| If you store files in a frequently used folder why not create a shortcut to this folder and add it to the Send To menu, so the shortcut is available from the right mouse click menu. 1/ Open Windows Explorer 2/ As the Send To folder is an hidden folder you will need to 'unhide' it. to do this click the Tools option on the main toolbar and, from the drop down menu, click Folder Options. In the Folder options window click View tab. Next click the radio button next to the 'show hidden files and folders' option and then click OK 3/ From the Windows Explorer menu click the Plus sign (+) next to My Computer 4/ Next click the Plus sign (+) next to the C: drive 5/ From the expanded menu that appears, click on the Documents and Settings Folder 6/ Next click on the folder for the User you want to add the shortcut for 7/ Now click the Send To Folder 8/ In the Send To Folder, click File on the main toolbar and select New 9/ From the menu that appears click the Shortcut option and follow the instructions for creating a shortcut 10/ After you have completed the task, the next time you right click on a file and click Send To the shortcut you created will be available |
How Do I Add An Item To The Send To Menu
How Do I Add A Logo And Support Information To My System Properties general Tab
| Adding a company logo and support information to the system properties general tab personalises the computer(s) you work on. To add a logo and support information is relatively simple. All you require is two files: 1) OEMINFO.INI and 2) OEMLOGO.BMP. To create these proceed as follows. 1/ Open Windows Notepad or some other text editor and type in the following text: [General] Manufacturer=(add your manufacturer name here) Model=(add the PC model details here) [Support Information] Line1="For technical Support Contact: (add your text here)" Line2="Add any other text here" Line3="Manufacturer Service Department: (add your text here)" Line4="add any further text here" Here is an example: [General] Manufacturer=John Barnett MVP Computer Journalist Model=4210 [Support Information] Line1="For technical Support Contact: John Barnett Line2="Telephone: xxxxx.xxxxxx" Please ensure that there is no extra line between [General] and manufacturer. If you leave an extra line your Logo may not display. There should also be no spaces between the = & the ". 2/ Once you have completed this information save the file as OEMINFO.INI 3/ Now create or import a BMP logo using Microsoft Paint or some other graphics application. The logo should be 172 x 100 Pixels for Windows XP (176 x 110 Pixels for Windows 2000) and should have a resolution of 256 colours. 4/ After creating the logo save it as OEMLOGO.BMP 5/ Now Copy both the OEMINFO.INI and OEMLOGO.BMP files to the C:/WINDOWS/System32 directory 6/ Now click Start>Control Panel>System 7/ In the System properties window on the General tab your logo should now be visible. 8/ If you also added Technical Support Information into the OEMINFO.INI file you will also see a Support button. Click on this and you will see the support information. |
How Do I Remove A Second Installation Of XP From The same Partition
| Having a second copy of Windows XP on the same partition is not particularly desirable, as it is possible that the second installation may conflict with the first. If it is imperative that you have two copies of XP on your PC (and be aware that you will require a separate license for each installed copy of XP on your PC) you should consider creating a dual boot system by installing the second copy of XP on a separate partition or hard drive. If, however, you are in the position of having two installations on the same partition, here is how to remove the surplus copy. 1/ Boot Up your PC 2/ At the boot menu select the Windows copy you intend keeping. At this point it would be wise to make a note of whether the copy you intend keeping is listed first or second on the boot menu. You will need this information when you finally come to edit the boot.ini file to remove the reference to the second (unwanted) copy of XP 3/ Once XP has booted to the desktop, click Start>All Programs>Accessories>Command Prompt 4/ At the command prompt type: echo %windir% and press Enter. This will provide you with the information regarding the current Windows folder you are accessing 5/ Next open Windows Explorer and click the Plus sign (+) next to My Computer 6/ Navigate to the C: drive and delete the folder containing the XP installation you want to remove. Check carefully that you have the correct folder before highlighting the folder for deletion. The original installation will be in the Windows folder. Additional installations may have names such as Windows1, Winnt, or you may have even used a name of your own for the installation, such as WindowsInstall. 7/ After deleting the 'correct' windows folder you will need to remove the Windows entry from the Boot.ini file. To do this click Start>Control Panel>System 8/ In System properties click the Advanced tab and press the Settings button in the Startup and recovery section 9/ In the Startup and Recovery settings window click the Edit button 10/ The boot ini file will now open in Windows Notepad 11/ before proceeding click File and then Save As 12/ Now rename the boot ini file to boot.inibak This is just as a precaution 13/ Now take a look at the boot ini file. It will have two entries for Windows XP 14/ Remove the line which refers to the Windows installation you have just removed. You were asked in step 2 of this tutorial to make a note of the position - first or second - of the installation you booted to. If you booted to the first option on the boot menu you will need to remove the second line. If you booted to the second option on the menu you will need to remove the first line. 15/ After you have removed the line referencing the installation you deleted look at the top of the menu for an entry marked Set Timeout=. Change the timeout figure (usually 30 seconds) to 0 (zero). This will enable the PC to boot directly into Windows without any time delay. 16/ Now click File>Save As 17/ Save the file as Boot.ini 18/ After the file has been saved Exit Notepad 19/ Finally reboot your PC and you should boot straight to the XP desktop. |
How Do I get Windows To Recognise A Missing CD-DVD Drive
| There are a number of reasons why the operating system does not recognise your CD-DVD drive; it may, for instance, simply be a case that the connection to the CD/DVD drive has become loose. Alternatively, a driver problem may occur, or it may simply be a registry problem. Either way we try to address the problem here. The BIOS Without getting technical, the BIOS is a chip on your motherboard that, basically, starts the PC. It looks at what hardware and memory you have on your machine and checks that it can communicate with it prior to the Windows operating system kicking in. If the hardware is not being recognised then the BIOS is the first to complain. However, before we look at the BIOS it is worth checking to see that the cable connections to the CD/DVD drive are secure. This is simple enough to do, requiring you to simply open up your computer case and physically check that the ribbon cable is connected properly to the CD/DVD and the IDE controller on the motherboard. You also need to check that the power cable to the CD/DVD drive is also connected. If this is okay then is the CD/DVD recognised by the BIOS? To check this you can either watch the screen as you boot or enter the BIOS itself. Not all PCs display the boot options. This is because they have been disabled to make the boot process quicker. If your machine does show the boot options then you should see the machine first check the memory and then a list of devices should appear, something like this: Primary Master: WDC WD800BD 00CAA1 Primary Slave: WDC WD800EB 00DJF0 Secondary Master: NEC DVD RW ND 1300A Secondary Slave: None If the BIOS has recognised the CD/DVD then there should be an entry in the Secondary Master or Slave area. If it say's 'None' then the drive has not been recognised. With a None recognised drive you will need to consult your PC's user manual for details on accessing the BIOS (in most cases it is simply a matter of pressing the 'Del' key or some other key while the PC is booting. The BIOS menu should then appear. You should ensure that the configuration is set to 'automatic' so that the BIOS automatically picks up the CD/DVD drive. Once again, in the BIOS menu, you should see the CD/DVD drive details displayed under the Secondary IDE Master or Slave sub menu. Driver Problems If the BIOS recognises the CD/DVD drive then the problem may be driver related. To check for this you need to take a look at the Device manager options in Control panel. You might also check the CD/DVD drive manufacturers' website to see if a later driver is available. If so download and install it. 1/ Click Start 2/ From the Start menu click Control panel 3/ In the control panel window click the System icon 4/ The system properties window will open 5/ In the System properties window click the Hardware tab 6/ On the Hardware tab click the Device Manager button 7/ The Device manager window will now open 8/ Look for your CD/DVD drive in the available list and click the + (plus) sign to expand the menu 9/ Does the CD/DVD drive have a ? next to it? If it does then click on the Actions menu and, from the drop down list, select Uninstall. This will uninstall the CD/DVD drive. 