The document discusses the application layer in the OSI model and TCP/IP protocols. It describes how the application layer generates data and provides an interface between users and networks via applications. Common application layer protocols like HTTP, DNS, SMTP, and Telnet are examined along with their roles in file transfer, email services, network management, and supporting client-server and peer-to-peer communication models. The document also reviews presentation and session layers in OSI and various application layer protocols used in networking labs.

1. Application Layer
Functionality and
Protocols
Network Fundamentals – Chapter 3
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2. Objectives
 Identify the Application layer as the source
and destination of data for communication
across networks.
 Role of protocols in supporting communication
between server and client processes.
 Features, operation, and use of well-known
TCP/IP application layer services (HTTP,
DNS, SMTP).
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3. Applications – generate data at the top
of the OSI model
 Applications provide the means for generating and
receiving data that can be transported on the network
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4. Applications – The Interface Between
Human and Data Networks
 Application layer provides an interface between the
user and the network via network applications
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5. OSI layers and TCP/IP Application layer
 OSI top layers map to TCP/IP Application layer
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6. Presentation and Session layers
 The Presentation layer has three primary functions:
 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.
 The Session Layer
 Creates and maintain dialogs between source and destination applications.
 Handles the exchange of information to initiate dialogs, keeps them active.
 Restarts sessions that are disrupted or idle for a long period of time.
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7. Networking Applications
•DNS is used to resolve
Internet names to IP
addresses.
•HTTP is used to transfer files
that make up the Web pages of
the World Wide Web
•SMTP is used for the transfer
of mail messages and
attachments.
•Telnet, a terminal emulation
protocol, is used to provide
remote access to servers and
networking devices.
•FTP is used for interactive file
transfer between systems.
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8. The Role of Protocols in Supporting
Communication Client - Server
 The client and server processes support data retrieval
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9. Peer 2 Peer network model
 Peer-to-peer networking and peer-to-peer applications
 Act as both a client and a server within the same
communication
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10. DNS Application Layer Service
 Domain Name Services DNS protocol and its Support of Name
resolution
 DNS provides a conversion of domain names to IP addresses.
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11. HTTP in the delivery of web pages
 Client requests a page.
 In response to the request, the HTTP returns the code for a web
page.
 The browser interprets the HTML code and displays a web page.
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12. E-mail, one of the most popular network
services
 Features of the Post Office Protocol (POP) and Simple Mail
Transfer Protocol (SMTP) protocols; Support e-mail services
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13. Telnet supports Communication and
management
 Telnet Common Client – Server Application Layer
services and protocols
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14. Telnet Application Layer Service
 Telnet protocol used in examining and managing networks
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15. Features, Operation, and Use of TCP/IP
Application Layer Services
 Server Message Block (SMB) protocol used in supporting file,
printer and directories sharing in Microsoft-based networks
 SAMBA does the same for UNIX, LINUS OS’s
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16. P2P Application Layer Service
 Gnutella protocol supports P2P services files sharing over the
internet. Clients include: BearShare, LimeWire, XoloX
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17. Labs
 4.5.2 TCP/IP Transport layer protocols TCP,UDP
 3.4.3 Email services and protocols
(SMTP,MUA,MDA,MTA, POP and Internet Message
Access Protocol; IMAP & Telnet)
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