V.34 handshake & modulation
used in 2-wire duplex modems
Handshake timing diagram
Phase 1 signals (V.8 network interaction)
CI: call indicator (optional, sent using V.21(L), here not present)
ANSam: amplitude modulated answer tone, with phase reversals (indicating V.8 capability)
CM: call Menu, sent using V.21(L)
JM: joint Menu, sent using V.21(H)
CJ: CM terminator, sent using V.21(L)
Phase 2 signals (line probing and ranging)
INFO: 4 sequences sent using 600 bps DPSK
L1/L2 : 21 tone line probing signals
A/A' : 2400 Hz tone with phase reversals
B/B' : 1200 Hz tone with phase reversals
Phase 3 signals (equalizer and echo canceller training)
S/S': symbol sequence pattern
MD: manufacturer defined training sequence for training the echo canceller (optional)
PP: training sequence for training the equalizer
TRN: training sequence (scrambled ones)
J/J': specific 16-bit patterns
MP: modulation parameter signal
Phase 4 signals (final training, full duplex mode)
J/J'/TRN: see phase 3
MP/MP'
E: end of MP
B1: scrambled ones
(adapted from 'ITU-T Recommendation V.34', 1996)
Analysis of a recorded call
Phase 1 signals (V.8 network interaction)
Phase 2 signals (line probing and ranging)
Phase 3 signals (equalizer and echo canceller training)
Phase 4 signals (final training, full duplex mode) - not shown
Note: The annotations shown here are but an over-simplification of the intricacies of the V.34 handshake.
For more details, consult the relevant ITU-T documentation.
Annotated spectral plot of recorded audio (Frequency/Hz against Time/s)
Modulation
V.34 improves upon V.32bis in a number of ways: in adaptivity, constellation shaping and precoding.
Adaptivity is achieved by using a range of carrier frequencies and symbol rates, including some beyond those in V.32bis.
Shaping is a technique used to minimize the average signal power for a given constellation, and a technique known as shell mapping is used, yielding a 0.8dB shaping gain.
Precoding is equalization applied at the transmitter based on information from the receiver, ensuring better use of the full bandwidth.
V.34 uses a larger, 1664-point super-constellation, with all symbols being a subset of this super-constellation.
For example, at 28,800 bps, Fc=1800 Hz, Rs=3000 baud, Symbols=1408; at 33,600 bps, Fc=1959 Hz, Rs=3429 baud, Symbols=1664.
V.34 was adopted in 1994.
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