JP2015154273A - Optical communication system, communication control method, and station side optical line terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a frequency of occurrence of collisions between registration request signals received from a plurality of ONUs (Optical Network Units) by an OLT (Optical Line Terminal).SOLUTION: An OLT: determines the number of groups of ONUs for which permission to transmit a registration request signal is given, on the basis of a reception frequency index value showing a reception frequency of registration request signals in a registration request signal acceptance period; selects a group according to the determined number of groups; and transmits a registration request transmission control signal storing transmission permission group information showing the selected group. An unregistered ONU transmits a registration request signal when any of groups shown by transmission permission group information stored in a received registration request transmission control signal agrees a group to which own ONU belongs.

Description

  The present invention relates to an optical communication system, a communication control method, and a station side optical line termination device.

  As one form of access network, PON (Passive Optical Network) is known. The PON is between an OLT (Optical Line Terminal) installed on the telecommunications carrier side and an ONU (Optical Network Unit: subscriber side optical line termination device) installed on the subscriber side. In the communication, the access network is configured to branch the optical signal into a plurality of parts by using a splitter which is a passive element without performing photoelectric conversion. In such a PON, since a single optical fiber can be shared by a plurality of users, an economical network can be constructed.

  Among the PONs, those in which the OLT and the ONU communicate with each other using an Ethernet (registered trademark, hereinafter the same) frame are referred to as EPON (Ethernet (registered trademark, the same hereinafter) PON).

  Among EPONs, GE-PON (Gigabit Ethernet PON) with a transmission speed of 1 Gbps is a high-speed and inexpensive FTTH (Fiber To The Home) network structure for access optical communication that draws optical fiber directly into the subscriber's home. System) service can be provided. For this reason, GE-PON is widely used especially in Japan. Recently, a standard specification of 10G-EPON having a transmission rate increased to 10 Gbps has been studied.

In recent years, studies have been made on optical repeaters for PON, and it has become possible to expand the standard and increase the number of branches. Specifically, conventional PONs were often used with 32 branches or less due to optical signal intensity restrictions, but multi-branch connections such as 1000 branches became possible.
In general, in PON, the direction of communication from the OLT to the ONU is referred to as the downstream direction, and the direction of communication from the ONU to the OLT is referred to as the upstream direction.

  In many PONs including EPON, upstream communication is performed by time division multiple access. By controlling the transmission timing of each ONU by the OLT, a plurality of ONUs can perform time division communication with the OLT. Similarly, 10G-EPON upstream communication is performed by time division multiple access. In 10G-EPON, a method in which a plurality of ONUs having different uplink transmission rates can be connected to one OLT is being studied. At this time, uplink communication is realized by time division multiple access even between ONUs of different speeds.

In many PONs in which uplink communication is performed by time-division multiple access, in order to efficiently use the uplink communication band, a band permitting uplink communication for each ONU is set as a communication status. It has a dynamic bandwidth allocation function that dynamically changes according to the frequency.
Here, the bandwidth for each ONU in the PON can be allocated, for example, by the OLT calculating a transmission permission amount for each ONU and securing the transmission time zone exclusively. The ONU transmits an upstream signal only in the time zone assigned by the OLT. For this reason, the waiting time for waiting for the assigned time zone is added to the transmission delay time.

  In EPON, a protocol called MPCP (Multi Point-Control Protocol) for controlling communication between a plurality of ONUs by one OLT is defined as a standard. As MPCP, there are known Discovery Processing for detecting an unregistered ONU and REPORT Processing / GATE Processing for controlling the transmission timing of an upstream signal transmitted by the ONU.

  In the EPON, when the ONU is connected to the PON, the OLT discovers the ONU, assigns an LLID (Logical Link ID) to the ONU, and automatically establishes a communication link. This function is called P2MP discovery (Point to multi-point Discovery). MPCP Discovery Processing is a protocol for realizing P2MP discovery.

The sequence diagram of FIG. 16 shows a communication procedure in P2MP discovery processing as Discovery Processing.
In the Discovery Processing, first, the OLT transmits a Discovery GATE frame, which is a GATE frame storing Discovery Information, to each ONU, and notifies the transmission timing (Step S1).
The GATE frame is a frame for notifying the ONU of control information related to transmission such as transmission timing, and the Discovery GATE frame is a frame for notifying the unregistered ONU of control information indicating the transmission timing of the REGISTER_REQ frame. The GATE frame is transmitted using Messages sent on broadcast channel.

  Next, when the ONU not registered in the OLT receives the Discovery GATE frame, it waits for a random delay time (Random delay) for collision avoidance, and then transmits a REGISTER_REQ frame (step S2). The REGISTER_REQ frame is transmitted using Messages sent on broadcast channel. The OLT sets the Discovery Window only for a time during which the REGISTER_REQ frame from the ONU may be received, and receives the REGISTER_REQ frame from each unregistered ONU during the set Discovery Window period.

Next, in response to reception of the REGISTER_REQ frame, the OLT newly registers an LLID that is an identifier of the ONU (or UNI port) that is the transmission source of the REGISTER_REQ frame. Then, the registered LLID is notified by a REGISTER frame (step S3). The REGISTER frame is transmitted using Messages sent on broadcast channel.
In this way, when the LLID is notified from the OLT to the ONU, the OLT and the ONU can execute communication using the LLID. That is, a link is established between the OLT and the ONU.

Subsequently, the OLT notifies the uplink transmission timing by the GATE frame (step S4), and the ONU returns REGISTER_ACK according to the notified timing (step S5).
The P2MP discovery process is realized by the processes in steps S1 to S5. This GATE frame and REGISTER_ACK are transmitted using Messages sent on unicast channels.
Thus, communication as Discovery Processing is executed between the OLT and the ONU (see, for example, Non-Patent Document 1).

The timing chart of FIG. 17 shows an example of transmission / reception timings of the Discovery GATE frame and the REGISTER_REQ frame in the P2MP discovery process. In correspondence with FIG. 16, transmission / reception of the Discovery GATE frame shown in FIG. 17 corresponds to step S1, and transmission / reception of the REGISTER_REQ frame corresponds to step S2.
Moreover, ONU200-k and ONU200-n shown by the figure each show one of several ONU. In the description of FIG. 17, a plurality of ONUs including the ONU 200-k and ONU 200-n are described as ONU 200 unless otherwise distinguished.

In FIG. 17, first, the OLT 100 transmits a Discovery GATE frame to each ONU 200 by broadcasting at time t0. Discovery GATE frame transmitted as described above, it includes a transmission permitted time _{T G,} the information specifying the start time t1 of the transmission permitted time _{T G} as control information.

In response to receiving the Discovery GATE frame, the unregistered ONU 200 transmits a REGISTER_REQ frame at random timing at a transmission permission time _TG that starts from the start time t1 specified by the Discovery GATE frame. When the communication distance of the ONU 200-n is the longest communication distance in the allowable range, the period by the time length T _DW shown in the figure is Discovery Window. Start timing of the period of the Discovery Window is the start time t1 in OLT 100, the end timing is the time delayed according to the propagation time until the OLT 100 from the end time of the transmission permitted time _{T G} in ONU 200-n. That is, the Discovery Window is a period during which a REGISTER_REQ frame from the unregistered ONU 200 is preferentially received.

The time length T _DW of the Discovery Window period is set based on the timing at which the OLT 100 transmits the Discovery GATE frame. During the Discovery Window period, the OLT performs control so that registered ONUs do not perform uplink transmission to the OLT.
For the EPON upstream communication, the OLT calculates the upstream transmission data amount of each ONU, and notifies the calculated transmission data amount, thereby performing bandwidth control so as to secure the transmission time for each ONU. . The Discovery Window period is a period during which a REGISTER_REQ frame from an unregistered ONU is received. In view of this, during the Discovery Window period, the OLT performs bandwidth control so that uplink transmission by registered ONUs is not performed. Thereby, it is possible to avoid a collision between a signal transmitted from a registered ONU and a REGISTER_REQ frame transmitted from an unregistered ONU.

IEEE std 802.3-2012 SECTION FIVE

If a REGISTER_REQ frame collision occurs in the P2MP discovery processing sequence, the collided REGISTER_REQ frame is discarded. In this case, for the ONU that is the source of the discarded REGISTER_REQ frame, the P2MP discovery sequence is not completed, and the link with the OLT is not established.
Therefore, the ONU that is the transmission source of the collided REGISTER_REQ frame needs to perform registration processing again by the next P2MP discovery processing.
In particular, when the transmission permission time _TG is short or when the number of unregistered ONUs to establish a link is large, the frequency of collision increases, until the ONU can start communication after the P2MP discovery process is completed. May take a long time.

In a communication system, in general, the shorter the time from link establishment to communication start and the shorter the delay time, the higher the communication performance.
The interval at which the P2MP discovery process is executed in EPON is as long as about 0.1 to 1.5 seconds. For this reason, even if only one retry occurs in the P2MP discovery process, the influence on the delay is great. Furthermore, when the P2MP discovery process is executed simultaneously with a large number of ONUs, such as when the system is started up, the frequency of REGISTER_REQ frame signal collision increases. In such a state, there may be two or more retries, and the delay further increases.

