JP2019022157A - Subscriber line terminal apparatus - Google Patents

Abstract

To provide a subscriber line terminal apparatus capable of accurately performing bandwidth allocation to a plurality of subscriber line terminating apparatuses communicating by time division multiplexing even when fluctuation occurs in a signal processing time.SOLUTION: An OLT 3 accommodates a plurality of ONUs 5 by time division multiplexing. A bandwidth allocation unit of the OLT 3 allocates a reception start timing of an uplink signal from the ONU 5 in its own device so as to provide a margin time with a reception completion timing of an uplink signal from the other ONU 5. The bandwidth allocation unit also determines a transmission start timing of an uplink signal to be allocated to the ONU 5 using the reception start timing assigned to the ONU 5 and the minimum value of a round trip time acquired for the ONU 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a subscriber line terminal station apparatus.

  Due to increasing needs for high-speed access services, FTTH (Fiber To The Home) is spreading worldwide. Most of the FTTH services are provided by the PON (Passive Optical Network) method. As shown in FIG. 4, in the PON system, one subscriber line terminal equipment (OLT: Optical Line Terminal) is connected to a plurality of subscriber line termination equipment (ONU: Optical Network Unit) by time division multiplexing (TDM). It is housed and is economical. The current main system in Japan is GE-PON (Gigabit Ethernet (registered trademark) PON) whose transmission speed is a gigabit class. GE-PON is a standard IEEE 802.3ah standardized by the IEEE (American Institute of Electrical and Electronics Engineers) 802 committee for the purpose of applying Ethernet (registered trademark) communication to an access network (see, for example, Non-Patent Document 1). Is one of the standards.

  FIG. 5 is a diagram showing the layer structure of IEEE 802.3ah. ONU_x indicates the xth (x is an integer equal to or greater than 1) ONU among a plurality of ONUs connected to the OLT. The ONU has a configuration including a physical layer called PHY (PHYsical sublayer) and a data link sublayer called MAC (Media Access Control). The MAC has a MAC control sublayer (MAC control client) and a MAC sublayer. The MAC control sublayer is an optional sublayer that performs real-time control and operation of the MAC sublayer. The MAC sublayer executes data MAC framing (framing, MAC address addition, error detection) and medium access (collision detection, postponement processing). The physical layer is connected to the MAC via an RS (Reconciliation sublayer) that acts as an intermediary between the MAC and the physical layer and a GMII (Gigabit media independent interface). Further, the physical layer has a part that encodes data called PCS (Physical Coding Sublayer) and a part that connects to a physical medium called PMD (Physical Medium Dependent). PCS and PMD are connected by PMA (Physical Medium Attachment). PMA serializes data.

In the PON system, the OLT performs RTT (Round Trip Time) measurement with each ONU during the discovery process. The RTT measurement is periodically performed, and is corrected as needed when a deviation occurs due to a change in line conditions or the like. RTT is measured as shown in FIG. T _response indicates the elapsed time from when the OLT transmits the Discovery GATE signal until the Register REQ signal is received, and T _wait indicates the time from when the ONU receives the Discovery GATE signal until it transmits the Register REQ signal. _Assuming that the downstream propagation delay to T _Downstream and the upstream propagation delay from the ONU to the OLT is T _Upstream , RTT is calculated by the following equation (1).

RTT = T _response −T _wait = T _Downstream + T _Upstream (1)

  In the PON system, uplink signal control is realized using a protocol called MPCP (Multi Point Control Protocol). The OLT uses the GATE frame to instruct each ONU about the transmission start time and the transmission amount so that each ONU can transmit an upstream signal without colliding in time. On the other hand, the ONU uses the REPORT frame to inform the OLT the amount of data waiting for transmission stored in its own buffer. Here, the function of dynamically allocating the upstream band from the ONU to the OLT according to the traffic amount is referred to as a dynamic bandwidth allocation (DBA) function. The OLT collects bandwidth requests of a plurality of ONUs in a short DBA cycle and switches the allocated bandwidth, so that bandwidth can be allocated to many ONUs without waste and the transmission waiting time for uplink data can be shortened.

