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Wednesday, February 10, 2010

Blu Ray DISC

Blu Ray  DISC
Blu-ray also known as Blu-ray DISC(BD) is a name of a next generation optical disc video recording format jointly developed by nine leading consumer electronics companies(Hitachi,LG, Matsuhita (Panasonic), pioneer, philips, samsung,sharp, sony, and Thomson). The format was developed to enable recording, rewriting and play back of high definition video(HDTV). Blu-ray makes it possible to record over 2 hours of digital high definition video(HDTV) or more than 13 hours of standard-definition video(SDTV/VHS Quality) on a 27 GB disc. there are also plans for higher capacity discs that are expected to hold up to 50 gb of data. the nine companies announced the joint establishment of the specification for blu- ray disc in feburary 19 2002 and after the hard work of the professionals of those companies it is in the market from April 10, 2003. An interesting factor about the blu-ray is that in near future we can find the collection Blu-ray disc of movies in the market as we get the collection of MP3 files.

Tuesday, February 9, 2010

Transparent Caching

the browsers should be configured explicitly to use a proxy server. this is not a headache anymore instructing each and every client to make proxy settings. Transparent caching is very handy in such cases. transparent caches are simple and they can be easily used in a network and do not require explicit coordination with other caches. Transparent caching in context of HTTP proxy caches means the transparent hijacking of the port 80, which is the default HTTP port. the cache hijacks the port 80 traffic whenever the client tries to request to the remote servers. the client does not have to configure his/her browser. instead squid transparently picks up requests and responses to the client. squid cache/proxy server acts as transparently caching servers and fulfils the clients requests of web objects, if available locally hence making efficient web browsing.

Web Caching

web caching refers to storing locally the once referenced web objects, should any future request come for that object, it is checked for in local store and if present there it is retrieved directly from the local store instead from the original server. It saves time, bandwidth and of course money. Web caching can be done at end users desktop or on dedicated cache server. Most of the present day browsers have support for caching to some extent though they are not of high performance and limited to a computer only. the most effective way to implement cache is by service provider. they can deploy a dedicated server and high performance web caching software. Wherever caching is done the goal is the same. It is better if ISPs cache web objects so that frequently referenced sites could be serve locally instead of downloading every time from the original servers. This increases throughput dramatically. the above discussions suggests that given sufficient storage, whole internet could be cached. However this is not true, Information is dynamic in nature and so is the web. If we cache everything we end up serving stale objects to the clients. this is worse than having slow access. there are methods to ensure the freshness of an object stored in a cache.

Wednesday, February 3, 2010

What is FTP ?

The FTP(File Transfer Protocol) utility program is commanly used for copying files to and from other computers. FTP is a general protocol that works on unix system as well as a variety of other (non unix) systems. FTP is basically used to promote sharing of files (computer programs and/or data), to encourage indirect or implicit(via programs) use of remote computers, to shield a user from variations in file storage systems among hosts, and to transfer data reliably and efficiently. FTP though usable direclty by a user at a terminal, is designed mainly for use by programs. FTP is in common use for downloading data and programs and for uploading files such as web sites to or from the servers of the same or different architecture.(such as windows PC,MAC ,etc).

Tuesday, January 26, 2010

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.

Monday, January 25, 2010

Telephone System

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

Sunday, January 24, 2010

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.

Saturday, January 23, 2010

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.

Wednesday, January 20, 2010

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.
data Warehouse
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.

Sunday, January 17, 2010

Embeded system

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.

Saturday, January 16, 2010


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.

Wednesday, January 13, 2010

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)
Mobile phoneSo 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.

Tuesday, January 12, 2010

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.

Monday, January 11, 2010


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.

Sunday, January 10, 2010


Frequency division multiple access is a technology in which multiple frequencys are sent in a same instant of time. As shown in the figure in the same time there are multiple call which are being transmitted. The main advantage of this access technology over TDMA is that it simple and easy to decode and does not require any complex mechanism to decode the signals. the major drawback of this kind of technology is that it requires higher bandwidth while transmitting thus this type of technology should not be used where frequency is minimum.

Saturday, January 9, 2010


Time Division multiple access(TDMA)
It is a type of a multiple access technology where in a common frequency, multiple channels can be sent. The frequency is divided into number of time slots and each in each slot channels are placed and at the recieving end channels are decoded accordingly. TDMA has a mojor advantage where multiple frequency is a issue. It is used in telephony technology, mobile communications etc. TDMA is much complex than FDMA and requires proper clocking for synchronisation.

Thursday, January 7, 2010

how to upload video on youtube

In order to upload video in youtube you need to first sign up with a username and password and create an account. and then you can add as many video as you like of your choice with the maximum size of 100 mb . to create an account go to www.youtube.com and then at the top right you will see a sign up button click there and get started.

What is internet

Simply internet is defined as network of networks. Lets explain internet with a very simple example suppose we have two computers in a room which are connected by a wire and we can share data within the two computers now this is called a network. suppose now one computer is in Asia and the other computer is in America which are connected by different means wired or wireless and we can share among those two computers then it is said to be in the internet. Hence internet can be defined as network of networks. in order for the two computers to communicate with each other we should gave computer there respective name which is know as IP address. so by the help of ip address we can communicate with any computers across the globe hence ip address should be unique. But remembering the long ip address of any site is very difficult hence we name then like http://www.google.com/ and it becomes easier for us to remember, which is translated to ip address by DNS Server.

