Delay-Based Congestion Control for Real-Time Media Transport
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Solution Overview
Problem
Current transport layer protocols, such as TCP and UDP, are inadequate for interactive real-time media applications as they either lead to high packet losses and video jitter due to aggressive congestion control or fail to provide the necessary reliability and low delay, resulting in suboptimal video quality and throughput.
Innovation Solution
A delay-based congestion control protocol with dynamic send buffer management and gap-based error control, which includes message dropping and out-of-band key frame requests, is implemented to reduce end-to-end delay and provide partial reliability tailored for real-time interactive media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TCP congestion control is used to ensure reliability, then packet loss is reduced, but sending delay and video jitter increase due to aggressive rate reduction
Solution Approach 1:
The send buffer size is made dynamic rather than fixed, allowing it to adjust based on current network conditions and delay thresholds. This enables the system to optimize between reliability and delay by adapting buffer capacity to real-time requirements, preventing both excessive packet loss and unnecessary sending delays
Solution Approach 2:
The congestion control mechanism changes from TCP's loss-based approach to a delay-based approach with explicit delay thresholds. By monitoring and responding to delay parameters rather than packet loss, the system can maintain reliability while avoiding the aggressive rate reductions that cause video jitter and sending delays
2Reliability
If TCP fixed-sized send buffer is used, then reliability is maintained, but adaptability to bandwidth changes is reduced and delay increases
Solution Approach 1:
The send buffer transitions from a fixed-sized structure to a dynamic buffer that can expand and contract based on available bandwidth and application requirements. This dynamic adjustment enables the system to adapt quickly to changing network conditions while maintaining reliable data delivery through controlled buffer management
Solution Approach 2:
The system performs preliminary assessment of buffer delay and bandwidth conditions before committing to data transmission. By evaluating delay thresholds and buffer states in advance, the system can prepare appropriate buffer sizes and transmission rates, enabling quick adaptation to bandwidth changes while maintaining reliability
3Loss of time
If UDP is used to reduce sending delay, then real-time performance improves, but packet loss increases and reliability deteriorates
Solution Approach 1:
An application-level transport protocol is introduced as an intermediary between UDP and the real-time media application. This intermediary layer provides selective reliability and delay control mechanisms, combining the low-delay advantage of UDP with improved reliability through controlled retransmission and buffer management specific to real-time media requirements
4Productivity
If loss-based congestion control is used to maximize throughput, then data transmission capacity increases, but queueing delay in network buffers increases
Solution Approach 1:
The congestion control parameter changes from loss rate to delay threshold. By monitoring queueing delay directly and adjusting sending rate based on delay thresholds rather than waiting for packet loss, the system can respond to congestion earlier, maintaining throughput while reducing queueing delay in network buffers
Data Source
AI summary
Methods, apparatuses, and computer program products for transporting data from a sender to a receiver with low delay for interactive real-time media applications are described.