|dc.description.abstract||Network measurementis becoming increasingly important as a meanst o assesst he performanceo f
packet networks. Network performance can involve different aspects such as availability, link
failure detection etc, but in this thesis, we will focus on Quality of Service (QoS). Among the
metrics used to define QoS, we are particularly interested in end-to-end delay performance.
Recently, the adoption of Service Level Agreements (SLA) between network operators and their
customersh as becomea major driving force behind QoS measurementm: easurementi s necessaryt o
produce evidence of fulfilment of the requirements specified in the SLA.
Many attempts to do QoS based packet level measurement have been based on Active Measurement,
in which the properties of the end-to-end path are tested by adding testing packets generated from
the sending end. The main drawback of active probing is its intrusive nature which causes extraburden
on the network, and has been shown to distort the measured condition of the network. The
other category of network measurement is known as Passive Measurement. In contrast to Active
Measurement, there are no testing packets injected into the network, therefore no intrusion is caused.
The proposed applications using Passive Measurement are currently quite limited. But Passive
Measurement may offer the potential for an entirely different perspective compared with Active
In this thesis, the objective is to develop a measurement methodology for the end-to-end delay
performance based on Passive Measurement. We assume that the nodes in a network domain are
accessible.F or example, a network domain operatedb y a single network operator. The novel idea is
to estimate the local per-hop delay distribution based on a hybrid approach (model and
measurement-based)W. ith this approach,t he storagem easurementd ata requirement can be greatly
alleviated and the overhead put in each local node can be minimized, so maintaining the fast
switching operation in a local switcher or router.
Per-hop delay distributions have been widely used to infer QoS at a single local node. However, the
end-to-end delay distribution is more appropriate when quantifying delays across an end-to-end path.
Our approach is to capture every local node's delay distribution, and then the end-to-end delay
distribution can be obtained by convolving the estimated delay distributions. In this thesis, our
algorithm is examined by comparing the proximity of the actual end-to-end delay distribution with
the estimated one obtained by our measurement method under various conditions. e. g. in the
presence of Markovian or Power-law traffic. Furthermore, the comparison between Active
Measurement and our scheme is also studied.
Network operators may find our scheme useful when measuring the end-to-end delay performance.
As stated earlier, our scheme has no intrusive effect. Furthermore, the measurement result in the
local node can be re-usable to deduce other paths' end-to-end delay behaviour as long as this local
node is included in the path. Thus our scheme is more scalable compared with active probing.||en_US