[ Computer Network ]
[ Unit 5 ]
[ Application Layer ]
The application layer in the OSI model is the closest layer to the end user which
means that the application layer and end user can interact directly with the
software application. The application layer programs are based on client and
servers.
The Application layer includes the following functions:
o Identifying communication partners: The application layer identifies the
availability of communication partners for an application with data to
transmit.
o Determining resource availability: The application layer determines
whether sufficient network resources are available for the requested
communication.
o Synchronizing communication: All the communications occur between the
applications requires cooperation which is managed by an application layer.
[ Services of Application Layers ] :
o Network Virtual terminal:
An application layer allows a user to log on to a remote host. To do so,
the application creates a software emulation of a terminal at the remote
host. The user's computer talks to the software terminal, which in turn,
talks to the host. The remote host thinks that it is communicating with one
of its own terminals, so it allows the user to log on.
,o File Transfer, Access, and Management (FTAM):
An application allows a user to access files in a remote computer, to
retrieve files from a computer and to manage files in a remote computer.
FTAM defines a hierarchical virtual file in terms of file structure, file
attributes and the kind of operations performed on the files and their
attributes.
o Addressing:
To obtain communication between client and server, there is a need
for addressing. When a client made a request to the server, the request
contains the server address and its own address. The server response to the
client request, the request contains the destination address, i.e., client
address. To achieve this kind of addressing, DNS is used.
o Mail Services:
An application layer provides Email forwarding and storage.
o Directory Services:
An application contains a distributed database that provides access
for global information about various objects and services.
o Authentication:
It authenticates the sender or receiver's message or both.
, The application layer provides several protocols which allow any software to easily
send and receive information and present meaningful data to its users.
The following are some of the protocols which are provided by the
application layer.
TELNET:
Telnet stands for Telecommunications Network. This protocol is used for
managing files over the Internet. It allows the Telnet clients to access the
resources of Telnet server. Telnet uses port number 23.
DNS:
DNS stands for Domain Name System. The DNS service translates the
domain name (selected by user) into the corresponding IP address. For example-
If you choose the domain name as www.abcd.com, then DNS must translate it as
192.36.20.8 (random IP address written just for understanding purposes). DNS
protocol uses the port number 53.
DHCP:
DHCP stands for Dynamic Host Configuration Protocol. It provides IP
addresses to hosts. Whenever a host tries to register for an IP address with
the DHCP server, DHCP server provides lots of information to the
corresponding host. DHCP uses port numbers 67 and 68.
FTP:
FTP stands for File Transfer Protocol. This protocol helps to transfer
different files from one device to another. FTP promotes sharing of files via
remote computer devices with reliable, efficient data transfer. FTP uses port
number 20 for data access and port number 21 for data control.
SMTP:
SMTP stands for Simple Mail Transfer Protocol. It is used to transfer
electronic mail from one user to another user. SMTP is used by end users to
send emails with ease. SMTP uses port numbers 25 and 587.
HTTP:
HTTP stands for Hyper Text Transfer Protocol. It is the foundation of the
World Wide Web (WWW). HTTP works on the client server model. This
protocol is used for transmitting hypermedia documents like HTML. This
protocol was designed particularly for the communications between the web
[ Unit 5 ]
[ Application Layer ]
The application layer in the OSI model is the closest layer to the end user which
means that the application layer and end user can interact directly with the
software application. The application layer programs are based on client and
servers.
The Application layer includes the following functions:
o Identifying communication partners: The application layer identifies the
availability of communication partners for an application with data to
transmit.
o Determining resource availability: The application layer determines
whether sufficient network resources are available for the requested
communication.
o Synchronizing communication: All the communications occur between the
applications requires cooperation which is managed by an application layer.
[ Services of Application Layers ] :
o Network Virtual terminal:
An application layer allows a user to log on to a remote host. To do so,
the application creates a software emulation of a terminal at the remote
host. The user's computer talks to the software terminal, which in turn,
talks to the host. The remote host thinks that it is communicating with one
of its own terminals, so it allows the user to log on.
,o File Transfer, Access, and Management (FTAM):
An application allows a user to access files in a remote computer, to
retrieve files from a computer and to manage files in a remote computer.
FTAM defines a hierarchical virtual file in terms of file structure, file
attributes and the kind of operations performed on the files and their
attributes.
o Addressing:
To obtain communication between client and server, there is a need
for addressing. When a client made a request to the server, the request
contains the server address and its own address. The server response to the
client request, the request contains the destination address, i.e., client
address. To achieve this kind of addressing, DNS is used.
o Mail Services:
An application layer provides Email forwarding and storage.
o Directory Services:
An application contains a distributed database that provides access
for global information about various objects and services.
o Authentication:
It authenticates the sender or receiver's message or both.
, The application layer provides several protocols which allow any software to easily
send and receive information and present meaningful data to its users.
The following are some of the protocols which are provided by the
application layer.
TELNET:
Telnet stands for Telecommunications Network. This protocol is used for
managing files over the Internet. It allows the Telnet clients to access the
resources of Telnet server. Telnet uses port number 23.
DNS:
DNS stands for Domain Name System. The DNS service translates the
domain name (selected by user) into the corresponding IP address. For example-
If you choose the domain name as www.abcd.com, then DNS must translate it as
192.36.20.8 (random IP address written just for understanding purposes). DNS
protocol uses the port number 53.
DHCP:
DHCP stands for Dynamic Host Configuration Protocol. It provides IP
addresses to hosts. Whenever a host tries to register for an IP address with
the DHCP server, DHCP server provides lots of information to the
corresponding host. DHCP uses port numbers 67 and 68.
FTP:
FTP stands for File Transfer Protocol. This protocol helps to transfer
different files from one device to another. FTP promotes sharing of files via
remote computer devices with reliable, efficient data transfer. FTP uses port
number 20 for data access and port number 21 for data control.
SMTP:
SMTP stands for Simple Mail Transfer Protocol. It is used to transfer
electronic mail from one user to another user. SMTP is used by end users to
send emails with ease. SMTP uses port numbers 25 and 587.
HTTP:
HTTP stands for Hyper Text Transfer Protocol. It is the foundation of the
World Wide Web (WWW). HTTP works on the client server model. This
protocol is used for transmitting hypermedia documents like HTML. This
protocol was designed particularly for the communications between the web
