JP2007288629A - Transmission allocation method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To present a transmission allocation method and device which improve down TCP throughput in a TDMA system. <P>SOLUTION: A distance measuring instrument 44 measures distance to each of ONUs 22-1 to 22-3 and stores the distance into a distance field 52 of a band allocation table 46. A transmitting interval/order determination device 48 refers to the distance to each of the ONUs 22-1 to 22-3 stored in the distance field 52 of the table 46 and determines transmitting intervals and transmitting order to each of the ONUs 22-1 to 22-3. Transmitting intervals (reference values) in inverse proportion to the distance are determined and transmission frequencies within unit time are determined from the reference values. The transmitting interval/order determination device 48 allocates transmission to each of the ONUs 22-1 to 22-3 at random with occurrence probability equivalent to ratio of the transmitting frequencies to individual ONUs 22-1 to 22-3 to the total transmitting frequencies. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission allocation method and apparatus in an optical transmission system using time division multiple access TDMA (Time Domain Multiple Access).

  An optical access method based on GE-PON (Gigabit Ethernet Passive Optical Network) is becoming widespread. Ethernet and Ethernet are registered trademarks. In the PON, a plurality of user optical terminator ONUs (Optical Network Units) are connected to an optical terminator OLT (Optical Line Terminal) disposed in a center station via an optical transmission line composed of an optical fiber and an optical coupler. GE-PON generally accommodates 16 or 32 ONUs with one optical fiber, but there is no upper limit to the number of ONUs that can be accommodated with one optical fiber, and 64 or 128 is standard. It is also possible to accommodate individual ONUs.

  In GE-PON, time domain multiple access (TDMA) is used for transmission of an upstream signal from the ONU. That is, the OLT notifies each ONU of the transmission timing and transmission period, and the ONU transmits a signal within the transmission period of the given transmission timing.

  In current Internet communication, TCP is used for file download. In the TCP communication, as shown in FIG. 5, the server transmits a certain amount of data WS (Window Size) data to the client, and the client returns an ACK signal as a reception notification to the server. When the server receives the ACK signal, the server transmits data next to the data amount WS to the client. These procedures are repeated until all data has been transmitted.

  As described above, the transmission of data of the data amount WS from the server to the client and the transmission of the ACK signal from the client to the server are set as a set, and the data is transmitted from the server to the client by repeating this. The time from when the server transmits data for WS until it receives the ACK signal from the client is called RTT (Round Trip Time). Since the data amount WS is transmitted at the time RTT, the TCP throughput is defined by WS / RTT.

  When GE-PON is interposed between the server and the client, TCP communication is realized by the procedure shown in FIG. (1) The ONU to which the client is connected temporarily stores the ACK signal from the client in the buffer. (2) This ONU notifies the OLT that there is data to be transmitted using a Report frame. (3) The OLT aggregates the Report frames from each ONU and notifies each ONU of the transmission timing and transmission period by using the Gate frame. (4) The ONU transmits an ACK signal to the server using the transmission timing and transmission period indicated by the Gate frame from the OLT.

  In practice, in GE-PON, the above procedure is performed in units of LLID (Logical Layer Identifier), but here, it is described in a simplified manner. A plurality of LLIDs can be assigned to the ONU.

In Patent Document 1, in GE-PON, an OLT performs scheduling based on multiple queue request information in a REPOT message transmitted from an ONU, and then gates a scheduling result integrated for a single ONU. A dynamic bandwidth allocation method is described in which the scheduler 70 of the ONU performs scheduling based on the bandwidth allocated by the OLT and allocates the transmission bandwidth to each queue belonging to itself.
Japanese Patent Laid-Open No. 2005-012800

  When GE-PON is used, since the ACK signal is temporarily accumulated in the ONU, the TCP throughput RTT includes the transmission waiting time of the ACK signal in the ONU, which greatly deteriorates the TCP throughput.

  If the transmission interval assigned to each ONU by the OLT is shortened, the transmission waiting time can be shortened. However, conventionally, since the transmission period is constant for any ONU, if the transmission interval is shortened, the transmission period is shortened. When the transmission period is shortened, the overhead increases relatively, so that the effective uplink bandwidth decreases.

