DART 300 Migration Guide Difference Summary
2110291 Rev 1.0 Page 15
3.2.4. UDP Characteristics DART 200 DART 300
UDP Server Supports multiple concurrent
clients.1
(Receive locking with FIFO
queue)
Supports both single and
multiple client sessions (by
setting +WS217).
(Receive locking with FIFO
queue and timer).
Server is active when
listening port +WS212 > 0.
Auto answer Based on S0=1 and *A2 to
configure UDP Server mode.
Based on S0=1 and listening
port > 0.
Friends Only mode Yes (up to 10 IP addresses) Yes (up to 10 IP addresses)
Dials using “random”
source port number
When “Basic” UDP is
disabled.
Always
1On the DART 200, Basic UDP requires client and server to use the same port number. Auto
answer is not supported in Basic UDP. The server must be in online mode (have previously
dialled the client) in order to accept data packets from the client.
3.2.4.1. UDP Receive Locking
Both the DART 200 and DART 300 support receive locking to enable the modem to act as a
server handling requests from multiple clients on a packet by packet basis. The models follow
almost identical behaviour but require differing setups.
A server can receive calls from multiple client devices, or from one client using different source
ports for different sessions. However, it can only save one client address and port, the one that
was extracted from the last datagram received, for sending any replies. For this reason, if multiple
clients are expected, the serving DART modem must use receive locking to delay accepting
subsequent datagrams until a response is sent to the source of the prior datagram.
If receive locking is enabled on the DART 200, all datagrams arriving after the first one,
regardless of their source address, are held in a First-In-First-Out (FIFO) buffer until a data
transmission (reply) occurs, or the time out period expires, releasing the first datagram in the
queue.
The only difference with the DART 300 is that datagrams arriving from the same source as the
first one are not held unless another datagram from a different source has been received. That
means that if there is only one calling client, datagrams are delivered as they are received, without
waiting for a reply (or timeout) for each individual packet.
The DART 200 enables the receive lock when bit 2 of register S82 is set. The timeout is set in
register S83. The value of the timeout is measured in tenths of a second; the default is 3.0
seconds. The feature is disabled when bit 2 of S82 is cleared, the default setting.
The feature is enabled on the DART 300 by setting +WS217=t where t is the timeout value in
tenths of a second. Disable the feature by setting the timer to zero (+WS217=0), the default
setting.
If the receive lock feature is not enabled, each UDP session must be closed (either directly by the
local host, or S30 timeout) before another session can be established. An open session can only
communicate with the single IP address and port of the first caller. Since each new UDP session
from a client will usually have a different port number, even the original caller may not be able to
re-connect.