Multi-server generalized processor sharing

End-hosts are increasingly equipped with multiple network interfaces, ranging from smartphones with multiple radios to servers with multi-homing. These interfaces are diverse; some are expensive to use (e.g. 4G), some are free (e.g WiFi) and they have different rates and reliability. On the other hand, end-hosts now run diverse applications with different priorities, from relatively less important web browsing to higher priority VoIP and video calls. Finally, users may have policies that constrain interface use (e.g. use 4G only for high priority flows). This paper tackles the question of how different applications can use different subsets of the available network interfaces, while ensuring a fair resource allocation among flows, while satisfying policy constraints. We generalize prior classical work on processor sharing (GPS) to the case of flows sharing different subsets of the available interfaces. We show a simple scheduling scheme for packet-by-packet GPS over multiple interfaces, and prove that it can provide bounded delay and rate guarantees.