Analytical Models of Selected DiffServ Network Elements Supporting Assured Forwarding; Ph.D. Thesis

Analytical models of selected DiffServ network elements supporting Assured Forwarding (AF) service in a Differentiated Services (DiffServ) network are proposed in the dissertation. Simple analytical models for main network elements: meter/markers and droppers are provided. Models of the following meter/markers were proposed: Single Rate Three Color Marker (srTCM), Two Rate Three Color Marker (trTCM), and Time Sliding Window Three Color Marker (TSW3CM). The model of the latter involves finding the distribution of the TSW-averaged traffic rate approximated by the rate estimator. A respective probability density function that, if integrated in appropriate bounds, allows finding packet marking probabilities, is proposed. Models for srTCM and trTCM, that use the token bucket mechanism, are based on the classical queuing theory. Namely, models based on the M/M/1/K and D/M/1/K queuing systems are considered. The implementation of a dropper uses a selected Active Queue Management (AQM) mechanism. Most often, droppers are implemented as Multi-RED queues. Models for the following commonly used types of Multi-RED queues are developed: Weighted RED (WRED) and RED with In/Out and Coupled virtual queues (RIO-C). Both types of queues are scrutinized under two types of configuration of dropping thresholds: staggered and overlapped. The proposed models use the M/M/1/K and M/D/1/K queuing models with balking (impatient customers). Such models are often denoted as M(n)/M/1/K and M(n)/D/1/K, respectively. Additionally, in the case of RIO-C, a Bernoulli scheme is adopted in the model. Since the models for DiffServ elements are independent of each other, they can be combined to model a more complex system. An example of such a model, supplemented by the model for a TCP throughput by the other author, is presented in the dissertation.