Application layer

The Internet protocol suite (TCP/IP) and the Open Systems Interconnection model (OSI model) of computer networking each specify a group of protocols and methods identified by the name application layer.

In TCP/IP, the application layer contains all protocols and methods that fall into the realm of process-to-process communications across an Internet Protocol (IP) network. Application layer methods 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, explicitly distinguishing additional 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.

Internet protocol suite
Application layer
BGP DHCP DHCPv6 DNS FTP HTTP IMAP IRC LDAP MGCP NNTP NTP POP RIP RPC RTP RTSP SIP SMTP SNMP SOCKS SSH Telnet TLS/SSL XMPP (more)
Transport layer
TCP UDP DCCP SCTP RSVP ECN (more)
Internet layer
IP IPv4 IPv6 ICMP ICMPv6 IGMP IPsec (more)
Link layer
ARP/InARP NDP OSPF Tunnels L2TP PPP Media access control Ethernet DSL ISDN FDDI (more)

The OSI model
7	Application layer
6	Presentation layer
5	Session layer
4	Transport layer
3	Network layer
2	Data link layer LLC sublayer MAC sublayer
1	Physical layer

TCP/IP protocols

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

• 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
• 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)
• 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
• 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
• SOCKS, the SOCKS internet 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
• 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

External links

• How The Application Layer Works (refers to the Internet Protocol Suite)