The Highlands

Centered on Earth, the Highlands represent the most scientifically and technologically advanced human civilization known.
The Earth itself, in the aftermath of the Great Compromise is divided between the Christian Compact and the Islamic States. World government is embodied in the Global Security Council which itself provides members to the Highland Parliament's Upper House. There are still other groups on the planet, but they are of small political note. Many radical groups from both camps left Earth long ago, most never survived more than a generation or two at their off world colonies.
While the B/G engine made interstellar travel possible, it was the hyperspacial drill which made it easy. The B/G engine allows any craft to open a passageway into subspace. In subspace it is theoretically possible for a ship to travel at the rate of one light year per hour. So its four hours to Alpha Century and a week and half to Polaris. But subspace has no stars. Instead subspace topology has a series of gravitational plateaus where large masses exist in normal space. Subspace navigation is the process of mapping those plateaus to corresponding points in normal space, a challenging mathematical exercise.
But a hyperspacial drill allows a portal to be open between normal and subspace. In that portal a gate can be planted. A gate with one side in subspace and one side in normal space. Then any craft, even one without a B/G engine configured for opening subspace, can enter subspace.
In the Highlands a series of navigation beacons have been strung between the gates of the major systems. They form a kind of major subspace road between the high population worlds. Where the roads cross great intersection gates are built. Between the minor worlds smaller beacons, scattered father apart, allow travel, but at a reduced rate of speed, less a beacon signal be lost, and a ship likewise be lost in subspace.
Between the major intersections communication signals are tight beam broadcast through subspace, giving effectively instantaneous interstellar communication. This hypercable communication system, as it is called, is limited to major population centers on major subspace routes. Areas off these routes, typically called Blue Highways after the way they are marked on maps, are usually limited to the speed of the Grand Postal System, That is no faster than a ship can travel.
There are still some worlds in the Highlands which are not even on the Blue Highways. Most are poor and low population. But even these are serviced by the Grand Post, though perhaps not every day or even every week.
The worlds themselves, at the top of the subspace gravitational plateaus have access to another technology. Though revealed by Barnes work on subspacial physics it took another fifty years to make the transmat portal a reality. Basically a transmat portal in nothing but two subspace gates back to back, so that one might step from real space to real space without traversing the real space in between. They only work within the same gravitational plateaus, so no interplanetary or interstellar portals, not even from orbit to surface.