How to send and receive direct SIP calls

[xso]

If I want to call someone who also has a voip phone, should this call alway's go via provider / gateway ? Or is it possible to directly connect to an target SIP adress ?

 

If so, what external line should be used to make an outgoing direct SIP call ?

 

How should such a address look like , for example: 101@yourdomain.com, where 101 is the extension number to be reached ?

 

 

thanks in advance,

 

Rinse