Introduction to Computer Networks
1. Local Area Networks (LAN)
A set of physical and logical elements that provide interconnection between devices in a private and restricted area.
Features:
- Geographical restriction
- Relatively high transmission speed
- Private network
- Low error rate and high transmission reliability
Types of LANs:
Peer-to-Peer Networks:
Computers share resources like disks and printers, with all devices having equal functionalities.
Client-Server Networks:
A centralized structure where a privileged computer (server) provides services to other computers (clients) and manages access control.
2. Wide Area Networks (WAN)
A network interconnecting computers across a wide geographical area using public lines. WANs are typically used when communication needs extend beyond a local area, are shared among many users, and have a higher error rate compared to LANs.
3. Other Network Types
This section covers Metropolitan Area Networks (MAN), Personal Area Networks (PAN), and Wireless Local Area Networks (WLAN).
Metropolitan Area Networks (MAN):
Used for data distribution within a city environment, often provided through cable TV infrastructure offering services like video, internet, and telephony.
Personal Area Networks (PAN):
Centering around a single user’s devices (e.g., a computer and a smartphone), PANs offer a personal network connection.
PAN Network Features:
- Easy or automatic network access configuration
- Limited radio network range, minimizing collisions
- Wireless transmission mode
- Low installation and operation costs, sometimes even free
Wireless Local Area Networks (WLAN):
Provide the convenience of wireless installation and lower costs. Examples include Bluetooth and Infrared for low-rate transfers, Wi-Fi for local area networks, and WiMAX for metropolitan networks. All these technologies fall under the WLAN umbrella.
Disadvantages of WLANs:
- Vulnerability to attacks due to the open nature of the air transmission medium
- Potential for channel saturation due to shared transmission medium
4. Characteristics of LANs
The IEEE defines a local area network as follows:
“A local area network is distinguished from other types in that communications are confined to a limited geographical area, such as an office building, using a communication channel with moderate or high speed and a low error rate. The essential elements of a local area network are: scope, security, and speed.”
5. Network Topologies
Network topology refers to the arrangement of equipment and wiring within a network. Several common topologies exist:
Star Topology:
A central hub or switch acts as the central connection point for all other devices, resembling a star shape. While offering structured connections, this topology can lead to cable clutter at the central hub.
Ring Topology:
Devices are connected in a closed loop or ring. This topology eliminates traffic congestion issues but is vulnerable to network failure if a single connection breaks.
Bus Topology:
All devices connect to a single linear cable (the bus). This simple topology is easy to implement but susceptible to traffic problems and cable breaks. Ethernet is an example of a bus topology.
6. Protocol Families
Preliminary Concepts:
Protocols are publicly defined sets of rules for communication. Adherence to these protocols ensures compatibility between devices from different manufacturers.
a) The Concept of a Layer:
To simplify network complexities, communication is divided into different layers, each responsible for a specific service.
b) Interface Between Layers:
Adjacent layers communicate and negotiate services through defined interfaces, ensuring seamless data flow.
c) Network Architecture:
The organized set of layers and protocols used for network communication between nodes.
d) Open Systems:
Systems comprising one or more computers, software, peripherals, and communication channels that adhere to open standards, promoting interoperability.
6.2 Common Protocol Families:
a) NetWare Family:
A widely used network operating system, traditionally employing dedicated servers that cannot act as clients.
b) TCP/IP Family:
A collection of protocols defined in documents called Request for Comments (RFCs), forming the foundation of the internet.
7. The OSI Reference Model
A layered architecture model for computer networks, providing a framework for understanding and standardizing network communication.
7.1 OSI Basic Overview:
The OSI model consists of seven layers, each representing a specific function in the communication process. From the physical layer (closest to the hardware) to the application layer (closest to the user), these layers ensure seamless data exchange.
8. Network Elements
8.1 Wiring, Connectors, and Physical Spaces:
The physical infrastructure of a network, including the wiring (copper or fiber optic), connectors, and the physical spaces where network devices are located.
8.2 Network Devices:
Specialized devices that perform specific network functions, such as modems, hubs, repeaters, switches, routers, and gateways, each operating at different layers of the OSI model.