JP6195785B2 - Communication device, server device, and program for storing transferred content - Google Patents

Description

  The present disclosure relates to a cache technology for content in a communication apparatus that has transferred content in a content distribution system.

  A network that routes content distribution request messages and distributes content based on the content name is proposed without the client device acquiring the content being aware of which server device stores the content to be acquired Has been. Patent Document 1 and Non-Patent Document 1 disclose a content-centric network (CCN) which is one of such networks.

JP 2009-277234 A

V. Jacobson, et al. , "Networking Named Content", in Proceedings of ACM CoNEXT 2009, December 2009

  In a content-centric network, a server device that publishes content divides the content into one or more segments, and a client device acquires content in segment units. In a content-centric network, a communication device (hereinafter referred to as an intermediate device) that has transferred a segment to a client device can store the segment. When the distribution request message of a certain segment is received from the client device, the segment held by the own device can be transmitted to the client device that is the transmission source of the distribution request message without transferring the distribution request message to the server device.

  Since the intermediate device holds the segment, the time until the client device receives the segment is shortened, and the network bandwidth consumed for the transfer of the segment can be reduced. In order to shorten the distribution time of the segment to the client device and to reduce the network bandwidth consumed for transferring the segment as much as possible, it is desirable that each intermediate device holds various segments of various contents. However, there is an upper limit on the storage capacity that the intermediate device can use to hold segments, and the number of segments that the intermediate device can hold is limited by this storage capacity. Therefore, it is desirable to select a segment to hold on some basis, rather than all the intermediate devices involved in the segment delivery holding the same segment. However, Patent Literature 1 and Non-Patent Literature 1 do not disclose anything about how the intermediate device determines a segment to be held.

  The present invention relates to a communication device that selects a segment to be effectively retained in a content distribution system in which content is divided into one or more segments and distributed, and the communication device can retain the transferred segment for subsequent distribution, The present invention provides a server device and a program for distributing content in a content distribution system.

  According to one aspect of the present invention, there is provided a communication device of a content distribution system that divides content into one or more segments for distribution, a holding unit that holds the segments, and a distribution request that indicates segments of the content that are not held When the message is received, the received distribution request message is transferred according to a predetermined criterion, and when the segment is received as a response to the transfer of the distribution request message, the received segment is directed to the transmission source of the distribution request message. And a communication unit that transfers the received segment, and a determination unit that determines whether or not to hold the received segment in the holding unit, the determination unit, after transferring the delivery request message indicating the segment, The segment is received as a response to the transfer of the delivery request message. Communication apparatus characterized by the round trip time of the segments is time to use the segment to determine whether to retain the holding means.

  The communication device can select a segment to hold effectively.

Explanatory drawing of a content centric network. 1 is a schematic configuration diagram of an intermediate device according to an embodiment. FIG. The figure which shows the data which the intermediate | middle apparatus by one Embodiment hold | maintains. The figure which shows the value set to the determination field by one Embodiment. The schematic block diagram of the server apparatus by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for describing the embodiment are omitted from the drawings. Moreover, the following embodiment is an illustration and does not limit this invention to the content of embodiment.

<First embodiment>
First, the outline of the content-centric network will be described with reference to FIG. A user who wants to publish content stores the content in the server device 1. The server device 1 divides the held public content into one or more segments, and notifies the other device of the content name held. The intermediate devices 21 and 22 responsible for content transfer create a routing table based on the content name from the content name notified by the server device 1. For example, it is assumed that the content desired to be acquired by the user of the client device 31 is held in the server device 1. At this time, when the user of the client apparatus 31 inputs the content name to be acquired to the client apparatus 31, the client apparatus 31 transmits an interest packet (distribution request message) including the input content name to the intermediate apparatus 21. To do. Since the client device 31 has not received any segment of the content corresponding to the input content name, the client device 31 includes the segment number “01” in the interest packet.

  The intermediate device 21 recognizes from the routing table that the server device 1 holds content corresponding to the content name included in the interest packet received from the client device 31, and sends this interest packet to the server device 1. Forward. The server device 1 that has received the interest packet from the client device 31 transmits the first segment of the content specified by the received interest packet to the intermediate device 21, and the intermediate device 21 has received from the server device 1. The segment is transmitted to the client device 31. Here, it is assumed that the intermediate device 21 can store the transferred segment, and in this example, stores it.

