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Transmission media | What are they and how are they classified?

The communication is understood as a transfer of information from one site to another and the data transmission media They allow you to establish a bridge between the data source and the destination.

What are the means of data transmission

A data transmission medium It is the device that is responsible for making the electrical or optical link between the receiver and the transmitter, in order to be the bridge of the union established between the source and the destination.

A transmission medium can be a coaxial cable, a pair of wires and if you want air as such. However, regardless of the type, each data transmission medium is going to be characterized by noise, attenuation, interference, fading and other factors that will prevent free propagation of the signal in the middle.

Classification of transmission media

The data transmission media are classified into two large groups, the guided media and the unguided media:

  • Guided media – They are tangible media which are confined to a copper conduit, metal containers or fiberglass. In that case they are limited to their environment and will not get out of it, with the exception of small losses. They are also known as confined media or guided media.
  • Unguided media – They are also known as unguided media or wireless media and in this case they are not contained in materials such as copper conduits, fiberglass, etc. They are non-physical means through which the radio frequency signals that are spread advance.

Guided Transmission Media (Wired)

Metal cable – It’s a uninsulated wire which was the first means of data transmission once the telegraph was invented in 1844. Today the wires are protected with insulating materials. Regarding the conductive material, it can be aluminum, copper or another class of conductive materials. They are used in conduction applications for telephony, electricity, networks, etc. As for the semiconductors They are built with materials that behave as insulators and conductors, thus allowing the circulation of electrical current in only one direction.

Coaxial cable – It is a cable with a fixed central conductor (axial) that is on a sheath of insulating materials, which in turn has a metallic cover in the form of a mesh that is the second conductor. Regarding the outer layer, it is the one that prevents the signal from other cables and even electromagnetic radiation from interfering. It is used in the base band wave broadband. It is very useful for cable TV, CCTV, and the like.

Coaxial cable


  • Thin coaxial cable – It is a flexible medium, easy to install and very economical. Almost all the cables in this family belong to the RG-58 which has an impedance of 50 khms. It is noted that the impedance It is an opposition that occurs between the conductor or the circuit to the passage of current.
  • Thick coaxial cable – It is a cable with a conductor with a thickness greater than approximately 13 mm. It also has an impedance of 50 ohms and transmits signals up to 500 meters, thus allowing a maximum of 100 nodes for an entire segment.

Twisted Pair Cable – It is made up of copper conductors insulated by a plastic material and twisted in pairs. Its braiding characteristic is because reduces crosstalk, noise and interference. With respect to braiding is on average three braids per inch. If better results are sought, the braiding should be varied between different pairs. They are inexpensive, easy to connect, very flexible and therefore stands out against coaxial cable. Anyway, the distances are limited and this is a disadvantage.

Braided cable

Optical fiber – It is a means of communication that uses light confined in a fiberglass, in order to transmit large amounts of information that go in the order of Gigabits (1 x 109 bits) per second. For the transmission of the light beams a light source such as an LED or a laser diode is used. For the receiving part, a photodiode is used to detect the emitted light. Finally, it is required in turn to put at the end at the ends a converter of light (optical) to electrical signals. It is a technology that has advanced significantly and that is why its capacity has increased. In the area of telecommunications It is very popular and its power has been exploited to the maximum in the sector of Internet. Even medicine has taken advantage of it with laparoscopy, colposcopy and endoscopy.

Optical fiber

Structured cabling – In principle there were two main specifications: data cables and the voice cables. Currently there are several types of service that can be provided in the same type of cable. The standard for structured cable is EIA / TIA from the USA and is a Category 5 UTP twisted pair cable.

Structured cabling

  • Entrance to the building – It is the point where the external wiring interfaces with the backbone wiring that is inside the building. It is the entrance of the telecommunication service.
  • Equipment room – It is a centralized space in a building where the network equipment is housed.
  • Back wiring – Enables the interconnection between telecommunications cabinets, building entrance services and telecommunications rooms.
  • Telecommunications Cabinet – It is an area of ​​a building with the equipment of the telecommunications cabling system.
  • Horizontal cabling – System that extends from the telecommunications work area to the telecommunications cabinet.
  • Work area – It goes from the telecommunications plug to the devices or stations.

You can read more about: ELECTRIC CABLES | Types of cables, parts, colors and insulators

There is another type of classifications that is based on its meaning (signals)

  • Simplex – It allows information to be transmitted in one direction and continuously, a good example is the TV
  • Semi-Duplex – It allows information to be transmitted in two directions but not continuously but alternates one direction and the other in such a way that both directions never transmit at the same time, a good example is the walkie-talkie
  • Duplex (Full) It allows the transmission of information in both directions simultaneously, that is, they can send information at the same time and thus correct errors quickly and permanently, an example is the telephone

Advantages of guided (wired) transmission media

  • Transmission stability.
  • Possibility to protect yourself from interference.

Uses of guided (wired) transmission media

  • The conduction of electricity.
  • Conduction of fixed telephone networks.
  • Internet services.
  • Local area network applications.
  • Computer networks.
  • In medicine with fiber optics.

Unguided (wireless) transmission media

The unguided data transmission media are those who use the air as their means of transmission and in turn each transmission medium is a service that uses a band of the frequency spectrum. That range of frequencies is known as the electromagnetic spectrum.

Each frequency band or subset in the electromagnetic spectrum exhibits its unique properties that are a result of changes in wavelength. Therefore, each sub-band will provide a different service, thus making it possible to listen to the radio, talk on a cell phone, watch television, etc.

Antenna – It is a metallic device that It is used for the transmission and / or reception of electromagnetic signals. Its mechanism of action is based on transforming electrical energy into electromagnetic waves and a receiving antenna performs the reverse function.

Examples: Satellite dishes (in telecommunications) or wifi antennas (In Internet).

Terrestrial microwave

Infrared – This technology fell into disuse for cell phone communication although it is very useful in military tactics for night vision. It is used to link a transmitter with a receiver which have the ability to modulate non-coherent infrared light and lack the ability to pass through walls.

Bluetooth – It is a technology that enables the transmission of data and voice between two devices through a radio frequency link. This technology allowed communications between devices efficiently eliminating the presence of cables

WIFI – The technology that has acquired the most name in the world today, allows the wireless interconnection of various electronic devices that have the Wi-Fi function enabled (such as computers, smart-tv, video game consoles, music players). To use Wi-Fi, you need a modem that transmits the signal so that it is captured by the devices that connect to that network.

Advantages of unguided (wireless) transmission media

  • Ease of installation.
  • Few physical material requirements.
  • Greater field extension of the transmission signal.

Uses of unguided (wireless) transmission media

  • Mobile phone networks.
  • Wireless internet networks.
  • Radio in FM or AM Modulated Frequency.
  • VHF bands for television and UHF.
  • Satellite telecommunications.

You can continue reading: SYNCHRONOUS AND ASYNCHRONOUS TRANSMISSION | What is it and how it works?

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