Unbounded / Unguided 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

 RADIO WAVES it has frequency between 10 K Hz to1 G Hz. Radio waves has the following types. That is Short waves, VHF (Very High Frequency) and 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

·         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

HIGH POWER, SINGLE FREQUENCY is the 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

MICRO WAVES

Micro waves travels at high frequency than radio waves and provide through put as a wireless network media. Micro wave transmission requires the sender to be inside of the receiver.

Microwave is divide by 2. That is Terrestial MicroWaves and Satellitte MicroWaves.

1.   TERRESTRIAL MICROWAVE
~ require line-of-sight transmission and reception microwave
~ the taller the antennas, the longer the sight distance
~ signals are propagate in one direction in a time
~ consist of repeater which function to increase the distance
~ two types of antenna

Parabolic Dish
~ catching a wide range of waves and directing to a focus
~ higher frequencies for higher data rates
~ 10-60 GHz
Horn
~ looks like a gigantic scoop
~ deflected the waves outward in a series of narrow parallel beams
~ received transmission are collected by the scooped shape

2. SATELLITE
~ acting as a super tall antenna and repeater
~ relay station : receive on one frequency, amplifies and repeats signal and transmits on another frequency
~ geosynchronous : orbital speed is based on distance from planet
~ 35.784km away from the planet
~ uplink : transmission from earth to the satellite
~ downlink : transmission from satellite to earth

3. WIRELESS @ Wi-Fi
~ transmits computer data over distances using radio waves
~ most commonly used is 802.11 b (11MBps)
~ 802.11 a (54MBps)

~ to communicate over the network, computer must be equipped with a Wi-Fi card
~ types of Wi-Fi card : Wi-Fi PC Cards, USB Adapter, PCI and ISA Adapter etc.

CABLING

Cable is a medium through which information usually moves from one network devices to another. There are several types of cable which are commanly used with LAN's and each of them have different characteristics.





Twisted-pair cable
It comes in two forms which is shielded and unshielded cable. As we know, there are two category of transmission media which is bounded and unbounded media and twisted-pair cable is on the bounded categories same goes to coxial cable and fibre-optic cable.






Bounded
Current : UTP, STP and Coxial Cable
Light : Fibre-optic Cable

1.  Unshielded Twisted-Pair Cable (UTP)

~ suitable for transmitting both data and voice.

~ consists of two conductors (usually copper).

~ help to eliminate and reduce the impact of noise.

~ cheap, flexible and easy to install.

~ connector : RJ-45 connector. 

2.  Shielded Twisted-Pair Cable (STP)
~ wrapped in a foiled shielding.
~ help provide more reliable datacommunication.
~ prevents and eliminate crosstalk.
~ networj using Token Ring.
~ more expensive. 

3.   Fibre Optic Cable  
~ consist of center glass core
~ surrounded by several protective materials.
~ transmit signals over much longer distance.
~carry information at vastly greater speeds.

3.    Co-axial Cable

~ has a single copper at its centre.

~ carries signal of higher frequency.

~ metal shield help to block outside interferences.

(fluorescent light, motors and others)

NETWORKING

Networking merupakan sambungan antara 2 atau lebih perkakasan komputer yang terpisah secara fizikalnya tetapi ianya disambung secara operasi dan merupakan satu sistem perkongsian data, perisian, pertukaran maklumat, komunikasi. Pemindahan maklumat ini boleh dilakukan melalui kabel, gelombang, infrared dan satelit.

Antara kelebihan networking adalah ;

·         Berkongsi fail, data dan perisian

·         Mudah untuk memindahkan fail

·         Kurang kos dan menjimatkan masa

·         Penggunaan email

Jenis-jenis sistem rangkaian :

1. LAN (Local Area Network)

2. MAN (Metropolitan Area Network)

3. WAN (Wide Area Network)

Komponen Rangkaian :

1.       Terminals, Workstations, Computers dll

Setiap satu komputer dikhaskan sebagai file server yang mana ianya menyimpan semua perisian yang mengawal rangkaian dan segala perisian boleh dikongsi oleh semua komputer yang disambungkan kepada rangkaian. Komputer-komputer yang bersambung dengan file server dikenali sebagai workstations.

2.      Transmission Media

Ianya merupakan media yang digunakan untuk menghantar data di dalam persekitaran rangkaian.

i) Bounded ; Twisted Pair Wire, Co-Axial Cable, Fibre Optic Cable

ii) Unbounded ; AM n FM radio, TV broadcasting, satellite communication, microwave radio dan infrared signal.

3.      Network Electronic Devices

Merupakan alat yang digunakan untuk mengawal penghantaran data daripada sumber kepada destinasi.

CONTOHNYA….. bridges, routers, private branch exchange (PBX), multiplexer, switched, hubs dll.

a) Bridges (Jambatan)

Ia berfungsi membenarkan satu rangkaian yang besar dibahagikan menjadi dua buah rangkaian yang kecil dan mempunyai protokol yang mana setiap bridges menyediakan antaramuka (interface) yang serasi.

b) Routers

Membina atau menguruskan satu jadual laluan yang telah dikenal pasti dan digunakan untuk menterjemah maklumat antara rangkaian yang berasingan serta urusan penghantaran isyarat adalah begitu berkesan.

c) Hubs

Merupakan tulang belakang bagi sesebuah rangkaian (main circuit) dan mengawal trafik aliran maklumat dalam rangkaian supaya tidak berlaku perlanggaran maklumat.

4. Software

Ia merupakan perisian pada node yang biasanya melibatkan teknik dan protokol yang bertugas untuk menentukan peraturan dan prosedur bagi menghantar data, menamatkan data, terjemah data, kawal kesalahan dan mempersembahkan data. Tujuan software adalah untuk memastikan data yang ingin dihantar sampai ke destinasi.

4.      Network Operating System (NOS)

Sistem ini bertanggungjawab untuk mengawal lalu lintas pada rangkaian, membenarkan dan menghalang pemindahan data antara workstations, mengelola permintaan dan pesanan di antara pengguna rangkaian dan ianya juga mengelolakan hubungan di antara jaringan dan lokasi-lokasi jarak jauh.