Application Layer
Application Layer Protocols
The Application Layer provides the interface to the network
Presentation and Session Layers
three primary functions
Coding and conversion of application layer data
Compression of the data
Encryption of the data for transmission and the decryption of data upon receipt by the destination
Functions create and maintain dialogs between source and destination applications
Handles the exchange of information to initiate dialogs, keep them active, and to restart sessions
TCP/IP Application Layer Protocols
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Domain Name Service Protocol (DNS) - used to resolve Internet names to IP addresses
Telnet - a terminal emulation protocol used to provide remote access to servers and networking devices
Bootstrap Protocol (BOOTP) - a precursor to the DHCP protocol, a network protocol used to obtain IP address information during bootup
Dynamic Host Control Protocol (DHCP) - used to assign an IP address, subnet mask, default gateway and DNS server to a host
Hypertext Transfer Protocol (HTTP) - used to transfer files that make up the Web pages of the World Wide Web
Common P2P Applications
With P2P applications, each computer in the network running the application can act as a client or a server for the other computers in the network running the application
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Common P2P applications include:
eDonkey
eMule
Shareaza
BitTorrent
Bitcoin
LionShare
Some P2P applications are based on the Gnutella protocol which enables people to share files on their hard disks with others
Well-Known Application Layer Protocols and Services
Three application layer protocols that are involved in everyday work or play are:
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Hypertext Transfer Protocol (HTTP)
browse the web
Simple Mail Transfer Protocol (SMTP)
used to enable users to send email
Post Office Protocol (POP)
used to enable users to receive email