Portal Network: The stargate plexus, which is the collection of all the stargate pairs in the Associated Worlds.  Pretty much every civilized system, except for really newly discovered ones, which may not, has at least one stargate in it.  Overall, the network vaguely resembles a spiderweb – the nodes being clusters of a few dozen systems (called constellations) linked together by a cluster of short-range wormholes, then hooked to neighboring clusters by longer-range wormholes.  The stargates themselves serve both to maintain the wormholes and act as communications relays for the extranet. Unlike many SF universes, these aren’t precursor gates; the system was established by the current polities, although only a few of the largest powers in the Worlds can manufacture their own gates – the Empire (and more specifically Ring Dynamics, ICC), and the Voniensa Republic (who make a point of maintaining their own state-run Portal Network – the Empire’s network, which forms most of the framework on which the Associated Worlds are based, they generously let the Accord of Galactic Polities treat as a common-carrier system, in exchange for, shall we say, consideration?) being the biggest two.  Almost everyone else piggybacks off theirs under the aegis of the Accord. While expansion used to be manual and painstaking, with improved automation making the Mark III Stargate more or less perpetually autonomous, most of the expansion of the network these days is being done by von Neumann wormhole-layers with only a little guidance from head office, so there are connected yet unexplored systems out there in the Periphery, and it’s entirely possible that the arrival of a stargate in their outer system, rather than that of explorers, will be many species’ first introduction to Life Out There.