CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage of International Application No. PCT/JP2019/018407 filed on May 8, 2019, which claims priority to Japanese Patent Application No. 2018-100013, filed May 24, 2018. The entire disclosures of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a transfer apparatus, a transfer method, and a transfer program.

BACKGROUND ART

In a network such as a mobile fronthaul (MFH), the function of a base station may be divided into a function on a higher layer side and a function on a lower layer side.FIG. 8is a diagram illustrating an example of a configuration of a mobile fronthaul. A mobile fronthaul100has a configuration of a centralized-radio access network (C-RAN). InFIG. 8, the mobile fronthaul100includes a plurality of central units (CUs)101and a plurality of distributed units (DUs)102.

The central unit101is an aggregate base station and executes a function on a higher layer side of the base station. For example, the plurality of central units101acquire signals constituted by a frame group from a higher network (not illustrated) in which frame delay requirements differ from each other. The plurality of central units101output the frames belonging to the signals having different delay requirements to a transfer apparatus103. The distributed unit (DU)102is a remote station and executes a function on a lower layer side of the base station. For example, the distributed unit102communicates with a user terminal using radio waves.

FIG. 9is a diagram illustrating an example of a detailed configuration of the mobile fronthaul100. The mobile fronthaul100includes the plurality of central units101, the plurality of distributed units102, the transfer apparatus103, and a passive optical network (PON)104. The passive optical network104is an optical network. The passive optical network104includes an optical line terminal (OLT)105, an optical splitter106, and a plurality of optical network units (ONUs)107.

The transfer apparatus103acquires the frames of the signals having different delay requirements from the plurality of central units101. The transfer apparatus103time-multiplexes the frames which are input from the plurality of central units101and transfers the time-multiplexed frames to the optical line terminal105. The optical line terminal105generates an optical signal depending on the time-multiplexed frame and outputs the generated optical signal to the optical splitter106. The optical splitter106demultiplexes the optical signal and outputs the demultiplexed optical signal to the optical network units107. The optical network unit107outputs an electrical signal corresponding to the optical signal to the distributed unit102.

A plurality of function split points for splitting functions of a base station of a fifth generation mobile communication system (5G) into functions on a higher layer side and functions on a lower layer side have been examined. For example, a lower layer split (LLS) is a function split point at which functions of a base station are divided within a lower layer (physical layer). For example, a higher layer split (HLS) is a function split point at which functions of a base station are divided within a higher layer (see Non Patent Literature 1).

A delay requirement (delay upper limit value) determined for a signal to which a frame belongs is different for each function split point. For example, the delay upper limit value of the LLS in the mobile fronthaul100is 250 s. For example, the delay upper limit value of the HLS in the mobile fronthaul100is from 1.5 ms to 10 ms (see Non Patent Literature 2).

The passive optical network104transmits the time-multiplexed frames to the plurality of distributed units102having different function split points. Thereby, the passive optical network104can improve the line concentration efficiency of the mobile fronthaul100.

The transfer apparatus103may control the order of transfer of the time-multiplexed frames to the passive optical network104based on strict priority queuing (SPQ).

FIG. 10is a diagram illustrating an example of a configuration of the transfer apparatus103. The transfer apparatus103includes a distribution unit108, a storage unit109, and a transfer unit110. The distribution unit108identifies the priority of a signal to which a frame input to the distribution unit108belongs on the basis of, for example, the value of a class of service (CoS) of a virtual local area network (VLAN) tag of the frame. The storage unit109includes a queue111for each priority of the signal to which the frame belongs. The distribution unit108stores the frame in the queue111for each priority of the signal to which the frame belongs.

The queue111has a first in, first out (FIFO) structure. The queue111stores the frame for each identified priority. The transfer unit110selects a queue111in descending order of the identified priority among the queues111which are not empty. The transfer unit110transfers a leading frame, which is a frame at the head of the queue, to the optical line terminal105from the selected queue111. Such strict priority queuing allows the transfer apparatus103to transfer a frame belonging to a signal having the highest priority to the optical line terminal105with a low delay (see Non Patent Literature 3).

