File Transfer And Access (FTP, TFTP, NFS)

Remote File Access, Transfer and Storage Networks For different goals variety of approaches to remote file access are there. 1. Lower the Cost 2. To Archive Data 3. Share Data across multiple programs, users or sites.

File Sharing Has two distinct forms: 1.On-Line Access 2.Whole File Copying (File Transfer)

On-Line Shared Access Allowing multiple programs to access a single file concurrently. Change to file take effect immediately and are available to all programs that access the file. Eg. An O.S. makes file available via a shared, on-line access protocol, remote OS can run s/w that accesses the files without requiring users to invoke a special application program.

Advantages and Disadvantages Advantages: (1) Remote File Access occurs with no visible changes to application programs. (2) Perform arbitrary computations on shared data. Disadvantages: (1) Network or Remote Machine is down (2) Remote machine may be overloaded or network may be congested. (3) In timeout conditions application programs seems less reliable.

Implementation 1.File names available on one computer may be impossible to map into the file namespace of another. 2.Must handle notions of Ownership, Authorization, and access protection. 3.File representation and operations vary from machine to machine, it may be difficult or impossible to implement all operations on all files.

Sharing by File Transfer Accessing remote data with a transfer mechanism is a two step process: First obtain a local copy of file and then operates on the copy. User must invoke a special-purpose client program to transfer files. Client contacts a server on the remote machine and requests a copy of file. Advantage: Efficiency and Speed.

FTP – TCP/IP File Transfer Protocol FTP offers many facilities beyond the transfer function. 1.Interactive Access: Interactive Interface that allows humans to interact with remote server. 2.Format Specification: Specify the type and representation of the stored data. 3.Authentication Control: Requires clients to authorize themselves by sending a login name and password to the server before requesting file transfers.

FTP Process Model Allow concurrent access by multiple clients. Clients use TCP to connect to server. FTP slave accepts and handles a control connection from the client, but uses an additional process and additional connection to handle each data transfer operations. A new TCP connection and a new process on both the client and server side is created for each data transfer operation.

Data Transfer Connections and the Data Transfer Processes, that use them are created dynamically, when needed, but the control connection persists throughout a session. If it disappears, the session is terminated and the software at both ends terminates all data transfer processes.

Operating System Operating System TCP/IP Internet Client System Server System Data Transfer Data Transfer Control Process Control Process Connection Lines