Login
Login

Application layer

{{Use American English|date = March 2019}}

{{Short description|Highest layer of a networked communication model}}

{{Use mdy dates|date = March 2019}}

An application layer is an abstraction layer that specifies the shared communication protocols and interface methods used by hosts in a communications network.{{Cite web|url=https://osi-model.com/application-layer/|title=Application Layer {{!}} Layer 7|website=The OSI-Model|language=en|access-date=2019-11-05}} An application layer abstraction is specified in both the Internet Protocol Suite (TCP/IP) and the OSI model.{{Cite web|url=http://www.omnisecu.com/tcpip/tcpip-model.php|title=Four Layers of TCP/IP model, Comparison and Difference between TCP/IP and OSI models|website=www.omnisecu.com|access-date=2019-11-05}} Although both models use the same term for their respective highest-level layer, the detailed definitions and purposes are different.{{Cite web|url=https://searchnetworking.techtarget.com/answer/What-is-the-difference-between-TCP-IP-and-IP-protocol|title=What is the difference between TCP/IP and IP protocol?|website=SearchNetworking|language=en|access-date=2019-11-05}}

Internet protocol suite

{{IP stack}}

In the Internet protocol suite, the application layer contains the communications protocols and interface methods used in process-to-process communications across an Internet Protocol (IP) computer network.{{Cite web|url=https://searchnetworking.techtarget.com/answer/What-is-the-difference-between-TCP-IP-and-IP-protocol|title=What is the difference between TCP/IP and IP protocol?|website=SearchNetworking|language=en|access-date=2019-11-05}} 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.{{Cite web|url=https://www.lifewire.com/transmission-control-protocol-and-internet-protocol-816255|title=What Is Transmission Control Protocol/Internet Protocol (TCP/IP)?|last1=SEO|first1=Bradley Mitchell An MIT graduate who brings years of technical experience to articles on|last2=computers|website=Lifewire|language=en|access-date=2019-11-05|last3=Networking|first3=Wireless}} Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in {{IETF RFC|1123}}) does rely on and recommend the robustness principle for application design.{{cite web

| title = RFC 1123: Requirements for Internet Hosts – Application and Support

| url = http://tools.ietf.org/html/rfc1123

| publisher = Network Working Group of the IETF

| editor = Robert Braden

| date = October 1989

}}{{Cite web|url=https://www.techopedia.com/definition/6006/application-layer|title=What is the Application Layer?|website=www.tutorialspoint.com|access-date=2019-11-05}}

OSI model

{{OSI model}}

In the OSI model, the definition of the application layer is narrower in scope.{{Cite web|url=https://www.networkworld.com/article/3239677/the-osi-model-explained-how-to-understand-and-remember-the-7-layer-network-model.html|title=The OSI model explained: How to understand (and remember) the 7 layer network model|last=Shaw|first=Keith|date=2018-10-22|website=Network World|language=en|access-date=2019-11-05}} The OSI model defines the application layer as only the interface responsible for communicating with host-based and user-facing applications.{{Cite web|url=https://www.cloudflare.com/learning/ddos/glossary/open-systems-interconnection-model-osi/|title=What Is The OSI Model?|date=2019|website=CloudFlare|access-date=November 4, 2019}} OSI then explicitly distinguishes the functionality of two additional layers, the session layer and presentation layer, as separate levels below the application layer and above the transport layer. OSI specifies a strict modular separation of functionality at these layers and provides protocol implementations for each. In contrast, the Internet Protocol Suite compiles these functions into a single layer.

=Sublayers=

Originally the OSI model consisted of two kinds of application layer services with their related protocols.{{Cite web|url=https://networkencyclopedia.com/application-layer/|title = Application Layer (Layer 7 of the OSI Model)|date = September 2, 2019}} These two sublayers are the common application service element (CASE) and specific application service element (SASE).{{cite book | last = Hura | first = Gurdeep | title = Data and Computer Communications: Networking and Internetworking | publisher = CRC Press LLC | year = 2001 |chapter= Application Layer |pages = [https://archive.org/details/datacomputercomm0000hura/page/710 710]–712 | isbn = 9780849309281 | url = https://archive.org/details/datacomputercomm0000hura | url-access = registration }} Generally, an application layer protocol is realized by using the functionality of several application service elements.{{Cite report|url=https://tools.ietf.org/rfc/rfc1095|title = Common Management Information Services and Protocol over TCP/IP (CMOT)|date = April 1989| doi=10.17487/RFC1095 | last1=Warrier | first1=U.S. | last2=Besaw | first2=L. | url-access=subscription }} Some application service elements invoke different procedures based on the version of the session service available.{{Cite web|url=https://tools.ietf.org/html/rfc1085|title = ISO presentation services on top of TCP/IP based internets|date = December 1988|last1 = Rose|first1 = Marshall T.}}

==CASE==

The common application service element sublayer provides services for the application layer and request services from the session layer.

It provides support for common application services, such as:

==SASE==

The specific application service element sublayer provides application-specific services (protocols), such as:

  • FTAM (File Transfer, Access and Manager)
  • VT (Virtual Terminal)
  • MOTIS (Message Oriented Text Interchange Standard)
  • CMIP (Common Management Information Protocol)
  • JTM (Job Transfer and Manipulation)[http://www.furniss.co.uk/jtm/index.html a former OSI standard]{{dl|fix-attempted=yes|date=July 2023}}
  • MMS (Manufacturing Messaging Specification)
  • RDA (Remote Database Access)
  • DTP (Distributed Transaction Processing)

Protocols

The IETF definition document for the application layer in the Internet Protocol Suite is RFC 1123. It provided an initial set of protocols that covered the major aspects of the functionality of the early Internet:

=Examples=

Additional notable application-layer protocols include the following:

{{div col|colwidth=20em}}

{{div col end}}

References

{{Reflist}}

External links

  • {{Commons category-inline|Application layer protocols}}
  • {{Wikiversity-inline|Application layer}}

Category:OSI model