OptionalacceptAccepted content types; defaults to message/cpim text/plain.
OptionaladdressAdvertised connection address (often a placeholder for an active, listen-less client).
Our MSRP URI (msrp://host:port/session-id;tcp), echoed as a=path.
OptionalportThe advertised MSRP port (nominal for an active client).
OptionalsessionSDP session id/version stamp (pass a stable value; the caller supplies it, no clock here).
Options for buildMsrpOffer.