WAN Path Quality Metric Segmentation for QoS-Aware Links
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Solution Overview
Problem
Existing wide-area network (WAN) and software-defined WAN (SD-WAN) solutions lack effective error-resilient transport methods for quality of service (QoS) aware links, leading to inefficient bandwidth usage and poor application performance due to out-of-order packet delivery and incorrect path quality metric calculations, especially in QoS aware links like MPLS, where heartbeat messages are mapped to the same service queue, causing false path outages.
Innovation Solution
A method to quantify the quality of service classes in a WAN by computing path quality metric values for each service class, allowing independent management of packet processing and traffic distribution across multiple service classes, using unique sequence numbers and differentiated service class identifiers to maintain accurate packet loss, delay, and jitter metrics, and dynamically selecting the best service class for packet forwarding based on real-time PQM values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heartbeat messages are sent on QoS aware links with default DSCP tag, then path outage detection can be performed, but all heartbeat messages are mapped to the same service queue causing false path outages and marking the entire path as unusable
Solution Approach 1:
The patent segments the monitoring function by sending heartbeat messages for different service classes separately. Each service class gets its own sequence number counter and independent quality metric tracking, allowing the system to assess the health of individual service queues without being affected by congestion in other queues. This resolves the contradiction by enabling reliable outage detection (improving reliability) while preventing false positives that would unnecessarily block bandwidth usage (maintaining productivity).
Solution Approach 2:
The patent applies local quality by computing path quality metrics independently for each service class rather than for the entire path. Each service class receives differentiated treatment with its own sequence numbers, counters, and quality assessments. This allows the system to identify and utilize operational service classes (maintaining productivity) while accurately detecting outages in specific service classes (improving reliability).
2Reliability
If packets are mapped to different scheduler service queues in transit QoS device, then QoS aware packet handling is achieved, but packets sent in sequence get out of order preventing proper packet loss computation
Solution Approach 1:
The patent segments the sequence numbering by creating independent sequence number counters for each service class. When packets are divided into different scheduler queues, each queue receives packets with sequence numbers from its own counter. This segmentation allows the receiving end to compute packet loss accurately for each service class independently, resolving the contradiction between QoS aware handling (which requires queue separation) and accurate measurement (which requires sequential tracking).
Solution Approach 2:
The patent introduces service class identifiers as intermediaries between the packet forwarding mechanism and the quality metric computation. These identifiers allow the system to track which service class each packet belongs to, enabling separate sequence number assignment and loss computation for each class. This intermediary mechanism preserves QoS aware packet handling while restoring measurement precision through class-specific tracking.
3Reliability
If retransmission and FEC methods are applied to provide transport error resiliency, then packet loss recovery is improved, but the complexity of error handling increases
Solution Approach 1:
The patent applies dynamics by making error handling methods adaptive to the quality of each service class. The system dynamically selects between retransmission and FEC based on real-time quality metrics of individual service classes. This dynamic approach improves reliability by applying appropriate error handling where needed while reducing complexity by avoiding unnecessary error handling in high-quality service classes. The adaptivity allows the system to optimize the trade-off between reliability and complexity for each service class independently.
Data Source
AI summary
Some embodiments provide a method for quantifying quality of several service classes provided by a link between first and second forwarding nodes in a wide area network (WAN). At a first forwarding node, the method computes and stores first and second path quality metric (PQM) values based on packets sent from the second forwarding node for the first and second service classes. The different service classes in some embodiments are associated with different quality of service (QoS) guarantees that the WAN offers to the packets. In some embodiments, the computed PQM value for each service class quantifies the QoS provided to packets processed through the service class. In some embodiments, the first forwarding node adjusts the first and second PQM values as it processes more packets associated with the first and second service classes. The first forwarding node also periodically forwards to the second forwarding node the first and second PQM values that it maintains for the first and second service classes. In some embodiments, the second forwarding node performs a similar set of operations to compute first and second PQM values for packets sent from the first forwarding node for the first and second service classes, and to provide these PQM values to the first forwarding node periodically.