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Computer Networks : WWW , TELNET and SSH
- 1. World Wide Web Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 2. World Wide Web • Web was first proposed by Tim Berners-Lee in 1989 at CERN†, the European Organization for Nuclear Research • Web is a repository of information is distributed all over the world and related documents are linked together • Web can be related to in the above statement: 1. distributed and two terms 2. linked. • Distribution allows the growth of the Web. Each web server in the world can add a new web page to the repository and announce it to all Internet users without overloading a few servers. • Linking allows one web page to refer to another web page stored in another server somewhere else in the world. The linking of web pages was achieved using a concept called hypertext, Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 3. Architecture the service provided is distributed over many locations called sites. Each site holds one or more web pages Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 4. Web Client (Browser) • display a web page • Each browser usually consists of three parts: 1. a controller, 2. client protocols, and 3. interpreters. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 5. Web Server • The web page is stored at the server. • Each time a request arrives, the corresponding document is sent to the client. • To improve efficiency, servers normally store requested files in a cache in memory; memory is faster to access than a disk. Example • web servers include Apache and Microsoft Internet Information Server. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 6. Uniform Resource Locator (URL) • A web page, as a file, needs to have a unique identifier to distinguish it from other web pages. • To define a web page, need four identifiers: 1. Protocol : to access the web page. HTTP (HyperText Transfer Protocol) and FTP (File Transfer Protocol). HTTP protocol is used for accessing the web page 2. Host: The host identifier can be the IP address of the server or the unique name given to the server. 3. Port: well-known port number is 80 4. Path: location and the name of the file in the underlying operating system. http://www.mhhe.com/compsci/forouzan/ defines the web page Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 7. Web Documents • Static Documents : fixed-content documents that are created and stored in a server. The client can get a copy of the document only. • dynamic document is created by a web server whenever a browser requests the document. When a request arrives, the web server runs an application program or a script that creates the dynamic document. • Active Documents : need a program or a script to be run at the client site. run a program that creates animated graphics on the screen or a program that interacts with the user. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 8. TELNET Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 9. Telnet • It stands for the TELetype NETwork. • It helps in terminal emulation. • It allows Telnet clients to access the resources of the Telnet server. • It is used for managing files on the internet. • It is used for the initial setup of devices like switches. • The telnet command is a command that uses the Telnet protocol to communicate with a remote device or system. • Port number of telnet is 23. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 10. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 11. Local versus Remote Logging • When a user logs into a local system, it is called local logging. • when a user wants to access an application program or utility located on a remote machine, it performs remote logging. Here the TELNET client and server programs come into use. • The characters are sent to the TELNET client, which transforms the characters into a universal character set called Network Virtual Terminal (NVT) characters Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 12. Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 13. SECURE SHELL (SSH) Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 14. Secure Shell (SSH) • It is a secure application program that can be used today for several purposes such as remote logging and file transfer • it was originally designed to replace TELNET. • There are two versions of SSH: SSH-1 and SSH-2, Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 15. Components • SSH Transport-Layer Protocol (SSH-TRANS) • TCP is not a secured transport-layer protocol, SSH first uses a protocol that creates a secured channel on top of the TCP. • Privacy or confidentiality of the message exchanged • Data integrity, which means that it is guaranteed that the messages exchanged between the client and server are not changed by an intruder • Server authentication • Compression of the messages • SSH Authentication Protocol (SSH-AUTH) • is established between the client and the server and the server is authenticated for the client, • SSH Connection Protocol (SSH-CONN) • is established and both server and client are authenticated for each other Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai
- 16. Applications • SSH for Remote Logging • SSH for File Transfer • Port Forwarding Dr.T.Abirami, Associate Professor , Department of IT, Kongu Engineering College,Perundurai