[Asterisk-Users] SIP newbie question:SIP proxy is necessary?

[Jeff]

Hi

a gateway and an ATA186 for test.

  
1.when I set them up in H323 mode, put gateway's IP in ATA186's
configuration ,ATA186 could send calls directly to gateway, and they
worked just well.
2. after I changed them to sip mode, and ATA186 got no dialtone.  


My question is:
 In order to send call from ATA186 to gateway,it is necessary to setup a
SIP proxy for ATA186/gateway?

( or it is possible for ATA186 to send call directly to Sip gateway? If
yes, How to setup ATA?)
  



Jeff