10/ After the driver has been uninstall, again click the Actions option and select the Scan for hardware changes option 11/ Windows will now scan for any new hardware and should pick up your CD/DVD drive. 12/ If that doesn't bring your CD/DVD back then you may need to edit the registry - see below Editing the Registry Before we go you should be aware that editing the registry can be dangerous, so before you begin make sure that you have a backup copy of your registry saved in a safe place (see Question 62 for more details). It is also wise to create a System restore point prior to changing registry entries. Now proceed as follows: 1/ Click Start 2/ from the Start menu click Run 3/ In the Run dialogue box type: regedit 4/ The registry editor will now open 5/ navigate to the following key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E965-E325-11CE-BFC1-08002BE10318} and look for the Upper Filters value 6/ Right click on the Upper Filter Value and, from the drop down menu click Delete 7/ Next navigate to the following key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\class\{4D36E965-E325-11CE-BFC1-08002BE10318} and look for the Lower Filter value 8/ Again Right Click on the Lower Filter Value and, from the drop down menu, click Delete 9/ Finally exit the registry editor and reboot your machine 10/ Hopefully, your CD/DVD drive should now be recognised |
How Do I Remove NTFS File System
1/ After restarting your PC the Windows Setup will begin
2/ At the Welcome to Setup screen press F10
3/ Pressing F10 opens the Recovery Console. This is a DOS based screen so you need to first specify the operating system location, i.e. C: Drive and then log in as using your Administrator Password.
4/ After logging in type map and then press Enter
5/Highlight the drive you want to reformat. Drive letters may differ in recovery console to those in windows xp
6/ Type format x: /fs:fat32 Substitute the 'x' for the drive letter you wish to reformat and then press Enter.
7/ Confirm your choice by typing Y and then pressing Enter
8/ Once the hard drive has finished formatting type Exit and then press Enter to restart your computer.
How Do I Rectify A Missing Or Corrupt Ntoskrnl Error
1/ Place your Windows XP CD into your CD-ROM and Reboot your PC
2/ XP's setup program will automatically start and files will be loaded to memory
3/When you reach the Welcome to Setup screen choose the Repair option by pressing R
4/ This will open the Recovery Console
4/ The list of Windows installations will appear
5/ As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be 1
6/ You now need to enter your Administrator password to gain access. If you are using Windows XP Home edition the administrator password is blank by default so simply press Enter
7/ At the command prompt change to the drive letter that contains your CD
8/ Next type: cd i386
9/ The directory should now change to the i386 directory
10/At the command prompt you now need to type: expand ntkrnlmp.ex_C:\Windows\System32\ntoskrnl.exe
11/The relevant file should now be expanded and copies to the windows\system32 directory of your C:\ drive
12/ Finally, remove the Windows XP cd from your CD-ROM and, at the command prompt type: Exit
How Do I Rectify A Missing Or Corrupt NTFS.SYS Error
Windows XP can be formatted in two different file systems, FAT32 and NTFS. If you are running a machine with a FAT32 files system and then decide to convert to NTFS using the converts option - see How do I convert my FAT32 file system to NTFS - on rebooting you may get a missing or corrupt ntfs.sys error. Here is how to rectify this problem
1/ Insert the Windows XP CD into your CD-ROM and reboot your pc
2/ Allow the basic setup files to load into memory
3/At the Welcome to Setup screen press R
4/ This will start the Recovery console and the list of Windows installations will appear
5/ As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be 1
6/ You will need to enter your Administrator password. If you are using Windows XP Home edition the administrator password is blank by default so simply press Enter
7/ At the Recovery Console command prompt type: cd \windows\system32\drivers
8/ Next press Enter
9/ The windows system 32 drivers directory will now open
10/ Now type: ren ntfs.sys ntfs.old
11/ Again press Enter
12/ If a message appears telling you that the Ntfs.sys file was not found, then the file is actually missing rather than corrupt
13/ The above command will change the name of your corrupt file from Ntfs.sys to Ntfs.old
14/Now type the following at the command prompt substituting the X (after copy) with the drive letter of your CD and the X (after drive) with the drive letter of your hard drive. The hard drive usually being the C:/ drive
15/ copy X:\i386\ntfs.sys drive X:\windows\system32\drivers
16/ Remove the Windows XP CD from your CD-ROM
17/ Now in the command prompt type: Exit
18/ Restart your PC to make sure the problem has been rectified
How Do I Correct An NTLDR Or NTDETECT.COM Not Found Error
For some reason or other this problem has appeared quite regularly in the XP newsgroups and while it can be an inconvenience - you not being able to boot your pc - the actual remedy is relatively simple. However, although the remedy is simple, the way you go about it will be dependant upon whether you are able to boot your system from the Windows XP CD or whether you need to boot from an older Windows 98/Me startup floppy disk.
Booting directly from the Windows XP CD
1/ Place your Windows XP CD into your CD-ROM and Reboot your PC
2/ XP's setup program will automatically start and files will be loaded to memory
3/When you reach the Welcome to Setup screen choose the Repair option by pressing R
4/ This will open the Recovery Console
5/ The list of Windows installations will appear
6/ As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be 1
7/ You now need to enter your Administrator password to gain access. If you are suing Windows XP Home the administrator password is blank by default so simply press Enter
8/Now enter the following depending upon which file you need to replace. In both instances replace the 'X' with the drive letter of your CD-ROM
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COPY X:\i386\NTLDR C\:
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COPY X:\i386\NTDETECT.COM C:\
11/ Finally remove your XP CD from the CD-ROM and then type Exit
12/ Reboot your machine to see if the the problem has been cured
Using a Windows 98/Me Startup Disk
1/ Insert a Windows 98 startup disk into your floppy drive and reboot your machine
2/ From the floppy menu make sure that you boot with CD-ROM support
3/ Once you are at the DOS 'A' prompt insert your Windows XP CD into your CD-ROM
4/ Next, at the 'A' prompt type X (where X is the drive letter of your CD-ROM)
5/ The DOS prompt letter should now change to that of your CD-ROM's drive letter
6/ Now type cd i386 (the cd in this case means change directory)
7/ You should now have access to the i386 directory on your CD-ROM
8/ Finally you need to copy either the NTLDR or the NTDETECT files from the i386 directory to the root of your C:/ drive.
