1. DATA COMMUNICATION
Lecture-22

2. Recap of Lecture 21 DTE-DCE Interface DTE-DCE Interface Standards
EIA-232
Null Modem

3. Overview of Lecture 22
EIA-449
EIA-530
X.21
Modems

4. EIA-449 Mechanical specifications
Combination of two connectors: DB-37 and DB-9

5. EIA-449 Functional specifications DB-37 Primary channel
Category I pins: Two sets of pins, each set is same with that of EIA-232
Category II pins: New functions defined, or redefined functions of EIA-232

6. EIA-449 Functional specifications DB-9 Secondary channel
Different connector from that of EIA-232

7. EIA-449 Two standards for electrical specifications
RS-423: Unbalanced mode
RS-422: Balanced mode

8. EIA-449

9. Canceling of Noise in the Balanced Mode

10. EIA-530 Does not support a secondary channel
Simplified version of EIA-449 that uses DB-25 pins
EIA-449 Category I pins + 3 pins from Category II
Does not support a secondary channel

11. X.21 Eliminates most of control pins of EIA standards
Control signals are encoded to control characters
Send control characters within the data line
More control information for digital telephony

12. X.21
For digital communication between devices over a network, rather than just between DTE and DCE
DB-15, Work with balanced circuits at 64Kbps

13. Modems Modulator Digital signal  analog signal: ASK, FSK, PSK, QAM
Demodulator
Analog signal  digital signal: Not an encoder

14. Modems

15. Bandwidth
Data rate depends on the type of encoding and the bandwidth of the medium
Every line has an upper limit and a lower limit on the frequencies of the signals it can carry

16. Bandwidth of a Telephone Line

17. Modem Speed: ASK

18. Modem Speed: FSK

19. Modem Speed: PSK & QAM Comparisons of bit rates: HDX and FDX

20. Summary
EIA-449
EIA-530
X.21
Modems

21. Suggested Reading
Section 6.4, 6.5, “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan