Guided and Unguided Media of Communications
Telecommunication links can broadly be classied into two categories, namely, guided media (wired) and unguided media(wireless). Both media are used for short distance (LANs, MANs) and long distance (WANs) communication.
As the name indicates, in guided media
- Electrical/Optical signals are passed through a solid medium (different types of cables/wires)
- As the path traversed by the signals is guided by the size, shape and length of the wire, this type of media is called guided media. Also, in guided media, the signals are confined within the wire and do not propogate outside of the wire/media.
- E.g., Copper Unshielded Twisted Pair (UTP), Copper Shielded Twisted Pair (STP), Copper Co-axial cables, Fiber Optic Cables.
Twisted Pair Copper:
- It is the most widely deployed media type across the world, as the last mile telephone link connecting every home with the local telephone exchange is made of twisted pair copper. These telephone lines are reused as last mile DSL access links to access the internet from home.
- They are also used in Ethernet LAN cables within homes and offices.
- They support low to High Data Rates (in order of Giga bits)
- However, they are effective only upto a maximum distance of a few kilometres/miles, as the signal strength is lost significantly beyond this distance.
- They come in two variants, namely UTP (unshielded twisted pair) and STP (shielded twisted pair). Within each variant, there are multiple sub-variants, based on the thickness of the material (like UTP-3, UTP-5, UTP-7 etc.)
- E.g. DSL, 10/100/1000Mbps Ethernet cables
Copper Co-axial Cables
- Co-axial copper cables have an inner copper conductor and an outer copper shield, separated by a di-electric insulating material, to prevent signal losses.
- It is primarily used in cable TV networks and as trunk lines between telecommunication equipments.
- It serves as an internet access line from the home.
- It supports medium to High Data Rates
- It has much better immunity to noise and hence signal strength is retained for longer distances than in copper twisted pair media.
Fiber Optic Cables
- Here, information is transmitted by propogation of optical signals (light) through fiber optic cables and not through electrical/electromagnetic signals. Due to this, fiber optics communication supports longer distances as there is no electrical interference.
- As the name indicates, fiber optic cables are made of very thin strands of glass (silica).
- As they support very high data rates, fiber optic lines are used as WAN backbone and trunk lines between data exchange equipments.
- They are also used for accessing internet from home through FTTH (Fiber-To-The-Home) lines.
- Additionally, they are used even for LAN environment with different LAN technologies like Fast Ethernet, Gigabit Ethernet etc. using optical links at the physical layer.
OC-48, OC-192, FTTC, HFC are examples of Fiber Optical links.
Unguided Wireless Media:
Here information is transmitted by sending electromagnetic signals through free space and hence the name unguided media, as the signals are not guided in any specific direction or inside any specific medium.
All unguided media transmission are classified as wireless transmission.
Wireless transmission can be used as the medium in both LAN and WAN environments, as illustrated in the diagrams below:
- Distance separating the end stations
- Frequency spectrum used by the electromagnetic signals
- Line Encoding technique used
Based on these attributes, a wide variety of wireless PHYs and different types of antennaes are used in wireless communication.
The diagram given below illustrates different types of antennaes typically used in wireless communication
As illustrated in the diagram, antennaes can be of many sizes and shapes. Some of them are point to point antennaes while others are omni-directional antennaes. Even satellites act as giant antenaes in the sky, by receiving and transmitting signals generated from the earth.
Wi-Fi, Wi-Max. 3G are example wireless networks used for internet communication