What is terrestrial microwave technology?

Terrestrial microwave technologies share with satellite microwave technologies many of the scientific and technical improvements used to accomplish microwave transmissions. They are different in that satellite microwave technolgies seek to neutralize the effects of the atmosphere in the microwave transmissions. On the other hand, terrestrial micowave technologies seek the aid of atmospheric effects on microwaves to extend the range limitations imposed by the Earth's curvature. Examples of these terrestrial technologies include those used to exploit troposcattering and meteor-burst in microwave communications--not used at all in satellites.

What is Unbound or Unguided media? 

UNBOUNDED / UN GUIDED MEDIA

Unbounded / Unguided media or wireless media doesn't use any physical connectors between the two devices communicating. Usually the transmission is send through the atmosphere but sometime it can be just across the rule. Wireless media is used when a physical obstruction or distance blocks are used with normal cable media. The three types of wireless media are:

• RADIO WAVES
• MICRO WAVES
• INFRARED WAVES

1. RADIO WAVES:-

It has frequency between 10 K Hz to1 G Hz. Radio waves has the following types.

• Short waves
• VHF (Very High Frequency)
• UHF (Ultra High Frequency)

SHORT WAVES:-

There are different types of antennas used for radio waves. Radio waves transmission can be divided into following categories.

• LOW POWER, SINGLE FREQUENCY.
• HIGH POWER, SINGLE FREQUENCY

1. LOW POWER , SINGLE FREQUENCY:-

As the name shows this system transmits from one frequency and has low power out. The normal operating ranges on these devices are 20 to 25 meter.

CHARACTERISTICS LOW POWER , SINGLE FREQUENCY:-

• Low cost
• Simple installation with pre-configured
• 1 M bps to 10 M bps capacity
• High attenuation
• Low immunity to EMI

2. HIGH POWER, SINGLE FREQUENCY:-

This is similar to low power single frequency. These devices can communicate over greater distances.

CHARACTERISTICS HIGH POWER, SINGLE FREQUENCY:-

• Moderate cost
• Easier to install than low power single frequency
• 1 Mbps to 10 Mbps of capacity
• Low attenuation for long distances
• Low immunity to EMI

Infrared

Infrared frequencies are just below visible light. These high frequencies allow high sped data transmission. This technology is similar to the use of a remote control for a TV. Infrared transmission can be affected by objects obstructing sender or receiver. These transmissions fall into two categories.

1. Point to point
2. Broadcast

(i) Point to Point: - Point to point infrared transmission signal directly between two systems. Many lap top system use point to pint transmission. These systems require direct alignment between many devices.

Characteristics of Point to point:-

• Wide range of cost
• Moderately easy installation.
• 100 k bps to 16 Mb of capacity.
• Variable attenuation.
• High immunity to EMI

(i) Broad Cast: - These infrared transmission use sprayed signal, one broad cast in all directions instead of direct beam. This help to reduce the problems of proper alignment and abstraction. It also allows multiple receiver of signal

Characteristics of Broad Cast:-

• In expensive.
• Single installation.
• 1M bps capacity.
• Variable attenuation.

radio frequency (RF, rf, orr.f.)

Radio frequency (abbreviated RF, rf, orr.f.) is a term that refers to alternating current (AC) havingcharacteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is generated suitable for wireless broadcastingand/or communications. These frequencies cover asignificant portion of the electromagnetic radiation spectrum, extending from nine kilohertz (9 kHz),the lowest allocated wireless communications frequency (it's within the range of human hearing), to thousands of gigahertz(GHz).

When an RF current is supplied to an antenna, itgives rise to an electromagneticfield that propagates through space. This field is sometimescalled an RF field; in less technical jargon it is a "radiowave." Any RF field has a wavelength that is inverselyproportional to the frequency. In the atmosphere or in outerspace, if f is the frequency in megahertz and sis the wavelength in meters, then

s = 300/f

The frequencyof an RF signal is inversely proportional to the wavelengthof the EM field to which it corresponds. At 9 kHz, the free-spacewavelength is approximately 33 kilometers (km) or 21 miles (mi). At the highestradio frequencies, the EM wavelengths measure approximately one millimeter (1 mm). As the frequency isincreased beyond that of the RF spectrum, EM energy takes the form ofinfrared (IR), visible, ultraviolet (UV), X rays, and gamma rays.

