6th week: topology

What is network topology?

-is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially:

- logical (virtual) and

- physical (real)

-interconnections between nodes

Logical topology

Is…….

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

Physical topology

Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network.

Types/classification

1.  Linear Bus

©      creates a network by connecting 2 or more hosts to a length of coaxial backbone cabling.

©      consists of a main run of cable (with terminator at each end)

©      all nodes connected to the linear cable.

©      Example: Think of the data as water; in this respect, the terminator must be placed in order to prevent the water from flowing out of the network.

©      The bus topology is regarded as one of the major network topologies of the networking world.

©      Ethernet and LocalTalk networks use a linear bus topology

Advantages

      Easy to connect a computer or peripheral to a linear bus

      Requires less cable length than a star topology

Disadvantages

v  Entire network shuts down if there is a break in the main cable.

v  A faulty cable or workstation will take the entire LAN down.

v  Terminators are required at both ends of the backbone cable.

v  Difficult to identify the problem if the entire network shuts down.

v  Not meant to be used as a stand-alone solution in a large building.

2.  Star

©      A star topology creates a network by arranging 2 or more host machines around a central hub.

©      A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator

©      Data on a star network passes through the hub or concentrator before continuing to its destination.

©      The hub 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.

©      usually Ethernet or LocalTalk use this

Advantages

      Easy to install, and wire.

      Easy to add new workstations

      No disruptions to the network when connecting or removing devices.

      Any non-centralised failure will have very little effect on the network

      Easy to detect faults and to remove parts.

      Centralized control

      Centralized network/hub monitoringges

Disadvantages

v  Requires more cable length than a linear topology.

v  If the hub or concentrator fails, nodes attached are disabled.

v  More expensive than linear bus topologies because of the cost of the concentrators.

3.  Star-Wired Ring

©      A star-wired topology may appear (externally) to be the same as a star topology.

©      Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring

©      The Token Ring protocol uses this.

4.  Tree

©      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.

©      Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages

      Point-to-point wiring for individual segments.

Disadvantages

v  Overall length of each segment is limited by the type of cabling used.

v  If the backbone line breaks, the entire segment goes down.

v  More difficult to configure and wire than other topologies.

Can refer to this website:

©     Click on the colour word =)

·        http://asiabizz.com/2232/various-types-of-computer-networks-and-network-topology/

·        http://errajib.hubpages.com/hub/Types-of-Networks

1.       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. Whereas network interface controllers were commonly implemented on expansion cards that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

2.       A networking operating system (NOS)(also referred as the Dialoguer) is the software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions. The network operating system is designed to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. The most popular network operating systems are Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, and Novell NetWare.

3.       A network switch (or switching hub) is a computer networking device that connects network segments or network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3) and above are often referred to as layer-3 switches or multilayer switches.The first Ethernet switch was introduced by Kalpana in 1990.

4.       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.

5.       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, running at a rate of 230.4 kbit/s. CSMA/CA was implemented as a random multiple access method.

6.       Token ring local area network (LAN) technology is a local area network protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop.Initially used only in IBM computers, it was eventually standardized with protocol IEEE 802.5.

7.       Ethernet has largely replaced competing wired LAN technologies. In the OSI reference system, Ethernet is at the Data Link layer. Systems communicating over Ethernet divide a stream of data into individual packets called frames. Each frame contains source and destination addresses and error-checking data so that damaged data can be detected and re-transmitted.

By Mhui

5th week: networking

Dr.Dayang shows us about the idea of networking, which is as old as telecommunication itself.

Do you realize that computer networking actually is just like communication we do in our daily life.

We need 2 people as sender and receiver in communication. Ofcoz there is a medium to let us communicate to each other. Computer networking is just like changing the people to computer devices, the medium is how the 2 computer connected to each other. Confuse to my explained isit? Alright....just use the word from note...

computer network

Based on the note given,

Computer networking is connecting a computer with other computers or other devices to enable them to communicate with each other.

Same as what I mentioned up there. (ok, the note given are in a pretty, simple sentences)

Computer networking can be:

©     computer devices/equipments

©     transmission media(send/control data/signal)

©     communication devices(transmit/send data frm sources to destination)

©     softwares

Type  of  network:

is based on geografhic coverage

PAN - Personal Area Network

LAN - Local Area Network

MAN - Metropolitan Area Network

WAN - Wide Area Network

beside that, also got other network like SAN, WLAN and so on.

network components:

~Terminals & workstation ,computer and other devices(end node)

Normally refers to data sources and destinations

Example:

\      personal computer,

\     terminals,

\      workstations,

\      computers,

\      automatic teller machines(ATM)

~Transmission media(physical media)

Used to transmit data in a networked environment

Transmit signal/electrical pulse through a medium

2 types:

\      bounded/guided

o   Twisted pair wire

o   Co-axial cable

o   Fiber optic cables

\      unbounded/unguided(air or a vacuum)

o   AM and FM radio

o   TV broadcasting

o   Satellite communication

o   Microwave radio

o   Infrared signals

o   bluetooth

~Network electronics devices

Control data frm sources to destinations

Also act as interface between different transmission media

Example:

(p.s. word in yellow are linked to website about it.)

