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Layer 5

Definition - What does Layer 5 mean?

Layer 5 refers to the fifth layer of the Open Systems Interconnect (OSI) Model, and is known as the session layer.

As the name suggests, this layer is dedicated to connection sessions and is the layer that establishes and manages the connections between two or more applications. Layer 5 coordinates, sets up and subsequently terminates communications between applications. The session layer is in charge of dealing with session connection and coordination.

Techopedia explains Layer 5

Layer 5, or the session layer, is the network mechanism for opening, closing and generally managing communication sessions between end-user applications and their processes. Sessions consist of requests and responses between communication applications or processes. It is also responsible for session checkpointing and recovery, and it allows information coming from different streams, from different origins to be synchronized and combined. A good example of this is in a video call or web conference where the video and audio must be synchronized to avoid lip-syncing problems.

A good example of a session layer protocol is the X.225 or ISO 8327 where in case connection is lost, the protocol tries to recover the connection. If a connection has not been used for a long period, the protocol may choose to close and then reopen it.

Some examples of protocols used in layer 5 include:

  • AppleTalk Session Protocol (ASP)
  • AppleTalk Data Stream Protocol (ADSP)
  • OSI Session Layer Protocol (X.225, ISO 8327)
  • Network Basic Input/Output System (NetBIOS)
  • Password Authentication Protocol (PAP)
  • Remote Procedure Call Protocol (RPC)
  • Point-to-Point Tunneling Protocol (PPTP)
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