On Jul 26, 1996 at 22:29 hrs, Dave Hatch of 3:711/808 wrote to Angus Tong:

Hello Dave,

 DH> The legit max level is -10dbm.  Using a S12 linecard, the actual 
 DH> optimal point is only about 1 db wide, and urgently needs to have the 
 DH> transmit level tuned to that point.  Of course, we're forbidden to 
 DH> adjust the level - and manufacturer spread is about 6dbm, 3 plus and 
 DH> minus of the nominal.  

 DH> US modems can adjust up to -9, which doesn't work at all well.  
 DH> Depending on your copper length, somewhere between -10 and -12 is 
 DH> optimal.  Too high a level produces clipping distortion, and wrecks 
 DH> the link well and truly.

The -10dbm is used as a standard for injection into cables as a reasonable
compromise between crosstalk and cable loss.  The allowance for loss in the
local loop is 7db so the level into the line card will vary between -10 and
-17dbm.  

I gather Telstra make no attempt to adjust for the local loop but do
maintain zero loss through the network so the level out of the last Telstra
exchange will be in the range -10 to -17dbm.  Allowing for far end local
loop of up to 7db the receieve level at the far end modem should be between
-10 and -24dbm.   
I've seen figures in here showing lower receive levels than this - either
Telstra run local loops over 7db or the network is not zero loss end to
end.


Regards ... John
@EOT:

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