  In view of the above circumstances, the present invention provides an optical communication system and a communication control capable of reducing the frequency of occurrence of collision of registration request signals received by a station-side optical line terminator from a plurality of subscriber-side optical line terminators. It is an object of the present invention to provide a method and a station side optical line termination device.

  One aspect of the present invention is a station-side optical line terminator, and a plurality of subscribers that are connected to the station-side optical line terminator via an optical communication path and are grouped so as to belong to any one of a plurality of groups A side optical line terminator, and the station side optical line terminator receives a registration request signal transmitted by the subscriber side optical line terminator for a request for registration to the station side optical line terminator. Based on the reception frequency index value acquisition unit that acquires the reception frequency index value that represents the reception frequency of the registration request signal in the registration request signal reception period that is received, and the reception frequency index value acquired by the reception frequency index value acquisition unit, A group number determination unit that determines the number of groups permitted to transmit a registration request signal, and the number of groups determined by the group number determination unit from the plurality of groups selected up to the previous time A group selection unit that selects a group different from a group different from the other group, and a registration request transmission control signal for causing the unregistered subscriber-side optical network unit to transmit the registration request signal. A registration request transmission control signal generation unit for storing transmission permission group information indicating the selected group in the registration request transmission control signal; and a registration request transmission control signal generated by the registration request transmission control signal generation unit as a subscriber-side optical signal. A transmission control unit that transmits to the line terminating device, and the subscriber side optical line terminating device has not yet registered itself in the station side optical line terminating device and has received registration If any of the groups indicated by the transmission permission group information stored in the request transmission control signal matches the group to which the own device belongs, a registration request signal is transmitted. If any of the groups indicated by the transmission permission group information stored in the received registration request transmission control signal does not match the group to which the own device belongs, a registration request signal is transmitted. It is an optical communication system provided with the transmission permission / inhibition determining unit that determines that it should not be.

  One aspect of the present invention is the above-described optical communication system, wherein the reception frequency index value acquisition unit continuously receives a signal during the registration request signal reception period and the registration request signal reception period. The ratio of the total reception time is calculated, and the calculated ratio is acquired as the reception frequency index value.

  One aspect of the present invention is the optical communication system described above, wherein the reception frequency index value acquisition unit calculates the number of subscriber-side optical line terminators registered in the station-side optical line terminator as the reception frequency index. Get as a value.

  One aspect of the present invention is a station-side optical line terminator, and a plurality of subscribers that are connected to the station-side optical line terminator via an optical communication path and are grouped so as to belong to any one of a plurality of groups A communication control method in an optical communication system comprising a side optical line termination device, wherein the subscriber side optical line termination device requests registration to the station side optical line termination device. The reception frequency index value acquisition step for acquiring the reception frequency index value indicating the reception frequency of the registration request signal in the registration request signal reception period for receiving the registration request signal to be transmitted, and the reception frequency index value acquisition step. A group number determining step for determining the number of groups permitted to transmit the registration request signal based on the received frequency index value; and A group selection step for selecting the number of groups determined in the group number determination step from a group different from the group selected so far, and for transmitting the registration request signal to an unregistered subscriber-side optical line terminator. A registration request transmission control signal generating step for storing transmission permission group information indicating a group selected in the group selection step in the registration request transmission control signal, and the registration request transmission control. A transmission control step of transmitting the registration request transmission control signal generated in the signal generation step to the subscriber-side optical line termination device, wherein the subscriber-side optical line termination device is connected to the station-side optical line termination device. Registration has not yet been performed and the transmission permission group stored in the received registration request transmission control signal. If any of the groups indicated by the information matches the group to which the own device belongs, it is determined that the registration request signal should be transmitted, and the transmission permission group stored in the received registration request transmission control signal This is a communication control method including a transmission permission / inhibition determination step for determining that a registration request signal should not be transmitted when none of the groups indicated by the information matches the group to which the own device belongs.

  One aspect of the present invention is a station-side optical line terminator connected via an optical communication path to a plurality of subscriber-side optical line terminators grouped to belong to any of a plurality of groups, A reception frequency index representing a reception frequency of a registration request signal in a registration request signal reception period in which reception of a registration request signal transmitted by the subscriber side optical line terminator for requesting registration to the station side optical line terminator is received. A reception frequency index value acquisition unit that acquires a value, and a group number determination that determines the number of groups permitted to transmit the registration request signal based on the reception frequency index value acquired by the reception frequency index value acquisition unit And a group for selecting the number of groups determined by the group number determination unit from among the groups different from the group selected up to the previous time. In generating a registration request transmission control signal for causing the registration unit to transmit the registration request signal to an unregistered subscriber-side optical line terminating device, transmission permission group information indicating a group selected by the group selection unit A registration request transmission control signal generation unit for storing in the registration request transmission control signal, and a transmission control unit for transmitting the registration request transmission control signal generated by the registration request transmission control signal generation unit to a subscriber-side optical network unit. It is a station side optical line termination device provided.

  INDUSTRIAL APPLICABILITY According to the present invention, an optical communication system, a communication control method, and station-side light capable of reducing the frequency of collision of registration request signals received by a station-side optical line termination device from a plurality of subscriber-side optical line termination devices. It is possible to provide a line termination device.

It is a figure which shows the structural example of the optical communication system in 1st Embodiment. It is a figure which shows an example of the transmission / reception timing of the REGISTER_REQ frame according to transmission of the Discovery GATE frame which does not store transmission permission group information in a P2MP discovery process. It is a figure which shows an example of the transmission / reception timing of the REGISTER_REQ frame according to transmission of the Discovery GATE frame which stored transmission permission group information in the P2MP discovery process in 1st Embodiment. In 1st Embodiment, it is a figure which shows an example of the transmission / reception timing of the REGISTER_REQ frame according to transmission of the Discovery GATE frame which stored transmission permission group information in the following P2MP discovery process with respect to FIG. It is a figure which shows the structural example of OLT in 1st Embodiment. It is a figure explaining the example of a calculation method of the reception time ratio which OLT performs in 1st Embodiment. It is a figure which shows the structural example of the Discovery GATE frame in 1st Embodiment. It is a figure which shows the example of a definition of the transmission permission group information (Discovery Group Bitmap) stored in the Discovery GATE frame in 1st Embodiment. It is a figure which shows the structural example of ONU in 1st Embodiment. It is a figure which shows an example of the group allocation method with respect to ONU in 1st Embodiment. It is a flowchart which shows the example of a process sequence which OLT in 1st Embodiment performs in relation to transmission of a Discovery GATE frame. It is a flowchart which shows an example of the transmission permission group number determination process which OLT in 1st Embodiment performs. It is a flowchart which shows the example of a process sequence which unregistered ONU in 1st Embodiment performs in response to reception of a Discovery GATE frame. It is a figure which shows the structural example of OLT in 2nd Embodiment. It is a flowchart which shows an example of the transmission permission group number determination process which OLT in 2nd Embodiment performs. It is a sequence diagram which shows the example of a communication procedure in a P2MP discovery process. It is a figure which shows an example of the transmission / reception timing of a Discovery GATE frame and a REGISTER_REQ frame in a P2MP discovery process.

<First Embodiment>
FIG. 1 shows a configuration example of an optical communication system in the first embodiment. The optical communication system shown in the figure corresponds to, for example, 10G-EPON.
The optical communication system shown in FIG. 1 includes one OLT (Optical Line Terminal) 100 and a plurality of ONUs (Optical Network Units: subscriber side optical line terminators) 200-1 to 200-n. Are connected via the optical communication path 500. The optical communication path 500 is formed with an optical splitter, an optical fiber or the like.
In the following description, the ONUs 200-1 to 200-n are described as ONUs 200 unless otherwise distinguished.

The OLT 100 is an optical line terminating device installed on the telecommunications carrier side. A host network 300 is connected upstream of the OLT 100. The host network 300 includes various servers that exist on the Internet, for example.
The OLT 100 performs, for example, signal conversion between an electrical signal and an optical signal or multiplexing of signals in communication between the host network 300 and the optical communication path 500.

  The ONU 200 is an optical line terminating device installed on the subscriber side. A lower network 400 (400-1 to 400-N) is connected to the downstream side of the ONU 200 (200-1 to 200-n). The lower network 400 includes network devices such as a personal computer used at a subscriber's home.

In the optical communication system configured as described above, the ONU 200 that is not registered on the OLT 100 side cannot communicate with the OLT 100 because a link with the OLT 100 is not established. Therefore, for the ONU 200 that is not registered in the OLT 100, it is necessary to establish a link with the OLT 100 to enable communication.
For this purpose, a P2MP discovery process according to the procedure shown in FIG. 16 is executed between the OLT 100 and the unregistered ONU 200.

In step S1 of FIG. 16, the OLT 100 transmits a Discovery GATE frame to all the ONUs 200 connected via the optical communication path 500 by broadcast. In the Discovery GATE frame, a transmission permission time _TG and a start time t1 of the transmission permission time _TG are stored. The transmission permission time _TG is a time length of a period (transmission permission period) during which transmission of a REGISTER_REQ frame (an example of a registration request signal) by the ONU 200 is permitted.
When the REGISTER_REQ frame is normally transmitted / received in step S2 of FIG. 16, the OLT 100 and the ONU 200 execute the processing after step S3 of FIG.

