Sierra Wireless DART 200 CDPD Modem - Manual (Page 73)

DART 200 CDPD Modem User’s Guide 5 DART Supported Protocols
PN1197-00 Revision 1.0 5-19
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).