Technology

for pay per post experiment

noreply@blogger.com (Nouman Ali) — Wed, 1 Dec 2010 02:13:00 -0800

Why am I getting strange traffic to my blog after I publish changes?

for pay per post experiment

noreply@blogger.com (Nouman Ali) — Wed, 1 Dec 2010 02:08:00 -0800

CSMA/CD

There is no central control management when computers transmit on Ethernet.

Exponential Back Off:

Even with random delays, collision may occur especially likely with busy segments.

Bit Stuffing

Byte stuffing refers stuffing with character oriented hardware and bit stuffing refers to bit oriented hardware.

The modified record may be written into an overflow

area, forcing either multiple read operations at query time or reorganizing and rewriting the

previous area.

Columnar database column-based structure

The newer column structure has gained interest as the indexing and data transfer

problems associated with record structures have proved problematic for analytics

applications.

small that the entire set of all data values can frequently stay in memory, affecting I/O

bandwidth only when the system is started.

Relational Database (RDBMS)

There are many commercial variations of record-based databases available.

In VBS, each unique data value is stored only once,

making the database extremely compact and fast.

Conclusion

Despite their limitations, rrecord-based relational databases have long been the prevailing

data structure used in data warehouse systems

that are impractical or impossible with other data structures

56k Modems

Uploading

Downloading

Result

Mode

Multimode Step-index Graded-index

Single Mode

LECTURE # 4

Performance of Medium:

Throughput

Propagation Speed

Propagation Time

Types of Digital Services

LECTURE # 21

Internet

Press	To
CTRL+C	Copy.
CTRL+X	Cut.
CTRL+V	Paste.
CTRL+Z	Undo.
DELETE	Delete.

SHIFT when you insert a CD into the CD-ROM drive

Prevent the CD from automatically playing.

F1	Display Help.
F4	Display the items in the active list.
BACKSPACE	Open a folder one level up if a folder is selected in the Save As or Open dialog box.

Search for computers.

Accessibility keyboard shortcuts

RIGHT ARROWDisplay current selection if it's collapsed, or select first subfolder

A computer running Windows XP Professional ("remote" computer) with a connection to a Local Area Network or the Internet.

Ensure that Remote Desktop Web Connection is installed and running on the Web server. For more information, see Setting up Remote Desktop Web Connection.

You can now make free calls from your pc to any mobile in the world

very Excelent Result of AVG 9.0 proofed.

When you publish to your blog, your blog goes into a huge database, listing blogs just updated. You can see a replica of this database in the Recently Updated Blogs list

More Traffic To Our Blogs?

AVG virus database

When you publish to your blog, your blog goes into a huge database, listing blogs just updated.

Randomly generated sentance

noreply@blogger.com (Nouman Ali) — Sun, 28 Nov 2010 23:40:00 -0800

When you publish to your blog, your blog goes into a huge database, listing blogs just updated.

AVG virus database

noreply@blogger.com (Nouman Ali) — Sun, 28 Nov 2010 16:41:00 -0800

AVG virus database. Via the update process, these new definitions are downloaded to your computer so that you are always reliably protected even against the latest threats.

Online Threats

More Traffic To Our Blogs?

noreply@blogger.com (Nouman Ali) — Sun, 28 Nov 2010 16:36:00 -0800

More Traffic To Our Blogs?

Recently, we see periodic queries about strange visitors to our blogs.

Why does my StatCounter log show odd links into my blog?

What is "www.blogger.com/navbar.g?targetBlogID=", and why do I see traffic from that link?

Why am I getting strange traffic to my blog after I publish changes?

More Traffic To Our Blogs?

noreply@blogger.com (Nouman Ali) — Mon, 1 Nov 2010 10:25:00 -0700

More Traffic To Our Blogs?

Recently, we see periodic queries about strange visitors to our blogs.

Why does my StatCounter log show odd links into my blog?

What is "www.blogger.com/navbar.g?targetBlogID=", and why do I see traffic from that link?

Why am I getting strange traffic to my blog after I publish changes?

All of these questions, until Mid November 2009, were related to the same thing - the "Next Blog" link in the Navbar. Now, all of this is changed.

When you publish to your blog, your blog goes into a huge database, listing blogs just updated. You can see a replica of this database in the Recently Updated Blogs list. The RUB list is huge - it shows a 10 minute slice of Blogger publishing, and at any time, will have from 4,000 - 8,000 entries, with new entries constantly being added (just as old ones drop off the list).

The RUB database is important to the Blogosphere. When anybody clicks on the "Next Blog" link in the Navbar, an entry from that database results in the link leading to someone's blog. Ifyour blog was just updated, chances are that someone will land on your blog, and your visitor meter will show another entry.

