The term bandwidth originates from the field of signal processing.
There, the bandwidth is the relevant parameter for the width of a frequency band. The width of a frequency band is determined by a lower and upper frequency. In the context of data transfers, however, the data throughput in a medium is described as a bandwidth. The following article refers to this definition

What does the bandwidth depend on?

The bandwidth of a data connection depends on the transmission medium and the used protocols. Each protocol specifies different requirements and values for a maximum possible bandwidth.

What is transmission media?

A transmission medium is the physical path that a signal takes from a source to a destination. The path can be wired, a radio signal or an optic transmission. Other types of transmission, e.g. through sound waves in the water, are also possible. However, these only occur in practice for special applications.

If multiple participants share the same transmission medium, the medium is called a shared medium. A shared medium has a disadvantage that with more participants sharing the same medium, the lower the bandwidth for each participant is.

Wired transmission

Wired tranmission media are usually made of copper. The transmission takes place with the help of low or high frequency signals. For network connections that use the standard 1000BASE-T, the copper cable is used exclusively between transmitter and receiver. The same is true für direct connections like RS-232 (serial port).

The following technologies use the cable as shared medium:

  • old network technologis like 10-BASEt (10 MBit/s over coaxial cable) or Token Ring. By using the CSMA/CD media access control method multiple partipciants can send and receive on the same cable.
  • ADSL/DSL use the same copper cable which is also used for telephony. Signals for DSL are transmitted in a another frequency band than telephony signals.
  • Internet access over cable, e.g by using Comcast XFINITY. Besides the fact that TV and Internet signals are shared by using the different frequency bands, the same cable is also used by multiple houses and apartments.

Wireless transmission

The wireless transmission of signals takes place via the air. The signals are sent via the antennas and receive.
Due to the principle, air is a Shared Medium. The best known protocols, transmitted over the air, are

  • WLAN (IEEE 802.11)
  • GSM
  • and 3G/4G/5G

Optical transmission

When using the light path, fiber optic cables are used. The signals are transmitted as an electromagnetic wave. In contrast to copper, glass fiber is a bit more expensive in material costs, but it allows a much higher bandwidth.

What are protocols?

Protocols define how a transmission of data has to be done. In principal it does not matter, which tramission medium is used.

Diplomatic protocols define the dress code or seating plan during official state visits. This allows a structured and regularized conversation between different participants without any misunderstandings due to cultural differences.

In communications engineering, the principle of a protocol is the same: it determines how different participants in a communication must transmit their data. The OSI model is relevant for understanding protocols and how they work together. It defines seven different layers. Each of these layer has a specific task. Each of these layers has a specific task. A protocol specifies how this task is technically implemented. Depending on the requirements, there are different protocols that fulfill the same task. The protocols themselves are specified by experts of different companies and organizations inside so called Request for Comments (RFC).

For the bandwidth of a connection, the layer 0 and layer 1 are mainly relevant. The layer 0 does not exist officially, but designates the underlying transmission medium. Layer 1 specifies the different protocols like 1000BASE-T. The WLAN specification IEEE 802.11 spans over layer 1 and layer 2.

How can a bandwidth be improved?

A bandwidth of a technology, e.g. WLAN or DSL, is limited by

  • physical properties
  • the amount of participants using the same medium
  • the protocol in use

It is therefore not possible to signifcantly increase the bandwidth of an already optimally established connection
improve. The only alternatives are

  • to change to another tranmission medium from a shared medium like air/WLAN to cable
  • to change the protocol, e.g. from WLAN IEEE 802.11b to 802.11n
  • to remove any existing source which is jamming the signal, e.g. defect cables or microwave ovens

Changing to a higher tariff of your internet provider improves your effective bandwidth. The original bandwidth of the transmission medium will be the same. It has been artificially lowered by your provider.

Can a proxy server improve the bandwidth?

A proxy is a server between source and target. Each requests to the target will by intercepted by the proxy. The proxy itselfs as the target for the response. The response is cached on the proxy server. If the same request has been already made before, the proxy can easily retrieve the old response from its local cache. The response to the source will be faster, the bandwidth itself won’t improve.

Can the bandwidth be improved by using compression?

Compression means that duplicates are removed within a stream of data. Videos streamed by Netflix, YouTube or Amazon Prime are compressed. For example the same-looking image information between two frames are simply removed in the next frame.
The removal of the image information means that the bandwidth is better utilized. An improvement The bandwidth can not take place through compression.

What is the difference between upload and download?

The upload is the available bandwidth when data is transmitted from the source, e.g. B. your notebook or Smartphone, to the destination. A higher upload for example allows you to post videos on YouTube faster.
The download is the available bandwidth with which data is received on the source after target has been requested. With a higher download bandwidth, YouTube allows you to receive faster a video stream in a better quality.

The same bandwidth of upload and download is called symmetrical. As a private person it is is difficult to order products with symmetrical bandwidths. Most products are only provided to companies.
If the the bandwidth of upload and download differs, it is called asymmetrical. In almost all cases for internet connections, the bandwidth of downloads is much higher than the bandwidth for upload.

How is the bandwidth measured?

The bandwidth is measured in bit.

  • 8 Bits = 1 Byte
  • 1000 Bytes = 1 KiloByte (= 8000 Bit)
  • 1000 KiloByte = 1 MegaByte (= 1.000.000 Byte = 8.000.000‬ Bit)
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