MEDIA
1. Transmission Media The means through which data is transmitted from one place to another is called transmission or communication media. There are two categories of transmission media used in computer communications.
2- Unbounded/unguided media
(a). Bounded Media Bounded media are the physical links through which signals are confined to narrow path. These are also called guide media. Bounded media are made up of a external conductor (Usually Copper) bounded by jacket material. Bounded media are great for LABS because they offer high speed, good security and low cast. However, some time they cannot be used due distance communication. Three common types of bounded media are used of the data transmission. These are
1- Twisted Pairs Cable2- Coaxial Cable
3- Fiber Optics Cable
2. Twisted Pair Cable
The most popular network cabling is Twisted pair. It is light weight, easy to install, inexpensive and support many different types of network. It also supports the speed of 100 mbps. Twisted pair cabling is made of pairs of solid or stranded copper twisted along each other. The twists are done to reduce vulnerability to EMI and cross talk. The number of pairs in the cable depends on the type. There are two types of twisted pairs cable.
2- Shielded twisted pair (STP)
(a) Unshielded twisted pair (UTP)
(aa) UTP is more common. It can be either voice grade or data grade depending on the condition. UTP cable normally has an impedance of 100 ohm. UTP cost less than STP and is easily available due to its many use.
(ab) UTP cables are generally used to construct an Ethernet network in a star arrangement. UTP connectors are called RJ-45 connector. UTP cable comes in various grades called Categories for example CAT 1, 2, 3, 4, 5& CAT 6 etc.
Categories of Unshielded Twisted Pair
|
Category
|
Speed
|
Use
|
| 1 | 1 Mbps | Voice Only (Telephone Wire) |
| 2 | 4 Mbps | Local Talk & Telephone (Rarely used) |
| 3 | 16 Mbps | 10BaseT Ethernet |
| 4 | 20 Mbps | Token Ring (Rarely used) |
| 5 | 100 Mbps (2 pair) | 100BaseT Ethernet |
| 1000 Mbps (4 pair) | Gigabit Ethernet | |
| 5e | 1,000 Mbps | Gigabit Ethernet |
| 6 | 10,000 Mbps | Gigabit Ethernet |
Characteristics of UTP
2- High attenuation.
3- Affected to EMI.
4- 100 meter distance limit.
Disadvantages of UTP
Short distance due to attenuation
(b). Shielded twisted pair (STP) It is similar to UTP but has a mesh shielding that’s protects it from EMI which allows for higher transmission rate. In STP, an extra layer of metal foil present between the twisted pairs of copper wires and the outer sheath. The purpose of this layer is to provide additional protection from EMI and RFI. However, this shielding reflects back the normal radiation emitted by the wires. This radiation may interfere with signal transmitted by the cable. To prevent this reflection a coating of dielectric insulator which absorbs the radiation is provided on the internal surface of the metal foil.
Characteristics of STP
2- Higher attenuation, but same as UTP
3- Medium immunity from EMI
4- 100 meter limit
3. UTP Connectors RJ45 (Registered Jack 45) is a standard type of connector for network cables. RJ45 connectors have eight pins to which the wire strands of a cable are connected.
(a) Colour coding of UTP cable
|
RJ 45 Pin NO
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
|
Colour coding
White/orange
Orange
White/green
Blue
White/blue
Green
White/brown
Brown
|
There are two types of UTP cable wires connections-
1- Straight through cables
2- Crossover Cables.
Straight-through cable means that wire 1 coming in connects to wire 1, going out wire 2 connects to wire 2 and so on.
|
Straight Cable Connection
|
|||||
|
RJ-45 Pin
|
Colour coding of UTP wires
|
Function
|
RJ-45 Pin
|
Colour coding of UTP wires
|
Function
|
|
1
|
White Orange
|
Tx+
|
1
|
White Orange
|
Rx+
|
|
2
|
Orange
|
Tx-
|
2
|
Orange
|
Rx-
|
|
3
|
White Green
|
Rx+
|
3
|
White Green
|
Tx+
|
|
4
|
blue
|
Not used
|
4
|
blue
|
Not used
|
|
5
|
White Blue
|
Not used
|
5
|
White Blue
|
Not used
|
|
6
|
Green
|
Rx-
|
6
|
Green
|
Tx-
|
|
7
|
White Brown
|
Not used
|
7
|
White Brown
|
Not used
|
|
8
|
Brown
|
Not used
|
8
|
Brown
|
Not used
|
A crossover cable directly connects two network devices of the same type to each other over Ethernet.
|
Cross Cable connection
|
|||||
|
Switch A side
|
Switch B side
|
||||
|
RJ-45 Pin
|
Colour coding of UTP wires
|
Function
|
RJ-45 Pin
|
Colour coding of UTP wires
|
Function
|
|
1
|
White Orange
|
Tx+
|
1
|
White Green
|
Tx+
|
|
2
|
Orange
|
Tx-
|
2
|
Green
|
Tx-
|
|
3
|
White Green
|
Rx+
|
3
|
White Orange
|
Rx+
|
|
4
|
blue
|
Not used
|
4
|
blue
|
Not used
|
|
5
|
White Blue
|
Not used
|
5
|
White Blue
|
Not used
|
|
6
|
Green
|
Rx-
|
6
|
Orange
|
Rx-
|
|
7
|
White Brown
|
Not used
|
7
|
White Brown
|
Not used
|
|
8
|
Brown
|
Not used
|
8
|
Brown
|
Not used
|
4. Coaxial Cable
Coaxial cable is very common & widely used communication media. e.g. TV wire is usually coaxial.