When transmitting the REGISTER_REQ frame, the ONU 200 transmits the REGISTER_REQ frame at a timing (random delay time) determined at random in the transmission permission time _TG to avoid collision as described in FIG. Yes. However, particularly in a situation where there are a large number of unregistered ONUs 200, the number of REGISTER_REQ frames transmitted during the limited transmission permission time _TG becomes large, so the probability that the REGISTER_REQ frames collide with each other increases.
FIG. 17 shows an example in which the REGISTER_REQ frame Rk transmitted from the ONU 200-k and the REGISTER_REQ frame Rn transmitted from the ONU 200-n collide with each other.

When a collision occurs in the REGISTER_REQ frame, the signal of the collision part is discarded because sufficient reliability cannot be secured. When the REGISTER_REQ frame is discarded in this way, the ONU 200 that is the transmission source of the collided REGISTER_REQ frame is not registered in the OLT 100, and therefore communication for retry is executed in the next P2MP discovery process. Such a retry causes a delay in communication time, which causes a deterioration in communication performance in an optical communication system, for example.
Thus, in the present embodiment, the frequency of occurrence of REGISTER_REQ frame collision is reduced by configuring the optical communication system as follows.

  In the optical communication system of the present embodiment, a plurality of ONUs 200 connected to the OLT 100 via the optical communication path 500 are grouped in advance as belonging to one of predetermined N groups (N is a natural number of 2 or more). Is done. A unique group identifier is assigned to each of the N groups.

  Further, the Discovery GATE frame in the present embodiment stores transmission permission group information indicating a group permitted to transmit the REGISTER_REQ frame. That is, the Discovery GATE frame in the present embodiment is a Discovery GATE frame in an extended format in which an area for storing a group identifier is further added to the standard structure.

The OLT 100 calculates an index value (reception frequency index value) indicating the reception frequency of the REGISTER_REQ frame during the Discovery Window period with the time length T _DW when registering all the unregistered ONUs 200 to establish a link.
The OLT 100 in the first embodiment obtains the reception time ratio RT as the reception frequency index value. The reception time ratio RT is a ratio between a time length of a Discovery Window period (an example of a registration request signal reception period) and a total reception time during which signals are continuously received in the Discovery Window period.

  As the number of unregistered ONUs 200 increases, the reception time ratio RT increases as the reception frequency of the REGISTER_REQ frame during the Discovery Window period increases. That is, the reception time ratio RT is established as one of index values indicating the reception frequency of the REGISTER_REQ frame in the Discovery Window period.

Then, the OLT 100 determines the number of groups permitted to transmit the REGISTER_REQ frame from the N groups based on the reception time ratio RT as the calculated reception frequency index value. Hereinafter, the number of groups determined in this way is expressed as a transmission permitted group number G (1 ≦ G ≦ N).
The OLT 100 determines the transmission permission group number G so that the transmission permission group number G decreases as the reception time ratio RT increases, that is, as the reception frequency of the REGISTER_REQ frame increases during the Discovery Window period. .
Note that when the first Discovery GATE frame is transmitted in the registration process of the unregistered ONU 200, the REGISTER_REQ frame is not received in the previous stage, and therefore the reception time ratio RT cannot be obtained. In this case, the OLT 100 may determine an initial value set in advance as the transmission permission group number G.

  The OLT 100 selects the number of groups corresponding to the determined transmission permitted group number G from the N groups. As a specific example, the ONU 200 is grouped by 8 (N = 8) groups from group 1 to group 8, and the transmission permitted group number G = 2 is determined when the first Discovery GATE frame is transmitted. Take the case as an example. In this case, the OLT 100 can select two groups, for example, group 1 and group 2.

Next, the OLT 100 generates a Discovery GATE frame storing transmission permission group information indicating that each of the groups 1 and 2 selected as described above is a group that permits transmission of the REGISTER_REQ frame.
Then, the OLT 100 transmits the Discovery GATE frame generated as described above to the ONU 200 by broadcasting.

The unregistered ONU 200 refers to the transmission permission group information stored in the received Discovery GATE frame in response to receiving the Discovery GATE frame transmitted as described above. The unregistered ONU 200 determines whether there is a group that matches the group to which the own device belongs among the groups indicated by the transmission-permitted group information.
If there is a matching group, the ONU 200 transmits a REGISTER_REQ frame in response to the reception of the current Discovery GATE frame to the OLT 100.
On the other hand, when there is no matching group, the ONU 200 does not transmit the REGISTER_REQ frame in response to the reception of the current Discovery GATE frame.

As described above, when the transmission permission group information indicates two groups, group 1 and group 2, the following operation is performed as a response on the ONU 200 side.
That is, among all the unregistered ONUs 200 that have received the Discovery GATE frame, only the unregistered ONU 200 belonging to group 1 and the unregistered ONU 200 belonging to group 2 transmit the REGISTER_REQ frame. Of all the unregistered ONUs 200, ONUs 200 belonging to groups other than group 1 and group 2 do not transmit a REGISTER_REQ frame.

By the above sequence, among the unregistered ONUs 200, the ONU 200 belonging to the group 1 and the ONU 200 belonging to the group 2 are registered. However, the ONUs 200 belonging to the remaining groups 3 to 8 remain unregistered.
Therefore, the OLT 100 obtains the reception time ratio RT in the Discovery Window period in which the REGISTER_REQ frame is received in response to the transmission of the Discovery GATE frame storing the transmission permission group information indicating the previous group 1 and group 2, for example.

The OLT 100 again obtains the transmission permission group number G according to the obtained reception time ratio. Then, the ONU 100 selects the number of groups according to the transmission permission group number G obtained this time from the groups that have not been selected so far in the N groups.
Specifically, in this case, group 1 and group 2 are selected from groups 1 to 8 last time. Therefore, this time, the OLT 100 selects the number of groups corresponding to the number G of transmission permitted groups from the groups 3 to 8 excluding the groups 1 and 2 from the groups 1 to 8.
Then, the OLT 100 transmits a Discovery GATE frame storing transmission permission group information indicating the selected group. Thereby, the ONU 200 belonging to the group indicated by the transmission permitted group information stored in the Discovery GATE frame transmitted for the second time is newly registered.

Thereafter, the OLT 100 determines the transmission permitted group number G based on the reception time ratio RT by the same procedure as described above until the registration of the ONU 200 corresponding to all the groups is completed, and according to the determined transmission permitted group number G Select a number of groups that have not yet been selected.
Then, the OLT 100 transmits a Discovery GATE frame storing transmission permission group information indicating the selected group. As a result, the ONUs 200 belonging to the group indicated by the transmission permitted group information are sequentially registered for each P2MP discovery sequence. By sequentially registering in this way, the registration of the ONUs 200 corresponding to all the groups 1 to 8 is finally completed when a certain number of P2MP discovery sequences are performed. Will do.

Here, a specific example of the P2MP discovery process in the optical communication system according to the present embodiment will be described with reference to FIGS.
FIG. 2 shows an example of the transmission / reception timing of the REGISTER_REQ frame corresponding to the transmission of the Discovery GATE frame that does not store the transmission permission group information. In this case, the ONU 200 is not particularly grouped.

  The Discovery GATE frame transmitted by the OLT 100 at time t0 is received by each of the ONUs 200. In this case, transmission permission group information is not stored in the Discovery GATE frame. Accordingly, whether or not the REGISTER_REQ frame can be transmitted in units of groups is not specified by the Discovery GATE frame.

For this reason, in response to the reception of the Discovery GATE frame transmitted by the OLT 100 at time t0, all the unregistered ONUs 200 transmit the REGISTER_REQ frame.
As described above, when all the unregistered ONUs 200 transmit the REGISTER_REQ frame, the frequency of the REGISTER_REQ frame received by the OLT 100 during the Discovery Window period increases.
As a result of increasing the reception frequency of the REGISTER_REQ frame in this manner, FIG. 6 shows a state in which the REGISTER_REQ frame received by the ONU 200 collides.
Specifically, a state in which the REGISTER_REQ frame Rj transmitted from the ONU 200-j, the REGISTER_REQ frame Rk transmitted from the ONU 200-k, and the REGISTER_REQ frame Rn transmitted from the ONU 200-n collide with each other is shown.

On the other hand, FIG. 3 shows an example of the transmission / reception timing of the REGISTER_REQ frame when the OLT 100 transmits a Discovery GATE frame storing transmission permission group information.
In the present embodiment, each group to which the ONU 200 belongs is represented by a group identifier. Further, the transmission permission group information indicates a group of the ONU 200 that permits the REGISTER_REQ frame by a group identifier. Hereinafter, the group identifier may be described as GID.
In the description of FIG. 3, an example is given in which ONUs 200 are grouped into four groups of GID = 1 to GID = 4. This also applies to FIG.

  In the example of FIG. 3, the ONU 200-i belongs to the group with GID = 3, the ONU 200-j belongs to the group with GID = 4, the ONU 200-k belongs to the group with GID = 1, and the ONU 200-n has GID = 2. Belongs to a group.

