Link Reachability Rate Computation Without Link Layer Acknowledgments
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Solution Overview
Problem
In Low Power and Lossy Networks (LLNs), computing the Expected Transmission Count (ETX) metric is challenging without link-layer acknowledgments, as existing methods are costly and inefficient, especially on low-throughput links like PLC.
Innovation Solution
A mechanism that uses traffic flow observation to locally compute link reachability rates by comparing transmission attempts values to successful attempts values, allowing for dynamic and cost-effective estimation of ETX without relying on link-layer acknowledgments, by utilizing end-to-end message flow and existing user traffic flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If link-layer acknowledgments are used to compute ETX, then measurement precision is improved, but device complexity increases and use of energy increases
Solution Approach 1:
The patent uses data plane packets as intermediaries to carry transmission attempt information. Instead of requiring a separate acknowledgment mechanism, the transmission attempt count is embedded within regular data packets that are already being transmitted for user traffic, thus measuring link quality without adding separate control overhead
Solution Approach 2:
The patent makes data plane packets serve multiple functions: they carry user data traffic and simultaneously serve as measurement probes for ETX computation. By embedding transmission attempt information in regular data packets, the same infrastructure is used for both data transmission and link quality measurement
2Measurement precision
If dedicated probe messages are sent to measure reachability rate, then measurement precision is improved, but productivity decreases due to control plane overhead
Solution Approach 1:
The patent merges the measurement function with the data plane traffic. Transmission attempt information is carried within regular user data packets rather than requiring separate probe messages. This combines control plane measurement traffic with data plane user traffic, eliminating dedicated measurement overhead
Solution Approach 2:
The patent enables continuous measurement of link quality by utilizing the ongoing data plane traffic flow. Instead of periodic probing that interrupts data transmission, the measurement occurs continuously as part of the normal data transmission process, maintaining uninterrupted useful action
3Reliability
If retransmission mechanisms are implemented without link-layer acknowledgments, then reliability is improved, but loss of information increases about actual link quality
Solution Approach 1:
The patent implements feedback by having receiving nodes send back information about transmission attempts to transmitting nodes. This feedback mechanism allows nodes to learn about link quality on the reverse direction by observing how many attempts the remote node made to transmit packets, enabling ETX computation without link-layer acknowledgments
Data Source
AI summary
In one embodiment, a device in a computer network receives a particular packet associated with a transmission attempts value, the associated transmission attempts value indicative of a first number of times a transmitter has attempted to transmit the particular packet. In response, the device increases by one a stored successful attempts value stored at the device, the stored successful attempts value indicative of a second number of times the device has received the same particular packet. As such, a reachability rate of a link from the transmitter to the device may be determined based on comparing the associated transmission attempts value to the stored successful attempts value.