Cable Modem Packet Re-sequencing for DOCSIS 3.0 Channel Bonding
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Solution Overview
Problem
DOCSIS 3.0 cable systems face challenges in re-sequenceing packets across multiple downstream channels due to timing skew, which can result in packets arriving out of order at the cable modem, requiring an efficient reordering mechanism with minimal processing impact.
Innovation Solution
A packet re-sequencing mechanism that stores received packets in memory, tracks sequence numbers, and uses a context table and max sequence snapshot table to ensure packets are released in the correct order, addressing potential timing skew between channels with minimal added processing delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If packets are transmitted over multiple downstream channels with channel bonding, then data throughput is increased, but packets may arrive out of order due to timing skew between channels
Solution Approach 1:
The patent implements preliminary actions by maintaining a buffer memory to temporarily store received packets and using sequence number tracking tables to pre-prepare for reordering. The system proactively monitors sequence numbers from multiple channels and prepares the reordering structure before packets need to be delivered in correct sequence, thus preventing delivery issues rather than reacting to them.
Solution Approach 2:
The patent introduces an intermediary reordering buffer between the multiple downstream channels and the packet delivery path. This buffer acts as a mediator that receives out-of-order packets from bonded channels, uses sequence number tables to track their proper order, and releases them in the correct sequence. The intermediary component isolates the timing skew issue from the final packet delivery, allowing high throughput while maintaining reliability.
2Reliability
If a re-sequencing mechanism is implemented to reorder packets, then packet sequence accuracy is improved, but processing complexity and memory requirements increase
Solution Approach 1:
The patent segments the re-sequencing function into distinct components: a buffer memory for storing packets, a sequence number tracking table for monitoring packet order, and a release control mechanism for delivering packets in correct sequence. This segmentation allows each component to perform its specific function efficiently, reducing overall system complexity compared to a monolithic re-sequencing design.
Solution Approach 2:
The re-sequencing mechanism uses self-service principles by having packets carry their own sequence numbers that automatically populate the tracking table upon receipt. The system monitors its own state through the sequence number table and automatically determines when packets are ready for release in correct order, without requiring external control or complex coordination logic.
3Reliability
If packets are buffered and re-sequenced to correct timing skew, then packet delivery accuracy is improved, but processing delay increases
Solution Approach 1:
The patent maintains continuity of useful action by keeping the buffer memory continuously occupied with received packets and the sequence number table continuously updated. Rather than stopping to reorder packets, the system continuously receives, buffers, and tracks packets in parallel, then releases them in correct sequence without interruption. This continuous operation minimizes idle time and reduces overall processing delay while ensuring accuracy.
Data Source
AI summary
A novel apparatus and method of packet re-sequencing applicable to systems wherein packets are assigned sequence numbers and transmitted over multiple channels with the requirement they be re-ordered at the receiving side. The mechanism is particularly suitable for use in cable systems adapted to implement the DOCSIS 3.0 specification which permits the bonding of a plurality of downstream channels into a single virtual high data rate pipe. In operation, received packets are stored in a memory whereby a pointer to the memory storage location is written into a context table diagram in accordance with the sequence number extracted from the packet. Packets are released in sequence order regardless of the order in which they were received.