9/ After copying has been completed Reboot your machine to check that the problem has been solved
How Do I Repair A Missing Or Corrupt HAL.DLL
There may be an occasion when you boot up your PC that you receive an error message such as HAL.DLL file is corrupt or missing. In many cases this can simply be a misconfiguration in the Boot.Ini file and can easily be corrected by instigating a suitable repair.
1/ Place your Windows XP CD into your CD-ROM and Reboot your PC
2/ XP's setup program will automatically start and files will be loaded to memory
3/When you reach the Welcome to Setup screen choose the Repair option by pressing R
4/ This will start the Recovery console and the list of Windows installations will appear
5/ As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be 1
6/ Type in your Administrator password. If you are using Windows XP Home edition the administrator password is blank by default so simply press Enter
7/Now type bootcfg /list
8/ A list will now appear of all the entries in your boot.ini file
9/ Next type bootcfg /rebuild
10/ Your boot.ini file should now be repaired
11/ Finally remove your XP CD from the CD-ROM and then type Exit
12/ Reboot your machine to see if the the problem has been cured
How Do I Change The Registered Owner Name In Windows XP
Sometimes when you purchase a PC that comes with XP pre-installed the actually copy of XP (usually on OEM (Original Equipment Manufacturer) copy) may be registered to the company that build the PC. To change the registration details do the following.
NOTE
Before proceeding to edit the Registry be sure to make a backup copy. This can be achieved by using a third party freeware application called ERUNT (see the Life Saver section for more details)
1/ Click the Start Button
2/ From the Start menu click Run
3/ In the Run dialog box type: regedit
4/ The Registry editor will now open
5/ Navigate to the following key: HKEY_Local_Machine\Software\Microsoft\WindowsNT\Current Version
6/ Once you have reached the Current Version key take a look in the Right Hand Pane and look for 'Registered Owner'
7/ Right click the Registered Owner key to edit it
8/ To edit the key Right click the entry and select Modify
9/ At the same time you might also like to change the Registered organisation. This option is situated just above the registered owner option.
10/ To edit the key Right Click the entry and select Modify
How do I Repair A Stop: c0000218 {Registry File Failure} The registry Cannot Load The Hive (File): \SystemRoot\System32\Config\Software Error
This type of error usually indicated that the pc has refused to start because of a corruption within the registry. The following should remedy the problem. However, it is important that you replace all five registry hives. Simply replacing one or two could, potentially, cause other problems.NOTEYou should not use the method two set of instructions below if your system has an OEM (Original Equipment Manufacturer) copy of Windows XP. Doing so will render your operating system inoperable. OEM installations create passwords and user name that did not previously exist. Therefore, in your own interest, these instructions will not remedy the problem. The easiest option with OEM copies of XP is to reinstall XP using the manufacturer’s recovery disks.Easy Method1/ Restart your PC2/ Keep tapping the F8 Button until a menu appears3/ When the menu appears use the UP and DOWN arrow keys to select the ‘Last known good configuration’ option.4/ Once selected press Enter5/ Your PC should now reinstall the ‘last know good configuration file’6/ Restart your PC and see if the problem has been solved7/ If it hasn’t go on to the Harder Method below.This fix was contributed by Peter Hayes.
Harder Method
Step On 1/ Insert the Windows XP CD into the CD-ROM and restart your pc 2/ At the ‘Welcome to Setup’ screen press R to start the recovery Console 3/ The Recovery Console will now open and the list of Windows installations will appear 4/ As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be 1 5/ When requested type in your Administrator password. If you haven’t set an administrator password, then simply press Enter6/ The Recovery Console command prompt window will now appear7/ At the Command prompt type the following, pressing Enter after you have typed each line.md tmp |
How Do I Change The Windows XP Product Key Number
Of course this may not be your fault. The copy of Windows XP may have come pre-installed on your pc and the store may have wittingly or unwittingly installed a pirated image of the software on your pc.
Either way, eventually, you are going to have to obtain a new product key number to make your copy legal. Once the new product key number is obtained it will be necessary to edit the registry in order to input the new product key. It should be noted that once the new product key has been inserted into the registry you will be required, once again, to Activate the new product coded copy of Windows XP
PLEASE NOTE
To rectify the problem you will need to edit the registry, therefore, before you proceed, you should ensure that you have backed up the registry either from within regedit itself or by using the third party software called ERUNT.
1/ Click the Start button
2/ From the Start Menu click Run
3/ In the Run dialogue box type: regedit
4/ The Windows Registry window will now open
5/ Navigate to the following registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents
6/ In the Right Hand Pane of the registry window Right Click on the OOBETimer value and select Modify
7/ Change at least one of the characters in the Modify dialogue box to either a number between 0 and 9 or a letter between A and F and close the registry
8/ This operation now Deactivates the current product key rendering it invalid
To Re-Activate Windows
1/ Click the Start button
2/ From the Start menu click Run
3/ In the Run dialogue box type: C:\windows\system32\oobe\msoobe.exe /a and press OK (If your copy of XP is an upgrade from Windows NT/2000 then substitute the above command for the following: C:\winnt\system32\oobe\msoobe.exe /a
4/ The Windows Activation Screen will now launch
5/ Select Yes i want to Telephone a Microsoft customer service representative and then click the Next button
6/ Select Change product key option and type in your new Product key number
7/ Click Update and then close the window
8/ On pressing Update the window may return to the previous screen. If it does so, then simply select the Remind Me later option
9/ Now Reboot your system
10/ When your PC has rebooted you will be asked to Re-Activate your copy of xp through the normal activation channel, i.e via the internet.
How Do I Install Windows XP On A SATA Hard Drive
| Serial ATA (SATA) drives are the latest in the hard drive fashion and, in theory, installing Windows on the drive should prove relatively simple. The problem is that Windows XP doesn’t contain the necessary drivers to allow windows to see the drive so that Windows can install it. To load Windows XP onto a SATA drive you need to proceed as follows: 1/ Copy the SATA drivers (these can usually be found on your pc or motherboards support disk. Usually these consist of PIDE/SATA Folders and TXTsetup.oem files. Alternatively they may have been supplied on a separate CD that accompanied your SATA drive, assuming you purchased it separately from the pc.) 2/ Insert the Windows XP CD (full retail version – you should not need to follow these instructions if your pc came with a recovery disk) into the CD-ROM and Reboot your PC 3/ Watch carefully as the Windows XP installation progresses and look carefully at the text at the bottom of each screen. 4/ At the Windows Setup Screen (this should be the second screen after installation starts) you should see, at the bottom of the screen) a message saying “Press F6 if you need to install a third party SCSI or RAID driver.” 5/ At this point press the F6 button 6/ When the next screen appears press S to specify an additional device 7/ Now insert the floppy disk containing the SATA drivers into your floppy drive 8/ Windows will next ask you to select a driver from the provided list 9/ Select VIA Serial (or whichever controller your motherboard supports) ATA RAID Controller (Windows XP) 10/ The SATA drivers on your floppy disk should now load 11/ After the drivers have loaded Windows XP will recognise your SATA hard drive and you can continue installing the Windows XP operating system |
How Do I Prevent CHKDSK From Running Every Time My PC Starts
| When your PC shuts down without warning or it has to be shutdown because of problems you may find, that on rebooting, the AUTOCHK application will start up and check your disk for errors. This can be tiresome, particularly if it occurs every time you boot your machine. To disable this feature do the following 1/ Click the Start Button 2/ From the Start menu click Run 3/ In the Run dialogue box type: cmd 4/ The command prompt window will now open 5/ In the command prompt window type: fsutil dirty query c: 6/ Press Enter 7/The response from the file system utility will probably be that the disk is 'dirty' 8/ Now type: CHKNTFS /X C: into the command prompt windows and press Enter. 9/ The X parameter, in this case, tells windows not to check the disk in question 10/ Next manually re-boot your pc 11/ You should now find that CHKDSK does not run on the selected drive 12/ Once you have confirmed that CHKDSK does not run and your PC has fully booted click Start>Runa again and type cmd 13/ In the command window now type: chkdsk /f/r c: and press Enter. Again replace the C: (If you have a dual boot system then replace the C: drive letter with the relevant drive letter you have been having problems with) 14/ After the drive has been scanned type: fsutil dirty query c: and press Enter 15/ Windows should now confirm that the 'dirty bit' has been disabled |
How to reinstall System Restore in Windows XP?
