Chapter 31 File Transfer & Remote File Access (NFS)

File Transfer Protocol (FTP) A file transfer service that can move a copy of a file from one computer to another, either interactively or in batch mode

FTP Commands (fig 31.1) (fig 31.1)(fig 31.1) Open, close Cd, lcd, pwd Ls, dir Prompt, binary Get, mget * Put, mput * quit

Anonymous FTP Used for public access of data files Username “anonymous” No password required

Client-Server Interaction in FTP When user runs ftp and opens a connection to a remote computer, the FTP client that uses TCP to create a control connection to an FTP server. client and server use the FTP protocol when they communicate across the control connection. user’s keystrokes are not passed directly to the server; instead, they are interpreted by the client. If interaction with server is needed, the client sends a request using the FTP protocol

Control and Data Connections A ‘control connection’ is used only to send commands and receive responses. Server listens on TCP port 21. A separate ‘data connection’ is created prior to each file transfer and closed at end of each file transfer. FTP client, acting as server, listens on port 20 (fig 31.2).(fig 31.2) Having separate connections for transfer and control: – helps make ftp protocol simpler and makes implementation easier since data and FTP commands are not mixed together – allows controls to be passed during middle of a file transfer, allowing files to be aborted easily – allows sender and receiver to use EOF condition on the data connection to indicate end of file.

Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP small set of commands only supports file transfer does not use password authentication: file can be transferred only if the file allows global access useful for bootstrapping a hardware device that is diskless or has no non-volatile memory to store operating system. – With minimal amount of ROM holding TFTP, UDP, and IP software, a device can broadcast a TFTP request across network for its binary operating system file.

Network File System(NFS) designed for remote file access in TCP/IP networks more efficient than FTP for reading or writing part of a file stored remotely. reduces network bandwidth requirements. allows an application to open a remote file, move to a specified position in the file, and read ore write data starting at that position. To append a file using NFS, the client sends the data to be appended to the server, and the server updates the file and returns an acknowledgement. NFS allows shared file access. Multiple clients using NFS client software can access a file on an NFS server. Uses remote procedure calls (RPC)