digital multiplexing

DIGITAL MULTIPLEXING

Multiplexing is a technique in which several massage signals are combined into a composite signals for transmitting over a common channel. In order to transmit a number of this signals over the same channel, the signals must be kept apart so that they do not interfere with each other, and hence they can be separated at the receiver end.

Basically multiplexing is two types as under:

1. Frequency division multiplexing (FDM)

2. Time division multiplexing (TDM)

Frequency division multiplexing (FDM): This technique permits a fixed frequency band to every user in the complete channel bandwidth. Such frequency slot is allotted contentiously to that user. As an example consider the channel bandwidth is 1Mhz. Let there be 10 user, each requiring up to 100KHz bandwidth. So each user will get 1000KHz bandwidth. This techniques is known as frequency division multiplexing (FDM). It is basically used for modulated signals. This is due to the fact that a modulated signal can be placed in any frequency band by just changing the carrier frequency. 

Time division multiplexing: In TDM the signal to be multiplexed are transmitted sequentially one after other. Each signal occupies a short time slot. Thus, the signals are isolated from each other in time domain, but all of them occupy the same slot in the frequency spectrum, therefore the complete bandwidth of the communication channel is available to each signal to be transmitted in TDM.

   

 

12 and 5 volt regulateed power supply

12 and 5 Volt Regulated Power Supply

Components required to build the power supply 

introduction to dbms

INTRODUCTION TO DBMS 

What is DBMS?

Ans: The data base management system consists of a collection interrelated and persistent data are referred to as database. A set of application programs used to access, update and manage the data forms the DBMS. The goal of DBMS is to store data into database and retrieve data from database. It allows different user application programs to concurrently access the same database.

 What is different level of data abstraction?

Ans: There are three level data abstraction.

 Physical Level: The lowest level of abstraction describes how the data are actually stored. At the physical level, complex low-level data structures are described in details.

Logical Level: The next-higher level of abstraction describes what data are stored in the database, and what relationship exists among those data. The entire database is thus described in terms of small number of relatively simple picture structure. The user of the logical level does not need to be aware of the complexity.

View Level: A view level is a subset of database it may contain virtual data that is derived from a table (database) files but is not explicitly stored. 

 

Mention advantage of DBMS over file-processing system?

Ans: 

• A database management system coordinates both physical and logical access to the data, where as a file processing system only coordinates the physical access.

• A database management system (DBMS) is designed to coordinate multiple users accessing the same database at the same time whereas in file-processing system one program is allowed to access one data at a time.

 

how to speed internet

How to Increase Internet Speed

For user Windows XP Professional, you can increase extra Internet connection speed 20%. By default Windows XP hold 20% of your Internet speed for various service such as Windows Update and others.

If your Internet speed is slow you can to tweak Internet speed. By default, the Packet Scheduler of Windows XP Professional limits the system to 20 percent of the bandwidth of a connection, but you can use this setting to override the default. That packet is QOS (Quality of Service) for Windows XP. This packet may not be often used, so why don't we change the setting to tweak Internet Speed.

Determines the Percentage of connection bandwidth that the system can reserve. This value limits the combined bandwidth reservation of all programs running on the system. If you enable the setting, you can use the "Bandwidth Limit" box to adjust the amount of bandwidth the system can reserve. If you disable this setting or do not configure it, the system uses the default value of 20 percent of the connection. 

How to Increase Internet Speed?