Editing Application layer (section)

==OSI model==
{{OSI model}}
In the [[OSI model]], the definition of the application layer is narrower in scope.<ref>{{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}}</ref> The OSI model defines the application layer as only the interface responsible for communicating with host-based and user-facing applications.<ref name=":0">{{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}}</ref> 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 [[OSI protocols|protocol implementations]] for each. In contrast, the Internet Protocol Suite compiles these functions into a single layer.<ref name=":0" /> 

===Sublayers===
Originally the OSI model consisted of two kinds of application layer services with their related protocols.<ref>{{Cite web|url=https://networkencyclopedia.com/application-layer/|title = Application Layer (Layer 7 of the OSI Model)|date = September 2, 2019}}</ref> These two sublayers are the common application service element (CASE) and specific application service element (SASE).<ref name="Hura">{{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 }}</ref><!-- this belongs in application layer?? --> Generally, an application layer protocol is realized by using the functionality of several application service elements.<ref>{{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. }}</ref> Some application service elements invoke different procedures based on the version of the session service available.<ref>{{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.}}</ref>

====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:
* ACSE ([[Association Control Service Element]])<ref name="Hura"/>
* ROSE (Remote Operation Service Element)
* CCR (Commitment Concurrency and Recovery)
* RTSE (Reliable Transfer Service Element)

====SASE====
The specific application service element sublayer provides application-specific services (protocols), such as:
* [[FTAM]] (File Transfer, Access and Manager)
* [[Virtual terminal|VT]] (Virtual Terminal)
* MOTIS (Message Oriented Text Interchange Standard)
* CMIP (Common Management Information Protocol)
* JTM (Job Transfer and Manipulation)<ref>[http://www.furniss.co.uk/jtm/index.html a former OSI standard]{{dl|fix-attempted=yes|date=July 2023}}</ref>
* [[Manufacturing Message Specification|MMS]] (Manufacturing Messaging Specification)
* RDA (Remote Database Access)
* DTP (Distributed Transaction Processing)