Study Group 15 is the home of standards for DSL. It also works on optical access and backbone technologies.

A key concern for many operators is to maximize network capacity in the last-mile (between the exchange and the customer premises). SG 15 standards on DSL are one way of helping towards this goal. The latest DSL flavours to be worked on are ADSL 2+ and VDSL2. Both give the copper cable owned by many incumbent telcos around the world an extended lease of life and bring higher bandwidth to small businesses and residential customers.

Less familiar, but equally as important are SG15 standards (ITU-T Recommendations) relating to passive optical networks (PONs). PONs are a effective way of implementing fiber to the home/building etc and a crucial step towards all-optical networks. PON technology is used in the local loop to connect residential and SME end users premises in an all-fibre network. By eliminating the dependence on expensive active network elements, the use of PON enables carriers to make significant savings.

SG 15 has also plays a leading role in the development of standards for the backbone including the key standard for synchronous data transmission over fiber optic networks, synchronous digital hierarchy (SDH). Wave division multiplexing (WDM) technology is another example of a technology in which ITU-T standards have played a very important role. WDM increases the data carrying capacity of an optical fibre by allowing simultaneous operation at more than one wavelength. Additionally SG 15 is working on automatically switched optical network (ASON). ASON provides quick and reliable service activation to service platforms like switches and routers. ASONs give operators a way to dynamically manage network traffic away from points of failure, for example.​