In addition, in the same figure, when the OLT 100 determines that the transmission permitted group number G = 1 in this P2MP discovery process, a Discovery GATE frame storing transmission permitted group information indicating only GID = 1 is transmitted. An example is shown.
In response to the transmission of the Discovery GATE frame storing the transmission permission group information indicating GID = 1 by the OLT 100, only the ONU 200-k belonging to the group of GID = 1 transmits the REGISTER_REQ frame Rk. In response, on the OLT 100 side, only the REGISTER_REQ frame Rk is received among the REGISTER_REQ frames Ri, Rj, Rk, and Rn. Thus, the state in which only the REGISTER_REQ frame Rk is received indicates that the REGISTER_REQ frame Rk does not collide with other REGISTER_REQ frames.

FIG. 4 shows an example of the transmission / reception timing of the REGISTER_REQ frame in the P2MP discovery process subsequent to the P2MP discovery process shown in FIG.
In the figure, transmission permission group information indicating three groups of GID = 2, GID = 3, and GID = 4 other than GID = 1 in response to the determination that the number of transmission permission groups G = 3. An example is shown in which a Discovery GATE frame in which is stored is transmitted.
Then, according to the transmission of the Discovery GATE frame, the ONU 200-i, ONU 200-j, and ONU 200-n belonging to each group of GID = 2, GID = 3, and GID = 4 are respectively REGISTER_REQ frames Ri, Rj, and Rn. Is sending.

  By transmitting the REGISTER_REQ frame as described above, among the REGISTER_REQ frames Ri, Rj, Rk, and Rn, the REGISTER_REQ frames Ri, Rj, and Rn are received on the OLT 100 side. In this state, the REGISTER_REQ frames Ri, Rj, and Rn do not collide with each other.

  As can be understood from the description with reference to FIGS. 3 and 4, in this embodiment, a plurality of P2MP discovery processes are performed when all unregistered ONUs 200 are registered. In each P2MP discovery process, the ONUs 200 that are permitted to transmit REGISTER_REQ frames are distributed in units of groups. Thereby, compared with the case where a P2MP discovery process is performed without grouping ONU200, the frequency with which a REGISTER_REQ frame collides can be made low.

In addition, in the present embodiment, the number of groups permitted to transmit the REGISTER_REQ frame in one P2MP discovery process is determined based on the reception time ratio RT as the reception frequency index value. That is, in the present embodiment, the number of ONUs 200 that are permitted to transmit the REGISTER_REQ frame is optimized in accordance with the reception frequency of the REGISTER_REQ frame during the Discovery Window period. Thus, the number of REGISTER_REQ frames received by the OLT 100 during the Discovery Window period is controlled to be within an appropriate range without being too much or too little.
In the case of this embodiment, since transmission of REGISTER_REQ frames by some groups is permitted for each P2MP discovery process, the P2MP discovery process is performed in multiple steps. At this time, as described above, by optimizing the number of ONUs 200 that are permitted to transmit the REGISTER_REQ frame, the number of times to perform the P2MP discovery process can be substantially minimized. Thereby, in this embodiment, the time until the registration of the ONU 200 is completed can be avoided.

  Next, a configuration example of the OLT 100 according to the present embodiment will be described with reference to FIG. The OLT 100 shown in the figure includes a wavelength multiplexer / demultiplexer 101, an optical receiver 102, a communication controller 103, and an optical transmitter 104.

  The optical communication system according to the present embodiment assigns different wavelengths to optical signals in the upstream direction (communication direction from the ONU 200 to the OLT 100) and the downstream direction (communication direction from the OLT 100 to the ONU 200). And a wavelength division multiplexing system that transmits and receives each optical signal in the downstream direction at the same time. In accordance with such a configuration, the OLT 100 of this embodiment includes a wavelength multiplexer / demultiplexer 101. The wavelength multiplexer / demultiplexer 101 includes a wavelength filter corresponding to the wavelength of each optical signal in the upstream direction and the downstream direction.

The wavelength multiplexer / demultiplexer 101 extracts the optical signal transmitted from the ONU 200 by separating the wavelength corresponding to the upstream optical signal from the optical signal transmitted by the optical fiber, and outputs the optical signal to the optical receiver 102.
The wavelength multiplexer / demultiplexer 101 synthesizes an optical signal having a wavelength corresponding to the downlink direction output from the optical transmission unit 104 into an optical signal transmitted through an optical fiber, and transmits the optical signal to the ONU 200.

The optical receiving unit 102 demodulates the optical signal input from the wavelength multiplexer / demultiplexer 101 into a data signal and outputs the data signal to the communication control unit 103.
The communication control unit 103 executes control related to communication with the ONU 200 and communication with the upper network 300.
The optical transmission unit 104 receives the transmission signal output from the communication control unit 103, converts the transmission signal into an optical signal having a wavelength corresponding to the downlink direction, supplies the converted optical signal to the wavelength multiplexer / demultiplexer 101, and supplies the ONU 200. Send to.

  Next, a configuration example corresponding to transmission of a Discovery GATE frame in the communication control unit 103 will be described with reference to FIG. Corresponding to the transmission of the Discovery GATE frame, the communication control unit 103 shown in the figure corresponds to a reception frequency index value acquisition unit 131, a group number determination unit 132, a group selection unit 133, a registration request transmission control signal generation unit 134, and a signal transmission. A control unit 135 is provided.

The reception frequency index value acquisition unit 131 acquires an index value (reception frequency index value) indicating the reception frequency of the REGISTER_REQ frame during the Discovery Window period. As described above, the reception frequency index value in the present embodiment is the reception time ratio RT.
In calculating the reception time ratio RT, the reception frequency index value acquisition unit 131 inputs an optical signal received by the optical reception unit 102. As described with reference to FIG. 2, the reception frequency index value acquisition unit 131 measures the reception time t _Rk of the optical signal continuously received by the optical reception unit 102 during the Discovery Window period. Receive frequency index value obtaining unit 131, as the ratio of the time length _{T DW} period of total and Discovery Window reception time _{t Rk} measured, calculates the reception time ratio RT.

Here, a specific example of the reception time ratio calculation method executed by the OLT 100 will be described with reference to FIG.
FIG. 6 shows a case where six REGISTER_REQ frames R1 to R6 are received during the Discovery Window period. Of the REGISTER_REQ frames R1 to R6, the REGISTER_REQ frames R1, R5, and R6 are received without colliding with other REGISTER_REQ frames. In contrast, the REGISTER_REQ frame R2 and the REGISTER_REQ frame R3 collide, and the REGISTER_REQ frame R3 and the REGISTER_REQ frame R4 collide. In this case, each signal as REGISTER_REQ frames R2, R3, R4 is continuously received.

If REGISTER_REQ frame R1~R6 as described above is received, OLT 100, first, measures the reception time _{t R1} signal as REGISTER_REQ frame R1 is continuously received.
The OLT 100 measures the reception time t _R2 when the signals as the REGISTER_REQ frames R2, R3, and R4 are continuously received.
The OLT 100 measures the reception time t _R3 when the signal as the REGISTER_REQ frame R5 is continuously received, and measures the reception time t _R4 when the signal as the REGISTER_REQ frame R6 is continuously received.

The OLT 100 obtains the total Σt _Rk (t _R1 + t _R2 + t _R3 + t _R4 ) of the reception times t _{R1 to} t _R4 measured as described above.
Sonouede, OLT 100 includes a total .SIGMA.t _Rk reception time _t R1 _{~t R4,} Discovery for receiving time ratio is the ratio of the time length _{T DW} period Window, a total .SIGMA.t _Rk reception time _t R1 _{~t R4} time _Obtained by dividing by the length _TDW .
That is, the OLT 100 can obtain the reception time ratio RT according to the following formula 1 when one reception time is expressed as t _Rk .

Returning to FIG. Based on the reception time ratio RT as the reception frequency index value acquired by the reception frequency index value acquisition unit 131, the group number determination unit 132 determines the number of groups (transmission permitted group number) G that is permitted to transmit the REGISTER_REQ frame. decide.
The number-of-groups determination unit 132 can calculate the number G of permitted transmission groups by, for example, the following formula 2, and can use the calculated number G of permitted transmission groups as a determination result.

In Equation 2, G _MAX is the maximum value that can be taken as the number G of transmission-permitted groups, and G _MIN is the minimum value that can be taken as the number G of transmission-permitted groups.
ΔG is a step width (unit increase width) in increasing the transmission permission group number G ″ calculated in the previous time, and ΔG ′ is a transmission permission group number G ″ immediately before the calculation of the transmission permission group number G ”. This is the step width (unit decrease width) in reducing
RT ₀ , RT ₁ , RT ₂ , and RT ₃ are thresholds for the reception time ratio RT, and are all predetermined constants. RT ₀ , RT ₁ , RT ₂ , RT ₃ have a relationship represented by RT ₀ <RT ₁ <RT ₂ <RT ₃ .
In this way, depending on the expression 2, the transmission permission group number G is set to the same value as the transmission permission group number G ”calculated last time or the number of transmission permission groups calculated last time depending on the value of the reception time ratio RT. By increasing / decreasing a certain value from G ″, the transmission permitted group number G is obtained.

  Alternatively, the group number determination unit 132 may calculate the transmission permission group number G by the following expression 3 instead of the above expression 2, and may use the calculated transmission permission group number G as a determination result.

