The Two Main Types of Network Devices

Every network, from a simple home setup to the global Internet, is built using two fundamental categories of devices: end devices and intermediary devices. Each plays a distinct but essential role in making communication possible.

End Devices (Hosts)

End devices are the starting points and destinations for all communication across a network. They are the devices that we, as users, interact with directly. They are often called hosts. The primary purpose of a network is to facilitate communication between these end devices.

Examples of End Devices

• Computers: Desktops, laptops, file servers, web servers.
• Network Printers: Printers that can be accessed over the network.
• VoIP Phones: Phones that make calls over the Internet instead of a traditional phone line.
• Security Cameras: Cameras that transmit video feeds over the network.
• Mobile Devices: Smartphones, tablets, barcode scanners, and PDAs.

Roles of Hosts

Depending on the software installed, an end device can play different roles in a communication session:

• Client: A host that requests information or services from a server. For example, your web browser acts as a client when it requests a webpage.
• Server: A host that provides information and services to other clients on the network. For example, a web server provides webpages to browsers.
• Dual Role: A host can simultaneously act as both a client and a server. For example, in a peer-to-peer (P2P) file-sharing application, your computer can both download files from others (acting as a client) and upload files to others (acting as a server).

Intermediary Devices

Intermediary devices connect the end devices to one another and can connect multiple individual networks to form an internetwork. They are the "plumbing" of the network, ensuring that data flows correctly and efficiently from its source to its destination.

Core Functions of Intermediary Devices

• Regenerate and retransmit signals: They clean up and strengthen communication signals to allow them to travel over longer distances.
• Maintain information about network pathways: Devices like routers build and maintain routing tables to make intelligent decisions about the best path for data.
• Notify other devices of errors and communication failures: They can send alerts about network problems, helping with diagnostics and rerouting traffic.
• Direct data along alternative pathways in case of a link failure: They provide redundancy, ensuring the network stays up even when some connections break.
• Classify and direct messages according to priorities (QoS): They can prioritize critical traffic, like voice calls or video streaming, over less time-sensitive data, like emails.
• Permit or deny the flow of data based on security settings: Devices like firewalls act as security guards for the network.

Common Intermediary Devices and Their Symbols

Network diagrams use standardized symbols to represent different devices. Understanding these symbols is key to reading and designing network topologies.

• Access Devices (e.g., Switches, Hubs, Wireless Access Points): These devices connect hosts to the network.
• Internetworking Devices (e.g., Routers): These devices connect multiple networks together (creating an internetwork, or "internet").
• Communication Servers and Modems: These devices concentrate user dial-in access or convert signals for different media.
• Security Devices (e.g., Firewalls): These devices provide security by filtering traffic.