Ankara : Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent University, 1995.Thesis (Ph.D.) -- Bilkent University, 1995.Includes bibliographical references leaves 81-83.The major source of errors in Asynchronous Transfer Mode (ATM.) networks
is expected to be buffer overflow during congestion, resulting in cell losses.
The large ratio of the end-to-end propagation time for a typical connection to
the cell transmission time makes lost cell recovery by means of retransmissionbased
error control techniques impractical especially for delay-sensitive highspeed
applications. As has been shown by many authors, forward error correction
is a promising alternative since it can improve end-to-end reliability without
requiring retransmissions. This thesis discusses the use of a two-level forward
error correction scheme for virtual channel and virtual path connections in ATM
networks. The performance of the scheme, which exploits erasure correcting
simple and interleaved block codes simultaneously, is studied via both analyses
and simulations. For a single-node virtual channel connection, a novel and
accurate discrete-time analytical cell loss model is developed first. Based on
this model, the reduction in the cell loss rate achieved by two-level coding is
then investigated extensively via iterative computational methods. For the case of a four-node, long-distance virtual channel connection that cannot tolerate any
loss, the use of the two-level coding scheme in conjunction with an automatic
repeat request mechanism is considered, and detailed simulations are made to
quantify the improvement achieved in the delay-throughput performance. The
results obtained indicate substantial performance improvements even for very
high network loads provided that an appropriate coding technique is chosen
according to the traffic characteristics. Typically, bursty traffic requires code
interleaving be used for effective loss recovery whereas small-latency simple block
codes suffice for random traffic. Two-level coding, which is shown to effectively
combine the fast and burst loss recovery capabilities of the individual coding
techniques, is attractive for traffic streams of unpredictable or time-varying
characteristics.Oğuz, Nihat CemPh.D
