Bandwidth modelling for network-aware applications

Network-aware applications attempt to adjust their resource demands in response to changes in resource availability, e.g., if a server maintains a connection to a client, the server may want to adjust the amount of data sent to the client based on the effective bandwidth realized for the connection. Information about current and future network performance is therefore crucial for an adaptive application. This paper discusses three aspects of the coupling of applications and networks: (1) a network-aware application needs timely information about the status of the network; (2) a simple bandwidth estimation technique per forms reasonably well for TCP-Reno connections without timeouts; (3) enhancements proposed to TCP-Reno to reduce the number of timeouts (i.e., SACKs and its variants) increase the bandwidth but also improve the accuracy of bandwidth estimators developed by other researchers. The empirical observations reported in this paper are based on an in-vivo experiment in the Internet. Over a 6-month period, we logged the micro dynamics of random connections between a set of selected hosts. These results are encouraging for the developer of a network-aware application since they provide evidence that a simple widening of the interface between applications and network (protocol) may provide the information that allows an application to successfully adapt to changes in resource availability.