ntroduction
System Restore is one of the most useful tools available in Windows XP, which can help you restore the computer to an earlier state, when a problem occurs in your computer. There are situations where you are required to reinstall System Restore in order to restore its functionality. This article explains how to reinstall System Restore using the INF file.
Caution: The following procedure will remove all the existing System Restore points, and resets the System Restore drive monitoring options to defaults (monitors all drives by default.)
Reinstalling System Restore
- Click Start, Run and type %Windir%\INF
- Locate the SR.INF file. If you have configured Windows Explorer to hide known file extensions, the file may show up as SR. To see the file extensions for all file types, then try this:
- On the Tools menu in My Computer, click Folder Options.
- Click the View tab.
- Clear the Hide extensions for known file types check box.
- Right-click the SR.INF file, and then click Install
- Windows will now attempt to reinstall System Restore, and may prompt you for the Windows installation source path. Point to %Windir%\ServicePackFiles folder, or insert your slipstreamed Windows XP (matching the Service Pack level of your system.)
- System Restore core files will be reinstalled. Restart Windows when prompted.
Notes
- Alternately, you can reinstall System Restore using the following command line:
rundll32.exe advpack.dll,LaunchINFSection %Windir%\Inf\sr.inf
- Slipstreaming process can be automated using the Freeware AutoStreamer utility. You can download the software from here: AutoStreamer. To do this manually, look for other Slipstreaming guides here.
Clean up the MRU listings using MRU Blaster
Most Recently Used (MRU) lists contain information such as the names and/or locations of the last files you have accessed. This information is mostly stored in the registry, but some applications still store the MRU in ini files. The MRU registry location depends upon the software which stores the entries in it's own registry key. This table will give you an idea about the registry locations and MRU lists.
MRU-Blaster is a program made to do one large task - detect and clean MRU (most recently used) lists on your computer. - Approx. 30,345 MRU items can be cleared using MRU-Blaster (3/28/2004). Download MRU-Blaster
Configure, and Scan
Install MRU-Blaster and run it it. From the main screen, click Settings. Deselect the MRU items that you don't want to remove. Once done, save settings and go back to the main screen. Similarly go to the Plugins section and configure the Cookies and Temporary Internet Files settings accordingly.
Click Scan from the main screen. Once the Scan results are displayed, you can click Clean Now to clear the list. For deselecting items from the Scan results, click Show Results button.
Methods to schedule a MRU cleanup
Use the Scheduler program supplied with MRU-Blaster.
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Configure MRU-Blaster as said above
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Open the MRU-Blaster folder (usually %ProgramFiles%\MRU-Blaster)
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Double-click the file named Scheduler.exe
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Configure the MRU cleanup time [ Seconds | Minutes | Hours ] accordingly
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Click Save/Apply Changes. This will activate the Scheduler's Timer
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Once done, click Minimize to Tray
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The Scheduler file takes ~4 MB of the System Memory and sits in the Tray. This file triggers MRU cleanup at every interval.
Use the Windows XP Task Scheduler to cleanup the MRU
MRU-Blaster supports -silent command-line argument which cleans the MRU lists without displaying it's window. This command-line argument is useful for Scheduling Tasks in Windows.
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Configure MRU-Blaster as said in the top of the page
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Click Start, Run and type control schedtasks
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Double-click Add Scheduled Task. The Scheduled Task Wizard starts
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Click Next
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Under Click the program you want Windows to run, click Browse
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In the Select Program to Schedule dialog box, open the %ProgramFiles%\MRU-Blaster folder
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Locate and click the MRUBlaster.exe file, and then click Open
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Under Perform this task, specify a name for the task and how frequently you want this task to run
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Click Next
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Under Select the time and day you want this task to start, specify a start time/date, and click Next
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Type the user name and password to run this task under, and then click Next
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Click to select the Open advanced properties for this task when I click Finish check box, and click Finish
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Click the Task tab. In the Run box, specify any additional parameters ( -silent )that you want to use with MRUBlaster.exe. Example: The command-line is:
"C:\Program Files\MRU-Blaster\MRUBlaster.exe" -silent
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Click OK
 | This method does not invoke MRU-Blaster's Scheduler.exe, and does not sit in the Notification area. |
How to backup the Windows XP Registry?
Introduction
Registry Editor is an advanced tool for viewing and changing settings in your system registry, which contains information about how your computer runs. Almost the entire settings are stored in the registry. For example, when you resize an application window, the window position (x,y points) is stored in the registry so that the settings are retained permanently. This is just an example, there are much more data stored in the registry, right from your user account names and passwords (if configured to store in the registry).
Although Registry Editor enables you to inspect and modify the registry, it's advisable to use Registry Editor only if the GUI does not provide the option you're looking for. Making incorrect changes in the registry can break your system. It's highly advisable to backup the registry before editing any portion of it.
Backing up the XP Registry - Three methods
Method 1: Using System Restore
One way to backup the registry is to create a System Restore snapshot. System Restore returns your computer to a previous snapshot without losing recent personal information, such as documents, history lists, favorites, or e-mail. It monitors the computer and many applications for changes and creates restore points. You restore these snapshots when your configuration isn't working. This method is unreliable in case you want to rollback the registry changes made a longtime ago, in which case the System Restore might have purged that particular restore point - due to space constraints or due to a recent system restore point or even a Restore point corruption. Please remember, System Restore points get deleted for many reasons, making it unreliable, especially in the long run.
For more help, see : Creating a System Restore point and Using System Restore to Undo Changes if Problems Occur
Method 2: Backing up the selected branch of the registry by exporting (Reliable)
This method is preferred if you're making changes to a specific key/area of the registry. To backup a selected branch/key in the registry, try this:
- Click Start, and then click Run.
- In the Open box, type regedit, and then click OK
- Locate and then click the key that contains the value that you want to edit
- On the File menu, click Export.
