Network Layer : Types and Its Design Issues

In the scope of entire computer science, the approach of Network Layer assists to know about convoluted network interactions. There comes the exposure of many network layers, but the one well-known model is the OSI approach with 7 layers. OSI (Open System Interconnection) model outlines the clear picture of data transmission through standard protocols. But, what exactly these seven layers perform? In this networking framework, the lower layers (1-4) mostly work on data transmission and upper layers (5-7) addresses application-level data. Each layer is consigned with corresponding tasks and then passes the information onto the next layer.  In this article, we shall go with the concept of the network layer, functionalities, issues, protocols, and services.

What is Network Layer?

The network layer holds the responsibility of managing subnet performance. This layer is more focused to control the operations of data transmission, routing and switching technologies, packet forwarding and sequencing, error handling, addressing the creation of logical routes, and congestion control.

Types of Network Layers

The collaborative performance of all the seven layers in the OSI networking model makes it as the most widely implemented approach in all the applications.

OSI Approach
OSI approach

The below session describes the functionality of each layer:

 1). Application Layer

It maintains all the human and computer interactions and where the application can have accessibility for the network activities.  It means the application layer offers services for activities such as e-mail, network software, and file transmissions. In the OSI model, this layer has communication protocols and interfacing approaches utilized for process-to-process communication through an IP. This layer just standardizes the communication and based on the below transport layer to administer information exchange and establish host-to-data data transfer routes.

 2). Presentation Layer

Here information is maintained in a usable format and here happens the functionality of data encryption. The presentation layer operates to transmit the information in the model that the application layer accepts. In few cases, this layer is termed as a syntax layer. This layer makes sure that data delivered by the application layer in one system is decipherable by the application layer of the other system.


 3). Session Layer

Works on the functionality of connections and holds the responsibility for managing various sessions and ports. The session layer works to co-ordinate and end up conversations, discussions between applications and exchanges.

 4). Transport Layer

This layer performs the activity of data transmission through protocols consisting of UDP and TCP. It transfers information across hosts and end systems. Manages end-to-end error recovery and flow regulation. The transport layer delivers services like flow management, multiplexing, connection-oriented communication and even manage consistency. This layer holds the responsibility for information delivery to the exact application process through the host computers. It also has statistical multiplexing where this goes with data segmentation, the addition of source and destination port ID’s in the transport layer header.

 5). Network Layer

It decides the address of the physical path that information has to be transmitted. This layer is more focused to control the operations of data transmission, routing and switching technologies, packet forwarding and sequencing, error handling, addressing creation of logical routes, and congestion control.

 6). Data Link Layer

This layer works on the operation of encryption and decryption of data packets. It provides information regarding transmission protocol and controls errors that occur in the physical layer, flow regulation, and frame synchronization. This layer provides services like data packet framing, frame synchronization, physical addressing, store-and-forward switching, and many others.

 7). Physical Layer

Transmits raw kind of information through the physical medium. The physical layer provides the mechanical, procedural and electrical interface for the transmission medium. It even describes broadcasting frequencies, the property of electrical connectors, and other low-level factors.

Functions of Network Layer

Let’s be clear on the above terminologies that network layer performs:

  • Addressing – Maintains both the source and destination addresses at the frame header. The network layer performs addressing to find out the specific devices on the network.
  • Packetizing – The network layer works on the conversion of packets those received from its upper layer. This feature is accomplished by Internet Protocol (IP).
  • Routing – Being considered as the major functionality, the network layer chooses the best path for data transmission from a source point to the destination.
  • Internetworking – Internetworking works to deliver a logical connection across multiple devices.

Network Layer Design Issues

Network layer comes up with certain design issues and they can be described as below:

 1). Store-and-Forward Packet Switching

Here, the foremost elements are the carrier’s equipment (the connection between routers through transmission lines) and the customer’s equipment.

Store-and-Forward Packet Switching
store-and-forward packet switching
  • H1 has a direct connection with carrier router ‘A’, while H2 is connected to carrier router ‘F’ on a LAN connection.
  • One of the carrier router ‘F’, is pointed outside the carrier’s equipment as it does not come under the carrier, whereas considered as protocols, software, and construction.
  • This switching network performs as Transmission of data happens when the host (H1) with a packet transfers it to the nearby router through LAN (or) point-to-point connection to the carrier. The carrier stores the packet until it completely arrives thus confirms the checksum.
  • Then after, the packet is transmitted over the path until H2 is reached.

