Abstract
M.Ing.
Application Layer Forward Error Correction (AL-FEC) is a relatively new concept which
uses erasure codes to add reliability insurance to particular application streams on a network.
This concept has become particularly popular for media streaming services. Fountain codes
have shown promise as the erasure code of choice for these implementations. The Fountain
code concept is a principle that has two popular instantiations, the Luby Transform (LT) code
and the Raptor code. While the Raptor code is the more efficient of the two, the LT code is
the focal point of our dissertation. Our main objective in this dissertation was broken up into
two different primary objectives which we had to satisfy in its completion.
The first of these primary objectives entailed the finding of sets of input parameters which
would yield an optimal implementation of the LT code for a given set of input block sizes.
The simulation work performed in this investigation was done on a wide range of input
parameters for each input block size concerned. While there have been a number of other
studies which have performed such parameter optimisation we have not found any that
present such comprehensive results as we do.
The second of the primary objectives related to the analysis of the code when applied as an
AL-FEC reliability mechanism for streaming media. This simulation work was performed on
simulated IP network environments using the NS2 network simulator. The codes which were
applied to the network were based on the optimal parameter sets found in the first objective.
We analysed the effective throughput achievable by the code in the face of various packet
loss rates. With the data obtained from the simulations we then derived a constraint on the
allowable bit-rate of media which uses the LT code as an AL-FEC reliability mechanism.
In performing the work in this dissertation it was identified that it was required to develop
the LT code related simulation tools for performing the respective investigations. This
involved development of a stand-alone LT code simulator as well as an LT code AL-FEC
reliability mechanism for NS2.