




























































































Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
A course material for the Computer Network course in the 6th semester of the B.Tech program in ECE. The document covers the basics of computer networks, including principles of network applications, web and HTTP, FTP, electronic mail, DNS, and application layer. The document also discusses client-server and P2P architectures, processes, sockets, and the World Wide Web architecture. HTTP, its methods, and headers are also explained in the document.
Typology: Study notes
1 / 104
This page cannot be seen from the preview
Don't miss anything!
Contents of Topic: Behrouz A. Forouzan Learning Outcome: Students get to know about basics of Computer Network
Figure 25.1: Logical connection at the application layer
1 Principles of network applications (^) 2 Web and HTTP 3 FTP 4 Electronic Mail 5 DNS 2: Application Layer 5
Client-server architecture (^) In client-server architecture there is an always-on host called server (^) Which services requests from many other hosts called clients (^) Clients do not directly communicate with each other (^) Server has a fixed well-known address called an IP address (^) A single server host is incapable of keeping up with all the requests from its clients Ex. News website server can quickly become overload if it has only one server handling all of its requests (^) For this reason clusters of hosts sometime referred to as a server farm are often used to create a powerful virtual server in client server architecture
server: ◦ (^) always-on host (called server) ◦ (^) permanent IP address ◦ (^) server farms for scaling clients: ◦ (^) communicate with server ◦ (^) may be intermittently connected ◦ (^) may have dynamic IP addresses ◦ (^) do not communicate directly with each other 2: Application Layer 8 client/server
◦ (^) Client server and P2P are two common architectures for network applications ◦ (^) However many applications are organized as hybrids of the client server and P2P architecture 2: Application Layer 10
Process: program running within a host. Process can be thought of as a program that is running within end system within same host, two processes communicate using inter-process communication (defined by OS). processes in different hosts communicate by exchanging messages Client process: process that initiates communication Server process: process that waits to be contacted 2: Application Layer 11 (^) Note: applications with P2P architectures have client processes & server processes
identifier includes both IP address and port numbers associated with process on host. (^) Example port numbers: (^) HTTP server: 80 (^) Mail server: 25 (^) to send HTTP message to web server: (^) IP address: 128.119.245. (^) Port number: 80 to receive messages, process must have identifier host device has unique 32-bit IP address (^) Q: does IP address of host on which process runs be enough for identifying the process? A: No, many processes can be running on same host 2: Application Layer 13
(^) 2.1 Principles of network applications (^) app architectures (^) app requirements (^) 2.2 Web and HTTP 2.4 Electronic Mail (^) SMTP, POP3, IMAP (^) 2.5 DNS 2.6 P2P applications (^) 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2: Application Layer 14
(^) The first section introduces the World Wide Web. It then discusses the HyperText Transfer Protocol, the most common client-server application program used in relation to the World Wide Web. (^) The second section discusses the File Transfer Protocol, which is the standard protocol provided by TCP/IP for copying a file from one host to another. (^) The third section discusses electronic mail, which involves two protocols: SMPT and POP. As we will see, the nature of this application is different from the other two previous applications. We need two different protocols to handle electronic mail.
(^) The fourth section discusses TELNET, a general client-server program that allows users to log in to a remote machine and use any application available on the remote host. (^) The fifth section discusses Secure Shell, which can be used as a secured TELNET, but it can also provide a secure tunnel for other applications. (^) The sixth section talks about the Domain Name System, which acts as the directory system in the Internet. It maps the name of an entity to its IP address.
26. 19
26. 20
The WWW today is a distributed client-server service, in which a client using a browser can access a service using a server. The service provided is distributed over many locations called sites. Each site holds one or more web pages. Each web page can contain some links to other web pages in the same or other sites.