Excerpts from the Introduction:

The present text aims to be a tutorial on the basics of the theory of network coding. The intent is a transparent presentation without necessarily presenting all results in their full generality. Part I is devoted to network coding for the transmission from a single source node to other nodes in the network. It starts with describing examples on network coding in the next section. Part II deals with the problem under the more general circumstances when there are multiple source nodes each intending to transmit to a different set of destination nodes.

Compared with the multi-source problem, the single-source network coding problem is better understood. Following [188], the best possible benefits of network coding can very much be achieved when the coding scheme is restricted to just linear transformations. Thus the tools employed in Part I are mostly algebraic. By contrast, the tools employed in Part II are mostly probabilistic.