T1

T1, or t1, is an acronym used in several different fields, each with its own distinct meaning. This article outlines some of the more common uses across technology, mathematics, business, typography, and medicine.

In telecommunications, a T1 line refers to a digital transmission link with a nominal capacity of 1.544 megabits per second. It carries 24 channels of 64 kilobits per second each and uses time-division multiplexing and framing to organize traffic. Historically widespread in North America and parts of Asia, T1 has supported voice and data services and remains in use in some legacy and enterprise networks, even as higher-capacity interfaces have become prevalent.

In typography, Type 1 fonts (often abbreviated as T1) describe the Adobe Type 1 font format used with PostScript. Type 1 fonts consist of separate outline data and metrics files and were central to desktop publishing in the 1990s. Although OpenType has largely superseded Type 1 in modern systems, many classic Type 1 fonts remain in use due to legacy workflows and compatibility.

In topology, a T1 space is a type of topological space that satisfies the T1 separation axiom. In a T1 space, for every pair of distinct points, each point has a neighborhood not containing the other. Equivalently, singletons {x} are closed. The T1 property is a standard part of the separation hierarchy and is satisfied by most familiar spaces, including Euclidean spaces.

In supply chain and manufacturing, Tier 1 (T1) denotes suppliers that provide direct components or assemblies to an original equipment manufacturer (OEM). Tier 1 suppliers typically bear primary responsibility for quality, delivery, and system integration, and they coordinate with Tier 2 and lower-tier suppliers to deliver complete products.

In medicine, T1 refers to the longitudinal relaxation time in magnetic resonance imaging (MRI). T1 characterizes how quickly protons realign with the magnetic field after excitation. T1-weighted images highlight tissues with short T1 times, such as fat, and are used to differentiate tissue properties and pathology alongside other imaging sequences.