Sierra Wireless DART 300 Data and Telemetry Considerations, DTR Transition, PAD Session Timeout

Feature Reference DART 300 Modem

To ensure that you can enter the complete string, you cannot set the maximum packet

length (+WS74) less than 6. You must also provide sufficient time in the PAD Inter-Character Timer (+WS70) to enter each character. If this is to be manually typed, the value should be set quite high (or disabled altogether). You must also avoid setting the PAD Primary Forwarding Character (+WS64) to one of the three characters in the TIES string (A=65, T=84, +=43).

Take note of the inter-relationship between TIES and the Time Dependent version described above. Guard time settings can influence the ability to use TIES.

6.6.3.3.DTR Transition

Devices not able to send an escape character sequence can still transition from data to command state by using the Data Terminal Ready (DTR) control signal. Use the &D command to control the modem’s behaviour on an on-to-off transition of DTR.

Setting &D0 will disable the use of DTR for escape. The signal is still required for flow control.

Setting &D1 will configure the modem to use DTR as a signal to change from data to command state without affecting the on-line condition. Any open session is kept open and the packet buffer is retained.

&D2 will configure the modem to change state and close any open session. Any partial packet in the buffer is discarded.

6.6.3.4.PAD Session Timeout

There is a possibility that the modem will lose signal and/or registration causing PAD sessions to fail. TCP sessions issue the NO CARRIER message, close the session, and revert to command state. UDP sessions issue the OK message instead.

Any partially assembled packet is discarded.

6.6.3.5.TCP Remote Disconnect

TCP connections include opening and closing handshakes. The remote terminal can initiate a disconnection and the modem will close the session, issuing the NO CARRIER message. The modem then reverts to command state.

Partial packet assembly at the local end is discarded if the remote handshakes a disconnection.

6.6.4.Data and Telemetry Considerations

If you are communicating data files or telemetry using one of the modem’s PAD services (UDP or TCP) that do not involve direct human interaction, you should make appropriate changes to the packet management features of the modem.

Exact settings will depend on the nature of your application and the quality of your network connection. What follows are some issues to consider.

In almost all telemetry cases, the PAD editing features are disabled. Local echo and backspace are turned off with +WS62=0 and +WS72=0 respectively.

If binary data is being communicated, you should disable the PAD Primary Forwarding Character feature (+WS63=0) and use the PAD Inter-Character Timer (+WS70=5) and/or limited packet length (+WS74) instead. This will prevent unusually small packets where the forwarding character might occur frequently in the binary data. It will also ensure data is forwarded to the network within a roughly known period. This allows the server to detect if problems have occurred at the local host end.

If the data stream from the host occurs at timed intervals, the inter-character timer should be set to as short a duration as feasible, allowing for brief stutters in the stream without missing the gap between streams. The packet length should be set to a suitable length to capture each stream.

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