Many types of wireless devices makeuse of RF fields. Cordless and cellular telephone, radio andtelevision broadcast stations, satellite communications systems,and two-way radio services all operate in the RF spectrum. Somewireless devices operate at IR or visible-light frequencies,whose electromagnetic wavelengths are shorter than those of RFfields. Examples include most television-set remote-controlboxes, some cordless computer keyboards and mice, and a fewwireless hi-fi stereo headsets.

The RF spectrum is divided into several ranges, orbands. With theexception of the lowest-frequency segment, each band represents an increaseoffrequencycorresponding to an order of magnitude (power of 10). The tabledepictsthe eightbands in the RF spectrum, showing frequency and bandwidth ranges. TheSHF and EHFbands are often referred to as themicrowave spectrum.

Wi-Fi (wireless fidelity)

Wi-Fi (short for "wireless fidelity") is a term for certain types of wireless local area network (WLAN) that use specifications in the 802.11 family. The term Wi-Fi was created by an organization called the Wi-Fi Alliance, which oversees tests that certify product interoperability. A product that passes the alliance tests is given the label "Wi-Fi certified" (a registered trademark).

Originally, Wi-Fi certification was applicable only to products using the 802.11b standard. Today, Wi-Fi can apply to products that use any 802.11 standard. The 802.11 specifications are part of an evolving set of wireless network standards known as the 802.11 family. The particular specification under which a Wi-Fi network operates is called the "flavor" of the network. Wi-Fi has gained acceptance in many businesses, agencies, schools, and homes as an alternative to a wired LAN. Many airports, hotels, and fast-food facilities offer public access to Wi-Fi networks. These locations are known as hot spots. Many charge a daily or hourly rate for access, but some are free. An interconnected area of hot spots and networkaccess points is known as a hot zone.

Unless adequately protected, a Wi-Fi network can be susceptible to access by unauthorized users who use the access as a free Internet connection. The activity of locating and exploiting security-exposed wireless LANs is called war driving. An identifying iconography, called war chalking, has evolved. Any entity that has a wireless LAN should use security safeguards such as the Wired Equivalent Privacy (WEP) encryption standard, the more recent Wi-Fi Protected Access (WPA), Internet Protocol Security (IPsec), or a virtual private network (VPN). 

CABLE

LAN Technology  Cabling
A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires. LAN utilizes spread-spectrum based on radio waves to enable communication between devices in a limited area, also known as the basic service set.

Types Of Cables

•  Unshielded Twiested Pair (UTP) cable  

•   Shielded Twisted Pair (STP) cable 

•  Coaxial Cable 

•  Fiber Optic Cable

•  Wireless LANs

Unshielded Twisted Pair (UTP) cable

 



 The standard connector for unshielded twisted pair cabling is an RJ-45 connector

 










RJ stands for REGISTERED JACK, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.


Shielded Twisted Pair (STP) cable

STP is to help provide a more reliable data communication, suitable for environments with electrical interference and consists of two individuals wires wrapped in a foil shielding.
  

Coaxial cable

 







The most common type is called barrel connector because of its shape. Coaxial connectors are familiar from cable TV and VCR hook-ups, which employ both threaded and slip-on styles.



Fibre Optics

The most common connector used with fibre optic cable is an ST connector. It is barrel shaped, similar to a BNC connector.


 Wireless

Wireless telecommunications is the transfer of information between two or more points that are not physically connected.


For Your Addition Notes:


UTP, STP and Coaxial Cable used current while Fiber Optic and Wireless used light.

NETWORK TOPOLOGY

Network topology also called network structures. It is the study of the arrangement or mapping of the elements (links,nodes) of a network, especially the physical and logical level.  The four main type of network topology are bus, star, ring and hybrid. 

A PHYSICAL TOPOLOGY

It is any given node in the LAN will have one or more links. There are some examples of physical topology:

• Ethernet 
• Local Talk

A LOGICAL TOPOLOGY

The mapping of the data flow of the data between the nodes in the network determines the logical topology of the network.

Linear Bus

A linear bus topology consists of a main run of cable with a terminator at each end and continuous length of cable that connects two or more devise together. A linear bus also called a backbone network. Only one computer can transfer information at a time. When a computers sends information, the information move s through the entire length of the cable. The destination computer must retrieve the information from the cable.

