A ''reserved bandwidth'' service is described as a quality of service
enhancement in the vBNS. Design of this service is based on the charac
teristics of VBNS user traffic and the state of the art of commerciall
y available technology. An evolutionary strategy is adopted for VBNS Q
oS development with this service as the initial offering. Its implemen
tation scheme and issues are discussed in detail. Future extension to
include differentiated services or CoS is also described.