This document describes the representation of identity information in POLICY_DATA object for supporting policy based admission control in the Resource ReSerVation Protocol (RSVP). The goal of identity representation is to allow a process on a system to securely identify the owner and the application of the communicating process (e.g.@ user id) and convey this information in RSVP messages (PATH or RESV) in a secure manner. We describe the encoding of identities as RSVP policy element. We describe the processing rules to generate identity policy elements for multicast merged flows. Subsequently@ we describe representations of user identities for Kerberos and Public Key based user authentication mechanisms. In summary@ we describe the use of this identity information in an operational setting. This memo corrects an RSVP POLICY_DATA P-Type codepoint assignment error and a field size definition error in ErrorValue in RFC 2752.