[asterisk-users] Asterisk as a SIP to SIP Gateway

Hi,

It is my second time when I try to use asterisk :)
I am starting with the following issue.
I want asterisk to behave as a gateway between two sip networks.

My architecture is the following:

SIP proxy (registrar - domain A)    ---------------   Asterisk Gateway ------------------------ SIP proxy (registrar - domain B)
                                                                            (number of UAC registered in domain B)

Asterisk form the point of view of the domain A and users registered in A is outbound proxy and from the point of view of domain B is a set of SIP clients.
Is it possible to configure asterisk in such way that for a particular user from domain A who calls through asterisk
the SIP signaling will be passed through some pointed user (asterisk user logged in domain B).
It is easy to achieve that in the other direction. when there is a connection from domain B to a particular user which was registered
by asterisk. One can forward such connection to some user registered in sip proxy in domain A.
Please point me how can make such a mapping between the calling user from domain A and a user in asterisk who is registered in domain B??

Thank You in advance.
Regards

Tomasz