Abstract: Network-aware content delivery is an attractive approach to mitigate the problems produced by the significant fluctuations of the available bandwidth present in today's Internet. Such network-aware application require information about the current condition of the network to adapt their resource demands. Such information can be obtained at the network level, the transport protocol level, or directly by the application. This paper compares two kinds of application-level monitoring (at the sender and receiver side) and transport-level monitoring with regard to their ability to provide useful information to network-aware applications. Our results indicate that transport-level monitoring can effectively and efficiently satisfy the need for timely and accurate bandwidth information. This observation has direct implications for protocol/OS design: It is desirable to widen the transport layer API to allow the application efficient access to network status information required for adaptation.