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:  Optimal Graphs 
1. Abstract of Cited Paper (BIB001):  Due to recent developments of parallel and distributed computing, the design and analysis of various interconnection networks has been a main topic of research for the past few years and is still stimulated by the new technologies of communication networks such as optic fibers. There are many advantages in using Cayley (di)graphs as models for interconnection networks. This work first surveys some classes of Cayley graphs which are well studied as models of interconnection networks. Results and problems related to routings in networks are then presented, with emphasis on loads of nodes and links in routings.

Literature Review:
A graph G is said to be vertex-optimal if π(G) = A(G), and edge-optimal if Heydemann et al  showed that the equality (3) is valid for any Cayley graph. Theorem 2.8 Let G be a connected Cayley graph with order n. Then From Theorem 2.8, Cayley graphs are vertex-optimal. Some results and problems on the forwarding indices of vertex-transitive or Cayley graphs, an excellent survey on this subject has been given by Heydemann BIB002 . Heydemann et al BIB001 have constructed a class of graphs for which the vertexforwarding index is not given by a minimal consistent routing. Thus, they suggested the following problems worthy of being considered. BIB001 ) For which graph or digraph G does there exist a minimal consistent routing R such that