In the recent past, there were hundreds of thousands of illegal blogs, created by spammers and being constantly published. Until January 2008, many people clicking on "Next Blog" would have landed on such a blog, which was created for the sole purpose of hacking your computer, and delivering spam to your desktop, and to other peoples email.

A bit over a week ago, Google put a stop to this. Now, owners of many (but not all) genuine blogs, like yours and mine, are seeing more traffic, when we publish changes. The traffic comes from the "Next Blog" link, which is seen in visitor logs as originating from "www.blogger.com/navbar.g".

If you see the new traffic in your logs, don't be alarmed. It's not somebody trying to hack you, or to steal blog content. It's ordinary bloggers, and bloggers readers, surfing to random blogs, using "Next Blog". It's what the "Next Blog" link was created for.

Enjoy the traffic to your blog. Publish more, and enjoy more. More readers for you, which is why you blog, right? Having said all of that, I will advise you that, if your blog contains any questionable content, particularly interesting pictures that you wouldn't want your kids to see, you need to be aware of, and you may need to use, the Content Warning setting in Settings - Basic. Or, you can block traffic from "Next Blog", if you really feel the need.

Note that this post is about the "Next Blog" link in the navbar. It's not here so you can get more traffic to your blog, by posting

Great post!
Here's my blog: http://mypimpedblog.blogspot.com

If that's your intent, go away.

(Update 2009/11/12): The next generation of "Next Blog" is here, and it's totally different.

very Excelent Result of AVG 9.0 proofed.

noreply@blogger.com (Nouman Ali) — Sun, 31 Oct 2010 08:04:00 -0700

The AVG virus database contains known virus definition. AVG virus experts work hard to identify and explain the latest viruses as soon as these become known (which happens every day), and add the definition to the AVG virus database. Via the update process, these new definitions are downloaded to your computer so that you are always reliably protected even against the latest threats.

Online Threats

Nowadays, there are far more threats out there than plain viruses. You have probably come across the term spyware as well, however, authors of hateful codes and dangerous websites are very modern, and new kinds of threats emerge quite often, the vast majority of which are on the Internet. Here are some of the most common:

Exploit is a malicious code that takes advantage of a flaw or vulnerability in an operating system, Internet browser, or other essential program.

Social engineering is a common term for various techniques used to trick people into giving away their personal information (passwords, bank account details, credit card numbers etc.). A typical example of social engineering is phishing – an attempt to acquire sensitive personal data by shamming a trustworthy and well-known organization. Usually, the potential victims are contacted by a bulk e-mail asking them to e.g. update their bank account details. In order to do that, they are invited to follow the link provided which then leads to a fake website of the bank.

Scam can be also considered a kind of social engineering; it includes false job offers, or ones that will abuse the workers for illegal activities, summons to withdraw a large sum of money, fraudulent lotteries and the like.

Hoax is a bulk e-mail containing dangerous, alarming or just bothering and useless information. Many of the above threats use hoax e-mail messages to spread.

Finally, malicious websites are ones that deliberately install malicious software on your computer, and hacked sites do just the same, only these are legitimate websites that have been compromised into infecting visitors.

To protect you from all of these different kinds of threats, AVG includes these specialized components:

·	Anti-Virus to protect your computer from viruses,
·	Anti-Spyware to protect your computer from spyware,

·	Online Shield (only in AVG Professional) to protect you from both viruses and spyware when surfing the Internet,
·	Link Scanner to protect you from other online threats mentioned in this chapter.

I am recommend you that daily update the AVG virus Database. To keep protected from the latest virus. And you very comfortable when you daily update the avg antivirus against the latest threats.

AVG Interface

System plate Icon

AVG 9.0 Free Edition launches automatically upon Windows startup, and you can see its icon in the system tray (right floor part of the screen). The icon indicates the current Security Status, i.e. whether AVG is working properly or not.

The purpose of the Security Status is to warn you instantly if there is a problem:

The AVG icon in the system tray (usually right bottom corner of your screen, see picture) shows an exclamation mark, and warning bubbles pop up above the system tray.

How do I fix error Security Status?

Main Screen

The main screen is the front of the AVG application, offering an overview of all installed mechanism and allowing you to access all functions. To display the Main Screen, either:

·	Double-click the AVG icon (on the desktop, or in the system tray), or
·	Use the Start menu -> Programs -> AVG 9.0 Free Edition -> AVG User Interface

What can I see on the Main Screen?

To shut down AVG Interface, use the Main Screen -> Main Menu File -> Exit.

Please note that you only close the interface indeed; the AVG system keeps running in the computer memory at all times.

Yahoo Messsenger Free Calls all over the world

noreply@blogger.com (Nouman Ali) — Sun, 31 Oct 2010 01:16:00 -0700

You can now make free calls from your pc to any mobile in the world.All you need is a Yahoo messenger,a mic and a decent internet connection.I'm now using this free call method for over a month now and the great thing is that, this trick can be used to make unlimited call to mobiles all over the world and not limited to United states.It even works to make free local mobile calls in India.

