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Unformatted text preview: the same order? file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/smtp_sim.htm (23 of 23) [12/09/2001 14.47.53] Chapter 29. NFS: Network File System NFS: Network File System
In this chapter we describe NFS, the Network File System, another popular application
that provides transparent file access for client applications. The building block of NFS is
Sun RPC: Remote Procedure Call, which we must describe first.
Nothing special need be done by the client program to use NFS. The kernel detects that
the file being accessed is on an NFS server and automatically generates the RPC calls to
access the file.
Our interest in NFS is not in all the details on file access, but in its use of the Internet
protocols, especially UDP. 29.2 Sun Remote Procedure Call
Most network programming is done by writing application programs that call systemprovided functions to perform specific network operations. For example, one function
performs a TCP active open, another performs a TCP passive open, another sends data
across a TCP connection, another sets specific protocol options (enable TCP's keepalive
timer), and so on. In Section 1.15 we mentioned that two popular sets of functions for
network programming (called APIs) are sockets and TLI. The API used by the client and
the API used by the server can be different, as can the operating systems running on the
client and server. It is the communication protocol and application protocol that determine
if a given client and server can communicate with each other. A Unix client written in C
using sockets and TCP can communicate with a mainframe server written in COBOL
using some other API and TCP, if both hosts are connected across a network and both
have a TCP/IP implementation.
Typically the client sends commands to the server, and the server sends replies back to the
client. All the applications we've looked at so far - Ping, Traceroute, routing daemons, and
the clients and servers for the DNS, TFTP, BOOTP, SNMP, Telnet, FTP, and SMTP-are
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