Sierra Wireless DART 200 CDPD Modem Dart 200 Cdpd Modem User’s Guide Dart Supported Protocols

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

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NOTE:

This bit should be set to 0 if there are no DARTs using basic UDP participating in the network.

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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.

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:

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