LLDP based link latency monitoring in software defined networks

Current latency monitoring approaches for Software Defined Network often use the control plane as the infrastructure to inject time-stamp data packets as probe packets to measure the network latency at a particular time, but suffer from three major issues when the network latency needs to be continuously monitored: 1) the increased control plane's overhead, 2) the feasibility of using data packets as probe packets, and 3) the increasing measurement error using OpenFlow messages to measure the time from the controller to a switch as the network scale grows. To overcome these issues, this paper proposes link latency monitoring using time-stamped Link Layer Discovery Protocol (LLDP) packets, aided by a linear calibration function to reduce errors of measuring switch-controller delays. Time-stamping LLDP packets, which are used to discover the global network topology in SDNs, does not add extra workload to the control plane and the results always reach the controller thus while avoiding measurement failures that might occur in existing approaches. Our linear calibration function can reduce the measurement error to less than 5% of the link latency measured by ping in a network with up to 30 switches and the link latency not less than 1ms.