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Chapter 10 - Application Layer

10.0 Application Layer

10.0.1 Introduction >10.0.1.1 Introduction

Upon the completion of this chapter you will be able to:

  • Explain the functions of the application layer, session layer, and presentation layer work together to provide network services to end user applications.
  • Describe how common application layer protocols interact with end user applications.
  • Describe, at a high level, common application layer protocols that provide Internet services to end-users, including WWW services and email.
  • Describe application layer protocols that provide IP addressing services, including: DNS and DHCP.
  • Describe the features and operation of well-known application layer protocols that allow for file sharing services, including: FTP, File Sharing Services, SMB protocol.
  • Explain how data is moved across the network, from opening an application, to receiving data.

10.0.1.2 Activity- Application Investigation

Network application:

  • Make communication in the workplace easier.
  • Affect the amount of work completed on a daily basis.
  • Reduce data communications time and costs.

10.0.1 Introduction >10.0.1.2 Activity - Application Investigation

The figure on this page shows three different applications: Instant Messaging, Podcasting, and Weblog.

Network Applications:

  • make communication in the workplace easier
  • affect the amount of work completed on a daily basis
  • reduce data communications time and costs

Objectives:

Explain the operation of the application layer in providing support to end-user applications.
In this activity, you will envision what it would be like not to have network applications available to use in the workplace. You may also estimate what it would cost to not be able to use networked applications for a short period of time.

See page notes for instructions.

10.1 Application Layer Protocols

10.1.1 Application, Session and Presentation >OSI and TCP/IP Models Revisited

The figure on this page shows the relationship between the TCP/IP model and the OSI model. OSI model layers 5, 6, and 7 map to the TCP/IP Transport layer. OSI model layer 4 maps to the TCP/IP model Transport layer. OSI model layer 3 maps to the TCP/IP model Internet layer. OSI model layers 1 and 2 map to the TCP/IP model Network Access layer.

OSI Model TCP/IP Model
Application Application
Presentation
Session
Transport Transport
Network Internet
Data Link Network Access
Physical

The description given for this table is "The key parallels are in the transport and network layers"

10.1.1 Application, Session and Presentation >10.1.1.2 Application Layer

The figure on this page shows sample Applications for the OS.I model Application layer. Examples include:

  • Domain Name System
  • Hypertext Transfer Protocol
  • Simple Mail Transfer Protocol
  • Post Office Protocol
  • Dynamic Host Configuration Protocol
  • File Transfer Protocol
  • Internet Message Access Protocol.

10.1.1 Application, Session and Presentation >10.1.1.3 Presentation and Session Layers

The figure on this page shows examples of the OSI Presentation Model. Examples include:

  • Quick Time
  • Motion Picture Experts Group (MPEG)
  • Graphics Interchange Format (GIF)
  • Joint Photographic Experts Group (JPEG)
  • Portable Network Graphics (PNG)

10.1.1 Application, Session and Presentation >10.1.1.4 TCP/IP Application Layer Protocols

The figure on this page shows examples of OSI layer functionality.

Application Layer Name System Host Config Email File Transfer Web
DNS BOOTP SMTP FTP HTTP
DHCP POP TFTP
IMAP
Application
Protocol
Description
DNSTranslate domain names, such as cisco.com, into IP addresses
BOOTP* Enables a diskless workstation to discover its own IP address, the IP address of a BOOTP server on the network, and a file to be loaded into memory to boot the machine
* BOOTP is being superseded by DHCP
DHCP* Dynamically assigns IP addresses to client stations at start-up//* Allows the addresses to be re-used when no longer needed
SMTP* Enables clients to send email to mail server
* Enables servers to send email to other servers
POP* Enables clients to retrieve email from a mail server
* Downloads email from the mail server to the desktop
IMAP* Enables clients to access email stored on a mail server
* Maintains email on the server
FTP* Sets rules that enable a user on one host to access and transfer files to and from another host over a network
* A reliable, connection-oriented, and acknowledged file delivery protocol
TFTP* A simple, connectionless file transfer protocol
* A best-effort, unacknowledged file delivery protocol
* Utilizes less overhead than FTP
HTTPSet of rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web

10.1.1 Application, Session and Presentation >10.1.1.5 Activity – Application Protocols and Standards

The figure on this page is an interactive activity that allows the learner to practice matching a protocol with its appropriate OSI model layer (5 Session Layer, 6 Presentation Layer, or 7 Application Layer) and TCP/IP Application Layer.

