computer network slides
TRANSCRIPT
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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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THANK YOU
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