ect with all other backbones in a nondiscriminatory manner. For example, if a backbone with a national presence on both coasts were to peer with regional backbones only on one coast, it would allow the regional backbone to free ride on the national backbone's infrastructure investments. Asymmetries in the size of the traffic being conveyed can lead to similar problems (Kende 2000). Networks in Telecommunications As we discuss in Chapter 4, network economic effects subject network providers to powerful incentives to interconnect with one another. 36 In addition, market structure plays a critical role in determining the competitive impact of a refusal to interconnect. Specifically, the models in which the refusal to interconnect to harms competition assume the existence of a dominant player. The backbone market has historically been composed of five players of roughly equal size (Kende 2000). When the market is structured in this manner, refusals to interconnect cannot plausibly lead to anticompetitive harms, since the demand-side economies of scale created by network economic effects would place any network that refused to interconnect at a decisive competitive disadvantage.37 It is for this reason that the FCC has traditionally declined to mandate intercon- nection access among backbone providers. As the agency noted in its 2001 Inter- carrier Compensation NPRM, "The backbones appear to be successfully negotiating interconnection agreements among themselves without any regulatory interven- tion, and we see no reason to intervene in this efficiently functioning market" (FCC 2001c, p. 9656). The FCC followed similar reasoning in its orders clearing the Verizon-MCI, SBC-AT&T, and AT&T-BellSouth mergers, ruling that competition among five backbone providers of roughly equal size was sufficient to obviate the need to mandate interconnection access (FCC 2005g, 2005h, 2007a). Conversely, in approving the WorldCom-MCI merger, the FCC raised the concern that the merger would give one company a sufficiently dominant market