Since the callee generally does not know or trust the callee's server, only cryptographic signatures can be used to ensure that the information is valid. For example, the outgoing proxy might be operated by an ISP, enterprise or phone company and sign for the identity of the caller, using the signed-by parameter, with the identity of the company verified by a public key certificate similar to those used by web sites. See section 13.2 of RFC2543bis for encryption details.
2000-Jul-02 10:50pm islepchin@dynamicsoft.com