The Client-Server ModelAserver is aprogramthatprovidea service.- It makes some resource available to other programs running somewhereonthenetwork- The resource could be anything: a database, a file system, a printer, amodem, a screen, or a scanner.- The server program runs on the machine which resource is attached to,and waits passively until the services are required.- Servers are often started up at boot-time, via commands in a start-upscript and Servers usually spent most of their time asleep, waiting forwork.A client is a program that uses a resource.- It may be running on the machine to which the resource is attached, or ona different machine.-A client actively makes a connectionacross the network to the server itrequires
The Client-Server Model • A server is a program that provide a service. − It makes some resource available to other programs running somewhere on the network. − The resource could be anything: a database, a file system, a printer, a modem, a screen, or a scanner. − The server program runs on the machine which resource is attached to, and waits passively until the services are required. − Servers are often started up at boot-time, via commands in a start-up script and Servers usually spent most of their time asleep, waiting for work. • A client is a program that uses a resource. − It may be running on the machine to which the resource is attached, or on a different machine. − A client actively makes a connection across the network to the server it requires
The Client-Server Model (continue)ThetermsclientandserveraresometimesusedtorefertoamachineWe may point out a computer on our network which has a large disk attached and sayThat is our file server, and these workstations here are its clients"We may refer to a machine with a printer attached as a print server"The term client and server refer to the relationship between individual programs, nottomachines.In general, machines cannot simply be labeled as clients and servers.One machine might be a server for a piece ofthe file system, but a client ofa remoteprint server.Example, a program which is a server for a database might itself contact a time servertoobtainan accurate timestamp to attachto a new record in the databaseIn UNIX world, theterm daemon is sometimes used to refer to a server.It means that the server is “permanently available, which implies that it is started atboot-time.Daemon usually provide a “system-related" service, such as: rlogind, telnetd, ftpdhttpd,nfsd.... etc
The Client-Server Model (continue) • The terms client and server are sometimes used to refer to a machine. • We may point out a computer on our network which has a large disk attached and say “That is our file server, and these workstations here are its clients”. • We may refer to a machine with a printer attached as a “print server”. • The term client and server refer to the relationship between individual programs, not to machines. • In general, machines cannot simply be labeled as clients and servers. • One machine might be a server for a piece of the file system, but a client of a remote print server. • Example, a program which is a server for a database might itself contact a time server to obtain an accurate timestamp to attach to a new record in the database. • In UNIX world, the term daemon is sometimes used to refer to a server. • It means that the server is “permanently available”, which implies that it is started at boot-time. • Daemon usually provide a “system-related” service, such as: rlogind, telnetd, ftpd, httpd, nfsd,. etc