[asterisk-users] BUSY vs. CONGESTION

[Joseph]

I have two lines, fax & voice. 
I usually call out on fax line (to have voice line available)

I need to set the dial line based on dial-status.  When I try to call out on fax line and it is receiving a fax will I get a BUSY or CONGESTION signal?

What is the difference in dial plan condition: "goto" and "gotoif"

exten => 1,1,Dial(SIP/7780${EXTEN}@pstn-9998,60,tr)
exten => 1,2,Goto(1-${DIALSTATUS},1)
exten => 1-BUSY,1,Dial(SIP/9780${EXTEN}@pstn-4444,60,tr)
exten => 1-CONGESTION,1,Dial(SIP/9780${EXTEN}@pstn-4444,60,tr)

vs.

exten => 1,1,Dial(SIP/7780${EXTEN}@pstn-9998,60,tr)
exten => 1,n,GotoIf($["${DIALSTATUS}"="BUSY"]?line2)
exten => 1,n,GotoIf($["${DIALSTATUS}"="CONGESTION"]?line2)
exten => 1-n(line2),1,Dial(SIP/9780${EXTEN}@pstn-4444,60,tr)

-- 
Joseph