CITATION LIST

Non Patent Literature

Non Patent Literature 1: 3GPP TR38.801 v14Non Patent Literature 2: Takehiro Nakamura, “Toward introduction of 5G in 2020”, pp. 21, MPLS Japan 2016, 2016Non Patent Literature 3: Iwao Toda, “Network QoS technology”, pp. 45-46, Ohmsha, Ltd., 2001

SUMMARY OF THE INVENTION

Technical Problem

However, in a transfer apparatus of the related art, a frame belonging to a signal having a low priority cannot be transferred to an optical line terminal with a low delay in a case where a frame belonging to a signal having a high priority is stored in a queue. In this manner, the transfer apparatus may not be able to transfer the frame belonging to the signal having a low priority so as to satisfy a delay requirement.

In view of the above-described circumstances, an advantage of the present disclosure is to provide a transfer apparatus, a transfer method, and a transfer program which are capable of transferring a frame belonging to a signal having a low priority so as to satisfy a delay requirement.

Means for Solving the Problem

An aspect of the present disclosure is a transfer apparatus including a distribution unit, a storage unit, and a transfer unit, in which the distribution unit is configured to identify a plurality of networks to which frames acquired from the plurality of networks belong, and distribute and store the frames in the storage unit for each of the plurality of networks based on identification results, the plurality of networks being different from each other in a delay upper limit value of each of the frames, the storage unit is configured to store information of a time at which a frame of the frames is stored in the storage unit and the frame in association with each other, and the transfer unit is configured to detect a period of time for which the frame stays in the storage unit, detect a remaining period to send which is a remaining time of a time for which the frame is permitted to stay in the storage unit, for each of the frames, based on a difference between the time for which the frame stays in the storage unit and the delay upper limit value, and output the frame to a predetermined apparatus based on the remaining period to send.

In the above-described transfer apparatus according to the aspect of the present disclosure, the storage unit is configured to store the frames in a queue for each of the networks, and the transfer unit is configured to detect the remaining period to send on the basis of a difference between a time for which a leading frame of the frames of the queue stays in the queue and the delay upper limit value, for each of the leading frames, and output the leading frame to a predetermined apparatus on the basis of the remaining period to send.

In the above-described transfer apparatus according to the aspect of the present disclosure, the transfer unit is configured to output the leading frame for which the remaining period to send is shortest to a predetermined apparatus.

In the above-described transfer apparatus according to the aspect of the present disclosure, the transfer unit is configured to output, in a case where the number of the leading frames for which the remaining period to send is shortest is plural, each of the leading frames to a predetermined apparatus in an order based on priority determined for the frames in advance.

In the above-described transfer apparatus according to the aspect of the present disclosure, the transfer unit is configured to detect, for the queue that is predetermined, a trigger time to send which is a time at which the leading frame stored in the queue predetermined is permitted to be output, and output the leading frame to a predetermined apparatus on or after the trigger time to send from each of the queues in which the trigger time to send is detected.

In the above-described transfer apparatus according to the aspect of the present disclosure, the transfer unit is configured to determine whether the frame for which the delay upper limit value is determined is stored in the storage unit, and output the leading frame belonging to a signal for which the delay upper limit value is not determined to a predetermined apparatus in a case where the frame for which the delay upper limit value is determined is not stored in the storage unit.

Another aspect of the invention is a transfer method executed by a transfer apparatus including a distribution unit, a storage unit, and a transfer unit, the transfer method including identifying, by the distribution unit, a plurality of networks to which frames acquired from the plurality of networks belong, distributing and storing the frames in the storage unit for each of the plurality of networks based on identification results, the plurality of networks being different from each other in a delay upper limit of each of the frames, storing, by the storage unit, information of a time at which a frame of the frames is stored in the storage unit and the frame in association with each other, and detecting, by the transfer unit, a period of time for which the frame stays in the storage unit, detecting a remaining period to send which is a remaining time of a time for which the frame is permitted to stay in the storage unit for each of the frames, based on a difference between the time for which the frame stays in the storage unit and the delay upper limit value, and outputting the frame to a predetermined apparatus based on the remaining period to send.

Still another aspect of the present disclosure is a transfer program for causing a computer to operate as the transfer apparatus described above.

Effects of the Invention

According to the present disclosure, it is possible to transfer a frame belonging to a signal having a low priority so as to satisfy a delay requirement.

