Transcript The Internet and Its Uses - Genesee Community College

Chapter 3
Application Layer
Functionality and
Protocols
Modified by Profs. Chen and Cappellino
Objectives

In this chapter, you will learn to:







Describe how the functions of the three upper OSI model
layers provide network services to end user applications.
Describe how the TCP/IP Application Layer protocols provide
the services specified by the upper layers of the OSI model.
Define how people use the Application Layer to communicate
across the information network.
Describe the function of well-known TCP/IP applications, such
as the World Wide Web and email, and their related services
(HTTP, DNS, SMB, DHCP, SMTP/POP, and Telnet).
Describe file-sharing processes that use peer-to-peer
applications and the Gnutella protocol.
Explain how protocols ensure services running on one kind of
device can send to and receive data from many different
network devices.
Use network analysis tools to examine and explain how
common user applications work.
The Application Layer of the OSI and TCP/IP Models





Layer _____________ of OSI
The top layer of both models
It is the layer that provides the
__________________________ we
use to communicate and the
______________________ over
which our messages are transmitted.
___________________________
______________________ between
programs running on the source and
destination hosts.
The __________________________
protocols fit roughly into the
framework of the top three layers of
the _________________________
____________________________
Application Layer
protocols
The Presentation Layer of the OSI Model


Layer _____________ of OSI
Three primary functions:
____________________________
Application layer data
______________________ of data

of
decompression by the destination device.
_________ of the data for transmission
 decryption of data upon receipt by the
destination.

Examples include:
Motion

Picture Experts Group (______).
MPEG is a standard for _______________ and
coding.
Graphics
Interchange Format (______),
Joint Photographic Experts Group
(____________)

Compression and coding standards for
_______________________ images,
The Session Layer of the OSI Model


Layer ___________ of OSI
_________________________
between source and destination
applications.

Handles the ______________
______________________
 _____________________ that
are disrupted or idle for a long
period of time.

________________, like web
browsers or e-mail clients,
________________________
_________________________
Common TCP/IP Application layer protocols






Domain Name Service Protocol (________) is used to
____________________________________
Hypertext Transfer Protocol (____________) is used to
______________________________________
Simple Mail Transfer Protocol (______________) is used
for the _________________________ and attachments.
______________, a terminal emulation protocol, is used to
________________________ to servers and networking
devices ________________________________
File Transfer Protocol (_________) is used for interactive
_______________________________________________
Dynamic Host Configuration Protocol (_________) assigns
____________________, subnet mask info, __________
___________________________________________
Application Layer _______________


The functions associated with the
Application layer protocols enable the
user to interface with the underlying
data network.
There are _____________________
programs or processes that provide
access to the network:
____________________________
 The ______________________________ to
communicate over the network.
 E-mail clients and web browsers are examples of
these types of applications.
______________________________
 ______________________ may need the
__________________________________ to use
network resources, like file transfer or network
print spooling.
 Though transparent to the user, these ______
_____________________________________
and prepare the data for transfer.
User Applications, Services and Application Layer Protocols

Applications that interact directly with people ____
_________________________________________
 Above

the Application layer
The three components in play…
While
______________________ provide people with a
___________________________ and
application layer ____________________ establish an
_________________________________
______________________ provide the ____________
____________________ that govern how data is treated.

All three components may be used by a single
executable program
Application Layer ______ Functions

Application layer protocols are _______________
______________________________ during a
communication session.


The protocols implemented on both sides must match.
Application layer protocols functions:
Protocols
establish consistent _____________________
______________________________________ loaded
on the participating devices.
Protocols specify ______________________________
_______________________ and the types of messages
that are sent between source and destination.

These messages can be requests for services, acknowledgments, data,
status, or error messages.
Protocols
also define ________________________
_________________________________________
_____________ in the course of a single conversation.
The ___________________ Model
Device ______________ the information is
called a ____________ and the device
_________ to the request is called a ______
 Client and server processes are considered
to be in the Application layer.

Application
layer protocols describe the format
of the requests and responses between clients
and servers.
Control info as well as data is transferred
 Can anyone think of an example of the
client/server model?

