Voice Over IP

THE V.110 AND V.120 RECOMMENDATIONS FOR ISDN INTERFACES

Several of the ITU-T V Series recommendations contain specifications on how certain signals are exchanged (and changed) between different types of networks. These standards have become increasingly important in the past few years as networks, carriers, and telephone administrations have implemented the ISDN and other digital-based systems, and the ISDN standards require the use of the specifications described here. On a conventional analog-based link (see Figure 6-2), V.110 and V.I120 define how certain V. 24-interchange signals are carried on the modulated analog signal. Both user data and modem control signals are carried across the link.

They are also applicable for systems in which modem ...