So how do we make a call from pc to mobile phone for free.
Install Yahoo messenger ,incase you don't have it (go for the latest one which have voice support).
Sign into your yahoo messenger.
Configure your microphone and headset(don't use speakers as it cause disturbances)
Inside your Yahoo messenger dial 18003733411 and press enter.
Now a small window pops up like the one shown below.

An operator greets you with a recorded welcome message along with an advertisement and asks you to select one of the Free411 service.Just hear the services options until they say the last one as “Free Call”.When you hear this,don't press any number on your keyboard and instead SAY “Free call” loudly on your microphone connected to your PC.

After this voice message is detected by their system ,they will run a short advertisement of their sponsor and make sure you don't press any number at this time.
WAIT UNTIL YOU HEAR THIS MESSAGE “Please dial the phone number country code first,don't forget to dial 1 for north america”
After you hear this message ,immediately dial the destination number of your choice along with the country code.(eg for north america it's 1 and for india it's 91)
Your call will get connected and you can talk for 7 minutes continuous for free.When it gets disconnected, repeat the same procedure again.You can make multiple and unlimited calls with this service.

It was never easy to make a free international call like this before
So what's the catch?
FREE411 service toll-free number is based in USA.This company gets paid for the advertisements from sponsors.

Are there any limits on the number of call which we can make?

No.There is no limit on the number of free calls which can be made through this system.
So enjoy this trick to make free international and local calls and make sure you don't abuse the system.

To connect to another computer using Remote Desktop Web Connection

noreply@blogger.com (Nouman Ali) — Sat, 30 Oct 2010 00:16:00 -0700

Ensure that Remote Desktop Web Connection is installed and running on the Web server. For more information, see Setting up Remote Desktop Web Connection.
Ensure that your client computer has an active network connection and that the WINS server service (or other name resolution method) is functioning.
On your client computer, start Microsoft Internet Explorer.
In the Address box, type the Uniform Resource Locator (URL) for the home directory of the Web server hosting Remote Desktop Web Connection.
The URL is "http://" followed by the Windows Networking name of your server, followed by the path of the directory containing the Remote Desktop Web Connection files (default = /Tsweb/). (Note the forward slash marks.) For example, if your Web server is registered with the WINS server as "Admin1", in the Address box you type: http://admin1/tsweb/, and then press ENTER. The Remote Desktop Web Connection page appears on the screen.
In Server, type the name of the remote computer to which you want to connect.
Optionally, specify the screen size and logon information for your connection.
Click Connect.

Notes

Remote Desktop Web Connection requires Internet Explorer 4.0 or higher.

Remote Desktop overview about working Remotely

noreply@blogger.com (Nouman Ali) — Sat, 30 Oct 2010 00:12:00 -0700

Remote Desktop overview

With Remote Desktop on Windows XP Professional, you can have access to a Windows session that is running on your computer when you are at another computer. This means, for example, that you can connect to your work computer from home and have access to all of your applications, files, and network resources as though you were in front of your computer at work. You can leave programs running at work and when you get home, you can see your desktop at work displayed on your home computer, with the same programs running.
When you connect to your computer at work, Remote Desktop automatically locks that computer so no one else can access your applications and files while you are gone. When you come back to your computer at work, you can unlock it by typing CTRL+ALT+DEL.
Remote Desktop also allows more than one user to have active sessions on a single computer. This means that multiple users can leave their applications running and preserve the state of their Windows session even while others are logged on.
With Fast User Switching, you can easily switch from one user to another on the same computer. For example, suppose you are working at home and have logged on to the computer at your office to update an expense report. While you are working, a family member needs to use your home computer to check for an important email message. You can disconnect Remote Desktop, allow the other user to log on and check mail, and then reconnect to the computer at your office, where you see the expense report exactly as you left it. Fast User Switching works on standalone computers and computers that are members of workgroups.
Remote Desktop enables a variety of scenarios, including:

Working at home - Access work in progress on your office computer from home, including full access to all local and remote devices.
Collaborating - Bring your desktop to a colleague's office to debug some code, update a Microsoft PowerPoint slide presentation, or proofread a document.
Sharing a console - Allow multiple users to maintain separate program and configuration sessions on a single computer, such as at a teller station or a sales desk.

To use Remote Desktop, you need the following:

A computer running Windows XP Professional ("remote" computer) with a connection to a Local Area Network or the Internet.
A second computer ("home" computer) with access to the Local Area Network via network connection, modem, or Virtual Private Network (VPN) connection. This computer must have Remote Desktop Connection, formerly called the Terminal Services client, installed.
Appropriate user accounts and permissions.