In the DBA function, the OLT calculates an upstream signal transmission start time T _granted of each ONU in order to supplement the measured RTT. FIG. 7 is a diagram for explaining DBA calculation in a conventional GE-PON system. In the following, the time at each timing related to reception, transmission, and the like is represented with reference to the time in the OLT. Assuming that the xth ONU (x is an integer of 1 or more) ONU # x, ONU # x upstream signal transmission start time T _{granted_x} is the upstream signal reception start time T _{desired_x} from ONU # x in OLT, Using the round trip time RTT _{x of} ONU # _x, it is expressed by the following equation (2).

T _{granted_x} = T _{desired_x−} RTT _x (2)

  On the other hand, as the demand for user traffic increases, the capacity and economy of optical access networks are increasing. To realize this, a DSP-PON system in which a digital signal processing (DSP) technology is applied to a PON system attracts attention, and research and development / practical use has been activated. The DSP-PON system may have a configuration in which both the OLT and the ONU include a DSP processing unit, or may have a configuration in which one of the DSP processing units is provided.

The RTT in the DSP-PON system is measured as shown in FIG. 8 because the time required for DSP processing in the OLT and ONU is added, and is expressed by Expression (3). The DSP processing delay of the transmitter in the OLT is T _OLT-Tx-DSP , the downstream propagation delay is T _Downstream , the DSP processing delay of the receiver in the ONU is T _ONU-Rx-DSP , and the DSP processing delay of the transmitter in the ONU is T _{It is assumed that ONU-Tx-DSP} , the upstream propagation delay is T _Upstream , and the DSP processing delay of the intra-OLT receiver is T _OLT-Rx-DSP .

RTT = T _response −T _wait
= T _OLT-Tx-DSP + T _Downstream + T _ONU-Rx-DSP + T _ONU-Tx-DSP + T _Upstream + T _OLT-Rx-DSP (3)

IEEE Standard 802.3ah, 2004

  In the DSP-PON system in which the DSP technology is applied to the PON system, there is a concern that the processing time of the DSP varies. For example, when OFDM (Orthogonal Frequency Division Multiplexing) technology is used, since the OFDM signal is transmitted at intervals of the symbol length T, the DSP processing delay varies by the OFDM symbol length. Further, when traffic is input to the ONU in a burst manner, the received traffic cannot be sent to the OLT in one cycle, but is sent over several cycles. For this reason, a delay several times the OFDM symbol length T occurs, and the processing delay varies by several times the OFDM symbol length.

Since the RTT varies as the DSP processing time varies in this way, when the transmission start time T _granted is calculated using the RTT measured for each ONU in the DBA function, as shown in FIG. There arises a problem that an upstream burst optical signal from an ONU may cause a collision. For example, the round trip time RTT ₃ of ONU # 3 varies between the _{RTT 3_Max} from the minimum _{RTT 3_min.} Therefore, when the RTT ₃ measured at a certain time is used to calculate the transmission start time T _{granted_3} by the equation (2), the upstream burst light transmitted by other ONUs before and after the ONU # 3 due to the fluctuation of the RTT ₃ Frame collision with the signal may occur.

  In view of the above circumstances, the present invention provides a subscriber line end capable of accurately performing bandwidth allocation to a plurality of subscriber line termination devices communicating by time division multiplexing even when fluctuations occur in signal processing time. The object is to provide a station apparatus.

  One aspect of the present invention is a subscriber line terminal device connected to a plurality of subscriber line terminators, and the reception start timing of an uplink signal from the subscriber line terminator in the subscriber line terminal device A bandwidth allocating unit that allocates a blank time between the reception completion timing of the uplink signal from the other subscriber line terminating device.

  One aspect of the present invention is the above-described subscriber line terminal station apparatus, further comprising an acquisition unit that acquires a minimum value of a round trip time of the subscriber line termination apparatus, wherein the bandwidth allocation unit includes the subscriber The transmission start timing of the uplink signal assigned to the line terminating device is determined using the reception start timing assigned to the subscriber line terminating device and the minimum value of the round trip time acquired for the subscriber line terminating device.

