Fiber Optic

Fiber optic transmission medium is one that can deliver information to a large capacity with high reliability. Unlike other transmission media, then the optical fiber, the carrier waves instead of electromagnetic waves or electricity, but light / laser light.
In fiber optics, digital signal denagn data is transmitted using light waves so it is quite safe for data transmission because it could not be tap in the middle of the road so that the data can be stolen in the middle of the transmission. As with the cables as coaxial and twisted pair. Another advantage of fiber optic is in terms of speed (100 Mbps up to 200,000 Mbps based on testing that has been done in the laboratory).

Physical Description

Diameter optical fibers are very thin, between 2-125 um. Various glass and plastic materials can be used to make optical fibers, the best and has the smallest loss is to use ultra pure fused silica fibers. The material is very difficult to produce, because it is replaced by another material that has a greater loss but still tolerable, namely plastic and glass mixture.

Fibre optic cylindrical and consists of 3 sections, core, cladding and jacket. Core is the deepest and consists of one or more fibers. Each fiber is surrounded by a cladding and then covered by a coating. The outer portion is the duty jacket protects the optical fiber from moisture, abrasion and damage.

Application
            The difference between the use of optical fiber with twisted pair and coaxial cable include:

·         Large capacity

2 Gbps data transmission within tens of kilometers to do, compared to the coaxial cable that can only transmit data within a few Mbps up to 1 km or twisted pair only up to 100 Mbps in the tens of meters.

·         Small size and lighter

Optical fibers are smaller in diameter and lighter weight.

·         Attenuation lower

Attenuation is much lower than other cables.

·         Isolation electromagnetic
Fiber optic is not affected by electromagnetic fields from outside cable, o is also vulnerable to noise or crosstalk.

·          Repeater spacing greater
Larger distance between repeaters, AT & T has a 318 km long optical fiber without a repeater while the twisted pair or coaxial repeater installed every few feet.

Main Components

Optical transmission system has three main components, namely the transmission medium, the light source and detector. As a medium of transmission used a very fine glass fibers or fused silica. The light source can make use of Light Emitting Code or laser diode which emits light pulses both when given an electrical current. As used photodiode detector, which serves to generate electrical pulses when there is light shining. By combining Leser diode or LED to one end and optics, it can be obtained undirected data transmission system that receives an electrical signal, and transmits the changing pulse of light and convert it back into an electrical signal output at the receiving end.

Transmission Characteristics

            And optical systems operate in areas up to 1 million 100 000 Ghz. The working principle and optical transmission are as follows.
1. Light from a source into a glass or plastic cylindrical core.
2. Light beam is reflected and propagated along the fiber, while the part is absorbed by the surrounding material. Propagation in single mode provides better performance than multimode, as with multimode transmission, any file with a length of the path is different and this is resulting in a transfer in the fiber causes signal elements spread out in time, so it can happen that the data received is not accurate. Since there is only a single transmission path in the transmission mode, it will not happen distorted. In optical fiber transmission, there are 3 types, namely single mode, multi-mode and multi-mode graded index.

Two types of light sources used in fiber optic systems is LED (Light Emitting Diode) and ILD (Injection Laser Diode). Both are semi-conductor device that will emit light ketikadiberikan voltage. LED type is cheaper, can operate over a wide temperature range and has a longer operating time. ILD type that operates on the principle of laser, more efficient and can forward data rate greater. There is a link between the wavelength used, transmission type and data rate that can be sent.

Use
            Fiber optic transmission is very useful for varying distances. As an illustration, the distance that can be taken for data transmission on optical fibers are as follows.

·         Remote
For telephone network, is 900 miles, with a capacity of 20 000 to 60 000 voice channels.

·         Metropolitan
Located 7.8 miles and can menampun 100 000 channel sound.

·         Regional Rular
Is between 25 to 100 miles that connects various cities.

·         Loop Subscriper
Used to connect central with customers directly.

·         LAN
Use local network links between offices.

