SEMESTER 1 Chapter 3
Application Layer Functionality and Protocols
V 4.0
3.1.1.1 What does the application
layer provide?
What are application layer
protocols used for?
3.1.1.2 What are the three primary
functions of the
Presentation Layer?
What is the main function of
the session layer?
3.1.1.3 What do the Application
Layer protocols of the
TCP/IP protocol specify?
3.1.2
What are the two forms of
software programs or
process that provide
network access in the
Application Layer
3.1.3
What do protocols provide?
3.1.4
3.2.1
3.2.2
What is the difference
between an application and
a service?
What do application layer
protocols do?
What 6 things do protocols
define?
the interface between the applications we use
to communicate and the underlying network
over which our messages are transmitted
to exchange data between programs running
on the source and destination hosts
Coding and conversion of Application layer
data to ensure that data from the source
device can be interpreted by the appropriate
application on the destination device.
Compression of the data in a manner that can
be decompressed by the destination device.
Encryption of the data for transmission and the
decryption of data upon receipt by the
destination.
create and maintain dialogs between source
and destination applications
the format and control information necessary
for many of the common Internet
communication functions
applications and services
the rules and formats that govern how data is
treated
Applications interact with the user and services
prepare data for the network
Protocols provide the rules and formats that
govern how data is treated.
1. processes on either end of the
communication
2. types of messages
3. syntax of messages
4. meaning of any informational fields
5. how messages are sent and the
expected response
6. interaction with the nextlower layer
What is the difference
the device requesting the information is called
between a client and a
a client and the device responding to the
server?
request is called a server
In general networking sense any device that responds to requests from
what is a server?
client applications is functioning as a server
Describe the 2 processes a "listening" for a request from a client, because
daemon uses (listening and
hears)?
3.2.3.2 Complete the packet tracer
lab examine a number of
packets to see what each
packet contains.
3.2.4
What is a peer-to-peer
network?
Are peer-to-peer networks
easy to secure?
3.2.4.2 What are peer-to-peer
applications?
3.3.1
What do port numbers
identify?
What does the DNS
protocol do?
3.3.1.2 What does the nslookup
utility allow you to do?
What does the command
ipconfig /displaydns show?
3.3.1.3 What happens if a DNS
server does not have a
name in its stored records?
If the same request is made
again where does the DNS
server look?
3.3.1.4 When is a server declared
to be an authoritative
server?
3.3.2.1 Define the three parts of a
url as listed on the page?
What type of request is sent
to the server when
retrieving a web page?
3.3.2.2 What does the POST
command do?
What does the PUT
command do?
What protocol is used for
they are programmed to respond whenever the
server receives a request for the service
provided by the daemon
"hears" a request from a client, it exchanges
appropriate messages with the client, as
required by its protocol, and proceeds to send
the requested data to the client in the proper
format
two or more computers are connected via a
network and can share resources (such as
printers and files) without having a dedicated
server
No
allows a device to act as both a client and a
server within the same communication
applications and Application layer services that
are the source and destination of data
defines an automated service that matches
resource names with the required numeric
network address.
allows the user to manually query the name
servers to resolve a given host name
Displays all of the cached DNS entries on a
Windows XP or 2000 computer system
It passes the request on to another DNS
server
In its cache
When the resource is directly held on that
server
http:- protocol
www.cisco.com- name of server
web-server.htm- name of file or page
GET
Sends information to the web server
Sends resources or content to the web server
HTTPS:
3.3.2.3
3.3.3
3.3.3.2
3.3.3.3
3.3.3.4
secure transmission across
the web?
Packet Tracer Lab
What 2 Application Layer
protocols are used in
sending and receiving
email?
What is another name for
an email application?
What are the two processes
that email servers perform?
What happens to emails in
many companies once the
email reaches the internal
server?
List and describe some of
the commands used by the
SMTP protocol.
3.3.4
What is File Transfer
Protocol (FTP)?
What are the 2 ports used
and their purpose in FTP?
3.3.5
What does Dynamic Host
Confirmation Protocol
(DHCP) do for a network?
3.3.5.2 What are the 4 types of
messages sent and
received in DHCP?
3.3.6
What is SMB (Server
Message Block)?
3.3.6.2 What are the 3 message
types of SMB messages?
3.3.8
What does the Telenet
application provide?
3.3.8.2 What protocol is
recommended alternative to
Telnet when security is a
concern?
3.4
We will skip these labs
3.5.1.2 This is a self scored quiz
that will help prepare for the
POP (Post Office Protocol) and SMTP (Simple
Mail Transfer Protocol)
MUA Mail User Agent
MTA Mail Transfer Agent
MDA Mail Delivery Agent
Converted to a proprietary protocol for mail
delivery
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
developed to allow for file transfers between a
client and a server
21- Used for control
20- Used for actual file transfer
allows a host to obtain an IP address
dynamically when it connects to the network
DHCP Discover
DHCP Offer
DHCP Request
DHCP Acknowledge
the structure of shared network resources,
such as directories, files, printers, and serial
ports
Start, authenticate, and terminate sessions
Control file and printer access
Allow an application to send or receive
messages to or from another device
provides a standard method of emulating textbased terminal devices over the data network.
SSH Secure Shell protocol
test
3.5.1.3 Packet Tracer Lab that is
relatively challenging and
should help preparing for
the exam. Not required, but
would be helpful.
3.6.1
Quiz that also prepares you
for the test.
* What are the characteristics of OSI application layer?
 Layer seven, is the top layer of both the OSI and TCP/IP models.
 It is the layer that provides the interface between the applications we use to
communicate and the underlying network over which our messages are
transmitted.
 Application layer protocols are used to exchange data between programs running
on the source and destination hosts.
* How does the application layer handle application requests from multiple different
clients at the same time?
 A single application may employ many different supporting Application layer
services;
 Servers typically have multiple clients requesting information at the same time.
The Application layer processes and services rely on support from lower layer
functions to successfully manage the multiple conversations
* What are the 2 types of the network application layer software?
 There are two forms of software programs or processes that provide access to
the network: applications and services.
* You need to know functions of the following Application Layer protocols.
 File Transfer Protocol (FTP) is used for interactive file transfer between systems

Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the
Web pages of the World Wide Web.

For secure communication across the Internet, the HTTP Secure (HTTPS)
protocol is used for accessing or posting web server information.

Telnet, a terminal emulation protocol, is used to provide remote access to
servers and networking devices.

SSH provides stronger authentication than Telnet and supports the transport of
session data using encryption

Domain Name Service Protocol (DNS) is used to resolve Internet names to IP
addresses.
o The DNS server stores different types of resource records used to resolve
names. These records contain the name, address, and type of record.
o Some of these record types are:




A - an end device address
NS - an authoritative name server
CNAME - the canonical name (or Fully Qualified Domain Name) for an
alias; 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

Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages
and attachments.
o SMTP is a long established Internet protocol that is used for the delivery
and receipt of e-mail.

Post Office Protocol (POP): In order to receive e-mail from an e-mail server, the
e-mail client can use POP.

Telnet, a terminal emulation protocol, is used to provide remote access to
servers and networking devices.

SMB: Server Message Block (SMB) is a client/server file sharing protocol.

The following are not application layer protocol (layer 7). We will discuss them in
a later chapter
- ARP
- ICMP
- PPP
* What is client-server network model? What are the advantages of the client-server
model?
 Centralized administration
 Security is easier to enforce
 the device requesting the information is called a client
 the device responding to the request is called a server.
 a client may transfer a file to the server for storage purposes (upload).
 Data from a server to a client as a download.
* What are the characteristics of “clients” in the client-server network?
 A P2P application, allows a device to act as both a client and a server within the
same communication
 Some P2P applications use a hybrid system where resource sharing is
decentralized but the indexes that point to resource locations are stored in a
centralized directory.
 Peer-to-peer applications can be used on peer-to-peer networks, client/server
networks, and across the Internet
 A simple home network with two computers sharing a printer is an example of a
peer-to-peer network.
* Study the following graphic very carefully.



What are the components used to forward mail between the servers?
What are the purposes of MTA?
o The MTA receives messages from the MUA or from another MTA on
another e-mail server.
o The MTA process is used to forward e-mail
o The SMTP transport of e-mail between e-mail servers (MTA).
What are the purposes of MDA?
o If the mail is addressed to a user whose mailbox is on the local server,
the mail is passed to the MDA.