In the GPO days, the Primary Cross Connection Point (P.C.P.) in the external cable network was known as a cabinet or CAB. It came in two sizes with the double door variety being most common. The two doors are held in place by two turnbuckle blocks secured by triangular headed bolts. The box spanner designed to unbolt these was known as a CAB key.
A smaller capacity CAB with a single door being more common in rural areas or in urban areas as a Secondary Cross Connection Point. Both examples shown have the letters GPO on the lid.
The street cabinet provides flexibility between thick often multi-100 pair cables to the exchanges allowing them to be cross connected to active pairs in the cable to the distribution point to the premises. Typically there are many more pairs of wires leaving a cabinet as not all will be in use, than arriving from the exchange.
If a small cabinet is used as a Secondary Cross Connection Point, it is connected between the Primary Cross Connection Point and the distribution point, allowing additional flexibility providing more economy in the provision of underground copper cables.