In the above Equation 3, G ₁ , G ₂ , G ₃ , G ₄ , and G ₅ are constants that are predetermined as possible values for the transmission permission group number G, and G ₁ <G ₂ <G ₃ <G ₄ have a relationship of _{<G 5.}
RT ₅ , RT ₆ , RT ₇ , RT ₈ are predetermined threshold values, and have a relationship of RT ₅ <RT ₆ <RT ₇ <RT ₈ .
Thus, depending on Equation 3, any one of the constants determined in advance according to the value of the reception time ratio RT is selected, and the selected constant is obtained as the transmission permitted group number G.

When the transmission permission group number G is obtained as shown in the above expression 2 or 3, it is preferable to set G _min as the initial value of the transmission permission group number G.
The timing for setting the initial value of the transmission permitted group number G is, for example, when the OLT 100 is restarted. When the OLT 100 is restarted, all registered contents of the ONU 200 before the restart are cleared. All ONUs 200 connected to the OLT 100 are unregistered. Therefore, during the registration process immediately after restart, REGISTER_REQ frames are transmitted from many ONUs 200.
Accordingly, if G _min is set as the initial value of the number G of permitted transmission groups in response to such a restart, the number of ONUs 200 that transmit REGISTER_REQ frames in the first P2MP discovery sequence is determined. It can be minimized.

  The group selection unit 133 selects the number of groups determined by the group number determination unit 132 from among a plurality of groups, among the groups different from the groups selected up to the previous time. As described above, the group selected by the group selection unit 133 is a group of the ONU 200 that is permitted to transmit the REGISTER_REQ frame.

The registration request transmission control signal generation unit 134 generates a Discovery GATE frame (an example of a registration request transmission control signal) for causing an unregistered ONU 200 to transmit a REGISTER_REQ frame (an example of a registration request signal) that requests registration to the OLT 100. To do.
When generating the Discovery GATE frame, the registration request transmission control signal generation unit 134 stores transmission permission group information indicating the group selected by the group selection unit 133 in the Discovery GATE frame.

  The signal transmission control unit 135 transmits the Discovery GATE frame generated by the registration request transmission control signal generation unit 134 to the ONU 200.

Here, with reference to FIG. 7, a structural example of the Discovery GATE frame generated by the registration request transmission control signal generation unit 134 will be described.
The Discovery GATE frame shown in the figure includes Destination Address, Source Address, Length / Type, Opcode, Timestamp, Number of Grants / Flags, Grant # 1 Start Time, Grant # 1 Start Time, Grant # 1 Start Time, Time / Reserved, FCS is stored.

Destination Address is an area of 6 octets and stores a destination address. In the case of a Discovery GATE frame, the Destination Address stores a broadcast address (Broadcast Address) indicating broadcast.
Source Address is an area of 6 octets and stores a transmission source address. In the case of a Discovery GATE frame, the Source Address stores the MAC address (OLT MAC Address) of the transmission source OLT 100.

Length / Type is a 2 Octets area, and stores information indicating the data length and type of the GATE frame. In the case of a Discovery GATE frame, for example, a predetermined value indicating MPCP is stored.
Opcode is an area of 2 Octets, and stores a code indicating the content of data stored in the Discovery GATE frame. The Opcode of the Discovery GATE frame under the standard is 0x0002. However, when the transmission permission group information is stored as an extended format of the Discovery GATE frame as in this embodiment, for example, a predetermined value other than 0x0002 is assigned.

Timestamp is an area of 4 Octets, and stores, for example, information indicating the transmission time of the Discovery GATE frame corresponding to time t0 in FIGS.
Number of grants / Flags is an area of 1 Octet. Information indicating the number of Grants (transmission permission) stored in the current Discovery GATE frame, a flag indicating whether or not a REPORT can be transmitted for each stored Grant, A flag indicating whether the GATE frame is a normal GATE frame (Normal GATE frame) or a Discovery GATE frame is stored.
Grant # 1 Start Time is an area of 4 Octets, and stores information indicating the start time of Grant # 1 (first transmission permission). In the case of the Discovery GATE frame, for example, the start time t1 of the transmission permission time _TG shown in FIGS. 3 and 4 is stored.
Grant # 1 Length is an area of 2 octets, and stores information indicating the length of transmission time permitted as Grant # 1 (first transmission permission). In the case of the Discovery GATE frame, for example, the time length of the transmission permission time _TG shown in FIGS. 3 and 4 is stored.

The Discovery Group Bitmap is an example of transmission permission group information in the present embodiment.
The Discovery Group Bitmap is an area of 1 Octet and indicates a group of ONUs 200 that are permitted to transmit a REGISTER_REQ frame in response to reception of a corresponding Discovery GATE frame.
Thus, the Discovery GATE frame of the present embodiment has an extended format in which an area for storing transmission permission group information is added to the standard Discovery GATE frame.

FIG. 8 shows an example of the structure of the Discovery Group Bitmap. The Discovery Group Bitmap shown in the figure corresponds to the case where the total number of groups is 8.
As shown in the figure, a group identifier of GID = 1 to GID = 8 is assigned to each bit of bit 1 to bit 8 as the Discovery Group Bitmap. In addition, the value of each bit indicates whether or not transmission is possible for the group indicated by the corresponding group identifier. Specifically, if the bit value is “1”, it indicates that transmission is permitted, and if the bit value is “0”, it indicates that transmission is prohibited.
In the figure, an example is shown in which bits 3 and 4 each have a value of “1” and the remaining bits 1, 2, and 5 to 8 have a value of “0”. That is, in the Discovery Group Bitmap shown in the figure, transmission is permitted for each group of GID = 3 and GID = 4, and transmission is prohibited for each group of GID = 1, GID = 2, GID = 5 to GID = 8. Indicates that

Returning to FIG. Option is an undetermined option area.
The Sync Time is an area of 2 Octets, and is information specific to the Discovery GATE frame, and stores information indicating the synchronization time requested by the OLT 100 to the ONU 200.
Pad / Reserved is an area of 29 Octets and stores padding data.
FCS (Frame Check Sequence) is an area of 4 octets, and stores FCS as an error detection code.

  Next, a configuration example of the ONU 200 of the present embodiment will be described with reference to FIG. The ONU 200 shown in the figure includes a wavelength multiplexer / demultiplexer 201, an optical receiving unit 202, a control unit 203, a user data transmission unit 204, and an optical transmission unit 205.

Similar to the wavelength multiplexer / demultiplexer 201 of the OLT 100, the wavelength multiplexer / demultiplexer 201 includes a wavelength filter corresponding to the wavelength of each optical signal in the upstream direction and the downstream direction. The wavelength multiplexer / demultiplexer 201 extracts the optical signal transmitted from the OLT 100 by separating the wavelength corresponding to the downstream optical signal from the optical signal transmitted by the optical fiber, and outputs the optical signal to the optical receiving unit 202.
The wavelength multiplexer / demultiplexer 201 synthesizes an optical signal having a wavelength corresponding to the upstream direction output from the optical transmission unit 205 into an optical signal transmitted by an optical fiber, and transmits the optical signal to the OLT 100.

  The optical receiving unit 202 demodulates the optical signal input from the wavelength multiplexer / demultiplexer 201 into a data signal and outputs the data signal to the control unit 203.

The control unit 203 executes control related to communication with the OLT 100 and communication with the lower network 400.
The user data transmission unit 204 receives user data transmitted from the lower network 400 to the ONU 200 and passes it to the control unit 203. In addition, the user data transmission unit 204 transmits the user data transferred from the control unit 203 to the lower network 400.
The optical transmission unit 205 inputs the transmission signal (user data, REPORT frame, REGISTER_REQ frame, etc.) output from the transmission signal storage unit 235 of the control unit 203, converts it into an optical signal having a wavelength corresponding to the upstream direction, The converted optical signal is supplied to the wavelength multiplexer / demultiplexer 201 and transmitted to the OLT 100.

  Next, a configuration example of the control unit 203 will be described with reference to the same FIG. The control unit 203 shown in the figure includes a signal discriminating unit 231, a transmission permission / inhibition determining unit 232, a group identifier storage unit 233, a registration request signal generating unit 234, a transmission signal accumulating unit 235, a transmission control unit 236, and a REPORT frame generating unit 237. Prepare.

The signal discriminating unit 231 discriminates the signal input from the light receiving unit 202.
In the signal transmitted from the OLT, a signal to be transmitted to each ONU is multiplexed. The signal discriminating unit 231 determines whether or not the received signal (frame) is addressed to itself. Here, the signal addressed to itself is a signal transmitted by broadcast from the OLT 100, or a signal whose LLID (Logical Link ID) stored in the frame matches its own LLID.
In the case of a signal transmitted by broadcast, a predetermined broadcast address indicating broadcast is stored in the destination address (DA). The signal discriminating unit 231 can determine whether or not the signal is transmitted by broadcasting by referring to the destination address (DA).

