On 11/09/2017 02:28, Michael Tharp wrote:
On 09/10/2017 08:39 PM, David Tiller wrote:
Since WSJT-X uses UDP, there is a chance that you can get more than 1
listener to receive all UDP packets. According to this article, if
all clients bind to the port using SO_REUSEPORT (and possibly
SO_REUSEADDR), all listeners will receive all datagrams. You may have
to convince the author of JTAlert to also make this change if it's
not already set.
At least according to socket(7) manpage on Linux, SO_REUSEPORT causes
datagrams to be sent to a single listener in a round-robin fashion
among all those that are listening, rather than broadcasting to all.
It also comes with the downside of requiring modifications to all the
listening apps. In some cases I can't even get apps to reliably use a
different port.
Hi Michael,
that's correct. WSJT-X does not "broadcast" UDP datagrams, they are sent
to a specific server, or multicast group. When sending to a multicast
group it is necessary for the server(s) to subscribe to the multicast
group in order to receive the datagrams. Currently JTAlert does not have
the capability to subscribe to a UDP multicast group. Solutions using an
intermediate UDP datagram multiplexer are available if necessary.
If you want to see multicast groups working, you can use WSJT-X and the
reference UDP server application we provide called message_aggregator.
If you configure one or more instances of WSJT-X to use a suitable UDP
multicast group address like 239.255.0.0 and likewise with as many
instances of message_aggregator as you wish, you will see that they all
interoperate without issues.
73
Bill
G4WJS.
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