Method of providing timing information for synchronizing MMT packet stream in MMT hybrid delivery service and method of synchronizing MMT packet stream in MMT hybrid delivery service

1. A method of providing timing information for synchronizing

packet streams delivered to a client from a first server and a second server, respectively, that are different from each other under a hybrid delivery service environment, the first server delivering a first packet including a first media object and the second server delivering a second packet including a second media object, the method comprising: generating, in the second server, timing information for synchronizing the second packet and the first packet with each other, wherein generating the timing information includes using a clock reference value of the first packet and using a clock reference value of the second packet; and providing, by the second server, the timing information and the second packet to the client.

2. The method of claim 1 , wherein the timing information is provided to the client by being included in a control message of an MMT S. 1 layer.

3. The method of claim 1 , wherein the timing information is provided to the client by being included in a header of an MMT D. 2 layer.

4. The method of claim 1 , wherein the timing information for synchronizing the first packet and the second packet with each other is delivered only once from the second server to the client through a first MMT packet.

5. The method of claim 1 , wherein the timing information includes:

an Hybrid_Network_Synch_Flag field that represents whether it includes timing information required for the synchronization;

an MCR_Resolution_Flag field that represents frequency resolution of an MMT clock reference (MCR);

an Initial_Clock_Ticks_Base field that represents an MCR clock value corresponding to an original service start time of the second media object as clock resolution of 90 kHz; and

an Initial_Clock_Ticks_Ext field that represents an MCR clock value corresponding to the original service start time of the second media object as clock resolution of 27 MHz.

6. The method of claim 5 , wherein when a value of the Hybrid_Network_Synch_Flag field is 1, it represents that the packet to be currently delivered from the second server includes an MMT packet or a control message having the timing information for synchronizing the hybrid delivery service and the MCR_Resolution_Flag field is present and has a valid value; and

when a value of the Hybrid_Network_Synch_Flag field is 0, it represents that the packet to be currently delivered from the second server is not the MMT packet or the control message including the timing information for synchronizing the hybrid delivery service.

7. The method of claim 5 , wherein when the value of the MCR_Resolution_Flag field is 1, it represents that the frequency resolution of the MCR is 90 kHz, the Initial_Clock_Ticks_Ext field is not present, only the Initial_Clock_Ticks_Base field is present, and the value of the Initial_Clock_Ticks_Base field is valid, and

when the value of the MCR_Resolution_Flag field is 0, it represents that the frequency resolution of the MCR is 27 MHz, both of the Initial_Clock_Ticks_Base field and the Initial_Clock_Ticks_Ext field are present, and the values of the Initial_Clock_Ticks_Base field and the Initial_Clock_Ticks_Ext field are valid.

8. The method of claim 5 , wherein the second server calculates a Start_Clock_Offset value obtained by converting Start_Time_Offset, a temporal difference value between an original start time and an actual start time of a program of the second media object into system clock frequency (SCF) precision of a system time clock (STC) of the second server,

the second server subtracts the Start_Clock_Offset value from an MCR value MCRn of the packet of the second media object initially delivered to the client to calculate the MCR value MCR 0 of the first packet delivered to the client, and

the second server sets the calculated MCR 0 value in the Initial_Clock_Ticks_Base field or both of the Initial_Clock_Ticks_Base field and the Initial_Clock_Ticks_Ext field according to the SCF of the second server.

9. The method of claim 1 , wherein the second server is a supplemental information server that delivers data of supplemental information through a broadband channel and the first server is a program stream server delivering data of broadcast contents such as a foreign language movie through a broadcast channel.

10. The method of claim 1 , wherein the generating timing information for synchronizing a second packet including the second media object and a first packet including the first media object with each other in the second server is performed when the second server receives a delivery request for the second media object from the client.

11. A method of synchronizing packet streams delivered from a

first server and a second server to a client, respectively, that are different from each other under a hybrid delivery service environment, the first server delivering a first packet including a first media object to the client and the second server delivering a second packet including a second media object to the client, the method comprising: generating, in the second server, timing information for synchronizing the second packet and the first packet , wherein generating the timing information includes using a clock reference value of the first packet and using a clock reference value of the second packet; and determining, in the client, whether the first packet and the second packet are synchronized with each other by using the timing information.

12. The method of claim 11 , wherein the timing information is provided to the client by being included in a control message of an MMT S. 2 layer.

13. The method of claim 11 , wherein the timing information is provided to the client by being included in a header of an MMT D. 2 layer.

14. The method of claim 12 , wherein at the determining whether the first packet including the first media object and the second packet including the second media object are synchronized with each other by using the timing information in the client, it determines whether the first packet and the second packet are synchronized with each other by calculating first Absolute_Presentation_Time of the first packet and second Absolute_Presentation_Time of the second packet for synchronizing the first packet including the first media object received from the first server and the second packet including the second media object received from the second server using the timing information in the client.

15. The method of claim 12 , wherein after the client receives a control message for providing synchronization from the second server or initially receives the second packet, APTi that is Absolute_Presentation_Time (APT) for any i-th second packet is calculated by the following Equation

APT

i

=

MCR

i

-

MCR

0

SCF

where MCR 0 is an MCR value of an initial second packet delivered to the client, the SCF is a system clock frequency, and the MCRi is an MCR value of any i-th second packet.

16. The method of claim 13 , wherein at the determining whether the first packet including the first media object and the second packet including the second media object are synchronized with each other by using the timing information in the client, it is determined whether the first packet and the second packet are synchronized with each other by comparing a difference value between the first Absolute_Presentation_Time of the first packet and the second Absolute_Presentation_Time of the second packet with a reference value.

17. The method of claim 11 , further comprising: reproducing the first and second packets together by determining that the first packet and the second packet are synchronized with each other when the difference value between the first Absolute_Presentation_Time of the first packet and the second Absolute_Presentation_Time of the second packet is smaller than the reference value.

18. A first server configured to provide timing information for synchronizing packet streams delivered to a client from the first server and a second server, respectively, that are different from each other under a hybrid delivery service environment, the first server delivering a first packet including a first media object and the second server delivering a second packet including a second media object, the first server comprising: a timing information generator configured to generate, using a clock reference value of the first packet and a clock reference value of the second packet, timing information for synchronizing the first packet and the second packet with each other; an MPEG Multimedia Transport (MMT) packet generator configured to packetize and generate the first packet; and an MMT packet delivery unit configured to deliver the first packet to the client.

19. The server of claim 18 , wherein the timing information generator is configured to deliver the timing information included in a control message of an MMT S. 2 layer to the client.

20. The server of claim 18 , wherein the timing information generator is configured to deliver the timing information included in a header of the MMT D. 2 layer to the client through the packet including the second media object.