Congestion controller and method for controlling congestion of network

A congestion controller that receives, via an IP packet transmitting/receiving network, a request message transmitted from a client to a web server, then after seeking for the destination web server via a DNS server, transfers the request message to the web server, and if the web server is congested, responds to the client with a congestion message instead of transferring the request message to the web server, the controller comprising:

• a communications processor that processes transmission/reception of packets present on the network;
• an HTTP processor that controls a protocol of communication with the web server;
• a DNS processor that controls a protocol of communication with the DNS server;
• an IP address caching section that retains information on an association between host names and IP addresses;
• and
• a congestion control manager that retains congestion state information on web servers assigned for each of the IP addresses;
• wherein:
• the DNS processor makes an inquiry to the DNS server and obtains an IP address associated with a host name included in the request message;
• the IP address caching section records the association between the host name and the IP address;
• and
• in accordance with the congestion state information retained in the congestion control manager and with the association between the host name and the IP address recorded in the IP address caching section, if the web server assigned to the IP address to which the request message is to be transferred is judged to be congested, the HTTP processor seeks for a second IP address associated with the host name of the web server which has been judged to be congested, and when the web server to which the second IP address is assigned is not congested, transfers the request message received from the client, to the web server having the assigned second IP address;
• and
• wherein, when the web server having the IP address to which the request message is to be sent is not congested, the HTTP processor transfers the request message to the web server.

A method for controlling congestion of a network, in which method, a request message transmitted from a client to a server via a network is received and when the server is congested, a congestion message is sent to the client as a response instead of the request message being transferred to the server, the control method comprising the steps of:

• acquiring an IP address of the server from the information contained in the request message;
• and
• recording information on an association between an acquired host name of the server and the IP address thereof;
• acquiring the IP address of the server from the information contained in the request message, and seeking for the server associated with the IP address from the information on the association between the acquired host name of the server and the IP address thereof;
• judging whether the server is congested, and if the server is congested, searching for a second IP address associated with the host name of the server which has been judged to be congested, the second IP address being assigned to a non-congested server;
• transferring the request message received from the client, to the server to which the second IP address that has been searched for is assigned;
• and
• if the server is not congested, transferring the request message to a server having a host name associated with the IP address.