signals with a level difference in encryption processing including the presence or absence of encryption from multiple transmitters in a time-sharing manner, and follow a burst signal including a predetermined preamble length with a predetermined time constant. There,
Predetermining the predetermined preamble length and the time constant based on the relative level of the randomness of the transmission signal depending on the encryption of each transmission device in advance;
Each transmitting device transmits a burst signal with the predetermined preamble length defined , and
Receiver, in accordance with the reception timing of the burst signal from each transmitting device, and follow the burst signal by a time constant that source of the burst signal corresponds to a preamble length granted in accordance with the encryption process received reception method characterized by a step of performing.   The receiving method according to claim 6, further comprising a step of instructing each transmitting apparatus to determine the predetermined preamble length determined by the receiving apparatus.