Hula: An Efficient Protocol for Reliable Delivery of Messages

We present a new protocol for reliable delivery of messages over a network that might lose, duplicate, reorder, or arbitrarily delay packets. It is the first protocol that guarantees exactly-once and ordered delivery on a connection while avoiding precursory handshakes. Avoiding handshakes reduces the overhead for sending small, intermittent messages as in remote procedure calls and protocols like HTTP. Like other practical protocols, it permits discarding information for idle connections. The protocol works by combining existing handshakebased and time-based protocols. It uses loosely synchronized clocks to avoid handshakes. A handshake is executed only upon an unexpectedly long packet delay or clock skew. Thus, unexpected conditions degrade performance but do not compromise reliability. The resultant protocol has the reliability of handshake-based protocols and the efficiency of time-based protocols.