Miao, Hwang, and Shieh use library redirection to add quality of service (QoS) awareness to legacy network applications built on user datagram protocol (UDP) and transmission control protocol (TCP). Their method, called RSVP library redirection (RLR), intercepts the standard socket calls of applications like file transfer protocol (FTP) by replacing standard dynamic linked libraries with RSVP-aware libraries. The new libraries call the standard socket libraries, but also invoke RSVP calls to make the necessary bandwidth reservations. The advantage of this technique is that existing applications need not be modified. Since many network applications exhibit similar protocol usage, the same interception library can provide upgraded service to many applications.

The technique is illustrated on FreeBSD Unix, using both standard datagram UDP applications (several versions of the file transfer program FTP), and connection-based TCP applications (real time audio and video programs). The results show that the technique does work. As background load increases, the applications maintain a constant throughput. The extra overhead of interception is negligible in most cases.

Call interception is not a new idea. RLR is an almost ideal situation for its use, and the authors’ work shows the idea to be practical in the real world. RLR can be applied in any situation where call interception is possible. One aspect of the strategy ignored by the authors is how RLR libraries get the information needed in order to make good quality of service decisions.

This paper is clearly organized and written. However, It would have benefited from further explanation of several anomalies in the reported performance results.