DATA COMMUNICATION Lecture-22

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

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

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

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

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

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

EIA-449

Canceling of Noise in the Balanced Mode

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

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

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

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

Modems

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

Bandwidth of a Telephone Line

Modem Speed: ASK

Modem Speed: FSK

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

Summary EIA-449 EIA-530 X.21 Modems

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