03. Network Layer of OSI Model (Layer3)

Network Layer is the 3rd layer in the 7Layer OSI Model after Data Link Layer. This is the place where most Routing and network stuff resides. It controls the Logical boundaries of Network. Most of the students confuse Layer2 & Layer3. There is a basic difference b/w Network Layer & Data Link Layer. Network Layer is concerned with data transfer from one computer to another computer even if it is on a remote network, while the data link layer only deals with devices that are local to each other & are within one network. PDU at Data Link Layer is called Packet. OSI Model divides the network communication processes into seven layers in order to simplify it.

Each layer performs specific functions to support the layers above it. The 7x Layer model starts from Physical till Application Layer & Network Layer the 3rd in this architecture as in below figure:

 

OSI Model Layers Waqas Karim

 

Functions/Duties of Network Layer

Each Layer in OSI Model Performs some important duties. Important functions performed by Network Layer are listed here:

  • It is responsible for Logical Addressing. It assigns a unique ID to each device on L3 Network which we call IP Address
  • Network Layer is also responsible for It processes the incoming packets, filters them & sends them to their desired destination
  • Encapsulation also falls under the responsibility matrix of Network Layer. It encapsulates Transport Layer segments into Layer3 Packets & forwards to Data Link Layer for further processing
  • It is also responsible for Fragmentation of packets to match the MTU size of L2 Frames
  • Error Control also falls under the responsibilities & functions of Network Layer. Is uses error control mechanisms to ensure reliable delivery of data. Due to these acknowledgement mechanisms, the receiver can detect how many Layer3 Packets have been corrupted during transmission. Receiver then requests the sender to send those Layer3 Packets again to ensure that no data is lost during transmission

 

Network Layer Protocols

The OSI Model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. Each layer on the OSI Model has some protocols associated with it. The most common protocol at Network Layer is of course the Internet Protocol which we know as IP.

Other important Protocols at Network Layer include:

OSI Model Network Layer Waqas Karim Pic2

 

Network Equipment/Components at Network Layer

Similar to protocols, each layer has associated equipment with it. Some important Equipment that operate at Physical Layer of OSI Model are listed in below:

OSI Model Network Layer Waqas Karim Pic1

 

Summary

  • It is the 3rd Layer in OSI 7 Layer Model
  • It performs important functions like Logical Addressing, Routing, Encapsulation, Fragmentation, Error Control, …
  • Important Protocols at Network Layer include IPv4, IPv6, RIP, OSPF, BGP, ICMP, EIGRP, IPSec, IPX, NAT, GRE, HSRP, VRRP, …
  • Equipment operating at Network Layer include Routers, L3 Switches, …
  • PDU is called Packet

 

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