Networking is the study of how nodes, links, protocols, and traffic interact under constraints of latency, reliability, throughput, energy, and security. At graduate level, it is essential to model a network as a graph $G = (V,E)$, a queueing system, and a distributed control system simultaneously.

Graphs capture connectivity, centrality, cuts, shortest paths, clustering, and robustness. Important quantities include node degree $k_v$, path length $\ell পথ$? and betweenness centrality. In networking, graph cuts often reveal bottlenecks, while spectral properties illuminate connectivity and expansion.

Layering decomposes complexity into physical, link, network, transport, and application concerns. The end-to-end argument remains central: functions such as reliability or security may be more correctly implemented at endpoints than inside the network core, depending on failure modes and performance goals.