Data Communications Networking Devices - 4th Ed.pdf

4.2 MODEMS _____________________________________________________________________ 407Figure 4.34 V. 32 terbo signal space diagram and mapping for 16 800 bps. Hexadecimalnumbers refer to Q7Q6Q5Q4 and Q3Y2Y1Y0. Diagram courtesy of AT&T Paradyne)In examining the constellation patterns illustrated in Figures 4.34 and 4.35, notethat each signal element is identi®ed in hexadecimal format. Y0 is the leastsigni®cant bit in the least signi®cant hexadecimal digit. Q4 is the least signi®cant bitin the second hexadecimal digit. At 19 200 bps, Q8 is the least signi®cant bit in thethird hexadecimal digit. Also note that the 16 800 bps signal space diagram is asubset of the 19 200 bps signal space diagram.Non-linear encodingAt the new data rates of 16 800 and 19 200 bps, the V.32 terbo signal space diagramsare modi®ed by non-linear encoding. Non-linear encoding is enabled only duringdata transmission at these rates and not during other sequence states. Non-linearencoding is disabled during startup and retraining.