To set up this computer to use Remote Desktop

Open System in Control Panel.
On the Remote tab, select the Allow users to connect remotely to this computer check box.
Ensure that you have the proper permissions to connect to your computer remotely, and click OK. You must be an administrator or a member of the Remote Desktop Users group on your computer. For more information, see To allow other users to connect to your computer.

Notes

You must be logged on as an administrator or a member of the Administrators group to enable the Remote Desktop feature.
To open a Control Panel item, click Start, click Control Panel, and then click the appropriate icon.

Windows Explorer keyboard shortcuts

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 23:38:00 -0700

Press	To
END	Display the bottom of the active window.
HOME	Display the top of the active window.
NUM LOCK+ASTERISK on numeric keypad (*)	Display all subfolders under the selected folder.
NUM LOCK+PLUS SIGN on numeric keypad (+)	Display the contents of the selected folder.
NUM LOCK+MINUS SIGN on numeric keypad (-)	Collapse the selected folder.
LEFT ARROW	Collapse current selection if it's expanded, or select parent folder.
RIGHT ARROW	Display current selection if it's collapsed, or select first subfolder

Tell your Experinece about using shortcut keys of keybord.And share your experinece.

Accessibility keyboard shortcuts

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 23:37:00 -0700

Press	To
Right SHIFT for eight seconds	Switch FilterKeys on and off.
Left ALT +left SHIFT +PRINT SCREEN	Switch High Contrast on and off.
Left ALT +left SHIFT +NUM LOCK	Switch MouseKeys on and off.
SHIFT five times	Switch StickyKeys on and off.
NUM LOCK for five seconds	Switch ToggleKeys on and off.
+U	Open Utility Manager.

Natural keyboard shortcuts

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 23:36:00 -0700

Press	To
	Display or hide the Start menu.
+BREAK	Display the System Properties dialog box.
+D	Show the desktop.
+M	Minimize all windows.
+Shift+M	Restores minimized windows.
+E	Open My Computer.
+F	Search for a file or folder.
CTRL+ +F	Search for computers.
+F1	Display Windows Help.
+ L	Lock your computer if you are connected to a network domain, or switch users if you are not connected to a network domain.
+R	Open the Run dialog box.
	Display the shortcut menu for the selected item.
+U	Open Utility Manager.

Dialog box keyboard shortcuts

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 23:34:00 -0700

Press	To
CTRL+TAB	Move forward through tabs.
CTRL+SHIFT+TAB	Move backward through tabs.
TAB	Move forward through options.
SHIFT+TAB	Move backward through options.
ALT+Underlined letter	Carry out the corresponding command or select the corresponding option.
ENTER	Carry out the command for the active option or button.
SPACEBAR	Select or clear the check box if the active option is a check box.
Arrow keys	Select a button if the active option is a group of option buttons.
F1	Display Help.
F4	Display the items in the active list.
BACKSPACE	Open a folder one level up if a folder is selected in the Save As or Open dialog box.

General keyboard shortcuts

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 23:33:00 -0700

Press	To
CTRL+C	Copy.
CTRL+X	Cut.
CTRL+V	Paste.
CTRL+Z	Undo.
DELETE	Delete.
SHIFT+DELETE	Delete selected item permanently without placing the item in the Recycle Bin.
CTRL while dragging an item	Copy selected item.
CTRL+SHIFT while dragging an item	Create shortcut to selected item.
F2	Rename selected item.
CTRL+RIGHT ARROW	Move the insertion point to the beginning of the next word.
CTRL+LEFT ARROW	Move the insertion point to the beginning of the previous word.
CTRL+DOWN ARROW	Move the insertion point to the beginning of the next paragraph.
CTRL+UP ARROW	Move the insertion point to the beginning of the previous paragraph.
CTRL+SHIFT with any of the arrow keys	Highlight a block of text.
SHIFT with any of the arrow keys	Select more than one item in a window or on the desktop, or select text within a document.
CTRL+A	Select all.
F3	Search for a file or folder.
ALT+ENTER	View properties for the selected item.
ALT+F4	Close the active item, or quit the active program.
ALT+Enter	Displays the properties of the selected object.
ALT+SPACEBAR	Opens the shortcut menu for the active window.
CTRL+F4	Close the active document in programs that allow you to have multiple documents open simultaneously.
ALT+TAB	Switch between open items.
ALT+ESC	Cycle through items in the order they were opened.
F6	Cycle through screen elements in a window or on the desktop.
F4	Display the Address bar list in My Computer or Windows Explorer.
SHIFT+F10	Display the shortcut menu for the selected item.
ALT+SPACEBAR	Display the System menu for the active window.
CTRL+ESC	Display the Start menu.
ALT+Underlined letter in a menu name	Display the corresponding menu.
Underlined letter in a command name on an open menu	Carry out the corresponding command.
F10	Activate the menu bar in the active program.
RIGHT ARROW	Open the next menu to the right, or open a submenu.
LEFT ARROW	Open the next menu to the left, or close a submenu.
F5	Refresh the active window.
BACKSPACE	View the folder one level up in My Computer or Windows Explorer.
ESC	Cancel the current task.
SHIFT when you insert a CD into the CD-ROM drive	Prevent the CD from automatically playing.

