The following table summarizes the protocols used at various points in the data transmission stream. See also the figure.
Pulse Code Modulated is known as PCM and Digital Multiplexed Interface is known as DMI.
Table 1: Protocol states for data communication
Transmission type |
Incoming DTE to DCE |
OSI layer |
Protocols DTE to DCE |
DCE to system port |
Inside system |
Analog |
Modem |
1 |
RS-232, RS-449, or V.35 |
analog |
PCM |
2 |
8- or 10-bit code |
Voice-grade data |
Voice-grade data |
ADU |
1 |
RS-232 |
ADU proprietary |
Raw bits |
2 |
Asynchronous 8-bit code |
Asynchronous 8-bit code |
DMI |
Digital |
Data Module |
1 |
RS-232, RS-449, or V.35 |
DCP or BRI |
Raw bits |
2 |
8-bit code |
DMI |
DMI |
Digital Signal Level 1 (DS1) |
1 |
Any |
DS1 |
PCM or raw bits |
2 |
8-bit code |
DMI or voice- grade data |
DMI or voice-grade data |
The physical-layer protocol and the DMI mode used in the connection are dependent upon the type of 8-bit code used at Layer 2 between the DTE and DCE equipment, as listed in the table and the table.
Table 2: Physical-layer protocol versus character code
Protocol |
Code |
RS-232 |
Asynchronous 8-bit ASCII, and synchronous |
RS-449 |
Asynchronous 8-bit ASCII, and synchronous |
V.35 |
Synchronous |
Table 3: DMI mode versus character code
DMI Mode |
Code |
0 |
Synchronous (64 kbps) |
1 |
Synchronous (56 kbps) |
2 |
Asynchronous 8-bit ASCII (up to 19.2 kbps), and synchronous |
3 |
Asynchronous 8-bit ASCII, and private proprietary |
