Voice Over IP

Appendix C. Tutorial on the V.34 and V.90 Modems

Welcome to the world of intelligent modems. Just a few short years ago, modems were rather prosaic instruments, and did little else but transport digital bits across the analog link. Today's modems are quite different from their predecessors, as we will see in this examination of V.34 and V.90. I have included V.34 in this discussion because the newer V.90 modem in the fall-back mode uses the V.34 operations on the analog side of the modem. V.90 also uses V.34 modulation in the upstream direction (from user modem to the network).