Sierra Wireless DART 200 CDPD Modem - Manual (Page 62)

DART 200 CDPD Modem User’s Guide 5 DART Supported Protocols
Sierra Wireless, Inc. 5-8
This feature is controlled by bit 1 of S-Register 82. The default is
backward compatibility enabled (bit 1 = 1). When this bit is on the
UDP server does not generate a random port number as the source
port when the MAS issues an ATDP, but instead uses the port
number specified in the destination address of the dial command. In
backward compatibility client mode, the destination port cannot be
the same as the modem’s listening port if the UDP server is active.
• UDP server communication - UDP communications with the UDP
server active are similar to those for basic UDP, with the exception
of the call establishment operation discussed in Basic UDP
communication, p. 5-2. A discussion of call establishment operation
with the UDP server active follows.
In active operation (client mode):
1. The MAS (or DTE) issues an ATDP command using the dial
string (ATDPn.n.n.n/x) or the dial list entry (ATDPSn) form to
put the M-ES into online mode. If no destination port is
specified the port number defaults to the standard telnet port
(23); this should be avoided.
2. Unless the application operates on a closed system, use port
numbers in the range of 1025 to 4999 to comply with industry
standards. The modem’s protocol stack generates a random
number for use as the source port for active mode sessions.
However, if the backward compatibility option is active the
source port number is forced to be the same as the destination
port address specified in the dial string.
As is the case with basic UDP, the CONNECT message received
when going into online mode does not imply that a logical
connection was established as it does with TCP. Instead, it
indicates to the MAS that the modem is in online mode, ready to
communicate, and that the destination address is saved for use in
constructing packet headers for data that follows.
3. In addition to putting the modem into online mode, the ATDP
generates a random port number for use in the packet source
address, which is also used as the active session listening port.
4. If the modem functions only as a client (*A0), the listening port
defined by the *L command is not active. The modem receives
datagrams on the active session listening port instead, and only
from the destination address (IP Address and port) specified in
the dial command.
If the modem functions in a dual role, both as client and server
(*A2), there are some additional items to be aware of, including:
? ?
NOTE:
This bit should be set to
0 if there are no DARTs
using basic UDP
participating in the
network.
? ?
NOTE:
The UDP server is
compliant with industry
standard client-server
models where client
systems originate calls
and server systems
answer calls. Another
aspect of these
standards is the
distinction between
active (client) and
passive (server)
operation.