• ADVANTAGE

1. Easy to connect a computer or peripheral to a linear bus
2. Requires less cable length than a star topology.
3. Often used to connect a few computers located in a small area.

• DISADVANTAGE

1. Terminators are required at both ends of the backbone
2. A faulty cable or workstation will take the entire LAN.
3. The other computers on the network cannot exchange information while the cable is broken.

STAR TOPOLOGY

Is designed with each node (file server,workstation) connected directly to a central network HUB or concentrator. Data on a star topology passes through the HUB before continuing to its destination. The HUB manages and controls all function of the network.

• ADVANTAGE

1. Easy to install and wire
2. Easy to add new workstations
3. Centralized control

• DISADVANTAGE

1. Requires more cable length than a linear topology
2. If the HUB fails ,nodes attached are disabled
3. Large amount of cable are also used in star topology.

RING TOPOLOGY

A ring topology consists of individual computers connected to a single length of cable arranged in a ring. The information on the ring network travels in one direction only. When computers transfer information it send the information to the computer lactated next to it.

• ADVANTAGE

1. Great for small networks as it easy to install and the cost is usually low.
2. The Media Access Unit (MAU) can also be used to help prevent network shutdown.
3. A break in rings occurs, all computer before break will be able to exchange information.

• DISADVANTAGE

1. Expending a ring network may be difficult that expanding other type of networks.
2. Ring networks can be slightly more expensive to set up the other types pf networks.

HYBRID NETWORK TOPOLOGY

A network structures used a mixture of many different kings of network structures. A hybrid network structures such as ring, star. and bus network in one large network. The bus, ring, star and hybrid, structures all can be used with a centralization network layout.

LAST BUT NOT LEAST :

1. NIC is a network interface controller (also known as a network interface card, network adapter, LAN adapter and by similar terms) is a computer hardware component that connects a computer to a computer network.
2. NOS is a networking operating system (NOS) the software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions.
3. An Ethernet hub or concentrator is a device for connecting multiple twisted pair or fibre optic Ethernetdevices together, making them act as a single segment.
4. LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers.
5. A gateway is a node that allows you to gain entrance into a network and vice versa. On the Internet the node which is the stopping point can be a gateway or a host node. A computer that controls the traffic your network or your ISP (Internet Service Provider) receives is a node. In most homes a gateway is the device provided by the Internet Service Provider that connects users to the internet.
6. In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination.
7. A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.

COMPUTER NETWORK

What is meant by computer network??

    Computer Network is connecting a computer with other computers or other devices to enable them to communicate with each other. In addition, communication devices to transmit or to send data from sources to destinations.

NETWORKING COMPONENTS

A network component's functions are not necessarily handled by a specific device. If you browse a networking products catalog, you will find that many products combine several networking components in a device. For example: a router that has a built-in switch, a residential gateway that includes a broadband modem, etc. So, be sure to check the product specification before buying to avoid duplication. You must also check interfaces that are supported by a product. They must be compatible with the ports available in your computers or other devices. A network component's functions may also be performed by a software application. For example, Windows XP provides built-in support for Network Bridging that handle a bridge's functions in a home network with mixed media. There are also built-in or add-on software applications that handle modem, router, or gateway functions. However, the software-only alternative is mostly suitable for small networks.

Do you know what are meant by:

1. Router: A specialized network device that determines the next network point to which it can forward a data packet towards the destination of the packet. Unlike a gateway, it cannot interface different protocols. 
2. AM : Amplitude Modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent.  
3. FM :   frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency.
4. Bridge: a device that connects multiple network segments along the data link layer. 

Basic Differences Between AM and FM

We need to mention a couple of other things before we leave the discussion of how radio works.  We've talked about AM and FM radio, but we haven't explained the real difference.

In fact, there is a lot of difference — and not just a difference in the station numbers on your radio dial.

The first type of radio service — the one we've been talking about in the last couple of modules — was AM (amplitude modulation) radio.

The term modulation refers to how sound is encoded on a radio wave called a carrier wave; or, more accurately, how the sound affects the carrier wave so that the original sound can later be detected by a radio receiver.

In the top-left of this drawing the RF energy (carrier wave) is not modulated by any sound.  There would be silence on your radio receiver.

In the broadcast process sound is made to affect (modulate) AM carrier wave by changing the amplitude (height) of the wave, as shown on the left.

