JP2004348494A - Content distribution network - Google Patents

Abstract

An object of the present invention is to provide a high-quality content distribution service to each user terminal in an environment in which a communication band between a content server and a user terminal greatly differs for each user.
A network management / control system holds a line bandwidth value of an access line notified from an access server accommodating a user terminal as a bandwidth value usable by the user terminal, and edits the bandwidth value in accordance with a plurality of communication bands. When a content server that holds a plurality of contents receives a content distribution request from a user terminal, the network management / control system queries the available bandwidth value for the user terminal to obtain a communication bandwidth equal to or less than the bandwidth value. A content distribution network that selects and distributes content appropriate for the user, and distributes the optimal content to user terminals.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a content distribution network, and more particularly, to a method of monitoring a communication band available to a user, selecting and distributing an optimum content according to the available communication band, and a method of performing load distribution. About.
[0002]
[Prior art]
The content distribution network is a network having a mechanism for delivering a large amount of content to a user with high quality. In order to deliver large-capacity content with high quality, generally, network construction for exclusive use of content distribution is performed to increase the bandwidth of the network, and load distribution is performed by distributing a plurality of content servers.
With the development of content distribution networks and the spread of broadband access services, it has become possible to deliver large amounts of content to users with high quality. However, in a broadband access service, the bandwidth of an access line may be significantly different for each user. For example, the communication band of a DSL (Digital Subscriber Line) service varies from several hundred Kbps to several tens of Mbps depending on physical line conditions. Also, even during the period of widespread use of broadband access services, there are users who use narrow-band access lines such as existing telephone networks and wireless services such as mobile phones.
In such a situation, the access line becomes a bottleneck and some users cannot receive high-quality services. For example, when a streaming content distribution service that requires a wide bandwidth is provided in anticipation of the spread of a content distribution network and broadband access, a user connected by an access line that does not have a bandwidth required by the content will increase the service. We cannot receive with quality. Therefore, in a content distribution network using various access lines, it is desirable to select and distribute content for each user in consideration of the bandwidth value of the access line. For example, if a plurality of streaming contents encoded for a plurality of communication bands are prepared, and the content is selected and distributed according to the bandwidth value of the access line of the user terminal or the communication state between the content server and the user terminal, each user can be provided with the content. Provides optimal content distribution services.
Up to now, a content distribution service for selecting and distributing content for each user by using position information and attribute information of the user has been put to practical use. Here, the content is selected using the IP address of the user terminal and the information included in the HTTP (Hyper Text Transfer Protocol) header. For example, in a content distribution service such as AKAMAI, a user-dependent content selection in a content server is realized by providing a database having correspondence information between a user terminal IP address and a user attribute to a content server operator. . As the user attribute information, an access line type, a provider name, and an actually measured throughput are used. However, even with this method, it is difficult to actually measure the throughput including the access line that is dynamically connected and disconnected. (1) It is not possible to select the content using the actual bandwidth value of the access line. Is an issue.
[0003]
In addition, an increase in traffic may cause a content server or a network node in the content distribution network to become a bottleneck. To cope with this, load distribution is performed by distributing a plurality of content servers in a network, selecting and assigning different content servers for each user. For example, in a content distribution service of AKAMAI, when a user requests a DNS (Domain Name System) server to convert an IP address of a host name, the DNS server transmits the IP address of a content server close to the user or the user and the content. By answering the IP address of a content server having a low load on the network path between the servers, a different content server is allocated to each user, and the load is distributed. Here, the load status on the network path between the user and the content server is confirmed by transmitting a ping packet or the like to the content server from some selected points in the network and measuring the response time. ing.
However, simply distributing the load distribution can (2) maintain the quality of the content distribution service if the required communication bandwidth cannot be secured even if the load on the entire network increases or the content server with a low load is selected. Not doing so is a problem.
