AutoSync Considerations

Increases in line speed are allowed when AutoSync is in use only and the current DTE speed supports AutoSync. The following DTE speeds are required for the indicated line speeds, and are established when the initial connection is made. If the line speed is reduced from the initial line speed of a call, then the DTE speed always supports a return to the initial line speed. The following table shows the maximum line speeds (in bits/s) that are supported by initial AutoSync DTE speeds.

Maximum AutoSync Line Speeds

Initial line speed   DTE speed     Maximum line speed        

2400                 9600          4800                      

4800                 9600          4800                      

7200                 19200         12000                     

9600                 19200         12000                     

12000                38400         19200                     

14400                38400         19200                     

16800                38400         19200                     

19200                38400         19200                     

21600                57600         28800                     

24000                57600         28800                     

28800                57600         28800

Note: AutoSync uses 11-bit characters on the DTE-DCE port and sends 8 bits to the phone line. Thus, the minimum ratio of port speed to line speed is 11/8, or 1.375. It is also necessary to insert end of frame control characters into received data, but this does not measurably increase the ratio needed, since flags (required between every frame anyway) are not delivered.

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