  One aspect of the present invention is the above-described subscriber line terminal station device, wherein the acquisition unit acquires a maximum value of a round trip time of the subscriber line termination device, and the bandwidth allocation unit includes the subscriber The reception start timing of the uplink signal from the line terminating device is acquired for the other subscriber line terminating device at the reception completion timing of the uplink signal according to the uplink data transmission amount from the other subscriber line terminating device. The difference between the maximum value and the minimum value of the round trip time, or a value obtained by multiplying the difference by a coefficient is calculated.

  According to the present invention, even when fluctuations occur in the signal processing time, it is possible to perform bandwidth allocation to a plurality of subscriber line terminating devices communicating by time division multiplexing with high accuracy.

1 is a configuration diagram of a DSP-PON system according to an embodiment of the present invention. It is a figure which shows the layer structure of the DSP-PON system by the embodiment. It is a figure for demonstrating calculation of DBA by the embodiment. It is a block diagram of the conventional PON system. It is a figure which shows the layer structure of the conventional GE-PON system. It is a figure which shows the round trip time in the conventional GE-PON system. It is a figure for demonstrating calculation of DBA in the conventional GE-PON system. It is a figure which shows the round trip time in a DSP-PON system. It is a figure which shows the frame collision of the upstream signal in a DSP-PON system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of a DSP-PON system 1 according to an embodiment of the present invention. The DSP-PON system 1 is configured such that one OLT (subscriber line terminal equipment) 3 accommodates a plurality of ONUs (subscriber line termination equipment) 5 by time division multiplexing (TDM). The downstream optical signal transmitted from the OLT 3 through one optical fiber is distributed to the optical fibers connected to each of the plurality of ONUs 5 by the optical splitter. Further, the upstream optical signals transmitted from each of the plurality of ONUs 5 in time division through the optical fiber are combined by the optical splitter and transmitted to the OLT 3 through one optical fiber.

  The OLT 3 includes a physical layer 31 called a PHY (PHYsical sublayer) and a data link sublayer MAC (Media Access Control) 32. The physical layer 31 of the OLT 3 includes a DSP processing unit 311. Similarly, the ONU 5 includes a physical layer 51 called PHY and a data link sublayer MAC 52. The physical layer 51 of the ONU 5 includes a DSP processing unit 511. The DSP processing unit 311 and the DSP processing unit 511 perform signal processing by the DSP. In the figure, both the OLT 3 and the ONU 5 are provided with DSP processing units, but a configuration may be provided in which only one of them is provided with a DSP processing unit.

FIG. 2 is a diagram showing a layer structure of the DSP-PON system 1.
The physical layer 31 (PHY) of the OLT 3 is provided with a DSP processor 311 and an ADC (Digital to Analog Converter) / DAC (Analog to Digital Converter) 312 in the PMD. The configuration is the same as that of the physical layer. Similarly, the physical layer 51 of the ONU 5 has the same configuration as the physical layer of the conventional ONU shown in FIG. 5 except that the DSP processing unit 511 and the ADC / DAC 512 are provided in the PMD.

  When transmitting a signal from the OLT 3 to the ONU 5, in the PMD in the physical layer 31 of the OLT 3, the DAC of the ADC / DAC 312 converts the transmission signal digitally processed by the DSP processing unit 311 into an analog signal, and the transmitter (Tx : Transmitter). In the PMD in the physical layer 51 of the ONU 5, the analog signal received by the receiver (Rx: Receiver) from the OLT 3 is converted into a digital signal by the ADC of the ADC / DAC 512, and the DSP processing unit 511 performs digital signal processing.

  When transmitting a signal from the ONU 5 to the OLT 3, in the PMD of the ONU 5, the transmission signal digitally processed by the DSP processing unit 511 is converted into an analog signal by the DAC of the ADC / DAC 512 and input to the transmitter (Tx). In the PMD of the OLT 3, the analog signal received by the receiver (Rx) from the ONU 5 is converted into a digital signal by the ADC of the ADC / DAC 312 and the DSP processing unit 311 performs digital signal processing.

  The MAC 32 of the OLT 3 and the MAC 52 of the ONU 5 have the same configuration as the MAC of the OLT and the MAC of the ONU shown in FIG. However, in the process in which the MAC control sub-layer (MAC control client) 321 of the MAC 32 assigns the bandwidth to each ONU 5, the minimum RTT (frame round trip time) obtained by performing RTT measurement a plurality of times for each ONU 5 The difference is that the value and the maximum value are used.