  The client device 31 transfers the interest packet including the input content name to the intermediate device 21 while incrementing the segment number by one, and the server device 1 receives the content name input from the server device 1 as described above. Receive the remaining segments. The last segment includes information indicating that it is the last segment, and the client device 31 recognizes that all segments of the content have been received based on this information. In this example, it is assumed that the intermediate device 21 holds all segments of the content requested by the client device 31.

  Thereafter, for example, when the client device 32 transmits an interest packet (the segment number includes “01”) for the same content acquired by the client device 31 to the intermediate device 22, the intermediate device 22 reads the routing table. The interest packet is transferred to the intermediate device 21 based on the above. Since the intermediate device 21 holds the segment of the content number 1 indicated by the received interest packet, the intermediate device 21 does not transfer the received interest packet to the server device 1 and does not transfer the content of the content held by itself. The segment of number 1 is transmitted to the intermediate device 22, and the intermediate device 22 transmits the received content to the client device 32. In this example, it is assumed that the intermediate device 22 stores the transferred content segment. Thereafter, the remaining segments are processed in the same manner, so that the intermediate device 22 also holds all the segments of the content by distributing the content to the client device 32. Thereafter, when the client device 33 requests acquisition of the same content that the client devices 31 and 32 have acquired, the client device 33 receives the content held by the intermediate device 22 from the intermediate device 22.

  FIG. 2 is a configuration diagram of the intermediate device 21 according to an embodiment. The configuration of the intermediate device 22 is the same as that of the intermediate device 21. When the communication unit 211 has a plurality of communication interfaces and receives a distribution request message indicating a segment of content from another device (client device or other intermediate device), the determination unit 212 receives the distribution request message. It is determined whether the holding unit 210 holds the segment to be shown. Here, when the holding unit 210 holds the segment, the communication unit 211 reads the segment from the holding unit 210 and transmits the segment to the transmission source device.

  On the other hand, when the holding unit 210 does not hold the segment, the communication unit 211 transfers the distribution request message received according to a predetermined determination criterion toward the server device 1. Note that the predetermined determination criterion is a criterion indicated by the routing table 213 in the present embodiment. At this time, the communication unit 211 stores, in the unprocessed table of the holding unit 210, a value indicating the segment specified in the distribution request message for the transferred distribution request message, an interface for transmitting a response to the distribution request message, Information indicating the transfer time of the delivery request message is added. FIG. 3B is an example of an unprocessed table. In FIG. 3B, the distribution request message requesting the second and third segments of the content named “Name2” is transferred to the server device 1 at time ta and tb, respectively, and the distribution request As a response to the message, when a segment is received from the server apparatus 1 or another intermediate apparatus, the received segment is output to the interface IF1 in order to distribute it to the apparatus that has transmitted the distribution request message.

  Note that when the distribution request message specifying the same segment as the distribution request message transferred to the server device 1 is received as a response to the already transferred distribution request message before receiving the segment, the communication unit 211 holds Information related to the delivery request message received later is added to the unprocessed table of the unit 210, but transfer to the server device 1 is not performed. In this case, since the delivery request message is not transferred, the transfer time field of the unprocessed table is left with a null value or a value indicating that no transfer is performed. Further, a plurality of values can be set in the transfer destination interface, and a distribution request message specifying the same segment as the distribution request message transferred to the server apparatus 1 is used as a response to the already transferred distribution request message. When the segment is received before the segment is received, the transfer destination interface for the delivery request message received later can be added to the entry for the segment in the unprocessed table. Specifically, in the state of FIG. 3B, when a distribution request message requesting the second segment of “Name2” is received and the transfer destination interface for this distribution request message is IF2, “Name2” It may be a form in which IF2 is added to the transfer destination interface of the entry corresponding to the second segment.

  When the communication unit 211 receives a segment as a response to the distribution request message transferred to the server device 1, the communication unit 211 transfers the segment according to the unprocessed table and deletes the entry of the unprocessed table related to the transferred segment. The determination unit 212 compares the round trip time of the received segment with a threshold value, and determines that the segment is not held when the round trip time is within the threshold value. Here, the round trip time is the difference between the transfer time of the distribution request message in the unprocessed table and the time when the segment is received as a response to the distribution request message. On the other hand, when the round-trip time of the received segment is larger than the threshold value, the determination unit 212 causes the holding unit 210 to hold the segment if the holding unit 210 has a free capacity to hold the segment.

