Apparatus of synchronization for DOCSIS upstream signal transmission through optical IP network and method of the same

1. A synchronization method for transmitting a Data Over Cable Service Interface Specification (DOCSIS) upstream signal, which is performed by a Radio over Internet Protocol (RoIP) terminal, comprising:

receiving a synchronization (SYNC) message periodically sent from a Cable Modem Termination System (CMTS), and thereby synchronizing a clock and generating a reference time;

receiving a ranging request signal, which is a Radio Frequency (RF) signal, from a Cable Modem (CM);

converting the ranging request signal, including information about a time at which the ranging request signal is received and information about a start time of an allocated ranging interval, into an Internet Protocol (IP) packet; and

transmitting the IP packet to an RoIP headend device over an IP network in order to enable the RoIP headend device to convert the IP packet into an RF signal and to transmit the RF signal to the CMTS,

wherein the RoIP terminal performs a clock synchronization with the CM, and

wherein the RoIP headend device performs a clock synchronization with the CMTS.

2. The synchronization method of claim 1 , further comprising:

synchronizing time with the CM using the ranging request signal.

3. The synchronization method of claim 2 , wherein synchronizing time with the CM is configured to synchronize time using a difference between the time at which the ranging request signal is received and the start time of the allocated ranging interval.

4. The synchronization method of claim 3 , further comprising:

receiving a ranging response message corresponding to the ranging request signal delivered from the CMTS;

adjusting time by interpreting the ranging response message; and

converting the ranging response message into an electric signal and transmitting the electric signal to the CM.

5. The synchronization method of claim 4 , wherein:

converting the ranging request signal into an IP packet is configured to convert both the information about the start time of the allocated ranging interval and the ranging request signal into an initial ranging IP packet when the ranging request signal is an initial ranging request signal;

transmitting the IP packet to the RoIP headend device is configured to transmit the initial ranging IP packet to the RoIP headend device over the IP network; and

the RoIP headend device is configured to convert the initial ranging IP packet into an RF signal and to transmit the RF signal to the CMTS in a last transmission opportunity when the ranging request signal is an initial ranging request signal.

6. The synchronization method of claim 5 , wherein the last transmission opportunity corresponds to a transmission time that makes an end time of the ranging request signal at the CMTS match an end time of the allocated ranging interval when the RoIP headend device transmits the ranging request signal to the CMTS.

7. The synchronization method of claim 6 , wherein converting the ranging request signal into an IP packet is configured to convert the ranging request signal, with setting a time at which the RoIP headend device is to transmit an IP packet to the CMTS to a time at which the ranging request signal is received, into an IP packet when the ranging request signal is not an initial ranging request signal.

8. A synchronization apparatus for transmitting a Data Over Cable Service Interface Specification (DOCSIS) upstream signal, comprising:

a communication unit for communicating with a Cable Modem Termination System (CMTS), a Radio over Internet Protocol (RoIP) headend device, and a Cable Modem (CM);

a synchronization unit for synchronizing a clock and generating a reference time by receiving a synchronization (SYNC) message periodically sent from the CMTS; and

a signal conversion unit for converting a ranging request signal, which is delivered from the CM and is a Radio Frequency (RF) signal, including information about a time at which the ranging request signal is received and information about a start time of an allocated ranging interval, into an Internet Protocol (IP) packet in order to transmit the ranging request signal to the RoIP headend device,

wherein the synchronization unit performs a clock synchronization with the CM, and

wherein the RoIP headend device performs a clock synchronization with the CMTS.

9. The synchronization apparatus of claim 8 , wherein the synchronization unit synchronizes time using a difference between the time at which the ranging request signal is received and the start time of the allocated ranging interval.

10. The synchronization apparatus of claim 9 , wherein:

the synchronization unit adjusts time by interpreting a ranging response message, corresponding to the ranging request signal, received from the CMTS; and

the signal conversion unit converts the ranging response message into an electric signal in order to send to the CM.

11. The synchronization apparatus of claim 10 , wherein:

the signal conversion unit converts both the information about the start time of the allocated ranging interval and the ranging request signal into an initial ranging IP packet when the ranging request signal is an initial ranging request signal; and

the communication unit transmits the initial ranging IP packet to the RoIP headend device over the IP network; and

the RoIP headend device converts the initial ranging IP packet into an RF signal and transmits the RF signal to the CMTS in a last transmission opportunity when the ranging request signal is the initial ranging request signal.

12. The synchronization apparatus of claim 11 , wherein the last transmission opportunity corresponds to a transmission time that makes an end time of the ranging request signal at the CMTS match an end time of the allocated ranging interval when the RoIP headend device transmits the ranging request signal to the CMTS.

13. The synchronization apparatus of claim 12 , wherein the signal conversion unit converts the ranging request signal, with setting a time at which the RoIP headend device is to transmit an IP packet to the CMTS to a time at which the ranging request signal is received, into the IP packet when the ranging request signal is not an initial ranging request signal.

14. A synchronization method for transmitting a Data Over Cable Service Interface Specification (DOCSIS) upstream signal, which is performed by a Radio over Internet Protocol (RoIP) headend device, comprising:

receiving a synchronization (SYNC) message periodically sent from a Cable Modem Termination System (CMTS) and thereby synchronizing a clock and generating a reference time;

receiving a ranging request signal, which is an Internet Protocol (IP) packet including information about a start time of an allocated ranging interval, from an RoIP terminal over an IP network, the ranging request signal being transmitted from a Cable Modem (CM);

converting the ranging request signal into a Radio Frequency (RF) signal; and

transmitting the RF signal to the CMTS,

wherein the RoIP terminal performs a clock synchronization with the CM, and

wherein the RoIP headend device performs a clock synchronization with the CMTS.

15. The synchronization method of claim 14 , further comprising:

synchronizing time with the CMTS through ranging.

16. The synchronization method of claim 15 , wherein receiving the ranging request signal is configured to receive the ranging request signal from the RoIP terminal, a time of which is synchronized with the CM using the ranging request signal.

17. The synchronization method of claim 16 , wherein receiving the ranging request signal is configured to receive the ranging request signal from the RoIP terminal, the time of which is synchronized with the CM using a difference between a time at which the ranging request signal is received and the start time of the allocated ranging interval.

18. The synchronization method of claim 17 , wherein transmitting the RF signal to the CMTS is configured to transmit the RF signal to the CMTS in a last transmission opportunity using the information about the start time of the allocated ranging interval included in the ranging request signal when the ranging request signal is an initial ranging request signal.

19. The synchronization method of claim 18 , wherein the last transmission opportunity corresponds to a transmission time that makes an end time of the ranging request signal at the CMTS match an end time of the allocated ranging interval when the ranging request signal is transmitted to the CMTS.

20. The synchronization method of claim 19 , wherein:

transmitting the RF signal to the CMTS is configured to transmit the RF signal to the CMTS at a transmission time set in the ranging request signal by the RoIP terminal when the ranging request signal is not an initial ranging request signal; and

the transmission time set in the ranging request signal is a time at which the ranging request signal is received.