Match the appropriate protocol names and standards to the correct OSI and TCP/IP network locations. Each answer will be used twice, once on the OSI model and once on the TCP/IP model locations.

The protocol names to be matched are:

  • HTML
  • POP
  • IMAP
  • TFTP
  • JPEG
  • MPEG
  • DNS
  • DHCP
  • HTTP

10.1.2 How Application Protocols Interact with End-User Applications >10.1.2.1 Peer-to-Peer Networks

This figure on this page shows an example of Peer to Peer networking using 2 computers on a LAN. Peer1 is the print client and file server while Peer2 is the file client and print server. The printer is directly connected to Peer2.

Peer1 has a callout saying, "I have files on my hard drive that are being shared for Peer2. I also have a page that I need to print through Peer2.""

Peer2 has a callout saying, "I need to access a file from the hard drive on Peer1. I also need to print a file that I received from Peer1, with a print request.""

The description given for this figure is, "A peer-to-peer exchange, both devices are considered equal in the communication process.".

10.1.2 How Application Protocols Interact with End-User Applications >10.1.2.2 peer-to-Peer Applications

The figure on this page shows communication using Instant Messaging as an example of a peer-to-peer application. This demonstrates a program acting as both client and server.

Client/Server1 sends the message "Meeting tonight." over the network which is received by Client/Server2. Client/Server2 sends the message "Ill be there." over the network which is received by Client/Server1. Client/Server1 sends the message "Good." over the network which is received by Client/Server2.

Both clients simultaneously:

  • Initiate a message
  • Recieve a message

10.1.2 How Application Protocols Interact with End-User Applications >10.1.2.3 Common P2P Applications

The figure on this page shows how Gnutella supports peer-to-peer communication with many peers simultaneously. The figure shows 6 machines connected over a network. PC1 has a callout saying, "Where is mysong.mp3?". PC3, PC5 and PC6 have callouts saying,"I've got it.".

The description given for this figure is, "Gnutella allows P2P applications to search for shared resources on peers.".

10.1.2 How Application Protocols Interact with End-User Applications >10.1.2.4 Lab – Researching Peer-to-Peer file Sharing

See Lab Descriptions.

10.1.2 How Application Protocols Interact with End-User Applications >10.1.2.5 Client-Server Model

The figure on this page shows an example of how downloads and uploads work in a client-server model. There is a server and there are 3 devices connected via a network; a computer, a mobile device, and an IP phone.

  • Resources are stored on the server.
  • A client is a hardware/software combination that people use directly.

The figure also has the following 2 buttons:

  • Download
  • Upload
  • Files are downloaded from the server to the client.
  • Files are uploaded from the client to the server for storage.

10.2 Well-Known Application Layer Protocols and Services

10.2.1 Common Application Layer Protocols >10.2.1.1Application Layer Protocols Revisted

The figure on this page shows the relationship between the TCP/IP model and the OSI model. OSI model layers 5, 6, and 7 map to the TCP/IP Application layer. OSI model layer 4 maps to the TCP/IP model Transport layer. OSI model layer 3 maps to the TCP/IP model Internet layer. OSI model layers 1 and 2 map to the TCP/IP model Network Access layer.

OSI Model TCP/IP Model
Application Application
Presentation
Session
Transport Transport
Network Internet
Data Link Network Access
Physical

The figure also shows three protocols that operate at the application layer:

  • Hypertext Transfer Protocol
  • Simple Mail Transfer Protocol
  • Post Office Protocol.

10.2.1 Common Application Layer Protocols >10.2.1.2 hypertext Transfer protocol and Hypertext Markup language

Figure 1 on this page shows a HTTP server and client connected to a network. The URL http://www.cisco.com/index.html is also shown.

