DATA COMMUNICATION Lecture22 Recap of Lecture 21 w

DATA COMMUNICATION Lecture-22

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

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

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

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

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

EIA-449

Canceling of Noise in the Balanced Mode

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

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

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

Modems

Bandwidth w Data rate depends on the type of encoding and the bandwidth of the medium w 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 w Comparisons of bit rates: HDX and FDX 2 -PSK 2400 1200 4 -PSK, 4 -QAM 4800 2400 8 -PSK, 8 -QAM 7200 3600 16 -QAM 9600 4800 32 -QAM 12000 6000

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

Suggested Reading w Section 6. 4, 6. 5, “Data Communications and Networking” 2 nd Edition by Behrouz A. Forouzan