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Data Communication and Host Modes
Raven EDGE/GPRS for Cingular - User Guide, version 2.31
When idle, after the time-out has occurred, the is in AT command mode on the serial port, and
any valid AT command may be entered during this time.
The Normal UDP Mode (MD3) can be combined with UDP auto answer to cause the incoming
serial data to be sent in UDP packets (instead of being treated as AT commands), while allowing
sessions to be established from different UDP sources. A UDP session will be initiated either by
incoming serial data or by an incoming UDP packet. The session, started by either method, will
be terminated when no data has been sent or received for the S82 period. Once the session termi-
nates, another may be initiated by either means.
It is best to ensure the idle time-outs for TCP and UDP are never 0 if you're
Note:
going to be using auto-answer, or either PAD mode. In those circumstances, you
will want the modem to close the socket if the connection goes idle for too long,
particularly if the other side doesn't normally close the connection.
When the session is initiated by serial data, the new session will be established using the destina-
tion address specified in S53. The S53 setting can be changed if the connect to last UDP setting
(*UDPLAST=1) is set. The address in S53 will be updated to reflect the address of the last ses-
sion initiated by an incoming UDP packet. So that when new data is received over the host serial
port while in the idle state, a session will be re-established with the last address. (This behavior is
the same as the previous Hybrid2 (MD6) mode).
TCP auto answer (S0) may also be set simultaneously with UDP auto
Note:
answer. Then, when in the idle state, the modem will accept either a TCP or UDP
incoming packet, and enter a TCP or UDP session as appropriate.
Reliable UDP
Reliable UDP adds a simple protocol on top of UDP to provide reliable delivery of data. When
data is received from the host serial port, a 2 byte header is added to the data, containing a mes-
sage type and a sequence number. The Raven will continue to send this data (buffering any
received data in the meantime) until it receives an acknowledgement with this sequence number.
If an acknowledgement is not received within the time-out period (specified in S7), the data will
be retransmitted. This will continue until an acknowledgement is received or the modem is reset.
Likewise any UDP packets received by the Raven are expected to have this simple header. The
Raven will issue an acknowledgement for any valid packets which are received.
To configure the Raven for a normal UDP session, you need to set the Startup Mode Default to 73
(ATMD73). If you are using two modems, configure the Destination IP and Port in each to point
to each other. Serial data will then be sent reliably between the two.
Although it adds reliability, the simple implementation of the Reliable UDP
Note:
mode in the does not check for duplicate packets.
UDP Multicast Mode
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