Abstract RSVP represents one of the most discussed network protocols in the last decade. Although there are a large number of papers that refer to the scalability problem of the protocol, only a very limited subset of those analyze the performance of RSVP. Up to this point no real evaluation exists on the efficiency and applicability of the scalability extensions proposed for RSVP. This paper presents a simulation study of RSVP and its scalability extensions in OPNET Modeler. The results obtained are put in context of the previous work done on the scalability of RSVP. It is found that the Summary Refresh extension considerably improves the performance of the protocol both in terms of message processing and message generation. An important finding of the present paper is that the scalability of RSVP is not directly linked to the specifications of the protocol and its extensions as such, but rather to the design choices of the actual implementation under evaluation.