R2C like service ... QUERY

Hi friends,

I want to use the PINT protocol to be able to provide an R2C "LIKE"  
service where I have the facility to connect two parties. But in this case
either of the parties involved in the call can be either an IP/SIP user or
a PSTN user ( Unlike in R2C where one party is a IP/SIP user and the other
is a PSTN user ). The reason I want all such calls to be routed through
my VoIP gateway ( governed by the PINT server ), so that when two IP
users are connected to each other their voice paths are switched through
my gateway enabling me to control such calls.

QUERY :
-------
    Currently the "to:" and the "c=" fields in the INVITE method for PINT
    are used to inform the PINT server about the two parties. This allows
    one party to be an IP/SIP user as indicated by the URI in the "to:"
    field and the other party to be a PSTN (TN network type) user or an
    IP (IN network type) user as indicated by the "c=" field.

    In my case I want to allow the originator of the service to be able
    to give any of the following destination combinations:

           ====================
           PartyA        PartyB
           ====================
           IP/SIP        IP/SIP
           PSTN          PSTN
           IP/SIP        PSTN   (Currently supported by "to:" and "c="
                                 field in INVITE of R2C service of PINT)
           ====================
    
    1). Which fields in the INVITE method can I use for this purpose ? 
    2). Can I specify a SIP URI in the "c=" field of the SDP header
        where the network type is "IN" indicating internet ? (The SDP
        rfc says that it is a fully qualified domain name)

  DG 
( RE - CDOT )
 
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           Whatever the mind can conceive and believe, it can achieve.
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