network protocols handbook.pdf

302Protocols GuideDECnet and ProtocolsDescriptionDECnet is a protocol suite developed and supported by Digital EquipmentCorporation (Digital or DEC, now part of HP). Several versions of DECnethave been released. The original DECnet allowed two directly attachedminicomputers to communicate. Subsequent releases expanded the DECnetfunctionality by adding support for additional proprietary and standardprotocols. Currently, two versions of DECnet are in wide use: DECnet PhaseIV and DECnet plus (DECnet V). The DECnet now is part of the HP Open-VMS.DECnet is developed under the framework of the Digital Network Architecture(DNA), which is a comprehensive layered network architecture that supportsa large set of proprietary and standard protocols.The DECnet Phase IV DNA is similar to the OSI architecture, which utilizes aseven layered approach. However, the Phase IV DNA is comprised of eightlayers. The DECnet Phase IV DNA specifies four upper layers to provideuser interaction services, network-management capabilities, file transfer,and session management. Specifically, these are referred to as the userlayer, network management layer, network application layer, and sessioncontrol layer.The DECnet phase V (or DECnet Plus or DECnet/OSI) defines a layeredmodel that implements three protocol suites: OSI, DECnet, and TCP/IP.DECnet plus conforms to the seven-layer OSI reference model and supportsmany of the standard OSI protocols. DECnet plus provides backward compatibilitywith DECnet Phase IV and supports multiple proprietary Digital protocols.DECnet plus supports functionality in the application, presentation,and session layers. The TCP/IP implementation of DECnet plus supports thelower-layer TCP/IP protocols and enables the transmission of DECnet trafficover TCP transport protocols.