Layer 7: Application Layer

Application Layer is a term used in categorizing protocols and methods in architectural models of computer networking. Both the OSI model and the Internet Protocol Suite (TCP/IP) define application layers.

In TCP/IP, the Application Layer contains all protocols and methods that fall into the realm of process-to-process communications via an Internet Protocol (IP) network using the Transport Layer protocols to establish underlying host-to-host connections.

In the OSI model, the definition of its Application Layer is not narrower in scope, distinguishing explicitly additional functionality above the Transport Layer at two additional levels: Session Layer and Presentation Layer. OSI specifies strict modular separation of functionality at these layers and provides protocol implementations for each layer.

The common application layer services provide semantic conversion between associated application processes. Note: Examples of common application services of general interest include the virtual file, virtual terminal, and job transfer and manipulation protocols.


Protocol examples
* 9P, Plan 9 from Bell Labs distributed file system protocol
* AFP,
* APPC, Advanced Program-to-Program Communication
* AMQP, Advanced Message Queuing Protocol
* BitTorrent
* Atom Publishing Protocol
* BOOTP, Bootstrap Protocol
* CFDP, Coherent File Distribution Protocol
* DDS, Data Distribution Service
* DHCP, Dynamic Host Configuration Protocol
* DeviceNet
* DNS, Domain Name System (Service) Protocol
* eDonkey
* ENRP, Endpoint Handlespace Redundancy Protocol
* FastTrack (KaZaa, Grokster, iMesh)
* Finger, User Information Protocol
* Freenet
* FTAM, File Transfer Access and Management
* FTP, File Transfer Protocol
* Gopher, Gopher protocol
* HL7, Health Level Seven
* HTTP, HyperText Transfer Protocol
* H.323, Packet-Based Multimedia Communications System
* IMAP, IMAP4, Internet Message Access Protocol (version 4)
* IRCP, Internet Relay Chat Protocol
* Kademlia
* LDAP, Lightweight Directory Access Protocol
* LPD, Line Printer Daemon Protocol
* MIME (S-MIME), Multipurpose Internet Mail Extensions and Secure MIME
* Modbus
* Netconf
* NFS, Network File System
* NIS, Network Information Service
* NNTP, Network News Transfer Protocol
* NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
* NTP, Network Time Protocol
* OSCAR, AOL Instant Messenger Protocol
* PNRP, Peer Name Resolution Protocol
* POP, POP3, Post Office Protocol (version 3)
* RDP, Remote Desktop Protocol
* Rlogin, Remote Login in UNIX Systems
* RPC, Remote Procedure Call
* RTMP Real Time Messaging Protocol
* RTP, Real-time Transport Protocol
* RTPS, Real Time Publish Subscribe
* RTSP, Real Time Streaming Protocol
* SAP, Session Announcement Protocol
* SDP, Session Description Protocol
* SIP, Session Initiation Protocol
* SLP, Service Location Protocol
* SMB, Server Message Block
* SMTP, Simple Mail Transfer Protocol
* SNMP, Simple Network Management Protocol
* SNTP, Simple Network Time Protocol
* SPTP, Secure Parallel Transfer Protocol
* SSH, Secure Shell
* SSMS, Secure SMS Messaging Protocol
* TCAP, Transaction Capabilities Application Part
* TDS, Tabular Data Stream
* TELNET, Terminal Emulation Protocol of TCP/IP
* TFTP, Trivial File Transfer Protocol
* TSP, Time Stamp Protocol
* VTP, Virtual Terminal Protocol
* Waka, an HTTP replacement protocol
* Whois (and RWhois), Remote Directory Access Protocol
* WebDAV
* X.400, Message Handling Service Protocol
* X.500, Directory Access Protocol (DAP)
* XMPP, Extensible Messaging and Presence Protocol