In data connectivity, the A-End (also called A-Loc) refers to the position of the location or network of the carrier on a telecommunications circuit, whereas the Z-end (also called Z-loc) identifies the location or network of the customer.

The position of each point — or letter — on the circuit can be physical or logical, such as a facility or a room within a facility, or connections to cabling or equipment. The terms A-end or A-loc (or any other letter indicating a point on a telecommunications circuit) may be seen on new circuit orders, customer or carrier trouble tickets, and circuit disconnect orders so that field technicians can easily discern what point to work on.