Servers




In a general networking context, any __________
__________________________________ is
functioning as a server.
A server is usually a computer that _________
___________________ with many client systems.
Some servers ____________________________
_________________________ to verify if the user
has permission to access the requested data
A server sometimes _______________________,
called a _________________________.
_____________________
and are not under an end
user's direct control.
Daemons _______________________ from a client
 When daemons "hear" a request from a client, they send
requested data to the client in the proper format
Application Layer Services and Protocols

A ________________________
___________________________
__________________________

what appears to the user as one
request for a web page may, in fact,
amount to dozens of individual
requests.

Servers typically have _________
___________________________
__________________________
For
example, a Telnet server may
have many clients requesting
connections to it simultaneously
_____________ Network Design:


___________________________ via a
network and ________________ (such as
printers and files) __________ having a
________________________
Every connected end __________ (known
as a peer) can ____________________
____________________________
 One
computer might assume the role of server for
one transaction while simultaneously serving as a
client for another.
A simple
__________ with two computers
_________________, games, internet
connection etc. is an example of a peer-to-peer
network.

Peer-to-peer networks generally ______
__________________________________
_______________________________
___________________________ and manage
users and resources

Peer-to-Peer Applications

A P2P application, allows a device to ________
________________________________________
______________________________

Require that each end device provide a user interface
and run a background service.

Some P2P applications use a hybrid system
where ____________________________ but the
_______________ that point to resource locations
are stored in a _________________________
In
a hybrid system, each peer accesses an index server
to get the location of a resource stored on another peer.

Peer-to-peer applications can be used on ____
_____________________, ______________
____________, and across the Internet.
Services and Protocol: Port Numbers

_________________ layer uses an addressing scheme
called a ____________________
______________________ and Application layer services that are
the source and destination of data.
Server programs generally use predefined port numbers that are
commonly known by clients.


Some of these services and port numbers are:
Domain
Name System (_______) - _________ Port ____
Hypertext Transfer Protocol (_________) - ____ Port ___
Simple Mail Transfer Protocol (_______) - ____ Port ___
Post Office Protocol (_________) - ______________
______________ - _____ Port __________
Dynamic Host Configuration Protocol (_______ - _____ Port ______
File Transfer Protocol (________) - _________ Ports ___________

Stay tuned for more on port numbers….
DNS

Provides an automated service that _________
_________________ (ex. www.yahoo.com) to the
_____________________________
In
data networks, devices are labeled with numeric IP
addresses used to send and receive messages over the
network.
Numeric addresses __________________________ so
domain names were created as a simple way to
remember a website address.



Example: www.cisco.com much easier to remember than
198.133.219.25 which is the actual numeric address for this
server.
Benefit: if a ___________________________
_________________, it is _______________,
since the domain name will remain the same
DNS uses a distributed set of servers to resolve
the domain names associated with IP addresses.
DNS Services and Protocol

DNS is a ____________________;
Unlike
other services which use a
client that is an application (such as
web browser), the _____________
___________________________


The DNS client, AKA the ____________,
supports name resolution
Computer operating systems also
have a utility called __________
that allows the ______________
________________ to resolve a
given host name.
This
utility can be used for
troubleshooting and verification
purposes
DNS Services and Protocol


A DNS server provides the name resolution using
the _________________
The DNS server stores different types of resource
records used to resolve names. Some are:
A - an end device address
NS - an authoritative name server
 _______________________________________________
________________________________, and not just a cached
answer that was given by another name server.
CNAME - the canonical name (or _________________
__________________) for an ________; used when
multiple services have the single network address but
each service has its own entry in DNS
MX - mail exchange record; maps a domain name to a
list of mail exchange servers for that domain
DNS Services and Protocol

When a client makes a query, the _____
_______________ first looks at its own
records to see if it can resolve the name.
If
it is ______ to resolve the name it _______
_________________ for name resolution

The request take extra time and consume
bandwidth.
Once
a match is found and returned to the
original requesting server, the server
temporarily __________________ that
matches the name in ______________.