Figure 2 on this page shows step one, the client requesting the web page http://www.cisco.com.

The description given for this figure is, "The client initiates an HTTP request to a server.".

Figure 3 on this page shows step two, the server response with an example of the HTML code for web page.

HTTP/1.1 200 OK
Date: Mon, 23 May 2005 22:38:34 GMT
Server: Apache/1.3.27 (unix) (Red-Hat/Linux)
Last-Modified: wed. 08 Jan 2003 23:11:55 GMT
Etag: "3f80f-1b6-3e1cb03b"
Accept-Ranges: bytes
Content-Length: 438
connection: close
content-Type: text/html; charset-UTF-8
<html>
<head>
<body>
...CONTENTS OF HTML PAGE...
<body>

The description given for this figure is, "In response to the request, the HTTP server returns code for a web page.".

Figure 4 on this page shows the web page rendering in a browser on the client.

The description given for this figure is, "The browser interprets the HTML code and displays a web page.".

10.2.1 Common Application Layer Protocols >10.2.1.3 HTTP and HTTPS

The figure shows the following HTTP GET request between a client and server:

Host: www.cisco.com
GET /index.html HTTP/1/1

The description given for this figure is, "Entering in the address bar of a browser generates the HTTP GET message.".

10.2.1 Common Application Layer Protocols >10.2.1.4 SMTP, POP, and IMAP

Figure1 on this page shows a client connected to a server. The client is a Mail User Agent (MUA). The client is sending mail using SMTP and receiving mail using POP.

The description given for this figure is, "Clients send emails to a server using SMTP and receive emails using POP3.".

Figure 2 on this page shows how mail gets relayed between ISPs before reaching its destination.

Mail for recipient@cisco.com is sent to ISP A mail server using SMTP. The message is then relayed to ISP B mail server using SMTP. The recipient receives the message from ISP B mail server using IMAP or POP3.

10.2.1 Common Application Layer Protocols >10.2.1.5 SMTP, POP, and IMAP (cont.)

The figure on this page shows a client (MUA) sending mail to recipient@domain.com.

The message reaches its Mail Transfer Agent (MTA). The MTA has a callout saying, "Is the recipient in my list of recipients? No. Forward email to another server.". The message is forwarded to another MTA. for delivery.

The description given for this figure is, "The Mail Transfer Agent process governs email handling between servers and clients.".

10.2.1 Common Application Layer Protocols >10.2.1.6 SMTP, POP, and IMAP (cont.)

The figure on this page shows the interaction between all devices involved with an e mail transmission.

The sender (MUA) sends the message to the MTA. The MTA has a callout saying, "I do not have the recipient listed. I have forwarded the email to another server.". The MTA forwards the message to another MTA. The second MTA has a callout saying, "I have recipient@domain.com listed. I will place this email in the recipient's mailbox.". Since this MTA has the address of the recipient, it acts as a Mail Delivery Agent (MDA). The message is then sent to the recipient (MUA) using POP3.

The description given for this figure is, "The Mail Delivery Agent process governs delivery of email between servers and clients.".

10.2.1 Common Application Layer Protocols >10.2.1.7 SMTP, POP, and IMAP (cont.)

The figure shows the completed cycle of an e. mail delivery.

  • Mail is sent from MUA to MTA using SMTP
  • The MTA forwards the message to another MTA using SMTP
  • The second MTA delivers the message to the recipient

The description given for this figure is, "SMTP is used to send emails from clients to server, and to forward emails between email servers. POP is used to deliver email.".

10.2.1 Common Application Layer Protocols >10.2.1.8 Packet tracer – Web and Email

Objectives:

Part 1: Configure and Verify Web Servers
Part 2: Configure and Verify Email Services

10.2.2 Providing IP Addressing Services >10.2.2.1 Domain Name Service

Figures 1 to 5 on this page display the steps involved in DNS resolution. In the figures a PC that is a client is connected to a DNS server through the network cloud.

