What is network bandwidth?

Network bandwidth is the maximum amount of data that can be transmitted over a communication channel per unit of time.

Traditionally measured in:

• bits per second (bps)
• Kbit/s, Mbit/s, Gbit/s

Short phrasing for the interview:

Bandwidth is the maximum data transmission speed that a network channel can provide.

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#A simple example for understanding

Picture a pipe:

• the wider the pipe,
• the more water flows through it per second.

In networking, the "width of the pipe" is the bandwidth of the channel.

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#How bandwidth differs from other metrics

#1. Bandwidth ≠ actual speed (Throughput)

• Bandwidth is the theoretical maximum
• Throughput is the real speed you get in practice

Over a 1000 Mbit/s link, the actual traffic may run at 930-950 Mbit/s due to overhead, delays, and load.

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#2. Bandwidth ≠ latency

• Bandwidth is how much data can be transferred
• Latency is how fast a packet travels the path

A comparison:

• A road can be wide (large bandwidth) but long (high latency).

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#3. Bandwidth ≠ useful throughput (Goodput)

Goodput is useful data without overhead traffic (TCP, headers).

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#What bandwidth depends on

#1. Type of transmission medium

• twisted pair (Fast Ethernet 100 Mbit/s, Gigabit 1 Gbit/s)
• fiber optic (10G, 40G, 100G+)
• Wi-Fi (real speeds are lower than advertised)
• mobile networks (4G, 5G)

#2. Equipment characteristics

• switch/router ports
• radio modules
• cable quality (Cat5e/6/6a, etc.)
• frequencies and channels in Wi-Fi

#3. Channel load

The more users/packets, the lower the actual speed.

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#Bandwidth examples (illustrated)

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#Where bandwidth matters

• transferring large files within a LAN
• 4K/8K streaming
• video conferencing
• server load
• cloud services
• gaming platforms / multimedia
• communication channels between data centers

If bandwidth is narrow, a "bottleneck" appears.

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#How to explain this in an interview

Network bandwidth is the maximum data transmission speed a communication channel can provide. It is measured in bits per second and depends on the transmission medium, equipment, and network characteristics. Bandwidth shows the theoretical maximum, unlike throughput, which reflects the real speed.

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#Cheat sheet (5 seconds before the interview)

• Bandwidth = maximum data volume/second.
• Measured in Mbit/s, Gbit/s.
• Bandwidth ≠ throughput (real speed).
• Depends on the medium (cable, Wi-Fi, fiber) and equipment.
• Determines how "wide" the channel's pipe is.