In the

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

business, sub-loop unbundling (SLU) is a type of unbundled access whereby a sub-section of the

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 ...

is unbundled. In practice this often means the competitor placing a small street cabinet with a

DSLAM A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...

, next to a telco local copper aggregation cabinet or

serving area interface The serving area interface or service area interface (SAI) is an outdoor enclosure or metal box that allows access to telecommunications wiring. Alternate names *Access point (AP) *Cabinet (cab) *B-box (breakout box) *Cross box *Cross-connect b ...

and using a "tie cable" to connect to the last part of the local loop into customers' homes. Lyddington in Rutland was the first example of SLU in the UK when local provider Rutland Telecom unbundled the cabinet to offer VDSL broadband.

Advantages

The short range brings superior bit-rate performance, compared to normal local loop unbundling (LLU). The local loop can be accessed using shared metallic path or full metallic path facilities. In the latter, which was first deployed in the UK in the village of Lyddington b
Rutland Telecom
the telco loses remote access to the part of the local loop between the cabinet and the customer's premises unless the SLU Operator allows IP-level access via their

. The street cabinet is connected to a

point of presence A point of presence (PoP) is an artificial demarcation point or network interface point between communicating entities. A common example is an ISP point of presence, the local access point that allows users to connect to the Internet with their ...

on the national network using long-range wireless or fibre. Where fibre is used, the technology is often referred to as fibre to the cabinet (FTTC) Where

VDSL Very high-speed digital subscriber line (VDSL) and very high-speed digital subscriber line 2 (VDSL2) are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber li ...

VDSL2 Very high-speed digital subscriber line (VDSL) and very high-speed digital subscriber line 2 (VDSL2) are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber lin ...

is used to deliver a service, competing SLU operators at the same site must adhere to tie cable length limitations to prevent interference. Other restrictions are in force to prevent interference with

ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over Copper wire, copper telephone lines than a conventional voiceband modem ...

ADSL2+ G.992.5 (also referred to as ADSL2+, G.dmt.bis+, and G.adslplus) is an ITU-T standard for asymmetric digital subscriber line (ADSL) broadband Internet access. The standard has a maximum theoretical downstream sync speed of 24 megabits per secon ...

frequencies on the local loop from the serving exchange. In the UK the incumbent telco aggregation cabinets are known as Primary Connection Points (PCPs) and each one is assigned a CAL (Cabinet Assigned Loss) value based on its distance from the serving exchange. Telecommunications economics Local loop {{telephony-stub