Figure 1 shows the client with the web address http://www.cisco.com/ in the address bar. The client makes a DNS query to a DNS server. The name is easy for people to use.

Figure 2 shows an NS record matching www.cisco.com to the IP address 198.133.219.25. The DNS server matches the domain name with numeric address. The devices use numbers.

Figure 3 shows the client sending the DNS request to the server.

Figure 4 shows the DNS server responding to the DNS query with the IP address for www.cisco.com.

The description given for this figure is, "The number is returned to the client for use in making requests of the server.".

Figure 5 shows the client now has the IP address to put in the layer 3 header as the destination IP for the HTTP request.

The description given for this figure is, "A domain name is resolved to its numeric network device address by the DNS protocol.".

10.2.2 Providing IP Addressing Services >10.2.2.2 DNS Message Format

The figure on this page shows the DNS message format.

DNS uses the same message format for:
* all types of client queries and server responses
* error messages
* the transfer of resource record information between servers
Header 
QuestionThe question for the name server
AnswerResource records answering the question
AuthorityResource records pointing toward an authority
AdditionalResource records holding additional information

10.2.2 Providing IP Addressing Services >10.2.2.3 DNS Hierarchy

The figure on this page shows the DNS hierarchy. At the bottom level is the DNS Client. At the Secondary level domain servers is the Local cisco.com DNS server. At the Top level domain servers are the .com, .org, .au, and .co servers. on the top level are the Root DNS servers..

The DNS client communicates with the local DNS server which has a callout saying, "I have the records for: www.cisco.com and mail.cisco.com.".
The Local DNS server communicates with the Top-level .com domain server which has a callout saying, "I have records to find who knows about: cisco.com and linksys.com.".
The Top-Level domain server communicates with the Root servers for any records they do not have. The Root servers have a callout saying,"I have records to find who knows about: .com, .org, .au, and .co.".

The description given for this figure is, "A hierarchy of DNS servers contains the resource records that match names with addresses.".

10.2.2 Providing IP Addressing Services >10.2.2.4 nslookup

The figure on this page shows the output from issuing an ns lookup command at a command prompt in Windows.

Microsoft Windows XP [Version 5.1.2600]
<C> Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\bradfjoh>cd..
C:\Documents and Settings>nslookup
Default Server: dns-sj.cisco.com
Address: 171.70.168.183
> www.cisco.com
Default Server: dns-sj.cisco.com
Address: 171.70.168.183
Name: www.cisco.com
Address: 198.133.219.25
cisco.netacad.net
Server: dns-sj.cisco.com
Address: 171.70.168.183
Non-authoritative answer:
Name: cisco.netacad.net
Address: 128.107.229.50
>

10.2.2 Providing IP Addressing Services >10.2.2.5 Syntax Checker – DNS CLI Commands in Windows and UNIX

The figure on this page is Syntax Checker used to practice entering the ns lookup command at a command prompt. The Syntax Checker is inaccessible:

The figure also has the following 3 buttons:

  • Reset: resets the Syntax Checker
  • Show Me: displays the next step in the configuration process
  • Show All: displays the completed configuration process as follows:

Enter the 'nslookup' command to begin a manual query of the name servers.

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
c:\>nslookup
Default Server: UnKnown
Address: 10.10.10.1

The output lists the name and IP address of the closest name server. in this case, the user is in a home network behind a router firewall. The address is the router. You are now in nslookup mode. Enter the domain name 'www.cisco.com'.

www.cisco.com
Server: e144.dsch.akamiedge.net
Addresses: 2600:1400:1:1:8500::90
      2600:1400:1:1:8200::90
      2600:1400:1:1:8100::90
      23.67.208.170
Aliases: www.cisco.com
      www.cisco.com.akadns.net
      wwwds.cisco.com.edgekey.net
      wwwds.cisco.com.edgekey.net.globalredir.akadns.net

The output lists all the addresses that the server 'e144' currently has in its database. Notice that IPv6 addresses are also listed. In addition, various aliases are shown that will resolve to 'www.cisco.com'.
Enter the 'exit' command to leave nslookup mode and return to the Windows command line.