  FIG. 7 shows an example of the arrangement of transmission frames when the transmission interval is large and small. FIG. 7A shows a case where the transmission interval is small, and FIG. 7B shows a case where the transmission interval is large. 7 (a) and 7 (b), it can be seen that the smaller the transmission interval, the shorter the waiting time until the next transmission timing, but the overhead portion is relatively increased and the effective data rate is decreased.

  In the access system, downstream throughput is more important than upstream throughput.

  An object of the present invention is to provide a transmission allocation method and apparatus for improving downlink TCP throughput in the TDMA scheme.

  A transmission allocation method according to the present invention includes a distance measurement step of measuring a distance to each user termination device in a data transmission system in which a plurality of user termination devices are accommodated and allowing transmission by TDMA to each user termination device; A transmission permission step of permitting transmission to each user terminal device at a transmission interval inversely proportional to the distance measured in the distance measurement step.

  A transmission allocation device according to the present invention includes a plurality of user termination devices, and a distance measurement device that measures a distance to each user termination device in a data transmission system that permits transmission by TDMA to each user termination device; And a transmission permission device that permits transmission to each user terminal device at a transmission interval inversely proportional to the distance measured in the distance measurement step.

  According to the present invention, the transmission interval of ACK signals for downlink TCP communication can be shortened, and as a result, the throughput of downlink TCP can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention. FIG. 2 shows a sequence from TCP connection to disconnection. Here, in order to facilitate understanding, it is assumed that three ONUs are accommodated. As described above, in general, more ONUs can be connected to the GE-PON system.

  An uplink port 10a of an optical termination device (OLT) 10 disposed in the center station is connected to the upper network 12, and a server 14 is connected to the upper network 12. The interface between the uplink port 10a and the upper network 12 is 1000Base-T or 1000Base-SX.

  The PON port 10 b of the OLT 10 is connected to the 1: n optical coupler 18 through the optical fiber 16. In the illustrated example, n = 3. The optical coupler 18 divides the downstream signal light from the optical fiber 16 into three parts and outputs the divided signal lights to the optical fibers 20-1 to 20-3. The other ends of the optical fibers 20-1 to 20-3 are connected to optical terminal units (ONUs) 22-1 to 22-3 disposed in the respective user houses. Computers 24-1 to 24-3 are connected to the respective ONUs 22-1 to 22-3. Of course, a plurality of computers can be connected to one ONU via a router or a gateway.

  The OLT 10 controls the transmission timing and transmission period of each of the ONUs 22-1 to 22-3 and relays data transmission between the ONUs 22-1 to 22-3 and the upper network 12.

  Downlink data signals from the upper network 12 are input to the LAN interface 30 via the uplink port 10a. The LAN interface 30 outputs the downlink data signal to the multiplexing device 32. The OLT control device 34 that controls the OLT 10 receives various control signals for the ONUs 22-1 to 22-3 (for example, a Gate message that indicates the transmission timing and transmission period of each ONU 22-1 to 22-3). Output to.

  The multiplexing device 32 multiplexes the control signal from the OLT control device 34 on the downlink data signal from the network interface 30 and applies the multiplexed signal to the electrical / optical converter 36. The electrical / optical converter 36 converts the multiplexed signal from the multiplexer 32 into an optical signal (downstream signal light) and applies it to the WDM optical coupler 38. The WDM optical coupler 38 outputs the downstream signal light from the electrical / optical converter 36 to the optical fiber 16 via the PON port 10b.

  Downstream signal light output from the PON port 10b of the OLT 10 is input to each ONU 22-1 to 22-3 via the optical fiber 16, the optical coupler 18, and the optical fibers 20-1 to 20-3.

  Each of the ONUs 22-1 to 22-3 converts the downstream signal light input from the optical fibers 20-1 to 20-3 into an electric signal, takes it if it is addressed to itself, and discards it if it is addressed to another. Each of the ONUs 22-1 to 22-3 internally processes a control signal addressed to itself among the captured downstream signals, and sends data signals addressed to the subordinate computers 24-1 to 24-3 to the computers 24-1 to 24- 3 is supplied.

