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3.1.10

Outline the characteristics of different transmission media.

 

Teaching Note:

Characteristics include: speed, reliability, cost and security.

Transmission media include: metal conductor, fibre optic, wireless.


 

Sample Question:


From Sample Paper 1 2014:

 

JSR Notes:

(First of all note that this could be, and probably should be, simplified further.)

 

Media

First of all a bit about an oft misunderstood or mis-applied word: media. It's another one of those words that can be used in so many differnet ways, but think if it in whatever context as being something that is a conveyor of somethings, or a conduit of something. The news media conveys news, or the magnetic media used for hard drives is the substance to convey stored information to a computer, or even a psychic is the medium between the this world and those who have passed beyond!

Types of Data Transmission Media

Transmission media is a pathway that carries information across a network from sender to receiver. The pathway can be:

Wired - an electrical one, with a current carried along a "bound" wire.

Wireless - electromagnetic energy pulses of various frequencies transmitted through the air (or even water or a vacuum).

 

Wired Transmission Media

Wired network media are also called Guided Media or Bound Transmission Media. They are physical wires/cables of a particular, limited length. Common wired transmission media include twisted pair cable, co-axial cable and fiber optical cable.

 

Metal Conductors

Twisted Pair

Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference from external sources, such as other wires. It was invented by Alexander Graham Bell. The two most common examples of twisted pair cables are telephone cables and Ethernet cables.

Twisted pair cable

 

Ethernet CAT 6 cable & RJ-45 connector (top) vs.
Telephone cable & RJ-11 connector
     

Use

Speed

The two most common CATegories of Ethernet cables now-a-days are CAT 5e and CAT 6:

Reliability

Cost

Security

 

 

Coaxial Cables

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

 

Coaxial cable    &    BNC connector

 

Coaxial cabling has several distinct advantages over twisted pair. For starters, interference is less, due to the braided metal shield, and furthermore, it can support greater lengths of cables - up to 200 or even 500 meters.
"Thinnet" coaxial cabling is more common, but there is also "thicknet" coaxial cabling, which has thicker plastic protection to keep moisture out, though the thicker plastic makes it less flexible.

The main disadvantage is that it is harder to install and maintain (as I personally found, almost daily, with computer labs in Africa in the mid to late 90s) due to the difficulty of securely attaching and crimping the @#!!@!$# connectors.

Use

Speed

Reliability

Cost

Security

 

 

Fiber Optic

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference.

Fiber optic cable has the ability to transmit signals over much longer distances, and often at much faster speeds than coaxial and twisted pair, up to 1 Gbps or more. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify.

Here is a great video about how fiber optics works.

Fiber optic cable

Use

Speed

Reliability

Cost

Security

 

 

Wireless Transmission Media

Wireless media are also called Unguided Media or Unbound Transmission Media. Wireless transmission uses microwaves, high frequency radio waves, infra red waves, and even lasers, to transmit data.

Wireless transmissions can be categorized as line-of-sight or scattered broadcast. Infrared from your phone to another phone is a typical example of line-of-sight, in which each phone has to be facing the other with no obstructions. Scattered broadcast is what the WiFi routers in our classrooms use, where the transmissions bounce off walls and ceilings until they eventually hit the receiver in your laptop or phone.

The Wi-Fi Alliance, a global, non-profit organization, ensures standards and interoperability for wireless networks. The original Wi-Fi standard (IEEE 802.11) was adopted in 1997, and the latest, 802.11n, stipulates a maximum speed of 100 Mbps, and a typical range of 300+ feet. Wi-Fi networks use the Ethernet protocol.

Use

Speed

Reliability

Cost

Security

Wireless networks are much more susceptible to unauthorized use than cabled networks. Hackers can eves-drop on unencrypted transmissions. Encryption across wireless networks is the best defense, using encryption standards such as WEP. Refer to assessment statement 3.1.15, and 3.1.16 for more on the security of wireless networks.

 

Final Points/Links

Do note that the speed of network activity is measured in bits per second, not bytes per second. So 50 Gbps is 50 Gigabits per second. This is tradition since most often data is transferred serially, one bit at a time. Whereas when referring to storage amounts, we use Byte, so Megabytes, Gigabytes and so on.

This is a great article about the different kinds of Internet services, and media involved.

https://www.youtube.com/watch?v=0TZwiUwZwIE for a wonderful video about laying a trans-Atlantic Internet cable.