Type of Fiber Optics

            Based on the characteristic properties of optical fiber types in abundance can be divided into 2, namely:

1.      Multi Mode

In this type of optical fiber propagation of light from one end to the other going through some streaks of light, as it is called multi-mode. Diameter (core) in accordance with the recommendations of the CCITT G.651 at 50 mm and is covered by a jacket sheath (cloding) with a diameter of 125 mm. While based on the composition of the index is usually multi-mode optical fiber has two profiles are graded index and step index.

In graded index fiber, optical fiber has a refractive index of light is a function of the distance to the axis / spindle fiber. Thus chaya that runs through some tracks will eventually arrive at the other end pda the same time. Unlike the graded index, then at step index optical fibers (mempuyai same light refractive index) that runs on an axis beam will reach the other end first (dispersion).

This can occur because the path through the process is shorter than that experienced light reflection on the wall of the optical fiber. As a result of dilation pulse or otherwise reduce the width of the field frequency. Therefore, in practice only a graded index optical fiber alone is used as a transmission channel multi mode optical fiber.

2.      Single Mode

Single mode optical fiber has a diameter or mono mode (core) is very small 3-10 mm, so that only one beam of light that can be through. Because only one beam of light there is no influence of the refractive index for light travel or the effect of differences in the arrival time of the light from one end to the other Valentine (no disepersi). Thus the single mode optical fiber is often used in optical fiber transmission systems remotely or outside the city (long haul transmission system). While the graded index used for the local telecommunications network (local network).

Table 1.1 : Comparison between Single mode and Multi mode

Bit Rate (Mbps)	Repeater Spacing Multi Mode	Repeater Spacing Single Mode
140	30	50
280	20	35
420	15	33
565	10	31

Advantages and Disadvantages

This type of cable is not affected by noise and can not be intercepted. But the cable is very expensive, difficult installation and teknoologi is still under development. In addition to fiber optic transmission has advantages over other transmission media. Advantages include:

·         Damping small transmission

Fiber-optic telecommunications systems have attenuation per km transmission is relatively small compared with other transmissions, such as coaxial cable or PCM cable. This means that the fiber optic is suitable for use in long-distance telecommunications, because it only requires a smaller number of repeaters.

·         Sector wide frequency

In theory, optical fiber can digunakandengan high speeds, up to several gigabits / sec. Thus this system can be used to carry signaling information preformance large numbers with just a single optical fiber is smooth.

·         Small size and lightweight

Thus greatly facilitates installation pengangkuta the location. For example, can be fitted with a cable lam, without having to create a new hole.

·         There is no interference

This is due to optical fiber transmission system using light / laser light As with the carrier wave. The result will be free of competent cross (cross talk) is common in other words biasa.atau cable transmission or telecommunication quality produced better than with cable transmission. With no interference will allow fiber optic cables installed on a network of high voltage electric power (high voltage) without fear of interference caused by high voltage.

Twisted Pair

Is the simplest type of cable compared to the others and is currently the most widely used as a medium of cable in building a computer network.

Physical Description

Twisted pair consists of two copper-sheathed wires are arranged in such a way as to form a spiral pattern. One pair of wire serves as a communication link. In the far distance, a single twisted pair cable bundles will be composed of hundreds of couples, the torsion of the cable will reduce the interference that occurs between the wires.

Application

            At this time the most common transmission medium used is twisted pair, for both analog and digital communications. For analog communications, twisted pair used for voice communications or telephone. Media that connect telephone terminal with LE (Local Exchange) is a twisted pair. For digital communications, media type is generally also used for digital signaling, connection to the digital data to the digital switch or PBX to the building.

Twisted pair is also often used for data communication within a local network (LAN). The data rate that can be handled by a twisted pair in data communications is about 10 Mbps, but in development, currently twisted pair has been able to handle the data rate of 100 Mbps. In terms of price, twisted pair is cheaper than two other guided transmission media and easier terms of use. But in terms of distance and data rate that can be handled, twisted pair is more limited than others.

Type Twisted Pair

As well as coaxial cable, twisted pair is also divided into two types, namely Unshielded Twisted Pair or better known by the acronym and Shielded Twisted Pair UTP or STP. As the name implies clearly that the difference between the two lies in the shield or wrapper. At STP cable in which there is a protective layer that protects the internal wiring of data transmitted from interference or disruption.

