Network Topology

Network Topologies

LANs and WANs- Geographical coverage

LANs

-A single geographical location, such as office building, school, etc.

-Typically High speed and cheaper.

WANs

-Spans more than one geographical location often connecting separate LANs.

-Slower.

-Costly hardware, routers, dedicated leased lines and complicated implementation procedures.

Topology- Physical and logical network layout

-Physical- actual layout of the computer cable and other network devices.

-Logical- the way in which the network appears to the devices that use it.

Common topologies: Bus, ring, star, mesh and wireless.

Bus topology

-Uses a trunk or backbone to which all of the computers on the network connect.

-System connect to this backbone using T connectors or taps.

-coaxial cablings (10Base-2, 10Base-5) were popular years ago.

Bus Topology

Advantages	Disadvantages
Cheap and easy to implements	Network disruption when computers are added or remove
Required less cable	A break in the cable will prevent all systems from accessing thee network
Does not use any specialized network equipment	Difficult to troubleshoot

Ring Topology

-Logical ring

- Meaning that data travels in circular fashion from one computer to another on the network.

-Typically FDDI, SONET or Token Ring technology are used to implement a ring network.

-Ring networks are most commonly wired in a star configuration.

Token ring has multi-station access  unit (MSAU), equivalent to hub or switch. MSAU performs the token circulation internally.

Advantages	Disadvantages
Cable faults are easily located, making troubleshooting easier	Expansion to the network can cause network distruption
Ring networks are moderately easy to install	A single break in the cable can distrup entire network

Star Topology

-All computers/ devices connect to a central device called hub or switch.

-Each device requires a single cable.

-Point-to-point connection between the device and hub.

-Most widely implement.

-Hub is the single point of failure.

Advantages	Disadvantages
Easily expanded without disruption to the network	Requires more cable
Cable failure affect only a single user	A central connecting device allows for a single point of failure
Easily to troubleshoot and isolate problem	More difficult to implement

Mesh Topology

-Each computer connects to every other.

-High level of redundancy.

-Rarely used.

         -Wiring is very complicated.

         -Cabling cost is high.

         -Troubleshooting a failed cable is tricky.

         -A variation hybrid mesh- create point to point connection between                                 in WAN implementation.

Advantages	Disadvantages
Provides redundant paths between Devices.	Requires more cable than the other LAN topologies
The network can be expanded without disruption to current uses.	Complicated implementation

Wireless networking

-Do not require physical cabling.

-Particularly useful for remote access for laptops users.

-Eliminate cable faults and cable breaks.

-Signal interference and security issues.

Advantages	Disadvantages
Allows for wireless remote access	Potential security issues associted with wireless transmissions
Network can be expanded without disruption to current users	Limited speed in comparison to other network topologies.

IEEE and Networking standards

-Institute of Electrical and Electronic

Engineers (IEEE) developed a series of

networking standards.

– Networking technologies developed by

manufacturers are Compatible.

– Cabling, networking devices and protocols are

  all interchangeable under the banner of a

             specific IEEE.

802.3 IEEE standard

-Defines characteristics for Ethernet networks.

-New additions,

   – 802.3u for Fast Ethernet

   – 802.3z for Gigabit Ethernet, referred to as 802.3x.

   – … …

   – 802.3ac 10gbits/s, expe. 2009

   – … …

-Speed: Original 10Mbps, Fast Ethernet 100Mbps, Gigabit Ethernet

1000Mbps

-Topology: bus or star.

-Media: Coaxial and twisted pair cabling, also fiber optic cable.

-Access method: CSMA/CD

802.5 IEEE standard

-Specifies the characteristics for Token Ring

Networks.

-Introduced by IBM in the mid 80s, network

topology of choice until the rise of the popularity

of Ethernet.

-Speed: 4 to 16Mbps

-Topology: logical ring and most often a physical

star. Logical ring is often created in the

Multistation Access Unit (MSAU)

-Media: twisted pair cabling.

-Access method: token passing.

Networking

Apa itu Sistem Rangkaian (networking) ?

•  Penghubung antara sesuatu komputer dengan alat-alat komunikasi yang lain bagi membolehkan komunikasi berlaku. 
•  sebagai alat media untuk menghantar/mengawal data/signal. 
•  sebagai alat komunikasi untuk menerima/menghantar data daripada sesuatu sumber ke destinasi yang lain.

Antara jenis-jenis sistem rangkaian

• LAN - Local Area Network
• WAN - Wide Area network
• MAN - Metropolitan Area Network

Komponen-komponen rangkaian

Terminal:

 Semua perisian yang mengawal rangkaian telah dikhaskan sebagai satu file server oleh setiap komputer dan apa-apa perisian boleh dikongsi dengan semua komputer yang disambungkan kepada rangkaian.

workstation dikenali sebagai komputer-komputer yang bersambung dengan file server.

