Sierra Wireless DART 200 CDPD Modem manual Sample TCP setups

DART 200 CDPD Modem User’s Guide 5 DART Supported Protocols

4.In any TCP application where the remote system only operates in server mode, consider the use of the TCP keep-alive option (*K). It is possible for the central client system to fail after establishing a session with a remote server. If the client fails its end of the TCP session closes, but the server end remains open.

Attempts to re-establish the connection with the server after the client recovers get a BUSY response because the prior session was not properly closed. The receive keep-alive option (*K2) enables a remote server to close its side of a session if data or a keep-alive character is not received within an end-user specified timeout period. The time out period is contained in S-Register 86 (default 120 minutes). A reasonable timeout value is on the order of 3 to 5 minutes.

The remaining parameters are application dependent and are covered in detail in Chapter 8, Application Programming.

Sample TCP setups

These settings give a general sense of the AT commands required to set up a DART 200 for a TCP application. All relevant AT commands are listed, even the defaults. All devices function differently, therefore, the setups listed in this section of the manual are general. These setups show specific items to examine, but it is a good idea to examine all of the setup values.

Two TCP setup examples are shown below: a remote telemetry application and a central client application. Remote TCP setup, p. 5-19 shows the setup for a server modem at a remote telemetry unit (an RTU) being polled by a host computer.

Host TCP setup, p. 5-21, shows the setup for a client modem at the host computer that does the polling. This modem at the host arrangement is suitable for bench testing and limited use pilot implementations. Production systems normally are direct connected through a leased line or frame relay to a router at the customer’s host system (F-ES).

Remote TCP setup

The remote modem is set up as a server at the remote telemetry unit where it responds to polls from a host computer. The specific RTU does not use flow control and the data being sent is binary, not character, data. This requires the TCP server with auto answer to respond to polling, no flow control, and timed data forwarding because of the binary data.

In Table 5-3, the line items marked with an R (required) or an O (optional) are changed from the default (D).

PN1197-00 Revision 1.0 5-19