Transcript Layer 7 The Application Layer

Layer 7
The Application Layer
Chapter Review
Layer 7
The Application Layer
The application layer is the OSI layer
closest to the end system. This determines
whether sufficient resources exist for
communication between systems.
The application layer does not provide
support for any other OSI layer.
Client - Server
Most applications that work in a networked
environment are classified as client-server
applications.
These applications, such as FTP, web
browsers, and e-mail, all have two
components, which allow them to function:
1. The client side
2. The server side
Network Applications
The World Wide Web (WWW), and the web
browsers Netscape Navigator, and
Internet Explorer, are probably the most
commonly used network applications.
Network Redirector
Redirector is a protocol that works with
computer operating systems and network clients
instead of specific application programs.
If a client wants to save a file from a word
processor to a network server, the redirector
enables the word processing application to
become a network client.
A network redirector enables data to be sent to
a device that is not directly connected to a
computer.
Two Types of
Communication
Make a connection - break a connection
and termination determined by client.
All communication activity falls into one of
these two categories.
Make a Connection
Break a Connection
The common cycle; make a connection break a connection, between client and
server, underlies all Web Page requests.
When downloading a web page, the
connection to the remote server will be
maintained only long enough to process
the transaction.
Client Determines
Termination
This is illustrated by the Telnet and FTP
examples, which establish a connection to
the server, and maintains that connection
until all processing has been performed.
 The client computer terminates the
connection when the user determines that
he/she has finished.
IP Addresses
the Internet is built on a hierarchical
addressing scheme. This allows for
routing that is based on classes of
addresses, as opposed to individual
addresses.
Domains
A domain is a group of computers that are
associated by their geographical location
or their business type.
A domain name is a string of characters
and/or numbers that represents the
numeric address of an Internet site.
In the URL http://www.cisco.com, the
“cisco.com” part identifies the domain.
DNS - Domain Name Server
A DNS server manages domain names and
responds to requests from clients to
translate a domain name into the
associated IP address.
E-mail
E-mail client applications, such as Eudora,
Outlook Express, and Netscape Mail, work with
the POP3 protocol.
For security, when message recipients check
their e-mail they are often prompted for a
password. The password can also be saved in
many e-mail programs.
An e-mail address consists of the recipient’s
username and postoffice address.
Telnet
Terminal emulation (Telnet) software
provides the ability to remotely access
another computer.
The Telnet application works mainly at the
application, presentation and session
layers of the OSI model.
FTP
File transfer protocol (FTP) is designed to
download files or upload files on the
Internet.
An FTP session is established the same
way in which a Telnet session is
established. Just like Telnet, the FTP
session is maintained until the client
terminates it, or there is some sort of
communication error.
Web Pages
Web pages are created with a format
language called Hypertext Markup
Language (HTML).
Hyperlinks make the World Wide Web
easy to navigate. A hyperlink is an object
on a Web page that, when clicked,
transfers you to a new Web page.
Conclusion
This concludes our review of chapter 15,
The Application Layer.
Congratulations on getting through all 15
chapters of Cisco Semester 1!
Now you’re prepared to take the chapter
15 online exam.