Network layer of the OSI model

len Alfred Ajibola - 01st November, 2021 @ 09:40 AM

Topics in ICT

Functions of the network layer Network layer of the OSI model Transport layer and its characteristics Session layer of the OSI model: Functions of session layer What is presentation layer? Functions of presentation layer Application layer and its functions Three-way handshake in TCP Stateless connection in UDP explained with examples Transport Layer: Functions of layer 4 in networking Transport layer: Layer 4 of the OSI model


Academic Questions in ICT

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

  • A. Click on the three dots on the top right hand corner

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  • D. Click on the settings icon located on the to top-center of the app

  • E. Click directly on the storage and data icon located on the top right corner

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The followings are ways to conserve data on android phones except _____.

  • A. Turning on data saving mode

  • B. Activating background apps

  • C. Use of Wi-Fi to update apps

  • D. Disable automatic image download on WhatsApp

  • E. Watch low resolution videos on youtube

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Twitter was launched in _____.

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  • B. 2004

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Network Layer:

The network layer is also referred to as layer 3 of the Open Systems Interconnection (OSI) model. Alongside the transport layer which utilizes TCP, layer 3 forms the basis of the internet through its IP protocol. For this reason, the network is oftentimes classified as the TCP/IP network. In today's network, data are moved in the form of packets through the Internet Protocol (IP) of the network layer.

The protocol through which the network layer utilizes in packet delivery from source machine to a destination address is the Internet Protocol (IP). The IP encapsulate and transports other routing protocols in the form of packets.

IP are of two versions. These are:

  • IPv4 (Internet Protocol version 4)

  • IPv6 (Internet Protocol version 6)

Please read on the application layer of the OSI model here

Other important protocols present at the network layer include:

  • Border Gateway Protocol (BGP)

  • Open Shortest Path First (OSPF)

  • Enhanced Interior Gateway Routing Protocol(EIGRP)

  • Routing Information Protocol (RIP)

  • Internet Control Message Protocol (ICMP)

  • Internet Group Management Protocol (IGMP)

  • Internet Protocol Security (IPsec)

  • Protocol Independent Multicast (PIM)

  • Connectionless-mode Network Service (CLNS)

  • Datagram Delivery Protocol (DDP)

Previous layer 3 protocols include Apple-Talk, DECnet and IPX. All are obsolete.

You can read on the presentation layer of the OSI model here

 

For networking to take place, the end devices (nodes) alongside the intermediary devices (routers and layer 3 switches) must have an Internet Protocol address (or IP address). This address is a 32 bit or 4 bytes value separated by a dot (.) into each of 8 bits. An example of an IP address is '192.168.0.1'.

Please read on the session layer and its functions here

 

IP addresses are typically allocated, hierarchical and specific. To this end, large networks are divided into subnetworks which connects with other networks based on a geographical size. As an instance, the Wide Area Network (WAN) is a very large network formed from the interconnection of networks around the world. In fact, this is what the internet or internetwork entails.

Please read on the types of computer network here

 

For an internet to work, the underlying networks must use specialized hosts, called routers, gateways or layer 3 switches to forward or route packets between networks.

Routers and layer 3 switches are devices found in the network layer (layer 3) of the OSI model. For this reason, they are often referred to as layer 3 devices.

Please read on routers and their functions here.

Below is an image of a router:

Cisco RV325 Dual Giganet WAN VPN Router - Len Academy
Cisco RV325 Dual Giganet WAN VPN Router

 

The network layer is associated with the following features in internetworking:

  1. Routing and switching technologies are found here.

  2. Although the term 'packet' may be generally used as the data unit in different layers of the OSI model; however, it officially represents the protocol data unit at the network layer. Meanwhile, understand that routing and packet forwarding occurs in layer 3.

  3. Error handling, congestion control and packet sequencing work at the network layer.

  4. Virtual circuits are created across communicating hosts.

  5. A variety of routing protocols are present at this layer. Examples are BGP, OSPF, EIGRP and RIP.

You can read on the characteristics of the transport layer here

 

It is the function of layer 3 to encapsulate the segments from layer 4 into packets. Also, it issues service requests to the data link layer below.


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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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NOTABLE POINTS IN ICT

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)