Data is represented by computers and other telecommunication devices using signals. Signals are transmitted in the form of electromagnetic energy from one device to another. Electromagnetic signals travel vacuum, air or other transmission mediums to travel between one point to another (from source to receiver). The first layer of the OSI model that is a physical layer is related to transmission media.
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Types of transmissions
A transmission can be simplex, half-duplex or full-duplex.
In simplex transmission, signals are transmitted in only one direction; one device act as a transmitter, and the other acts as a receiver, for example, the person talking at a radio station act as a transmitter, and the person with a radio who is listening to act as a receiver.
In the half-duplex transmission, both stations can transmit and receive but only one at a time, for example, walky-talky, one can only talk at a time when the other is on listening mode then when one goes to listening mode the other is able to talk.
In full-duplex transmission, both devices can transmit and receive simultaneously, example on the telephone both the users can talk as well as listen at the same time. Hence in full-duplex transmission, the medium is carrying signals in both directions at the same time.
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there are two types of transmission media:
- Guide or Wired. 2. Unguided or wireless.
Wired media: Transmission media that can be seen physically and has a proper bounded channel to flow the signal.
Types of wired transmission media:
- Coaxial Cable 2. Twisted Pair Cable 3. Optical Fiber Cable
Common Straight Cable Cross Cable
O.W O.W G.W
O O G
G.W G.W OW
B B B
B.W B.W B.W
G GO O
BR.W BR.W BR.W
BR BR BR
Wireless Media: Wireless transmission media is the one in which data signals get transmitted through the air. They are not guided or bound to a channel to follow.
Types of wireless Transmission media:
- Radio Transmission 2. Microwave Transmission
| STP | UTP |
| It is used for telephone networks | It is used for computer networks |
| 2 pair of wires | 4 pair of wires |
| That means it has 4 wires | It has 8 wires |
| Less EMI | More EMI |
| The connector used in STP is RJ-11 | The RJ-45 connector is used in UTP |
| Speed is 10 to 100 Mbps | Speed is 10 to 1000 Mbps |
| The average cost per node is moderately expensive | The average cost per node is Least expensive |
| Media and connector size is medium to large | Media and connector size is small |
| The maximum cable length is 100 m | The maximum cable length is 100 m |
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UTP cables are classified according to their categories. UTP cable category is shortened to CAT.
Category 1 (CAT 1)
Two pairs, four-wire twisted pair cable is category 1 cable. It supports signals limited to the 1 MHz frequency range.
Category 2 (CAT 2)
Four pairs, eight wire twisted pair cable is category 2 cable which handles up to 4 Mbps, with a frequency limitation of 10MHz.
Category 3 (CAT 3)
four pairs, eight wire twisted pair cable with three twists per foot is category 3 cable that can handle transmission up to 16MHz. Ethernet connection up to 10 Mbps.
Category 4 (CAT 4)
Four pairs, eight wire twisted pair cable is category 4 with a frequency limitation of 20MHz which were used in 16 Mbps Token Ring networks. The category is also obsolete.
Category 5 (CAT 5)
Four pairs, eight wire twisted pair cable is category 5 with a frequency limitation of 100MHz uses for 100Base-TX Fast Ethernet.
Category 5e (enhanced)
Four pairs, eight wire twisted pair cable is category 5e with a frequency limitation of 100MHz. it can be used for 100Base-T(Gigabit Ethernet).
Category 6 (CAT 6)
Four pairs, eight wire twisted pair cable is category 6 with a frequency limitation of 250MHz. It is also used for 100Base-T(Gigabit Ethernet).
Wiring Standard
Wiring standards are used to set Ethernet cables according to their connection of between similar or dissimilar devices.
There are three types of Ethernet cables available
- Straight-through cable
2. Crossover cable
3. Rolled cable
T-568A and T568B are the two wiring standards for the RJ-45 connector data cable specified by the TIA/EIA-568-A wiring standard document. The two wiring standards are used to create a cross-over cable where T-568-A used on one end and t-568B is is on the other end. In straight-through cable where on both ends you can use T568A or T-568B wiring standard.
Straight-through cable: It is used to connect dissimilar devices like computers to switch, computer to hub.
Crossover cable: It is used to connect similar devices like computer to computer, hub to hub, switch to switch.
Rollover cable: A rollover cable is a network cable that connects a computer terminal to a network router’s console port.
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