TCP IP Illustrated

There are better ways to compress files for ftp if we

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ata connection. a. Stream mode. (Default) The file is transferred as a stream of bytes. For a file structure, the end-of-file is indicated by the sender closing the data connection. For a record structure, a special 2-byte sequence indicates the end-of-record and end-of-file. b. Block mode. The file is transferred as a series of blocks, each preceded by one or more header bytes. c. Compressed mode. A simple run-length encoding compresses consecutive appearances of the same byte. In a text file this would commonly compress strings of blanks, and in a binary file this would commonly compress strings of 0 bytes. (This is rarely used or supported. There are better ways to compress files for FTP.) If we calculate the number of combinations of all these choices, there could be 72 different ways to transfer and store a file. Fortunately we can ignore many of the options, because they are either antiquated or not supported by most implementations. Common Unix implementations of the FTP client and server restrict us to the following choices: q q q q Type: ASCII or image. Format control: nonprint only. Structure: file structure only Transmission mode: stream mode only. This limits us to one of two modes: ASCII or image (binary). This implementation meets the minimum requirements of the Host Requirements RFC. (This RFC also requires support for the record structure, but only if the operating system supports it, which Unix doesn't.) Many non-Unix implementations provide FTP capabilities to handle their own file formats. The Host Requirements RFC states "The FTP protocol includes many features, some of which are not commonly implemented. However, for every feature in FTP, there exists at least one implementation." FTP Commands The commands and replies sent across the control connection between the client and file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (4 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol server are in NVT ASCII. This...
View Full Document

This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

Ask a homework question - tutors are online