Information delivery system, network server and method of controlling network server

1. An information delivery system comprising:

a terminal; and

a network server configured to communicate with the terminal via a network, wherein

the terminal transmits a first request requesting time information to the network server,

the network server transmits, in response to the first request, a second request requesting time information to a time server connected to the network,

the network server receives, from the time server, first time information as a response to the second request, and

after a lapse of a predetermined time from reception of the first request, the network server transmits second time information measured based on the first time information to the terminal.

2. The information delivery system according to claim 1 , wherein

the second time information is calculated by adding a transmission delay time among the network server and the terminal to the first time information.

3. The information delivery system according to claim 2 , wherein

the terminal measures an internal time, and modifies the internal time based on time information acquired by adding, to the second time information, an internal delay time from reception of the second time information to confirmation of the second time information.

4. The information delivery system according to claim 3 , wherein

the network server periodically transmits a third request requesting time information to the time server.

5. The information delivery system according to claim 4 , wherein

the network server uses, as the first time information, time information acquired from a satellite signal transmitted from a navigation satellite or a standard radio wave transmitted from a standard radio wave transmission station.

6. The information delivery system according to claim 5 , wherein

the network server acquires, from another server, at least one type of information, among three types of information including time difference information, daylight saving time information and leap second time information and transmits the information to the terminal along with the second time information.

7. A network server comprising:

a network interface configured to communicate with a terminal via a network; and

a control device configured to control the network interface, wherein

the control device causes the network interface to receive a first request requesting time information from the terminal, transmit a second request requesting time information to a time server connected to the network in response to the first request, receive, from the time server, first time information as a response to the second request, and

after a lapse of a predetermined time from reception of the first request, transmit second time information measured based on the first time information to the terminal.

8. A method of controlling a network server that is configured to communicate with a terminal via a network, the method comprising:

receiving a first request requesting time information;

transmitting a second request requesting time information to a time server connected to the network in response to the first request;

receiving, from the time server, first time information as a response to the second request; and

after a lapse of a predetermined time from reception of the first request, transmitting second time information measured based on the first time information to the terminal.

9. The method of controlling a network server according to claim 8 , wherein

the second time information is calculated by adding a transmission delay time among the network server and the terminal to the first time information.

10. The method of controlling a network server according to claim 9 , wherein

the terminal measures an internal time, and modifies the internal time based on time information acquired by adding, to the second time information, an internal delay time from reception of the second time information to confirmation of the second time information.

11. The method of controlling a network server according to claim 10 , wherein

the network server periodically transmits a third request requesting time information to the time server.

12. The method of controlling a network server according to claim 10 , wherein

the network server uses, as the first time information, time information acquired from a satellite signal transmitted from a navigation satellite or a standard radio wave transmitted from a standard radio wave transmission station.

13. The method of controlling a network server according to claim 11 , wherein

the network server uses, as the first time information, time information acquired from a satellite signal transmitted from a navigation satellite or a standard radio wave transmitted from a standard radio wave transmission station.

14. The method of controlling a network server according to claim 12 , wherein

the network server acquires, from another server, at least one type of information, among three types of information including time difference information, daylight saving time information and leap second time information and transmits the information to the terminal along with the second time information.

15. The method of controlling a network server according to claim 13 , wherein

the network server acquires, from another server, at least one type of information, among three types of information including time difference information, daylight saving time information and leap second time information and transmits the information to the terminal along with the second time information.