Systems and methods for providing synchronization in a networked environment
View Patent ↗Described herein are systems and methods for synchronization in a networked environment. For example, some embodiments provide methods for synchronizing a client device having a client media time reference with a server device having a server media time reference. In some cases such methods are embodied in computer readable code that is executable on one or more processors. Furthermore, some embodiments provide hardware, such as networked media devices that are configured to perform such methods. In overview, in some embodiments a client obtains timing information from a server and, on the basis of this timing information, applies an adjustment to a client control time reference, thereby to synchronize the client media time reference with the server media time reference. Some embodiments are particularly directed to the situation where there is a desire to synchronize networked media devices across a combination of wired and wireless networks.
1. A method, performed by a networked slave device, for synchronizing a local clock of the networked slave device with respect to a master clock of a master device, the method including:
(a) providing a group of probe frames to the master device, thereby to receive responses in respect of at least a selection of these probe frames, wherein each response includes data for allowing determination of an estimated clock offset, wherein the master device has access to observe a global clock value for a wireless network, and wherein the slave device and the master device are connected to different communication media;
(b) filtering the responses, thereby to identify one or more best responses for the group of probe frames;
(c) repeating steps (a) and (b) for successive groups of probe frames thereby to identify a respective one or more best responses for the successive groups of probe frames;
(d) selectively calculating estimated clock offset values using the one or more best responses in respect of each group of probe frames to determine a relative clock offset drift based on:
(i) Return Trip Times (RTTs) for the one or more best responses with respect to their respective probe frames;
(ii) a probe frame transmission timestamp taken with respect to the local clock of the networked slave device;
(iii) a probe frame receiving timestamp taken with respect to the master clock of the master device;
(iv) a response transmission timestamp taken with respect to the master clock of the master device; and
(v) a response receiving timestamp taken with respect the local clock of the networked slave device; and
(e) repeatedly adjusting the local clock of the networked slave device based on calculations of the relative clock offset drift.
2. A method according to claim 1 wherein the networked slave device communicates with the master device over hybrid network including at least one wired communications path and one wireless communications path.
3. A method according to claim 1 wherein the data for allowing determination of an estimated clock offset includes timing information associated with the probe frame by the slave device and timing information associated with the probe frame by the slave device the master device.
4. A method according to claim 1 wherein the probe frames in the group are generated for successive transmission with a small gap between successive frames.
5. A method according to claim 1 including processing the responses based on RTT value, and discarding responses with RTT value greater than a predefined threshold value.
6. A method according to claim 1 including for each identified best response, computing a value indicative of how close the response under consideration is to an ongoing average value.
7. A method according to claim 1 wherein a prediction algorithm is used to track the clock offset drift on an ongoing basis thereby to predicatively to adjust the VCO feed value.
8. A method according to claim 1 wherein the slave device is configured for playing back media data in synchronicity with the master device.
9. A method according to claim 1 wherein the slave device is a networked media playback unit.
10. A non transitive computer readable medium carrying computer executable code that, when executed by one or more processors of a device, configure the device to perform a method according to claim 1 .
11. A networked device, configured to operate as a networked slave device, for synchronizing a local clock of the networked slave device with respect to a master clock of a master device, the networked slave device including:
(i) a processor; and
(ii) a memory device configured to store software instructions to configure the slave device to perform a method including:
(a) providing a group of probe frames to the master device, thereby to receive responses in respect of at least a selection of these probe frames, wherein each response includes data for allowing determination of an estimated clock offset, wherein the master device has access to observe a global clock value for a wireless network, and wherein the slave device and the master device are connected to different communication media;
(b) filtering the responses, thereby to identify one or more best responses for the group of probe frames;
(c) repeating steps (a) and (b) for successive groups of probe frames thereby to identify a respective one or more best responses for the successive groups of probe frames;
(d) selectively calculating estimated clock offset values using the one or more best responses in respect of each group of probe frames to determine a relative clock offset drift based on:
(i) Return Trip Times (RTTs) for the one or more best responses with respect to their respective probe frames;
(ii) a probe frame transmission timestamp taken with respect to the local clock of the networked slave device;
(iii) a probe frame receiving timestamp taken with respect to the master clock of the master device;
(iv) a response transmission timestamp taken with respect to the master clock of the master device; and
(v) a response receiving timestamp taken with respect the local clock of the networked slave device; and
(e) repeatedly adjusting the local clock of the networked slave device based on calculations of the relative clock offset drift.
12. A device according to claim 11 wherein the networked slave device communicates with the master device over hybrid network including at least one wired communications path and one wireless communications path.
13. A device according to claim 11 wherein the data for allowing determination of an estimated clock offset includes timing information associated with the probe frame by the slave device and timing information associated with the probe frame by the slave device the master device.
14. A device according to claim 11 wherein the probe frames in the group are generated for successive transmission with a small gap between successive frames.
15. A device according to claim 11 wherein the method includes processing the responses based on RTT value, and discarding responses with RTT value greater than a predefined threshold value.
16. A device according to claim 11 wherein the method includes for each identified best response, computing a value indicative of how close the response under consideration is to an ongoing average value.
17. A device according to claim 11 wherein a prediction algorithm is used to track the clock offset drift on an ongoing basis thereby to predicatively to adjust the VCO feed value.
18. A device according to claim 11 wherein the slave device is configured for playing back media data in synchronicity with the master device.
19. A device according to claim 11 wherein the slave device is a networked media playback unit.