[0004]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention is to solve the problems of the prior art: (1) the inability to select content using the actual bandwidth value of the access line; and (2) when the load on the entire network increases, the content server and the network with low load It is to solve the problem that even if a node is selected, the quality of the content distribution service cannot be maintained.
[0005]
First, in order to solve the problem (1), in the content distribution network of the present invention, the access server accommodating the user terminal transmits the network bandwidth value of the access line connecting the user terminal and the access server and the identification information of the user terminal to the network. Notify the management and control system. Here, the network management / control system is a device that has a network management server function such as SNMP and monitors and controls the network and the content server. The network management / control system uses the line bandwidth value notified from the access server and the identification information of the user terminal. It has a function to associate and hold. Here, the line bandwidth value is defined as “available bandwidth value” for the content distribution from the content server by the user terminal indicated by the user terminal identifier. Then, when the content server holds a plurality of contents edited according to a plurality of communication bands and receives a content distribution request from the user terminal, the network management / control system informs the network management / control system of the “available bandwidth value of the user terminal”. And selects and distributes a content suitable for a communication band equal to or less than the band value.
[0006]
Next, in order to solve the problem (2), in the content distribution network of the present invention, the network management / control system determines the load status of each content server and the network node on the route between the plurality of content servers and the user terminal. The line usage rate and the packet discard rate are monitored periodically, and if these values exceed a predetermined threshold, the user terminal held by the network management / control system uses the "terminal" for content distribution from the content server. Reduce the "possible bandwidth values". The threshold is determined by evaluating the service measurement quality as a value that does not degrade the service quality. When there are a plurality of content servers, the network management / control system determines the "available bandwidth value" between each content server and the terminal, reflecting the load of the access server, the load of the network node, and the bandwidth value of the access line. Will be retained. In the present invention, each terminal performs load distribution in a network by using a content server having the largest “available bandwidth value”. Further, when the content server selects and distributes the content using the “available bandwidth value” as in the case of the problem solving method of (1), if the load on the entire network increases, the load state is reduced. Suitable content is selected and distributed. As a result, when the load on the entire network increases and the effect of load distribution cannot be obtained, the distribution content is distributed to a content suitable for a lower bandwidth, and the degradation of service quality can be reduced.
[0007]
The assignment of the content server to each terminal is performed by any of the following methods. (A) A DNS server that translates a host name and an IP address of a content server inquires a network management / control system at the time of processing a name resolution request from a user terminal, recognizes an appropriate content server, and recognizes the IP of the content server. A method of notifying an address to a user terminal. (B) A method in which an access server has an address conversion function and converts a packet including a content distribution request from a user terminal to a content server into a packet addressed to an appropriate content server. (C) A method in which the access server has a packet encapsulation function and encapsulates a packet including a content distribution request from a user terminal to a content server into a packet addressed to an appropriate content server.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
FIG. 1 is a schematic diagram of a content distribution network of the present invention. The content distribution network 1 of the present invention includes a plurality of network nodes (routers or switches) 11a to 11c, user terminals 5a to 5d, access servers 4a and 4b accommodating user terminals, a network management / control system 2, and a content server. 3. In the content distribution network 1 of the present invention, the network management / control system 2 manages and controls the status of the access server, the network node, and the content server in the content distribution network 1 so as to optimize the user terminal. Distribute content.
[0010]
FIG. 2 is a schematic configuration diagram of the network management / control system 2 of the present invention. The network management / control system 2 includes an AAA (Authentication, Authorization, and Accounting) server function such as a TCP / UDP communication function 25 and a RADIUS server function 23, a network management server function such as an SNMP server function 26, a request transmission / reception function 27, and a connection state. The monitoring function 24 is configured. These functions are realized by software on one or more computers. When the functions are realized by a plurality of computers, each function is arranged on a different computer, and the functions are connected using a TCP, a UDP communication function, or the like.