Data Communication All possible Terminologies

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 00:37:00 -0700

Try to explain itself check your concept

Modems Standards

Traditional modems

56k Modems

Uploading

Downloading

Result

Lecture 1

Cable Modems

Downloading

Uploading

Electromagnetic Energy

Classes of Transmission Media

Transmission Media:

Guided

Unguided

Two classes of Transmission Media

Guided Media

Unguided Media

Guided Media

Guided Media:

Twisted-Pair cable

Coaxial cable

Fiber-optic cable

Twisted pair cable:

Unshielded Twisted Pair UTP

Shielded Twisted Pair (STP)

Frequency range for twisted pair cable

100Hz 5MHZ

Unshielded Twisted Pair (UTP)

Parallel Flat Wire

Noise Effect on Twisted-Pair

Advantages of UTP

Categories of UTP Cable

Category 1

Category 2

Category3

Category4

Category5

UTP Connectors

Lecture # 2

Shielded Twisted Pair (STP)

Coaxial Cable

Frequency Range of Coaxial

Coaxial cable

100 kHz 500 MHz

Coaxial Cable standards

Coaxial Cable Connectors

T-Connector

Terminators

Optical Fiber

The Nature of Light

Refraction

Example of Refraction

Direction of Refraction

Critical Angle

Refraction

Optical Fibers & Reflection

Propagation Modes:

Mode

Multimode Step-index Graded-index

Single Mode

Multimode Fiber

Disadvantage of Multimode Step-index Fiber

Multimode Graded-index Fiber

Lecture # 3

Single Mode Fiber

Fiber Sizes

Light Sources for Optical Cable

LED:

LASER:

Fiber Optic connectors

Advantages of Optical Fiber

Noise Resistance:

Less Signal Attenuation

Higher Bandwidth

Disadvantages of Optical Fiber

Cost

Installation

Disadvantages of Optical Fiber

Fragility

Unguided Media

Radio Frequency Allocation

Propagation of Radio Waves

Types of Propagation:

Space

TROPOSHERE

IONOSPHERE

Surface Propagation

Troposphere Propagation

Line-of-Sight

Broadcast

Ionosphere propagation

Line of Sight propagation

Space Propagation

LECTURE # 4

Propagation of Specific Signals

Very Low Frequency (VLF)

3 kHz Long-range radio navigation 30 kHz

Low Frequency (LF)

30 KHz Long-range radio navigation 300 KHz

Middle Frequency (MF)

AM radio

300 KHz 535 KHz 1.605 MHz 3 MHz

High Frequency (HF)

CB radio

3MHz 30Mhz

Very High Frequency (VHF)

Paging TV FM Aircraft TV

30MHz 54 88 108 174 216 300MHz

Ultra High Frequency (UHF)

Mobile Telephone UHF TV Cellur ra paging Microwave 3Ghz.

300 MHz 470 806

Super High Frequency (SHF)

Microwave

3GHz 30Ghz

Extremely High Frequency (EHF)

Microwave

30 GHz 300GHz.

Terrestrial Microwave

Repeaters

Antennas

Parabolic Dish

HORN

Satellite Communication

Geosynchronous Satellite

Satellite Frequency Bands

Cellular Telephony

Each service area is divided into small ranges called cells.

Operations of Cellular Telephony

Transmitting

Receiving

Handoff

Transmission Impairments

Impairment

Attenuation

Distortion

Noise

Attenuation

Decibel (dB)

Distortion

LECTURE # 5

Transmission Impairments

Impairment:

Attenuation

Distortion

Noise

Attenuation

Decibel (dB)

Distortion

Noise

Induced Noise

Crosstalk:

Impulse Noise

Performance of Medium:

Throughput

Propagation Speed

Propagation Time

Throughput

Propagation Speed

Propagation Time

WAVELENGTH

Shannon Capacity

Media comparison

Cost:

Speed:

ATTENUATION:

EM Interference:

SECURITY:

Lecture # 6

Introduction to Multiplexing

Multiplexing

Path:

Channel:

Categories of Multiplexing

Multiplexing

Frequency-division multiplexing (FDM)

Time-Division multiplexing (TDM) Synchronous Asynchronous

Wave-division multiplexing (WDM)

FDM

FDM (Guard Bands)

GURD BANDS

DEMULTIPLEXING

Wave Division Multiplexing (WDM)

Mechanism of WDM

PRISM

TDM

Implementation of TDM

Synchronous TDM

Synchronous TDM Example

Synchronous TDM Frames

Interleaving

Weakness of Synchronous TDM Figure

Demultiplexing Process

Framing Bits

Synchronous TDM

LECTURE # 7

Bit Stuffing

Asynchronous TDM

Advantages of Asynchronous TDM

Asynchronous TDM Figure 1

Asynchronous TDM Figure 2

Asynchronous TDM Figure 3

Aspects of Asynchronous TDM

Addressing and Overhead

Inverse Multiplexing

Why do we need inverse Multiplexing?

