The OSI application layer Flashcards
What is the role of applications in the network?
Provide the means for generating and receiving data that can be transported along the network
What are the 3 components of the application layer?
Applications, services and protocols.
What is the 1st (5) step that the application layer performs in OSI model communication?
People create the communication
What is the 2nd (5) step that the application layer performs in OSI model communication?
Software and hardware convert communication into digital format
What is the 3rd (5) step that the application layer performs in OSI model communication?
Application layer services initiate the data transfer
What is the 4th (5) step that the application layer performs in OSI model communication?
Each layer plays its role
What is the 5th (5) step that the application layer performs in OSI model communication?
The application layer receives data from the network and prepares it for human use
What is another role of the application layer in OSI model communication?
The application layer prepares human communication for transmission over a data network
What does the application layer provide?
An interface between the applications we use to communicate and the underlying network over which messages are transmitted.
What are application layer protocols used for?
To exchange data between programs running on source and data hosts
What is the 1st (3) of the presentation layer’s primary functions?
Coding and conversion of Application layer to ensure data on the source device can be interpreted by the appropriate application on the destination device
What is the 2nd (3) of the presentation layer’s primary functions?
Compression of data in a manner that can be decompressed by the destination device
What is the 3rd (3) of the presentation layer’s primary functions?
Encryption of data for transmission and decryption when data reaches destination
What protocol stack is associated with the presentation layer?
No particular one
Why is no particular protocol stack associated with presentation layer?
Multiple standards for image and video
What are some video standards?
Quicktime
Motion Picture Experts Group (MPEG)
What is quicktime?
A specification for video and audio
What is MPEG?
A standard for video compression and coding
What are some well known graphics image standards?
Graphics interchange format (GIF)
Joint photographics expert group (JPEG)
Tagged image file format (TIFF)
What are GIF and JPEG?
Coding and compression standards for graphic images
What is TIFF?
Standard coding format for graphic images
What is the role of the session layer?
Create and maintain dialogues between source and destination applications
What is the 1st thing (3) the session layer does?
Handles exchange of information to initiate dialogues
What is the 2nd thing (3) the session layer does?
Handles exchange of information to keep dialogues active
What is the 3rd thing (3) the session layer does?
Restarts sessions that are disrupted or idle for long periods of time
What is the role of TCP/IP application layer protocols.
Specify the format and control information necessary for many common internet functions
What is the 1st (5) of commonly known TCP/IP application layer protocols?
Domain Name Service (DNS) - Used to resolve internet names to IP addresses
What is the 2nd (5) of commonly known TCP/IP application layer protocols?
Hypertext transfer protocol (HTTP) - Used to transfer files that make up webpages of the world wide web
What is the 3rd (5) of commonly known TCP/IP application layer protocols?
Simple mail transfer protocol (SMTP) - Used to transfer mail messages and attachments
What is the 4th (5) of commonly known TCP/IP application layer protocols?
Telnet, a terminal emulation protocol - Used to provide remote access to servers and networking devices
What is the 5th (5) of commonly known TCP/IP application layer protocols?
File transfer protocol (FTP) - Used for interactive file transfer between systems
What defines the protocols in the TCP/IP suite?
Requests for comments (RFCs) - standards for TCP/IP suite
What is an executing program loaded on a device known as in the world of networks?
A process
What are the two forms of software programs or processes that provide access to a network in the application layer?
Applications and services
What are applications?
Software programs used by people to communicate over a network
What is a network-aware application?
An application that implements the application layer and can communicate directly with the lower levels of the stack
What are 2 examples of network aware applications?
Email client and web browser
How does and application or network service know what data formats and standards to use?
Protocols
What protocols does the application layer use?
The ones that are implemented in applications and network services
What components could ‘Telnet’ refer to?
Application, service or protocol
What is the 1st thing (4) that protocols specify in the application layer?
What messages are exchanged between source and destination hosts
What is the 2nd thing (4) that protocols specify in the application layer?
The syntax of the control commands
What is the 3rd thing (4) that protocols specify in the application layer?
The type and format for the data being transmitted
What is the 4th thing (4) that protocols specify in the application layer?
The appropriate methods for error notification and recovery
Which devices use application layer protocols during communication?
Source and destination
What is an examples of multiple protocols being used in the same conversation?
One protocol may specify how to establish network communication while another may describe the process for data transfer when the message is passed two another layer
What is the 1st (5) example of a message that a protocol will structure?
Requests for services
What layer are client/server processes in?
Application
What is the 2nd (5) example of a message that a protocol will structure?
Acknowledgements
What is the 3rd (5) example of a message that a protocol will structure?
