Introduction to Networking
Networking is the act of linking computing devices together to share information and resources. This involves various components and terminologies, with each playing a unique role in the process. The complexity of networking calls for a structured approach to understanding the distinct elements involved.
Network Interface Card (NIC): Often known as a network controller, network adapter, or LAN adapter, the NIC is a hardware component that links a device to a computer network. This could be either physical or wireless.
Computer Network: This involves computers connected via cable that exchange data and share resources.
Network Protocol: Network protocols are a set of rules and conventions governing the communications between network devices. They range from HTTP and FTP to TCP/IP, among others.
Router: A router is a device that receives data from a device and decides where to forward it based on the cost of the route or communication distance.
IP Address: Internet Protocol Address is a unique numeric address given to each device on a computer network.
DHCP: Dynamic Host Configuration Protocol (DHCP) allows a router to assign IP addresses to devices connected to it.
DNS: Domain Name System (DNS) converts domain names to IP addresses that identify computer networks.
Physical Components of the Network
Physical components of a network include cables, switches, network interface cards, and wireless access points. The cables and switches are physically interconnected to allow networking.
Endpoints: These are devices that retrieve or provide information.
Interconnections: These are components such as network interface cards and cables that connect devices in a network.
Switches: They provide intelligent switching of data within a local area network (LAN).
Routers: Routers connect different networks and intelligently choose pathways between them.
Wireless Access Point: This connects wireless devices to a physical server.
Characteristics of a Network
Networks have various characteristics that describe their performance and structure. These include:
Topology: Networks have a physical and logical topology. Physical topology describes how devices and components are interconnected in the network, while logical topology details the path of data transfer.
Speed: The speed of a network is the measure of the data rate of any given link in the network, usually measured in bits per second.
Cost: This is the expense involved in purchasing network components, as well as installing and maintaining them.
Security: Describes the protection level of a network against threats from inside and outside.
Availability: This is the measure of the probability that a network will be available when needed.
Scalability: This shows how easily a network can grow to accommodate more users and loads.
Reliability: This is the dependability of the components that constitute the network.
Logical Components of the Network
Logical components describe how data is transported in the network, mainly through various protocols, with Internet Protocol being the most common.
Network Topology Types
Bus: Devices were traditionally connected on a line of coaxial cable. Modern devices use a switch and twisted pair wiring in a star topology.
Ring: In a ring topology, the devices are interconnected in a circuit, forming a ring.
Star: This is a common physical implementation where a central device (switch) is connected to each device, but the devices are not connected to each other.
Mesh: Each device in the network is connected to multiple devices. This creates redundant links to increase network reliability and allow the network to heal itself.
Applications and Their Impact on Network Performance
Various types of applications can affect network performance, hence impacting the user experience.
Batch Applications: These require little or no user interaction once initiated and often consume as much bandwidth as available.
Interactive Applications: These require human interaction. Response time is a critical metric for these applications.
Real-Time Applications: These require high-quality service and minimal delay. Timely delivery of data is critical.
OSI Model – Open Systems Interconnection Model
The OSI model, developed by the International Organization for Standardization, standardizes communication between devices and software using a layered approach. Each layer is independent of the others.
The model consists of seven layers:
- Application (Layer 7)
- Presentation (Layer 6)
- Session (Layer 5)
- Transport (Layer 4)
- Network (Layer 3)
- Datalink (Layer 2)
- Physical (Layer 1)
Data undergoes a process of encapsulation and de-encapsulation at the point of transmission and when it is received. Each layer only communicates with the corresponding layer, between systems.
The Open Systems Interconnection (OSI) model is a conceptual model that defines the various network functions into seven distinct layers. Each layer in the OSI model has a specific role and interacts directly only with the layer immediately beneath it and the layer immediately above it. Here’s a more detailed look at each layer of the OSI model:
Layer 1: Physical Layer
The physical layer is the lowest layer of the OSI model and is responsible for the transmission and reception of unstructured raw data between a device and a physical medium such as a network cable. This layer manages the physical connectivity of devices in a network. It sets standards for connections, voltage levels, timings, and the physical data rates. It also defines the electrical and mechanical specifications for devices, such as the layout of pins, voltages, cable specifications, hubs, repeaters, network adapters, host bus adapters and more.
Layer 2: Data Link Layer
The data link layer provides node-to-node data transfer—a link between two directly connected nodes. It also corrects errors that may occur at the physical layer. This layer is responsible for physical addressing, network topology, error notification, frame sequencing, and flow control. It is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it, while the LLC layer controls frame synchronization, flow control, and error checking.
Layer 3: Network Layer
The network layer is responsible for receiving frames from the data link layer and delivering them to their intended destinations based on the addresses they contain. This layer manages network structure and controls routing and relaying, as well as addressing, internetworking, error handling, congestion control, and packet sequencing. Protocols used in this layer include the Internet Protocol (IP), which is used for routing packets, and Internet Control Message Protocol (ICMP), which reports errors and helps provide information about the network.
Layer 4: Transport Layer
The transport layer provides transparent transmission of data from source to destination and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer and also provides services such as multiplexing, segmentation, and reassembly. The two best-known transport protocols are the Transmission Control Protocol (TCP), which uses a sequence of acknowledgments to guarantee packet delivery, and the User Datagram Protocol (UDP), which offers fast but less-reliable messaging.
Layer 5: Session Layer
The session layer establishes, maintains, and terminates connections between applications at each end. It controls the dialogues/connections between computers and manages how data is exchanged during a session, whether in one direction or both. It offers services like dialog control and synchronization. Examples of session-layer protocols include the Session Control Protocol (SCP) and the AppleTalk Protocol.
Layer 6: Presentation Layer
The presentation layer is responsible for data translation, code formatting, and data encryption. This layer transforms data from the application layer into a universally acceptable format for transmission. For outgoing messages, it translates data into a generic format for the end-to-end transmission. For incoming messages, it translates data from the generic format to a format that the application layer can understand. Examples of presentation layer protocols include ASCII, Unicode, JPEG, GIF, TIFF, and MPEG.
Layer 7: Application Layer
The application layer, the highest layer in the OSI model, provides the interface between the applications we use to communicate and the underlying network over which our messages are transmitted. This layer interacts with software applications that implement a communicating component. It provides services to application processes (such as email, file transfer, and web browsing). The application layer is the front-end layer and is the closest to the end-user. Both the end-user and the application layer interact with the software applications. Common examples of application-layer protocols include HTTP (websites), SMTP (email), FTP (file transfers), and DNS (Domain Name System).
Each layer of the OSI model offers specific services to higher layers while shielding these layers from the details of how these services are implemented. Understanding the functions of each OSI model layer helps IT professionals in troubleshooting network problems and in the design and implementation of new networks.
TCP/IP model vs OSI Model
The TCP/IP model, with its four layers, differs from the seven-layer OSI model. In reality, a hybrid of these models is often used, separating the Network access layer into two layers: the Data Link Layer and the Physical Layer.
Understanding the components, terminologies, and models related to networking aids in designing and managing effective networks. It facilitates the making of informed decisions to optimize network performance, security, and reliability.