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In networking, when we send data, then it is broken down into small pieces or chunks. Each piece is referred to as a packet or network packet.
So, when you request any web page or send an email, data is broken down into a series of packets, sent or received as a series of packets. The series of packets received at the other end is recombined to their original form.
The whole process takes place in an integrated and connectionless network known as a packet-switched network.
We will look after how the whole process of packets traveling from source to destination takes place, what a packet consists of, and how it works.
What is a Network Packet?
A network packet or IP packet is a small amount of data sent from source to destination over TCP/IP protocol within an Internet or packet-switched network.
Moreover, the network packet can hold information ranges from 1 KB to 1.5 KB.
In other words, a network packet is a basic unit of information, which is formed by fragmenting or breaking down a big chunk of information and send over a computer network such as the Internet.
The fragmentation of information into a smaller unit, known as a network packet, enables quick and easy data transmission in a packet-switched network.
The real-life analogy would be like you are sending some email or uploading videos. In both cases, the information which you are sending or uploading is first divided into smaller chunks.
Each chunk is a network packet, which was assigned with the identifier. It can be identified and re-assembled at the receiver end to its original forms, such as email or video.
The transmission of each network packet takes the best possible route, and if the packet is lost in the route, it is re-sent to the destination address.
So, the transmission of every information on the Internet through packets, which includes web pages, email, digital communication.
Before we move further, it is good to know what is a packet-switched network.
What is a Packet-Switched Network?
A packet-switched network is a data communication network. The data or information is divided into small packets before it travels from source to destination through multiple routes.
Moreover, the packet-switched network is a connectionless network or connection-oriented network depending on the type of protocol.
The advantage of using the packet-switched network is that each packet is independent of others. It means that each packet can take the best possible route to reach the same destination.
Also, packets from multiple computers can travel through the same network equipment because of a packet-switched network. Because of the packet-switched network, billions of information are exchanged through multiple devices on the Internet.
Critical components of a network packet
The network packet structure is divided into three parts:
- Header
- Trailers or Footer
- Payload
The analogy of a network packet would be the postal package. So, the header in the network packet is very similar to the box or envelope of a postal package.
Further, the Payload is similar to the content you keep inside a box or envelope. And, the Trailer in the network packet is somewhat identical to the signature that validates the package.
Let’s look into each part separately and understand what does it means.
What is a packet header?
The network packet header is just like the “label” that depicts the crucial information like the packet’s origin, destination, and content snippet.
It contains vital information like source and destination IP address. Let’s look into some of the necessary instructions that the network packet header contains.
Checksum, which is a string of numbers that detect errors in the data
Identification number, which consists of 16-bit.
Flags give information to the router that packets can be fragmented or not.
Fragmentation offset helps in reconstructing the fragmented packets
Source and Destination IP address
Hops indicate the number of intermediates the packet can or has crossed.
Length of the packet indicates the size of the packet, which may vary in some networks, or it can be of fixed-length packages in some networks. The length of the packet includes the size of the header and the Payload.
Time-to-Live (TTL) indicates the period till how long a packet can exist on a computer network before being discarded.
The Packet number is just the sequence number, which helps the re-assembling of the packets.
Additionally, the other information includes the network protocol or the type of packet, synchronization bits, and much more.
The network protocol attached with the header helps in formating data by the destination computer or server. The most common protocols include Transmission Control Protocol (TCP) and an Internet Protocol (IP).
What is Payload in network packet?
The Payload is the data that the network packet carries to the destination address. Moreover, the Payload is the fragmented data of the larger file, which is re-assembled to form a complete file.
For better understanding, you can refer to email or video examples. The thousands of packets are combined to form a single email or video.
Each packet carries a small part of the email or video, which is recombined to form a complete email or video at the receiver end.
What are Packet trailers or footers?
The trailers or footers of the network packet contains additional information, which is not adopted by all network protocol.
Some of the protocols like ESP (Encapsulating Security Protocol) require that trailers be attached to the network packets.
The packet trailers are used in error checking or to differentiate good and bad packets. If the Trailer doesn’t match the Payload, the destination computer will re-send the request to the source computer.
Moreover, it also informs the receiving device that the packet has reached the end of the destination.
How does the Network packet work?
To understand the working of network packets, you need to understand the OSI model, the conceptual framework, and the TCP/IP model, the operating framework.
In the OSI model, the network protocol is used in different layers. The data passing through different layers are broken down before being transmitted to the destination address.
In the TCP/IP protocol suite, the data is processed from the transport layer to the network or internet layer and then processed back into the network access layer.
Process in Transport Layer
The data, when it is processed in the transport layer, is called segmentation.
The transport layer uses two protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). When data is processed through TCP, the processed data is named Packets, and when it is processed through UDP, it is called a Datagram. So, this is the basic difference between Packets and Datagram.
But, you will observe that Packets and Datagram are used interchangeably, and Datagram is also considered an alternative term for “packet.”
Later, when the segmented data is transferred to the network or Internet layer, it is named IP packet when processed through TCP.
It is named IP Datagram when processed through UDP.
The primary difference between TCP and UDP is that TCP is a connection-oriented protocol requiring confirmation or acknowledgment from the other side. In response to this, it has high latency and bandwidth, but it provides assured delivery and reliability.
On the other hand, UDP is a connectionless protocol requiring confirmation or acknowledgment from different sides. Thus, it makes UDP unreliable but better in latency and consumes less bandwidth.
Process in Internet Layer or Network Layer
When the data or message is received as a packet or Datagram, it is encapsulated with additional information such as source and destination IP address, identifiers, Quality of Service (QoS).
Now, the data is termed as IP packet or Datagram. Later, it is forwarded to the network interface card (NIC).
Process in Network Interface Layer
When the Network Interface Card receives an IP packet or Datagram, it is again encapsulated as a Frame depending on data-link layer technologies.
Ethernet, token ring, and frame relay are some of the most common data-link layer technologies, and if it is processed through Ethernet, it is termed Ethernet frame.
Frame act as a series of binary signals forwarded to physical layer such as fiber, coax, hubs, attached with NIC.
The problem of Network Packets
As we know, the Internet layer processes messages into multiple IP packets, but it cannot handle all the consequences of packets.
The network packets may face multiple problems during transmission from source to destination. Some of the most common issues are:
Can send multiple packets – The source computer can send multiple packets simultaneously, which need to identify and separate packets belonging to the particular message.
Packets arrived out of order – This is one of the most common problems with packets when two different packets take two different routes and arrive at the destination address.
Corrupted packets – When the received packets don’t match the sent packets, they are corrupted packets.
Loss of packets occurs when there is a problem with the physical layer, and some packets are lost during transmission.
Duplicate packets – This occurs when the source computer sends the same packets again accidentally.
