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Application Protocols in Computer Network
There are several user-friendly protocols at the application layer
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For email for
example, eMail
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For example DNS
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UDP is employed for transport layer communication
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Email addresses
and fully qualified domain names (FQDN) are set up on the DNS
server and mapped to the appropriate Internet Protocol
addresses
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DNS uses UDP port 53
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The user's email client
software (User Agents) is used to carry out this task
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When an email is
requested to be sent, the Message Transfer Agent, which is often
included in email client software, handles the sending process
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While servers
typically utilize SMTP to send and receive emails, end users
typically just use it to send emails
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Client software uses Internet Message Access Protocol (IMAP) or
POP protocols to receive emails
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FTP operates on TCP port
21 and communicates using TCP/IP
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Out-of-band controlling, or FTP FTP transmits data via TCP port
21 while transferring control information over TCP port 20
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When the server receives
a request for a file, it opens a TCP connection for the client and
transfers the file
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For a second file, client requests again and the
server reopens a new TCP connection
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When a client needs to retrieve mails from server, it opens a
connection with the server on TCP port 110
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POP3 works
in two modes
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The second mode, the keep mode, does not
delete the email from mail server and gives the user an option to
access mails later on mail server
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The pages of text documents are connected by
hyperlinks in a well-organized hypertext system
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The client computer at the user's
end starts a TCP connection to the server on port 80 whenever a
user wishes to browse any HTTP website on the internet
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To access the web pages, a client normally uses web browsers,
who are responsible for initiating, maintaining, and closing TCP
connections
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HTTP versions

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HTTP 1
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At most one object
can be sent over a single TCP connection
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1 uses persistent HTTP
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Network Services
Computer systems and computerized systems help human
beings to work efficiently and explore the unthinkable
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Some basic services
computer network can offer are
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This software system helps to
store the information, organize it, and provides various means of
accessing it
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Directory
Services provide means of storing this information in
cryptic form and make available when requested
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User accounts can
be set into hierarchical structure and their access to

resources can be controlled using authorization
schemes
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This system maps IP addresses
to domain names, which are easier to remember and
recall than IP addresses
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File Services
File services include sharing and transferring files over the
network
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File sharing enables its users to share their
data with other users
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As an alternative, user can make its file shared
on its own computer and provides access to intended
users
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Network
enables its user to locate other users in the network
and transfers files
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This
is the basis of today’s internet features
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All its users are
provided with unique IDs
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• Social Networking
Recent technologies have made technical life social
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• Internet Chat
Internet chat provides instant text transfer services
between two hosts
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These days, voice chat
and video chat are very common
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It enables the
users to put queries, questions, suggestions etc
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Other may respond as
well
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This feature is known as Remote

desktop
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g
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Application Services
These are nothing but providing network based services to the
users such as web services, database managing, and resource
sharing
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This may include
Servers, Printers, and Storage Media etc
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It stores data and information, processes it,
and enables the users to retrieve it efficiently by using
queries
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Web Services
World Wide Web has become the synonym for
internet
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