| Introduction to Data Communications |
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13. Modems (cont'd) |
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- Speed
The speed at which the modem can send data in bps (bits per second). Typically modem speeds are: 300, 600, 1200, 2400, 4800, 9600, 14.4K, 19.2K, 28.8K bps
- Auto Dial /Redial
Smart Modems can dial the phone number and & auto redial if a busy signal is received.
- Auto Answer
Most modems can automatically answer the phone when an incoming call comes in. They have Ring Detect capability.
- Self-Testing
New modems have self-testing features. They can test the digital connection to the terminal /computer and the analog connection to a remote modem. They can also check the modem's internal electronics.
- Voice over Data
Voice over Data modems allow a voice conversation to take place while data is being transmitted. This requires both the source and destination modems to have this feature.
- Synchronous or Asynchronous Transmission
Newer modems allow a choice of synchronous or asynchronous transmission of data. Normally, modem transmission is asynchronous. We send individual characters with just start and stop bits. Synchronous transmission or packet transmission is used in specific applications.
13f. Features of Modems