Characteristics

In a computer network, every device or component connected to the network is referred to as a node. A node can be a sender or a receiver of data. Nodes may be destination nodes, which consume the data sent to them. Nodes may also be forwarding nodes, which do not consume the data but forward the data to the next node to the intended destination node.

Emails, documents, web pages, images, videos, audio, or any other information sent over a network are broken up into something referred to as data packets. A data packet is a formatted unit of data carried by a network. A packet consists of control information and a payload. The payload is a part of the actual data that is being transmitted over the network. Control information is used by nodes to deliver the payload to the correct destination to ensure that the integrity of the data is maintained during the transmission.

Networks can be classified by many characteristics, including size and scope, performance, connection type and communication protocol.

This is an example of what a complex network can look like. Computing devices connect with each other to form a network, and such networks connect to other networks to form a network of networks.

Size and Scope

The size of a network is measured by the number of nodes (computing devices) and how they spread out over distance and geography. The size is an important aspect to consider since the design of the network in terms of the components used (switches, routers) and the connection medium (wired or wireless) depends on the distance data packets may need to travel.

The scope of a network is an indication of the number of users and their relationship with each other. The number of users and their relationship to each other determines the level of security that must be enforced to prevent misuse of the network and to prevent users from accessing other connected computing devices without authorization.

Let's see three examples:

• Personal Area Network (PAN)

  A personal area network connects computing devices located in close proximity such as in a house and is used by a small number of people with a high degree of trust, usually the members of a family. Such networks have a simple configuration with basic security and generally do not connect to any other PAN.

  The smallest network could be considered to have just two devices, for example, your computer and printer.

• Local Area Network (LAN)

  A local area network connects computing devices over larger areas, such as schools and offices within a building, and is used by a fairly large number of users, from a few hundred to a few thousand. The users belong to the same organization and there is a fair amount of trust between users. Such networks may need powerful and multiple network components, and the security needs to be higher than that of a PAN.

• Wide Area Network (WAN)

  A wide area network connects computing devices over very large areas ranging from multiple buildings on campus, buildings across a city or a country and finally, buildings across countries. Such large networks may have hundreds of thousands of users across wide geographies and possibly from multiple organizations. Such networks need extremely powerful and multiple network components and a very high level of security.

  A WAN is usually a network of LANs, and larger WANs are networks of smaller WANs.

The Internet

The largest network is the Internet which has billions of computing devices connected to each other. The Internet can be considered to be the mother of all networks since almost every PAN, LAN and WAN (and therefore all the computing devices on those networks) is connected to the Internet and therefore indirectly to each other. The devices, communication channels, and protocols are very powerful and sophisticated, and the security controls are of the highest level possible.

Performance

Network performance is a measure of how quickly data packets travel between the sending and receiving computing devices. When users send or receive data over a network, they need reliable and fast data transmission. A high-performance network is required to provide a good user experience, especially in solutions such as video streaming and cloud computing.

Several factors influence the performance of a network. The distance between the source and the destination, the number of interconnected networks in the path, the quality of the network equipment, and the quality of the transmission medium can all add to the delays in transmitting data, thus degrading network performance.

The following two measures of network performance are most relevant to the average user (while network engineers use many more measures):

• Bandwidth:

Bandwidth is defined as the maximum data transfer capacity of a network between any two nodes (devices). In other words, it is a measure of how much data can be sent and received over the connection between two nodes in a given period. Bandwidth is technically measured in bits per second (bps) but gives the generally high bandwidth of modern networks measured in megabits per second (Mbps) or gigabits per second (Gbps).

• Throughput:

Throughput is defined as the actual amount of data that is transmitted between any two nodes on a network. While the network may have a rated bandwidth, other factors can determine how much data is actually transmitted successfully in a given period.

Toll Booth Analogy

Bandwidth and throughput are closely related. The relationship can be understood with an analogy of toll booths on a highway. A 6-lane highway can be assumed to have a bandwidth sufficient for 6 cars to go through without stopping. If 6 toll booths are added to the highway, the bandwidth will still be sufficient for 6 cars. As the number of cars increases, the load is exceeding the bandwidth and the cars will have to queue up at the toll booths, taking longer to get through.

On the same 6-lane highway, if the number of toll booths is reduced to 3, the 6 cars would take longer to get through, effectively reducing the throughput to less than the bandwidth.

Building wider highways is expensive. So if the maximum expected peak load is 6 cars, building a 12-lane highway and 12 toll booths will be a waste of bandwidth. Bandwidth is also expensive, so similarly, when setting up a network or buying bandwidth the expected data volume should be carefully estimated.

A consequence of low bandwidth or low throughput is increased latency, which is the time taken for data packets to reach from source to destination. Video streaming, voice calls and other such applications required high volumes of data to be transmitted with very low latency so their bandwidth and throughput requirements are high. Browsing websites with text or images or exchanging emails or text messages requires much lesser bandwidth and throughput.

When setting up a network at home or in an office, for optimal performance, both bandwidth and throughput must be measured. If your service provider offers a 16 Mbps connection, but it is shared with 15 other users, your throughput could effectively be only 1 Mbps, whereas if it is 16 Mbps dedicated to you, you would get a throughput of 16 Mbps.