[0011]
FIG. 3 is a schematic configuration diagram of the access servers 4a and 4b. The network node includes a packet switch unit 41, a node control unit 42, and various line units such as a DSL line accommodation unit 43, a Dial Up line accommodation unit 44, a wireless line accommodation unit 45, and a WAN line accommodation unit 47. Further, in the embodiment described later, since the address conversion function and the packet encapsulation function are used, an address conversion and packet encapsulation function section 46 is provided between the packet switch section 41 and the WAN line section 47. The node control unit 42 also has a RADIUS client function 421 for notifying the RADIUS server function 23 of the network management / control system 2 of a user ID, a password, and a connection line bandwidth value, and a connection for monitoring the connection state and the line bandwidth of the line unit. It has a monitoring function 422. When the user terminal connects to the access server, or when the connection line band between the user terminal and the access server changes, the connection monitoring function 422 transmits the user ID, the password, and the connection line band via the RADIUS client function 421. The value is notified to the network management / control system 2.
The RADIUS server function 23 of the network management / control system 2 has a user registration information table 21 shown in FIG. The user registration information table 21 has an entry including a user ID, a password, and subscription service information. The RADIUS server function 23 authenticates the user terminal by confirming the correspondence between the user ID and password notified from the access server and the user ID and password in the user registration information table 21, determines whether connection is possible, and determines the result. Notify the access server. When the connection is possible, the IP address to be assigned to the user terminal is notified at the same time. Further, when the subscription service information in the user registration information table 21 corresponding to the user ID of the connected user terminal indicates the SLA guarantee, the RADIUS server function 23 stores the user ID, the IP address assigned to the user terminal, and the connection line band value. To the connection status monitoring function 24.
[0012]
The connection state monitoring function 24 holds the user connection state information table 22 shown in FIG. The user connection status information table 22 has entries including a user ID, an IP address of a user terminal, and an available bandwidth value. The connection status monitoring function 24 sets the user ID and IP address passed from the RADIUS server function 23 as the user ID and IP address of the user connection status information table 22. Also, the connection line bandwidth value is set as the available bandwidth value.
In the content distribution network, in order to perform high-quality content distribution, it is required that the content distribution network of the content distribution network maintain sufficient capacity of the content server and the network node in response to a user's content distribution request. On the other hand, the connection line between the access server and the user terminal is, specifically, a DSL line, a dial-up line, a wireless line, or the like, and the communication band is determined by a data transmission technology to be used, a communication environment, contract conditions, and the like. Therefore, the connection line band value differs for each user. For this reason, the upper limit of the communicable band value that can be used by the user terminal is the connection line band value which is the connection line band value between the access server and the user terminal, and greatly differs between the user terminals. Therefore, in order to perform optimal content distribution for each user, it is effective to perform content selection and distribution using the connection line bandwidth value. In the present invention, as described above, the network management / control system holds the connection line bandwidth value as the available bandwidth value. Then, using this available bandwidth value, the most appropriate content is selected and distributed to each user.
[0013]
FIG. 6 is a schematic diagram showing an embodiment of the content distribution system of the present invention. Here, an example is shown in which the user terminal 5d makes a content distribution request to the content server 3. First, the user terminal 5d transmits a content distribution request to the content server 3. Upon receiving the content distribution request, the content server 3 transmits a reference request for the user status information table 22 to the network management control system 2. The reference request includes the user ID or the IP address of the user terminal as the identification information of the user terminal 5d. The connection status monitoring function 24 of the network management / control system 2 receives the reference request using the TCP / UDP communication function 25 and the request transmission / reception function 27, and uses the user ID or IP address of the user terminal as a key to set the user connection status information table. With reference to 22, the available bandwidth is returned to the content server 3.
The content server 3 selects the content using the available bandwidth value and distributes the content to the user terminal 5d. For example, a plurality of contents (31, 32) in which the same moving picture information is encoded at different bit rates are prepared, and the content having the maximum bit rate that satisfies the condition not more than the available bandwidth value of the terminal 5d is selected and distributed. As a result, optimal services can be provided to each user terminal.
