Ethernet Switches play a crucial role in data transfer between devices in computer networking, operating at different layers of the Open Source Interconnect (OSI) model which refers to the layer of a generic protocol. The generic protocol model specifies common rules for sending and receiving packets between different network layers. Layer 2 switches forward packets using MAC addresses within the same network, while Layer 3 switches use IP addresses to transfer data between different networks. Apart from the OSI model, the Transmission Control Protocol (TCP) and Internet Protocol (IP) model is another conceptual model used to describe network communication, consisting of four layers. The OSI has seven and TCP/IP has four layers. Understanding these models is vital for efficient and secure network design and implementation.
OSI Reference Model Layers
The OSI model consists of seven layers as a conceptual framework that standardizes the division of labor and interaction among various software and hardware components involved in network communication.
Layer 7: Application Layer
The OSI model's application layer is responsible for providing communication functions to software applications as needed, making it the layer closest to end users. Its primary functions include confirming the availability of communication resources and partners to facilitate data transfer. Additionally, this layer defines protocols for end applications, such as DNS, FTP, HTTP, IMAP, POP, SMTP, SNMP, and Telnet (which emulates a terminal).
Layer 6: Presentation Layer
The compatibility of data with communication resources is checked by the presentation layer, which can convert it into a format that is acceptable to both the application layer and lower layers. It ensures that data is transmitted accurately by formatting it in a way that the receiving application can understand. This layer is responsible for data compression, encryption, and decryption, and it also handles the conversion of data between different character encoding schemes. The presentation layer's main objective is to ensure that the data received by the application layer is presented in a format that the application can understand, regardless of the underlying network protocols used for transmission. The presentation layer is responsible for safeguarding the integrity of data transmission and ensuring accuracy and security during data transfer.
Layer 5: Session Layer
The session layer manages the communication links between computers. Its primary functions are to create, manage, sustain, and terminal the connections between the local and remote applications. Additionally, Layer 5 software handles authentication and authorization processes and ensures the successful delivery of data.
Layer 4: Transport Layer
The transport layer is responsible for transmitting data sequences from the source host to the destination host. It ensures that the data being transferred is of high quality and integrity via error correction and similar functions. One of the main functions of the transport layer is to provide explicit flow control, which helps to manage the rate at which data is sent and received to prevent network congestion. Although the TCP and User Datagram Protocols (UDP) do not strictly conform to the OSI model, they are considered essential protocols in layer 4 due to their ability to handle data transmission in different scenarios. The transport layer can make sure the data transmission is more efficient and reliable.
Layer 3: Network Layer
The network layer manages packet routing using logical addressing and switching functions. A network connects multiple nodes, and each node has an address. When a new message is transmitted from one node to another, it provides the message content and the destination node's address, and the network delivers the message to the destination node, The network might split a lengthy message into multiple segments and transmit them individually, possibly redirecting them through other nodes. reassembling the fragments at another node.
Layer 2: Data Link Layer
The data link layer serves as a means of transferring data from node to node, handling the packaging and unpacking of information into frames. Additionally, it defines protocols for establishing and terminating connections between physically connected devices, such as Point-to-Point Protocol (PPP). The data link layer is typically comprised of two sublayers, one called the media access control (MAC) layer, and the other one is the logical link control (LLC) layer. The MAC layer is responsible for managing how devices in a network gain access to media and obtain permission to transmit data, while the logical link control layer can identify and encapsulate network layer protocols, as well as oversee error checking and frame synchronization.
Layer 1: Physical Layer
The physical layer defines the medium on which data is transmitted and defines all the electrical and physical specifications of all data transmission links. such as the voltage levels, current, and signaling rate of the transmission medium, and the characteristics of the transmission medium, such as fiber type, bandwidth, and operating wavelength. Additionally, it ensures the accurate transmission and reception of data by encoding, modulating, and detecting errors in the signals. Ultimately, the physical layer is responsible for converting digital data into signals that can be transmitted over the communication medium.
TCP/IP Model Layers
The TCP/IP model, which is also referred to as the Internet protocol suite, is a layered reference model consisting of four layers. Although TCP and IP are the foundational protocols and give the model its name, there are not only TCP/IP protocols but also other protocols utilized within this framework.
In the TCP/IP model, the application layer enables applications to access services from other layers and establishes the protocols utilized by applications to exchange data. Some well-known protocols in the application layer are HTTP, FTP, SMTP, Telnet, DNS, SNMP, and the Routing Information Protocol (RIP).