Media Penghantaran:

untuk segala jenis penghantaran data dan mengawal signal.

• (Bounded) : twisted pair, wire, co-axial cable, fibre optic cable.
• (Unbounded): Tv broadcasting, microwave radio, infrared signal, AM dan FM radio dan komunikasi satelit .

Alat-alat rangkaian elektronik:

·         Mengawal penghantaran data daripada sumber kepada destinasi.

e.g. bridges, routers, private branch exchange (PBX), hubs, multiplexor, switched dan seterusnya.

(a)Routers

·         Menterjemahkan maklumat antara rangkaian yang berasingan.

·         Menguruskan atau menyediakan  satu jadual laluan yang telah dikenal pasti.

·         Kerja-kerja penghantaran isyarat adalah begitu berkesan.

(b)Bridges (Jambatan)

·         Melakukan  satu rangkaian yang besar kemudiannya dibahagikan menjadi dua buah rangkaian yang kecil.

·         Menggunakan protokol yang mana setiap bridges menyediakan antaramuka (interface) yang serasi dan berkesan.

c) Hubs 

·         merupakan nadi bagi sesebuah rangkaian (main circuit).

·         Ada pengawalan trafik aliran maklumat dalam rangkaian supaya tidak berlaku percanggahan maklumat.

Software:

Sesuatu perisian pada node yang melibatkan protokol dan teknik yang bekerja bagi menentukan peraturan dan prosedur bagi menamatkan data, terjemahan data, menghantar data, mengawal kesalahan dan mempersembahkan data. Software dihasilkan bertujuan untuk memastikan data yang ingin dihantar sampai ke destinasi.

Data Communication

 

Definition.
-Is concerns the transmission of digital messages to devices external to the message source.Have electrical transmission system.
e.g: (Telephone lines and satellites)


Basic requirements for working of a communication
system

• The sender (source) who creates the message to be transmitted.
• A medium that carries the message.
• The receiver (sink) who receive the message.

Data : A collection of facts in raw form forms that become information after processing.
Signals : Eletric or electromagnetic encoding of data.
Signaling : Propagation of signals across a communication medium.
Transmission : Communication of data achieved by t he processing of signals.

Data sequencing : A long message to be transmitted is broken into

smaller packets of fixed size for error free data transmission.

Data Routing : It is the process of finding the most efficient route

between source and destination before sending the data.

Flow control : All machines are not equally efficient in terms of speed.

Hence the flow control regulates the process of sending data between

fast sender and slow receiver.

Error Control : Error detecting and recovering is the one of the main

functions of communication software. It ensures that data are transmitted

without any error.

Data transmission mode

Simplex : The communication can take place in one

direction. The receiver receives the signal from the transmitting device.

The flow of information is Uni-directional. Rarely

used for data communication.  

 

e.g : television / radio station because always transmit the signak to its listenners and never allow transmitting data.

Half-duplex : The communication channel is used

in both directions, but only in one direction at a time. Thus a half-duplex

line can alternately send and receive data.

e.g : walky talkie.

 

Full-duplex : The communication channel is used in both

directions at the same time. Use of full-duplex line improves the

efficiency as the line turn around time required in half-duplex arrangement

is eliminated.

 

e.g: telephone line.

Digital And Analog Transmission

-Data is transmitted from one point to another point by means of electrical signals

  that may be in digital and analog form.

 

Analog signal:

-The transmission power varies over a continuous range with respect to sound, light and radio waves.

 E.g. computer and computer related equipment. Measured in Volts and its frequency is in Hertz (Hz).

Digital signal:

-A digital signal may assume only discrete set of values within a given range.

-A sequence of voltage represented in binary form. When digital

data are to be sent over an analog form the digital signal must be converted to

analog form.

• Digital signal is converted to analog signal – Modulation.
• Analog signal is converted to digital signal –Demodulation

The device is used is Modem.

Asynchronous and Synchronous Transmission

-Data transmission through a medium can be either asynchronous or synchronous.

Asynchronous transmission :

-Data is transmitted character by character as you

go on typing on a keyboard.

-There is irregular gaps between characters.

-It is cheaper to implement, as you do not have to save the data before

sending.

• Serial transmission – Transmits all the bits one after another ona single line. This style is a bit slower compare to parallel. 

  

Synchronous transmission :

-The saved data is transmitted block by block.

-Each block can contain many characters.

-well suited for remote communication between a computer and related devices like card reader and printers.

• Parallel transmission – a group of bits is transmitted simultaneously by using a separate line for each bit.