Multiplexing Application

The Telephone System

LECTURE # 8

Telephone Services

Services

Analog services

Digital Services

Common Carrier Services & Hierarchies

Analog Services

Switched Analog Services

Analog Leased Service

Conditional lines

Analog Hierarchy

Digital Services

Types of Digital Services

Digital Services

Switched/56 DDS Ds

Swithced/56 service

Digital Data Service (DDS)

Digital Signal (DS) Service

T Lines

LECTURE # 9

T Lines

T Lines for Analog Lines

T1 Frame (Figure)

Fractional T Lines (Figures)

E-Lines

Fiber to the Curb (FTTC)

FTTC in Telephone Network

FTTC in Cable TV Network

ERROR DETECTION AND CORRECTION

Introduction

Types of Errors

ERRORS

Single-bit

Burst Errors

Error Detection

Redundancy

Types of Redundancy checks

Vertical Redundancy check (VRC)

Performance of VRC

Lecture # 10

Error Detection and Correction Methods

Longitudinal Red Check (LRC)

Performance of LRC

Cyclic Redundancy check (CRC)

Qualities of CRC

The CRC Generator

The CRC Checker

Polynomials

Selection of a Polynomial

Popular polynomials for CRC

Performance of CRC

LECTURE # 11

Error Detection and Correction Method

Checksum

One’s Complement

CHECKSUM Generator

Cecksum Figure

Performance of Checksum

ERROR CORRECTION

Single-bit Error Correction

Lecture# 12

Hammming Code

Redundancy Bits (r)

Haming code

Data Link Layer

Introduction

Data Link Layer & Its Functions

Data Link Control

Line Discipline

Flow Control:

Error Control:

Line Discipline:

Ways to do Line Discipline

Enquiry/Acknowledgment (ENQ/ACK)

Poll /Select

LECTURE # 13

Line Discipline

Enquiry/Acknowledgement (ENQ/ACK)

How it works?

Poll/Select

Polling

SELECTING

Addressing

Select

Poll

Flow Control-Definition

LECTURE # 14

Flow Control stop-and-wait sliding window

Flow Control-Explanation

Flow Control-Buffer

Methods for Flow Control

Stop and wait

Advantages of stop and wait

Simplicity

Disadvantages of Stop and wait

INEFFICIENT (slow)

Sliding window

AUTOMATIC REPEAT REQUEST (ARQ)

Categories of Error Control

Error control

Stop-and-wait Sliding window

ARQ

GO-Back-n Selective-reject

Stop and wait ARQ

Damaged Frame

Lost Frame

Lost ACK, NAK Frame

LECTURE # 15

SLIDING WINDOS ARQ

Go Back n ARQ

Go Back n-Damaged Frame

Go Back n-Lost Data Frame

Go Back n-Lost ACK

Selective Reject ARQ

Selective Reject ARQ vs. Go Back n

Protocols

Protocol

Protocol in Data Comm.

Data Link Protocols:

Categories of Data Link Protocols

Data Link protocols

Asynchronous Synchronous

Protocols protocols

Asynchronous Protocols:

Synchronous protocols:

Asynchronous Protocols

Inherent Slowness is a disadvantage:

Not Complex and Inexpensive to implement

Different Asynchronous Protocols

XMODEM

Transmission in XMODEM

Control Frames in XMODEM

Control Frames from the receiver

-ACK: Acknowledgement

-NAK: Error or Start of transmission

-CAN: Aborts the Transmission

LECTURE # 16

YMODEM

ZMODEM

BLAST

KERMIT

Synchronous Protocols

Classes of Synchronous protocols

Character-Oriented Protocols

Bit-Oriented Protocols

Binary synchronous Communication (BSC)

CONTROL FRAMES

DATA FRAMES

Data Frame with Header

Multiblock Frame

Multi

Frames

Control Frames

LECTRUE # 17

Bit-Oriented Protocols

SDLC HDLC LAPs LANs

High Level Data Link Control (HDLC)

Characterization of HDLC

STATION TYPES (1)

STATION TYPES (2)

Primary station

STATION TYPES (4)

Combined station

Configuration (1)

Configuration (2)

Unbalanced configuration

Configuration (3)

Symmetrical Configuration

Configuration (4)

Balanced Configuration

Station Types & Configurations

Modes

Normal Response Mode (NRM)

