The Scheduled Transfer (ST) Protocol

Abstract

This paper describes the Scheduled Transfer (ST) protocol that can be used by applications to bypass the operating system (OS) for network communications. The design of ST has been influenced by two overriding goals. First, we want ST to be used to move data between multiple vendors’ machines and over different media; therefore, we have proposed ST as an ANSI standard and defined a network protocol that is independent of the underlying physical layer. Second, ST has been designed to operate in a large, heavily-loaded scientific computing environment, and this goal is manifested in several ways. ST has been designed to minimize receive processing, relieving network congestion that could occur if the receiver exerts backpressure into the network. ST provides a mechanism by which upper layer protocol (ULP) headers can be separated from application data, a capability that is generally necessary to avoid a subsequent memory-to-memory copy in the host. ST includes support for reassembly of application messages that are striped across multiple physical interfaces. ST also includes a flow control mechanism that relieves the ULP from this responsibility and provides the opportunity for the implementor to offload this function to the network interface (NI).