Service access procedure (SAP) for a transport layer protocol

Abstract The article presents the concept and design of a Service Access Procedure (SAP) for establishing transparent and reliable connections between the top three layer protocols of the ISO Open System Interconnection (OSI) and the corresponding bottom four layer protocols. The SAP allows a user to utilize network authentication services and accommodates for a single network login while establishing an active connection. Of the bottom four layers, the transport and network protocols are often selected to be the U. S. Department of Defense (DoD) standard Transmission Control Protocol (TCP) and Internet Protocol (IP), respectively. The upper layer protocols are usually a part of the host processor's software whereas the TCP/IP and the subsequent lower layer protocols might be resident in a physically distinct device such as an interface unit (IU). The rationale for residency of the TCP/IP in IUs, the concept and design of a TCP SAP, and the basis for selection of the lower layer protocols that constitute the host-front-end protocol set are presented in this article.