Starfleet Communications

From Memory Alpha, the free Star Trek reference.

Starfleet Communications was the division of Starfleet responsible for subspace communications between its many vessels and starbases. The Communications Research Center was based in San Francisco on Earth. It was home to the Pathfinder Project during the late 2370s. The facility included several holodecks. (VOY: "Pathfinder")

As of 2377 its staff included Admiral Owen Paris, Commander Peter Harkins, and Lieutenant Reginald Barclay. (VOY: "Pathfinder", "Inside Man", "Endgame")

The Starfleet Communications building is a modified picture of the Bank of China Tower in Hong Kong.

The branches of Starfleet
United Earth: Command • Materiel Supply Command • Medical • Mission Control • Security • Section 31 • Training Command
United Federation of Planets: Administration • Administrative Operations • Advanced Technologies • Command • Communications • Control • Dental • Engineering Corps • Exploratory Division • Information • Inspector General • Intelligence • Internal Affairs • Judge Advocate General • Materiel Supply Command • Medical • Mission Operations • Operational Support Services • Operations • Orbital Operations • OSHC • Research and Development • Science • Section 31 • Security • Shipyards Operations • Stellar Imaging • Tactical • Training Command • Warp Technologies