Application layer

In computer network programming, the application layer is an abstraction layer reserved for communications protocols and methods designed for process-to-process communications across an Internet Protocol (IP) computer network. Application layer protocols use the underlying transport layer protocols to establish host-to-host connections.

In the OSI model, the definition of its application layer is narrower in scope. The OSI model defines the application layer as being the user interface. The OSI application layer is responsible for displaying data and images to the user in a human-recognizable format and to interface with the presentation layer below it.^[1]

It separates functionality above the transport layer at two additional levels, the session layer and the presentation layer. OSI specifies strict modular separation of functionality at these layers and provides protocol implementations for each layer.

TCP/IP protocols

The following protocols are explicitly mentioned in RFC 1123 (1989), describing the application layer of the Internet protocol suite.^[2]

• Remote login category
  • Telnet
• File transfer category
  • FTP
  • TFTP
• Electronic mail category
  • SMTP
  • IMAP
  • POP
• Support services category
  • DNS
  • RARP
  • BOOTP
  • SNMP
  • CMOT

Other 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
• CFDP, Coherent File Distribution Protocol
• CoAP, Constrained Application Protocol
• DDS, Data Distribution Service
• DeviceNet
• eDonkey
• ENRP, Endpoint Handlespace Redundancy Protocol
• FastTrack (KaZaa, Grokster, iMesh)
• Finger, User Information Protocol
• Freenet
• FTAM, File Transfer Access and Management
• Gopher, Gopher protocol
• HL7, Health Level Seven
• HTTP, HyperText Transfer Protocol
• H.323, Packet-Based Multimedia Communications System
• IRCP, Internet Relay Chat Protocol
• Kademlia
• KAP, Anonymous File Transfer over UDP/IP (KickAss Protocol)^{[citation needed]}
• 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
• RDP, Remote Desktop Protocol
• RELP, Reliable Event Logging Protocol
• RIP, Routing Information 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
• SNTP, Simple Network Time Protocol
• SSH, Secure Shell
• SSMS, Secure SMS Messaging Protocol
• TCAP, Transaction Capabilities Application Part
• TDS, Tabular Data Stream
• TSP, Time Stamp Protocol
• VTP, Virtual Terminal 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

References

External links