  On the other hand, the computers 24-1 to 24-3 output data signals directed to the upper network 12 to the ONUs 22-1 to 22-3, respectively. Each ONU 22-1 to 22-3 outputs the upstream signal light to the optical fibers 20-1 to 20-3 at the transmission timing and transmission period permitted by the OLT 10, respectively. This upstream optical signal is a data signal (including a control signal and a response signal for the server 14 and the like) addressed to a device (for example, the server 14) connected to the upper network 12 from the subordinate computers 24-1 to 24-3. The ONUs 22-1 to 22-3 carry control signals output to the OLT 10. The control signal addressed to the OLT unit 10 includes a control signal for establishing a logical link, a response signal (for example, a Report message in response to a Gate message), and the like. The optical coupler 18 outputs upstream optical signals from the optical fibers 20-1 to 20-3 to the optical fiber 16. In this way, the upstream signal light output from each of the ONUs 22-1 to 22-3 is input to the WDM optical coupler 38 via the PON port 10 b of the OLT 10.

  The WDM optical coupler 38 supplies the upstream signal light from the PON port 10 b to the optical / electrical converter 40. The optical / electrical converter 40 converts the upstream signal light from the WDM optical coupler 38 into an electrical upstream signal. The separation device 42 supplies a signal addressed to the OLT 10 among the electrical upstream signals output from the optical / electrical converter to the OLT control device 34, and supplies an upstream signal addressed to the upper network 12 to the LAN interface 30.

  The LAN interface 30 outputs the upstream signal from the separation device 42 to the upper network 12.

  In this embodiment, the OLT control device 34 dynamically controls the transmission timing and transmission period of each ONU 22-1 to 22-3 in order to improve the downlink TCP throughput. For this purpose, the OLT control device 34 measures the distance to each ONU 22-1 to 22-3, the measured distance, and the ONUs 22-1 to 22-3 according to the distance. A bandwidth allocation table 46 that stores parameters for determining the allocated bandwidth and a transmission interval order determination device 48 that determines the transmission intervals and order of the ONUs 22-1 to 22-3 are provided. The functions of the distance measuring device 44, the bandwidth allocation table 46, and the transmission interval order determining device 48 can be realized by a microcomputer memory and a program.

  An operation of assigning an upstream signal band to each of the ONUs 22-1 to 22-3, which is a characteristic function of the present embodiment, will be described.

  FIG. 3 shows an example of the bandwidth allocation table 46. The table 46 includes a field 50 for designating an ONU (or LLID), a distance field 52 for storing a distance to each ONU 22-1 to 22-3, a transmission interval field 54, and a transmission frequency field 56. The transmission interval field 54 and the transmission frequency field 56 are reference values tentatively referred to in the process of quantitatively determining the uplink transmission interval of the uplink band assigned to each ONU 22-1 to 22-3.

  The OLT control device 34 gives an LLID to each of the ONUs 22-1 to 22-3 when the ONUs 22-1 to 22-3 are powered on. In the assigning process, the distance measuring device 44 of the OLT control device 34 measures the distance to each of the ONUs 22-1 to 22-3 and stores it in the distance field 52 of the bandwidth allocation table 46.

The transmission interval order determination device 48 refers to the distance to each ONU 22-1 to 22-3 stored in the distance field 52 of the table 46, and sets the transmission interval and order for each ONU 22-1 to 22-3 as follows. Determine by the method shown. In this embodiment, the transmission interval is inversely proportional to the distance. For this purpose, a reference transmission cycle (Tbasic) is determined in advance. Here, Tbasic = 500 μs. Then, an average level of distances to all ONUs is calculated. In the example shown in FIG.
Lave = (L1 + L2 + L3) / 3≈12 (km) (1)
It is. The transmission interval Ti for the ONU 22-i (i = 1 to 3) is
Ti = Tbasic × Lave / Li (2)
To decide. This result is stored in the field 54.

  In the distance example shown in FIG. 3, T1 = 300 μs, T2 = 600 μs, and T3 = 1200 μs. If the transmission interval Ti is too long, for example, if it is long enough to exceed several ms, it will be disadvantageous for communications such as VoIP. Therefore, an upper limit is set, and Ti exceeds the upper limit in equation (2). Is regulated by the upper limit. The transmission interval order determination device 48 re-executes the calculations of equations (1) and (2) each time an ONU (or LLID) is added or deleted.

