Appendix: Modem Standards
Tables 7.4 and 7.5 list Bell and ITU modem-speed standards. Standards have changed in two ways: Initially, they were set by the Bell system (AT&T). Now the International Telecommunications Union headquartered in Geneva, Switzerland, sets them. Standard modem speeds have increased from 300 bps to 56,000 bps.
| Standard | Modem Type | Speed (bps) | Fall-Back Speed | Comments |
|---|---|---|---|---|
| Bell 103 | Dialup | 300 | ||
| Bell 212 | Dialup | 1200 | ||
| Bell 208A | Leased | 4800 | ||
| Bell 208B | Dialup | 4800 | ||
| V.21 | Dialup | 300 | 300 | Used by Group 3 fax in half duplex mode for negotiation and control. |
| V.22 | Dialup, leased | 1200 | 300 | |
| V.22bis | Dialup | 2400 | 1200 | Compatible with V.22. |
| V.23 | Dialup | 1200 | 600 | Specifies 75-bps reverse channel. |
| V.27ter | Dialup | 2400 4.8Kbps | 2400 ... |
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