UTP cable is much more popular than the STP and the most widely used as a wired network. UTP organization specified by EIA / TIA or the Electronic Industries Association and Telecommunications Industries Association UTP categorize it in 8 categories. You may have heard of UTP CAT 5 and so on. It is one of the categories of UTP. The UTP category on the market today is the category 1,2,3,4,5,5 +, 6.7. As for the difference in this category, especially in transmission speed issues. In the first category or 1 can only transmit sound / voice does not include data. In category 2, the maximum transmission speed of up to 4 Mbps, to 10 Mbps category 3, category 4 to 16 Mbps, category 5 to 100 Mbps and paint 5 +, 6 and 7 was able to reach 1 Gbps or 1000 Mbps.

As an example of using UTP cable for everyday is telephone cable. One of the main reasons why this type of UTP cable is very popular compared to other cable types is due to the use of a telephone cable UTP cable. Many buildings use this cable to the phone system and no extra cables are usually installed to meet future development. Because this cable can also be used to transmit data and voice, hence the choice to build a computer network. What distinguishes anatara phone to a computer with the use of UTP cable is located on the jack or plug.

On computers that use RJ-45 cable connection can accommodate 8 sedangakan on phone use RJ-11, can accommodate 4 cable connections and smaller. More details can be seen a connection from your phone using the RJ-11.

Transmission Characteristics

For analog signal amplifier required for each distance of 5 to 6 km. For digital signal repeaters required every 2 to 3 km.

Advantages and Disadvantages

The advantage of using twisted pair media in a computer network is the ease of installation and build a relatively cheap price. However, within range and speed of data transmission on twisted pair is relatively limited. Addition, the media is easily influenced noise.

Coaxial cable

            Today the coaxial cable is a transmission medium most widely used on the Local Area Network and a choice of many people because in addition to low cost, this type of cable is also easy to use.

Physical Description

            Coaxial consists of two conductors, set up to operate on a large frequency band. Consists of the core conductor and surrounded by small wires. Among the core conductors with conductors separated by an insulator surrounding (jacket / shield). Coaxial cables are less likely to interfere due to the shield. Coaxial can be used to remotely support more terminal preformance a common pathway.

Apikasi
            Coaxial cable users in general are:

·         Antenna Television

·         Transmission distance phone

·         Link the computer

·         LAN

Type Coaxial Cable

Coaxial cable is divided into 2 parts baseband coaxial cable (50 ohm cable) used for digital transmission and broadband coaxial cable (75 ohm cable) used for analog transmission.

·         Baseband Coaxial Cable

            This type of coaxial cable consists of copper wire as the hard core, surrounded by an insulating material. Isolator is wrapped by a cylindrical conductor, which often takes the form of woven fabric. Outer conductor enclosed in a protective plastic sheath.

            Construction and protective coating coaxial cables provide a good combination of large bandwidth and noise immunity privilege. Bandwidth depends on the length of the cable. For a cable length of 1 km, the data rate can reach 1 to 2 Gbps. Longer cable could also be used, but will only reach a lower data rate. Coaxial cable is widely used in telephone systems, but at this time for longer distances used type of fiber optic cable.

·         Broadband Coaxial Cable

            Other coaxial systems using analog transmission systems on cable television wiring standard. Such a system is called broadband. Because broadband networks require cable television technology standards, cables used up to 300 MHz and can operate almost 100 km with respect to analog signaling, which is more secure than digital signaling.

            To mantransmisikan digital signals on analog networks, the interface must be installed on every electronic device to turn off the bit stream into an analog signal and the incoming analog signal into a stream of bits.
An important difference between the baseband with broadband is that the broadband system covering a wide area compared to the baseband system.

Type Coaxial Cable

Coaxial cable is divided into 2 types of tin (thinnet) and thick (thicknet). The difference is the thin cable is more flexible, easier to use and more importantly cheaper than thick wires. Thick cable is thicker and more difficult to bend and reach further than the thin, which makes it more expensive. For comparison the thin cable range is 185 meters while the thick cables reaching up to 500 meters. Both types of these cables use the same components known as the BNC (British Naval Connector) to connect the cable to the computer. Components of this include the BNC connector BNC cable, BNC T connector, BNC connector and a BNC terminator barrel.

