Network Elements

Four elements of a network

A basic model of a communication network distinguishes four elements. Distinguishing them organizes the description of network operation: the data being transmitted, the transmission method, the source and destination, and the rules governing communication.

• Messages (packets and frames): These are information units carried through the network. A longer message is divided into smaller blocks that can be packets or frames, depending on the layer and technology.
• Network devices: These are physical hardware components that send, receive, and forward messages. They form the physical part of the network.
• Transmission medium: This is the physical channel through which a message reaches its destination from its source. It can be a cable, an optical fiber, or free space for radio transmission.
• Rules (protocols): These are sets of rules and agreements that define how messages are formatted, transmitted, routed, and interpreted. They enable devices from different vendors to exchange data.

A closer look at network devices

Network devices fall into two main categories: end devices, which originate or receive data, and intermediary devices, which forward data and connect network segments. The classification depends on the device's role in a particular flow.

End devices (hosts)

An end device, or a host, is where network applications run and where data communication starts or ends. Its interface can have a network address, such as an IP address.

Examples of end devices: Desktop computers, laptops, servers, network printers, VoIP phones, security cameras, and mobile devices such as smartphones, tablets, and barcode scanners.

Depending on its software, a host can perform one role or combine several roles in a communication session:

• Client: A host that requests information or services from a server.
• Server: A host that provides information or services to clients.
• Dual role: A device can act as both a client and a server at the same time, depending on the application. In a peer-to-peer (P2P) application, a computer downloads files from other hosts and shares its own files.

Intermediary devices

Intermediary devices forward data between hosts and networks, forming an internetwork. They connect hosts to a network segment or connect several networks. Their operation depends on the device type and the layer at which it operates.

Examples of intermediary devices: Access devices such as hubs, switches, and wireless access points, as well as devices that connect networks, such as routers.

Functions of intermediary devices

These devices can perform the following functions related to data flow:

• Regenerate and retransmit signals: Repeaters restore a signal and send it onward, extending the transmission section.
• Maintain information about network paths: Routers build and update routing tables to select the next hop for a packet.
• Notify other devices of errors and failures: Some devices report link problems, which supports diagnosis and route changes.
• Direct data along alternate pathways in case of a link failure when a backup connection is available.
• Classify and direct messages according to Quality of Service (QoS) priorities.
• Permit or deny the flow of data according to access-control rules.

Network media: transmission paths

A transmission medium is the physical channel through which messages travel from source to destination. Media types differ in their characteristics, costs, and performance levels, and they require different signal-encoding methods.

Types of media and signal encoding

• Metal wires within cables (copper media): This is a commonly used type of cabling, including coaxial and twisted-pair cables.
  • Signal encoding: Data is represented by patterns of electrical impulses.
• Glass or plastic fibers (fiber-optic media): These cables transmit data as pulses of light, providing high speeds and resistance to electromagnetic interference.
  • Signal encoding: Data is represented by pulses of light, typically in the visible or infrared spectrum.
• Wireless transmission: Data is transmitted using electromagnetic waves, such as radio waves.
  • Signal encoding: Data is represented by patterns and modulations of electromagnetic waves.