This course aims to develop an understanding of the tools and technologies for understanding and improving the performance of communication networks such as the Internet. It will introduce students to quantitative methods for loss and delay analysis in packet networks, using techniques from stochastic traffic modelling, Markov chains, and queueing theory. It will expose students to frameworks for optimisation and orchestration of network performance, including emerging paradigms such as software defined networking. The quantitative methods studied in this course will be applied to practical examples from network architecture and design, in domains ranging from data centres and wide-area networks to home networks, mobile networks, and content-delivery networks.