3am Systems - Wireline Modem Handshakes and Modulations

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 - Adopted in 1994, V.34 improves upon V.32bis by using a range of carrier frequencies and symbol rates beyond 2400 baud, and a 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.

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