  Based on the case where a client device acquires a segment from a certain communication device (server device or intermediate device), an intermediate device located on the path between the client device and the communication device holds the segment. In this case, the reduction amount of the acquisition time is equal to the round trip time of the segment in the intermediate device. Therefore, even if a segment with a small round trip time is held, the effect of reducing the segment acquisition time in the client device is small. On the other hand, holding a segment with a long round trip time can greatly reduce the segment acquisition time in the client device. Therefore, in the present embodiment, it is determined whether or not the segment is to be saved by comparing the round trip time with a threshold value.

  However, even if the round trip time of the received segment is larger than the threshold value, there is a case where there is no free capacity for holding the segment in the holding unit 210. In this case, the determination unit 212 determines whether to discard the received segment without saving it or to discard any of the segments held by the holding unit 210 and hold the received segment. For this determination, the holding unit 210 can hold, as an example, a management table as shown in FIG. 3A for managing the held segments. As shown in FIG. 3A, in this example, the management table includes information indicating the segment name held by the holding unit 210 and the round trip time of the segment. The management table can also include, for example, information (not shown) indicating the storage position of the segment.

  If the round-trip time of the received segment is larger than the threshold value, but the holding unit 210 does not have a free capacity for holding the segment, the determination unit 212 determines that the segment already held in the holding unit 210 and the newly received segment The disposal order is calculated from the above, and it is determined that the one with the highest disposal order is discarded. That is, when the segment with the highest discard order is already held in the holding unit 210, the communication unit 211 deletes the segment with the highest discard order from the holding unit 210 and holds the newly received segment. 210. When the segment with the highest discard order is a newly received segment, the communication unit 211 discards the received segment after transfer. Note that when the determination unit 212 adds or changes a segment to be held by the holding unit 210, the management table is also updated accordingly.

  For example, the discard order can be calculated based on the round trip time of each segment. In this case, the discard order is increased as the round trip time is shorter. Based on the case where a client device acquires a segment from an intermediate device, the amount of change in the acquisition time when the intermediate device does not hold the segment is the round trip time of the segment at the intermediate device. Will be equal. Therefore, even if a segment with a short round trip time is deleted, the influence on the time required to acquire the segment in the client device is small.

  Furthermore, the long round trip time of a segment means that the distance from the intermediate device to the intermediate device or server device that holds the segment is long, and this is due to the fact that it passes through many transmission sections. It means that there is a high possibility. Therefore, when a segment having a long round trip time is deleted, if a delivery request message indicating the segment is received later, a large amount of network resources are consumed by forwarding the delivery request message and receiving the subsequent segment. Become. Therefore, the network usage efficiency can be improved by deleting the segment with the short round trip time first.

  In addition to or instead of the round trip time of each segment, the discard order can be calculated in consideration of the segment request frequency. In this case, the lower the land trip time, the higher the discard order, and the smaller the content request frequency, the higher the discard order. For example, the discard order can be calculated based on a value obtained by multiplying the round trip time and the content request frequency. Note that the request frequency can be the average number of requests in the past predetermined period, the cumulative number of requests since the segment is held, or the number of requests in each predetermined period. Further, weighting can be performed with a weighting coefficient that decreases as the time from the present time to the time requested in the past increases. Since the request frequency of the newly received segment is 0 or a small value, when using the request frequency, the newly received segment can always be saved as a target for calculating the discard order. Furthermore, the request frequency of the newly received segment can be a predetermined value other than 0, for example, a value based on the request frequency of the already held segment, for example, an average value, a minimum value, or a maximum value.

  As described above, each intermediate device determines the round trip time of the segment and compares the round trip time with a threshold value to determine whether or not the segment is a storage target. With this configuration, it is possible to prevent the same segment from being unnecessarily held by many intermediate devices while shortening the time required for distribution to the client device 1. As a method for determining the threshold value, the administrator of the intermediate apparatus can set a value in advance. Moreover, it can be a value calculated using the average value, median value, minimum value, maximum value, etc. of the round trip times of all the segments held by the holding unit 210 indicated by the management table. Furthermore, instead of the segments held by the holding unit 210, the values calculated using the average value, median value, minimum value, maximum value, etc. of the round trip times of the predetermined number of segments transferred most recently can also be used.