  From the transmission interval of the field 54, the number of transmissions per second (= 1 / Ti) is calculated. The number of transmissions calculated here is the number of transmissions on the assumption that one ONU (or LLID) occupies 1 second. The data size per transmission count of the uplink signal is constant. In the example shown in FIG. 3, there are 3333 times for the ONU 22-1, 1666 times for the ONU 22-2, and 833 times for the ONU 22-3. The total number of transmissions within one second is 5832 (= 3333 + 1666 + 833). By randomly allocating this number within one second, the transmission interval inversely proportional to the distance to each ONU 22-1, 22-2, 22-3. You can assign a transmission at Specifically, the transmission interval order determination device 48 randomly assigns transmissions to the ONU 22-1 with a probability of occurrence of 3333/5832 within a certain time (for example, 1 second), and 1666 to the ONU 22-2. A transmission is randomly assigned with an occurrence probability of / 5832, and a transmission is randomly assigned to the ONU 22-3 with an occurrence probability of 833/5832.

  Assuming that the data size of the uplink signal is constant, more uplink data can be transmitted per time as the transmission interval is shorter. To alleviate this, the data size is increased once for ONUs (or LLIDs) with a small transmission interval. In this embodiment, since the reference value of the number of transmissions (the value in the field 54) is inversely proportional to the distance, each ONU (or LLID) is set to make the data amount per unit time equal between the ONUs 22-1 to 22-3. ) Is allowed to be proportional to the distance. FIG. 4 shows an example of the configuration of the bandwidth allocation table 46a having such a data size modification function. A field 58 that accommodates the maximum amount of transmission data per time is added. In this case, the transmission interval order determination device 48 permits transmission of the amount of data requested by each ONU 22-1 to 22-3 within the range of the maximum value of the field 58.

  For example, if the ONU 22-3 always requests the maximum amount of data transmission, if this is permitted, the transmission interval of the ONU 22-1 will be widened, and the original intention will not be met. In order to prevent this, for example, it is also effective to reduce the number of transmissions according to an increase in the amount of data transmission. Thereby, on average, the transmission interval can be shortened for ONUs that are close in distance, and the transmission interval can be lengthened for ONUs that are far in distance.

  In the above method, for example, the number of transmissions (reference value) for a remote ONU may be extremely small. In order to prevent this, it is only necessary to define the number of transmissions (guaranteed transmission number) which is a base common to the whole, and to distribute the number of transmissions exceeding the reference transmission number according to the distance.

For example, since three ONUs 22-1 to 22-3 are connected, a total of 6000 transmissions are possible at the reference transmission interval Tbasic (= 500 μs). For example, if the guaranteed number of transmissions is 500, the number of transmissions at which the distribution destination can be changed is 4500 (= 6000−500 × 3). When this is distributed according to the distance, the number of transmissions to the ONU 22-1 is
4500 × L1 / (L1 + L2 + L3) + 500 = 3071
The number of transmissions to the ONU 22-2 is
4500 × L2 / (L1 + L2 + L3) + 500 = 1786
The number of transmissions to ONU22-3 is
4500 × L3 / (L1 + L2 + L3) + 500 = 1143
It becomes.

  According to this result, the transmission interval order determination device 48 randomly assigns transmissions to the ONU 22-1 with a probability of occurrence of 3071/6000 within a certain time (for example, 1 second), and 1786/6000 to the ONU 22-2. Transmission is randomly assigned with an occurrence probability of 6000, and transmission is randomly assigned to the ONU 22-3 with an occurrence probability of 1143/6000.

  Also in this method, as in the first embodiment, the maximum data amount that can be transmitted at one time may be set larger as the distant ONU. In this case, according to the adjustment of the maximum data amount that can be transmitted, the number of transmissions that is a basis for calculating the occurrence probability may be adjusted by a method similar to the method of the first embodiment.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of one Example of this invention. It is a schematic diagram which shows the sequence from the connection of TCP to a cutting | disconnection. 2 shows an example of the configuration and numerical values of a bandwidth allocation table. The structure of a bandwidth allocation table and the example according to a numerical value are shown. It is a schematic diagram which shows the sequence of TCP communication from a server to a client. It is a schematic diagram which shows the sequence of TCP communication from a server to a client in case a PON system intervenes. It is an example of arrangement | positioning of the transmission frame on a PON transmission line, (a) shows the case where a transmission interval is small, and (b) shows the case where it is large.