As described above, in the content distribution network, in order to distribute high-quality content to each user, it is necessary to keep sufficient capacity of network nodes and content servers in the content distribution network in response to a user's content distribution request. desirable. However, the increase in content servers or network nodes cannot keep up with the increase in content distribution requests, and these may cause service quality degradation. For example, when the line utilization rate of the network node increases, the delay of all communication between the content server and the user terminal passing through the line increases, and the quality of service for many users decreases. When the packet loss rate increases, the user terminal cannot normally view the received content.
Therefore, in the content distribution network 1 of the present invention, the connection status monitoring function 24 uses the SNMP server function 26 to execute the load status such as the CPU usage rate of the content server of the content distribution network 1, the line usage rate of the network node, and the buffer. Periodically monitor the packet loss rate due to overflow. In order to provide high-quality services to the user terminals, it is only necessary to deliver contents within an allowable range that can suppress the load on the content server, the line utilization rate of the network node, and the packet loss rate. Therefore, when these values exceed a certain threshold, the available bandwidth value of the content server or the user terminal related to the corresponding network node is reduced. The threshold is determined by evaluating the service measurement quality as a value that does not degrade the service quality.
[0014]
FIG. 7 shows an example of monitoring the network nodes 11a and 11c and the access server 4a on the route relating to the content server 3 and the user terminal 5a. The network management / control system 2 uses the SNMP server function 26 to monitor the load status such as the CPU usage rate of the content server 3, the line usage rates of the network nodes 11a and 11c, and the access server 4a, and the packet loss rate. When the load on the content server 3 or the utilization rate of the lines 12a, 12b, 12c or the packet loss rate exceeds the threshold, the user terminal 5a held by the connection state monitoring function 24 of the network management / control system 2 By reducing the available bandwidth value of, the amount of content delivered to the user terminal 5a is reduced, and the service quality is prevented from deteriorating.
[0015]
FIG. 8 is a schematic diagram showing an embodiment of the present invention in which a plurality of content servers 3a and 3b are installed. In the content distribution network of the present invention, when there are a plurality of content servers, by associating a user terminal with a content server having a low load, or a content server having a low load on a network node on a route between the content server and the user terminal, Higher quality content distribution to user terminals.
FIG. 9 is a user connection state information table 29 used by the connection state monitoring function 24 of the network management control system 2 in the present embodiment. The user connection status information table 29 has entries including a user ID, an IP address of a user terminal, a host name of a content server, an IP address of a content server, and an available bandwidth value. The user connection state information table 29 holds available bandwidth values for each of a plurality of content servers for each user terminal. For example, in FIG. 9, the content server having the host name server1 is composed of two servers having IP addresses 192.168.0.1 and 192.168.1.1, and the content server having the host name server2 is provided. The server is composed of two servers having IP addresses 192.168.0.1 and 192.168.1.1.
Also in this embodiment, the network management / control system 2 periodically monitors the load state of the content server, the line utilization rate of the network node, and the packet loss rate due to buffer overflow, as in the above-described embodiment. Then, when these values exceed a certain threshold, the available bandwidth value of the user terminal related to the corresponding network node or the content server is reduced. Therefore, the available bandwidth value for the entity of the content server with a low load or the entity of the content server with a small delay on the route and the packet discard rate becomes larger than the entity of the content server with no other. For example, FIG. 9 shows that the load of the entity of the content server having the IP address 192.168.1.1 is low with respect to the content server having the host name server1.
[0016]
In the present embodiment, the load in the network is distributed by associating each terminal with the content server having the maximum available bandwidth value. For example, in FIG. 9, the user ID is abc @ xyz. com requesting content distribution from the content server 1, the available bandwidth from the content server having the IP address 192.168.0.1 and the content server having the IP address 192.168.1.1 The IP address 192.168.1.1 having a large value is selected and associated with the user terminal. The method of associating the user terminal with the content server will be described later.