The host-to-host transport layer, also referred to as the transport layer, works for furnishing the application layer with session and datagram communication services. The primary protocols employed by this layer include TCP and UDP. TCP delivers a dependable communication service that is connection-oriented and one-to-one. It assumes responsibility for ordering and acknowledging transmitted packets, as well as retrieving any lost packets during transmission. On the other hand, UDP offers a connectionless, one-to-one, or one-to-many, unreliable communication service. It is commonly utilized when transferring small amounts of data that can fit into a single packet.
The Internet layer bears the responsibility of executing host addressing, packaging, and routing tasks. Its main protocols include IP, ARP, ICMP, and IGMP. IP, a routable protocol, handles IP addressing, routing, packet fragmentation, and reassembly. ARP, on the other hand, discovers the network access layer address, which may refer to a hardware address associated with a specific Internet layer access. ICMP provides diagnostic functionalities and error reporting in case IP packet delivery fails. IGMP manages IP multicast groups. The IP header, which contains the IP address, is added to the packets in this layer. Presently, both 32-bit IPv4 and 128-bit IPv6 addresses are in use.
Network Access Layer
The network access layer, also called the link layer, is accountable for placing TCP/IP packets onto the network medium and retrieving TCP/IP packets from the network medium. TCP/IP is intentionally designed to be agnostic to the network access method, frame format, and medium, which means it is not tied to any particular network technology. Consequently, TCP/IP can facilitate communication across various types of networks.
What Is The Process of Data Transmission And How Is Data Processed During It?
A protocol data unit (PDU) is the format in which data is exchanged between different layers in a layered system. The table below displays various types of PDUs utilized in such systems.
When the user performs a web browsing operation on their device, the remote server software initiates the process by providing the requested data to the application layer. From there, the data is processed sequentially through each layer, The network protocol's individual layers have distinct functions, and the data flows through the physical layer of the network. As it ascends through the layers, the data is assured of reaching its intended destination, whether it be a target server or another device. Each layer performs its assigned operations until it is ultimately utilized by the receiving software.
Encapsulation is the process where each layer, during transmission, adds either a header or a footer, or both to the Protocol Data Unit (PDU) received from the upper layer. This added information directs and identifies the packet. The header (and footer) and the original data from the PDU for the next lower layer. This process is repeated until the lowest-level layer (physical layer or network access layer) is reached, from where the data is transmitted to the receiving device.
Upon receiving the data, the receiving device de-encapsulates the data at each layer by extracting the header and footer information, which directs the de-encapsulation process. Finally, the application uses the extracted data. The entire process will accompany the whole process of data transfer including transmit and receive.
Troubleshooting By TCP/IP and OSI Models
With an understanding of network layering, it becomes possible to diagnose the cause of a connection failure. It is generally advisable to begin troubleshooting from the lowest layer of the network and work upwards, rather than starting from the highest layer. This is because each layer is designed to serve the layer above it, making it easier to deal with any problems that arise at the next layer.
In the event of a network problem, the first step should be to check the physical layer. This includes ensuring that the network cable is properly connected, checking that the wireless access point (WAP) is connected to the switch, and verifying that the RJ45 pins are in good condition.
TCP/IP Model vs. OSI Model
There are many differences between the TCP/IP model and the OSI model, as appeared earlier. The following example shows the corresponding relationship between them.
When comparing the layers of the TCP/IP model with those of the OSI model, it can be observed that the application layer of the TCP/IP model corresponds to layers 5, 6, and 7 of the OSI model. However, the TCP/IP model does not have separate layers to represent the presentation and session layers. The transport layer in TCP/IP takes on the functions of the OSI transport layer and some aspects of the OSI session layer. Meanwhile, the network access layer in TCP/IP encompasses the physical and data link layers in the OSI model. On the other hand, the sequencing and acknowledgment services available at the data link layer of the OSI model are not used by the Internet layer of the TCP/IP model.
The OSI model and the TCP/IP model are two networking models that define how communication between devices on a network should be structured. Both models have similar layers that perform similar functions, but the OSI model is more theoretical and provides a standardized framework for networking, while the TCP/IP model is used in practice for networking on the Internet. The OSI model's development aimed to create a universal framework that would make it easier for different devices to communicate with each other. In contrast, the TCP/IP model was developed specifically for the ARPANET, the predecessor to the modern-day Internet, to provide reliable communication across a network of interconnected computers. Despite their differences, both models are still used today, and their concepts and principles are incorporated into modern networking protocols and standards.
In this article, we have provided a comprehensive overview of both the TCP/IP model and the OSI model, which are abstract frameworks designed to explain all forms of network communication. TCP/IP, in particular, plays a significant role in facilitating internet operations. When discussing network equipment layers 2, 3, and 7, we typically reference the OSI model. Meanwhile, the TCP/IP model serves as a model for the contemporary internet infrastructure and establishes a standard set of regulations governing all network transmissions.