- application layers provide a user interface
- function of application layer of the OSI model is file, print, message, database, and application services.
The application layer of the OSI model marks the spot where users actually communicate to the computer. This layer only comes into play when it's apparent that acces to the network is going to be needed soon.
Layer 7 provides an interface between a host’s communication software and any necessary external applications (such as email, file transfers, and terminal emulation). This layer can also evaluate what resources are necessary to communicate between two devices and determine their availability.
Application Protocols Supported by the Application Layer:
- Telnet : a TCP/IP protocol that provides terminal emulation to a remote hostby creating a virtual terminal. Secure CRT is one program that can be installed on a user computer to create telnet sessions. This protocol requires authentication via a username and password
- Hypertext Transfer Protocol (HTTP) : Enables web browsing with the transmission of Hypertext Markup Language (HTML) documents on the Internet.
- Secure Hypertext Transfer Protocol (HTTPS) : Enables secure web browsing. A secure connection is indicated when the URL begins with https:// or when there is a lock symbol at the lower-right corner of the web page that is being viewed.
- File Transfer Protocol (FTP) : Enables a user to transfer files. Provides access to files and direc- tories. Securely implemented with telnet, which allows remote authentication to an FTP server.
- Trivial File Transfer Protocol (TFTP) : A bare-bones version of FTP that does not provide access to directories. With TFTP you can just send and receive files. Unlike FTP, TFTPs not secure and sends smaller blocks of data.
- Domain Name System (DNS) : Resolves hostnames such as www.cisco.com into IP addresses.
- Simple Mail Transfer Protocol (SMTP) : Sends electronic mail across the network.
- Post Office Protocol 3 (POP3) : Receives electronic mail by accessing an Internet server.
- Network File System (NFS) : Enables users with different operating systems (for example, NT and Unix workstations) to share files.
- Network News Transfer Protocol (NNTP) : Offers access to Usenet newsgroup postings.
- Simple Network Management Protocol (SNMP) : Monitors the network and manages configurations. Collects statistics to analyze network performance and ensure network security.
- Network Time Protocol (NTP) : Synchronizes clocks on the Internet to provide accurate local time on the user system.
- Dynamic Host Configuration Protocol (DHCP) : Works dynamically to provide an IP address, subnet mask, domain name, and a default gateway for routers. Works with DNS and WINS (used for NetBIOS addressing).
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