AVB Clock Reference Stream Distribution for Jitter Reduction
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Solution Overview
Problem
In Audio Video Bridging (AVB) networks, existing methods for clock synchronization face challenges such as clock jitter and phase offsets, especially as the number of devices increases, leading to unpredictable system behavior and inefficiencies in media data transmission.
Innovation Solution
A clock reference stream distribution system is introduced, where a media clock master device generates and transmits timing information separately from media streams, allowing for precise synchronization of audio/video devices with minimal bandwidth usage, using a Precision Time Protocol (gPTP) and Stream Reservation Protocol (SRP), enabling efficient clock dissemination across the network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clocking information is embedded in transmitted data signals, then point-to-point clock synchronization works well, but clock jitter cascades and builds through each device that recovers and re-transmits the clocking information
Solution Approach 1:
The patent segments the clock synchronization function by separating clock recovery from data transmission. Instead of extracting clock from data signals at each device, a dedicated clock reference stream is transmitted separately, allowing devices to synchronize without recovering and re-transmitting clock information through the data path, thus preventing jitter cascading.
Solution Approach 2:
The patent introduces an intermediary clock reference stream that carries timing information independently from the data traffic. This intermediary stream acts as a mediator between the master clock and slave devices, providing a clean synchronization path that does not suffer from the jitter accumulation problems of embedded clocking.
2Measurement precision
If a network clock signal is generated at a specific point and distributed to all devices, then system time synchronization is achieved, but devices at different locations receive the clock signal with phase offsets depending on propagation delay
Solution Approach 1:
The patent applies preliminary action by having each device measure its propagation delay from the master clock before synchronization. Devices use this pre-measured delay information to compensate for phase offsets, adjusting their local clocks to account for the time it takes for the synchronization signal to reach them, thereby achieving uniform phase alignment across the network.
Solution Approach 2:
The patent implements feedback mechanisms where devices monitor their received clock signal phase offsets and adjust their local oscillators accordingly. This closed-loop feedback allows devices to compensate for propagation delays and maintain synchronized timing despite being at different network locations.
3Productivity
If Time Division Multiplexing is used to allocate time slots for transmission, then clock distribution is achieved, but the total available number of channels is limited
Solution Approach 1:
The patent makes the clock reference stream universal by designing it to support multiple media clock domains simultaneously. Instead of dedicating separate TDM time slots for each channel, the clock reference stream can serve multiple devices and clock domains through a single infrastructure, greatly increasing the number of supported channels without requiring additional time slot allocations.
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
An apparatus used to communicate with a plurality of audio/video (A/V) end nodes in an Audio Video Bridging (AVB) network. The apparatus may include a first A/V end node. The first A/V end node may be configured to transmit a clock reference stream including a plurality of timestamps to a plurality of A/V end nodes. The plurality of A/V end nodes may transmit a media stream including a plurality of video samples and a plurality of audio samples to one another. The media stream may be separate from the plurality of timestamps. The plurality of A/V end nodes may be arranged to syntonize or synchronize the plurality of video samples and the plurality of audio samples with one another for playback in response to the plurality of timestamps.