Editing Session layer (section)

{{Use American English|date = March 2019}}
{{Short description|Layer in standard computer networking model}}
{{Use mdy dates|date = March 2019}}
{{Redirect|Layer 5|the political layer sometimes included in the [[OSI model]]|Layer 8}}
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In the seven-layer [[OSI model]] of [[computer network]]ing, the '''session layer''' is '''layer 5'''.

The session layer provides the mechanism for opening, closing and managing a [[Session (computer science)|session]] between end-user application processes, i.e., a semi-permanent dialogue. Communication sessions consist of requests and responses that occur between applications. Session-layer services are commonly used in application environments that make use of [[remote procedure call]]s (RPCs).<ref>{{Cite web |title=What Is Remote Procedure Call (RPC)? Definition from SearchAppArchitecture |url=https://www.techtarget.com/searchapparchitecture/definition/Remote-Procedure-Call-RPC |access-date=2022-08-04 |website=SearchAppArchitecture |language=en}}</ref>

An example of a session-layer protocol is the [[OSI protocol suite]] session-layer protocol, also known as X.225 or ISO 8327. In case of a connection loss this protocol may try to recover the connection. If a connection is not used for a long period, the session-layer protocol may close it and re-open it. It provides for either [[duplex (telecommunications)|full duplex]] or [[duplex (telecommunications)|half-duplex]] operation and provides [[synchronization point]]s in the stream of exchanged messages.<ref>[http://www.itu.int/rec/T-REC-X.225/en/ ITU-T Recommendation X.225]</ref>

Other examples of session layer implementations include [[Zone Information Protocol]] (ZIP) – the [[AppleTalk]]<ref>{{Cite web |title=ZIP |url=https://developer.apple.com/library/archive/documentation/mac/pdf/Networking/ZIP.pdf |website=Apple.developer.com}}</ref> protocol that coordinates the name binding process, and Session Control Protocol (SCP)<ref>{{Cite web |title=Session Control Protocol (SCP) |url=https://www.w3.org/Protocols/HTTP-NG/http-ng-scp.html |access-date=2022-08-04 |website=www.w3.org}}</ref> – the [[DECnet]] Phase IV session-layer protocol.

Within the service layering semantics of the OSI network architecture, the session layer responds to service requests from the [[presentation layer]] and issues service requests to the [[transport layer]].