Explanation of symbols

10: Optical termination device (OLT)
10a: Uplink port 10b: PON port 12: Host network 14: Server 16: Optical fiber 18: Optical couplers 20-1 to 20-3: Optical fibers 22-1 to 22-3: Optical termination unit (ONU)
24-1 to 24-3: Computer 30: LAN interface 32: Multiplexer 34: OLT control device 36: Electric / optical converter 38: WDM optical coupler 40: Optical / electrical converter 42: Separating device 44: Distance measuring device 46: Bandwidth allocation table 48: Transmission interval order determination device

Claims (8)

In a data transmission system in which a plurality of user termination devices are accommodated and each user termination device is allowed to transmit by TDMA (Time Domain Multiple Access),
A distance measuring step (44) for measuring the distance to each user termination device;
A transmission permission step (48) for permitting transmission to each user terminal device at a transmission interval inversely proportional to the distance measured in the distance measurement step.
A transmission allocation method comprising: The transmission permission step is
Determining a reference transmission interval inversely proportional to the distance measured in the distance measuring step;
Determining the number of transmissions per unit time from the reference transmission interval;
Random transmission is made to each user terminal device with an occurrence probability corresponding to the ratio of the number of transmission times of each user terminal device within the unit time to the total value of the number of transmissions of the user terminal device within the unit time. The transmission allocation method according to claim 1, further comprising a transmission allocation step of allocating. Furthermore,
Determining the maximum amount of data to be transmitted to each user termination device according to the distance of each user termination device;
The transmission allocation method according to claim 2, further comprising a step of adjusting the number of transmissions within the unit time of each user terminal device according to the maximum transmission data amount. The transmission permission step is
A step of calculating the number of transmissions that can be transmitted in a unit time according to a reference transmission cycle;
Distributing the number of transmissions excluding the guaranteed number of transmissions to each user terminal device from the number of transmissions that can be transmitted in the uplink, to each user terminal device according to the distance of each user terminal device;
2. The method of claim 1, further comprising the step of randomly assigning transmissions to each user termination device with an occurrence probability corresponding to a sum of the number of transmissions allocated to each user termination device and the guaranteed number of transmissions. The transmission assignment method described.   The transmission allocation method according to any one of claims 1 to 4, wherein the data transmission system is a PON (Passive Optical Network) system. In a data transmission system in which a plurality of user termination devices are accommodated and each user termination device is allowed to transmit by TDMA (Time Domain Multiple Access),
A distance measuring device (44) for measuring the distance to each user termination device;
A transmission permission device (48) that permits transmission to each user terminal device at a transmission interval inversely proportional to the distance measured in the distance measurement step.
A transmission allocation apparatus comprising: The transmission permission device is
An apparatus for determining a reference transmission interval that is inversely proportional to the distance measured in the distance measurement step;
An apparatus for determining the number of transmissions within a unit time from the reference transmission interval;
Random transmission is made to each user terminal device with an occurrence probability corresponding to the ratio of the number of transmission times of each user terminal device within the unit time to the total value of the number of transmissions of the user terminal device within the unit time. The transmission allocation apparatus according to claim 6, further comprising a transmission allocation apparatus to be allocated. The transmission permission device is
A device for calculating the number of transmissions that can be transmitted in a unit time according to a reference transmission cycle;
A device that distributes the number of transmissions excluding the guaranteed number of transmissions to each user terminal device from the number of transmissions that can be transmitted in the uplink, to each user terminal device according to the distance of each user terminal device;
7. The apparatus according to claim 6, further comprising: a device that randomly assigns transmissions to each user termination device with an occurrence probability corresponding to a sum of the number of transmissions allocated to each user termination device and the guaranteed number of transmissions. The transmission allocation apparatus as described.

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