Asynchronous Response Mode (ARM)

Asynchronous Balanced Mode (ABM)

HDLC Frames

1-Frames

S-Frames

U-Frame

Flag Field

HDLC Address Field

HDLC Control Field

P/F bit

HDLC Control Field –EXTENDED

Piggybacking

Link Access Procedures

LECTURE# 18

Local Area Network

Architectures for LANs

LAN compared with OSI

Logical Link control (LLC)

Medium Access Control (MAC)

PROJECT 802

IEEE 802.II

LLC

MAC

Protocol Data Unit (PDU)

DSAP and SSAP

CONTROL

ETHERNET

IEEE 802.3 define two categories

Access Method: CSMA/CD

Need for Access Method

COLLISIONS

Carrier Sense Multiple Access with collision Detection (CSMA/CD)

NA CSMA CSMA/CD

CSMA/CD

CSMA

Addressing

Data Rate

Implementation

10 Base 5: Thick Ethernet

Size limitations of 10 Base 5

Topology of 10 Base 5

RG-8 Cable

TRANSCEIVER

AUI Cables

TRANSCEIVER TAP

VAMPIRE TAP

LECTURE # 19

Ethernet

802.3 Baseband Digital (Manchester) Broadband Analog(PSk)

10Base 2: Thin Ethernet Advantages

Disadvantages

Physical Topology of 10 base 2

NIC

RG-58 Cable

BNC-T

10 base T: Twisted pair Ethernet

1 Base 5: STAR LAN

DAISY CHAINING

Switched Ethernet

Fast Ethernet

100 Base-TX and 100 Base-FX

100 Base-T4

Gigabit Ethernet

Token Bus

LECTURE # 20

Token Ring

Access Control of Token Ring

Monitor stations

Token Ring Frame

Data Frame Fields

Implementation

Token Ring Switch

Multi station Access Unit (MAU)

FDDI

FDDI Time Registers

FDDI Timers

Station procedure

Dual Ring (Figure-1)

Dual Ring (Figure-2)

LECTURE # 21

Internet

Connecting devices (Figure-I)

Connecting devices (Figure-2)

Repeaters (Figure-I)

Repeaters (Figure-2)

Repeaters (Figure-3)

Bridges

TCP/IP Protocols

Good luck for your future

if you have passion about data communication take further advance courses

like CCNA .CCNP .

Data Warehose concept

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 00:13:00 -0700

RDBMS record-oriented structure

The record-based structure is the most common choice for data warehouse applications.

In this structure, data is stored in physical records using the common physical location of

data values as the logical connection across all data points of the individual record. For

example, to find a customer address, the system must first locate the customer using an

indexed value such as customer number, then scan across the record to the position for

address. As a result, the smallest addressable unit of storage is an entire record, and all

physical I/O functions will always move complete records or sets of complete records.

Since entire records are physically written and read as single units, selecting any field

requires reading the entire record, and changing a single value requires reading and

rewriting the entire record. If the new value requires more space than the original,

extensive additional I/O is needed. The modified record may be written into an overflow

area, forcing either multiple read operations at query time or reorganizing and rewriting the

previous area.

Columnar database column-based structure

The newer column structure has gained interest as the indexing and data transfer

problems associated with record structures have proved problematic for analytics

applications. The column-based DBMS stores all of the values from one column of a table

in a contiguous data set. This allows the reading and/or writing of parts of records. It

conserves I/O bandwidth by transferring only the values that may be used in the query.

Since most data warehouse applications use only a few columns from a table during a

typical single access, the resulting bandwidth savings can be substantial.

Writing new records requires updating each of the column sets that belong to the record.

Reading a complete record requires locating the correct value from each column set and

assembling those into the original record format. Therefore, full record operations show

little improvement over record-based systems and, in some cases, even can perform more

slowly.

Correlation DBMS value-based structure

The most recent innovation, value-based storage (VBS)—used in the correlation database

management system (CDBMS)—also avoids the indexing problems of record structures,

but in addition, it has exploratory and analytical features not available with either recordoriented

or column-based structures. The value-based model stores each unique value

once, then uses extended metadata to maintain the information needed to manage record

formatting. VBS minimizes bandwidth consumption, as the actual data value storage is so

small that the entire set of all data values can frequently stay in memory, affecting I/O

bandwidth only when the system is started.

Relational Database (RDBMS)

There are many commercial variations of record-based databases available. All share the

common characteristic of storing related values in a physically contiguous record. The

most commonly used form used for data warehousing and analytics is the RDBMS, which

has dominated the entire database market for years due to its strengths in processing and

storing transactions and in generating reports.

Columnar Database

A columnar database stores data much differently than does a RDBMS. In this structure,

data is stored in sets by column—that is, all of the values stored in column one are stored

in one set, all the values in column two in another set, and so on. In addition to the values,

the information needed to reinsert them into the proper position in the original record

format is stored with each set.

