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Data Communication is exchange of data between two devices. In computers data exchange is in form of 0 and 1. This course discuss how computer communicate, what is medium and what are expenses. This handout includes: Modem, Standards, Commercial, Modems, Automatic, Answering, Machine, Popular, Intelligent
Typology: Study notes
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o Bell modems
o ITU-T modem standards
o Intelligent modems
BELL Modems
ITU-T Modems
Traditional Modems o Traditional modems are limited to a data rate of 33.6 Kbps as determined by Shannon’s formula Data rate Signal-to-noise ratio o New modems with bit rated of 56 Kbps are wide spread now
o TX of data from A to B o Digital data is modulated by the modem at site A o Analog data is sent from the modem to to the switching station at site A using the local loop
o Tx of data from ISP to the modem at site A follows these steps: o Digital data is sent by the computer of ISP through the digital telephone network o At the switching station, digital data is converted to analog using inverse PCM o Analog data is sent from the switching station at site A to the modem on the local loop o Analog data is demodulated by modem at site A o Note that in this direction there is no quantization of data using PCM. o The limitation when uploading is not an issue an here a o Data can be sent at 56 Kbps o This is what user is looking for since larger files are typically downloaded from internet
The maximum data rate in the uploading direction is still 33.6 Kbps but the data rate in downloading direction is now 56 Kbps Why 56Kbps?
Summary
MODEM Standards
Reading Sections
Section 6.4, 6.5, 6.6,“Data Communications and Networking” 4th Edition by Behrouz A. Forouzan