  The discovery processing unit (Discovery process) 3211 of the MAC control sublayer 321 controls the execution of the discovery process for discovering the ONU 5 connected to the OLT 3 and performs RTT measurement during the process, as in the prior art. . For example, the discovery processing unit 3211 transmits an RTT measurement signal transmission request to the ONU 5 whose connection with the OLT 3 has been confirmed, and the response transmission time set in the response returned from the ONU 5, the response in the OLT 3 RTT is acquired based on information such as the reception time of the OLT 3 and the clock deviation of the OLT 3 and the ONU 5. A report processing unit (Reporting process) 3212 of the MAC control sublayer 321 performs band allocation to allocate a band for transmitting an uplink signal to each ONU 5. In bandwidth allocation, the transmission start time of each ONU 5 and the amount of uplink data permitted to be transmitted are determined.

Next, processing of the DSP-PON system 1 will be described.
The DSP-PON system 1 periodically performs RTT measurement between the OLT 3 and the ONU 5. The discovery processing unit 3211 of the OLT 3 obtains the maximum value and the minimum value of RTT obtained by performing RTT measurement a plurality of times for each ONU 5. Let RTT _{x_min} and RTT _{x_max} be the RTT minimum and maximum values acquired for ONU # x, which is the xth (x is an integer equal to or greater than 1) ONU # x. The discovery processing unit 3211 _outputs the RTT _{x_min} and the RTT _{x_max} obtained for each ONU # x to the report processing unit 3212.

FIG. 3 is a diagram for explaining the calculation of DBA in the ONU 5. In the figure, the time of each timing related to reception, transmission, and the like is represented with reference to the time in the OLT 3.
The report processing unit 3212 of the OLT 3 uses the transmission data amount notified from each ONU ₅ and the RTT _{x_min} and RTT _{x_max} of each ONU # x received from the discovery processing unit 3211 to _perform the DBA function of the DSP-PON system 1. Run. In this DBA function, the report processing unit 3212 sets the transmission start time T _{granted_x} of the upstream signal (upstream burst optical signal) in each ONU _#x , the reception start time T _{desired_x} of the upstream signal from the ONU _#x in the OLT 3, and the ONU Using the minimum value RTT x_min of the round trip time of _#x , the following equation (4) is used for calculation.

T _{granted_x} = T _{desired_x−} RTT _{x_min} (4)

The report processing unit 3212 calculates the reception start time T _{desired_x} of the uplink signal from the ONU # x used in Expression (4) as follows. Another ONU 5 that transmits an upstream signal before ONU # x is assumed to be ONU # y (y ≠ x, where y is an integer of 1 or more). The report processing unit 3212 calculates the uplink signal reception start time T _{desired_x} from the ONU # x by adding the margin time to the uplink signal reception completion time _{Tend_y} from the ONU # y. Margin time, ONU # y round trip time maximum RTT _{y_max} and minimum value RTT _{y_min} and the difference _{d y (= RTT y_max -RTT y_min} ), or a value obtained by multiplying a predetermined coefficient to the difference _{d y} is there. The report processing unit 3212 sets the upstream signal reception completion time T _{end_y} from the ONU _#y to the upstream signal reception start time T _{desired_y} from the ONU _#y , and the time taken to transmit the upstream data amount permitted to the ONU _#y. Calculate by adding. For example, the amount of uplink data can be converted into the number of time slots that are unit times of data transmission. Therefore, the position of the time slot obtained by adding the number of time slots corresponding to the uplink data amount to the time slot corresponding to the reception start time represents the reception completion time.

When the OLT 3 instructs the transmission start time T _{granted_x} to the ONU _#x , the timing _{indicating the} transmission start time T _{granted_x} in the ONU _#x is taken into account in consideration of time lag and propagation delay between the OLT 3 and the ONU _#x . Notify information.

  The process in which the DSP-PON system 1 performs RTT measurement is not limited to the discovery process. The RTT measurement other than the discovery process may be executed by the discovery processing unit 3211 of the OLT 3, may be executed by the report processing unit 3212, or may be executed by a function unit (not shown) in the MAC control sublayer 321. . For example, in the discovery process, RTT measurement is performed using the time stamp set in the REGISTER REQ message transmitted from the ONU 5 to the OLT 3, and thereafter, the time stamp set in the REPORT message periodically transmitted from the ONU 5 to the OLT 3 is used. RTT measurement can be performed.

