Applications: The Interface Between The Networks

Question 1

Two Important Concepts

Answer 1

• Application Layer
• Application Software

Question 2

Application Layer

Answer 2

The application layer of the OSI model provides the first step of getting data onto the network

Question 3

Application Software

Answer 3

Applications are the software programs used by people to communicate over the network. Examples of application software, including HTTP, FTP, E-mail, and others, are used to explain the differences between these two concepts.

Question 4

OSI Encapsulation Process

Answer 4

1. People create the communication
2. The application layer prepares human communication for transmission over the data network
3. Software and hardware convert communication to a digital format
4. Application layer services initiate the data transfer
5. Each layer plays its role
6. The application layer receives data from the network and prepares it for human use.

Question 5

3 primary functions of the Presentation Layer

Answer 5

• Coding and conversion if application layer data to ensure that data from the source device can be interpreted by the appropriate application on destination device
• Compression of the data in a manner that can be decompressed by the destination device
• Encryption of the for transmission and decryption of data upon receipt by the destination

Question 6

Session Layer

Answer 6

• Functions at the session layer and maintain dialogs between source and destination applications
• The session layer handles the exchange of information to initiate dialogs and keep them active, and to restart sessions that are disrupted or idle for a long period of time

Question 7

TCP/IP ApplicationLayer Protocols

Answer 7

• Domain Name System (DNS): used to resolve Internet names to IP addresses.
• Hypertext Transfer Protocol (HTTP): used to transfer files that make up the web pages of the World Wide Web.
• Simple Mail Transfer Protocol (SMTP): used for transfer of mail messages and attachments.
• Telnet: a terminal emulation protocol, used for remote access to servers and networking devices.
• File Transfer Protocol (FTP): used for interactive file transfer between systems.

Question 8

Application Layer Services

Answer 8

• Establish an interface to the network where protocols provide the rules and formats that govern how data is treated.
• Other programs, such as file transfer or network print spooling, might need the assistance of application layer services to use network resources.
• Interface with the network and prepare the date for transfer
• Different types of data — whether it is text, graphics, or video — require different network services to ensure that it is properly prepared for processing by functions occurring at the lower layers of OSI model.

Question 9

Application Layer Protocols Functions

Answer 9

• Establish consistent rules for exchanging data between applications and services loaded on the participating devices.
• Specify how data inside the messages is structured and types of messages that are sent between source and destination. These messages can be requests for services, acknowledgments, data messages, status messages, or error messages.
• Define message dialogues, ensuring that a message being sent is met by the expected response and that the correct services are invoked when data transfer occurs.

Question 10

Network-Aware Applications

Answer 10

• Provide the human (user) interface
• Rely on lower layers to complete the communication
• Implement the application layer protocols and are able to communicate directly with the lower layers of the protocol stack
• Example: W-mail clients and we browsers