Adaptive Play-out Buffer for VoIP Clock Synchronization
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Solution Overview
Problem
Current technologies fail to adequately synchronize clocks in packet-switched networks, leading to delays and quality degradation in real-time voice and video communications, particularly in VoIP systems, due to asynchronous transport and variable network delays, resulting in slips and pitch modification effects.
Innovation Solution
The implementation of an adaptive play-out buffer mechanism that uses controlled slips and frequency adjustments to synchronize the analog-to-digital and digital-to-analog converters, along with adaptive clock control, to minimize clock offsets and buffer overflow/underflow events, thereby maintaining optimal communication quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a jitter buffer is used to compensate for network delay variation, then packet loss is reduced, but end-to-end delay increases
Solution Approach 1:
The patent implements a dynamic jitter buffer that continuously adapts its size and characteristics based on real-time network conditions. The buffer dynamically adjusts between a smaller initial buffer for low-latency operation and a larger buffer when network variation increases, resolving the contradiction between reliability and delay by making the buffer size flexible rather than fixed
Solution Approach 2:
The system changes the operational parameters of the jitter buffer based on measured network conditions. When network delay variation is high, the buffer size and timing parameters are increased to prevent packet loss. When network conditions are stable, parameters are reduced to minimize end-to-end delay, thus adapting the buffer behavior to current conditions
2Adaptability or versatility
If asynchronous transport is used in packet networks, then network flexibility and routing options increase, but clock synchronization becomes difficult
Solution Approach 1:
The patent employs feedback mechanisms where the receiving end monitors the arrival times of packets and sends timing information back to the transmitting end. This feedback loop enables both ends to adjust their clock operations to maintain synchronization despite asynchronous transport, resolving the contradiction between network flexibility and clock synchronization reliability
Solution Approach 2:
The system introduces timing markers and synchronization protocols as intermediaries that carry clock information through the asynchronous packet network. These intermediaries enable the transmitting and receiving ends to coordinate their operations without requiring direct clock connection, thus maintaining synchronization over flexible packet routes
3Productivity
If packetization buffering is used to fill packet payloads, then transmission efficiency increases, but encoding/decoding delay increases
Solution Approach 1:
The patent applies partial buffering by collecting only the necessary amount of data to fill packet payloads efficiently, rather than waiting for complete data sets. This partial action approach achieves sufficient transmission efficiency while minimizing the buffering delay, resolving the contradiction between productivity and time loss
Data Source
AI summary
Methods and apparatus for a play-out buffer that may adjust offsets between clocks of two ends of a network link with an adaptive play-out buffer and adaptive clock control. The play-out buffer is a circular jitter buffer that permits the absorption of a frequency offset using controlled slips between two nodes of a network. The play-out buffer also accommodates some wander introduced by the time-delay variation across the network. The adaptive clock control reduces the frequency offset between the clocks of the two nodes. In this manner, even though some offsets between two nodes would render communication inefficient, embodiments of the present invention allow the effects of these offsets to be mitigated, thus providing for a better quality coupling.