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

1. RADIO WAVES:- 

It has frequency between 10 K Hz to 1 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

2.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.

Following are the types of Micro waves.

1. · Terrestrial Micro waves
2. · Satellite Micro waves

1. Terrestrial Micro waves:-

• Terrestrial Micro waves are used are used to transmit wireless signals across a few miles. Terrestrial system requires that direct parabolic antennas can be pointed to each other. These systems operate in a low Giga Hertz range.

CHARACTERISTICS of Terrestrial Micro waves:-

• Moderate to high cost.
• Moderately difficult installation
• 1 M bps to 10 M bps capacity
• Variable attenuation
• Low immunity to EMI

2.Satellite Micro waves

• Satellite micro wave transmission is used to transmit signals through out the world. These system use satellites in orbit about 50,000 Km above the earth. Satellite dishes are used to send the signals to the satellite where it is again send back down to the receiver satellite. These transmissions also use directional parabolic antenna’ with in line of side.

• In satellite communication micro wave signals at 6 GHz is transmitted from a transmitter on the earth through the satellite position in space. By the time signal reaches the satellites becomes weaker due to 50,000 Km distance. The satellite amplifies week signals and transmits it back to the earth at the frequency less than 6 GHz.

Characteristics Satellite Micro waves:

• High cost
• Extremely difficult and hare installation.
• Variable attenuation.
• Low immunity to EMI
• High security needed because a signal send to satellite is broadcasts through all receivers with in satellite.

3.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

1.      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

2.      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.

Apa Itu Wi-Fi??...

•  Wi-Fi merupakan kependekan dari Wireless Fidelity, yang memiliki pengertian iaitu komplotan standar yang digunakan untuk Jaringan Lokal Nirkabel (Wireless Local Area Networks - WLAN). Awalnya Wi-Fi ditujukan untuk penggunaan perangkat nirkabel dan Jaringan Area Lokal (LAN), namun saat ini lebih banyak digunakan untuk mengakses internet. Ini kerana, wi-fi menghubungkan seseorang dengan komputer melalui kartu nirkabel (wireless card) atau personal digital assistant (PDA) untuk berhubung dengan internet dengan menggunakan titik akses (atau dikenal dengan hotspot) terdekat.

Spesifikasi Wi-Fi

Wi-Fi dirancang berdasarkan spesifikasi IEEE 802.11. Sekarang ini ada empat variasi dari 802.11 iaitu:-

• 802.11a
• 802.11b
• 802.11g
• 802.11n

Spesifikasi b merupakan produk pertama Wi-Fi. Variasi g dan n merupakan salah satu produk yang memiliki penjualan terbanyak pada tahun 2005. 

Spesifikasi Wi-Fi
Spesifikasi	Kecepatan	Frekuensi Band	Cocok dengan
802.11b	11 Mb/s	~2.4 GHz	b
802.11a	54 Mb/s	~5 GHz	a
802.11g	54 Mb/s	~2.4 GHz	b, g
802.11n	100 Mb/s	~2.4 GHz	b, g, n

Wi-fi Hardware

•  Hardware wi-fi yang ada di pasaran saat ini ada berupa :

1. PCI

2. USB 

3. PCMCIA 

4. COMPACT FLASH

 

TOPOLOGY….!!!!

What is a Topology?

• The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.

Main Types of Physical Topologies

The following sections discuss the physical topologies used in networks and other related topics.

• Linear Bus
• Star
• Tree ( Expanded Star )
• Considerations When Choosing A Topology
• Summary Chart

Linear Bus

• A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable. 

                                                                           Fig. 1

Advantages of a Linear Bus Topology

• Easy to connect a computer or peripheral to a linear bus.
• Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

• Entire network shuts down if there is a break in the main cable.
• Terminators are required at both ends of the backbone cable.
• Difficult to identify the problem if the entire network shuts down.
• Not meant to be used as a stand-alone solution in a large building.

 Star

• A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator (See fig. 2).

• Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable. 

                                                                             Fig. 2

Advantages of a Star Topology

• Easy to install and wire.
• No disruptions to the network when connecting or removing devices.
• Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

• Requires more cable length than a linear topology.
• If the hub, switch, or concentrator fails, nodes attached are disabled.
• More expensive than linear bus topologies because of the cost of the hubs, etc.

Tree or Expanded Star

• A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 3). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

                                                                             Fig 3

Advantages of a Tree Topology

• Point-to-point wiring for individual segments.
• Supported by several hardware and software venders.

Disadvantages of a Tree Topology

• Overall length of each segment is limited by the type of cabling used.
• If the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies. 

What Is a Computer Operating System?

• Computers use low-level software called an operating system (O/S) to help people build and run their own programs. Operating system software runs not just on laptop computers but also on cell phones, network routers and other so-called embedded devices.

Concentrator

• As generally used, a concentrator is a device that acts as an efficient forwarder of data transmission signals. A remote access hub is sometimes referred to as a concentrator. The term aggregator is also frequently used with approximately the same meaning. A typical concentrator or remote access hub is a device that handles incoming dial-up calls for an Internet (or other network) point-of-presence and performs other services. A concentrator or hub may be able to handle up to 100 dial-up modem calls, support a certain number of ISDN connections, and support leased line and frame relay traffic while also functioning as a router.

CABLING...!!!!

What is Network Cabling?

• Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. 

The following sections discuss the types of cables used in networks and other related topics.

• Unshielded Twisted Pair (UTP) Cable
• Shielded Twisted Pair (STP) Cable
• Coaxial Cable
• Fiber Optic Cable
• Cable Installation Guides
• Wireless LANs
• Unshielded Twisted Pair (UTP) Cable

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks.

• The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

 

Categories of Unshielded Twisted Pair

Category	Speed	Use
1	1 Mbps	Voice Only (Telephone Wire)
2	4 Mbps	LocalTalk & 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

 

Unshielded Twisted Pair Connector

• The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. 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. 

Kabel Jenis Shielded Twisted Pair (STP)

Sejenis kabel telefon kuprum yang mempunyai 2 wayar kuprum digabungkan bersama yang disaluti untuk melindungi kabel tersebut.Bahagian yang disaluti melindungi dari gelombang elecktromagnet dari kerosakan kabel.Kerap digunakan dalam Ethernet terutamanya dalam penghantaran data yang laju.

Ia sesuai untuk persekitaran elektrik sebab disaluti lebih tebal kabelnya.Ia menggunakan kuprum kabel untuk menyambungkan komputer dengan syarikat telekomunikasi.Sesuai digunbakan dalam rangkaian Token Ring Topology.

Walaupun STP melindungi ganguan lebih baik dari UTP,ia lebih mahal dan amat sukar untuk dipasang.Ia kerana pelindung yang berkilat (metallic shielding) mesti dibumikan kedua-duanya.Disebabkan kesukaran untuk memasang dan konfigurasi ia jarang digunakan dan hanya di Eropah sahaja lebih digunakan.

Ciri-ciri kabel STP:

• Kelajuan dan keluaran —10 – 100 Mbps
• Purata harga satu node — Mahal
• Saiz media dan sambungan—Sederhana – Besar
• Panjang maksimum —100 m (paling pendek)

 

Coaxial cabling

This is cabling where the central cable that transmits the data is surrounded by a shield of copper braiding. This protects it from interference and so coaxial cabling is found in places such as factories, where there is a lot of possible interference.

Fibre Optic Cabling 

Fibre Optic cales transmit data as pulses of light. The light is reflected along the cable as shown:

A fibre optic cable looks similar to this cable shown below.

Fibre Optic Advantages:

·         It is very difficult to break

·         Does not suffer from electrical or magnetic interference.

·         Transmits at very high speeds.

•          Fibre Optic Disadvantage:

·         Very expensive to buy and install.