Xpress Transport Protocol version 4

The Xpress Transport Protocol (XTP) has been designed to support a variety of applications ranging from real-time embedded systems to multimedia distribution to applications distributed over a wide area network. In a single protocol it provides all the classic functionality of TCP, UDP, and TP4, plus new services such as transport multicast, multicast group management, transport layer priorities, traffic descriptions for quality-of-service negotiation, rate and burst control, and selectable error and flow control mechanisms. XTP has the same interconnectivity as TCP/UDP/TP4 because it operates over any network layer (IP, CLNP), any datalink layer (LLC, MAC), or directly on top of the AAL of ATM. In general, XTP avoids coupling policy with mechanism; XTP offers services but the user´s application defines what communications paradigm is most appropriate for its particular environment. XTP is a high performance protocol, and can sustain high throughput (92 Mbits/s over FDDI between a pair of IBM RS/6000 model 370s) and low latency (350 μs to move 100 bytes from user memory to user memory on two 50 MHz PCs connected by FDDI). Since XTP can run in parallel with all other transport protocols, and can run over whatever network layer (if any) is provided, it represents a low-risk way to exploit the increased functionality required for distributed applications without sacrificing connectedness or interoperability