Experience with the Xpress transfer protocol

This paper discusses our experience in implementing the Xpress Transfer Protocol. XTP is a transport and network layer protocol suitable for use as a Safenet Transfer Service in the Navy’s emerging SAFENET specification. We describe the background of SAFENET and XTP, the essential features of the protocol, our implementation environment, our communications architecture, the user interface, a description of some working X T P demonstration programs, and finally some measured performance results. 1. SAFENET The U.S. Navy is currently developing a specification for SAFENET (Survivable Adaptable Fiber Optic Embedded Network) [4,5] which is intended to address the communications requirements of Navy missioncritical computer resources. SAFENET is a communications architecture which uses local area networks and their protocols to provide connectivity among computer systems. SAFENET provides a protocol architecture as shown in Figure 1. In the upper layers of the OS1 Reference Model (layers 5-7), SAFENET User Services may be provided by either a MAP Application Interface (including FTAM and ACSE) in the Application Layer and the standard IS0 protocols in the Presentation and Session layers, or by a Lightweight Application Interface and Lightweight Support Services. In the middle layers (layers 3 4 , SAFENET Transfer Services may be provided by either the IS0 transport (connection-oriented and connectionless) and IS0 network (connectionless) protocols, or by the Xpress Transfer Protocol (XTP). In the lower layers (layers 1-2). SAFENET I specifies the IEEE 802.5C token ring, operating at 16 Mbit/s, using a dual counter-rotating ring topology and all fiber optic media. SAFENET I1 specifies the ANSI Fiber Distributed Data Interface (FDDI) LAN, again using a dual counterrotating ring topology and all fiber optic media, and operating at a data transmission rate of 100 Mbit/s. SAFENET USER MAP APPLICATION ~~~L~~~~~ (NTERFACE INTERFACE -