  The increasing use of middleboxes (e.g., NATs, firewalls) in the Internet has
made it harder and harder to deploy new transport or higher layer protocols, or
even extensions to existing ones. Current work to address this Internet
transport ossification has led to renewed interest in UDP as an encapsulation
for making novel transport protocols deployable in the Internet. Examples
include Google's QUIC and the WebRTC data channel. The common assumption made
by these approaches is that encapsulation over UDP works in the present
Internet. This paper presents a measurement study to examine this assumption,
and provides guidance for protocol design based on our measurements.
  The key question is "can we run new transport protocols for the Internet over
UDP?" We find that the answer is largely "yes": UDP works on most networks, and
impairments are generally confined to access networks. This allows relatively
simple fallback strategies to work around it. Our answer is based on a twofold
methodology. First, we use the RIPE Atlas platform to basically check UDP
connectivity and first-packet latency. Second, we deploy copycat, a new tool
for comparing TCP loss, latency, and throughput with UDP by generating
TCP-shaped traffic with UDP headers.