Unfortunately, this type of modulation is subject to static interference from such things as household appliances — and especially from lightening.

AM also limits the loud-to-soft range of sounds that can be reproduced (called dynamic range) and the high-to-low sound frequency range (called frequency response, to be explained below).  

FM radio, which came along in the 1930s, uses a different approach than AM. It's virtually immune to any type of external interference, it has a greater dynamic range, and it can handle sounds of higher and lower frequencies. This is why music, with its much greater frequency range than the human voice, sounds better on FM radio.

Note on the left that when the carrier wave of FM radio is modulated with sound that the distance between the waves, or the frequency of the carrier wave, changes.  

Thus, AM radio works by changing the amplitude of the carrier wave and FM radio works by changing the frequency of the carrier wave.

TERMINAL AND WORKSTATION

A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to amainframe computer terminal or a PC connected to a network. 

 In computers, a terminal (sometimes qualified as a "dumb" terminal) is an end-use device (usually with display monitor and keyboard) with little or no software of its own that relies on a mainframe or another computer (such as a PC server) for its intelligence.

Transmission Media is to transmit signal or electrical pulse through a medium. There are two types of transmission media such as BOUNDED AND UNBOUNDED.

Example for BOUNDED are:

• Twisted Pair Wire
• Co-Axial
• Fiber Optic Cable

Example for UNBOUNDED are:

• Tv Broadcasting
• Microwave radio
• Infrared signals

NETWORK ELECTRONIC DEVICES

Network devices are components used to connect computers or other electronic devices together so that they can share files or resources like printers or fax machines. Devices used to setup a Local Area Network (LAN) are the most common type of network devices used by the public. A LAN requires a hub, router, cabling or radio technology, network cards, and if online access is desired, a high-speed modem. Happily this is much less complicated than it might sound to someone new to networking.

In a network, one computer is designated as the server, and the others, clients. The server is connected to an external hub, which the clients are also connected to. Now that the computers each have one foot in a common electronic door (the hub), they can use the hub to pass signals back and forth. To direct these signals, the hub contains a device known as a router. The router is the equivalent of an electronic traffic cop that handles data traffic between the computers. Example of network electronic devices are bridges, routers, HUBS, gateway and Front End Processors.

NETWORK OPERATING SYSTEM

 A network operating system (NOS) is a computer operating system system that is designed primarily to support workstation, personal computer, and, in some instances, older terminalthat are connected on a local area network (LAN). Artisoft's LANtastic, Banyan VINES, Novell's NetWare, and Microsoft's LAN Manager are examples of network operating systems. In addition, some multi-purpose operating systems, such as Windows NT and Digital's OpenVMS come with capabilities that enable them to be described as a network operating system.

A network operating system provides printer sharing, common file system and database sharing, application sharing, and the ability to manage a network name directory, security, and other housekeeping aspects of a network.

DATA COMMUNICATIONS....
Data Communications

Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.

In Local Area Networks, we are interested in "connectivity", connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources.

The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications.

TYPES OF SIGNAL:

• ANALOGUE SIGNAL

            Analogue Signal on the other hand is like the human voice. It is formed by continuously varying voltage levels that create a wave that can be grasped by an analogue transmitter like microphone. These are typically represented by their characteristics of wave.

• DIGITAL SIGNAL

              Digital Transmission is the transmission of binary electrical or light pulses that only have two possible states 0, and 1. This is the language of computers. Graphically they are represented as a square wave.

Bit (binary digit)

A bit (short for binary digit) is the smallest unit of data in a computer. A bit has a singlebinary value, either 0 or 1. Although computers usually provide instructions that can test and manipulate bits, they generally are designed to store data and execute instructions in bit multiples 

called bytes. In most computer systems, there are eight bits in a byte. The value of a bit is usually stored as either above or below a designated level of electrical charge in a single capacitor within a memory device.

Half a byte (four bits) is called a nibble. In some systems, the term octet is used for an eight-bit unit instead of byte. In many systems, four eight-bit bytes or octets form a 32-bit word. In such systems, instruction lengths are sometimes expressed as full-word (32 bits in length) or half-word (16 bits in length).

In telecommunication, the bit rate is the number of bits that are transmitted in a given time period, usually a second.