In this embodiment, as in the above-described embodiment, the content server selects and distributes the content according to the load state of the network using the available bandwidth value. Therefore, even if the bottleneck of content distribution from all content servers is not the access line but the content server or network node in the content distribution network, the content suitable for the load state is selected and distributed. Therefore, the deterioration of service quality can be reduced.
The method of associating the user terminal with the content server is a method using DNS and a method using an address translation function. There is a method using a packet encapsulation function.
First, a method using DNS will be described. FIG. 8 is a schematic diagram showing an embodiment of the present invention using DNS. In the present embodiment, when the user terminal uses the DNS server 6 to convert the host name of the content server into an IP address, the DNS server 6 notifies the user terminal of the appropriate IP address of the content server. Associate the terminal with the content server. There are the following two methods for converting the host name of the content server into the IP address by the DNS server 6.
The first method is a method in which the DNS server 6 makes an inquiry to the network management / control system 2. The DNS server 6 that has received the request to convert the host name of the content server into the IP address from the user terminal sends the request to convert the host name to the IP address together with the IP address of the user terminal to the network control / management system 2. The connection status monitoring function 24, which has received the conversion request via the TCP / UDP communication function 25 and the request transmission / reception function 27, uses the connection status management table 29 to transmit the notified content regarding the IP address of the notified user terminal. The IP address of the content server having the host name of the server and having the maximum available bandwidth is selected and answered to the DNS server 6. Then, the DNS server 6 returns this IP address to the user terminal.
[0017]
The second method is a method in which the network management / control system 2 sets correspondence information between the host name and the IP address held by the DNS server 6. When the available bandwidth value is set or changed, the connection status monitoring function 24 of the network management / control system 2 determines the IP address of the content server having the largest available bandwidth value from a plurality of content servers having a certain host name. Is set, and the IP address is set in the DNS server 6 as the IP address of the content server having the host name. In this case, the DNS server 6 has a name resolution information table 61 shown in FIG. The name resolution information table 61 has entries including the IP address of the user terminal, the host name of the content server, and the IP address of the content server. Using the name resolution information table 61, the DNS server 6 converts the host name of the content server into an IP address in consideration of the user terminal that has transmitted the inquiry request.
[0018]
Next, a method of associating a user terminal with a content server using the address conversion function of the access servers 4a and 4b will be described. FIG. 11 shows that the network management / control system 2 sets the address translation function of the access server 4b and sends a content distribution request from the user terminal 5d to the content server 3a (IP address 192.168.0.1). (IP address 192.168.1.1). Specifically, the access server converts the destination IP address 192.168.0.1 of the IP packet 91 including the content distribution request transmitted from the user terminal 5d into the destination address 192.168.1.1, and transmits the content distribution request. Is transferred to the content server 3b as an IP packet 92 containing Also, the IP packet 93 containing the distribution content from the content server 3b has the sender address 192.168.1.1, but the access server converts this to 192.168.0.1 and converts the distribution content to 192.168.0.1. The packet is transferred to the terminal 5d as the IP packet 94 including the packet. The IP address 192.168.0.1 used by the user terminal 5d as the IP address of the content server is an IP address notified by the DNS server 6 or the like as the IP address of the content server regardless of the load state of the network. .
[0019]
The address conversion function of the access server according to the present embodiment is set by the network management / control system 2. The connection status monitoring function 24 of the network management / control system 2 obtains an appropriate IP address of the content server by using the user connection status information table 29 when the user terminal 5d connects to the access server. Then, an address translation function of the access server 4b is set via the request transmission / reception function 27 and the TCP / UDP communication function 25.