  In the above embodiment, it is determined that the data is not stored when the round trip time is equal to or less than the threshold. However, the round trip time may be determined in combination with other conditions. In other words, the fact that the round trip time is equal to or less than the threshold is one of the conditions for determining that the data is not stored, and it is determined that the data is not stored when the round trip time is equal to or less than the threshold and other conditions are satisfied. Other than that, it may be determined to be a storage target. Further, in the above embodiment, when the round trip time is larger than the threshold, it is determined that the round trip time is to be held, and if the holding unit 210 has a free space, the holding unit 210 holds it. However, other conditions other than the round trip time can be used in combination. In other words, the fact that the round trip time is larger than the threshold value is one of the conditions for determining that the data is to be stored, and if the round trip time is larger than the threshold value and other conditions are satisfied, it is determined that the data is to be stored. The other configuration may be determined not to store.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. For example, when many intermediate devices are involved in segment transfer and the threshold for determining whether or not to save is the same in all intermediate devices, the intermediate device involved in segment transfer is the same in the configuration of the first embodiment. Of these, all intermediate devices on the client device side from a certain intermediate device have the segment as a storage target. That is, when all intermediate devices on the client device side from a certain intermediate device can hold the segment, all the intermediate devices hold the same segment. This embodiment prevents such a state.

  For this reason, in this embodiment, the determination field is provided in the header area of the signal including the segment to be distributed. Then, the server device or the intermediate device that transmits the saved segment to the client device sets the value “0” in the determination field and transmits the segment. If the intermediate device that transfers the received segment does not store the received segment, the intermediate device transfers the received segment without changing the value of the determination field. On the other hand, when storing the segment to be transferred, the intermediate device sets the round trip time of the segment in its own device in the determination field and transfers it.

  Hereinafter, the processing in this embodiment will be described with reference to FIG. In FIG. 4, only the intermediate device 24 holds the segment requested by the client device 31, and the intermediate device 24 transmits the requested segment, and this segment is stored in the intermediate device 23, 22, 21. It is assumed that they are transferred in order and delivered to the client device 31. In addition, the transfer delay between the devices is “t” for simplicity, and the processing time in each device can be ignored. Accordingly, the round trip times of the segments in the intermediate devices 21, 22, and 23 are “6t”, “4t”, and “2t”, as shown below the corresponding devices in FIG. In addition, the threshold used for determining whether or not to store a segment is set to “3t” for each intermediate device.

  The intermediate device 24 sets the value “0” in the determination field and transmits the segment to the intermediate device 23. In FIG. 4, the numbers of arrows between the devices indicate values set in the determination field. The intermediate device 23 subtracts the value set in the determination field from the round trip time of the segment, and determines that the received segment is not stored when the value is equal to or less than the threshold value. Since the value obtained by subtracting the value of the determination field from the round trip time in the intermediate device 23 is “2t”, which is equal to or less than the threshold value “3t”, the intermediate device 23 determines not to store the received segment. Since the intermediate device 23 does not store the received segment, the intermediate device 23 transfers the received segment to the intermediate device 22 without changing the determination field.

  A value obtained by subtracting the value of the determination field from the round trip time in the intermediate device 22 is “4t”, which is larger than the threshold value “3t”. Accordingly, the intermediate device 22 determines that the received segment is a storage target, and stores the received segment when the holding unit 210 has a free space. Here, it is assumed that the intermediate device 22 stores the received segment. In this case, the intermediate device 22 sets “4t”, which is the round trip time in the own device, in the determination field, and transfers the received segment. If the received segment is not saved because the holding unit 210 has no free space or the like, the received segment is transferred without changing the determination field.

  A value obtained by subtracting the value of the determination field from the round trip time in the intermediate device 21 is “2t”, which is equal to or less than the threshold value “3t”. Therefore, the intermediate device 21 determines not to store the received segment.