- In the Save in box, select a location where you want to save the Registration Entries (.reg)
- In the File name box, type a file name, and then click Save.
(Backing up a selected branch/key of the registry)
Now that you've created a Registry backup for that particular key. Save the REG file in a safer location in case you want to undo the registry changes made. You can restore the settings by just double-clicking the REG file. It automatically merges the contents to the Registry.
Method 2 (a) : Export registry keys using a command-line (Console Registry Tool)
You can use the Console Registry Tool for Windows (Reg.exe) to edit the registry. For help with the Reg.exe tool, type reg /? at the Command Prompt, and then click OK.
Example: To export the key [HKEY_CURRENT_USER\Software\IOLO] and it's sub-keys, try this from Command Prompt:
REG EXPORT HKCU\Software\IOLO C:\IOLO.REG
To view the REG contents type notepad C:\iolo.reg in Start, Run dialog. Console Registry Tool is extremely handy for network admins and also for home users.
Method 3: Backing up the whole registry ("System state")
For backing up the whole registry, use the NTBackup utility to back up the System State. The System State includes the registry, the COM+ Class Registration Database, and your boot files. See section "Back Up the Whole Registry" in the following article:
HOW TO: Back Up, Edit, and Restore the Registry in Windows XP
NOTE: NTBACKUP is not installed by default in Windows XP Home Edition. Install it using the instructions available at: Q302894.
Manual steps to back up the registry in Windows Vista or in Windows XP
Windows Vista
| 1. | Click Start , type systempropertiesprotection in the Start Search box, and then press ENTER. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow. |
| 2. | Wait for Windows to search for available disks and most recent restore points. In the System Properties dialog box, on the System Protection tab, click Create, |
| 3. | Type a name for the restore point and then click Create. |
| 4. | After the restore point has been created successfully, click OK two times. |
Windows XP
| 1. | Click Start, click Run, type %SystemRoot%\system32\restore\rstrui.exe, and then click OK. |
| 2. | On the Welcome to System Restore page, click Create a restore point, and then click Next . |
| 3. | On the Create a Restore Point page, type a name for the restore point and then click Create |
| 4. | After the restore point has been created, click Close. |
Back to the topRestore the registry
Manual steps to restore the registry in Windows Vista or Windows XP
Use System Restore to undo registry changes in Windows Vista or in Windows XP
Windows Vista
| 1. | Click Start, type systempropertiesprotection in the Start Search box, and then press ENTER. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow. |
| 2. | In the System Properties dialog box, on the System Protection tab, click System Restore, |
| 3. | In the System Restore dialog box select Choose a different restore point, and then click Next |
| 4. | Select the restore point that you want to use, and then click Next. |
| 5. | Confirm your restore point, and then click Finish System restore restores the selected Windows Vista configuration and then restarts the computer. |
| 6. | Log on to the computer. When the System Restore confirmation page appears, click OK.. |
Windows XP
| 1. | Click Start, click Run, type %SystemRoot%\System32\Restore\Rstrui.exe, and then click OK. |
| 2. | On the Welcome to System Restore page, click Restore my computer to an earlier time (if it is not already selected), and then click Next . |
| 3. | On the Select a Restore Point page, click the system checkpoint. In the On this list select the restore point area, click an entry that is named "Guided Help (Registry Backup)," and then click Next. If a System Restore message appears that lists configuration changes that System Restore will make, click OK. |
| 4. | On the Confirm Restore Point Selection page, click Next. System Restore restores the previous Windows XP configuration and then restarts the computer. |
| 5. | Log on to the computer. When the System Restore confirmation page appears, click OK.. |
Configure Windows XP to Automatically Login
After downloading fixes from Windows Updates page or via Automatic Updates, you may notice that Windows XP no longer logs into your account automatically. This is usually caused after the installation of .NET Framework from Microsoft. It creates an additional user account called ASP.NET, which you can see in the Control Panel User Accounts applet. But, you neither need to remove this update nor delete this account. You can still configure Windows XP to automatically login using these methods:
Method 1
For Windows XP Home, don't try to auto-login as the built-in Administrator, as you'll receive an error message.
Method 2: Using TweakUI
TweakUI v2.00 for Windows XP | v2.10 for Windows XP/SP1 and above
How to manage Windows startup?
Introduction
It's a good practice to frequently inspect the startup entries for security. The System Configuration Utility will not list applications loaded in all possible startup locations. Most other entry points are hidden and unknown to the end-user. This article will provide a clear picture about the start locations of applications and drivers. Some of the locations mentioned in this article may not apply to Windows 95/98/ME systems.
Startup locations
HKCU refers to HKEY_CURRENT_USER
HKLM refers to HKEY_LOCAL_MACHINE
HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce
HKCU\Software\Microsoft\Windows\CurrentVersion\RunServices
HKCU\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce
HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
HKCU\Software\Microsoft\Windows\CurrentVersion\Run
HKCU\Software\Microsoft\Windows NT\CurrentVersion\Windows
(In right-pane, Value named "Run" & "Load")
HKLM\Software\Microsoft\Windows\CurrentVersion\Run
HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices
HKLM\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce
HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce
HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnceEx
HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit
C:\Documents and Settings\All Users\Start Menu\Programs\Startup
C:\Documents and Settings\{Username}\Start Menu\Programs\Startup
Note Items marked in blue are those which MSCONFIG can manage.
Using Windows Defender to manage Windows startup
Windows Defender (included by default in Windows Vista) helps you inspect/manage your startup programs.
-
Open Windows Defender.
-
Click Tools, and then click Software Explorer.
-
In the Category list, select Startup Programs.
-
To list startup entries for the system, click Show for all users.
-
You can enable, disable or remove startup entries from there.
Advanced stuff - additional Windows Startup launch-points
Silentrunners.org covers many more startup launch-points. It is possible that a malware is present in any of the locations described. Additionally, it's worth verifying the contents of ShellExecuteHooks key here:
HKEY_LOCAL_MACHINE \ Software \ Microsoft \ Windows \ CurrentVersion \ Explorer \ ShellExecuteHooks
Excellent utility to manage Windows startup
Inspecting all the keys manually may be a tiring task. Your best bet is to use a third-party software to inspect the startup. Though there are many freeware utilities which can track/log the startup entries, the following tool is very impressive.
http://technet.microsoft.com/hi-in/sysinternals/bb963902(en-us).aspx
Autoruns - This utility covers most of the start locations. It allows you to edit the startup for other user profiles (Windows 2000/XP/Vista) as well. This tool is my personal favorite.
Additionally, you can enable or disable certain shell extensions, Browser Helper Objects, other Internet Explorer add-ons, drivers, Winsock providers etc.
View and manage Windows XP Services and Drivers
http://www.nirsoft.net/utils/serviwin.html
ServiWin utility displays the list of installed drivers and services on your system. For some of them, additional useful information is displayed: file description, version, product name, company that created the driver file, and more. In addition, ServiWin allows you to easily stop, start, restart, pause, and continue service or driver, change the startup type of service or driver (automatic, manual, disabled, boot or system), save the list of services and drivers to file, or view HTML report of installed services/drivers in your default browser.