Memory capacity and data storage capacity for computers are measured in bytes. File sizes are also measure in bytes (one byte is 8 bits, remember). However, a byte is small (it can hold only one character) so we use larger units:

A kilobyte (KB) is approximately 1,000 bytes. But it is NOT exactly 1,000 bytes; it is 1,024 bytes. Why a strange number like 1,024? Because 1,024 is exactly 10000000000 in binary; a nice multiple of two is very handy for the computer. So remember: When the computer tells you that your file takes up 40 kilobytes, it is actually using 40,960 bytes (not 40,000). But you can think of a kilobyte as “roughly 1,000 bytes,” which is how it got its name. This web page file is approximately 20 KB in size.

Similarly, you can think of a megabyte (MB) as approximately a million bytes, but it is precisely 1,048,576 bytes (1,024 x 1,024). The MS Word application takes up about 13 MB on the computer’s hard disk (depending on version). A typical personal computer may have 512 MB of memory.

A gigabyte (GB) is approximately one billion bytes (1,073,741,824 exactly). The root word for the giga is the same one our word giant comes from, so gigabyte should technically be pronounced with a soft g—but the pronunciation with either hard or soft g is acceptable. The storage capacity of a typical hard disk is measures in the tens or hundreds of GB.

In case you are wondering, a trillion bytes is a terabyte, but PC capacities haven’t gotten into that range yet.

Data Transmission Modes

• Data travel over a network in various

characteristics: form, amount of data : type,

direction and timing :

– Analog vs digital

– Bandwidth

– Serials Vs Parallel

– Transmission timing

– Transmission directions

– Circuit switched, Packet‐Switched, and Broadcast

Connections

Or the other hand, transmission modes is a given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterised by:

• the direction of the exchanges
• the transmission mode: the number of bits sent simultaneously
• synchronisation between the transmitter and receiver

Simplex, half-duplex and full-duplex connections

There are 3 different transmission modes characterised according to the direction of the exchanges:

• A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).
  
• A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.
  
• A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.
  

Serial and parallel transmission

The transmission mode refers to the number of elementary units of information (bits) that can be simultaneously translated by the communications channel. In fact, processors (and therefore computers in general) never process (in the case of recent processors) a single bit at a time; generally they are able to process several (most of the time it is 8: one byte), and for this reason the basic connections on a computer are parallel connections.

Parallel connection

Parallel connection means simultaneous transmission of N bits. These bits are sent simultaneously overN different channels (a channel being, for example, a wire, a cable or any other physical medium). Theparallel connection on PC-type computers generally requires 10 wires.

These channels may be:

• N physical lines: in which case each bit is sent on a physical line (which is why parallel cables are made up of several wires in a ribbon cable)
• one physical line divided into several sub-channels by dividing up the bandwidth. In this case, each bit is sent at a different frequency...

Since the conductive wires are close to each other in the ribbon cable, interference can occur (particularly at high speeds) and degrade the signal quality...

Serial connection

In a serial connection, the data are sent one bit at a time over the transmission channel. However, since most processors process data in parallel, the transmitter needs to transform incoming parallel data into serial data and the receiver needs to do the opposite.

These operations are performed by a communications controller (normally a UART (Universal Asynchronous Receiver Transmitter) chip). The communications controller works in the following manner:

• The parallel-serial transformation is performed using a shift register. The shift register, working together with a clock, will shift the register (containing all of the data presented in parallel) by one position to the left, and then transmit the most significant bit (the leftmost one) and so on:
  
• The serial-parallel transformation is done in almost the same way using a shift register. The shift register shifts the register by one position to the left each time a bit is received, and then transmits the entire register in parallel when it is full:
  

synchronous transmission

  

Data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals. In contrast, asynchronous transmission works in spurts and must insert a start bit before each datacharacter and a stop bit at its termination to inform the receiver where it begins and ends. Most network protocols (such as Ethernet, SONET, Token Ring) use synchronous transmission whereas asynchronous transmission is used commonly for communications over telephone lines.

asynchronous transmission 

Data transfer method in which signals are sent in spurts, spaced by varying time intervals. Each data character is preceded by a start-bit and is followed by an end-bit to inform the receiving equipment where the character begins and ends. This arrangement is in contrast to synchronous transmission where data is sent in continuous blocks of characters (called 'frames' or 'packets') spaced by fixed time intervals. Asynchronous transmission is used commonly for communications over telephone lines, whereas most network protocols (such as Ethernet, SONET, Token Ring) use synchronous transmission.