Caching reduces both the DNS query data network
traffic and the workloads of servers higher up the
hierarchy.
DNS Client service on ______________
_______________________________
in memory

The _______________________ command
displays all of the cached DNS entries on a
Windows XP machine
DNS Services and Protocol

The Domain Name System uses a
________________________________
____________ to provide name resolution.
The
_____ servers can correspond with _____
_______, which in turn have records that point to
the ________________________ etc.
Examples of top-level domains are:




.com - a business or industry
.org - a non-profit organization
.it - Italy
For example, as shown in the figure,
the
root DNS server may not know exactly
where the e-mail server mail.cisco.com is
located, but it maintains a record for the "com"
domain located within the top-level domain.
Likewise, the servers within the "com" have a
record for the "cisco.com" domain.
The servers within the cisco.com domain have
an MX record for mail.cisco.com.
WWW Service and HTTP

When a web address (or _____) is typed into a web
__________, the web _____________________
________________________________
____________________ using the HTTP protocol.
The
browser then _____________________________
www.cisco.com into a numeric IP address, which it uses
to connect to the server.
Using the HTTP protocol, the ___________________
_____________ to the server asks for file index.html.
The __________________________________ for this
web page to the browser.
Finally, the __________________________ and formats
the page for the browser window.

Other types of data, may require another service or program, typically
referred to as plug-ins
HTTP and HTTPS

HTTP specifies a request/response protocol. The three
common message types are GET, POST, and PUT.
______________________________________
initiated by entering
a URL into the browser.

Once the server receives the GET request, it responds with a status line, such
as HTTP/1.1 200 OK, and a message of its own, the body of which may be the
requested file.
_______________________________________________
_____________________________________
 ________________________ able to be intercepted and read

For secure communication across the Internet, the _____
____________________ protocol is used for accessing or
posting web server information.
HTTPS
can _________________________________ as it travels
between the client and server.

Encryption renders data unreadable should it be intercepted
HTTPS
specifies ____________________________ between the
Application layer and the Transport Layer.
E-mail Service and SMTP/POP Protocols


E-mail requires several applications and
services.
Two of the most popular application layer
protocols:
Simple Mail Transfer Protocol (__________)
 ___________________________________ uses
formats and command defined by the SMTP protocol.
Post



Office Protocol ___________________
____________________________________
In order to _________ from an e-mail server, the
____________________________
When people compose e-mail messages,
they typically use an application called a
Mail User Agent (________), or _______
The


MUA comprises two processes:
allows messages to be sent
places received messages into the client's
mailbox.
Mail User Agent
(MUA), or e-mail
client
E-mail Server Processes - MTA and MDA

The ____________ operates
two separate processes:
Mail



The _________ process is used to
_______________________
The MTA ____________________
___________ on another e-mail server.
MTA determines- based on the
message header, how and where to
forward the e-mail.
Mail

Transfer Agent (______)
Delivery Agent (______)
If the mail is addressed to a user whose
mailbox is on the _____________
___________________________
MTA and MDA
E-mail Server Processes - MTA and MDA


The ______ can also ______
______________, such as ____
____________________, and
return-receipt handling.
Other alternatives for e-mail
delivery in instead of using MUA,
MTA, and MDA.
IBM's
Lotus Notes, Novell's
Groupwise, or Microsoft's
Exchange.

These systems often have their own internal
_______________________________
As
another alternative, computers
that do not have an MUA can still
______________________
_________ in order to retrieve and
send messages in this manner.
E-mail Server Processes - MTA and MDA

Recall: POP3 are inbound mail delivery
protocols.
 They
deliver e-mail from the e-mail server (MDA)
to the client (MUA).

SMTP is responsible for

the transfer of outbound e-mail from the sending
client to the e-mail server
 the transport of e-mail between e-mail servers
(MTA).


SMTP enables e-mail to be _______________
____________________________________
____________________________
SMTP protocol message format uses a rigid set
of commands and replies such as:
 HELO
- identifies the SMTP client process to the
SMTP server process
 EHLO - Is a newer version of HELO, which
includes services extensions
 MAIL FROM - Identifies the sender
 RCPT TO - Identifies the recipient
 DATA - Identifies the body of the message
File Transfer Protocol (FTP)


_____ an application layer protocol- was
developed to ________________________
__________________________
An FTP client is an application that runs on a
computer
_______________________ file from server
 ___________________________ file to server.


To transfer files, FTP requires two connections
between client and server:
The
____________________________ to the server on
_______________________

It consists of client commands and server replies to _____________
The
_____________________________ to the server
over _______________________.

