 39.7). To show how this relates in sequential negotiation before actual transmission can take place. performance terms, the baud rate for V.22bis is 600bit/s. Each baud The V.32 transmission standard introduced 5 years ago, pushed full duplex operation over 2 wires up to 9600bit/s. The first to use a technique called echo cancellation, it was made possible only be- cause of the development of Digital Signal Processing (DSP) tech- Table 39.2 Error correction standards Standard Description CCITT Standard for error correcting protocols including LAP/M and MNP4 Level 1 Error correcting/Throughput reduced to 70% Level 2 Error correcting/Throughput reduced to 84% Level 3 Error correcting/Throughput up to Level 4 Error correcting/Throughput up to Figure 39.6 A signal space diagram (or constellation for V.22 bis modems Modem standards 39/7 Table 39.4 Interface standards Electrical Mechanic Functional Procedure Signals Protocols Protocols Interface Interface RS-232-C (V.24) (V.28) (ISO-2110) (X.21bis) (ISO 4903) RS-422-A (V.11/X.27) Figure 39.7 A signal space diagram for V.32 modems (ISO 4902) (V.24) (V.54) RS-423-A contains a 4 bit digital code (or 16 combinations), 600 baud X 4 bits (V.10/X.26) equals 2400bit/s. The baud rate for V.32 is much higher i.e. 2400bit/s. Four of the five bit V.32 code is used for information, the fifth for Trellis encoding. 2400 baud X 4 bits equals 9600bit/s (ISO 2593) performance. The recently ratified V.32bis standard builds on V.32 by using a 7 bit digital sequence per baud. With six bits for information and a but, when the specification was written, cable technology imposed similar baud rate, V.32bis performance is pushed up to 14400bit/s a limit of about 50 feet. over 2 wires. Standards must equally be applied to the DTE-DCE boundary Improvements made since can deliver four times that distance (Table 39.4; Enslow, 1988). Although perceived as a mundane without exceeding the capacitance limit, although V.28 sets no such subject, specifications and standards are in a continual state of f