Coaxial cable gets its name because it contains two conductors that are parallel to each other. The centres conductor in the cable is usually copper. The copper can be either a solid wire or stranded martial.
Outside this central Conductor is a non-conductive material. The other Conductor is a fine mesh made from Copper. It is used to help shield the cable form EMI.
There are two types of coaxial cable-
1- Thin coaxial cable
2- Thick coaxial cable
Characteristics Of Coaxial Cable
2- Medium immunity from EMI.
3- Medium attenuation.
Connector of coaxial cable
5. Fiber Optics Fiber optic cable uses electrical signals to transmit data. In fiber optic cable light moves in one direction, for two way communication to take place a second connection must be made between the two devices. It is actually two stands of cable. Each stand is responsible for one direction of communication. A laser at one device sends pulse of light through this cable to other device. These pulses translated into "1’s" and "0’s" at the other end.
In the center of fiber cable is a glass stand or core. The light from the laser moves through this glass to the other device around the internal core is a reflective material known as CLADDING. No light escapes the glass core because of this reflective cladding. Fiber optic cable has bandwidth more than 2 Gbps (Gigabytes per Second)
Characteristics Of Fiber Optic Cable
2- Extremely low attenuation
3- No EMI interference
Connectors
6. Fiber Optic Cable Connectors
(a) SC Connector A fiber-optic cable connector that uses a push-pull latching mechanism similar to common audio and video cables. For bi-directional transmission, two fiber cables and two SC connectors (Dual SC) are generally used.
(b) ST Connector A fiber-optic cable connector that uses a half-twist bayonet type of lock to keep the connection secure. For bi-directional transmission, two fiber cables and two ST connectors are generally used.
(c) MTRJ The MTRJ connector is a small form-factor fiber optic connector which resembles the RJ-45 connector used in Ethernet networks.
(d) FC The FC connector is a fiber-optic connector with a threaded body, which was designed for use in high-vibration environments. It is commonly used with single-mode optical fiber. FC connectors are used in data com, telecommunications, measurement equipment, and single-mode lasers. They are becoming less common, displaced by SC and LC connectors.
7. Media Type Comparison
| Media Type | Maximum Segment Length | Speed | Cost | Advantages | Disadvantages |
| UTP | 100 m | 10 Mbps to 1000 Mbps | Least expensive | Easy to install; widely available and widely used | Susceptible to interference; can cover only a limited distance |
| STP | 100 m | 10 Mbps to 100 Mbps | More expensive than UTP | Reduced crosstalk; more resistant to EMI than Thinnet or UTP | Difficult to work with; can cover only a limited distance |
| Coaxial |
500 m (Thicknet) 185 m (Thinnet) |
10 Mbps to 100 Mbps | Relatively inexpensive, but more costly than UTP | Less susceptible to EMI interference than other types of copper media |
Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network
|
| Fiber-Optic |
10 km and farther (single-mode) 2 km and farther (multimode) |
100 Mbps to 100 Gbps (single mode) 100 Mbps to 9.92 Gbps (multimode) |
Expensive | Cannot be tapped, so security is better; can be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twisted-pair cable | Difficult to terminate |
8. Wireless media Wireless communication uses radio frequencies (RF) or infrared (IR) waves to transmit data between devices on a LAN. For wireless LANs, a key component is the wireless hub, or access point, used for signal distribution
To receive the signals from the access point, a PC or laptop must install a wireless adapter card (wireless NIC).
No physical medium is necessary for wireless signals, making them a very versatile way to build a network. Wireless signals use portions of the RF spectrum to transmit voice, video, and data.
Wireless frequencies range from 3 kilohertz (kHz) to 300 gigahertz (GHz). The data-transmission rates range from 9 kilobits per second (kbps) to as high as 54 Mbps.
Low-frequency electromagnetic waves have a long wavelength while high-frequency electromagnetic waves have a short wavelength.
Applications of wireless comn
1- Accessing the Internet using a cellular phone
2- Establishing a home or business Internet connection over satellite
3- Beaming data between two hand-held computing devices
4- Using a wireless projectors, keyboard and mouse for the PC
5- Another application of wireless data communication is the wireless LAN (WLAN), IEEE 802.11 standards. WLANs typically use radio waves ( 902 megahertz ), microwaves ( 2.4 GHz), and IR waves ( 820 nanometers) for communication.
Categories:
COMPUTING KNOWLEDGE
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