-
To view Services list, click the View menu and choose Services [F8 key]
-
To view Drivers list, click the View menu and choose Drivers [F7 key]
-
To find out the list of third-party drivers, sort the column named Company
You may also use DriverQuery command built-in with Windows XP, to view the list of all the device drivers installed in your system. You can transfer the list to a file for troubleshooting purposes. Type driverquery /? in Command Prompt for more information:
Usage / Examples
DRIVERQUERY /SI [This lists the drivers signing status, whether Signed or Unsigned]
DRIVERQUERY /V [ Generates a detailed report ]
DRIVERQUERY [ Lists all device drivers ]
To redirect the output to a file, use:DRIVERQUERY /SI >C:\driverslist.txt
Related
Description of Svchost.exe in Windows XP
Each instance of svchost.exe process seen in the Task Manager hosts a group of services. To see the list of services hosted by each instance of svchost.exe, you may use the Tasklist.exe console utility available in Windows XP Professional Edition.
-
Click Start, Run and type CMD.EXE
Type tasklist /svc >c:\taskList.txt
The taskList.txt will contain the list of Processes, their Process IDs and the Services running under each Process.
Understanding TCP/IP: Chapter 1 - Introduction to Network Protocols
Just as diplomats use diplomatic protocols in their meetings, computers use network protocols to communicate in computer networks. There are many network protocols in existence; TCP/IP is a family of network protocols that are used for the Internet.
A network protocol is a standard written down on a piece of paper (or, more precisely, with a text editor in a computer). The standards that are used for the Internet are called Requests For Comment (RFC). RFCs are numbered from 1 onwards. There are more than 4,500 RFCs today. Many of them have become out of date, so only a handful of the first thousand RFCs are still used today.
The International Standardization Office (ISO) has standardized a system of network protocols called as ISO OSI. Another organization that issues communication standards is the International Telecommunication Union (ITU) located in Geneva. The ITU was formerly known as the CCITT and, being founded in 1865, is one of the oldest worldwide organizations (for comparison, the Red Cross was founded in 1863). Some standards are also issued by the Institute of Electrical and Electronics Engineers (IEEE). RFC, standards released by RIPE (Réseaux IP Européens), and PKCS (Public Key Cryptography Standard) are freely available on the Internet and are easy to get hold of. Other organizations (ISO, ITU, and so on) do not provide their standards free of charge—you have to pay for them. If that presents a problem, then you have to spend some time doing some library research.
First of all, let's have a look at why network communication is divided into several protocols. The answer is simple although this is a very complex problem that reaches across many different professions. Most books concerning network protocols explain the problem using a metaphor of two foreigners (or philosophers, doctors, and so on) trying to communicate with each other. Each of the two can only communicate in his or her respective language. In order for them to be able to communicate with each other, they need a translator as shown in the following figure:
Figure 1.1: Three-layer communication architecture
The two foreigners exchange ideas, i.e., they communicate. But they only do so virtually. In reality, they are both handing over information to their interpreters, who then transmit this information by sending vibrations through the surrounding air with their vocal cords. Or if the parties are far away from each other, the interpreters communicate over the phone; thus the information is physically transmitted over phone lines. We can therefore talk about virtual communication in the horizontal direction (philosophical communication, the shared language between interpreters, and electronic signals transmitted via phone lines) and real communication in the vertical direction (foreigner-to-interpreter and interpreter-to-phone). We can thus distinguish three levels of communication:
- Between two foreigners
- Between interpreters
- Physical transmission of information using media (phone lines, sound waves, etc.)
Communication between the two foreigners and between the two interpreters is only virtual. In fact, the only real communication happens between the foreigner and his or her interpreter.
Even more layers are used in computer networks. The number of layers depends on which system of network protocols you choose to use. The system of network protocols is sometimes referred to as the network model. You most commonly work with a system that uses the Internet, which is also referred to as the TCP/IP family. In addition to TCP/IP, we will also come across the ISO OSI model that was standardized by the ISO.
Figure 1.2: Comparison of TCP/IP and ISO OSI network models
The TCP/IP family uses four layers while ISO OSI uses seven layers as shown in the figure above. The TCP/IP and ISO OSI systems differ from each other significantly, although they are very similar on the network and transport layers.
Except for some exceptions like SLIP or PPP, the TCP/IP family does not deal with the link and physical layers. Therefore, even on the Internet, we use the link and physical protocols of the ISO OSI model.
1.1 ISO OSI
Communication between two computers is shown in the following figure:
Figure 1.3: Seven-layer architecture of ISO OSI
1.1.1 Physical Layer
The physical layer is responsible for activating the physical circuit between the Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE), communicating through it, and then deactivating it. Additionally, the physical layer is also responsible for the communication between DCEs (see Figure 1.3a). A computer or router can represent the DTE. The DCE, on the other hand, is usually represented by a modem or a multiplexer.
Figure 1.3a: DTE and DCE
To put it differently, the physical layer describes the electric or optical signals used for communicating between two computers. Physical circuits are created on the physical layer. Other appliances such as modems modulating a signal for a phone line are often put in the physical circuits created between two computers.
Physical layer protocols specify the following:
- Electrical signals (for example, +1V)
- Connector shapes (for example, V.35)
- Media type (twisted pair, coaxial cable, optical fiber, etc.)
- Modulation (for example, FM, PM, etc.)
- Coding (for example, RZ, NRZ, etc.)
- Synchronization (synchronous and asynchronous communication, time source, and so on)
1.1.2 Data Link Layer
As for serial links, the link layer provides data exchange between neighboring computers as well as data exchange between computers within a local network.
For the link layer, the basic unit of data transfer is the data link packet frame (see Figure 1.4). A data frame is composed of a header, payload, and trailer.
Figure 1.4: Data link packet or frame
A frame carries the destination link address, source link address, and other control information
in the header. The trailer usually contains the checksum of the transported data. By using the checksum, we can find out whether the payload has been damaged during transfer. The network‑layer packet is usually included in the payload.
In Figure 1.3a, the link layer does not engage in a conversation between DTE and DCE (the link layer does not see the DCE). It is engaged, however, in the frame exchange between DTEs. (It relies on the physical layer to handle the DCE issue.)
The following figure illustrates that different protocols can be used for each end of the connection on the physical layer. In our case, one of the ends uses the X.21 protocol while the other end uses the V.35 protocol. This rule is valid not only for serial links, but also for local networks. In local networks, you are more likely to encounter more complicated setups in which a switch that converts the link frames of one link protocol into link frames of a second one (for example, Ethernet into FDDI) is inserted between the two ends of the connection. This obviously results in different protocols being used on the physical layer.
Figure 1.5: Link layer communication
A serial port or an Ethernet card can serve as a link interface. A link interface has a link address that is unique within a particular Local Area Network (LAN).
1.1.3 Network Layer
The network layer ensures the data transfer between two remote computers within a particular Wide Area Network (WAN). The basic unit of transfer is a datagram that is wrapped (encapsulated) in a frame. The datagram is also composed of a header and data field. Trailers are not very common in network protocols.
