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  Layer 7 Application Layer


Top Level APIs; Application Networking

Services, applications and network management. The application layer provides functions for applications. This layer provides the connection to the lower layers. At this level, the data input and output takes place. The applications themselves are not in the layer.

Typical Applications: web browser, email client, ...

OSI Layer 7 - Application Layer

An application layer is an abstraction layer that specifies the shared protocols and interface methods used by hosts in a communications network. The application layer abstraction is used in both of the standard models of computer networking; the Internet Protocol Suite (TCP/IP) and the Open Systems Interconnection model (OSI model).

Although both models use the same term for their respective highest level layer, the detailed definitions and purposes are different.

In TCP/IP, the application layer contains the communications protocols and interface methods used in process-to-process communications across an Internet Protocol (IP) computer network. The application layer only standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client-server or peer-to-peer networking model. Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in RFC 1123) does rely on and recommend the robustness principle for application design.

In the OSI model, the definition of the application layer is narrower in scope. The OSI model defines the application layer as the user interface responsible for displaying received information to the user. In contrast, the Internet Protocol model does not concern itself with such detail. OSI also explicitly distinguishes additional functionality below the application layer, but above the transport layer at two additional levels; the session layer and the presentation layer. OSI specifies a strict modular separation of functionality at these layers and provides protocol implementations for each layer.


Popular Application Layer Protocols

9PPlan 9 from Bell Labs distributed file system protocol
AFPApple Filing Protocol
APPCAdvanced Program-to-Program Communication
AMQPAdvanced Message Queuing Protocol
AtomPublishing Protocol
BEEPBlock Extensible Exchange Protocol
BitcoinDigital currency
BitTorrentpeer-to-peer file sharing
CFDPCoherent File Distribution Protocol
CoAPConstrained Application Protocol
DDSData Distribution Service
DeviceNetautomation industry protocol
eDonkeyclassic file sharing protocol
ENRPEndpoint Handlespace Redundancy Protocol
FastTrackfilesharing, known from KaZaa and more
FingerUser Information Protocol
Freenetcensorship resistant p2p network
FTAMFile Transfer Access and Management
GopherGopher protocol
HL7Health Level Seven
HTTPHyperText Transfer Protocol
H.323Packet-Based Multimedia Communications System
IRCPInternet Relay Chat Protocol
Kademliap2p hashtables
LDAPLightweight Directory Access Protocol
LPDLine Printer Daemon Protocol
MIME (S-MIME)Multipurpose Internet Mail Extensions and Secure MIME
ModbusSerial communications protocol
MQTT ProtocolMQ Telemetry Transport
NetconfNetwork Configuration Protocol
NFSNetwork File System
NISNetwork Information Service
NNTPNetwork News Transfer Protocol
NTCIPNational Transportation Communications for Intelligent Transportation System Protocol
NTPNetwork Time Protocol
OSCARAOL Instant Messenger Protocol
PNRPPeer Name Resolution Protocol
RDPRemote Desktop Protocol
RELPReliable Event Logging Protocol
RIPRouting Information Protocol
RloginRemote Login in UNIX Systems
RPCRemote Procedure Call
RTMPReal Time Messaging Protocol
RTPReal-time Transport Protocol
RTPSReal Time Publish Subscribe
RTSPReal Time Streaming Protocol
SAPSession Announcement Protocol
SDPSession Description Protocol
SIPSession Initiation Protocol
SLPService Location Protocol
SMBServer Message Block
SMTPSimple Mail Transfer Protocol
SNTPSimple Network Time Protocol
SSHSecure Shell
SSMSSecure SMS Messaging Protocol
TCAPTransaction Capabilities Application Part
TDSTabular Data Stream
Toranonymity network
TSPTime Stamp Protocol
VTPVirtual Terminal Protocol
Whois (and RWhois)Remote Directory Access Protocol
WebDAVWeb Distributed Authoring and Versioning
X.400Message Handling Service Protocol
X.500Directory Access Protocol (DAP)
XMPPExtensible Messaging and Presence Protocol