14.4 Speed Table
It's best to have at least a 16650 UART for a 56k modem but few modems or serial ports provide it. Second best is a 16550 that has been tweaked to give 230,400 bps (230.4 kbps). Most people still use a 16550 that is only 115.2 kbps but it's claimed to only slow down thruput by a few percent (on average). This is because a typical compression ratio is 2 to 1 and for downloading compressed files (packages) it's 1 to 1. There's no degradation for these cases. Here are some suggested speeds to set your serial line if your modem speed is:
- 56k (V.92): use 115.2 kbps or 230.4 kbps (best)
- 56k (V.90): use 115.2 kbps or 230.4 kbps (best)
- 33.6k (V.34bis): use 115.2 kbps
- 28.8k (V.34): use 115.2 kbps
- 14.4k (V.32bis): use 57600 bps
- 9.6k (V.32): use 38400 bps
- slower than a 9600 bps (V.32) modem: Set the speed to the same speed as the modem (unless you have data compression).
All the above speeds may use V.42bis data compression and V.42 error correction. If data compression is not used then the speed may be set lower so long as it's above the modem speed.
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