Data Communication and Host Modes
•TCP auto answer is enabled (S1), a TCP connection request is received, and the modem is not in a data session.
•Data is received on the serial port and
·The Startup Mode Default (MD) is 4 (auto TCP)
·The remote TCP destination, as defined in S53, success‐ fully responds to the TCP connection request.
The value of S7 (TCP Connection Time‐out) specifies the number of seconds to wait, after initiating a TCP connection attempt, for a successful connection to be established. If the connection has not been successfully established before the time‐out occurs, ERROR/BUSY is returned.
TCP packet assembly is affected by the values of S50 (PAD Forwarding Time‐out) and S51 (PAD Forwarding Character). Data received in the serial buffer will be transmitted when the idle inter‐character time‐out specified in S50 (in tenths of seconds) occurs or when a character is received that matches S51 (if non‐zero).
The TCP session will be terminated if no data is transmitted or received for the time interval specified in TCPT and TCPS. TCPT is the number of minutes (TCPS=0) or seconds (TCPS=1) used for this idle time‐out.
Caution: TCPT should never be 0 when using the TCP mode. A broken TCP session can result in the modem being left with a TCP
TCP Auto Answer
TCP auto answer (S0=12) also allows a TCP connection request to be “answered” when the modem is idle, not in a data session. The TCP connection requestʹs destination port has to match the modemʹs device port.
Note: UDP auto answer may also be set simultaneously with TCP auto answer. Then, when in the idle state, the modem will accept either a TCP connection request or UDP incoming packet, and enter a TCP or UDP session as appropriate.
Hybrid Modes
Hybrid modes are supported mainly for legacy implementa‐ tions. Some previous hybrid modes (MD=5, 6) are no longer implemented as special, unique modes. Now that UDP auto answer (UDP Half‐open, S82=2) can be enabled in conjunction
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