Wednesday, January 6, 2010

Routing Protocols

A routing protocol is the software or hardware implementation of the routing algoirthm. what routing protocol does is it describes the best route for the packet to reach from the source to its destination. Best path is selected based on the calculation of the metric for any ip packet. The parts that constitute a metric includes:-hopcount(number of devices to reach the destination network),load, delay,bandwidth etc. there are two major classes of routing protocols
i)Distance vector routing protocols
ii)Link state routing protocols
i)Distance Vector routing protocols: It decides the path of the packet based on how far it is and how many hops does it require to reach the destination, so whichever path has small number of hops it sends its data through it. the examples are RIP,IGP
ii)Link state routing protocols: the major drawback of distance vector is that it does not consider the congestion,delay, bandwidth of the path since for small number of hops may cause greater delay than that of longer hops so link state routing protocols over comes this problem by taking into consideration the bandwidth,congestion in all the corresponding path and selects the best path for the packet to be send hence nowadays it is most widely used routing protocols. the examples are OSPF and IS-IS

OSI layer

OSI layer
OSI(Open System Interconnection) is the communication protocol which is an ISO standard for worldwide communications in the network across different equipmetnts and application for different vendors. It consist of seven layers and most of the new networking models that are designed are based on the OSI Layer. The seven layers are as follows:-
Physical: it is the physical medium in which actual data are being transferred as electrical signals eg are coaxial cables twisted pair cables etc.
Data link: It defines the format of the data in the network, it communicates with the host with the ethernet address which is the 48 bit Mac address.
Network:It uses internet protocol which is responsible for tracking the routes from source to destination.
Transport:it divides the user buffer into network buffer sized datagrams and enforces desire transmission control. there are two transmission protocols in transport layer connection oriented (TCP) and connectionless (UDP).
Session:this layer describes the format of the data sent in a network.
Presentation:it translates the local representation of the data sent into the network to its canaonical for and vice versa
Application: it provides the user interface for eg: ftp,http,telnet, mail etc..


Router is a networking device which connects two or more different sub networks. The main function of the router is to show the optimum path for ip packets to reach its destination. This is done by the help of routing table stored inside of a router based on which decides the path for the packets to reach its destination. A computer can also act as a router if proper software in its has been configured. Router acts in network layer of the TCP/IP model. Cisco and Juniper are the major companies which produces router. Routers can also be treated as firewall by defining proper access list inside the router one can block unwanted access to the network. Routers use different protocols in order to trace the path from source to destination. The routing protocols that are being widely popular are RIP, OSPF, IGRP,EIGRP, BGP etc.

Tuesday, January 5, 2010

What is DNS?

DNS(Domain Name System)
DNS is a database that translate a fully qualified domain name into a IP address. In a network computers are identified by their respective IP address, which is of the form so rembering the ip of each and every computer that we use is very tedious and difficult. But if each computer is given a name then it is easier for us to remember hence we are more comfortable remembering www.google.com rather than its complex IP address. Hence DNS does the trick for us it converts the domain name to a IP address and we are connected to the remote computer. so each organization must have a DNS servers which keep records of all the ipaddress inside of its network and also it should search on behalf of the organization to query the respective ipaddress.

TCP IP Model

TCP IP Model
The TCP/IP is protocol that is used in order to maintain a standard in the field of communication. there are lots of networks in the internet which has to be accessed by all over the globe hence if a proper standard is not set, then the two different networks will wont be able to communicate with each other and thus the concept of internet will be meaningless. Hence the standard has been defined which is named after two important protocols TCP(Transmission Control Protocol) and IP(Internet Protocol). The TCP/IP model consists of four different layers which are link layer, Internet layer, Transport Layer and Application Layer .
Link Layer Delivers data through ethernet and also in this layer error detection is done.
Internet Layer manages packets and defines the route of the packet from source to destination.
Transport Layer manages the transfer of data through connection oriented and connectionless transfer protocols.
Application Layer refers to various services like http, ftp, telnet etc.

Network Topology

A network is a group of more than two computers, based on geographic locations Network can be defined into following types. LAN, WAN and MAN
LAN(Local Area Netwwork) Network Topology
This type of network is defined where the distance is very short. The typical examples are office, buildings etc. the local area network is usually used in offices to share printers, files etc. LAN is typically in a single sub network and is managed moslty by a Layer2 switch.
WAN(Wide Area Network)
As the name suggest WAN covers a large geographical area, Internet is the largest WAN. Network TopologyWAN can be group of LAN, unlike LAN WAN are not owned by a single body or a organization but rather they are managed by a group of organizations. The network structure of WAN is much complex and the consists of Routers and switches.
MAN(Metropolitian Area Network)
It is a computer network struture which is larger than LAN but smaller than WAN. This type of structure is typically confined to a city or country, and is managed by single ownership like government of internet service providers.

IP Address

An IP(Internet Protocol) address is an address that is assigned to any computer or media which is connetcted to a computer network. The main concept of an IP address is to name a computer in a network so that it can be easily identified. There are two types of IP addressing that exist in the current world scenario- they are IPV4(Internet Protocol Version 4) and higher version is IPV6(Internet Protocol Version 6). IPV4 is 32 bit addressing mode from which we can address upto 2^32 computers. initially designers thought it would be enough for the world but as the technology is growing so much rapidly and most of the electronic media are IP based hence the need of IP address is growing rapidly hence the 32 bit IP addressing is not enough so now designers have chosen a new addressing scheme which consists of 128 bit addressing mode so we can address upto 2^128 computers. With this new scheme of IP address there wont be scarcity of ip address for long years to come.