I'm currently reading the Engines of Light trilogy by Ken MacLeod. In that universe, there is no FTL travel nor communication, but starships can travel literall

I'm currently reading the Engines of Light trilogy by Ken MacLeod. In that universe, there is no FTL travel nor communication, but starships can travel literally at the speed of light. There are "spheres of influence" spanning some tens of lightyears, and the information delay between worlds is indeed a plot element.