In the field of computer networks, what is a protocol?

Assembling the physical pieces of a computer network by itself is insufficient to make it function; connected devices also require a method of communication. These communication languages are called network protocols.

Without protocols, devices would lack the ability to understand the electronic signals they send to each other over network connections. Network protocols serve these basic functions:

Address data to the correct recipients.
Physically transmit data from source to destination, with security protection if needed.
Receive messages and send responses appropriately.

Consider a comparison between network protocols with how a postal service handles physical paper mail. Just as the postal service manages letters from many sources and destinations, network protocols keep data flowing along many paths continuously.

Unlike physical mail, however, network protocols provide advanced capabilities. These include delivering a constant flow of messages to one destination (called streaming) and automatically making copies of a message for delivery to multiple destinations at once (called broadcasting).

No one protocol exists that supports all the features every computer network needs. Still, each serves as a key that unlocks a given network device or service. Different network protocols have been invented over the years, each attempting to support certain types of network communication.

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The three basic characteristics that distinguish one type of protocol from another are:

Simplex vs. duplex: A simplex connection allows only one device to transmit on a network. Duplex network connections allow devices to transmit and receive data across the same physical link.
Connection-oriented or connectionless: A connection-oriented network protocol exchanges (a process called a handshake) address information between two devices that allow them to carry on a conversation (called a session). Connection-less protocols deliver individual messages from one point to another without regard for similar messages sent before or after (and without knowing whether messages are successfully received).
Layer: Network protocols typically work together in groups (called stacks because diagrams often depict protocols as boxes stacked on top of each other). Some protocols function at lower layers closely tied to how different types of wireless or network cabling physically work. Others work at higher layers linked to how network applications work, and some work at intermediate layers in between.

The common network protocols in public use belong to the Internet Protocol family. IP is the basic protocol that enables home and other local networks across the internet to communicate with each other.

IP works well for moving individual messages from one network to another. It does not support the concept of a conversation (a connection over which a stream of messages can travel in one or both directions). The Transmission Control Protocol (TCP) extends IP with this higher layer capability. Because point-to-point connections are essential on the internet, the two protocols are paired together and known as TCP/IP.

Both TCP and IP operate in the middle layers of a network protocol stack. Popular applications on the internet have sometimes implemented their protocols on top of TCP/IP. HyperText Transfer Protocol is used by web browsers and servers worldwide. TCP/IP, in turn, runs on top of lower-level network technologies like Ethernet. Other popular network protocols in the IP family include ARP, ICMP, and FTP.

The internet and most other data networks work by organizing data into small pieces called packets. To improve communication performance and reliability, each large message sent between two network devices is often subdivided into smaller packets by the underlying hardware and software. These packet switching networks require packets to be organized in specific ways according to the protocols the network supports. This approach works well with the technology of modern networks as these handle data in the form of bits and bytes (digital 1s and 0s).

Each network protocol defines rules for how its data packets must be organized. Because protocols like Internet Protocol often work together in layers, some data embedded inside a packet formatted for one protocol can be in the format of some other related protocol (a method called encapsulation).

Protocols typically divide each packet into three parts—header, payload, and footer. Some protocols, like IP, do not use footers. Packet headers and footers contain the contextual information required to support the network, including addresses of the sending and receiving devices. Payloads contain the data to be transmitted.

Headers or footers often include special data to improve the reliability and performance of network connections, such as counters that keep track of the order in which messages were sent and checksums that help network applications detect data corruption or tampering.

The operating systems of network devices include built-in support for some lower-level network protocols. All modern desktop computer operating systems support Ethernet and TCP/IP, for example. Many smartphones support Bluetooth and protocols from the Wi-Fi family. These protocols connect to the physical network interfaces of a device, like its Ethernet ports and Wi-Fi or Bluetooth radios.

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Network applications support the higher-level protocols which talk to the operating system. A web browser, for example, translates addresses like http://lifewire.com/ into HTTP packets that contain the data that a web server can receive and send back the correct page. The receiving device is responsible for re-assembling individual packets into the original message by removing the headers and footers and concatenating packets in the correct sequence.

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Types of Network Protocols
There are three main types of network protocols, including network management protocols, network communication protocols and network security protocols.
Which Protocol is Right for You?
Your business needs and size will determine which protocol you'll need for your network.

In the era of Computer and Mobile technologies, computer network technology is growing at a very fast speed and frequency. Billions of electronic devices and gadgets are operating to make this happen. These devices are designed and manufactured by different manufacturers. They may have been developed using different hardware and software resources. Due to this, they are unable to establish a connection and communicate with each other for sharing data and other information. Hence, to resolve this problem, we need protocols. Protocols provide us with a medium and set of rules to establish communication between different devices for the exchange of data and other services.

Protocols are needed in every field like society, science & technology, Data Communication, media, etc. But in this blog, we’ll mainly concentrate on the protocols used in computer networks and data communication. We'll further focus on the types, key elements, and functionalities of protocols. So, let's get started with the basics of protocols.

Protocols are a fundamental aspect of digital communication as they dictate how to format, transmit and receive data. They are a set of rules that determines how the data will be transmitted over the network.

It can also be defined as a communication standard followed by the two key parties(sender and receiver) in a computer network to communicate with each other.

It specifies what type of data can be transmitted, what commands are used to send and receive data, and how data transfers are confirmed.

