ITU-T V.27 PDF

Introduction

This modem is intended to be used primarily on Recommendation M.1020 [1] circuits but this does not preclude the use of this modem over circuits of lower quality at the discretion of the Administration concerned.

On leased circuits, considering that there exist and will come into being many modems with features designed to meet the requirements of the Administrations and users, this Recommendation in no way restricts the use of any other modems.

The principal characteristics for this recommended modem for transmitting data at 4800 bits per second on leased circuits are as follows:

a) it is capable of operating in a full-duplex mode or half-duplex mode;

b) differential eight-phase modulation with synchronous mode of operation;

c) possibility of a backward (supervisory) channel at modulation rates up to 75 bauds in each direction of transmission, the use of these channels being optional;

d) inclusion of a manually adjustable equalizer.