Sierra Wireless DART 200 CDPD Modem - Manual (Page 69)

DART 200 CDPD Modem User’s Guide 5 DART Supported Protocols
PN1197-00 Revision 1.0 5-15
This bit is significant only when the TCP connection is established
passively (server mode). When the connection is established actively (by
an ATDT command), incoming packets are accepted from the
destination address specified in the dial command regardless of whether
or not it is contained in the friends list.
In both modes of operations, the source address (IP Address and port
number) of the last accepted packet is saved in a temporary variable for
use as the current destination address for all packets being sent by the
MAS during the current session. This source address information is also
saved in S-Register 53 where it can be obtained with an ATS53?
command.
TCP communication
To participate in a TCP session the DART 200 must be registered on the
CDPD system. Refer to Channel acquisition, p. 2-10, and Registration,
p. 2-15 for details on registering the DART 200 on the CDPD network.
A TCP session can be started by the central site system (host or F-ES) or
remote system (MAS); it is application dependent. If the MAS is the
client it starts a session with the ATD command and the T (for TCP)
modifier followed by the host IP Address and port number (Ex.
ATDT198.225.176.43/2100). If no port is specified the port number
defaults to the standard telnet port (23); this should be avoided.
Unless the application is being run on a closed system, use port numbers
between 1025 and 4999 for compliance with industry standards.
Alternatively, the dial could reference an IP Address/port stored in the
DART 200 dial list by the ATDTSn command where n is the position
number of the desired IP Address in the dial list. Refer to the &Z
command in Modem dial directory, p. 8-24, Appendix F, DART AT
Command Set, for more details.
When a connection with the server is established:
1. The modem enters online mode and presents a CONNECT response
to the MAS. It is customary (but not required) for the client to do the
first data transmission.
2. The MAS begins data transfer by writing application data to the
DART 200 through the RS-232 port using device specific
commands.
3. This data is assembled until a data forwarding condition occurs, as
described in Data forwarding, p. 8-8.
4. The DART 200 attaches the TCP header and sends the packet onto
the network.