OSI model Presentation Application Session Transport Network Data Link Physical ftp, telnet, smtp http tcp;udp ip NIC, MAC application protocols socket, streams, readers

OSI model Presentation Application Session Transport Network Data Link Physical ftp, telnet, smtp http tcp;udp ip NIC, MAC application protocols readers, writers streams sockets

Simplified layered model application protocols readers, writers streams sockets application protocols readers,writers server side (unix daemons) client side ftp, telnet, smtp http session NIC, MAC transport network streams sockets ftp, telnet, smtp http session NIC, MAC transport network

Services daemon Pronounced "demon." A UNIX program that executes in the background ready to perform an operation when required. Functioning like an extension to the operating system, a daemon is usually an unattended process that is initiated at startup. Typical daemons are print spoolers and handlers or a scheduler that starts up another process at a designated time. The term comes from Greek mythology meaning "guardian spirit." © 2001 Computer Language Company Inc. on unix: httpd, ftpd, telnetd… see /etc/services on windows: services

Remote Procedure Calls Client ObjectServer Object RPC Runtime marshall method & args call rpc unmarshall return val RPC Runtime unmarshall method & args marshall return val invoke remote methodinvoke local method

Java RMI Similar to RPC but –Object context maintains state between calls –Server can load needed classes from client –No symmetric mechanism needed at client –Methods as well as data can be transferred. This supports remote compute engines with computation not defined at engine initialization! Dynamic protocol invocation from discovered formal spec???

Simplified layered model application protocols readers, writers sockets streams, application protocols readers,writers server side (unix daemons) client side ftp, telnet, smtp http session NIC, MAC transport network streams sockets ftp, telnet, smtp http session NIC, MAC transport network

readers, writers streams sockets application protocols readers,writers server side (unix daemons) client side http session NIC, MAC transport network streams sockets http session NIC, MAC transport network SOAP, Z39.50, … application SOAP, Z39.50, … application

readers, writers streams sockets application protocols readers,writers server side (unix daemons) client side NIC, MAC URL Connection streams sockets NIC, MAC URL Connection SOAP, Z39.50, … application SOAP, Z39.50, … application