Inverse Multiplexing for ATM
Inverse Multiplexing for ATM (IMA) is a standardized technology used to transport ATM traffic over a bundle of T1 or E1 lines, which is called an IMA Group. This allows for gradual increase in data link capacity where implementing a higher capacity solution like T3/E3 or SONET/SDH is not deemed feasible.
Source: Wikipedia — Inverse Multiplexing for ATM (CC BY-SA 4.0)