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Design Issues of Network Layer
Network Layer in OSI Model and design issues of network layer are covered in this tutorial. This tutorial will be helpful in understanding the concepts of different protocols of the network layer, network layer functions, OSI model of networking.
This network layer of OSI tutorial is prepared for computer science students and also for those students who are preparing for the GATE(CS/IT) or UGC NET ( CS) exam.
Students are requested to read the Design Issues of Network Layer related tutorial till the end and ask their query in the comment section
Frequently Asked Questions
Apart from the design issues of network layer this tutorial also will be helpful for a computer science graduate to get the answer to the following questions
- What is Network Layer in the OSI Model?
- Which Networking Functions Occur at the Network Layer of OSI Model?
- What is the TCP/IP Model in Computer Networks?
- What is Packet?
- What are different protocols used at the network layer?
- What is Address Resolution Protocol?
- What is Reverse Address Resolution Protocol?
- What is ICMP?
- What is IGMP?
- What is Datagram?
- What is Routing in Computer Networks?
- What do you understand by Congestion Control at Network Layer?
- What is the IP Address and IP Addressing?
- What is Network Id and Host ID?
Design Issues of Network Layer
Following design issues are considered related to the network layer in OSI model. These issues can also be considered as network layer functions.
A key network layer design issue is to determine how packets are routed from source to destination.
These Routes can be based on static tables that are made into the network and rarely changed.
Routes also may be dynamic; when a new packet arrived, then as per the network load route may be changed to reflect the current network load.
There may be a situation when too many packets are present in the subnet at the same time.
This is known as congestion in the network. To control such congestion is also a network layer design issue.
However, to ensure the quality of service provided( such as delay, transmit time, jitter, etc.) is also a network layer design issue.
Moreover, When a packet has to move from the source network to another to get to its destination, many problems can arise, such as
- The addressing used by the destination network may be different from the source network.
- The destination network may not accept the packet at all because it is too large.
- The protocols may differ, and so on.
Network Layer of OSI or TCP/IP model
The network layer of the TCP/IP model in a computer network is responsible for taking the packets from the source node or host and deliver them to the destination node.
The PDU or protocol data unit at the network layer is known as a packet or data packet.
The packet goes through several intermediate nodes and network router during its transmission from source to destination.
The correct delivery of an entire message or data packet at the destination side is verified at the Transport layer by TCP protocol.
Network Layer Protocols
The network layer in OSI the model suite supports the Internetworking Protocol, which provides the fundamental packet delivery to all TCP/IP networks.
Various Network Layer Protocols are ARP, RARP, ICMP and IGMP are network-layer protocols to achieve functioning.
Let’s Understand these network layer protocols one by one.
Address Resolution Protocol (ARP)
ARP is known as address resolution protocol which is used to find out the physical address corresponding to an IP address.
It is required because the final delivery of the data packet is at the Physical Address of the host.
Reverse Address Resolution Protocol (RARP)
Reverse address resolution protocol is used to find the IP address for a physical address it requires when we first time connect a computer to a network.
Internet Control Message Protocol ( ICMP)
ICMP is known as Internet Control Message Protocol, and this protocol is used by a node or gateway to send the notification related to datagram problems back to the sender. ICMP sends query and error reporting messages.
Internet Group Management Protocol ( IGMP)
Internet group management Protocol is used by the host and adjacent routers on the network to making the multicast group membership.
After study of these network layer protocols we will learn about network layer functions and services in the next section.
Network Layer Functions and Services
The primary network layer functions and network layer services are as follows –
(1) Define the Datagram: Datagram is the basic unit of transmission on the internet. Internet Protocol transports data in the packet called datagram, and each of the datagrams is transported separately.
A datagram can travel along different routes and can be arrived out of order at the destination host and may be duplicated.
(2)Routing: Routing in computer networks is a process of moving data across the network from source to destination. During this movement, at least one intermediate node is encountered.
The routing process basically consists of two tasks.
First, it decides the path for data transfer and, after that, send the packet on the decided path. At router routing algorithm decides which output line or path is used to transfer the packet.
This is also important to keep in mind that routers and gateway operate at the network layer. The network layer implements a mechanism that routes the packets to the destination.
(3)Congestion Control: At Network Layer, Congestion may occur at the router when data packet arriving at the router are coming at more data rate as compared to the data rate used for routing the data packet from the router.
Congestion may be caused by many factors. When data packets reach the router, these data packets are put into a queue in the order in which these arrived.
In this situation, a condition may arise when for all incoming packets, the same path is selected for transmission.
This situation cause congestion at the router. There may be another reason for congestion, such as low bandwidth and the limited amount of memory.
(4) IP Addressing: IP Addressing or logical addressing is the main function of network layer in computer networks. The IP address is also known as a logical address, which is assigned to each host present in a network.
In an IP addressing scheme, two devices can not have the same IP address.
In a private network, an IP address can be managed easily. In order to maintain the uniqueness of the IP address is registered to the Internet Network Information Center.
When a particular organization apply for registration, then the corresponding authority provides a network address to the applicant organization. Which then make the network for its use and assign the IP address to each host in that network.
Now let us discuss what the IP Address is. Actually, an IP address is a 32 bits number ( as per IPV4), and This 32 bits number is divided into two parts.
(1) Network Address or Network ID.
(2) The Host Address or Host ID.
The first part of the IP address provides the information about the network address on which the host resides, and the second part is the host id which is used to identify a particular host on the given network.
The network layer also handles the error control and packet sequence control and also establishes a connection. If the size of the data packet is enormous, then the network layer breaks the data packets into smaller data packets.
Problems Handled by Network Layer
When a packet travels from one network to a destination network, then it may be possible that the destination network may have a different addressing scheme as compare to the source network.
Sometimes it may be possible that the destination network may not accept all the data packet coming from the source network, and protocols used by the source networks and destination networks may be different.
The network layer handles all the problems and provides communication between these source and destination networks having different characteristics. Such types of networks are known as heterogeneous networks.
Critical Key Points about Network Layer
Some important key points about the Network Layer of the OSI model are as follow –
- Translates logical network address and names to their physical Address; it means device name to Physical Address.
- The Network Layer of the OSI Model is responsible for the following –
(i) Addressing
(ii) Determining route for the sending
(iii) Managing Network problems such as packet switching, data congestion and routing.
- Breaks the data into smaller units and assembles data.
- Shield higher layers from details of how the data gets to its destination.
Conclusion and Summary
Design issues of network layer are discussed in this tutorial. Various network layer protocols and their function are also explained.
I hope this tutorial will be helpful for students in understanding the network layer concepts and related design issues.
