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:  Theorem 2.4 (Heydemann et al 
1. Abstract of Cited Paper (BIB001):  To measure the efficiency of a routing in network, Chung et al [The forwarding index of communication networks. IEEE Trans. Inform. Theory, 33 (2) (1987), 224-232] proposed the notion of forwarding index and established an upper bound (n − 1)(n − 2) of this parameter for a connected graph of order n. This note improves this bound as (n − 1)(n − 2)− ( 2n− 2−∆ ⌊ 1 + n−1 ∆ ⌋) ⌊ n−1 ∆ ⌋ , where ∆ is the maximum degree of the graph G. This bound is best possible in the sense that there is a graph G attaining it.

Literature Review:
and the equality π(G) = π m (G) = B(G) is true if and only if there exists a minimal routing in G which induces the same load on every edge. The graph that attains this upper bound is a complete bipartite graph K n 2 , n 2 . Recently, Xu et al. BIB002 have showed the star K 1,n−1 is a unique graph that attains the upper bound in (1). Problem 2.5 Note that the upper bound given in (2) can be attained. Give a characterization of graphs whose vertex-or edge-forwarding indices attain the upper bound in BIB001 . Although the two concepts of vertex-and edge-forwarding index are similar, no interesting relationships is known between them except the following trivial inequalities. Theorem 2.6 (Heydemann et al  ) For any connected undirected graph G of order n, maximum degree ∆, minimum degree δ, The inequality in (a) is also valid for minimal routings. No nontrivial graph is found for which the forwarding indices hold one of the above equalities. Thus, it is necessary to further investigate the relationships between π(G) and ξ(G) or between π m (G) and ξ m (G). Problem 2.7 For a graph G and its line graph L(G), investigate the relationships between ξ(G) and π(L(G)) or between ξ m (G) and π m (L(G)).