asterisk users - Dec 2008 - connect a LAN server to a WAN server as a sip client

hello
I have a asterisk server on WAN, and one server on LAN. And now there are
some users on the LAN server. Users on the LAN server need to make phone
calls to PSTN through the WAN server.
Now on WAN server, there is a user account for the LAN server to register,
and it's an account  with multiple ports.(So more than one users on the LAN
server can make phone calls through the WAN server at the same time)
Here are my config files of the LAN server:


sip.conf:
[general]
register=>121022:123456 at 122.102.5.42 <121022%3A123456 at
122.102.5.42>
[121022]
type=peer
username=121022
secret=123456
host=122.102.6.43
fromuser=121022
canrenvite=no
insecure=very
quality=yes
nat=yes
context=1111

extensions.conf:
[1111]
exten=>_013X.,1,Dial(SIP/${EXTEN}@121022)
exten=>_010XXXXXXXX,1,Dial(SIP/${EXTEN}@121022)
exten=>_X.,1,Dial(SIP/${EXTEN},60)

The good news is that user on the LAN server can make call throught the WAN
server; the problem is there can be only one user make phone calls at one
time. Can anyone tell me how to fix it? thanks
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