Rethinking TCP and UDP on Shared Satellite Links

The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are the two main traditional transport protocols on the Internet. TCP's congestion control algorithms allow TCP senders to "back off" when they detect packet loss, a feature that UDP does not implement. TCP is thus generally regarded as being "fair" towards other TCP connections, in contrast to UDP. Internet Service Providers (ISPs) with upstream narrowband satellite connectivity often block UDP on their satellite links as it is perceived to be disruptive in the presence of TCP. This paper argues that in practice, many TCP flows on satellite links are too short-lived to back off, and that therefore, these TCP flows behave like UDP. This poses the question as to how much is gained by blocking UDP, a transport protocol that has gained in importance in recent years with the emergence of QUIC and UDP-based peer-to-peer applications.