In networking, there are different frameworks, or protocols that systems, and endpoints both hardware and software use to enable a free-flow transmission of data without compromising on security. The role of these models in networking is important to maintain secure communication within and outside a network. With these models, the overall operations in communication are broken down into chunks, which are also known as layers, each of these layers has an activity they perform in the communication.

Networking Protocols

1. The OSI model

2. The TCP/IP model

This article explores these two models, breaking down their features, the unit of information transmitted, and the protocol/technology/syntax used in each layer.

Open System Interconnection (OSI) Model

The International Organization for Standardization(ISO) developed the OSI Model to establish a standard framework for describing the communication architecture of networked systems. The OSI model can be defined as a conceptual or theoretical picture of how network protocols operate in real-time. This model, though theoretical, is a widely used conceptual framework for analyzing the hierarchy of networking components and how they communicate with one another.

OSI model - The Open System Interconnection(OSI) model lays the seven-tier operations through which communication moves via a networking system and outlines the levels at which the computer system utilizes these operations to communicate over a network. These layers support communication flow between two endpoints, every layer is in charge of carrying out specific functions.

The seven layers are referred to by the layer name or by the layer number. The numbering sequence flows in descending order while communication is transmitted from layer 1 up to layer 7:

Layer 7 —-----> Application layer

Layer 6 —-----> Presentation layer

Layer 5 —-----> Session layer

Layer 4 —-----> Transport layer

Layer 3 —-----> Network layer

Layer 2 —-----> Data-link layer

Layer 1 —-----> Physical layer

Layer 1 - Physical Layer

The physical layer works using actual devices and effectively examines the overall connection of a workstation to another distinct station. This layer primarily works with physical hardware components such as cables, wires, signals, etc., and other components necessary to carry information signals.

Data-link layer receives services from this layer and in the same order, renders services to the upper layer, the data-link layer, and sends information to it in the form of bits. These Bits of information pass through electrical pulses which are transmitted through either wired or wireless means.

The unit of information that is processed by this layer is in Bits

The protocol/technology/syntax that is used is Network Interface Card(NIC), cables, hubs, repeaters, modem, coax, etc.

Layer 2 - Data-link Layer

The data-link layer collects the bits of data from the physical layer that was sent through electrical signals, puts them together into frames, and then moves them to the upper layer - the network layer.

This layer is Responsible for creating a reliable link between two directly connected systems. It uses Sub-layers: Logical Link Control (LLC) and Media Access Control (MAC) to handle error detection and synchronization of frame, and control communication flow.

The unit of information that is processed by this layer is in Frames

The protocol/technology/syntax that is used is Ethernet, network switch, fiber channel, etc.

Layer 3 - Network Layer

The network layer is also referred to as the internet layer. This layer manages traffic flow and routing to ensure a timely and correct data transmission between hosts or endpoints and across networks. When this layer receives information, it breaks it into packets.

The reason why data is broken down into packets by this layer is for the network to achieve a faster and more reliable transfer. When these packets get to the receiving end, they are put back to resemble the original data i.e. the way the data was before they were broken down into packets.

This layer may take a little longer to transfer these packets when there is a lot of internet traffic, but there is a lower likelihood that any error that occurs will corrupt the information being sent.

The unit of information that is processed by this layer is in Packets.

The protocol/technology/syntax that is used is IP, IPsec, ICMP, ARP, etc.

Layer 4 - Transport Layer

The transport layer is the heart of the OSI model. This layer determines the mode of delivery of data based on the nature of the information being shared. This layer uses two communication protocols to transmit messages.

The first protocol that may be used by this layer is -Transmission Control Protocol(TCP). This protocol is used when this layer needs to maintain the integrity of data for a highly secure and reliable transmission of the information. TCP does not mind the slow speed it may use in communicating information, all it cares about is the integrity of the information it is sending per time.

The second protocol is -User Datagram Protocol(UDP), This protocol is not as secure as the TCP but is usually the best option when there is a need for a more speedy transmission of data. E.g. during a video streaming from YouTube or Social media. Security is not so important here, speed is. The transport will use UDP for data transfer. But when you are sending information like emails, the transport layer knows that the message needs integrity and security, it will automatically use TCP instead of UDP.

When transmitting data, The transport layer breaks the data into segments and assigns sequence numbers to these segments. It also uses a method called, the Three-Way Handshake - SYN(Synchronize), SYN-ACK(Synchronize-Acknowledgement), and ACK(Acknowledgment). The transport layer SYNs the initial segment with a sequence number to the receiving system and once received, the receiving system returns the SYN-ACK to the sending system to acknowledge its receipt, then An ACK is also made by the sending system to acknowledge that the communication has successfully established.

The unit of information that is processed by this layer is in: Segments

The protocol/technology/syntax that is used is TCP or UDP.

Layer 5 - Session Layer

This layer is responsible for setting up, maintaining, or canceling sessions - a session is the time spent in communication. This layer also keeps track of sessions, which are used in client/server communication.

The sessions between local and distant applications and the pipeline of transfer are opened, initiated, controlled, and terminated by this layer. In this layer, there is no breaking down of information. The message is always at the data stage.

The unit of information that is processed by this layer is in the Data

The protocol/technology/syntax that is used is SDP, PPTP, RTCP, PAP, ADSP, etc.

Layer 6 - Presentation Layer

The presentation layer prepares or integrates data for the application layer. This layer provides the encryption and decryption tasks required to send the message securely and efficiently. Based on the nature of the information being transmitted, this layer specifies the data format and encryption needs.

The presentation layer is also known as the syntax layer because it is in charge of ensuring that the data it receives or transmits to other layers is transmitted with the correct syntax. The presentation layer has less to do with protocols but more to do with syntax and the format for data transmission - This is the layer with the function of encoding, compression, and encrypting pieces of data.

Also, in this layer, there is no breaking down of information, neither is data sent in plain text. The data that is being transmitted can only change its format, but cannot be broken down.

The unit of information that is processed by this layer is in Data.

The protocol/technology/syntax that is used is ASCII, SSL, MPEG, TAR, PNG, etc.

Layer 7 - Application Layer

The application layer is a collection of programs or protocols that enable users to access and share resources within and across networks. When end users issue communication such as requesting a web page from the web browser, it is the application layer that determines the nature of communication.

It also determines the protocol to be used, resource requirements, communication partners, and general coherence for the communication. There is also no breaking down of data at this layer.

The unit of information that is processed by this layer is in the Data

The protocol/technology/syntax that is used is HTTP/HTTPS, FTP/SFTP, SMTP/SMTP with TLS, Telnet/SSH, DNS, etc.

Transmission Control Protocol/Internet Protocol (TCP/IP)

The TCP/IP model is an offshoot of the OSI model. Even though the OSI model is broader, this model is the model that describes the actual flow and implementation of computer networking. This protocol defines how communication is gathered, broken down, addressed, routed, and sent over a network to ensure that the recipient receives the same information that was initially sent without any alterations.

Layers of the TCP/IP Model

..Application layer

..Transport layer

..Internet layer

..Physical layer

In the TCP/IP model, the only application layer performs the function that the Session, Presentation, and Application layers of the OSI model perform distinctively. The transport layer and network layer have the same function as their counterpart in the OSI model while the physical and datalink layer have their functions fused in the link layer.