Inducing Precise Network Latency via PFC Pause Frames
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Solution Overview
Problem
Existing network devices lack mechanisms to induce precise delays in the forwarding path, making it challenging to test and verify their congestion management features, such as packet ECN marking and selective dropping.
Innovation Solution
The use of Priority-Based Flow Control (PFC) streams with precisely selected quanta and controlled PFC frame rates allows for the induction of precise delays in network devices, enabling the testing of their traffic aging and delay behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traffic flooding is used to induce latency in a router, then the router buffers fill up and latency increases, but precise timing control is lost and the method simply floods the router with traffic
Solution Approach 1:
The system pre-calculates and pre-configures the exact pause duration and traffic quanta values needed to induce specific latency values before actual testing begins. This preliminary preparation enables precise latency control during the actual measurement phase without requiring trial-and-error flooding.
Solution Approach 2:
The system dynamically adjusts traffic parameters including pause duration, quanta values, and frame rates to precisely control the induced latency. By changing these parameters in a controlled manner, the system can induce specific latency values (e.g., 5ms, 10ms, 15ms) with precise timing control rather than uncontrolled flooding.
2Loss of time
If egress ports are disabled to induce latency, then traffic stops transmitting and buffers fill, but no precise timing control is achieved
Solution Approach 1:
Instead of statically disabling egress ports, the system dynamically controls egress port behavior using Priority-Based Flow Control (PFC) pause frames with dynamically adjusted pause durations. This allows the system to induce latency in a controlled, reversible manner while maintaining precise timing control and the ability to resume normal operation when needed.
3Measurement precision
If precise latency induction is implemented using PFC streams with controlled quanta and frame rates, then traffic aging functionality can be consistently exercised, but device complexity increases
Solution Approach 1:
The system introduces PFC pause frames as an intermediary mechanism between the test controller and the network device under test. These pause frames act as a mediator to precisely control traffic flow and induce latency without requiring direct modification of the network device's internal timing mechanisms, thereby managing complexity while achieving precise measurements.
Solution Approach 2:
The system implements feedback loops that monitor actual latency measurements and adjust PFC pause duration and quanta values accordingly. This feedback mechanism enables the system to compensate for variations and achieve consistent, repeatable latency induction while automating the complexity of precise timing control.
Data Source
AI summary
Techniques and architecture are described for inducing precise delays in a network device (network node) that has the capability to act on packets/traffic flows based on policy configurations of the network device and delays experienced by traffic in the network device. This capability may be used for testing and verification of the network device to verify that the network device meets the configured policies. Additionally, this capability may be utilized in an operational network to selectively induce delays and measure its impact for purposes such as, for example, planning, stress testing, resiliency, etc.