Sierra Wireless DART 300 manual UDP Client Features, Closing UDP Sessions

User’s Guide Protocols and Packet Assembly Features

Disabling the server does not prevent the modem from answering a PING or from responding to the Sierra Wireless GroupWatcher™ remote monitoring program.

6.2.2.UDP Client Features

When the modem dials a client session, it will randomly generate a source port number for the session. The called server will pick up this port number from the packet header in order to route replies to the correct client process. Each session is assigned a new originating port number so that delayed replies to closed sessions will be discarded.

Client sessions can be dialed by a local host AT command, or automatically when the modem starts. Auto-dial on Start-up is discussed in Section 5.3 above. The following description is for local hosts using the dial command.

The Dial command (D) can dial any IP and destination port, or it can “quick dial” a member of the Friends List (Section 5.1). When dialing, the modem can immediately change to data state or wait to ensure registration before connecting.

Details

If the modem is not registered when the dial command is issued, the modem will automatically begin the registration process. Since UDP is “connectionless”, the modem allows the transition to data state immediately after the dial command without waiting for registration to complete. Register +WS179 controls this feature.

When +WS179=0, the modem will return the CONNECT result, assert DCD, and transition to data state without waiting for registration. If registration fails, the local host will have no way of knowing unless it escapes data state and queries +WS56. The modem will continue to try to register indefinitely. The local host can send packets to the modem buffers and close the session. The modem will continue to try to register and send the packets even after the local host closes the session.

If +WS179=1, the modem will wait up to the duration set in register +WS198 (Registration Wait Time) for the modem to register. If the modem is successfully registered within the time allowed, the CONNECT result is returned, DCD is asserted, and the modem transitions to data state. If registration fails, the NO CARRIER result is returned and the modem remains in command state, waiting for another command. The local host must be able to manage these connection failures.

Implementation

For a discussion of Auto-dial on Start-up, consult Section 5.3.

For a discussion of the Dial command, consult the AT Command Reference, Section 12.2.

6.2.3.Closing UDP Sessions

Sessions remain open until one of these events occur:

•The modem receives the command to hang-up (H) the session. This assumes the host has escaped data state as described in Section 6.6.3 below.

•DTR is de-asserted, presuming the modem is configured to use DTR for this (&D2).

•The PAD Session Timeout (S30) expires due to inactivity on the connection.

•The modem is reset or power-cycled (and is not using auto-dial).

For applications where distinct sessions are desirable (exclusive connections to differing remotes) and the host device is unable to issue the escape sequence and hang-up command, or toggle DTR to close the session, UDP can still use the PAD Session Timeout (S30) to close sessions. This can place significant restrictions on the timing of sessions.

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