  Current IP based networks support a wide range of delay-sensitive
applications such as live video streaming of network gaming. Providing an
adequate quality of experience to these applications is of paramount importance
for a network provider. The offered services are often regulated by tight
Service Level Agreements that needs to be continuously monitored. Since the
first step to guarantee a metric is to measure it, delay measurement becomes a
fundamental operation for a network provider. In many cases, the operator needs
to measure the delay on all network links. We refer to the collection of all
link delays as the Link Delay Vector (LDV). Typical solutions to collect the
LDV impose a substantial overhead on the network. In this paper, we propose a
solution to measure the LDV in real-time with a low-overhead approach. In
particular, we inject some flows into the network and infer the LDV based on
the delay of those flows. To this end, the monitoring flows and their paths
should be selected minimizing the network monitoring overhead. In this respect,
the challenging issue is to select a proper combination of flows such that by
knowing their delay it is possible to solve a set of a linear equation and
obtain a unique LDV. We first propose a mathematical formulation to select the
optimal combination of flows, in form of ILP problem. Then we develop a
heuristic algorithm to overcome the high computational complexity of existing
ILP solvers. As a further step, we propose a meta-heuristic algorithm to solve
the above-mentioned equations and infer the LDV. The challenging part of this
step is the volatility of link delays. The proposed solution is evaluated over
real-world emulated network topologies using the Mininet network emulator.
Emulation results show the accuracy of the proposed solution with a negligible
networking overhead in a real-time manner.