 2). Services Provided to the Transport Layer

Through the network/transport layer interface, the network layer delivers its services to the transport layer. One might come across the question of what type of services does the network layer provides?

So, we shall move with the same query and find out the services offered.

Services offered by the network layer are outlined considering few objectives. Those are:

  • Offering services must not depend on router technology
  • The transport layer needs to be protected from type, number and the topology of the available routers.
  • Network addressing the transport layer needs to follow a consistent numbering scenario also at LAN and WAN connections.

Note: Next comes the scenario of connection-Oriented or connectionless

Here, two groupings are possible based on the offered services.

Connectionless – Here, routing and insertion of packets into subnet is accomplished individually. No additional setup is necessary

Connection-Oriented – Subnet must offer reliable service and all the packets are transmitted over a single route.

 3). Implementation of Connectionless Service

In this scenario, packets are termed as datagrams and the corresponding subnet is termed as datagram subnet. Routing in datagram subnet is as follows:

Datagram Subnet
datagram subnet
Truth Table
truth table

When the message size that has to be transmitted is 4 times the size of the packet, then the network layer divides into 4 packets and then transmits each packet to router ‘A’ through a few protocols. Each router is provided with a routing table where it decides the destination points.
In the above figure, it is clear that packets from ‘A’ need to be transmitted either to B or C even when the destination is ‘F’. The routing table of ‘A’ is clearly outlined above.

Whereas in the case of packet 4, the packet from ‘A’ is routed to ‘B’, even the destination node is ‘F’. Packet ‘A’ chooses to transmit packet 4 through a different path than the initial three paths. This might happen because of traffic congestion along the path ACE. So, the

 4). Implementation of Connection-Oriented Service

Here, the functionality of connection-oriented service works on the virtual subnet. A virtual subnet performs the operation of avoiding a new path for each packet transmission. As a substitute for this, when there forms a connection, a route from a source node to a destination node is selected and maintained in tables. This route performs its action at the time of traffic congestion.

At the time when the connection is released, the virtual subnet also gets dismissed. In this service, every packet carries its own identifier that states the exact address of the virtual circuit. The below diagram shows the routing algorithm in the virtual subnet.

Implementation of Connection-Oriented Service
Implementation of Connection-Oriented Service

Network Layer Routing Protocols

Network routing protocols are of many types. All the protocols are described below:

 1). Routing Information Protocol

This protocol is mainly implemented in the LAN and WAN network. Here, it is classified as an interior gateway protocol internal to the utilization of a distance-vector algorithm.

 2). Interior Gateway Routing Protocol

This protocol is used for routing of information internal to the independent system. The main aim behind this protocol is to annihilate the limitations of RIP in the complicated networks. It even manages various metrics for every path along with consistency, bandwidth and delay load. The greatest hop is of 255 and routing updates are transmitted at the rate of 90 seconds.

 3). Open Shortest Path First

It is considered as the active routing protocol mostly utilized in internet protocols. Especially, it is the link-state routing protocol and moves into the classification of interior gateway protocol.

 4). Exterior Gateway Protocol

The best routing protocol chosen for internet activity is the exterior gateway protocol. It has a different scenario when compared with path and distance vector protocols. This protocol follows the topology like that of a tree.

 5). Enhanced Interior Gateway Routing Protocol

It is the distance-vector routing protocol in improvement in the optimization decreasing instability in routing that happens after topology modification, in addition to the usage of bandwidth and processing capability. In general, optimization is dependent on DUAL work from SRI that makes sure of the loop-free process and provides scope for a quick junction.

 6). Border Gateway Protocol

This protocol is responsible for the maintenance of a table of internet protocol networks that manage network approaching ability between AS. This is articulated in the form of a path vector protocol. Here, general IGP metrics are not implemented but goes with decisions depending on the path and network rules.

 7). Intermediate System-to-Intermediate System

This is mostly employed by network devices where it decides the best method for the transmission of a datagram and this scenario id termed as routing.

Network Layer Services

The network layer provides services that permit end devices for information exchange across the network. To achieve this, it makes use of four processes where those are of

  • Addressing end devices
  • Encapsulation
  • Routing
  • De-encapsulation

With all the routing protocols, types, services, and other frameworks, the network layer stands as a great support for the OSI model. The functionality of the network layer contains in every router. The most general protocols that are in relation to the network layer are Internet protocol and Netware IPX/SPX. As network layer been in implementation by many organizations, learn deeper insights on what are the approaches that network layer is associated with?