DART 200 CDPD Modem User’s Guide | 5 DART Supported Protocols |
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NOTE:
Even though a successful ATDP command receives a CONNECT response a connection was not established.
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NOTE:
A good
Even though a successful ATDP command receives a CONNECT response a connection was not established. The ATDP merely passes the IP Address and port number of the destination system to the DART 200, where they are stored for use in constructing UDP headers for the data packets that follow. If the communication session is being set up between two DARTs, both have to execute a UDP dial command to go into online mode so that communications can begin.
If data transmission is initiated by the MAS:
1.The MAS writes application data blocks to the DART 200.
2.Data blocks are assembled until a data forwarding condition, as described in Data forwarding, p.
3.The DART 200 attaches the UDP header and checksum and sends the packet to the network.
4.The datagram (packet) is directed by the network routers to the appropriate port on the designated host. If the host or host port is inactive the data is lost and the local application is not informed.
Good UDP application design includes packet sequence checking, and acknowledgments to ensure that both the sender and receiver can determine if all application data arrived successfully.
If the MAS is on the receiving end:
1.When expecting a message following the initial CONNECT message or in response to an output message, the MAS reads continuously until all expected data is received.
2.When the data block is received it should be checked against preceding blocks for sequence errors before proceeding.
3.The DART 200 passes the data portion of the incoming datagram on to the MAS after removing the source IP Address and port number from the header for use as the destination address in the response (if required). This address data is available to the MAS through
The handling of network connectivity issues (such as loss of carrier), as well as data delivery and sequencing, is the responsibility of the MAS. Refer to Modes of operation, p.
Session termination may or may not be necessary. If the MAS originates sessions, it must terminate the first session before starting a second. Terminate sessions by the escape function followed by a
