Application Layer Flashcards
What does the Application Layer Protocol provide?
A means to easily build protocol-compliant applications
Can applications implement multiple, different application layer protocols?
Yes, they can
What are the communicating entities in an application layer protocol? What are they not? Can these entities reside on the same device?
Application programs / processes, usually remotely located
Users / devices
Yes
Are application layers for the network core? How is this evidenced?
No, they aim to push complexity to the network edge
Routers generally do not run applications and application layer protocols. Instead, devices do
For this course, up to what layer do routers implement protocols, and for what layers do end devices?
Routers implement protocols of layer 1-3 (physical, link, and network), while end devices implement protocols of layers 4 and 5 (transport and application)
What are the three primary functions of the Application Layer?
Architecture Styles
Addressing
Service Models
What is meant by the “Architecture Styles” function?
The choice in between client-server, peer-to-peer and hybrid architecture styles
Client-server - one device (client) requests services or resources from another device (server)
Peer-to-peer - all devices act as both clients and servers (no central server)
Hybrid - combines elements of both client-server and peer-to-peer architecture styles
What is meant by the function of “addressing”? What are some examples of addresses?
The process of uniquely identifying and locating network entities (such as applications or services) to facilitate communication
student@tue.nl and tue.nl
What is a socket address used for? What do socket address consist of?
Used by web client processes to find web server processes
An IP address and a port number
What is an IP address?
A numerical label assigned to each device connected to a computer network that uses the Internet Protocol for Communication
What is a port number? What does the existence of multiple sockets allow for?
A numerical identifier used to distinguish different communication endpoints (sockets) within a device in a computer network
Multiple services to operate concurrently
What does the “Service Models” application protocol function refer to? For example?
The provision of services to the applications running on top of it, as well as the receiving of services from the transport layer
Simple Mail Transfer Protocol, a service for the mail client applications that allows the application to send e-mail messages to an email-server
What is the difference between a program and a process? Can multiple processes be created from a single program?
A process is a program under execution, and a program is just program code defining variables and actions on variables
Yes
What is a client process?
The process that initiates contact and requests services from a server
What are three characterists of servers in the Client-Server Model?
Permanent network addresses
Fixed entry points for incoming requests
Always-on server processes
Do clients always have to be online? Can they change their IP addresses?
No
Yes
What is meant by pure clients? What must it mean if two clients communicate directly with each other?
Clients that do not communicate directly with each other
One of them has both client and server parts
Are there always-on server processes in peer-to-peer applications? Can peers change their IP address?
No, peers that communicate with each other can go online and offline as they wish
Yes, they can
What is one way of dealing with the fact that there are no fixed, reference IP addresses in P2P? (Three Steps
Repeatedly trying a list of candidate peers until getting a (TCP) connection to a remote peer
The new peer then sends a (ping) message to this remote peer, which is forwarded (flooded) to a number of other peers
In return, these peers reply with a (pong) message, allowing the new peer to make connections to them
What three things are needed to address any resource on the internet? What is used as an alternative to this combination due to its inconvenience?
IP address, port number, directory structure
Identifier Formats
What is the technical name for identifier formats? What is a specific type of URI? What does this type of URI do?
Uniform Resource Identifiers (URI)
Uniform Resource Locator (URL)
Points to the location of the resource and the way to reach it
What is a Uniform Resource Identifier (URI)?
A compact string of characters used for identifiying an abstract or physical resource
What are the four primary fields of URLs? How are these four arranged in an URL?
The application layer protocol being used (e.g., FTP or HTTP)
The host (computer where the resource is located)
The port (port number of destination process)
The path (path name of the file, i.e., the resource)
Protocol://Host:Port/Path
What are the four primary transport layer services used by application layer protocols?
Reliability Supports - Ensures that no data is lost in transit
Delay/Timing Support - ensures that the constraints of maximum delay (jitter) set by certain applications are not exceeded
Throughput Support - Aids in the number of bits transferred per second
Security Support - Provides security services
