fai

Hello guys,
I'm new member Fai. I'm new to telephony (about 2 months).And I have some questions I don't understand please help

1. In table DNATTRS is it only use for modify display number ?? And how to use SDNA to modify the table DNATTRS rather than ADDRESS ( I have ask why they don't change ADDRESS and use DNATTRS is due to always not enough space)
2. When I type add 123 456 7890 public pn 1234567 y $ $ $ What is pn means? And why have 3 $?
3. Where can I get more information about MAPCI?
4. When IOD have OM I alarm, why people use table dirphold -> lis all ->then del the OM files. What is OM files?
5. Where can I get informations about table CLLI, DIRPHOLD, CFX..etc.
6. When someone complains about the VOIP's noise level, I use to
set tcid 10 txgain -5
set tcid 10 rxgain -5
to lower the electric noise. Is it the right thing to set ? And how to reboot just one port rather than the whole thing.
7. Where can I get more information about travser command ?

Thanks for help :)