Furthermore, when the received signal is a signal transmitted to itself, the signal discriminating unit 231 determines the type of the received signal.
For example, when the information (Number of grants / Flags in correspondence with FIG. 7) indicating the type of data (frame) in the frame of the signal transmitted by broadcasting indicates that it is a Discovery GATE frame (Discovery Flag = TRUE) The discrimination unit 231 determines that the type of the received signal is a Discovery GATE frame. In addition, the signal discriminating unit 231 refers to the Opcode in the frame of the signal transmitted by broadcasting.
If the Opcode indicates that it is an Extended Discovery GATE (see FIG. 7), the signal discriminating unit 231 determines that the type of the received signal is a Discovery GATE frame with an extended type.
On the other hand, if it is indicated in Opcode that it is not Extended Discovery GATE (see FIG. 7), it is determined that the frame is a Discovery GATE frame according to the standard format.
In the present embodiment, unless otherwise specified, when described as a Discovery GATE frame, it indicates a Discovery GATE frame of an extended format having the structure shown in FIG.

  When it is determined that the Discovery GATE frame has been received, the signal discriminating unit 231 outputs the received Discovery GATE frame to the transmission permission determination unit 232 and the transmission control unit 236.

Further, the signal discriminating unit 231 receives information indicating the data (frame) type in the received signal frame for the self-addressed GATE frame of a type other than the extended format Discovery GATE frame (Discovery according to the standard format). The received signal is determined to be a GATE frame.
In this case, the signal discriminating unit 231 outputs the received GATE frame to the transmission control unit 236.

  The signal discriminating unit 231 determines that the received signal is user data when the information indicating the data (frame) type in the frame of the received signal addressed to the user indicates user data. In this case, the signal discriminating unit 231 transmits the received user data from the user data transmission unit 204 to the lower network 400.

The transmission permission / inhibition determining unit 232 has not yet registered its own device in the OLT 100, and any of the groups indicated by the transmission permission group information stored in the received Discovery GATE frame is the own device. If it matches the group to which it belongs, it is determined that the REGISTER_REQ frame should be transmitted.
In addition, the transmission permission / inhibition determination unit 232, if any of the groups indicated by the transmission permission group information stored in the received Discovery GATE frame does not match the group to which the own device belongs, Determine that it should not be sent.
Here, the group indicated by the transmission permission group information stored in the Discovery GATE frame is indicated by the GID associated with the bit position indicating the value of “1” in the Discovery Group Bitmap as described in FIG. It is a group.

When determining whether any of the groups indicated by the transmission-permitted group information in the Discovery GATE frame matches the group to which the own device belongs, the transmission permission / inhibition determination unit 232 stores the group stored in the group identifier storage unit 233 Refer to the identifier (GID).
The group identifier stored in the group identifier storage unit 233 indicates the group to which the own device belongs.
Therefore, the transmission permission / inhibition determination unit 232 recognizes the GID associated with the bit position indicating the value “1” in the Discovery Group Bitmap that is the transmission permission group information. Then, the transmission permission / inhibition determination unit 232 may determine whether there is a GID recognized from the Discovery Group Bitmap that matches the GID stored in the group identifier storage unit 233.

Here, an example of a method for assigning groups to the ONU 200 will be described with reference to FIG. Here, a case where the total number of groups is six (GID = 1 to GID = 6) is taken as an example.
Since the ONU 200 is a network device, each has a unique MAC address.
Therefore, one of the group identifiers is assigned to each of the lower 4 bits of the MAC address of the ONU 200.
In the example of FIG. 10, it is shown that GID = 1 is assigned to the ONU 200 whose lower 4 bits of the MAC address are 0x0, 0x1, and 0x2.
In addition, it is shown that GID = 2 is assigned to the ONU 200 whose lower 4 bits of the MAC address are 0x3, 0x4, and 0x5.
Further, it is shown that GID = 3 is assigned to the ONU 200 whose lower 4 bits of the MAC address are 0x6, 0x7, and 0x8.
Further, it is shown that GID = 4 is assigned to the ONU 200 whose lower 4 bits of the MAC address are 0x9, 0xA, and 0xB.
In addition, it is shown that GID = 5 is assigned to the ONU 200 in which the lower 4 bits of the MAC address are 0xC and 0xD.
Further, it is shown that GID = 6 is assigned to the ONU 200 whose lower 4 bits of the MAC address are 0xE and 0xF.

In the example in the figure, when the total number of groups is six (GID = 1 to GID = 6), the lower 4 bits of the MAC address are associated with each other. However, in the present embodiment, grouping can be performed in the same manner as shown in the figure by associating, for example, the total number of groups other than 6 with the values of a plurality of bits at predetermined positions in the MAC address. .
Also, the ONUs 200 that are close to each other tend to be close in timing for transmitting the REGISTER_REQ frame. Conversely, the greater the distance between the ONUs 200, the greater the possibility that the timing deviation for transmitting the REGISTER_REQ frame will increase. Therefore, if the allocation is performed so that the group identifiers of the ONUs 200 that are close to each other are not the same, the frequency with which the REGISTER_REQ frames collide can be further reduced.

Returning to FIG. The registration request signal generation unit 234 generates a REGISTER_REQ frame when the transmission permission determination unit 232 determines that a registration request signal should be transmitted.
The REGISTER_REQ frame generated as described above is accumulated in the transmission signal accumulation unit 235 and then output to the optical transmission unit 205 under the control of the transmission control unit 236 and transmitted from the wavelength multiplexer / demultiplexer 201 to the OLT 100. The

On the other hand, the registration request signal generation unit 234 does not generate a REGISTER_REQ frame corresponding to the Discovery GATE frame received this time, when the transmission permission determination unit 232 determines that the registration request signal should not be transmitted. Also, the transmission control unit 236 discards the Discovery GATE frame received this time, and does not execute transmission control according to the Discovery GATE frame received this time.
In this case, the REGISTER_REQ frame corresponding to the Discovery GATE frame received this time is not transmitted to the OLT 100.

  Only when one of the groups indicated by the transmission-permitted group information stored in the received Discovery GATE frame matches the group to which the own device belongs as a result of the determination by the transmission permission determination unit 232 as described above. Control is performed so that a REGISTER_REQ frame is transmitted. As a result, it is possible to transmit the REGISTER_REQ frame only to the ONUs 200 belonging to the group for which the OLT 100 permits the response to the Discovery GATE frame.

  In the control unit 203, the transmission signal accumulation unit 235 is a buffer that temporarily accumulates transmission signals waiting to be transmitted. The transmission signal accumulated by the transmission signal accumulation unit 235 is generated by, for example, user data transmitted from the lower network 400 via the user data transmission unit 204, the REGISTER_REQ frame generated by the registration request signal generation unit 234, and the REPORT frame generation unit 237. For example, a REPORT frame.

  The transmission control unit 236 performs transmission control according to the band (data transmission amount) notified by the GATE frame and the transmission timing. That is, the transmission control unit 236 transmits the transmission signal of the data transmission amount notified by the GATE frame among the transmission signals stored by the transmission signal storage unit 235 at the transmission timing notified by the GATE frame. To output. Thereby, the transmission signal of the data transmission amount notified by the GATE frame is transmitted to the OLT 100 at the transmission timing notified by the GATE frame.

The REPORT frame generation unit 237 generates a REPORT frame. The REPORT frame is a frame that notifies the OLT 100 from the ONU 200 of the data amount of the transmission signal waiting for transmission stored in the transmission signal storage unit 235.
The REPORT frame generation unit 237 generates a REPORT frame storing data amount information indicating the data amount of the transmission signal waiting for transmission accumulated in the transmission signal accumulation unit 235.
The generated REPORT frame is temporarily accumulated in the transmission signal accumulation unit 235 and then transmitted to the OLT 100 under the control of the transmission control unit 236.

The OLT 100 that has received the REPORT frame, based on the data amount indicated by the data amount information stored in the REPORT frame and the data amount of the ONU 200 other than the transmission source of the REPORT frame, should be assigned to the ONU 200 that is the transmission source of the REPORT frame. Bandwidth (data transmission amount) and transmission timing are calculated. The transmission timing calculated here is, for example, the start time t1 of the transmission permission time _TG shown in FIGS.
The OLT 100 generates a GATE frame storing information on the calculated data transmission amount and transmission timing, and transmits the GATE frame to the ONU 200 that is the transmission source of the REPORT frame.

  The GATE frame received by the ONU 200 is input by the transmission control unit 236 in the control unit 203 as described above. The transmission control unit 236 executes transmission control for transmission signals waiting to be transmitted that are accumulated in the transmission signal accumulation unit 235 based on the data transmission amount and transmission timing indicated by the input GATE frame.

  Next, an example of a processing procedure executed by the OLT 100 in relation to the transmission of the Discovery GATE frame will be described with reference to the flowchart of FIG. As can be understood from the above description, the Discovery GATE frame transmitted by the OLT 100 of the present embodiment is an expanded format for storing transmission permission group information (Discovery Group Bitmap) as illustrated in FIG. It is.

  The group number determination unit 132 in the OLT 100 waits until the start timing of the P2MP discovery sequence is reached (step S101—NO). In other words, the group number determination unit 132 waits until the timing for starting the process for registering the unregistered ONU 200 is reached.