\      Bridges

\      Concentrators

\      Routers

\      Front End Processors

\      Private Branch

\      Switches  Exchange (PBX)  

\      Hubs

\      Multiplexers

\      Gateways

~Software

Control data transmit

Send, end, display data

Measure the data transmits to the destination

NOS - software control a network and its msg

~Network architecture standards

Blueprint of standards for a network

Consisting of choice of media, media interfaces, encoding methods, transmission protocols, routing protocols

needed to ensure interoperability between various devices and equipment made by different vendors. 

bluetooth vs infrared

what i get on9 searching~~

As stated earlier, Bluetooth does not use infrared technology. The Infrared Data Association (IrDA) has introduced two standards: IrDA – Data, for high – speed, short- ranged, line – of – sight, and point – to – point data transfer, and IrDA – Control, for lower speed communication such as wireless keyboards, and joysticks. The range of IrDA is around one meter and requires line- of – sight between the transmitter and receiver. Moreover, IrDA communication is subjected to light interferences. The biggest advantages of IrDA over Bluetooth for point- to – point communications is its high throughput, which makes it suitable for multimedia applications requiring high – speed transmissions. However, Bluetooth has larger range, does not require line – of – sight, and is not prone to light interferences.

what i know~~

Infrared is most older technology and slower compared to bluetooth.

Both used for transferring data without wire but bluetooth is latest technology and fast

Bluetooth is prone to virus

By Mhui

4th week: Data communication

here come how the data can communicate between user and computer.

ü definition of data communication

ü type of signal

ü data transmission mode

ü data flow

definition of data communication

Data communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel. The data are represented as an electromagnetic signal.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an Analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes.

type of signal

2 type of signal:

~ Analogue signal

Ø formed by continuously varying voltage level

Ø wave can be grasped by an analogue transmitter

Ø frequency is a completed wave’s cycles, measured in hertz(Hz)

Ø Hz is cycle per second

Ø Amplitude is the wave’s height, measured in Volt(V)/decibel(dB)

Ø Strong signal create higher amplitude

Ø Signal transmit via PSTN line (phone line)

~ Digital signal

Ø Transmission of binary electrical

Ø Is language of computer

Ø Represent of a square wave

data transmission mode

parallel communication is a method of sending several data signals simultaneously over several parallel channels. This distinction is one way of characterizing a communications link.

A parallel channel will generally have additional control signals such as a clock, to indicate that the data is valid, and possibly other signals for handshaking and directional control of data transmission.

                               

serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. Serial communication is used for all long-haul communication and most computer networks, where the cost of cable and synchronization difficulties make parallel communication impractical. 

there are 2 serial mode:

v Synchronous

o   Large group of data in blocks [frame]

v Asynchronous

o   Bit into small group

o   Transmit independently

data flow

 

Network devices use three transmission flow to exchange data, or "talk" to each other, as follows: simplex, half duplex, and full duplex.

• Simplex transmission is like a one-way street where traffic moves in only one direction. Simplex mode is a one-way-only transmission, which means that data can flow only in one direction from the sending device to the receiving device. 

   Simplex (One-Way Street)

  
• Half-duplex transmission is like the center lane on some three-lane roads. It is a single lane in which traffic can move in one direction or the other, but not in both directions at the same time. Half-duplex mode limits data transmission because each device must take turns using the line. Therefore, data can flow from A to B and from B to A, but not at the same time.
  
  

   Half Duplex (Center Turn Lane)

  
• Full-duplex transmission is like a major highway with two lanes of traffic, each lane accommodating traffic going in opposite directions. Full-duplex mode accommodates two-way simultaneous transmission, which means that both sides can send and receive at the same time. In full-duplex mode, data can flow from A to B and B to A at the same time.

  Full Duplex (Interstate Highway)

  

Full-duplex transmission is, in fact, two simplex connections: One connection has traffic flowing in only one direction; the other connection has traffic flowing in the opposite direction of the first connection.

multiplexing 

multiplexing (also known as muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium.

The aim is to share an expensive resource.

A device that performs the multiplexing is called a multiplexer (MUX).

In telecommunications, a multiplexer is a device that combines several input information signals into one output signal, which carries several communication channels, by means of some multiplex technique.

A demultiplexer is, in this context, a device taking a single input signal that carries many channels and separates those over multiple output signals.

enjoy some video about 

data communication

as usual, click on the icon below to the link 

By Mhui