The EGRB measured by EGRET can be represented as of the power-law form
between 0.1 and ~ 50 GeV (statistics limited) . At energies below 30 MeV, the EGRB spectrum appears to be steeper, as determined from an analysis of COMPTEL data .
Figure 1, taken from Ref. , shows a comparison between the diffuse inner-galactic and extragalactic spectra measured by EGRET. It shows that these diffuse spectra have fundamentally different origins. The galactic spectrum shows evidence of the predicted "bump" from neutral pion decay ,  whereas the extragalactic spectrum shows no such feature as would be expected from cosmic ray p - p interactions. This type of direct spectral information eliminates purely diffuse extragalactic cosmic-ray interaction origin models, such as have been proposed  as explanations for the EGRB.
Figure 1. Comparison of Galactic and extragalactic diffuse spectra as determined by EGRET.