>exit

You can directly query the DNS servers by simply adding the domain name to the 'nslookup' command. Enter'nslookup www.google.com'.

c:\>nslookup www.google.com
Server: UnKnown
Address: 10.10.10.1
Non-authoritative answer:
Name: www.google.com
Addresses: 2001:4860:4002:802::1014
      74.125.227.81
      74.125.227.84
      74.125.227.83
      74.125.227.82
      74.125.227.81
c:\>

-- -- -- -- -- -- -- -- -- -- -- --
'''You are now in a different location on a Linux machine. The nslookup command
is the same.
Enter the 'nslookup' coomand to beginn a manual query of the name servers.

user@cisconetacad$ nslookup
Server: 127.0.1.1
Address: 127.0.1.1#53
Non-authoritative answer:
www.cisco.com canonical name = www.cisco.com.ajadns.net.
www.cisco.com.akadns.net canonocal name =
wwwds.cisco.com.edgekey.net.
wwwds.cisco.com.edgekey.net canonical name =
wwwds.cisco.com.edgekey.net.globalredir.akadns.net.
wwwds.cisco.com.edgekey.net.globalredir.akadns.net canonical
name = e144.dscb.akamaiedge.net.
Name: e144.dscb.akamaiedge.net
Address: 23.60.112.170

Notice the output is similar as what you got from the Windows command line.
Enter the 'exit' command to leave nslookup mode and return to the Linux
command line.

exit

As in Windows, you can directly query the DNS servers by simply adding the
domain name to the 'nslookup' command. Enter 'nslookup www.google.com'.

user@cisconetacad$ nslookup www.google.com
Server: 127.0.1.1
Address: 127.0.1.1#53
@@Non-authoritative answer:
Name: www.google.com
Address: 74.125.225.209
Name: www.google.com
Address: 74.125.225.210
Name: www.google.com
Address: 74.125.225.211
Name: www.google.com
Address: 74.125.225.12
Name: www.google.com
Address: 74.125.225.208
user@cisconetacad$@@

You successfully used the nslookup command to verify the status of domain names.

10.2.2 Providing IP Addressing Services >10.2.2.6 Dynamic Host Configuration Protocol

The figure on this page shows a cloud, or the Internet, connected to 4 networks.

Each network has its own DHCP server. Each network is a different size ranging from a single home to a corporate network.

In the figure there are three ISP’s; ISP 1, ISP 2 and ISP 3 as well as ISP DHCP server in the network cloud.

ISP 1 router is connected to a single home PC where the router acts as a DHCP server and the PC is the DHCP client.

ISP 2 router is connected to the router on a corporate network with 6 PCs connected to two switches and the switches are connected to a router and a server this server is the Local DHCP Server and the PCs are DHCP clients.

ISP 3 router is connected to the wireless router of a home and small business network. The router is connected to three PCs through wireless connections, here the wireless router is a DHCP server and the PCs are DHCP clients.

10.2.2 Providing IP Addressing Services >10.2.2.7 DHCP Operation

The figure on this page shows the DHCP conversation between a DHCP Client and a DHCP Server. The following 4 steps are listed as explained in the page notes:

DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPPACK

10.2.2 Providing IP Addressing Services >10.2.2.8 Packet Tracer – DHCP and DNS Servers.

Objectives:

Part 1: Configure Static IPv4 Addressing
Part 2: Configure and Verify DNS Records

10.2.2 Providing IP Addressing Services >10.2.2.9 Lab – Observing DNS Resolution

See Lab Descriptions.

10.2.3 Providing File Sharing Services >10.2.3.1 File Transfer Protocol

The figure on this page shows an FTP conversation between client and server. There are two connections, the control and the data use two different TCP ports.

  1. Control Connection:
    Client opens first connection to the server for control traffic.
  2. Data Connection:
    Client opens second connection for data traffic.

The description given for this animation is, "Based on commands sent across control connection, data can be downloaded from server or upload from client."

