1 Online communication: remote login and file transfer

2 Online communication: summary The following gives an overview of the classical, older, well established techniques to communicate online with a remote computer. 1.First comes login into a remote computer to use some information source or facility offered by that computer. 2.Then comes transferring/copying files online from one computer to another.

3 Online communication: prerequisites Before using online communication systems, you should ideally have some knowledge and skills related to computer hardware computer software the Internet

4 Remote terminal log-in / access: definition The ability to access a computer from outside a building in which it is housed. This requires communications hardware, software, and actual physical links, although this can be as simple as common carrier (telephone) lines or as complex as telnet login to another computer across the Internet.

5 Telnet: description The Internet standard protocol for remote terminal connection service; on top of the TCP/IP protocol suite Allows a user at one site to interact with a remote timesharing system at another site as if the user's terminal was connected directly to the remote computer Includes VT100 terminal emulation

6 Telnet: available client programs Client programs which allow a remote login according to the telnet protocol with telnet servers, are available for most operating systems, including »[Unix (“telnet”,...)] »Apple »[DOS (e.g. “NCSA telnet”; telnet programs included in TCP/IP packages)] »Windows (e.g. telnet programs included in TCP/IP packages and in Windows 95, EWAN, Procomm, WinQVT,...)!

7 Telnet: character-based user interface for Unix and DOS client program Some important commands in a typical program with a character-based user-interface: »Open connection telnet computer_address »Quit / exit telnet telnet> quit or telnet> exit *---

8 !? Question !? Task !? Problem !? Which client program will YOU use for telnet?

9 !? Question !? Task !? Problem !? Make a telnet connection with a remote telnet server computer.

10 Data communication: downloading The electronic transfer of information (whole file or fragments) from one computer to another, generally from a larger computer to a smaller one (such as from a server under Unix to a microcomputer).

11 Data communication: downloading methods The method used depends on the amount of the information which is displayed that has to be captured: »Copying a small fragment ! »(Storing a large part in a log file)

12 Data communication: downloading by copying a fragment Capturing a small fragment of the information displayed: 1. select information on the display, 2. copy, and 3. paste in a document managed by another program.

13 !? Question !? Task !? Problem !? Capture some information displayed by a remote computer, using select, copy and paste.

14 !? Question !? Task !? Problem !? Capture some information displayed by a remote computer, by creating a log file.

15 Data communication: file transfer Copying + downloading / transfer of a whole file Requires a transfer protocol with error correction

16 Protocols for error correction during file transfer Name of protocol ASCII = text (= no program) Xmodem Ymodem Zmodem Kermit (ASCII / binary) ftp (ASCII / binary) Error correction - + A version of the protocol (program) runs at both computers, during file transfer. Applications Public databanks BBS Internet *---

17 ftp: file transfer protocol in the Internet A high-level protocol = application protocol in the Internet. For transferring files from one computer to another (free of errors). Provides the capability »1. to connect to a remote computer, »2. to execute a few simple tasks (such as listing the directory), »3. to copy files to or from the remote computer quickly.

18 ftp: client programs for Windows Primitive ftp program included in Windows 95, 98,… (several files at the time) WS_ftp (several files at the time) Netscape (only 1 file at the time) Microsoft Internet Explorer (only 1 file at the time)... Examples

19 !? Question !? Task !? Problem !? Which ftp client program will YOU use ?

20 !? Question !? Task !? Problem !? Copy a file from a remote computer to your own, using ftp; for instance from ftp://ftp.vub.ac.be/