Next, a method of associating a user terminal with a content server using the encapsulation function of the access servers 4a and 4b will be described. FIG. 12 shows that the network management / control system 2 sets the encapsulation function of the access server 4b and sends a content distribution request from the user terminal 5d to the content server 3a (IP address 192.168.0.1). (IP address 192.168.1.1). More specifically, an IP packet 91 having a destination IP address of 192.168.0.1 including a content distribution request transmitted by the user terminal 5d is an IP packet having a destination address of 192.168.1.1. It is encapsulated and transferred to the content server 3b as an IP packet 92 containing a content distribution request. Further, the IP packet 93 including the distribution content from the content server 3b is encapsulated in the IP packet having the sender address 192.168.1.1, but the access server decapsulates the transmission packet including the distribution content. Is transferred to the terminal 5d as an IP packet 94 having a user address of 192.168.0.1. Here, the IP address 192.168.0.1 used as the IP address of the content server by the user terminal 5d is notified by the DNS server 6 or the like as the IP address of the content server irrespective of the load state of the network. Address.
[0020]
The encapsulation function of the access server according to the present embodiment is set by the network management / control system 2. The connection status monitoring function 24 of the network management / control system 2 obtains an appropriate IP address of the content server by using the user connection status information table 29 when the user terminal 5d connects to the access server. Then, the encapsulation function of the access server 4b is set via the request transmission / reception function 27 and the TCP / UDP communication function 25.
As described above, the encapsulation method using an IP packet has been described as an encapsulation method. In addition, the encapsulation method using an MPLS frame is also possible.
[0021]
【The invention's effect】
As described above, according to the present invention, by selecting content and distributing the load according to the bandwidth value of the access line, the load of the content server, and the load of the network node, the user terminal can be highly evaluated. It is possible to provide quality content distribution services.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of the configuration of a content distribution network according to the present invention.
FIG. 2 is a schematic configuration diagram of a network management / control system used in the present invention.
FIG. 3 is a schematic configuration diagram of an access server used in the present invention.
FIG. 4 is a user information registration table held by the network management / control system.
FIG. 5 is a user connection status information table held by the network management / control system.
FIG. 6 is a schematic diagram showing an example of processing of the configuration of the content distribution network of the present invention.
FIG. 7 is a diagram showing network monitoring by the network management / control system.
FIG. 8 is a schematic diagram showing an example of the configuration of a content distribution network that performs load distribution by DNS.
FIG. 9 is a user connection status information table when there are a plurality of content servers.
FIG. 10 is a name resolution information table of a DNS server used in the present invention.
FIG. 11 is a schematic diagram showing an example of a configuration of a content distribution network that performs load distribution by an address translation function.
FIG. 12 is a schematic diagram illustrating an example of a configuration of a content distribution network that performs load distribution by a tunnel function.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Content distribution network, 11a, 11b, 11c ... Network node, 2 ... Network management / control system, 3, 3a, 3b ... Content server, 4a, 4b ... Access server, 5a-5d ... User terminal, 21 ... User information Registration table, 22: User information registration table.

Claims (8)

A content distribution network configured by a content server that distributes content to user terminals, a plurality of access servers that accommodates a plurality of user terminals in a network, a plurality of network nodes, and a network management and control system,
The access server has a function of notifying the network management / control system of a line bandwidth value of an access line connecting the user terminal and the access server and identification information of the user terminal,
The network management / control system retains the line bandwidth value notified from the access server as an available bandwidth value available between the user terminal indicated by the identification information of the user terminal and the content server, and makes an inquiry from the content server. In response, it has the function of notifying the available bandwidth value to the content server,
When the content server holds a plurality of contents edited according to a plurality of communication bands and receives a content distribution request from a user terminal, the network management / control system inquires an available band value of the user terminal, When the available bandwidth value is received from the network management / control system, it selects the content suitable for the communication bandwidth equal to or less than the available bandwidth value and distributes it to the user terminal. A content distribution network characterized by distribution. 2. The content distribution network according to claim 1, wherein the access server monitors a change in a line bandwidth of an access line connecting the access server and the user terminal, and when the line band of the access line changes, the changed line. It has the function of notifying the bandwidth value to the network management / control function,
