TCP IP Illustrated

Htm 1 of 24 12092001 144749 chapter 27 ftp file

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Unformatted text preview: this server. This connection is used for commands from the client to the server and for the server's replies. The IP type-of-service for the control connection should be "minimize delay" since the commands are normally typed by a human user (Figure 3.2). 2. A data connection is created each time a file is transferred between the client and server. (It is also created at other times, as we'll see later.) The IP type-of-service for the data connection should be "maximize throughput" since this connection is for file transfer. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (1 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol Figure 27.1 shows the arrangement of the client and server and the two connections between them. Figure 27.1 Processes involved in file transfer. This figure shows that the interactive user normally doesn't deal with the commands and replies that are exchanged across the control connection. Those details are left to the two protocol interpreters. The box labeled "user interface" presents whatever type of interface is desired to the interactive user (full-screen menu selection, line-at-a-time commands, etc.) and converts these into FTP commands that are sent across the control connection. Similarly the replies returned by the server across the control connection can be converted to any format to present to the interactive user. This figure also shows that it is the two protocol interpreters that invoke the two data transfer functions, when necessary. Data Representation Numerous choices are provided in the FTP protocol specification to govern the way the file is transferred and stored. A choice must be made in each of four dimensions. 1. File type. a. ASCII file type. (Default) The text file is transferred across the data connection in NVT ASCII. This requires the sender to convert the local text file into NVT ASCII, and the receiver to convert NVT ASCII to the loc...
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