Test bed configuration:
source gateway (Asterisk 172.16.4.13) ->Asterisk (ooh323, 172.16.4.59)->destination gateway (Asterisk 172.16.4.9)

ooh323.conf:
[general]
bindaddr=0.0.0.0
h323id=ObjSysAsterisk
e164=100
callerid=asterisk
gatekeeper=DISABLE
context=SDSTest
disallow=all
allow=gsm
allow=ulaw
dtmfmode=rfc2833

extensions.conf:
[SDSTest]
exten => _XXXX.,1,NoOp(SDSTest)
exten => _XXXX.,n,Dial(OOH323/${EXTEN}@172.16.4.9,15,o)
exten => _XXXX.,n,Hangup
exten => h,1,NoOp(hangup cause is ${HANGUPCAUSE})