The network management / control system has a function of updating an available bandwidth value based on a bandwidth value notified from an access server, thereby performing content distribution according to a change in a bandwidth value of an access line. Content distribution network. 3. The content distribution network according to claim 2, wherein the network management / control system periodically measures a load state of the content server and a utilization rate and a packet loss rate of each line of the plurality of network nodes. If the load on the content server exceeds a predetermined threshold, the available bandwidth of the user terminal receiving the content distribution from the content server is reduced, and the line utilization rate of the network node or the network node If the packet loss rate exceeds a predetermined threshold, the content distribution amount is reduced by reducing the available bandwidth value of the user terminal having the corresponding network node on the content distribution path from the content server, According to the load status of the distribution network Content delivery network which is characterized in that the content delivery. 3. The content distribution network according to claim 2, wherein the content server has a function of notifying a load state of the content server to the network management / control system, and the plurality of network nodes determine a line utilization rate of the network node. 4. Has a function of notifying the network management and control system of the packet loss rate,
When the notified load of the content server exceeds a predetermined threshold, the network management / control system reduces the available bandwidth value of the user terminal receiving the content distribution from the content server, and When the usage rate or the packet loss rate of the network node exceeds a predetermined threshold, the content distribution is performed by reducing the available bandwidth value of the user terminal having the relevant network node on the content distribution route from the content server. A content distribution network wherein the content is reduced and the content is distributed according to the load state of the content distribution network. The content distribution network according to claim 3, further comprising a plurality of content servers having the same host name, further comprising a DNS server function in the content distribution network,
The network management / control system holds, for each user terminal, an available bandwidth value and an address of the content server for each of the user terminal and the plurality of content servers, and the host name of the content server together with the identification information of the user terminal from the DNS server. A function of receiving the address of the content server having the largest available bandwidth value among the plurality of content servers with respect to the user terminal,
When the DNS server receives a conversion request from the user terminal to the address of the host name of the content server, the DNS server obtains the address of the content server having the largest available bandwidth value by querying the network management and control system, and obtains the address. A content distribution network having a function of notifying the user terminal of the content distribution, thereby performing load distribution in consideration of a load state of the content distribution network. The content distribution network according to claim 3, further comprising a plurality of content servers having the same host name, further comprising a DNS server function in the content distribution network,
The network management / control system holds, for each user terminal, an available bandwidth value and an address of the content server for each of the user terminal and the plurality of content servers, and for each user terminal, a host name and an available bandwidth value of the content server. Has the function of notifying the DNS server of the address of the content server with which
When the DNS server has correspondence information between the host name and the address of the content server for each user terminal and receives a conversion request from the user terminal to the address of the host name of the content server, the content server associated with the user terminal A content distribution network having a function of notifying a user terminal of the content distribution network, thereby performing load distribution in consideration of a load state of the content distribution network. The content distribution network according to claim 3, wherein the access server has an address translation function that can be set from the network management / control function,
The network management / control system holds, for each user terminal, an available bandwidth value and an address of the content server for each of the user terminal and the plurality of content servers, and the available bandwidth value is determined and changed when the available bandwidth information for the user terminal is changed. The content server having the largest bandwidth value is selected, and the access server is set to convert the destination address of the content distribution request from the user terminal into the address of the selected content server. A content distribution network having a function of transferring to a content server having the largest available bandwidth value, thereby performing load distribution in consideration of a load state of the content distribution network. The content distribution network according to claim 3, wherein the access server has a packet encapsulation function that can be set from the network management / control function,
The network management / control system holds, for each user terminal, an available bandwidth value and an address of the content server for each of the user terminal and the plurality of content servers, and the available bandwidth value is determined and changed when the available bandwidth information for the user terminal is changed. The content server having the largest bandwidth value is selected, and the access server is set to encapsulate the packet including the content distribution request from the user terminal with the packet addressed to the address of the selected content server. A content distribution request having the function of transferring the content distribution request to the content server having the largest available bandwidth value, thereby performing load distribution in consideration of the load state of the content distribution network.

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