This is the default implementation of the AddressResolver. The AddressResolver is a NIST-SIP specific
feature. The address resolover is consulted to convert a Hop into a meaningful address. The default
implementation is a passthrough. It only gets involved in setting the default port. However, you
can register your own AddressResolver implementation
The RI checks incoming via headers for resolving the sentBy field. If you want to set it to
some address that cannot be resolved you should register an AddressResolver with the stack.
This feature is also useful for DNS SRV lookup which is not implemented by the RI at present.