1. 1 CCITTInternationalTelegraph and Telephone Consultative Commitee (now ITU-T) ITU-TInternational Telecommuncations Union, Telecommunication Standardization Sector (former CCITT) V.nnITU-T (CCITT) recommended standards modulation standards Bell 103, V.21110, 150, 300 bps Bell 212A, V.221200 bps V.22bis2400 bps V.322400, 4800, 9600 bps V.32bis7200, 9600, 12000, 14400 bps V.Fastpreliminary V.34 V.3428800,..., 14400 bps V.34bis33600,..., 14400 bps V.9056.700 bps modulation fallback V.90 --> V.34 --> V.32bis --> V.32 --> V.22bis --> V.22 Async. modem glossary

2. 2 speed buffering interface speed connection speed flow control RTS/CTShardware control by special wires XON/XOFFsoftware control through special characters (Ctrl-Q/Ctrl-S) ASLAutomatic Speed Leveling during retraining error control MNP 1, 2, 3, 4Microcom Networking Protocol (de facto standard) V.42Link Access Protocol for Modems (LAPM) error-control fallback V.42 --> MNP4 --> MNP3 --> MNP2 --> MNP1 --> none Async. modem glossary

3. 3 data compression MNP3, 4protocol optimization (108-120%) MNP5, V42bistrue compression, (up to 400%, depends on data) compression fallback V.42bis --> MNP5 --> none DTEData Terminal Equipment (computer) DCEData Communication Equipment (modem) DTE-DCE signalling DTRData Terminal Ready, set by DTE DSRData Set Ready, set by modem RTS, CTSReday To Send, Clear To Send, used to hanshake on sped buffering CDCarrier Detect, set by modem when communication to remote modem is established Async. modem glossary