ISDN Compared to Analog Modems


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 ISDN Compared to Analog Modems  

 

 

 

 

The ISDN receiving hardware is often referred to as a modem, when it really should be referred to as a digital modem or, more exactly, an ISDN terminal adapter. With the costs of ISDN continuing to drop across the United States (although prices vary a great deal by region), this technology answers the need for many people who must transfer large amounts of data but do not require a T1 dedicated link to the Internet. Companies and small or home businesses can use ISDN technology for their intranets (internal communications networks within a company), allowing high-speed data connections to move large amounts of data quickly and efficiently within their infrastructures. Individuals can benefit from ISDN for their Internet connections to send and receive data quickly and more error-free when compared to using analog modems. ISDN is also a great vehicle to use with conferencing software with which you can see streaming video of the person you are connected to and also hear their voice. This type of conferencing is much easier when using a higher connection rate, like that of ISDN, and a virtually all-digital line from you to the receiver and back.


Note:  Modem is short for modulator/demodulator. It converts (modulates) the computerís digital signals of ones and zeroes (on and off) to audio signals transmittable over telephone lines. The modem also translates (demodulates) the incoming audio signals (analog) to digital data before passing the data to the computer. This translation is one of the necessary tasks that slows analog modem speed.


The analog modem sending information as sound pulses is the weak link in the communications chain. As the sound travels over the phone lines, it is affected by noise (any external electrical interference such as lightning, microwaves, radio waves, etc.). The sound representing a computerís data is also affected by distance due to resistance from the phone line itself. As the distance increases along the telephone route, there are amplifiers that regenerate and increase the signal strength of the sound. Any interference that has been introduced and mixed with the signal is also amplified. The amplification of the noise does not affect voice communications that much but certainly wreaks havoc with analog computer data traveling over those same phone lines.

Any errors in the ones and zeroes can completely destroy an executable program that is being received. Using some of the compression methods available, like PKZip, on the file itself helps reduce errors during a transfer, but then slows the file since it has changed to binary data. Binary data such as executable files, .GIFs, .JPEGs, and other graphic files are already compressed to near maximum. Errors that are introduced into text files are not as noticeable because it may only alter one or a few characters within a complete document. The farther the modulated data has to travel over the telephone lines, the more likely it is that the sound receives external interference altering the data.

To eliminate errors introduced into the analog data, the data packets also contain checksum information, which allows the receiving modem to ensure the data is not corrupted, and the modem can then make best-guess corrections to the received information based on the checksum file. The error-correcting analog modems help ensure reliable data, but this process introduces an overhead of additional information and reduces the amount of actual data that is sent per second. If you have taken the time to download binary data or files that have been compressed with PKZip, from 3 to 5 megabits or higher, only to find the program does not work when received, you have suffered from the problem of line interference affecting the computer code within your received program.

ISDN sends and receives the data as digital information. Since the modulating and demodulating process is eliminated, this aids in increasing the speed of transferring actual data. The binary data is less susceptible to alteration from external electrical interference. This is due to the way the digital information is sent and packaged: A one is equal to a 5-volt electrical pulse, and the zero is an absence of an electrical pulse. Distance also affects digital signals, however, and instead of an amplifier boosting the data signal and noise, there are regenerators. These digital devices detect the received binary data and regenerate the received information of ones and zeroes and then sends the new enhanced digital signals on their way. The regenerators also use a checksum file to ensure accuracy when regenerating and improving the data file.

What benefits are there for you when using ISDNís high-speed data transfer compared to analog modems for connectivity? Here is a simple example:

You are using Microsoft FrontPage 97. Microsoft announces a new version available for download, and you have a new Web site to create. Of course, you would like to obtain the new version and use it to create your new Web pages. Assuming you are currently using a 28.8 modem that transfers data at 28,800 bps, or even a 33,600 bps modem, the download time for the full package will be roughly seven hours and thirty minutes. The time to download this data is calculated assuming optimal transfer rates, not a common occurrence on the World Wide Web. It is safe to say it would take you about eight hours to get all the needed data across the Web and to your computer using an analog modem. A full workday is expended in obtaining the needed program. If you were to use an ISDN connection to obtain the same amount of data, you would have the entire package on your computer in under two hours, and this would allow you a good six hours of production time with the new software package. This high-speed data transfer method will be the technology of choice for many who have outgrown the current analog modem technology, currently limited to modems transferring binary data at 33,600 and receiving up to 53,000 bps. Many of the 56K modems are not V.90 compliant, so they connect at well under 56K, but most can be updated for compliance with the new 56K V.90 standard. There are telephone regulations that limit the download speed to 53K.

From the preceding example, you donít need to be a rocket scientist to figure out the time savings and increased productivity that can be obtained by using the type of high-speed connection that ISDN offers. If you or your organization have the need to transfer large amounts of data on a daily basis, you will realize a cost savings over standard modem technology.

With the ISDN system, there is no delay waiting for a modem-to-modem handshake. Analog modems take as much as 30 seconds, or more, to establish a completed connection, and you normally obtain around 85 to 90 percent transfer efficiency over standard dial-up telephone connections. When downloading from the Web you will also notice that you are not getting a full 53K transfer rate. The transfer rate is less because you are using the HTTP protocol designed more for transferring HTML files to browsers instead of a true file transfer protocol such as FTP (File Transfer Protocol). In many areas around the country, the telephone line quality is quite poor and even with a 33,600 modem, you are lucky to obtain connections at 24,000 to 26,400 bps. With an ISDN connection, aside from connecting within two to four seconds, there is virtually no line degradation commonly experienced with your analog modem. If you are calling long-distance to reach the Internet, you will see a cost savings just from eliminating the need for the modem-to-modem handshake and connection times of ISDN compared to analog modems.

 

 

 

 

 
 
 
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