On Mon 29 Jul at 22:14 John Clarke (3:713/730{at}fidonet) wrote to Dave Hatch:

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

True, see TS 027 under "Transmission Loss".

 JC> I gather Telstra make no attempt to adjust for the local 
 JC> loop but do maintain zero loss through the network so the 

There is 6 dB loss deliberately engineered in the inter-exchange network
(IEN), except for ISDN calls where the loss is inserted by the Terminal
Adaptor, ISDN phone or PABX.

 JC> level out of the last Telstra exchange will be in the range 
 JC> -10 to -17dbm.  Allowing for far end local loop of up to 7db 
 JC> the receieve level at the far end modem should be between 
 JC> -10 and -24dbm.   I've seen figures in here showing 
 JC> lower receive levels than this - either Telstra run 
 JC> local loops over 7db or the network is not zero loss 
 JC> end to end.

A max -10 dB transmit, max 7 dB CAN loss, 6 dB IEN loss, max 7 dB CAN loss
makes for a minimum receive level of -30 dB.

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