Session layer of the OSI model: Functions of session layer

len Alfred Ajibola - 30th October, 2021 @ 10:51 AM

Topics in ICT

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What is the first step towards disabling automatic image download on WhatsApp?

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Twitter was launched in _____.

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Session Layer:

The session layer (or layer 5 of the OSI model) is responsible for starting, synchronizing, managing and terminating network connections between end-user applications. In general, layer 5 handles and manipulates data which it receives from the presentation layer above and transport layer below.

Please read on application layer and its functions here.


Protocols found on layer 5 include the followings:

  • Remote Procedure Call (RPC): RPC is a session layer protocol utilized for requesting services among computers within or outside a network. RPC protocol ensures that the devices are able to communicate over the network without prior information about the network.

  • Point-to-Point Tunneling Protocol (PPTP): It establishes Virtual Private Network (VPN) tunnels between a computer device and a public network like the internet.

  • AppleTalk Session Protocol (ASP): The ASP create sessions between multiple ASP workstation applications with a server at once.

  • Session Control Protocol (SCP): It enables lightweight connections from a single TCP connection. In addition, these connections can be activated simultaneously.

  • Internet Storage Name Service (iSNS): iSNS automates the discovery and management of iSCSI enabled devices over a TCP/IP storage network. In this regard, it stores vital information, for instance, the IP addresses of the devices, the names of Internet Small Computer Systems Interface (iSCSI) devices, their portal groups and so on.

  • Session Description Protocol (SDP): The SDP defines all parameters for transferring multimedia files between two end devices.

  • AppleTalk Data Stream Protocol (ADSP): It transfers full-duplex streams of data over the AppleTalk internetwork. It is a stateful (connection oriented) protocol.

You can read on the transport layer of OSI model here.

Other protocols found at the session layer include:

  • Network File System (NFS)

  • Structured query Language (SQL)

  • NetBios Names

  • Call Control Protocol for Multimedia Communication

  • Password Authentication Protocol (PAP)

  • OSI session-layer protocol (X.225, ISO 8327)

  • Layer 2 Tunneling Protocol

  • Layer 2 Forwarding Protocol

Session Layer - Len Academy
Session layer of the OSI model


In simple terms, layer 5 controls the dialogue connections between computers. It is responsible for full-duplex, half-duplex or simplex communication. Also, graceful close of sessions occurs at this layer. You can think of 'graceful close' as a connection termination after the software function and the operating system (OS) is allowed to perform its tasks of safely shutting down processes of closing connections. It is a perfect way of ending a communication session between two devices.

Note: The session layer is implemented in application environments that use remote procedure calls.


It is important to state that the functions of layers 5, 6 and 7 are expected to be handled by the computer programmer while the responsibility of layers 1 through 4 lies in the operations of the networking engineers.

You can read on computer hardware here.


Functions of session layer

  1. The session layer creates and track dialogs between systems, thus creating a session between the communicating devices.

  2. The session layer creates single or multiple connections so that end-users can simultaneously communicate with the application in use.

  3. Sessions on web browsers are implemented through this layer. Protocols such as AppleTalk protocol and Session Control Protocol (SCP) are utilized here.

  4. It facilitates audio and video streams merger from two different sources, merging both without any form of overlapping.

  5. Session recovery and restoration during a lost communication can be achieved through Zone Information Protocol (ZIP) of the session layer.

  6. The session layer enables token management by protecting two lines from undergoing critical operations simultaneously.

  7. Session layer can identify errors in network communication. As a result, it can prevent the sudden loss of data.

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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.

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Computer hardware is the collection of physical parts of a computer system.

Physical parts of a computer are those parts that you can see and touch. It may also be referred to as the 'equipment of the computer'.

When the computer case is opened (with a screwdriver), one would see the different hardware components inside of it. It's important to state that some other hardware components are present outside the computer case; and these are termed peripherals.

Below are hardware components seen inside the computer case:

  • Motherboard

  • Central Processing Unit (CPU)

  • Graphics Processing Unit (GPU)

  • Power supply Unit (PSU)

  • Northbridge

  • Southbridge

  • Peripheral Component Interconnect (PCI) slots

  • Network Interface Card (NIC)

  • Random Access Memory (RAM)

  • Ventilation fans

  • Heat sink

  • Hard Disc Drive (external present)
  • Solid State Drive (SSD)

  • CMOS battery

  • Optical Disc Drives (external present)

  • USB port, PS2 port, Ethernet port and other ports

  • Expansion Ports / Slots

Please read more on computer hardware here

Hardware components seen outside the computer case are called peripherals. The peripherals are grouped into the following:

  1. Input devices: They provide information to the computer.

  2. Output devices: Brings out information from the computer.

  3. Storage devices: They store information or data.

Below are examples of some peripherals:

  • Keyboard (input)

  • Monitor (output)

  • Mouse (input)

  • Webcam (input)

  • Touch Pad (input)

  • Universal Serial Bus (USB) flash drive or memory card (storage)

  • Hard disc drive (storage)

  • Stylus (input)

  • Joystick(input)

  • Printer (output)

  • Speaker (output)

  • Headphones (output)