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:  Degree Constraint 
1. Abstract of Cited Paper (BIB001):  For a given 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 edge forwarding index of a network (G,R), denoted π(G,R) is the maximum number of paths of R going through any edge e of G. The edge forwarding index of G, denoted π(G), is the minimum of π(G,R) taken over all the possible routings R of G. Given n ≤ 15 and Δ ≤ n − 1 we determine πΔ,n, the minimum of π(G) taken over all graphs G of order n with maximum degree at most Δ. This is known as the edge forwarding index problem. © 1993 by John Wiley & Sons, Inc.

Literature Review:
Although Saad  showed that for any graph determining the forwarding index problem is NP-complete, yet many authors are interested in the forwarding indices of a graph. Specially, it is still of interest to determine the exact value of the forwarding index with some graph-theoretical parameters. For example, Chung et al BIB001 , Bouabdallah and Sotteau BIB002 proposed to determine the minimum forwarding indices of (n, ∆)-graphs that has order n and maximum degree at most ∆. Given ∆ and n, let