Transmission characteristics

Coaxial can be used for analog signals and digital signals. Because it is formed by using a shield then less likely to interfere, and the cross talk. For transmission of analog signals, each several kilometers should be given amplifier. The spectrum used for signaling is around 400 Mhz. Likewise for digital signals, repeaters are needed in every kilometer.

Advantages and Disadvantages

Cable noise is virtually unaffected and relatively inexpensive. However, the use of these cables easily hijacked. In addition, the type of thick coaxial is not allowed to be installed in some kind of space.

Transmission Media

In accordance with its function is to bring the bit stream of data from one computer, then the data transfer requires a transmission medium that will be used for transmission purposes. Each medium has certain characteristics, the bandwidth, delay, cost and ease of installation and maintenance.

Transmission medium is a physical path between transmitter and receiver in a data transmission system. Transmission media can be classified as guided (guided) or unguided (not guided). Both can occur due to the form of electromagnetic waves. With a wave of media is guided through a solid medium such as twisted copper cable (twisted pair) copper coaxial cable and fiber optics. Atmospheric and air are examples of unguided media, in the form of the transmission medium is referred to as wireless transmission.
            Several factors related to the transmission media and signaling as a determinant of the data rate and distance are as follows:

·         Bandwidth

The greater the bandwidth, the greater the signal data can be handled.

·         Transmission Impairement

For guided media, twisted pair cable in general damaged transmission over the coaxial cable, and coaxial experienced over optical fiber.

·         Interference

Interference of the signal in each frequency band overlapping can cause distortion or damage a signal.

·         Number of Recipients (Receiver)

A guided media can be used to build a relationship of point-to-point or a connection that can be used together.

After knowing the factors related to the transmission medium and can determine a suitable topology for the network to be built of course, we certainly need to know what equipment is needed to build a computer network. The media is needed in addition to the computer regardless of the type of network that will be built are:

·         Cable

·         Transmission cordless (wireless) and

·         Network Interface Card (NIC) or network card

Physical Layer

Physical Layer Basics

Physical layer is the basis of all the networks in the OSI reference model that is characteristic of hardware whose function is to transmit data signals both analog data and digital data. Besides the physical layer of the system is also a means to send data to other devices connected within a computer network.

The physical layer is the lowest layer of the OSI reference model that serves to determine the characteristics of the cable used to connect computers in a network. On the transmitter side, the physical layer functions apply electrical, mechanical, and procedures to establish, maintain and release the communication circuit to transmit information in the form of digits Binner to the side of the receiver. While the physical layer on the side of the receiver will receive and transmit the data to the upper layer.

 

Signal Data

In the communication process, the data will be transmitted first encoded in the form of analog signals and digital signals.

1.      Analog Signals

The analog signal is a signal waveform data in the dial-connect or continuous, there is no sudden change and have the scale, the amplitude and frequency.

By using analog signals, then the data transmission range can reach distances, but it is easily affected signal noise. Waves in general sinusoidal analog signal that has three basic variables, namely amplitude, frequency and phase.

a.      Amplitude

Amplitude is a measure of the high and low voltage analog signals. The images below will show more clearly what is meant by amplitude.

b.      Frequency

Frequency is the number of analog signal waveform in one second. The interface can be seen in the picture below.

c.       Phase

               Phase is a great angle of the analog signal at a given time. Phase at angles 0⁰, 90⁰,  180⁰, 270⁰, and 360⁰. 

  Digital Signal

A digital signal is a signal in the form of pulses of data that can undergo sudden changes which have scale 0 and 1 as shown in the picture below.

A digital signal has only two states, that is 0 and 1, which are not easily affected by noise, but the transmission of digital signals only reach the range of data dispatch close relative.

In the process of data transmission, disunakan a tool called a modem. Modulator standard modem demodulator. As a modulator, the modem will translate the data or information in the form of a digital signal into an analog signal which then combine with the carrier frequency (carrier), while the demodulator, the modem will separate from the carrier frequency and translates the data or information signals are analog signals into digital form.

There are four possible pair of data signal shape and signal transmission that occurs after experiencing a data transmission process.