Bit rate is the number of bits per second that is transferred. Baud rate is the number of times per second the signal changes between states. Baud rate and bits per second are not necessarily the same because each baud could be more or less than one bit. Most high speed connections use a "multiple-state modulation" to transfer more than one bit per baud. This is where instead of each baud representing a 1 or a 0 depending on it's current state, it could be divided into frequency ranges, each range is equal to a sequence of bits.

Telephone lines are only analog and were only designed with analog signals in mind. This is the limiting factor for modem connections. All dial-up modems use the same channels as standard telephones do. The way in which telephone offices process signals limits the connection speed to 64kbps. Because of signal distortion and interference, the maximum speed in which modems can connect is 53kbps. For digital computer signals to use analog phone lines, a modem has to be used. Modem's got their name from what they do. They are a modulator / demodulator. Modems convert the computer's binary digital signal into electrical waves. The computer's 1's and 0's are converted to electrical peaks and valleys.

Modems use the phone line to send an analog signal to the internet service provider. This is much like a regular phone call, it still consumes a phone line, and the call still has to be dialed. In this case, instead of using a telephone to dial, the modem dials, and communicates in the same frequencies that a human voice would. When the analog signal reaches the ISP, the signal is converted back to digital form. The ISP in most cases has a digital phone line to the public switched telephone network (PSTN). If the ISP does not have a digital line to the PSTN, then the signal is again converted to analog. The signal is sent through either the ISP's digital or analog signal to the PSTN, which has a direct connection to the Internet backbone. The Internet backbone is a group of high bandwidth lines, either fiber optics, multiple digital lines, or satellites, which are used to get signal to its destination PSTN.

Standard DialUp Modem

Dial-up connections are the slowest, but most popular connection to the Internet. The first dial up modems were limited to 9600 baud, but went through advances to 28.8 k baud, and then 33.3k baud. And 33.3k baud is were it settled. But then new advancements came in 1997 when 2 competing 56k baud transmission specifications were first introduced. There was Rockwell's 56kflex and US Robotics' 56kX2. These both were capable of 56k baud download and 33.3k baud uploads, and only worked when the ISP had a digital line to the PSTN. Both of these had their advantages, and became equally popular. Because both of these standards were incompatible, modems were limited to either one or the other, depending on the brand of modem that was purchased. But lucky for the end user, most ISP's decided to upgrade their technology to support both standards. Later, to establish some conformity, the 2 56k technologies were merged into what is known as 56k V.90; which took the possitive aspects of each previous version, along with a new compression algorithm, resulting in a faster and more reliable connection.

The successor to the V.90 standard, the V.92 standard was recently agreed upon, and modems are expected on the market in the fall of 2000. The V.92 transmission specification has a faster handshaking, 25% more efficient compression, and a 48k baud upload speed.

Dial-up modems have their advantages. They are able to use standard phone lines, use inexpensive hardware, and can not only connect to the Internet, but can double as phone appliances, such as a fax machine, answering machine, or telephone. The disadvantages of a dialup connection are it has slow transfer rates, high pings, and they consume a telephone line when in use.

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