Airlink Raven GPRS - Manual (Page 39)

Cingular GPRS Raven User Guide Version 2.01 31
Host Modes
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 terminates, another
may be initiated by either means.
When the session is initiated by serial data, the new session will be established
using the destination 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 session 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).
Note: TCP auto answer (S0) may also be set simultaneously with UDP
auto 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 message 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.
Configure the Raven as for a normal UDP session. Set the Startup Mode Default to
3, and the UDP Mode Default to 7 (ATMD73). If 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
Note: Although it adds reliability, the simple implementation of the
Reliable UDP mode in the Raven does not check for duplicate packets.