how are networks categorized??

its usually classified using three properties:

• topology
• protocol
• architecture

Network Topology 

• network topology is also called network structures
• indicates how a network is design or lay out
• has both a logical level & physical level
• The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
• The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices
• has 4 main type :

1. bus
2. star ring
3. hybrid

                                          

     

Bus topology
A linear bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable.Ethernet and LocalTalk networks use a linear bus topology.The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more. If the workstation address matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.

 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

• Entire network shuts down if there is a break in the main cable. 
• A faulty cable or workstation will take the entire LAN down 
• 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 topology 
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; however, it can also be used with coaxial cable or fiber optic cable.The protocols used with star configurations are usually Ethernet or LocalTalk.

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 monitoring

Disadvantages

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

3.Star-Wired
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 a star-wired topology.

4. tree topology 
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.

Network Interface Controller

network interface controller - (NIC or "network interface card") An adapter circuit board installed in a computer to provide a physical connection to a network.

Network Operating System

An operating system that is designed for network use. Normally, it is a complete operating system with file, task and job management; however, with some earlier products, it was a separate component that ran under the OS; for example, LAN Server required OS/2, and LANtastic required DOS.

Unix, Linux, NetWare, Windows 2000 Server and Windows Server 2003 are examples of network operating systems designed for use in stand-alone servers. Such products may also include a Web server, directory services, messaging system, network management and multiprotocol routing capabilities.

Multiuser File Sharing
A network operating system (NOS) manages concurrent requests from clients and provides the security necessary in a multiuser environment. A file sharing component is installed in each client machine that interacts with the server to share files and applications as well as network devices such as printers, faxes and modems.

Peer-to-Peer Operating Systems
In a peer-to-peer network, such as Windows 98, XP, Vista or Win7, where each client machine can also be a server, the OS might still be considered a network operating system, but it is more lightweight than a full-blown NOS.

Network Switch

A network switch or switching hub is a computer networking device that connects network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model. Switches that additionally process data at the network layer and above are often referred to as layer-3 switches or multilayer switches.

Repeater

(1) A communications device that amplifies (analog) or regenerates (digital) the data signal in order to extend the transmission distance. Available for both electronic and optical signals, repeaters are used extensively in long distance transmission. They are also used to tie two LANs of the same type together. Repeaters work at layer 1 of the OSI model.

(2) The term may also refer to a multiport repeater, which is a hub in a 10Base-T network.

Local Talk

LocalTalk refers to the physical networking -- that means the built-in controller in many Apple computers, the cables and the expansion cards required on some systems. The "official" Apple cabling system typically uses a "bus topology" where each device in the network is directly connected to the next device in a daisy chain. The illustration on the Farallon book cover below gives an idea of how a bus looks.

Token Ring

A local area network (LAN) access method developed by IBM. Conforming to the IEEE 802.5 standard, Token Ring uses a token ring access method and connects up to 255 nodes in a star topology at 4, 16 or 100 Mbps. All stations connect to a central wiring hub called the "Multistation Access Unit" (MAU) using twisted wire cable.

Different than Ethernet
The Token Ring MAU may be a central hub, but does not function like a shared Ethernet hub. The Token Ring method is more deterministic and ensures that all users get regular turns at transmitting their data. With Ethernet, all users compete to get onto the network.

Type 1 and Type 3
Type 1 Token Ring networks allow up to 255 stations per network and use shielded twisted pair wires with IBM style Type 1 connectors. Type 3 Token Rings allow up to 72 devices per network and use unshielded twisted pair (Category 3, 4 or 5) with RJ-45 connectors.

  

introduction to Networking

as we know, the idea of networking is probably as old as telecommunications itself. long time ago, people only use a drum or other things to communicate with other people. But nowdays, we have computers talk to each other over vast assemblages of wires, fibre optics, microwave and satellite.

What is a NETWORKS??

• it is a collection of connected intelligent computing devices.
• example of network is a connection between two computers by direct cabling.
• networking is the practice of linking two or more computing devices together for the purpose of sharing data.
• networks are made up from mix of computer hardware & software.
• many type of networks exist,but the most common types of networks are :

1. (LANs) Local-Area Networks
   It is work as a c0vers relatively small g0egraphical such as in a h0me, sch0ol and 0ffice area. 
2. (WANs) Wide-Area Networks
   It consist 0f tw0 0r m0re LAN c0nnected t0gether using c0mmunicati0ns techn0l0gy internet is the largest WAN. 
   
   FM (Frequency M0dulati0n) radi0

• c0nvey inf0rmati0n 0ver a carrier wave by varying its instantane9us frequency.
• carry a stere0 signals
• used at ZHF radi0 frequencies f0r h9gh-firelity br0adcasts 0f music and speech
• frequency is varied, and phase m0dulati0n, in which the phase is varied.

