COMMUNICATION DEVICES

Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.
The most familiar example is a voiceband modem that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Ethernet, serial, or network connection. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". They can also be classified by Baud, the number of times the modem changes its signal state per second.
Baud is not the modem's speed in bit/s, but in symbols/s. The baud rate varies, depending on the modulation technique used. Original Bell 103 modems used a modulation technique that saw a change in state 300 times per second. They transmitted 1 bit for every baud, and so a 300 bit/s modem was also a 300-baud modem. However, casual computerists confused the two. A 300 bit/s modem is the only modem whose bit rate matches the baud rate. A 2400 bit/s modem changes state 600 times per second, but due to the fact that it transmits 4 bits for each baud, 2400 bits are transmitted by 600 baud, or changes in states.
Faster modems are used by Internet users every day, notably cable modems and ADSL modems. In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optical fibers. Most intercontinental data links now use optical modems transmitting over undersea optical fibers. Optical modems routinely have data rates in excess of a billion (1x109) bits per second. One kilobit per second (kbit/s or kb/s or kbps) as used in this article means 1000 bits per second and not 1024 bits per second. For example, a 56k modem can transfer data at up to 56,000 bits (7kB) per second over the phone line.

E-mail

Electronic mail, often abbreviated as e-mail, email, or e-Mail, is any method of creating, transmitting, or storing primarily text-based human communications with digital communications systems. Historically, a variety of electronic mail system designs evolved that were often incompatible or not interoperable. With the proliferation of the Internet since the early 1980s, however, the standardization efforts of Internet architects succeeded in promulgating a single standard based on the Simple Mail Transfer Protocol (SMTP), first published as Internet Standard 10 (RFC 821) in 1982.
Modern e-mail systems are based on a store-and-forward model in which e-mail computer server systems, accept, forward, or store messages on behalf of users, who only connect to the e-mail infrastructure with their personal computer or other network-enabled device for the duration of message transmission or retrieval to or from their designated server. Rarely is e-mail transmitted directly from one user's device to another's.
While, originally, e-mail consisted only of text messages composed in the ASCII character set, virtually any media format can be sent today, including attachments of audio and video clips.
Sources : http://en.wikipedia.org/wiki/Email

Social Networks part-2

Comparison Of Social Networks

Name: Friendster

Founded : 2002

Website : http://www.friendster.com

Type of site : Social network service

Launched : March 22, 2002

Current Status : Active

Name: Myspace

Founded : 2003

Website : Myspace.com

Type of site : Social network service

Launched : August 2003

Current status : Active

Founded : Cambridge,Massachusetts

Website : facebook.com

Type of site : Social network service

Launched : February 2004

Social Networks part-1

What is Social Network?

A social network is a social structure made of nodes (which are generally individuals or organizations) that are tied by one or more specific types of interdependency, such as values, visions, ideas, financial exchange, friendship, kinship, dislike, conflict or trade. The resulting graph-based structures are often very complex.

Social network analysis views social relationships in terms of nodes and ties. Nodes are the individual actors within the networks, and ties are the relationships between the actors. There can be many kinds of ties between the nodes. Research in a number of academic fields has shown that social networks operate on many levels, from families up to the level of nations, and play a critical role in determining the way problems are solved, organizations are run, and the degree to which individuals succeed in achieving their goals.

In its simplest form, a social network is a map of all of the relevant ties between the nodes being studied. The network can also be used to determine the social capital of individual actors. These concepts are often displayed in a social network diagram, where nodes are the points and ties are the lines.

INTERNET AND COMMUNICATION Part 1

THE HISTORY OF INTERNET AND COMMUNICATION

The history of the Internet began with the ARPANET and connected mainframe computers on dedicated connections. The second stage involved adding desktop PCs which connected through telephone wires. The third stage was adding wireless connections to laptop computers. And currently the Internet is evolving to allow mobile phone Internet connectivity ubiquitously using cellular networks.

The history of communication dates back to the earliest signs of life. Communication can range from very subtle processes of exchange, to full conversations and mass communication. Human communication was revolutionized with speech about 200,000 years ago. Symbols were developed about 30,000 years ago, and writing about 7,000. On a much shorter scale, there have been major developments in the field of telecommunication in the past few centuries.

Communication

Communication is the most popular use of the Internet, with email topping the list of all the technologies used. Some of the types of communication technologies used also include email discussion groups, Usenet news, chat groups, and IRC. These are unique to networked computer environments and have come into wide popularity because of the Internet. Other technologies, including video and audio conferencing and Internet telephony, are also available on the Internet. They require more multimedia capabilities of computer systems and are more taxing of network resources than the others. They also are adaptations of other technologies to the Internet.

When you’re communicating on the Internet take special care not to give out personal information to strangers and to treat others with respect. Be aware of the risks involved in communicating with people you cannot see and may never meet in person. Take time to consider what you write to others, and be careful to avoid humor and sarcasm except with the best of friends. You can’t assume that your messages are private, so be careful about what you write.

Several issues related to ethical and legal considerations arise from using the Internet for communication. The manner in which communication is implemented on the Internet makes it susceptible to monitoring. You can’t assume that communications are private. Some believe that sending email is like sending a message on a postcard. Some laws have been enacted to help protect privacy during electronic communications. These, however, have been difficult to enforce and are rarely applied. One way to protect privacy is to encrypt or code a message. A common way of encrypting messages is through the use of public and private keys. Although software for encryption is readily available, current policies and laws prohibit its export.

Another area of concern is dealing with abusive or offensive communications. Laws that apply to libel, harassment, and abuse have been applied to cases where the offending behavior has occurred on the Internet. Unsolicited email or other forms of communication is called spam. It definitely is an annoyance, but also quite costly to the people who receive the junk email or other communications. It’s relatively inexpensive to produce, because most of the cost of transporting the email is shifted to the receiver and all people that use the networks supporting the Internet.

Sources:

http://en.wikipedia.org/wiki/History_of_the_Internet

http://en.wikipedia.org/wiki/History_of_communication