10.2.3 Providing File Sharing Services >10.2.3.2 Packet Tracer – FTP

Objectives:

Part 1: Configure FTP Services on Servers
Part 2: Upload a File to the FTP Server
Part 3: Download a File from the FTP Server

10.2.3 Providing File Sharing Services >10.2.3.3 Lab – Exploring FTP

See Lab Descriptions.

10.2.3.4 Server Message Block

Figure 1 on this page shows a client computer using SMB protocol to access documents on a remote Windows server and a printer connected to the remote Windows server. The client PC is connected to the server to which a printer is connected. The client sends SMB requests and Server replies with SMB responses.

Shared resources are:

  • File systems
  • Printers
  • Mail slots
  • APIs

The description given for this animation is, "SMB is a client-server, request-response protocol. Servers can make their resources available to clients on the network."

Figure 2 on this page shows two clients using SMB to share files.

The description given for this animation is, "A file may be copied from PC to PC with Windows Explorer using the SMB protocol."

10.3 The Message Heard Around the World.

10.3.1 Move It! >10.3.1.1 The Internet of Things

The image on this page displays buildings in the background with many network able devices connecting to each other. The figure is titled "THE INTERNET OF EVERYTHING IS HERE. As the Internet evolves, so will we.". The figure also states that "37 billion new things will be connected by the year 2020."

10.3.1 Move It! >10.3.1.2 Message Travels Through a network

This flash animation on this page shows computer H1 on one LAN connected to the Internet and a server on another LAN connected to the Internet. Computer H1 uses the TCP/IP model and passes the message down through the various layers as follows:

  • The Application layer sends the stream of HTTP GET data to the Transport layer for encapsulation.
  • The Transport layer divides the application stream into segments and adds a TCP header.
  • The Transport layer passes the segment to the Internet layer.

10.3.1 Move It! >10.3.1.3 Getting the data to the End Device

The figure on this page shows the same network as the previous page. The Transport layer handing the segments to the Internet layer. The Internet layer creates an IP datagram or packet. The packet includes the source and destination IP addresses. The packet is passed to the Network Access layer..

10.3.1 Move It! >10.3.1.4 Getting the data through the Internetwork

The figure on this page shows the same network as the previous page. The Network Access layer frames the packet with source and destination MAC addresses, and then converts the frame to electrical signals.

10.3.1 Move It! >10.3.1.5 Getting the data to the Right Application

This flash animation on this page shows a computer and a server connected to the Internet. The server is running the following three services:

  • HTTP
  • File Transfer
  • Electronic Mail

The following three packets are received by the server:

HTTP Port Number
File Transfer Port Number
Electronic Mail Port Number

Each packet is delivered to the appropriate service based on the destination port number.

The description given for this animation is, "At the end device, the service port number directs the data to the correct conversation.".

10.3.1 Move It! >10.3.1.6 Warriors of the Net

The YouTube video on this page , titled " Warriors of the Net " follows the journey of an IP packet. It can be accessed via the following link:
http://www.youtube.com/watch?v=PBWhzz_Gn10

10.4 Summary

10.4.1 Summary >10.4.1.1 Modeling Activity – Make it happen!

The figure on this page shows people around a table collaborating on blueprints.

Network applications use protocols to facilitate data communication...

  • POP
  • IMAP
  • HTTP
  • FTP

...and the list goes on!

10.4.1 Summary >10.4.1.2 Packet Tracer Multiuser – Tutorial

Objectives:

Part 1: Establish a Local Multiuser Connection to another instance of Packet Tracer
Part 2: Verify Connectivity across a Local Multiuser Connection

10.4.1 Summary >10.4.1.3 Packet Tracer Multiuser – Implement Services

Objectives:

Part 1: Establish a Local Multiuser Connection to another instance of Packet Tracer
Part 2: Server Side Player - Implement and Verify Services
Part 3: Client Side Player - Configure and Verify Access to Services

10.4.1 Summary >10.4.1.4 Summary

The figure on this page shows a client and a web server connected to the Internet and the client is viewing a web page.

End of Chapter 10: Application Layer.

Next - Chapter 11: Its a Network.

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Page last modified on October 22, 2014, at 05:59 AM