Internet Self-Similarity, Modelling and Performance Evaluation

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Addis Ababa University


Understanding the nature of traffic and its associated delay process in high traffic systems, such as the Internet, is essential for Engineering, Operations & Performance evaluation of these networks. It has been a common practice to assume packet arrivals as a Poisson Process in modelling high Traffic Networks. However, data communication traffic levels fluctuate over time, and delays through congestion can occur even on lightly utilized links. These fluctuations can occur over very short periods of time giving rise to the concept of a burst of traffic. This high variability or bursty nature can be explained through Self-Similarity and Long-Range Dependence. In this thesis work an attempt is made to verify the Self-Similarity or Long-Range Dependence nature of Internet Traffic and its associated Packet Round Trip Delay process. Also Fractional Auto-Regressive Integrated Moving Average (FARIMA) Model is found to fit the long memory as well as the short memory properties of the collected Internet Traffic Data. An artificial traffic trace synthesis program based on the FARIMA model is also developed. While the research convincingly establishes the presence of LRD over a wide range of time scales in the packet traffic and delay processes, its implication to Queueing performance is a center of argument, in one hand arguments acknowledging LRD in packet traffic affecting Queueing performance, and in the other hand arguments emphasizing LRD has no practical impact and need not be incorporated into performance models. In this research it is tried to do experimentation, which demonstrates the first argument, that LRD in traffic indeed affects Queueing Performance. TCP, the reliable transport protocol of TCP/IP, employs an ACK (acknowledgment)-based window control, that is, a TCP sender updates its congestion window size every time it randomly measures Round Trip Time (RTT) or Packet Round Trip Delay. With the most basic mechanism in the Internet to detect losses, the sender re-transmit a segment if it's ACK has not been received in the expected amount of time. Therefore, TCP throughput performance depends on the RTT. Investigation on the relation between RTT Self-Similarity and TCP throughput performance as measured by the amount of bandwidth wastage due to premature timeouts is also covered. vi Real time traffic must get a fairly regulated number of packets through to the destination in a timely manner. If these packets are late enough to have missed their “play” window, they are useless. Voice over Internet Protocol (VoIP) is one real-time application carried over the Internet. Packet delay variations in Internet tend to create voice degradations, unless proper Quality of Service (QoS) measures are implemented. In this thesis work investigation on Packet Delay and VoIP relations have been done and QoS measures suggested.



High Traffic Networks