On Aug 01, 1996 at 20:16 hrs, Arthur Marsh of 3:800/812 wrote to John Clarke:

Hello Arthur,

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

 AM> True, see TS 027 under "Transmission Loss".

I'll look it up when I get back to the office.  Thanks for the reference.

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

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

Ah!  That explains some of the levels we have been measuring.

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.

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

That is about what we have been getting on some dial-in links.  I am
pushing our people to see if we can get the local loops amplified and
equalized to take up to 14db out of the equation.

Regards ... John
@EOT:

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