Bandwidth is the capacity of a wired or wireless network communications link to transmit the maximum amount of data from one point to another over a computer network or internet connection in a given amount of time -- usually one second. Synonymous with capacity bandwidth describes the data transfer rate. Bandwidth is not a measure of network speed -- a common misconception.
While bandwidth is traditionally expressed ;bits per second (bps), modern network links have greater capacity, which is typically measured in millions of bits per second (megabits per second, or Mbps) or billions of bits per second (gigabits per second, or Gbps).
Bandwidth connections can be symmetrical, which means the data capacity is the same in both directions to upload or download data, or asymmetrical, which means download and upload capacity are not equal. In asymmetrical connections, upload capacity is typically smaller than download capacity.
How bandwidth works
The more bandwidth a data connection has, the more data it can send and receive at one time. Bandwidth can be compared to the amount of water that can flow through a water pipe. The bigger the pipe, the more water can flow through it at one time. Bandwidth works on the same principle. So, the higher the capacity of the communication link, or pipe, the more data can flow through it per second.
End users pay for the capacity of their network connections, so the greater the capacity of the link, the more expensive it is.
The maximum capacity of a network connection is only one factor that affects network performance. Packet loss, latency and jitter can all degrade network throughput and make a high-capacity link perform like one with less available bandwidth. An end-to-end network path usually consists of multiple network links, each with different bandwidth capacity. As a result, the link with the lowest bandwidth is often described as the bottleneck, because the lowest bandwidth connection can limit the overall data capacity of all the connections in the path.
Considerations for calculating bandwidth
Technology advances have made some bandwidth calculations more complex, and they can depend on the type of network link being used. For example, optical fiber using different types of light waves and time-division multiplexing can transmit more data through a connection at one time, which effectively increases its bandwidth. In wireless networks, bandwidth is defined as the spectrum of frequencies operators license from the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration for use in mobile services in the U.S.
Effective bandwidth, which is the highest reliable transmission rate a link can provide, can be measured using a bandwidth test in which the link's capacity is determined by repeatedly measuring the time required for a specific file to leave its point of origin and successfully download at its destination.
In addition to testing, organizations need to calculate how much bandwidth they need to run all of the applications on their networks. To find out how much capacity they need, organizations need to calculate the maximum number of users who might be using the network connection at one time, then multiply that number times the bandwidth capacity required by each application.
To calculate needed bandwidth for the cloud, it's important to know the capacity needed to send and receive traffic from public clouds. Capacity can be affected by any congestion on the connections used to reach public cloud providers, particularly if that data is traveling over the internet.
Bandwidth on demand
In addition to dedicated communication links with maximum amounts of available bandwidth, which is typically sold at a set price by the month, bandwidth on demand -- also called dynamic bandwidth allocation or burstable bandwidth -- is an option that allows subscribers to increase the amount of available bandwidth at specific times or for specific purposes. Bandwidth on demand is a technique that can provide additional capacity on a communications link to accommodate bursts in data traffic that temporarily require more bandwidth.
Rather than over-provisioning the network with expensive dedicated links, dynamic bandwidth allocation provided by service providers is frequently used in wide area networks to increase capacity as needed for a particular event or at a particular time of day. Using this technique, bandwidth on a shared telecommunications network can be increased, and users pay for only the additional bandwidth they consume.
Burstable bandwidth is available through many service providers, because the network links they provide to customers have additional bandwidth available through them, but customers pay only for the capacity they need. For example, a 100 Mbps link might be able to burst up to a gigabit because the service provider's connection has available capacity. If a user needed more than the absolute maximum bandwidth available on that link, another physical connection would be required.
Occasionally, a service provider will allow customers to burst above their subscribed bandwidth cap without charging additional usage fees.
SD-WAN eases bandwidth needs
Software-defined WAN technology provides customers with extra capacity because it makes bandwidth from multiple connections, rather than one, available to users. These often include a Multiprotocol Label Switching (MPLS) connection or other types of dedicated bandwidth link, plus a broadband internet link or cellular connection.