In orbit inside the orbit of the torus, but beyond the gasseous envelope are six massive asteroid-stations. They are in an inner orbit, so their orbital velocity is higher than the velocity of the torus - they revolve around the neutron star faster than the torus - so anything in their orbit moves around faster than in the torus. If an airship climbs up out of the Necklace and into the rarified air near the boundary between the vacuum of space and the atmosphere of the torus, tugs from the next station sweeping by can dock with the airship and speed it up to the station.
Here they can dock, either wait to drop back down into the torus when they reach their goal - at a far faster speed than they could flying around *in* the torus - or they can hire, or take passage with, a space ship also docked at the station, as required. Conversely, space ships can dock at the station and hire or take passage on an airship bound for the Necklace.
Also orbiting the torus further out - thus in a slower orbit - are six more asteroid-stations. The procedure to use these outer stations is the same as for the inner stations, but these stations are moving slower, thus they are convenient for reaching areas of the torus behind your starting place.
In effect, they are like highway lanes - the innermost on the left is a high speed lane, the center lane is a travel lane, and the right lane moves slower. If you assume the center lane - the Necklace - as your default, the left/inner lane moved forward faster, and the right lane moves backward in relation to you.
The stations are towns in themselves, with a transient and a permanent population. Some are mining the asteroid, others are storing and trans-shipping goods and passengers, and others yet are selling the transients services while they are there. They are made up of people from all the folks of the Necklace, and outsiders.