telephone line
A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or oth ...
, the term D-side or distribution side refers at any point on a
local loop
In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the co ...
connection between a customer's premises and a
telephone exchange
A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...
to the wires (or pairs of copper wires) leaving into the direction of the customer. Conversely, E-side is the exchange side of a telephone line, that is the wires leaving any connection point into the direction of the
telephone exchange
A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...
.
These terms are used, for example, by technicians of
Openreach
Openreach Limited is a company wholly owned by BT Group plc, that maintain telephone cables, ducts, cabinets and exchanges that connect nearly all homes and businesses in the United Kingdom to various national broadband and telephone networks. T ...
,
Virgin Media
Virgin Media Limited is a British telecommunications company which provides telephone, television and internet services in the United Kingdom. Its headquarters are at Green Park in Reading, England. It is owned by Virgin Media O2, a 50:50 ...
and other UK phone companies when referring to wiring connections going from a Primary Connection Point (PCP) telecoms cabinet to a point closer to a residence or business known as the "Distribution Point" (DP). On its way, it may pass through a Secondary Connection Point (SCP) telecoms cabinet, sometimes known as pillars, where again the wires going in the direction of the customer are called D side and those going back to exchange are called E side.
In the event of a broadband or phone line problem, technicians will test at any connection point whether the problem is D-side or E-side of that point, by disconnecting the wires on both ends and measuring connectivity and insulation. One potential correction that might be made is then to connect an alternative wire pair on the affected side, if available, or identify and repair the cable fault location.