Figure 1.6: Network packet and its insertion in the link frame
As shown in the figure above, the datagram header, together with data (network-layer payload), creates the payload or data field of the frame.
There is usually at least one router on WANs between two computers. The connection between two neighboring routers on the link layer is always direct. The router unpacks the datagram from a frame, only to wrap it again into a different frame (or, more generally, in a frame of different link protocol) before sending it to a different line. The network layer does not see the appliances on the physical and link layers (modems, repeaters, switches, etc.).
The network layer does not care about what kind of link protocols are used on route between the source and the destination.
Figure 1.7: Network layer communication
A serial port or an Ethernet card can be used as a network interface. A network interface has a one or more unique address within a particular WAN.
1.1.4 Transport Layer
A network layer facilitates the connection between two remote computers. As far as the transport layer is concerned, it acts as if there were no modems, repeaters, bridges, or routers along the way. The transport layer relies completely on the services of lower layers. It also expects that the connection between two computers has been established, and it can therefore fully dedicate its efforts to the cooperation between two distant computers. Generally, the transport layer is responsible for communication between two applications running on different computers.
There can be several transport connections between two computers at any given time (for example, one for a virtual terminal and another for email). On the network layer, the transport packets are directed based on the address of the computer (or its network interface). On the transport layer, individual applications are addressed. Applications use unique addresses within one computer, so the transport address is usually composed of both the network and transport addresses.
Figure 1.8: Transport layer connection
In this case, the basic transmission unit is the segment that is composed of a header and payload. The transport packet is transmitted within the payload of the network packet.
Figure 1.9: Inserting transport packets into network packets that are then inserted into link frames
1.1.5 Session Layer
The session layer facilitates exchange of data between two applications. In other words, it serves as a checkpoint and is involved in synchronizing transactions, correctly closing files, and so on. Sharing a network disk is a good example of a session. The disk can be shared for a certain period of time, but the disk is not used for the entire time. When we need to work with a file on the network disk, a connection is established on the transport layer from the time when the file is opened to when it is closed. The session, however, exists on the session layer for the entire time the disk is being shared.
The basic unit is a session layer PDU (Protocol Data Unit), which is inserted in a segment. Other books often illustrate this with a figure of a session-layer PDU, composed of the session header and payload, being inserted in the segment. Starting with the session layer, however, this does not necessarily have to be the case. The session layer information can be transmitted inside the payload. This situation is even more noticeable if, for example, the presentation layer encrypts the data, and thus changes the whole content of the session-layer PDU.
1.1.6 Presentation Layer
The presentation layer is responsible for representing and securing data. The representation can differ on different computers. For example, it deals with the problem of whether the highest bit is in the byte on the right or on the left. By securing, we mean encrypting, ensuring data integrity, digital signing, and so forth.
1.1.7 Application Layer
The application layer defines the format in which the data should be received from or handed over to the applications. For example, the OSI Virtual Terminal protocol describes how data should be formatted as well as the dialogue used between the two ends of the connection.
Figure 1.10: Examples of network protocols from the ISO OSI protocols family
1.2 TCP/IP
With a few exceptions, the TCP/IP family does not deal with the physical or link layers. In practice, Internet protocols often use protocols that adhere to the ISO OSI standards for the physical and link layers.
What is the correlation between the ISO OSI protocols and TCP/IP? Each group of protocols has its definition of its own layers as well as the protocols used on these layers. Generally speaking, ISO OSI protocols and TCP/IP are incompatible. In practice, ISO OSI-compliant communication appliances need to be used for transferring IP datagrams, or on the other hand, services based on ISO OSI need to be provided via the Internet.
1.2.1 Internet Protocol
Internet Protocol (IP) basically corresponds to the network layer. IP is used for transmitting IP datagrams between remote computers. Each IP datagram header contains the destination address, which is the complete routing information used for delivering the IP datagram to its destination. Therefore, the network can only transmit each datagram individually. IP datagrams of one session can be transmitted through different paths and can thus be received by the destination in a different order than they were sent.
Each network interface on the large Internet network has one or more IP address that is unique worldwide. (One network interface can have several IP addresses, but one IP address cannot be used by many network interfaces.) The Internet is composed of individual networks that are interconnected via routers. Routers are also referred to as gateways in old literature.
1.2.2 TCP and UDP
TCP and UDP correspond to the transportation layer. TCP transports data using TCP segments that are addressed to individual applications. UDP transports data using UDP datagrams.
TCP and UDP arrange a connection between applications that run on remote computers. TCP and UDP can also facilitate communication between processes running on the same computer, but this is not very interesting for our purposes.
The difference between TCP and UDP is that TCP is a connection-oriented service—the destination confirms the data received. If some data (TCP segments) gets lost, the destination requests a retransmission of the lost data. UDP transports data using datagrams (the delivery is not guaranteed). In other words, the source party sends the datagram without worrying about whether it has been received. UDP is connectionless-oriented service.
The port is used as the address. To understand the difference between an IP address and port number, think of it as a mailing address. The IP address corresponds to the address of a house, while the port tells you the name of the person that should receive the letter.
TCP is described in Chapter 9 and UDP in Chapter 10.
1.2.3 Application Protocols
Application protocols correspond to several ISO OSI layers. The session, presentation, and application ISO OSI layers are reduced to one TCP/IP application layer.
The absence of a presentation layer is made up for by introducing specialized presentation-application protocols such as SSL and S/MINE that specialize in securing data or the Virtual Terminal and ASN.1 protocols that are designed for presenting data. The Virtual Terminal protocol (not to be confused with the ISO OSI protocol of the same name) specifies the network data presentation for character-oriented network protocols (Telnet, FTP, SMTP, and, partly, HTTP). Similarly, ASN.1 is often used for binary-oriented network transport. ASN.1 (including BER or DER encoding) was initially used by SNMP, but today it is also used by S/MINE.
There are many different application protocols. For practical purposes, they can be divided into two groups:
- User protocols utilized by user applications (HTTP, SMTP, Telnet, FTP, IMAP, PIP3, and so on).
- Service protocols, i.e., the protocols that ordinary Internet users rarely encounter. These protocols make sure the Internet functions correctly. For example, these could be routing protocols that are used for mutual communication by routers to correctly set their routing tables. Another example is SNMP usage in network administration.
Figure 1.11: Some protocols of the TCP/IP family
1.3 Methods of Information Transmission
There are many different network protocols and several protocols can be available even on a single layer. Especially with lower-layer protocols, we distinguish between the types of transmission that they facilitate, whether they provide connection-oriented or connection-less services, if the protocol uses virtual circuits, and so on. We also distinguish between synchronous, packet, and asynchronous transmission.
1.3.1 Synchronous Transmission
Synchronous transmission is needed when it is necessary to provide a stable (guaranteed) bandwidth, for example, in audio and video. If the source does not use the provided bandwidth it remains unused. Synchronous transmission uses frames that are of fixed length and are transmitted at constant speeds.