In response to the timing at which the P2MP discovery sequence should be started (step S101—YES), the group number determination unit 132 sets G _min that is a predetermined minimum value as the initial value of the transmission permitted group number G. (Step S102).
In addition, the group selection unit 133 substitutes 1 for a variable i indicating the numbers assigned to the N groups obtained by grouping the ONUs 200 (step S103).

  Next, the group selection unit 133 selects the number of transmission permission groups corresponding to the number G of transmission permission groups determined in step S102 or step S109 (step S104). As an example, the group selection unit 133 selects GID = i, GID = i + 1,..., GID = i + G−1 as a transmission permission group using the current variable i. That is, the group selection unit 133 selects G groups in the ascending order of values (numbers) indicated by GID, with GID = i as the first.

Next, the registration request transmission control signal generation unit 134 generates transmission permission group information (Discovery Group Bitmap) indicating the group identifier selected in Step S104 as a group permitted to transmit the REGISTER_REQ frame (Step S105).
Specifically, the registration request transmission control signal generation unit 134 stores “1” in the bit position corresponding to the group identifier selected in step S104 in the bit string as the transmission permission group information illustrated in FIG. On the other hand, the registration request transmission control signal generation unit 134 stores “0” in the bit position corresponding to the group identifier not selected in step S104.
The registration request transmission control signal generation unit 134 stores the transmission permission group information generated as described above in the Discovery GATE frame. In this way, transmission permission group information is generated in the present embodiment.
Then, the signal transmission control unit 135 transmits the Discovery GATE frame generated in step S105 from the optical communication path 500 to each ONU 200 (step S106).

Of the unregistered ONUs 200 that have received the Discovery GATE frame transmitted in step S104, the ONUs 200 belonging to the same group as indicated by the transmission-permitted group information transmit a REGISTER_REQ frame to the OLT 100.
Although not shown in the figure, the communication control unit 103 performs registration processing (LLID setting) corresponding to steps S3, S4, and S5 in FIG. 16 in response to reception of the REGISTER_REQ frame transmitted from the ONU 200. Notification, transmission of a GATE frame, reception of REGISTER_ACK).

After completing the transmission of the Discovery GATE frame in step S106, the group number determination unit 132 updates the variable i by adding the value of the current transmission permitted group number G to the variable i so far (step S107). ).
In addition, the group number determination unit 132 determines whether or not the variable i exceeds the maximum value (step S108). The maximum value of the variable i corresponds to the total number N of groups of the ONU 200.

  When the variable i is equal to or less than the maximum value (step S108—NO), there are still groups whose transmission permission is not indicated by the transmission permission group information. Therefore, in this case, a group number determination process is executed for transmission of the next Discovery GATE frame (step S109).

  In addition, according to the process of step S104 shown to the same figure, selection of the transmission permission group according to the number G of transmission permission groups follows the ascending order of the number corresponding to a group identifier (GID). However, the selection of the transmission permission group is not limited to the ascending order of the group identifier (GID) as long as the number according to the transmission permission group number G is selected from the groups that have not been selected up to the previous time.

The flowchart of FIG. 12 shows the group number determination process as step S109 of FIG.
As the group number determination process, first, the reception frequency index value acquisition unit 131 measures the reception time of the REGISTER_REQ frame in the immediately preceding (last) Discovery Window period (step S111). The reception time measured here is t _Rk of each reception time of the REGISTER_REQ frame in the Discovery Window described with reference to FIG.
Next, the reception frequency index value acquisition unit 131 uses Equation 1 described above by using the total Σt _Rk of the reception time t _Rk measured in Step S111 and the time length T _DW of the Discovery Window period. A reception time ratio RT is calculated by calculation (step S112).
Next, the number-of-groups determination unit 132 calculates the number G of transmission-permitted groups using the reception time ratio RT calculated in step S112 by the calculation using the previous expression 2 or expression 3 (step S113). The number G of transmission permitted groups calculated in this way is a result of determining the number of groups by the group number determining unit 132.

Returning to FIG. After the group number determination process as step S109 is executed as described above, the group selection unit 133 returns the process to step S104. Thus, when returning from step S109 to step S104, the group selection unit 133 uses the transmission permission group number G determined in step S109 and the variable i updated in the last step S107 to permit transmission. Select a group.
As a result, a transmission permission group is selected from among groups that are not yet permitted to transmit, and transmission of a Discovery GATE frame that stores transmission permission group information indicating the selected transmission permission group is executed.

Then, all the groups are selected as transmission permission groups, and it is determined that the variable i exceeds the maximum value as transmission of the last Discovery GATE frame is completed (step S108—YES).
Thus, when the variable i exceeds the maximum value, the OLT 100 returns to the process of step S101, and waits again until the next P2MP discovery timing is reached.

  Next, an example of a processing procedure executed by the unregistered ONU 200 in response to receiving the Discovery GATE frame will be described with reference to the flowchart of FIG. Note that the Discovery GATE frame received here is also in an expanded format for storing transmission permission group information (Discovery Group Bitmap) as illustrated in FIG.

  In the ONU 200, the signal discriminating unit 231 waits for the Discovery GATE frame to be received (step S201—NO). That is, the signal discriminating unit 231 waits until a discrimination result indicating that the received signal is a Discovery GATE frame (Extended Discovery GATE frame) is obtained.

  In response to the reception of the Discovery GATE frame (step S201—YES), the transmission propriety determination unit 232 determines whether or not the own apparatus is not yet registered in the OLT 100 ( Step S202).

  When the own device is in an unregistered state (step S202—YES), the transmission permission determination unit 232 further includes a group that matches the own device in the transmission permission group information stored in the Discovery GATE frame received this time. It is determined whether it is indicated (step S203). For this purpose, the transmission permission / inhibition determination unit 232 may determine whether or not the GID whose transmission permission group information indicates transmission permission has the same GID stored in the group identifier storage unit 233. (Step S203).

When the same group as the own device is indicated in the transmission permission group information (step S203—YES), the transmission permission determination unit 232 determines that the REGISTER_REQ frame should be transmitted (step S204).
In response to the determination result of step S204, the registration request signal generation unit 234 generates a REGISTER_REQ frame (step S205). The generated REGISTER_REQ frame is stored in the transmission signal storage unit 235.
Then, the transmission control unit 236 executes control for transmitting the REGISTER_REQ frame stored in the transmission signal storage unit 235 to the OLT 100 at a timing corresponding to the notification of the GATE frame, for example (step S206).

On the other hand, when the group identifiers do not match (step S203—NO), the transmission availability determination unit 232 determines that the REGISTER_REQ frame should not be transmitted (step S207). Also, even when the own device has already been registered in the OLT 100 (step S202—NO), the transmission availability determination unit 232 determines that the REGISTER_REQ frame should not be transmitted (step S207).
In accordance with the determination result of step S207, the transmission control unit 236 discards the Discovery GATE frame received corresponding to step S201 (step S208).
In this case, the registration request signal generation unit 234 does not generate a REGISTER_REQ frame, and the transmission control by the transmission control unit 236 according to the Discovery GATE frame received corresponding to step S201 is not executed. That is, transmission of the REGISTER_REQ frame in response to the Discovery GATE frame received in step S201 is not executed.

  By executing such processing, the ONU 200 according to the present embodiment has a group that matches the group to which the own device belongs among the groups indicated in the transmission permission group information stored in the received Discovery GATE frame. Only the REGISTER_REQ frame is transmitted.

Second Embodiment
Next, the second embodiment will be described.
In the second embodiment, the number of registered ONUs 200 is handled as the reception frequency index value of the REGISTER_REQ frame in the Discovery Window period. The OLT 100 determines the transmission permitted group number G using the number of registered ONUs 200.

FIG. 14 shows a configuration example of the OLT 100 in the second embodiment. In the figure, the same parts as those in FIG.
The OLT 100 illustrated in FIG. 14 is configured to further include a registration processing unit 136 in the communication control unit 103 illustrated in FIG. 6.

  The registration processing unit 136 executes processing for registering the ONU 200 that is the transmission source of the REGISTER_REQ frame in accordance with the REGISTER_REQ frame received every Discovery Window period. That is, in response to receiving the REGISTER_REQ frame, the registration processing unit 136 newly assigns an LLID to the ONU 200 that is the transmission source of the REGISTER_REQ frame. Also, the registration processing unit 136 notifies the ONU 200 of the LLID through the communication in steps S3 to S5 in FIG. When the registration is completed as described above, communication between the ONU 200 and the OLT 100 is established.

  In addition, the reception frequency index value acquisition unit 131 of the present embodiment monitors the number of ONUs 200 registered in the OLT 100 (the number of registered ONUs). The reception frequency index value acquisition unit 131 monitors the registration processing status of the registration processing unit 136 and changes the number of registered ONUs managed by the registration processing unit 136 every time the ONU 200 is newly registered by the registration processing unit 136.

Since the number of unregistered ONUs 200 decreases as the number of registered ONUs increases, the frequency of receiving REGISTER_REQ frames during the Discovery Window period also decreases. On the other hand, the smaller the number of registered ONUs, the greater the number of unregistered ONUs 200 and the higher the REGISTER_REQ frame reception frequency during the Discovery Window period.
As described above, the number of registered ONUs corresponds to the reception frequency of the REGISTER_REQ frame in the Discovery Window period. Therefore, the number of registered ONUs can be treated as a reception frequency index value for the REGISTER_REQ frame during the Discovery Window period.

