[Asterisk-Users] PRI incoming call????

[Ning Zhou]

Hi all,

I have a E100P digium card installed in my server, and now I am
working with the incoming call to this PRI interface.

my extensions.conf file for incoming call is: 
[default]
exten =>  , 1,Answer
exten => s,1,Dial(SIP/2001,20)
exten => s,2,Hangup

And when the incoming call comes, it appears:

    -- Executing Dial("Zap/1-1", "SIP/2001|20") in new stack
    -- Called 2001
    -- Accepting call from '' to '' on channel 0/1, span 1
    -- SIP/2001-5ef8 is ringing
    -- SIP/2001-5ef8 answered Zap/1-1
    -- Channel 0/1, span 1 got hangup
  == Spawn extension (default, s, 1) exited non-zero on 'Zap/1-1'
    -- Hungup 'Zap/1-1'

My question is what's the meaning of "Accepting call from '' to '' on
channel 0/1, span 1", and why I must have something like "exten =>  ,
1,Answer" in the 'default' context?

Since if I remove the "exten =>  , 1,Answer" 
[default]
exten => s,1,Dial(SIP/2001,20)
exten => s,2,Hangup

It appears some error in the asterisk 
 -- Extension '' in context 'default' from '' does not exist. 
Rejecting call on channel 0/1, span 1

Any idea will be highly appreciated!!

Thank you in advance!!

BR,
ning