Bandwidth is the maximum amount of data a network connection can carry in a given time, usually stated in megabits per second (Mbps) or gigabits per second (Gbps). When a provider sells a “500 Mbps” or “1 Gig” service, the number is the bandwidth. It sets the ceiling on how much traffic a site can send and receive at once, but it is not the same as how fast things feel, which also depends on latency, congestion and the equipment along the way.
At a glance
- Bandwidth is capacity: how much data per second a connection can carry, not how quickly a single packet arrives.
- It is measured in bits per second (Mbps, Gbps); file tools often show bytes per second, which is eight times smaller.
- Services may be symmetrical (same speed up and down) or asymmetrical, as many broadband plans are.
- What you are promised varies: broadband is usually sold as an “up to” speed, while dedicated services commit to a rate.
- More bandwidth helps only when the connection is actually full; it does not cure latency or packet loss on its own.
What problem it solves
Every application at a site shares the same connection. Video meetings, cloud applications, phone calls, software updates, backups and guest Wi-Fi all draw on it at once. When their combined demand exceeds the available bandwidth, traffic queues and some of it is dropped, and people experience slow pages, frozen video and long transfers.
Sizing bandwidth correctly is how a buyer avoids that. Too little and the site congests at busy times; too much and the business pays every month for capacity it never uses. Knowing what bandwidth is, and what it is not, also helps a buyer tell whether a performance problem is really a capacity problem or something else.
How it works
Port speed versus purchased rate. A circuit is delivered on a physical port, such as 1 Gbps or 10 Gbps Ethernet. The bandwidth you buy may equal the port speed or be a lower rate enforced by the provider, for example 300 Mbps on a 1 Gbps port. That leaves room to upgrade without new hardware.
Committed versus best-effort. With dedicated internet access, the provider commits to a rate, often called the committed information rate, and some services allow a burst rate above it. With broadband, the advertised figure is usually a maximum shared with other customers, so actual speeds vary by time of day.
Throughput. The data rate an application actually achieves is called throughput. It is lower than the bandwidth because of protocol overhead, and it can fall further because of congestion, Wi-Fi conditions, distance to the server, latency and how the application handles it.
Sharing inside the site. Bandwidth is also a limit on internal links, from Wi-Fi to switch uplinks. When the internet link is busy, Quality of Service (QoS) settings can give voice and video priority so they degrade last.
When it matters for buyers
- Opening or moving an office. Size the connection from headcount, planned applications and growth, and check what each provider can actually deliver at the address.
- Moving to the cloud. Shifting files, phones or applications to cloud services moves traffic that used to stay on the local network onto the internet link, especially uploads.
- Adding video or voice. Real-time traffic needs consistent capacity in both directions, so upload bandwidth matters as much as download.
- At renewal. Bandwidth prices often fall over time in competitive markets, so an older contract may buy more capacity for the same spend.
- When users complain. Look at utilization graphs before upgrading; if the link is not near capacity, the cause is probably elsewhere.
For help comparing services and sizing a site, see our internet access solution page.
Questions to ask vendors
- Is the bandwidth committed or best-effort, and what speed can we expect at our busiest hour?
- Is the service symmetrical? If not, what is the upload speed?
- What is the physical port speed, and how quickly can we upgrade the rate on the same port?
- Is bursting above our rate allowed, and how is it billed?
- Where is the rate measured, and what happens if we consistently get less than we pay for?
- Do you provide utilization reports so we can see how full the connection is?
How it differs from latency
Bandwidth and latency are often lumped together as “speed”, but they measure different things. Bandwidth is how much data a connection can carry per second; latency is how long it takes data to get from one end to the other. A wide highway with a long drive is high bandwidth and high latency. Large downloads and backups depend mostly on bandwidth, while voice calls, video meetings and interactive applications are often more sensitive to latency. Adding bandwidth does not shorten the distance data travels, so a connection can be “fast” on a speed test and still feel sluggish.