Then, the group number determination unit 132 in this embodiment determines (calculates) the transmission permitted group number G based on the number of ONUs 200 registered in the OLT 100 that the reception frequency index value acquisition unit 131 acquires as the reception frequency index value. )
The group number determination unit 132 can calculate the transmission permission time _TG by, for example, calculation using the following Equation 4.

In Equation 4 above, N _R is the number of registered ONUs. N _R0 , N _R1 , N _R2 , and N _R3 are threshold values for the registered ONU count N _R , respectively, and are predetermined constants. N _R0 , N _R1 , N _R2 , and N _R3 have a relationship represented by N _R0 <N _R1 <N _R2 <N _R3 .
In this way, depending on the value of the number of registered ONUs N _R , the same value as the transmission permission group number G ”calculated last time is used as the transmission permission group number G, or the transmission permission group calculated previously The transmission permitted group number G is obtained by increasing or decreasing a certain value from the group number G ″.

  Alternatively, the group number determination unit 132 may calculate the transmission permission group number G by the following expression 5 instead of the above expression 4, and may use the calculated transmission permission group number G as a determination result.

In Equation 5 above, G ₆ , G ₇ , G ₈ , G ₉ , G ₁₀ are constants that are predetermined as possible values for the transmission permission group number G, and G ₆ <G ₇ <G ₈ <G ₉ have the relationship of _{<G 10.} N _R5 , N _R6 , N _R7 , and N _R8 are predetermined threshold _values , and have a relationship of N _R5 <N _R6 <N _R7 <N _R8 .
As described above, according to Equation 5, any one of the predetermined constants is selected according to the value of the registered ONU number N _R , and the selected constant is obtained as the transmission permitted group number G.

<Example of processing procedure>
An example of the processing procedure executed by the OLT 100 in relation to the transmission of the Discovery GATE frame in the second embodiment is the same as that in FIG. However, the OLT 100 according to the second embodiment executes the process shown in the flowchart of FIG. 15 as the group number determination process in step S109.

  In FIG. 15, the registration processing unit 136 executes registration processing of the ONU 200 according to each REGISTER_REQ frame received in the immediately preceding (last) Discovery Window period (step S <b> 121).

The reception frequency index value acquisition unit 131 updates the number of registered ONUs N _R as the reception frequency index value according to the registration processing result in step S121 (step S122). That is, the reception frequency index value acquisition unit 131 adds the number of ONUs registered in step S121 to the number of registered ONUs N _R registered in step S121 up to the previous time, thereby adding the number of registered ONUs N. Update _R.

Then, the number-of-groups determination unit 132 calculates the number G of transmission-permitted groups using Equation 4 or Equation 5 using the registered ONU number N _R updated in Step S122 (Step S123).

By performing the group number determination process in step S109 as described above, the OLT 100 according to the second embodiment can appropriately determine the transmission permitted group number G according to the number of registered ONUs 200. Thereby, also in the second embodiment, the ONU 200 that transmits the REGISTER_REQ frame in one P2MP discovery sequence is limited by one or more group units as in the first embodiment. As a result, also in the second embodiment, the frequency with which the REGISTER_REQ frame received by the OLT 100 collides can be reduced.
The configuration of the ONU 200 in the second embodiment may be the same as that in the first embodiment.

  In addition, you may make it implement | achieve operation | movement of OLT100 and ONU200 in embodiment mentioned above with a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be a program for realizing a part of the above-described functions, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. You may implement | achieve using programmable logic devices, such as FPGA (Field Programmable Gate Array).

  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.

DESCRIPTION OF SYMBOLS 100 ... OLT, 101 ... Wavelength multiplexer / demultiplexer, 102 ... Optical receiving part, 103 ... Communication control part, 104 ... Optical transmission part, 131 ... Reception frequency index value acquisition part, 132 ... Group number determination part, 133 ... Group selection 134: Registration request transmission control signal generation unit, 135 ... Signal transmission control unit, 136 ... Registration processing unit, 200 ... ONU, 201 ... Wavelength multiplexer / demultiplexer, 202 ... Optical reception unit, 203 ... Control unit, 204 ... User data transmission unit, 205... Optical transmission unit, 231... Signal discrimination unit, 232... Transmission enable / disable determination unit, 233... Group identifier storage unit, 234 ... registration request signal generation unit, 235 ... transmission signal storage unit, 236. 237 ... REPORT frame generator 300 ... Upper network 400 ... Lower network 500 ... Optical communication path

Claims (5)

A station-side optical line terminator, and a plurality of subscriber-side optical line terminators connected to the station-side optical line terminator via an optical communication path and grouped so as to belong to one of a plurality of groups. Prepared,
The station side optical line terminator is:
A reception frequency index representing a reception frequency of a registration request signal in a registration request signal reception period in which reception of a registration request signal transmitted by the subscriber side optical line terminator for requesting registration to the station side optical line terminator is received. A reception frequency index value acquisition unit for acquiring a value;
Based on the reception frequency index value acquired by the reception frequency index value acquisition unit, a group number determination unit that determines the number of groups permitted to transmit the registration request signal;
A group selection unit for selecting from among the plurality of groups, a group different from the group selected up to the previous time, the number of groups determined by the group number determination unit;
In generating a registration request transmission control signal for causing an unregistered subscriber-side optical line terminating device to transmit the registration request signal, transmission permission group information indicating a group selected by the group selection unit is transmitted as the registration request transmission. A registration request transmission control signal generation unit to be stored in the control signal;
A transmission control unit that transmits the registration request transmission control signal generated by the registration request transmission control signal generation unit to a subscriber-side optical line termination device;
The subscriber side optical line terminator is:
Any of the groups indicated by the transmission permission group information stored in the received registration request transmission control signal has not been registered in the station-side optical line terminator yet. If it matches the group to which the device belongs, it is determined that the registration request signal should be transmitted, and all of the groups indicated by the transmission permission group information stored in the received registration request transmission control signal are An optical communication system comprising: a transmission permission / non-permission determining unit that determines that a registration request signal should not be transmitted if the group does not match. The reception frequency index value acquisition unit
A ratio between a time length of the registration request signal reception period and a total reception time during which signals are continuously received in the registration request signal reception period is calculated, and the calculated ratio is acquired as the reception frequency index value. Item 4. The optical communication system according to Item 1. The reception frequency index value acquisition unit
The optical communication system according to claim 1, wherein the number of subscriber side optical line terminators registered in the station side optical line terminator is acquired as the reception frequency index value. A station-side optical line terminator, and a plurality of subscriber-side optical line terminators connected to the station-side optical line terminator via an optical communication path and grouped so as to belong to one of a plurality of groups. A communication control method in an optical communication system comprising:
The station side optical line terminator is:
A reception frequency index representing a reception frequency of a registration request signal in a registration request signal reception period in which reception of a registration request signal transmitted by the subscriber side optical line terminator for requesting registration to the station side optical line terminator is received. A reception frequency index value acquisition step of acquiring a value;
Based on the reception frequency index value acquired by the reception frequency index value acquisition step, a group number determination step for determining the number of groups permitted to transmit the registration request signal;
A group selection step of selecting the number of groups determined by the group number determination step from among the plurality of groups from a group different from the group previously selected;
In generating a registration request transmission control signal for causing an unregistered subscriber-side optical line terminating device to transmit the registration request signal, transmission permission group information indicating a group selected by the group selection step is transmitted as the registration request transmission. A registration request transmission control signal generation step to be stored in the control signal;
A transmission control step of transmitting the registration request transmission control signal generated by the registration request transmission control signal generation step to a subscriber-side optical line termination device;
The subscriber side optical line terminator is:
Any of the groups indicated by the transmission permission group information stored in the received registration request transmission control signal has not been registered in the station-side optical line terminator yet. If it matches the group to which the device belongs, it is determined that the registration request signal should be transmitted, and all of the groups indicated by the transmission permission group information stored in the received registration request transmission control signal are A communication control method comprising: a transmission permission / inhibition determining step for determining that a registration request signal should not be transmitted if the group does not match. A station side optical line terminator connected via an optical communication path to a plurality of subscriber side optical line terminators grouped to belong to any of a plurality of groups,
A reception frequency index representing a reception frequency of a registration request signal in a registration request signal reception period in which reception of a registration request signal transmitted by the subscriber side optical line terminator for requesting registration to the station side optical line terminator is received. A reception frequency index value acquisition unit for acquiring a value;
Based on the reception frequency index value acquired by the reception frequency index value acquisition unit, a group number determination unit that determines the number of groups permitted to transmit the registration request signal;
A group selection unit for selecting from among the plurality of groups, a group different from the group selected up to the previous time, the number of groups determined by the group number determination unit;
In generating a registration request transmission control signal for causing an unregistered subscriber-side optical line terminating device to transmit the registration request signal, transmission permission group information indicating a group selected by the group selection unit is transmitted as the registration request transmission. A registration request transmission control signal generation unit to be stored in the control signal;
A station side optical line termination device comprising: a transmission control unit that transmits a registration request transmission control signal generated by the registration request transmission control signal generation unit to a subscriber side optical line termination device.

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