Content distribution system, cache server, and content distribution method

1. A content distribution system, comprising:

a distribution server that distributes content;

a packet forwarding apparatus that forwards a packet to be sent and received between the distribution server and a user terminal; and

a cache server connected to the packet forwarding apparatus,

wherein the cache server comprises:

a content temporary storage unit that temporarily stores at least some of the content;

a bit rate calculator that calculates a bit rate when the content is sent, based on a TCP (Transmission Control Protocol) response signal received from the user terminal;

an acquisition unit that searches for a file or stream of the content requested in a content request message received from the user terminal, a corresponding bit rate of the file or stream not being greater than the bit rate, from the content temporary storage unit or the distribution server, stores the file or the stream in a packet of a prescribed protocol, and sends the packet; and

a transmission unit that reads the packet from the acquisition unit and sends the packet to the packet forwarding apparatus,

the bit rate calculator measures a packet response time as difference between time at which a prescribed packet is transmitted from the transmission unit and time at which a TCP response signal to the prescribed packet is received from the user terminal, and calculates the bit rate based on the packet response time,

the bit rate is B,

the bit rate calculator calculates the bit rate B according to:

B =(1−α)× Bc +α×β×( Ta−T ), and

the packet response time is T, a prescribed target response time is Ta, a prescribed convergence factor is α, a prescribed conversion factor by which time change is converted to bit rate is β, and a previous packet transmission bit rate is Bc.

2. The content distribution system according to claim 1 , wherein the cache server is one of a plurality of cache servers,

the content distribution system further comprises a control apparatus that controls the plurality of cache servers,

the control apparatus determines screen resolution of the user terminal based on information included in the content request message received from the user terminal, determines the cache server holding the content of the screen resolution from among the plurality of cache servers, and instructs the cache server to distribute the content,

the acquisition unit searches for the file or stream of the content requested in the content request message, having the screen resolution and the corresponding bit rate, from the content temporary storage unit or the distribution server, stores the file or stream in the packet of the prescribed protocol, and

the transmission unit reads the packet from the acquisition unit and sends the packet to the packet forwarding apparatus.

3. The content distribution system according to claim 2 , wherein the control apparatus extracts an extracted plurality of cache servers that store the content of the screen resolution from among the plurality of cache servers, and selects the cache server from among the extracted plurality of cache servers in accordance with information concerning whether the user terminal is in a service area.

4. The content distribution system according to claim 2 , wherein the plurality of cache servers are a transparent or a fully transparent proxy server.

5. The content distribution system according to claim 1 , wherein the packet forwarding apparatuses are a SGSN (Serving General packet radio service Support Node) apparatus, a GGSN (Gateway General packet radio service Support Node) apparatus or an SGSN/GGSN apparatus in a mobile packet network, or an S-GW (Serving Gateway) apparatus, a P-GW (Packet data network Gateway) apparatus or an S/P-GW apparatus in a mobile LTE (Long Term Evolution)/EPC (Evolved Packet Core) network.

6. The content distribution system according to claim 1 , wherein the content comprises at least one of video, still images, speech, audio, software, applications and data.

7. A cache server connected to a packet forwarding apparatus that forwards a packet to be sent and received between a user terminal and a distribution server that distributes content, the cache server comprising:

a content temporary storage unit that temporarily stores at least some of the content;

a bit rate calculator that calculates a bit rate when the content is sent, based on a TCP (Transmission Control Protocol) response signal received from the user terminal;

an acquisition unit that searches for a file or stream of the content requested in a content request message received from the user terminal, a corresponding bit rate of the file or stream not being greater than the bit rate, from the content temporary storage unit or the distribution server, stores the file or stream in a packet of a prescribed protocol, and sends the packet; and

a transmission unit that reads the packet from the acquisition unit and sends the packet to the packet forwarding apparatus;

wherein the bit rate calculator measures a packet response time as difference between time at which a prescribed packet is transmitted from the transmission unit and time at which a TCP response signal to the prescribed packet is received from the user terminal, and calculates the bit rate based on the packet response time,

the bit rate is B,

the bit rate calculator calculates the bit rate B according to:

B =(1−α)× Bc +α×β×( Ta−T ), and

the packet response time is T, a prescribed target response time is Ta, a prescribed convergence factor is α, a prescribed conversion factor by which time change is converted to bit rate is β, and a previous packet transmission bit rate is Bc.

8. A content distribution method, comprising:

by a cache server connected to a packet forwarding apparatus that forwards a packet to be sent and received between a user terminal and a distribution server that distributes content, temporarily storing at least some of the content in a content temporary storage unit of the cache server;

calculating a bit rate when sending the content based on a TCP (Transmission Control Protocol) response signal received from the user terminal;

searching for a file or stream of the content requested in a content request message received from the user terminal, a corresponding bit rate of the file or stream not being greater than the bit rate, from the content temporary storage unit or the distribution server, storing the file or stream in a packet of a prescribed protocol, and sending the packet,

wherein the cache server measures a packet response time as difference between time at which a prescribed packet is transmitted from a transmission unit and time at which a TCP response signal to the prescribed packet is received from the user terminal, and calculates the bit rate based on the packet response time,

wherein the bit rate is B,

the bit rate B is calculated according to:

B =(1−α)×β+ a ×β×( Ta−T ), and

the packet response time is T, a prescribed target response time is Ta, a prescribed convergence factor is α, a prescribed conversion factor by which time change is converted to bit rate is β and a previous packet transmission bit rate is Bc.

9. The content distribution method according to claim 8 , wherein the cache server is one of a plurality of cache servers, and

the content distribution method further comprises:

by a control apparatus that controls at least one of a plurality of the cache servers, determining screen resolution of the user terminal, based on information included in the content request message received from the user terminal;

by the control apparatus, determining the cache server holding the content of the screen resolution from among the plurality of cache servers, and instructing the selected cache server to distribute the content; and

by the cache server that has received the instruction from the control apparatus among the plurality of cache servers, searching for the file or stream of the content requested in the content request message, having the screen resolution and the corresponding bit rate, from the content temporary storage unit or the distribution server, storing the file or stream in the packet of the prescribed protocol, and sending the packet.

10. The content distribution method according to claim 9 , comprising:

by the control apparatus, extracting an extracted plurality of cache servers that store the content of the screen resolution from among the plurality of cache servers, and selecting the cache server from among the extracted plurality of cache servers in accordance with information concerning whether the user terminal is in a service area.

11. The content distribution method according to claim 9 , wherein the plurality of cache servers are a transparent or a fully transparent proxy server.