The Resource reSerVation Protocol (RSVP) version 1 is the dominant Internet protocol for signaling Quality of Service (QoS) requirements. It has been extended for use in a wide variety of Internet signaling applications, such as traffic engineering and label distribution. However, the multiple features of the extended RSVP increase its complexity, and interactions among the features could cause confusion. In addition, due to the constraints of the original architecture, it is difficult to specify requirements for new Internet applications, such as mobile IP.  The Internet Engineering Task Force has mandated discussion of a new Internet Signaling Protocol Suite (ISPS). One proposal coming from this discussion is the Internet Draft "A Two-level Architecture for Internet Signaling". It proposes a Common Signaling Transport Protocol (CSTP), concentrating on state management and reliable data delivery, coupled with separate Application Layer Signaling Protocols, which implement the features of individual signaling applications.  Starting from the English specification of CSTP in the Internet Draft, a specification of CSTP has been written in the formal specification language SDL, and validated for several scenarios, which were based on the typical operation of RSVP version 1. Several errors have been found in the original specification, and solutions to these problems have been proposed.