SEMESTER 1 Chapter 3
Application Layer Functionality and Protocols

 V 4.0

What does the application layer provide?

the interface between the applications we use to communicate and the underlying network over which our messages are transmitted


What are application layer protocols used for?

to exchange data between programs running on the source and destination hosts

What are the three primary functions of the Presentation Layer?

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.


What is the main function of the session layer?

create and maintain dialogs between source and destination applications

What do the Application Layer protocols of the TCP/IP protocol specify?

the format and control information necessary for many of the common Internet communication functions


What are the two forms of software programs or process that provide network access in the Application Layer

applications and services


What do protocols provide?

the rules and formats that govern how data is treated


What is the difference between an application and a service?

Applications interact with the user and services prepare data for the network


What do application layer protocols do?

Protocols provide the rules and formats that govern how data is treated.


What 6 things do protocols define?

  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 between a client and a server?

the device requesting the information is called a client and the device responding to the request is called a server


In general networking sense what is a server?

any device that responds to requests from client applications is functioning as a server


Describe the 2 processes a daemon uses (listening and hears)?

"listening" for a request from a client, because 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

Complete the packet tracer lab examine a number of packets to see what each packet contains.



What is a peer-to-peer network?

two or more computers are connected via a network and can share resources (such as printers and files) without having a dedicated server


Are peer-to-peer networks easy to secure?


What are peer-to-peer applications?

allows a device to act as both a client and a server within the same communication


What do port numbers identify?

applications and Application layer services that are the source and destination of data


What does the DNS protocol do?

defines an automated service that matches resource names with the required numeric network address.

What does the nslookup utility allow you to do?

allows the user to manually query the name servers to resolve a given host name


What does the command ipconfig /displaydns show?

Displays all of the cached DNS entries on a Windows XP or 2000 computer system

What happens if a DNS server does not have a name in its stored records?

It passes the request on to another DNS server


If the same request is made again where does the DNS server look?

In its cache

When is a server declared to be an authoritative server?

When the resource is directly held on that server

Define the three parts of a url as listed on the page?

http:- protocol name of server

web-server.htm- name of file or page


What type of request is sent to the server when retrieving a web page?


What does the POST command do?

Sends information to the web server


What does the PUT command do?

Sends resources or content to the web server


What protocol is used for secure transmission across the web?


Packet Tracer Lab



What 2 Application Layer protocols are used in sending and receiving email?

POP (Post Office Protocol) and SMTP (Simple Mail Transfer Protocol)


What is another name for an email application?

MUA Mail User Agent

What are the two processes that email servers perform?

MTA Mail Transfer Agent

MDA Mail Delivery Agent

What happens to emails in many companies once the email reaches the internal server?

Converted to a proprietary protocol for mail delivery

List and describe some of the commands used by the SMTP protocol.

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


What is File Transfer Protocol (FTP)?

developed to allow for file transfers between a client and a server


What are the 2 ports used and their purpose in FTP?

21- Used for control

20- Used for actual file transfer


What does Dynamic Host Confirmation Protocol (DHCP) do for a network?

allows a host to obtain an IP address dynamically when it connects to the network

What are the 4 types of messages sent and received in DHCP?

DHCP Discover

DHCP Offer

DHCP Request

DHCP Acknowledge


What is SMB (Server Message Block)?

the structure of shared network resources, such as directories, files, printers, and serial ports

What are the 3 message types of SMB messages?

Start, authenticate, and terminate sessions

Control file and printer access

Allow an application to send or receive messages to or from another device


What does the Telenet application provide?

provides a standard method of emulating text-based terminal devices over the data network.

What protocol is recommended alternative to Telnet when security is a concern?

SSH Secure Shell protocol


We will skip these labs

This is a self scored quiz that will help prepare for the test

Packet Tracer Lab that is relatively challenging and should help preparing for the exam. Not required, but would be helpful.



Quiz that also prepares you for the test.