  According to the embodiment described above, the subscriber line terminal station apparatus accommodates a plurality of subscriber line termination apparatuses by time division multiplexing. For example, the subscriber line terminal equipment is OLT3, and the subscriber line termination equipment is ONU5. The subscriber line end station apparatus sets the reception start timing of the uplink signal from the subscriber line termination apparatus in the subscriber line end station apparatus to the reception completion timing of the uplink signal from another subscriber line termination apparatus. A bandwidth allocating unit that allocates the margin time. The bandwidth allocation unit is, for example, the report processing unit 3212.

  The subscriber line terminal device further includes an acquisition unit that acquires the minimum value and the maximum value of the round trip time of the subscriber line terminal device. The acquisition unit is, for example, the discovery processing unit 3211. The band allocating unit uses the transmission start timing of the uplink signal allocated to the subscriber line terminating device, using the reception start timing allocated to the subscriber line terminating device and the minimum value of the round trip time acquired for the subscriber line terminating device. To decide.

  In addition, the bandwidth allocating unit sets the reception start timing of the uplink signal from the subscriber line termination device to the reception completion timing of the uplink signal according to the uplink data transmission amount from the other subscriber line termination device, to other subscribers. The difference is calculated by adding the difference between the maximum value and the minimum value of the round trip time acquired for the line terminating device, or a value obtained by multiplying the difference by a coefficient.

  In a PON using digital processing, a time lag is generated by the DSP calculation time compared to a conventional method in which DSP processing is not performed. Since this time lag varies, there is a time lag in the timing control from the OLT to the ONU, and a delay due to collision of upstream signals from the ONU to the OLT occurs when bandwidth allocation is performed in the same manner as before. . Therefore, as in the above-described embodiment, in the OLT 3, by determining the reception start time of the upstream signal from each ONU 5 and the transmission start time of the upstream signal of the ONU 5 so as to absorb the fluctuation of the DSP processing delay, Even when the round trip time fluctuates, collision of upstream burst optical signals from a plurality of ONUs 5 can be prevented. Therefore, the accuracy of bandwidth allocation from the OLT 3 to the ONU 5 can be maintained regardless of the DSP processing delay. Thereby, the capacity of the OLT can be increased by digital signal processing by the DSP.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  It can be used for a device that communicates by TDMA (Time Division Multiple Access).

DESCRIPTION OF SYMBOLS 1 ... DSP-PON system, 3 ... OLT, 5 ... ONU, 31 ... Physical layer, 32 ... MAC, 51 ... Physical layer, 52 ... MAC, 311 ... DSP processing part, 312 ... ADC / DAC, 321 ... MAC control sub Layer, 3211 ... discovery processing unit, 3212 ... report processing unit, 511 ... DSP processing unit, 512 ... ADC / DAC

Claims (3)

A subscriber line terminal device connected to a plurality of subscriber line terminators,
A blank time is provided between the reception start timing of the uplink signal from the subscriber line termination device in the subscriber line terminal station device and the reception completion timing of the uplink signal from the other subscriber line termination device. Bandwidth allocation unit to allocate,
A subscriber line terminal apparatus. An acquisition unit for acquiring a minimum value of the round trip time of the subscriber line termination device;
The bandwidth allocating unit sets the transmission start timing of the uplink signal allocated to the subscriber line terminating device, the reception start timing allocated to the subscriber line terminating device, and the minimum round trip time acquired for the subscriber line terminating device. To determine using the value,
The subscriber line terminal apparatus according to claim 1. The acquisition unit further acquires a maximum value of a round trip time of the subscriber line termination device,
The band allocating unit sets the reception start timing of the uplink signal from the subscriber line termination device to the reception completion timing of the uplink signal according to the uplink data transmission amount from the other subscriber line termination device. The difference between the maximum value and the minimum value of the round trip time acquired for the subscriber line termination device, or a value obtained by multiplying the difference by a coefficient,
The subscriber line terminal station apparatus according to claim 2.

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