Computer Network Slides

7/30/2019 Computer Network Slides

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Applications

Mr. Shylesh B C


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Text BookComputer and Communication Networks

By Nader F. Mir

Pearson Edition, 2007

Chapters 9.1 to 9.6, 18.1,18.2


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Contents Application-layer overview

Domain Name System (DNS)

Remote login protocols

Electronic mail (e-mail)

File transfer and FTP

World Wide Web (WWW) and HTTP

Overview of IP telephony VoIP signaling protocols


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Application-layer overview The application layer is built on the transport

layer and provides network services to userapplications

The application layer defines and performs such

applications as electronic mail (e-mail), remote access to computers,

file transfers, newsgroups, and the Web, as well as

streaming video, Internet radio and telephony, P2Pfile sharing, multi user networked games, streamingstored video clips, and real-time video conferencing.


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Web communication between two

end systems


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Domain Name System (DNS) One of the most important components of the application

layer is the Domain Name System (DNS) server.

DNS is a distributed hierarchical and global directory thattranslates machine or domain names to numerical IPaddresses.

DNS can be thought as a distributed database systemused to map host names to IP addresses, and viceversa.

DNS is an application-layer protocol, and every Internetservice provider whether for an organization, a universitycampus, or even a residence has a DNS server.


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Hierarchy of domain name space,

labels, and domain names


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Hierarchy of DNS domain name

servers


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Name/Address Mapping

Recursive mapping

Iterative mapping


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Remote login protocols A client/server model can create a

mechanism that allows a user to establisha session on the remote machine and thenrun its applications.

This application is known as remote login.

Two remote login protocols are

TELNET

SSH.


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TELNET Protocol TELNET (terminal network) is a TCP/IP

standard for establishing a connection to aremote system.

TELNET allows a user to log in to aremote machine across the Internet by firstmaking a TCP connection and then pass

the detail of the application from the userto the remote machine.


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Secure Shell (SSH) Protocol Secure Shell (SSH), another remote login

protocol, is based on UNIX programs.SSH uses TCP for communications.

It is more powerful and flexible thanTELNET and allows the user to moreeasily execute a single command on a

remote client.


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Electronic mail (e-mail) It is Simple Mail Transfer Protocol (SMTP) and

E-mail The Simple Mail Transfer Protocol (SMTP) plays

a major role in transferring Internet electronicmail.

This protocol transfers electronic mail (e-mail )from the mail server of a source to the mailservers of destinations.

SMTP is older than the Hypertext TransferProtocol (HTTP), the Web communicationprotocol, and imposes certain restrictions, suchas limits on the size of e-mail content.

T h i il


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Two users exchanging e-mail

through SMTP


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File transfer and FTP

File transfer is another computer

networking application. It is always essential that files and

information geographically distributed over

different locations be shared among themembers of a working group.

Two file transfer protocols are FTP SCP.


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File Transfer Protocol (FTP)

File Transfer Protocol (FTP) is part of the

TCP/IP suite and is very similar toTELNET.

Both FTP and TELNET are built on the

client/server paradigm, and both allow auser to establish a remote connection.

However, TELNET provides a broaderaccess to a user, whereas FTP allowsaccess only to certain files.


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Secure Copy Protocol (SCP)

The Secure Copy Protocol (SCP) is similar toTELNET but is secure.

Incorporated in the SCP structure are a number ofencryption and authentication features that aresimilar to those in SSH.

Also similar is the exchange of commandsbetween local and remote hosts.

SCP commands automatically prompt the user for

the password information when it is time toaccess a remote machine. SCP cannot handle file transfer between

machines of significantly different architectures.


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World Wide Web (WWW) & HTTP

The World Wide Web (WWW), or simplyWeb, is a global network of servers linked

by a common protocol allowing access toall connected hypertext resources.

When a client host requests an object, aWeb server responds by sending therequested object through browsing tools.

A browser is a user agent displaying therequested Web page.

The Hyper Text Transfer Protocol (HTTP)

transfers that page at the application layer.


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HTTP uses TCP rather than UDP, sincereliability of delivery is important for Web pages

with text. The TCP connection-establishment delay in

HTTP is one of the main contributing delay

factors associated with downloading Webdocuments. HTTP is based on the client/server idea, having

a client and a server program, both of which canbe executed on different end systems.

The communication is carried out through anexchange of HTTP messages.


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Web Caching (Proxy Server)


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Overview of IP telephony

An IP telephone can be used to make telephone callsover IP networks.

Voice over IP (VoIP), or IP telephony, uses packet-switched networks to carry voice traffic in addition to datatraffic.

The basic scheme of IP telephony starts with pulse code

modulation. The encoded data is transmitted as packetsover packet-switched networks.

At a receiver, the data is decoded and converted back toanalog form.

The packet size must be properly chosen to prevent largedelays.

The IP telephone system must also be able to handle thesignaling function of the call setup, mapping of phonenumber to IP address, and proper call termination.


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Voice over IP system


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VoIP signaling protocols

The IP telephone system must be able to handlesignaling for call setup, conversion of phonenumber to IP address mapping, and proper calltermination.

Signaling is required for call setup, callmanagement, and call termination.

In the standard telephone network, signalinginvolves identifying the user's location given aphone number, finding a route between a callingand a called party, and handling the issue of callforwarding and other call features.


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