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A network, in computing, is a group of two or more devices or nodes that can communicate. The devices or nodes in question can be connected by physical or wireless connections. The key is that there are at least two separate components, and they are connected.
The scale of a network can range from a single pair of devices or nodes sending data back and forth, to massive data centers and even the global Internet, the largest network in existence. What all of these networks have in common, from the smallest ones to the largest, is that they allow computers and/or users to share information and resources. Networks may be used for:
Communications such as email, instant messaging, chat rooms, etc.
Shared hardware such as printers and input devices.
Shared data and information through the use of shared storage devices.
Shared software, which is achieved by running applications on remote computers.
One way to understand networks is to look at examples of large-scale networks as they have developed over the past few decades: for example, computer networks of the late 1950s included the U.S. military’s Semi-Automatic Ground Environment (SAGE) and the commercial airline reservation system called the Semi-Automatic Business Research Environment (SABRE).
Based on designs developed in the 1960s, the Advanced Research Projects Agency Network (ARPANET) was created in 1969 by the U.S. Department of Defense and was based on circuit switching – the idea that a single communication line, such as a two-party telephone connection, deserves a dedicated circuit for the duration of the communication. This simple network evolved into the present day Internet.
Another way to look at networks is to understand the evolutions in how they have been built over time. Again, a network is simply any collection of connected hardware pieces or node points. From the simplest link between two servers to the gigantic global Internet, all of that spectrum consists of network activity.
A history of evolving networks can help provide a better picture of what networks look like now, and what they've looked like in the past.
The first computer networks were links between physical workstations, personal and desktop computers either linked by ethernet cabling, or later, wirelessly connected. Each computer had its own physical hard drive, and the hard drives of the computers were often represented by different drive letters on the workstation’s operating system interface and different kinds of software applications. A user could go onto a physical computer with its own drive, pull from the computer’s drive, or log onto network software to access the drive of a different computer in a different part of a room or building.
In these early setups where end-users often selected access to a networked drive from a drop-down list, engineers used specific network topologies to link these workstation components together.
Hub, ring, bus, star and tree topologies were some of the common networking structures used to allow the individual computers to “talk” to one another and share information. The computers were usually co-located in a particular building but perhaps networked throughout various rooms or offices.
Later, the virtual network emerged along with other virtualized computing processes. This happened in conjunction with the practice of remote networking, as the cloud and other innovations promoted wide-area network designs.
Virtual computing is the practice of abstracting a physical hardware device into a logical partition with the same attributes in terms of processing power and available memory. A virtual machine is a logical representation of a traditional hardware computer with its CPU and RAM delivered by a pool of resources in the system.
Along with virtualization in general came virtual networks.
Today, we have virtual local area networks (virtual LANs) where logical partitions are built on top of physical network nodes.
The virtual LAN uses the OSI data link layer (also referred to as layer 2) to facilitate this kind of transmission. Here, engineers build these virtual networks within the physically connected physical hardware nodes.
For instance, in a traditional LAN, the components of the network were physical devices like hubs, routers, switches and firewalls. In a virtual LAN, the pieces of a network use a physical connection as a highway, and a physical server or CPU/RAM bearing component as a kind of “host.” The OSI model allows for sending packets to different network destinations over the very same physical cabled or wireless connection.
This understanding of networks shows how much different today’s networks are, and how abstracted they have come to be in modern computing.