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 in terms of transmission media you can think of it, in whatever context, as being something that is a conveyor of something, 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. (The way this works at a physical level is very complicated, but here are a couple of videos to send you off on the right direction if you want to invsigate it: link 1, link 2 (particularly 16:40 - 17:15)). Twisted pair 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

• Twisted pair is commonly used for Ethernet LAN networks, and for telephones. CAT 5 & 6 "Ethernet" cables are what make up most of the network cabling of our school, and most LANs. Because of this twisted pair, or unshielded twisted pair (UTP) cables are often just referred to as Ethernet cables.

Speed

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

• "CAT 5e" Ethernet cables can get up to 1 Gbps
• "CAT 6" Ethernet cables can get up to 10 Gbps.

Reliability

• The most widely used twisted pair cable is UTP (unshielded twisted pair) - like for Ethernet. It is lightweight, thin and flexible, reliable under 100 meters, and inexpensive. But over 100 meters, data loss can occur due to signal degradation and propagation delay. Even though the twisting of the wires helps, UTP cables are still somewhat sensitive to electromagnetic interference, which we technically refer to as noise. This noise can come from such things as electric motors and electric lights etc. This can impede on the performance of UTP cables.

Cost

• Twisted pair cables are relatively cheap as compared to other forms of wired media both in terms of manufacturing and installation. And they are most certainly cheaper than fiber optic.

Security

• Unless run through metal conduit tubing that is buried with in the concrete walls of a building, twisted pair cables are quite susceptible to physical hacks. By simply clamping onto the wires within the cable one can setup a physical connection to the already existing network. See the following YouTube video for more details 4 Clever Ethernet Cable Hacks
• Security really depends more on other features of the LAN such as authentication and encryption.

 

 

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.

A main disadvantage is that it is older, slower technology. Also, 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

• For home Internet access using existing TV cable lines and cable modem.

Speed

• Coaxial cables thinnet and thicknet cables have speeds of 10 Mbps, so slower than current twisted pair standards.

Reliability

• Coaxial cables due to its shielding are less susceptible to outside electromagnetic interference noise, as compared to twisted pair.
• Thinnet cables are very reliable up to lengths not exceeding 200 meters. Thicknet is reliable up to 500 meters.

Cost

• Compared to UTP cables, coaxial cables themselves are slightly more expensive, but they do not require any network device if you wanted to link one or no more than 15 computers together in what is known as a "daisy chain" system through T-Junction connectors.
• In terms of home Internet access, if they already exist for cable, there is no additional costs for cables, and cost of Internet access is often bundled with TV delivery.

Security

• It is quite difficult to do a physical hack on this type of cable, compared to twisted pair. But if the cables are shared through a residential community, there are still security issues.

 

 

Fiber Optic

Fiber optic cabling consists of a center glass core or multiple cores 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 10 Gbps and more. The cost of the fiber optic cabling is comparable to copper cabling; however, with the equipment needed it is more expensive, and it is more difficult to install and modify.

Here is a great video about how fiber optics works.

Fiber optic cable

Use

• Mainly for the backbone of LANS, but increasingly for the whole network itself.

Speed

• Typically 1 Gbps, though ranging from 100 Mbps to 10s of Gbps.

Reliability

• Fiber optics cables are impervious to electromagnetic interference. They can run up to distances of 2 Kilometers.

Cost

• Fiber optics cables are expensive to manufacture, install and implement, both the fiber optic cables themselves, as well as the specialized connectors and signal equipment. It depends on the type and the number of cores, but including set-up, it can cost from around $2 USD per meter all the way up to tens of USD per meter.

Security

• Due to the nature of the type of signal transmission that is used which is light, this makes physical hacks of the cables practically impossible.

 

 

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 100+ meters. Wi-Fi networks use the Ethernet protocol.

Use

• For places where people use mobile devices - which is just about everywhere today.

Speed

• 802.11n, stipulates a maximum speed of 100 Mbps, and a typical range of 200+ meters.

Reliability

• Generally fine, with the major exception of security issues.
• But with every passing year, it is increasingly reliable, with technological advances from 2G to 3G to 4G, but still no where near as reliable as wired networks.

Cost

• The costs are down all the time, with the spread of wireless technology.

Security

Wireless networks are much more susceptible to unauthorized use than cabled networks - and no physical access to cables etc. is necessary. 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.

 

Summary:

	Speed	Reliability	Cost	Security
Metal - Twisted Pair (Ethernet)	100 Mbps - 10 Gbps	Good	Low	Good
Metal - Coaxial	Slow - 10 Mbps ***	Better	Low	Better
Fiber Optic	100 Mbps - 10 Gbps	Best	High (incl. set-up) ***	Best
Wireless	100 Mbps max.	Not too bad, but...	Not too bad	Issues ***

 

 

 

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.