Test Result; What Could Go Wrong - ZyXEL Communications ZyWALL 110 Handbook

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Router(config)# no alg sip direct-signalling
Router(config)# no alg sip direct-media

Test result

Connect SIP phone to the USG, and check the register status. Register successfully.
Check the SIP register status on PBX.

What could go wrong?

SIP phone does not support transform itself, but the "SIP Transformations" does not be
checked.
SIP phone will contact with outside as not direct-signalling and direct media, but the
default setting on USG is on
413/749