Correlation Database (CDBMS)

The newest entry in the data warehouse platform arena is the correlation database

(CDBMS) with its value-based storage (VBS) model. This structure stores data values

independently from the logical schema and uses extended metadata to maintain the

information needed to reconstruct the original records. VBS offers performance equal to or

better than the columnar structures, plus additional features not provided by either

RDBMSs or columnar databases. In VBS, each unique data value is stored only once,

making the database extremely compact and fast.

Although in my point of view relational databases (RDBMS) are the most common choice for data warehouse implementations, their record-based structure is far from ideal. There are many commercial variations of record-based databases available. All share the

common characteristic of storing related values in a physically contiguous record. The

most commonly used form used for data warehousing and analytics is the RDBMS, which

has dominated the entire database market for years due to its strengths in processing and

storing transactions and in generating reports.

As data volumes grow and users demand more sophisticated analytical capabilities, the deficiencies of the RDBMS to data storage become more conspicuous.

Conclusion

Despite their limitations, rrecord-based relational databases have long been the prevailing

data structure used in data warehouse systems. However, as data volumes have

increased and analytical needs have become more sophisticated, the shortcomings of the

RDBMS—most significantly, the design compromise required between optimizing for

performance versus query flexibility—have spurred the development of alternative data

structures.

Columnar databases offer faster query performance and require less disk storage space

than do RDBMSs, but they force their own compromise between optimizing for new record

insertion versus record selection and retrieval.

The newest data warehouse database, correlation DBMS, uses a value-based storage

(VBS) model that eliminates design compromises. The upfront physical design effort is

minimized since the CDBMS is optimized for both query performance and flexibility

automatically as data is loaded. The correlation DBMS provides load speeds comparable

to RDBMS and columnar systems, minimizes disk space requirements, optimizes query

performance, and enables unique types of queries—such as associative and incremental

queries—that are impractical or impossible with other data structures.

Concepts about Internet

noreply@blogger.com (Nouman Ali) — Fri, 29 Oct 2010 00:11:00 -0700

CSMA/CD

There is no central control management when computers transmit on Ethernet.

For this purpose the Ethernet employs CSMA to coordinate transmission among multiple attached computers.

CSMA is a coordination scheme that defines how to take turns using a shared cable.

A computer listen to codes i.e. it sense the carrier. If the cable is idle it starts transmitting and if the cable is in use then it waits.

If simultaneous transmission occurs, the frames interfere with each other and this phenomenon is called collision.

COLLISION DETECTION:

As explained earlier, the signals from two computers will interfere with each other and the overlapping of frames is called a collision. It does not harm to the hardware but data from both frames is grabbled.

ETHERNET CD:

To detect the collision , Ethernet interfaces include hardware to detect transmission. It performs two operations:

It monitors outgoing signals.

Grabbled signal is interpreted as a collision.

After collision is detected computers stop transmission . Internet uses CSMA/CD to coordinate transmission.

All wiring technologies use identical Ethernet specifications .e.g they use same frame format. They use same CSMA/CD algorithms. They can mix different technologies in a Ethernet.

For Example :

In a bus topology all computers are attached to single long cable and any computer can send data to any other computer.

For this purpose , coordination is required to decide which computer has to use the line at what time. In this situation , they use CSMA/CD to sense the carrier if line is idle , they transmit their data to other computer attached on this line.

Recovery From Collision :

Computer that detects sends special signal to force all other interfaces to detect collision.

Computer then waits for other to be idle before transmission . But if both computers wait for same length of time, frames will collide again. So the standard specifies maximum delay and both computers choose random delay, which is lesser . After waiting, computers use carrier sense to avoid subsequence collision.

After waiting, computers use carrier sense to avoid subsequence collision.

The computer with shorter delay will go first and other computer may transmit later.

Exponential Back Off:

Even with random delays, collision may occur especially likely with busy segments. Computers double delay with each subsequent collision. It reduces likely hood of sequence of collision.

Data Stuffing

Sometimes the special character (i-e soh and eot) may appear in data as a part of data they will be misinterpreted as framing data.

The solution to this problem is Byte stuffing.

In general to distinguish between data being sent and control information such as frame delimiters network systems arrange for the sending side to change the data slightly before it is sent because systems usually insert data or bytes to change data of transmission , the technique is known as Data Stuffing.

There are two types of data stuffing:

Byte Stuffing

Bit Stuffing

Byte stuffing refers stuffing with character oriented hardware and bit stuffing refers to bit oriented hardware.

Byte stuffing translates each reserved byte into two unreserved bytes . For example:

It can use esc as prefix followed by x for soh, y for eot and z for eco.

The receiver then replaces each occurrence of esc y and esc z by the corresponding single character .