Two main types of network devices
Networks ranging from home installations to the Internet use two basic categories of devices: end devices and intermediary devices. End devices originate or receive data, while intermediary devices forward it between devices and networks. The same system can perform more than one role, depending on its software and forwarding functions.
End devices (hosts)
End devices are the sources and destinations of communication on a network. Users often interact with them directly, but a host can also run services without direct user control. A device of this type is called a . The network carries data between these endpoints.
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 its software, an end device can perform one role, or combine several roles, in a communication session:
- Client: A host that requests information or services from a server. A browser acts as a client when it retrieves a webpage.
- Server: A host that provides information and services to other clients on the network. A web server provides webpages to browsers.
- Dual role: A host can act as a client and a server at the same time. In a peer-to-peer (P2P) file-sharing application, a computer downloads files from other hosts and uploads its own files.
Intermediary devices
Intermediary devices forward data between hosts and between networks, forming an internetwork. Their tasks depend on the device type and layer. A repeater regenerates a signal, a switch forwards frames, a router selects the next hop, and a firewall filters traffic.
Core functions of intermediary devices
- 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 communication failures: Some devices report link problems, which supports diagnosis and route changes.
- Direct data along alternate pathways after a link failure: Routing mechanisms can select another path when the network has a backup connection.
- Classify and direct messages according to QoS priorities: Devices with quality-of-service functions can allocate resources to voice and video traffic before data that is less sensitive to delay, such as email.
- Permit or deny the flow of data based on security settings: Firewalls filter traffic according to access-control rules.
Common intermediary devices and their symbols
Network diagrams use established symbols to represent devices. Recognizing them helps readers interpret connections and design a topology.
- Access devices, such as switches, hubs, and wireless access points: These devices connect hosts to the network.
- Internetworking devices, such as routers: These devices connect multiple networks into an internetwork.
- Communication servers and modems: These devices concentrate user dial-in access or convert signals for different media.
- Security devices, such as firewalls: These devices filter traffic according to security rules.