Quality of service issues in ATM and IP networks

In this dissertation some quality of service problems in ATM and IP networks are investigated and efficient resource allocation methods are proposed in order to achieve required absolute and relative quality of service requirements of different network users or administrators.; For a shared memory ATM switch architecture, the problem of achieving optimum loss performance for cells with multiple loss priority classes is tackled using sample path dominance methods, numerical calculations and simulation techniques. In this problem we study the problem of the optimal design of buffer management policies for a shared memory ATM switch or demultiplexer. A system with cells of two different loss priorities is considered. Our objective is to determine the optimal policy that minimizes the total weighted cell loss. The problem of finding the optimal policy within the class of pushout and expelling policies is considered. Using sample path techniques the search space for the optimal policy is reduced to a subset of the entire policy set for each policy class. A numerical study based on the value iteration technique is used to investigate the structure of the optimal policy. This technique is also used to calculate the loss probabilities for different classes of cells for a system with small buffer size. Similar results are obtained for a shared memory ATM switch with a large buffer size which is fed by multi-priority on-off traffic, by simulation.; Furthermore, subsequently we studied the problem of creating an analytical model for TCP which can be embedded into a fluid model based network analyzer for TCP. In this work we develop an analytical model for TCP-Reno based on delay differential equations. Our intention is to match the window, throughput and queue evolution curves obtained from the model to that offered by a simulation output. We claim that this analytical model provides the basis for a analyzer that can be a substitute for the simulators that performs a packet by packet simulation. Some results that relate throughput to buffer and capacity allocation are presented.