Data messages
What is the 4th (5) example of a message that a protocol will structure?
Status messages
What is the 5th (5) example of a message that a protocol will structure?
Error messages
Protocols define message dialogues. What does this mean?
A message dialogue ensures a message gets the correct response and that corrected services are invoked when data transfer occurs
How does the client begin a client/server exchange?
By requesting data from the server
How does the server respond to a clients request in a client/server exchange?
By sending one or more streams of data to the client
What do application layer protocols describe in a client/server exchange?
Format of the requests and responses
What control information may be required in a client/server exchange?
User authentication
Identification of data file to be transferred
In an email example, what is the client role in a client/server exchange?
Email client issues a request for any unread email to the email server
In an email example, what is the server role in a client/server exchange?
Servers responds by sending requested email to client
Where does data flow in client/server exchange?
From server -> client and from client -> server
In general networking terms, what is a server?
A device that responds to requests from client appliations
What is the 1st (6) example of files that can be stored on servers?
Web page
What is the 2nd (6) example of files that can be stored on servers?
Document
What is the 3rd (6) example of files that can be stored on servers?
Database
What is the 4th (6) example of files that can be stored on servers?
Picture file
What is the 5th (6) example of files that can be stored on servers?
Video file
What is the 6th (6) example of files that can be stored on servers?
Audio file
How does a network printer work in a client/server exchange?
Print server delivers client print request to specified printer
Why might some servers require the authentication of user account information?
To verify if the user has permission to access particular data or a specific operation.
What do servers that authenticate user accounts rely on?
Central list of user accounts along with their permissions (for data and operations)
What is an example of permissions in FTP client/server?
When uploading, you may have permission to write to your specific folder, but not anybody elses folder
What is a server service, or process, sometimes called?
A daemon
Why are daemons described as ‘listening’?
They are programmed to respond to any request of a service provided by that daemon
What does a daemon do when it “hears” a request from a client?
Exchanges appropriate messages with client, as dictated by its protocols, then sends client requested data in correct format
How must a server handle multiple client requests in order to succeed?
Simultaneously and seperately
How many application layer services could 1 application need?
Many
What does the application layer rely on to successfully manage multiple conversations?
Support from lower layer functions
What is the 1st (2) peer-to-peer networking form?
Peer-to-peer networking design
What is the 2nd (2) peer-to-peer networking form?
Peer-to-peer applications (P2P)
What is a peer-to-peer network?
Two or more computers are connected over a network and can share resources.
What is each end device on a peer-to-peer network known as?
A peer
What can each peer in a peer-to-peer network act as?
A client and a server on a per request basis
What is a simple example of a peer-to-peer network?
Two connected computers on a home network sharing a printer.
What is another example of a peer-to-peer network?
Two computers connected to a network that uses software applications to share resources between one another on the network
Where can information be found on a peer-to-peer network?
Anywhere on any connected device. It is decentralised.
Why is it difficult to enforce security and access policies on a peer-to-peer network?
Since user account information is not centralised, this information would have to be set up on every device connecting to the network
How does a P2P application differ from a P2P server?
A P2P application allows a device to act as a client and server in the same communication
What do P2P applications require?
Each end device to have a user interface and run a background service
What is the P2P hybrid system?
Resource sharing is decentralized but an index server stores the locations of resources
What is another role an index server can play?
It can help connect two peers, but after that, the peers only communicate with each other
What is the 1st (7) application layer service and port number?
Domain Name System (DNS) TCP/UDP Port 53
What is the 2nd (7) application layer service and port number?
Hypertext transfer protocol (HTTP) TCP Port 80
What is the 3rd (7) application layer service and port number?
Simple Mail Transfer Protocol (SMTP) TCP Port 25
What is the 4th (7) application layer service and port number?
Post Office Protocol (POP) TCP Port 110
What is the 5th (7) application layer service and port number?
Telnet TCP Port 23
What is the 6th (7) application layer service and port number?
Dynamic Host Configuration Protocol (DHCP) UDP Ports 67 and 68
What is the 7th (7) application layer service and port number?
File Transfer Protocol (FTP) TCP Ports 20 and 21
What is the 1st (4) basic DNS step?
User types in easy to use URL
What is the 2nd (4) basic DNS step?
DNS server matches URL (human address) with IP address (numeric address)
What is the 3rd (4) basic DNS step?
Numeric address is returned to client making requests of the server
What is the 4th (4) basic DNS step?
Legible name has been resolved into numbers by DNS
What are two advantages of domain names?
Easy to remember
If IP address is changed, user will not notice
What single format do DNS communications protocols use?
A message
What does the DNS protocol include the formats for?
Queries, responses and data formats
