CMTS Late Discard for Cable Modem Buffer Bloat
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Solution Overview
Problem
Buffer bloat in cable networks causes latency and throughput issues due to excessive TCP buffering, which existing technologies like Random Early Discard (RED) struggle to address effectively, especially in pre-DOCSIS 3.0 cable modems where software updates are impractical and not applicable.
Innovation Solution
The Cable Modem Termination System (CMTS) implements a late discard mechanism, recognizing congestion by estimating upstream queue sizes and deliberately dropping upstream TCP packets after reception, rather than requiring cable modem software updates or early discards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If early discard mechanism is implemented in cable modem, then buffer bloat is reduced, but device complexity increases and software updates are required
Solution Approach 1:
Instead of having the cable modem (transmitting element) perform early discard of packets, the invention inverts the approach by having the CMTS (receiving element) perform late discard of packets. This inversion transfers the buffer management function from the cable modem to the CMTS, reducing cable modem complexity while maintaining buffer bloat mitigation.
Solution Approach 2:
The invention introduces an intermediary mechanism where the CMTS acts as a mediator between the cable modem and the network. The CMTS receives queue size information from the cable modem and makes discard decisions based on this information, effectively mediating the buffer management process without requiring complex changes to the cable modem itself.
2Object-affected harmful factors
If cable modem software is updated to implement buffer management, then buffer bloat is reduced, but ease of operation deteriorates due to update requirements
Solution Approach 1:
The CMTS serves as an intermediary that implements the buffer management logic externally. By moving the discard decision-making to the CMTS and having it communicate with existing cable modem functionality, the invention avoids the need for software updates on cable modems while still achieving buffer bloat reduction.
3Reliability
If TCP buffering is increased to prevent packet loss, then reliability improves, but latency increases due to buffer bloat
Solution Approach 1:
The invention implements a feedback mechanism where the cable modem reports its queue size to the CMTS, and the CMTS uses this feedback information to make informed discard decisions. This feedback loop allows the system to maintain adequate buffering for reliability while dynamically adjusting to prevent buffer bloat and reduce latency.
Solution Approach 2:
The invention dynamically changes the effective buffer size by selectively discarding packets at the CMTS based on real-time queue conditions. Instead of using a fixed large buffer that causes buffer bloat, the system dynamically adjusts the buffer utilization through packet discard, maintaining reliability when needed while preventing latency during congestion.
Data Source
AI summary
Buffer bloat continues to cause latency problems for all kinds of network traffic, e.g., internet protocol traffic. Implementing network based control of packet upstream packet discards enables a scheduler of packets to manage congestion, instead of the network element with bloat. In embodiments, a cable modem termination system may schedule delivery of packets and, after receiving the scheduled packets, discarding packets. The cable modem termination system may determine when to discard a packet based on a detected backlog of data in a cable modem upstream flow queue. For example, a late discard of such packets may be based on information in a schedule request received from the network element.