Telephone line

A telephone line is usually connected to the telephone exchange by about three miles(4.83 km) of a twisted pair of 0.54mm copper wires known by phone company as "the loop". Although a copper is a good conductor of, it does have resistance. the resistance of No 22 AWG wire is 16.46 ohms over 1000 ft at 77 degrees F(25 degree C). Because telephone apparatus is generally considered to be current driven, all phone measurements refer to current consumption not voltage. the length of the wire connecting the subscriber to the telephone exchange effects the total amount of the current that can be drawn by anything at subscribers end of line.

When the telephone is in on-hook stage the "TIP" is about 0 Volt, while the "RING" is about -28 Volt with respect to ground. when in offf-hook state and current is drawn, TIP goes negative and RING goes positive. A typical off-hook condition is TIP is about -20 V and RING is about 28 V. This means there are about 8 V voltage between the wires going to telephone in normal operation condition. The DC resistance of typical telephone equipment is about 200-300 ohms range and current flowing through the telephone is in 20-50 mA range.

Telephone System

Telephone system involves the conversion of the sound signals into an audible frequency analog electrical signal, which can be then transmitted by radio, or wire. thus the telephone systems involves subscriber, suitable transmitting media and switching center. the establishment of voice communication between customers at a distant location is the main functin of the telephone system. It must provide many other services primarily the wide variety of computer data transmission. the telephone system is mostly multipurpose digital transmission network. In modern days due to the growth of technology most of the telecommunication environment is digital. all the proceeding of the voice as well as the digital data is done digitally in the switching center. the question arises why the digital communication is being chosen over the analog one. the following points suggests some reasons.

1. Ease of multiplexing

2. Ease of signalling

3. Use of modern technology

4. Integration of transmission and switching.

5. Signal regeneration

6. performance monitoring

7. Accomodation and other services

8. Less number of repeater are required

BroadBand communication

The broad band Era has arrived as the information superhighway in the form of high speed connections to the home reaches the doorsteps. the impact of this revolution will be profound ultimately touching all aspects of our lives, from the way we recieve news, information, and entertainment to the way we communicate with others around the globe. Education, health care, commerce, and civic affairs will all be affected as advanced telecommunications services via cable, telephone lines, fiber optics, or wireless connections that link telephones, televisions computers and appliances yet to be invented become a central part of our daily lives.
We have already begun to get glimpse of this interactive future, as cable internet services in introduced as digital televisioni makes its debut, and as high speed telephone service become more widely available. there will be other breakouts to be sure, but there are no guarantees that the public intrest will be served as the broadband market place evolves. Ironically, the more things that become possible in the online environment, the more imperative it is for the nonprofit sector and other independent voices to establish a secure foothold in the new digital landscape. the higher the bandwidth the higher the stakes, in short, for those who fall behind now in the broadband revolution are at risk of never catching up.

Mail Server

A mail server is an application that receives incoming e-mail from local users (people within the same domain) and remote senders and forwards outgoing e-mail for delivery. A computer dedicated to running such applications is also called a mail server. Microsoft Exchange, qmail, Exim and sendmail are among the more common mail server programs. The mail server works in conjunction with other programs to make up what is sometimes referred to as a messaging system. A messaging system includes all the applications necessary to keep e-mail moving as it should. When you send an e-mail message, your e-mail program, such as Outlook or Eudora, forwards the message to your mail server, which in turn forwards it either to another mail server or to a holding area on the same server called a message store to be forwarded later. As a rule, the system uses SMTP (Simple Mail Transfer Protocol) or ESMTP (extended SMTP) for sending e-mail, and either POP3 (Post Office Protocol 3) or IMAP (Internet Message Access Protocol) for receiving e-mail.

Distributed Warehouse data model

The heart of any data warehouse is its database, where all the information is stored. most traditional data warehouses use one of the relational products for this purpose. they can manage extremely large amount of data even hundreds of terabytes. Mainframe relational databases such as DB2 are used for some of the worlds largest data warehouses. Universal data servers such as those from oracle or informix may be a good choice for medium sized warehouses because they can manage a variety of data types.Multidimensional databases are becoming increasingly popular but they limit the size of a ware house to less than 5 Gigabytes.

In relational storage systems the attributes of a tuple are placed coniguously in storage with this row store architecture, a single disk writes suffices to push all of the fields of a single record out to disk hence high performance writes are achieved. A DBMS with a row store architecture is called a write optimized system. In contrast systems oriented towards oriented toward querying a large amount of data should be read optimized. Data warehouse represent one class of read optimized systems in which periodically a bulk load of new data is performed followed by a ralatively long period of hoc queries. in such environments, a column store archietecture, in which values for each column are store contiguously should be more efficient. with column store architecture a DBMS need only read values of columns requred for processing a given query and avoid bringing into memory irrelevant attributes. in data warehouse environments where typical queries involve aggregates performed over a large number of data items a column store has a sizeable performance advantage.

Embeded system

Embeded system denotes computer system that are integrated into a technical context, to control to regularize or to monitor the technical system. therefore Embeded systems are suited and optimized for a special task. Embeded systems are increasingly used in many domains. it is a known fact that about 98 % of used computer systems are using Embeded systems. In a modern car about 98% of used computer systems are using Embeded systems. with an increasing number of cooperating systems, it is extremely important to pay attention in development process. This can affect the coworking of existing as well as future of Embeded systems. within the development process of a new product many Embeded systems especially the softwares of the system are reinvented although a reuse might be useful.

XML

Extensible Markup language offers a means of representing less structured as well as structured data together with some level of self description. It is a well accepted technology that supports interoperability at a technical rather than a semantic level. Xquery, a language for querying XML, can combine documents, web pages, and links to relational databases. Query languages for semi-structured data usually adopt an underlying hierarchical data model, for instance a unidirectional graph. Required objects are specified by providing a path expression in a language that is quite usually intuitive. There are however inherent problems with hierarchical data model such, such as difficulty in representing many to many relationships .In spite of this the hierarchical model has been embraced by web community as a useful intuitive and practical structure.

How Mobile phone works?

The topic here which I am going to discuss is GSM technology which is derived from the european standard. GSM normally works under two band of frequencies 900 and 1800 bands. In a mobile network basically there are BTS(Base Tranciever System), BSC(Base Station Controller) and MSC (Mobile switching center)
So when any user makes a call first it is recieved by BTS and then it is transferred to BSC and then it is transferred to MSC after that MSC checks whether the called party is Mobile subscriber or PSTN subscribers and routes the call accordingly if the called party is mobile subsciber then the same reverse process is accomplished.

how to check who is online in facebook?

In Facebook chat there is no option of status, and you only one option and that is to go online and see who is online but by doing this other friends will know that you are online and you dont want to create this situation. so in Facebook if you want to check who is online and who is not without going online , there is a application called onlinenow you can go to that and you can first see who is online and who is not and then you can change your status accordingly. you can also block users in facebook. search for the application onlinenow and then book mark it so every time at first you go to that application and then only go online.

CDMA

CDMA stands for Code Division Multiple Access which is a channes access technology used in

radio and mobile communications. The main theme of multiple access technology is to send multiple channels in a single channel so that the bandwidth consumed is saved. In TDMA the signals are alotted based upon time, In FDMA the signals are alloted based upon frequency but in CDMA each signals are given a code which is known as PseudoRandom code and the signals are generated and decoded based upon that code. CDMA also follows spread spectrum signalling in which there is a single frequency and all channels are spreaded in the spectrum as a random code.