asterisk users - May 2005 - newbie problem with registration of sip client

hello all,

now, i want to do configuration to make sip client
have extension on my asterisk.but i have a problem
with registration of sip client. 

*CLI> May 31 13:58:01 WARNING[4927]: chan_sip.c:886
retrans_pkt: Maximum retries exceeded on call
4b5cbb235a46d6ee0bcd278c1e294105@192.168.8.125 for
seqno 115 (Critical Request)
May 31 13:58:15 NOTICE[4927]: chan_sip.c:4585
sip_reg_timeout:    -- Registration for
'mustafa@192.168.8.188' timed out, trying again
May 31 13:58:21 WARNING[4927]: chan_sip.c:886
retrans_pkt: Maximum retries exceeded on call
4b5cbb235a46d6ee0bcd278c1e294105@192.168.8.125 for
seqno 116 (Critical Request)
May 31 13:58:35 NOTICE[4927]: chan_sip.c:4585
sip_reg_timeout:    -- Registration for
'mustafa@192.168.8.188' timed out, trying again

and if try the kphone from other pc to registration :

May 31 14:11:10 NOTICE[4927]: chan_sip.c:9138
handle_request_register: Registration from '"mustafa"
<sip:mustafa@station.net.my>' failed for
'192.168.8.188'

sip.conf:

[general]
context=default
bindport=5060                
bindaddr=192.168.8.125       
srvlookup=yes                
register =>
mustafa:mustafa@192.168.8.188:5060/20531604

[20531604]
context=mustafa
type=friend
;secret=mustafa
host=dynamic
defaultip=192.168.8.188
mailbox=1604

extension.conf :

[mustafa]
include =>default
                                                      
                                                      
 
exten => 20531604,1,Dial(SIP/20531604@mustafa,2Killed
[root@upm asterisk]# inging
exten => 20531604,3,wait(10)
exten => 20531604,4,Answer
exten => 20531604,5,Voicemail(s1604)
exten => 20531604,6,hangup

can anyone give advise and correct my configuration..
thanks..

regard,
shahdan..

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com