This document describes MIME types for application/ISUP and application/QSIG objects for use in SIP applications, according to the rules defined in RFC 2048. These types can be used to identify ISUP and QSIG objects within a SIP message such as INVITE or INFO, as might be implemented when using SIP in an environment where part of the call involves interworking to the PSTN. [STANDARDS-TRACK]