CONNECTIVITY AND PROTOCOLS - THE TECHNICAL SIDE - OSI AND TCP IP, FTP, TELNET, SR, ILL, UPDATE/

Networks are modeled in layers. For each layer, one or more services a re defined, and for each service a protocol is specified. Two OSI appl ication level protocols have been defined for library services: SR and ILL. The underlying layers are supposed to be OSI services, but some implementations are using TCP/IP, and some are using a mixture of OSI and TCP/IP. The systems based directly on TCP/IP can not communicate w ith those based purely on OSI. The article discusses the pros and cons for choosing OSI or TCP/IP. Gateways between the OSI and TCP/IP netwo rks are needed. The ISO protocol SR and the ANSI protocol Z39.50 are b oth ''search and retrieve'' protocols. The SR is almost a subset of th e Z39.50, but they may become identical in the future. There is only o ne protocol for interlibrary loan, the ISO ILL protocol. It covers thr ee models of interlibrary loan and all services connected with ILL. Ot her services such as Explain, Scan and Update are presently being disc ussed in ISO TC 46. The library community also needs network services such as file transfer, remote login, directories, and electronic mail. These are discussed in the paper.