Figure 1.12: Frames divided into slots in synchronous transmission
In synchronous transmission, the guaranteed bandwidth is established by dividing the transmitted frames into slots (see Figure 1.12). One or more slots in any transmitted frame are reserved for a particular connection. Let's say that each frame has slot 1 reserved for our connection. Since the frames follow each other steadily in a network, our application has a guaranteed bandwidth consisting of the number of slot 1s that can be transmitted through the network in one second.
The concept becomes even clearer if we draw several frames under each other, creating a 'super-frame' (see Figure 1.13). The slots located directly under each other belong to the same connection.
Figure 1.13: Super-frame
Synchronous transmission is used to connect your company switchboard to the phone company exchange. In this case, we use an E1(or T1 in United States) link containing 32 slots of 64 Kbps each. A slot can be used for making a phone call. Therefore, in theory, 32 calls are guaranteed at the same time (although some slots are probably used for servicing).
The Internet does not use synchronous transmission, i.e., in general, does not guarantee bandwidth. Quality audio or video transmission on the Internet is usually achieved by over-dimensioning the transmission lines. Recently, there has been a steady increase in requests for audio and video transmission via the Internet, so more and more often we come across systems that guarantee bandwidth even on the Internet with the help of Quality of Service (QoS). In order for us to reach the expected results, however, all appliances on route from the source to the destination must support these services. Today, we are more likely to get involved with only those areas on the Internet that guarantee bandwidth such as within a particular Internet provider.
1.3.2 Packet Transmission
(From now onwards we will use the term packet to refer to 'packet', 'datagram', 'segment', 'protocol data unit'.) Packet transmission is especially valuable for transferring data. Packets usually carry data of variable size.
Figure 1.14: Packet data transmission
One packet always carries data of one particular application (of one connection). It is not possible to guarantee bandwidth, because the packets are of various lengths. On the other hand, we can use the bandwidth more effectively because if one application does not transmit data, then other applications can use the bandwidth instead.
1.3.3 Asynchronous Transmission
Asynchronous transmission is used in the ATM protocol. This transmission type combines features of packet transmission with features of synchronous transmission.
Figure 1.15: Asynchronous data transfer
Similarly to synchronous transmission, in asynchronous transmission, the data are transmitted in packets that are rather small, but are all of the same size; these packets are called cells. Similarly to packet transmission, data for one application (one connection) is transmitted in one cell. All cells have the same length; so if we guarantee that the nth cell will be available for a certain application (a particular connection), the bandwidth will be guaranteed by this as well. Additionally, it doesn't really matter if the application does not send the cell since a different application's cell might be sent instead.
1.4 Virtual Circuit
Some network protocols create virtual circuits in networks. A virtual circuit is conducted through the network and all packets of a particular connection go via the circuit. If the circuit gets interrupted anywhere, then the connection is interrupted, a new circuit is established, and data transmission continues.
Figure 1.16: Virtual circuit
In the figure above, a virtual circuit between nodes A and D is established via nodes B, F, and G. All packets must go through this circuit.
Datagrams can be transmitted via the virtual circuit in two ways:
- The circuit does not guarantee the datagram's delivery to its destination. (If network congestion occurs, the circuit can even throw the datagram away.) An example is the Frame Relay protocol.
- The virtual circuit can establish a connection and guarantee the data delivery, i.e., the data packets transmitted are numbered and the destination confirms their reception. If any data gets lost, a request to resend the data is made. For example, this mechanism is used in the X.25 protocol.
The advantage of virtual circuits is that they are first established (using signalization) and then the data is inserted only into the established circuit. Each packet does not have to carry the globally unique address of the destination (complete routing information) in its header. It only needs the circuit ID.
The virtual mechanism is not used on the Internet, which was primarily aimed for use by the U.S. Department of Defense, since the destruction of a node in the virtual circuit would result in the transmission being interrupted—a fact that the authors of TCP/IP did not like. For this reason, IP does not use virtual circuits. Each IP datagram carries a destination IP address (complete routing information) and is therefore transported independently. If a node is destroyed, only the IP datagrams currently being transmitted through that particular node are destroyed. The remaining datagrams are routed via different nodes.
Figure 1.17: IP does not use virtual circuits
As the figure above shows, IP datagrams 1, 2, and 3 start from the node A to node B, but from this point, datagrams 1 and 3 are routed through a different path than datagram 2. The destination (node D) is then reached by each of them via a different path. Generally, IP datagrams may reach their destination in a different order than the order in which they were sent. So our IP datagrams could be received in the following order: 2, 1, and then 3.
In the Internet hierarchy, TCP—a higher-layer protocol that establishes a connection and guarantees the delivery of data—is used above the connectionless IP. If some of the data packets are lost, their retransmission is requested. If the data packets were lost due to the destruction of a node along the way and there is another routing possible within the network, then the transmission is automatically repeated using the other path.
Virtual circuits are divided into the following groups:
- Permanent (Permanent Virtual Circuit (PVC)), i.e., circuits permanently built by the network administrator.
- Switched (Switched Virtual Circuit (SVC)), i.e., virtual circuits that are created dynamically as the need arises. An SVC is created with the help of signalizing protocols that can be used for communicating between the user and the network itself. The network signalizes to the user various events that can be used for network monitoring and administration. SVC communication consists of two steps: creating the virtual circuit and using it for communication.
PVC corresponds to leased lines and SVC corresponds to the dial-up lines of a phone network.
Note:
Protocols using virtual circuits are called Connection-Oriented Network Services (CONS) and protocols transporting their packets without using virtual circuits are called Connection-Less Network Services (CLNS).
Understanding TCP/IP: A clear and comprehensive guide to TCP/IP protocols
You are probably wondering whether to refer to this book to understand more about TCP/IP or to read some other good books describing similar topics and containing the word TCP/IP in their titles. Let us explain to you what moved us to write another publication about the TCP/IP protocols on which the Internet is based.
Publications about the Internet are usually of two types:
- Publications involved with concrete operating systems (Microsoft Windows,
UNIX, CISCO, etc.). The goal of such publications is to train readers in a
particular TCP/IP implementation, while describing the main TCP/IP principles is only their secondary goal. - Publications written for the academic environment. Even if their main goal is to describe the basic TCP/IP principles, they could be too tedious for many readers.
So we faced the task of creating a basic TCP/IP guide, independent from any concrete environment (for example, Microsoft Windows, UNIX, CISCO, etc.), emphasizing presentation of the text in a clear and apt form to readers so that they understand the main coherences. To explain the basic principles and coherences in the best way, we have used a lot of illustrations. These illustrations were not created by chance. We drew and constantly refined them according to the requirements from our countless TCP/IP courses. First we chalked them on a blackboard, next we drew them on a white blackboard, and finally we drew them in Microsoft Visio. It has been twenty years since we started teaching TCP/IP.
If you say to yourself that you will not pay for this book and will study TCP/IP directly from
the Internet RFC standards, you have unknowingly found the next goal of this publication. Exploring the huge number of RFC standards takes a lot of time, and moreover their study is very difficult for a beginner. (The idea of someone reading international standards as a novel in his or her bed before sleep is funny.) So another goal of this publication is to equip readers with such knowledge that they would be able to study RFC by themselves after reading this book.