You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: The Forwarding Indices of Graphs -- a Survey 
Chapter Title:  For Cartesian Product Graphs 
1. Abstract of Cited Paper (BIB001):  For a given connected graph $G$ of order $n$, a routing $R$ is a set of $n(n-1)$ elementary paths specified for every ordered pair of vertices in $G$. The vertex-forwarding index $\xi(G)$ (the edge-forwarding index $\pi(G)$) of $G$ is the maximum number of paths of $R$ passing through any vertex (resp. edge) in $G$. In this paper we consider the vertex- and the edge- forwarding indices of the cartesian product of $k\,(\ge 2)$ graphs. As applications of our results, we determine the vertex- and the edge- forwarding indices of some well-known graphs, such as the $n$-dimensional generalized hypercube, the undirected toroidal graph, the directed toroidal graph and the cartesian product of the Petersen graphs.

Literature Review:
The cartesian product can preserve many desirable properties of the factor graphs. A number of important graph-theoretic parameters, such as degree, diameter and connectivity, can be easily calculated from the factor graphs. In particular, the cartesian product of vertex-transitive (resp. Cayley) graphs is still a vertex-transitive (resp. Cayley) graph (see Section 2.3 in BIB001 ). Since quasi-Cayley graphs are vertex-transitive, the cartesian product of quasi-Cayley graphs is still a quasi-Cayley graph. Thus, determining the forwarding indices of the cartesian product graphs is of interest. Heydemann et al  obtained the following results first. Theorem 2.14 Let G and G ′ be two connected graphs with order n and n ′ , respectively. Then The inequalities are also valid for minimal routings. Moreover, the equality in (a) holds if both G and G ′ are Cayley digraphs. Recently, Xu et al BIB002 have considered the cartesian product of k graphs and obtained the following results. By Theorem 2.15 and Theorem 2.10, the cartesian product of quasi-Cayley graphs is vertex-optimal and the cartesian product of orbital regular graphs is edge-optimal.