Active Measurement of the Latency in Cloud-based Networks

This paper presents a software tool for the active measurement of the one-way delay (latency) based on cyclic-path delay method in cloud. The principle consists in sending packets from the source node to every node belonging to a multicast group. Copies of the original packet will be forwarded through every possible path in the network before returning to the source node. The original idea is represented by the breaking of the well-known flooding rules which do not allow sending back the packet to the issuing node. The software tool is composed of two modules: one in C for measuring the latency on cyclic paths (packet generation and timestamping) and one in MATLAB for the estimation of one-way delays. The equation system derived from the cyclic-path delays is underdetermined, therefore the estimation of some latencies is needed. The estimation problem is formulated as a constrained optimization problem. The calibration was performed by means of a software tool, previously developed within Unified Communications Labs (UC Labs), where all the authors are currently working. The values of the latencies have a precision of nanoseconds and a good tracking ability of unexpected delay variations. The tool is scalable for both clouds orchestrated by OpenStack and physical networks, regardless of the topology and number of nodes.