Asterisk 408: request time out

I am using the running asterisk on ec2.
Here is my config settings:

[general]
context=default
allowoverlap=no
enablestatic=yes
bindport=5060
bindaddr=0.0.0.0
srvlookup=yes
disallow=all
allow=ulaw
externip="xxx.xxx.xxx.xxx"
localnet=10.0.0.0/255.0.0.0

[atif]
type=friend
context=phones
host=dynamic

[tauquir]
type=friend
context=phones
host=dynamic

My caught packet:

U 2011/09/20 15:26:47.030827 10.0.1.12:5068 -> 122.248.248.170:5060
REGISTER sip:122.248.248.170 SIP/2.0.
Via: SIP/2.0/UDP 10.0.1.12:5068;rport;branch=z9hG4bKhdtfjkns.
Max-Forwards: 70.
To: “tauquir” sip:tauquir@122.248.248.170.
From: “tauquir” sip:tauquir@122.248.248.170;tag=xtubh.
Call-ID: xrxkwyoikneecza@studiomarch2.
CSeq: 775 REGISTER.
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,PRACK,REFER,NOTIFY,SUBSCRIBE,INFO,MESSAGE.
User-Agent: Twinkle/1.4.2.
Content-Length: 0.
.

U 2011/09/20 15:26:51.031204 10.0.1.12:5068 -> 122.248.248.170:5060
REGISTER sip:122.248.248.170 SIP/2.0.
Via: SIP/2.0/UDP 10.0.1.12:5068;rport;branch=z9hG4bKhdtfjkns.
Max-Forwards: 70.
To: “tauquir” sip:tauquir@122.248.248.170.
From: “tauquir” sip:tauquir@122.248.248.170;tag=xtubh.
Call-ID: xrxkwyoikneecza@studiomarch2.
CSeq: 775 REGISTER.
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,PRACK,REFER,NOTIFY,SUBSCRIBE,INFO,MESSAGE.
User-Agent: Twinkle/1.4.2.
Content-Length: 0.

Yestarday it was running fine but one way communication. Now it is not running at all giving me the timeout. My softphone client is “twinkle”.