In simple terms, a protocol is similar to a language. Every language has its own rules and vocabulary. Protocols have their own rules, specifications, and implementations. If two people share the same language, they can communicate very easily and effectively. Similarly, two hosts implementing the same protocol can connect and communicate easily with each other. Hence, protocols provide a common language for network devices participating in data communication.

Protocols are developed by industry-wide organizations. The ARPA (Advanced Research Project Agency) part of the US Defense program was the first organization to introduce the concept of a standardized protocol. Support for network protocols can be built into the software, hardware, or both. All network end-users rely on network protocols for connectivity.

Protocols use a specific model for their implementation like the OSI (Open System Interface) Model, TCP/IP (Transmission Control Protocol / Internet Protocol) Model, etc. There are different layers (for instance, data, network, transport, and application layer, etc.) in these models, where these protocols are implemented.

Combining all these, we can say that protocol is an agreement between a sender and a receiver, which states how communication will be established, and how to maintain & release it. It is the communication between entities in different systems, where entities can be a user application program, file transfer package, DBMS, etc., and systems can be a remote computer, sensor, etc.

There are mainly three levels of a protocol, they are as follows:

Hardware Level: In this level, the protocol enables the hardware devices to connect and communicate with each other for various purposes.
Software Level: In the software level, the protocol enables different software to connect and communicate with each other to work collaboratively.
Application Level: In this level, the protocol enables the application programs to connect and communicate with each other for various purposes.

Hence protocols can be implemented at the hardware, software, and application levels.

Protocols can be broadly divided into the following two types:

Standard Protocols
Proprietary Protocols

Let's learn one by one:

Standard Protocols

A standard protocol is a mandated protocol for all devices. It supports multiple devices and acts as a standard.

Standard protocols are not vendor-specific i.e. they are not specific to a particular company or organization. They are developed by a group of experts from different organizations .

These protocols are publicly available, and we need not pay for them.

Some of the examples of Standard Protocols are FTP, DNS, DHCP, SMTP, TELNET, TFTP, etc.

Proprietary Protocols

Proprietary protocols are developed by an individual organization for their specific devices. We have to take permission from the organization if we want to use their protocols.

It is not a standard protocol and it supports only specific devices. We may have to pay for these protocols.

Some of the examples of Proprietary Protocols are IMessage, Apple Talk, etc.

The key elements of the protocol determine what to be communicated, how it is communicated, and when it is communicated.

There are mainly three key elements of a protocol, they are as follows:

Let's learn these elements in detail.

Syntax

Syntax refers to the structure or format of data and signal levels. It indicates how to read the data in the form of bits or fields. It also decides the order in which the data is presented to the receiver.

Example: A protocol might expect that the size of a data packet will be 16 bits. In which, the first 4 bits are the sender’s address, the next 4 bits are the receiver’s address, the next 4 bits are the check-sum bits, and the last 4 bits will contain the message. So, every communication that is following that protocol should send 16-bit data.

Semantics

Semantics refers to the interpretation or meaning of each section of bits or fields. It specifies which field defines what action. It defines how a particular section of bits or pattern can be interpreted, and what action needs to be taken. It includes control information for coordination and error handling.

Example: It interprets whether the bits of address identify the route to be taken or the final destination of the message or something else.

Timing

Timing refers to two characteristics:

when the data should be sent?
what will be the speed of sending and receiving the data?

It performs speed matching, sequencing and flow control of the data items.

Example: A sender can send the data at a speed of 100 Mbps, but the receiver can consume it only at a speed of 20 Mbps, then there may be data losses or the packets might get dropped. So, proper synchronization must be there between a sender and a receiver.

Following are the main functionalities of a protocol:

Data Sequencing: It mainly refers to dive data into packets i.e. it divided the whole data into some packets.
Data Flow: It mainly deals with sending data to the correct destination i.e. the flow of the data is correct or not.
Data Routing: It refers to select the best path for data transmission between a sender and a receiver because there can be many routes from sender to receiver and you should select the best possible route.
Encapsulation: It refers to the process of taking one protocol and transferring it to some other another protocol.
Segmentation & Reassembly: It deals with segmenting the data message i.e. diving the data into packets when data flows from the upper protocol layer to lower, and reassembly is vice-versa of segmentation i.e. all the segmented packets are recollected in the correct order at the receiver side.
Connection Control: It ensures connection oriented data transfer for lengthy data items.
Multiplexing: It allows combining multiple transmission unit signals or channels of higher-level protocols in one transmission unit of a lower-level protocol. Multiplexing can be upward or downward.
Ordered Delivery: Protocol facilitates ordered delivery of data, by providing a unique sequence number to each data packet. It is the function of the sender to maintain ordered delivery. By doing so, the receiver will receive the data in the same order as sent by the sender.
Transmission Services:  It mainly deals with priority, Quality of Service (QoS), and security of data packets.
Addressing: It mainly deals with addressing levels, addressing scope, communication identifiers, and addressing modes.
Flow Control: It facilitates to limit the flow of data. It is the function of the receiver's end to maintain flow control of data.
Error Control: It deals with error detection (using the checksum bits) and its control. If any error is detected during the transmission of the data, a request for retransmission of data is sent to the sender by the receiver, and the corrupt data packet is discarded.