On Wed 21 Aug at 22:57 Poe Lim (3:623/630) wrote to Arthur Marsh:

 AM> If it supports V.32/V.32bis/V.34 it would answer with 
 AM> 2100 Hz incorporating phase reversals which would be 
 AM> detected by the echo cancellers. 

 PL> At what stage would the 2100Hz signal be sent? I know HST 
 PL> handshake is pretty quick, and I wonder if the USR looks for 
 PL> something at the start to go straight into HST mode.

The 2100 Hz answer tone is sent fairly early on in the piece... if the USR
HST responded quickly enough to prevent the sending of 2 phase reversals of
the 2100 Hz answer tone to the echo cancellers, then the echo cancellers
probably wouldn't get disabled. This would be helpful when an HST-only
modem calls a dual-standard HST/V.thirtysomething modem.


Echo cancellers apparently look for 2 phase reversals before being disabled.

--- msgedsq 2.1