Transcript Chapter 15 - YSU Computer Science & Information Systems

Cisco – Chapter 15
Application Layer
closest to you as an end-user,
when you are interacting with
software
Layer 7 Responsibilities
• Identifying and establishing the availability
of intended communication partners
• Synchronizing cooperating applications
• Establishing agreement on procedures for
error recovery
• Controlling data integrity
Layer 7 Protocols
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Client-Server
Redirectors
Domain Name System
E-mail
Telnet
FTP
HTTP
Protocols Explained
• The World Wide Web uses the HTTP protocol.
• Remote access programs use the Telnet protocol
for directly connecting to remote resources.
• E-mail programs support the POP3 application
layer protocol for electronic mail.
• File utility programs use the FTP protocol for
copying and moving files between remote sites.
• Network data gathering and monitoring use the
SNMP protocol.
Telnet Explained
• When the data reaches the remote host
computer, the data link, network, and
transport layers, reassemble the original
data commands. The remote host computer
executes the commands and transmits the
results back to the local client computer by
using the same process of encapsulation
• All work done by remote host
FTP Explained
• 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.
• Uploads and downloads files
• Requires login id and password
– Anonymous is login id and e-mail address is password
HTTP Explained
• http://" tells the browser which protocol to
use. The second part, "www", tells the
browser what type of resource it wishes to
contact. The third part, "cisco.com,"
identifies the domain of the Web server IP
address. The last part, "edu" identifies the
specific folder location (on the server) that
contains the Web page.
Layer 6 Protocols
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POP
Usenet
FTP
HTTP
Telnet
DNS
SNMP, NFS
Relationship to Other Layers
• Does not provide services to any other OSI
layer.
• It does provide services to application
processes lying outside the scope of the OSI
model
– Spreadsheets, databases, etc
Client-Server Environment
• Most applications that work in a networked
environment
– FTP, web browsers, and e-mail
– Client side and server side
• Web browser is probably the most commonly used
network applications
– accesses a web page by requesting a uniform resource
locator (URL), or web address, on a remote web server.
Redirector
• Protocol that works with computer operating
systems and network clients instead of specific
application programs
– Apple File Protocol, NetBIOS Extended User Interface
(NetBEUI), Novell IPX/SPX protocols, Network File
System (NSF) of the TCP/IP protocol suite
• Applications on the client never have to recognize
the network
• Allow users to share documents, templates,
databases, printers, and many other resource types
Two Types of Connection
FTP and Telnet
Establish and maintain until all
communication is complete
Network Services
Make/Break, Make/Break, Make/Break
DNS Domains
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Edu
Gov
Com
Org
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Int
Mil
DNS Server and E-Mail
• Resolves (translates) DNS name to IP
address
• E-mail Address
– [email protected]. It consists of two parts:
the recipient’s name (located before the @
sign); and the recipient’s post office address
(after the @ sign).