Modeling and improving the performance of interactive TCP traffic in computer networks
Creators: name: Dimopoulos, Peter
Publisher: name: RMIT University
Year: 2024

description: The Internet has become one of the most widely used forms of communication available. Many applications used on the Internet require the user to interact constantly with the network. For example web browsing where the user will expect the browser to respond quickly, to finish loading pages quickly and to do all of this at an equal level for all users. The network's performance is dependant on the protocols it uses and how the resources of the network are distributed. This is why TCP (Transmission Control Protocol) is one of the most important protocols, because it controls the amount of data entering the network and provides reliability to most interactive applications.<br><br>The thesis starts by introducing a basic TCP model which is later extended to model the effects of burstiness produced by TCP. Burstiness can cause a routers buffer to unnecessarily overflow. These overflows cause TCP connections to under-utilise link bandwidth because of unnecessary packet retransmissions. A model to define a quantitative measure of both burstiness and throughput of a system of TCP connections is introduced. The model gives insight into how the TCP protocol causes burstiness and can be used to find scenarios where burstiness is decreased. This helps to improve the utilization of links by reducing the burstiness of protocols.<br><br>An important performance metric for interactive traffic is user perceived delay, the delay that an end user would encounter when using an application. An example of user perceived delay is the time a user waits before a HTML web page starts loading. The retransmission delays are the most important type of delay for interactive traffic because they are usually very large. A dynamic priority RED Queue (DPRQ) is introduced which changes the priority of the queues based on the goodput (throughput of succesfully transmitted packets) threshold of the interactive traffic. Using dynamic priority allows packet loss to be reduced by up to eight times for interactive traffic, which intern reduces retransmission delay.<br><br>Fairness measures how equally network resources are allocated amongst different connections. When a link with TCP connections is overloaded each connection on the link will reduce its throughput to allow all the connections to have approximately equal load. This does not take into account that other links may be under utilized. The fairness issue is addressed by introducing Multipath TCP (MATCP) which allows path selection to occur at the TCP layer. This allows each unique flow to take a different path, instead of all the flows of one source using the same path. Using MATCP, a finer grain of load-balancing can be achieved and the complexity and state required in the network is greatly reduced.<br><br>Two analytic models are provided in chapters three and four, which investigate slow start and TCP burstiness. In chapter five the DPRQ queue is introduced to reduce user perceived delay. An analytic model of the DPRQ is provided and verified through experimental simulation. In chapter six an analytic model of Multipath TCP is provided, which is also verified by simulation. <br>