Signalling area
Also: td area, signal box, signalling centre
The patch of railway one signal box or control centre looks after.
The network is split into signalling areas, each controlled from one place: anything from a small lever-frame box to a huge control centre. Network Rail is gradually moving signalling into a handful of large Rail Operating Centres.
Each area has its own Train Describer, with a two-character code, so a berth is only unique together with its area.