        

       

         AM (Amplittude M0dulati0n)

• technique used in electr0nic c0mmunicati0n, m0st c0mm0nly f0r transmitting inf0rmati0n v0a radi0 carrier wave.
• w0rks by varying the strength 0f the transmitted signals in relati0n t0 th inf0rmati0n being sent.
• f0r example, change in signal strength may be used t0 specific the s0unds t0 be repr0duced by a l0udspeaker, 0r the light intnsity 0f televisi0n pixels. 

Bridges

A Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network

Hub

The network 'Hub' allows computers to share data packets within a network.

switches

A switch has a number of ports and it stores the addresses of all devices that are directly or indirectly connected to it on each port.
As a data packet comes into the switch, its destination address is examined and a direct connection is made between the two machines.

Protocol

It is a rather technical word. But it simply means an agreed method of doing something.
A 'NETWORK PROTOCOL' is the agreed method of communication to be used within the network.
Each device / computer will use this protocol.

End Nodes

Within a vast computer network, the individual computers on the periphery of the network, those that do not also connect other networks, and those that often connect transiently to one or more clouds are called end nodes. Typically, within the cloud computing construct, the individual user / customer computer that connects into one well-managed cloud is called an end node. Since these computers are a part of the network yet unmanaged by the cloud's host, they present significant risks to the entire cloud. This is called the END Nodes Problem. There are several means to remedy this problem but all require instilling trust in the end node computer.

Gateways

A gateway converts the data passing between dissimilar networks so that each side can communicate with each other. i.e converts data into the correct network protocol.
The gateway is a mixture of hardware components and software.
This is unlike a standard 'Bridge' which simply joins two networks together that share the same protocol.

Router
A Router is a device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route.

Data Communications

DEFINITION

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. data, text, voice, still picture, graphics and video is a example of information.

TYPES OF SIGNAL
Data comes in two forms:
digital signal

• transmission of binary electrical or light pulses
• have two possible states, 0 and 1
• represented as square wave
• need to be changed into analogue signal to be transmitted through PSTN
• PSTN (Public Switched Telephone Network) act as the media transmission
• modulation is a name of process of changing analogue to digital signal and demodulation is a process of changing digital to analogue.
• the hardware is used to do this process is a MoDem

 analogue signal

• formed by continuously varying voltage levels
• typically represented by their characteristic sine wave
• involves 2 parameters,which are frequency (the number of completed wave's circles) and amplitude (the height of wave).

             

BINARY DIGITS

Binary digit are basic or smallest units of measurement in digital that only consist the value of either 0 or 1. A byte is equal to 8 bit.

                                             

Understanding the Basics of Binary

 

Data Transmission Mode

Parallel transmission

• a group of bits is transmitted simultaneously by using a separate line of each bit. 

Serial transmission

• transmits all the bits one after another on a single line
• slower than parallel transmission
• best suit data communication needs to transmit data in a long distance
• there are 2 serial transmission modes which are synchronous and asynchronous transmission

 a) synchronous transmission

•  frame is a large group of data is transmitted in block
• In this method, both the sending device and the recieve device are operated simultanously and resynchronised
• it is occur after each few thousand data signal bits are transmitted

b) asynchronous transmission

• it is used when the bits are devided into small group (bytes) and sent independently
• the groups of bits can be sent at any time but the reciever never knows when they will arrive

Data Flow

1) 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.

example of simplex(television)

 2) 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.

example of Half Duplex(walkie talkie)

3)  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.

example of Full Duplex( telephone)

Introduction to web browser

 

What is web browser?

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users easily to navigate their browsers to related resources. A web browser can also be defined as an application software or program designed to enable users to access, retrieve and view documents and other resources on the Internet.

Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by web servers in private networks or files in file systems. The major web browsers are Firefox, Google Chrome, Internet Explorer, Opera, and Safari. 

     The major web browsers

      
    
    

search engine

 

 

A web search engine is designed to search for information on the World Wide Web and FTP servers. The search results are generally presented in a list of results often referred to as SERPS, or "search engine results pages". The information may consist of web pages, images, information and other types of files. Some search engines also mine data available in databases or open directories. Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.

Directories

   

     Subjects

•           built by human selection -- not by computers or robot programs 
•             organized into subject categories, classification of pages by subjects -- subjects not standardized and vary according to the scope of each directory 
•             NEVER contain full-text of the web pages they link to -- you can only search what you can see (titles, descriptions, subject categories, etc.) -- use broad or general terms 
•             small and specialized to large, but smaller than most search engines -- huge range in size 
•             often carefully evaluated and annotated (but not always!!)