This modem is intended to be used primarily on special quality leased circuits, e.g. Recommendation M.1020 [i] or M.1025 [2] circuits but this does not preclude the use of this modem over circuits of lower
quality at the discretion of the administration
ITU-T V.33-1988 history
1988ITU-T V.33-1988 14 400 BITS PER SECOND MODEM STANDARDIZED FOR USE ON POINT-TO-POINT 4-WIRE LEASED TELEPHONE-TYPE CIRCUITS