What can we learn about cosmic-ray sources from the isotropic gamma-ray background?

The isotropic gamma-ray background (IGRB) is the residual all-sky gamma-ray emission after subtracting the individual sources and diffuse gamma-ray emission in the Galactic plane. It contains the hadornic emission of cosmic ray via the interactions with gas and photon field in their propagation, and hence bring information of cosmic-ray sources. I will discuss the implication of the IGRB for the Galactic and extragalactic cosmic-ray sources based on my recent works.