Fundamental Concepts of Computer Networks

The computer network is the core infrastructure of modern information technology. This page covers its basic concepts, component structure, functional characteristics, and classification.

Definition of a Computer Network

A computer network is a system of interconnected computers and their peripheral devices that share resources and exchange information according to network protocols.

Key Aspects of the Definition

• Interconnection: multiple computers are connected through communication links
• Protocol conformance: communication follows a unified set of network protocols
• Sharing: hardware, software, and data resources are shared
• Distribution: the computer systems are geographically dispersed

Components of a Computer Network

A computer network consists of the following parts:

1. Host Systems

• Function: provide computing and storage capacity
• Types: servers, workstations, personal computers
• Characteristic: have independent processing capability

2. Communication Subnet

• Transmission media: twisted pair, optical fibre, wireless, and so on
• Switching equipment: routers, switches, hubs, and so on
• Function: carry out data transfer and route selection

3. Network Protocols

• Purpose: define the rules and formats of communication
• Layers: a layered protocol hierarchy
• Standards: ensure interoperability between devices from different vendors

Functions of a Computer Network

1. Data Communication

• File transfer: move files between different computers
• Electronic mail: provide electronic communication service
• Remote login: let users access other computers remotely
• Real-time communication: support real-time traffic such as voice and video

2. Resource Sharing

• Hardware sharing: printers, scanners, storage devices, and so on
• Software sharing: applications, databases, and so on
• Data sharing: files, database contents, and other information
• Computing resources: shared CPU time and memory

3. Distributed Processing

• Load balancing: distribute tasks across several computers
• Parallel computing: several computers work together on a complex computation
• Fault tolerance: a single point of failure does not bring down the whole system
• Scalability: the system grows in size as demand requires

4. Improved Reliability

• Redundancy: backup for critical devices and links
• Fault recovery: faults are detected and repaired automatically
• Data backup: important data is kept in multiple copies
• Service continuity: services stay available

Classification of Computer Networks

By Geographic Range

1. Wide Area Network (WAN)

• Coverage: spans cities, countries, or the whole globe
• Transmission distance: tens to thousands of kilometres
• Transmission rate: relatively low, typically a few Mbps to a few Gbps
• Typical applications: the Internet, corporate WANs
• Technical characteristics: uses public communication facilities, so the cost is high

2. Metropolitan Area Network (MAN)

• Coverage: covers a single city or region
• Transmission distance: a few to tens of kilometres
• Transmission rate: moderate, typically tens of Mbps to a few Gbps
• Typical applications: city networks, campus networks
• Technical characteristics: sits between a LAN and a WAN

3. Local Area Network (LAN)

• Coverage: within a building or a campus
• Transmission distance: a few hundred metres to a few kilometres
• Transmission rate: high, typically 10Mbps to 10Gbps
• Typical applications: office networks, home networks
• Technical characteristics: high rate, low delay, relatively low cost

4. Personal Area Network (PAN)

• Coverage: around a single person’s devices
• Transmission distance: a few to tens of metres
• Transmission rate: low, typically a few Mbps to a few hundred Mbps
• Typical applications: Bluetooth devices, wireless earphones
• Technical characteristics: short range, low power consumption

By Topology

1. Bus Topology

• Structural characteristics: every device connects to one shared transmission line
• Advantages: simple structure, low cost, easy to extend
• Disadvantages: a failure affects a wide area, and transmission efficiency drops as devices are added
• Typical applications: early Ethernet

2. Star Topology

• Structural characteristics: every device connects to a central node
• Advantages: good fault isolation, easy management, convenient expansion
• Disadvantages: a failure of the central node affects the whole network, and the cost is high
• Typical applications: modern Ethernet, wireless networks

3. Ring Topology

• Structural characteristics: devices are linked in a closed loop
• Advantages: high transmission efficiency, easy fault localization
• Disadvantages: a single point of failure affects the whole network, and expansion is difficult
• Typical applications: token ring, FDDI

4. Mesh Topology

• Structural characteristics: devices have several connection paths between them
• Advantages: high reliability, many possible transmission paths
• Disadvantages: expensive, complex to manage
• Typical applications: Internet backbone, military networks

By Users

1. Public Network

• Characteristics: open to the general public
• Management: operated by a telecommunications carrier
• Charging: billed according to usage
• Typical applications: the Internet, the telephone network

2. Private Network

• Characteristics: serves a specific organization or group of users
• Management: run by the organization itself
• Charging: usually not charged to outsiders
• Typical applications: corporate intranets, banking networks

Code Example for Network Classification

// Network type enumeration
typedef enum {
    NETWORK_TYPE_WAN = 0,
    NETWORK_TYPE_MAN = 1,
    NETWORK_TYPE_LAN = 2,
    NETWORK_TYPE_PAN = 3
} NetworkType;

// Topology enumeration
typedef enum {
    TOPOLOGY_BUS = 0,
    TOPOLOGY_STAR = 1,
    TOPOLOGY_RING = 2,
    TOPOLOGY_MESH = 3
} TopologyType;

// Network classification structure
typedef struct {
    NetworkType type;
    TopologyType topology;
    char name[64];
    int max_distance;  // Maximum transmission distance (metres)
    int max_bandwidth; // Maximum bandwidth (Mbps)
    int device_count;  // Number of devices
} NetworkClassification;

// Network classification function
NetworkClassification classify_network(NetworkType type, TopologyType topology) {
    NetworkClassification net;
    net.type = type;
    net.topology = topology;

    switch(type) {
        case NETWORK_TYPE_WAN:
            net.max_distance = 1000000; // 1000km
            net.max_bandwidth = 1000;   // 1Gbps
            strcpy(net.name, "Wide Area Network");
            break;
        case NETWORK_TYPE_MAN:
            net.max_distance = 50000;   // 50km
            net.max_bandwidth = 10000;  // 10Gbps
            strcpy(net.name, "Metropolitan Area Network");
            break;
        case NETWORK_TYPE_LAN:
            net.max_distance = 5000;    // 5km
            net.max_bandwidth = 10000;  // 10Gbps
            strcpy(net.name, "Local Area Network");
            break;
        case NETWORK_TYPE_PAN:
            net.max_distance = 100;     // 100m
            net.max_bandwidth = 100;    // 100Mbps
            strcpy(net.name, "Personal Area Network");
            break;
    }

    return net;
}