  FIG. 5 is a configuration diagram of the server apparatus according to the present embodiment. The holding unit 110 holds the content to be distributed by dividing it into one or more segments. When receiving the distribution request message indicating the content segment, the communication unit 111 sets a value indicating 0 in the determination field of the signal including the segment, and transmits the value to the transmission source of the distribution request message. The configuration of the intermediate device is as shown in FIG. 2, and in this embodiment, the determination unit 212 determines whether to save the segment by the method described above, and when the segment is stored, the communication unit 211 transfers the segment. The round trip time of the segment in the intermediate device is set in the determination field of the signal including the segment. If not stored, the communication unit 211 does not change the value of the determination field of the signal including the segment to be transferred. In the above embodiment, the round trip time is set in the determination field. However, the round trip time may be set or a value capable of calculating the round trip time may be set.

  With the above configuration, it is possible to prevent the same segment from being redundantly stored in intermediate devices located close to each other in the network, thereby reducing the time until the client device receives the segment and transferring the segment. It is possible to reduce the bandwidth of the consumed network.

  The intermediate device 21 and the server device 1 according to the present invention can be realized by programs that cause a computer to operate as the intermediate device 21 and the server device 1, respectively. These computer programs can be stored in a computer-readable storage medium or distributed via a network.

Claims (13)

A communication device of a content distribution system that distributes content into one or more segments,
Holding means for holding the segment;
When a distribution request message indicating a segment of content that is not held is received, the received distribution request message is transferred according to a predetermined criterion, and when the segment is received as a response to the transfer of the distribution request message, the received A communication means for transferring a segment toward a transmission source of the delivery request message;
Determining means for determining whether or not to hold the received segment in the holding means;
With
The determination means determines the round trip time of the segment, which is the time from when the distribution request message indicating the segment is transferred to when the segment is received as a response to the transfer of the distribution request message. A communication apparatus used for determining whether or not to hold a holding means.   The communication apparatus according to claim 1, wherein the determination unit determines that the round trip time of a segment is greater than a threshold as one of the conditions for determining that the holding unit holds the segment.   2. The communication apparatus according to claim 1, wherein the determination unit determines that the round trip time of a segment is equal to or less than a threshold as one of the conditions for determining that the segment is not held by the holding unit.   The determination means uses a difference between a round trip time of a segment and a value based on a setting value of a determination field of a signal including the received segment for determining whether or not the holding means holds the segment. The communication apparatus according to claim 1.   The communication apparatus according to claim 4, wherein the determination unit determines that the difference with respect to the received segment is greater than a threshold as one of the conditions for determining that the holding unit holds the segment.   5. The communication apparatus according to claim 4, wherein the determination unit determines that the difference regarding the received segment is equal to or less than a threshold is one of the conditions for determining that the segment is not held by the holding unit.   The value based on the setting value of the determination field of the signal including the received segment has one or more other communication devices that hold the segment when the segment is transferred on the upstream side of the communication device. 7. The round trip time at a communication device closest to the communication device among the one or more other communication devices is indicated. 7. Communication device.   When the determination unit determines that the holding unit holds the segment received as a response to the transfer of the delivery request message, the communication unit directs the received segment to the transmission source of the delivery request message. 8. The communication device according to claim 4, wherein, when transferring, a value corresponding to the round trip time is set in a determination field of a signal including the received segment. 9.   When the determination unit determines that the holding unit does not hold the segment received as a response to the transfer of the delivery request message, the communication unit directs the received segment to the transmission source of the delivery request message. 9. The communication device according to claim 4, wherein a setting value of a determination field of a signal including the received segment is not changed when transferring. 9.   When the communication means receives the distribution request message indicating the segment of the content held, the communication means sets a value indicating that the round trip time is 0 in the determination field of the signal including the segment, and sets the value of the distribution request message. The communication apparatus according to claim 4, wherein transmission is performed toward a transmission source.   A program that causes a computer to function as the communication device according to claim 1. A server device of a content distribution system that distributes content by dividing it into one or more segments,
Holding means for holding the segment;
A communication unit that, upon receiving a distribution request message indicating a segment held by the holding unit, sets a value indicating 0 in a determination field of a signal including the segment and transmits the value to a transmission source of the distribution request message;
With
When the communication device that transfers the segment holds the segment, the determination field includes a response indicating that the communication device has transferred the distribution request message after transferring the distribution request message indicating the segment. A server apparatus used for setting a value indicating a round trip time until a segment is received.   A program for causing a computer to function as the server device according to claim 12.

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