This connection is for the __________________________________
there is a file transferred.
Dynamic Host Configuration Protocol (_____)


A service which __________________________
__________________________________________
_________________ from a DHCP server.
When the DHCP server is contacted and an address
requested.
The
____________________________ from a configured range of
addresses called a ______________ and assigns ("leases") it to the
host for a set period.
If the host is powered down or __________________, the
________ is _____________________________.


Helpful with mobile users that come and go on a network.
DHCP can run on various devices
Dedicated server
 When connecting to the Internet from home- located at the ISP
 Home router- for home network

Dynamic Host Configuration Protocol (DHCP)
DHCP can pose a security risk because ___
___________________________________
___________________________
 Many networks use both DHCP (dynamic)
and static addressing.

DHCP
is used for _____________________
such as ______________________
Fixed (________) ____________ are used for
network devices such as ______________
________________________________
DHCP

When a DHCP-configured device boots up,
 The
_____________________ packet to identify any
available DHCP servers on the network.
 A ________________________________, which is a
lease offer message with an IP address, subnet mask,
DNS server, and default gateway.
 The client may receive multiple DHCP OFFER packets if
there is more than one DHCP server on the local
network,

it ____________________________________ packet that
identifies the explicit server of the offer it chose.
 Assuming
that the IP address offered by the server is
still valid, the ____________________________
message that acknowledges to the client the lease is
finalized.
If
the ____________________, the selected
server will respond with a ______________
message (Negative Acknowledgement).


If a DHCP NAK message is returned, then the selection
process must begin again from the beginning
Once the client has the lease, it must be renewed prior to
the lease expiration through another DHCP REQUEST
message
File Sharing using the SMB Protocol

The Server Message Block (_________) is a
_____________________________
 It
is a request-response protocol, _______________
____________________________
 Once the connection is established, ________ resources
can be _______________________________

SMB file-sharing and print services are part of Microsoft
networking- starting with Win2000.
 ______________________________



resource sharing
______________________ operating systems provide
a method of sharing resources with Microsoft networks
using a version of SMB called ________________.
_______________ operating systems also use the
____________________ in resource sharing
SMB messages share a common format
 fixed-sized
header followed by a variable-sized parameter
and data component

SMB messages can:
 Start, authenticate, and terminate sessions
 Control file and printer access
 Allow an file application to send or receive messages
from another device
to or
P2P Service and Gnutella Protocol
Application layer ____________________
 With P2P applications based on the Gnutella
protocol, people can make _____________
_____________________ for downloading.

Gnutella-compatible
client software allows
users to
__________________________________ and
to ___________________________ shared by
other ___________________________

Popular Gnutella-compatible client applications
including: LimeWire, Morpheus, WinMX etc.
P2P Service and Gnutella Protocol

P2P applications generally __________
____________________ to record all the files
available on the peers.


Devices on the network each tell the other what
files are available when queried
When a user is connected to a Gnutella service,
the client applications will _____________
________________ to connect to.
 Those
nodes handle queries for resources, replies
and control messages which help discover other
nodes
 The actual _____________________________
services.

The Gnutella protocol defines five different packet
types:
 ping - for device discovery
 pong - as a reply to a ping
 query - for file location
 query hit - as a reply to a query
 push - as a download request
Telnet Service and Protocol


One of the ___________ Application layer
protocol in the TCP/IP suite
Telnet provides a standard method of ________
_______________________________________
________________________________
 Enabled
user to ______________________
systems as if directly attached terminals


Both the protocol itself and the client software
that implements the protocol are commonly
referred to as Telnet.
A _____________ using Telnet is called a Virtual
Terminal (_________) session, or connection.
 To
support Telnet client connections, the ______
_____________________________________
 A virtual terminal connection is established from an
end device using a _____________________

Example: Hyperterminal
 On
a Microsoft Windows PC, Telnet can be run
from the _____________________________

Telnet used to program network devices…
Telnet Service and Protocol



Telnet is a client/server protocol and it specifies
how a VTY session is established and terminated.
Telnet protocol _________________________,
_________________ the transport of ________
_______________________
All
data exchanged during a Telnet sessions is
transported as ________________________

For security, best practice suggests using Secure
Shell (_____________) protocol instead of telnet
SSH
provides ___________________ than Telnet and
____________________________________________