> Harry Campigli wrote:
>
>> I also have a sim built of multiple machines and would add support to
Johns
>> comments about a socket to feed or maybe even just sync AI to other
machines.
>
>> The other consideration possibility is allowing for a mechanism in future
>> feeding external live AI sources, for instance I have an adsb receiver and
>> would like to fit in real world air traffic from the receiver data stream,
>> supported with the local off air comms.
>
> As mentioned above, feeding aircraft, ships, railways and whatever else
from various sources will render the system unmaintainable (at least in
the long run) if clear abstraction layers are not being considered and
it also won't facilitate the task of interfacing FlightGear to other sim
networks in the future.
>
> I've been mentioning HLA because it's the tool precisely made for this
sort of interfacing complex simulation setups together. It provides
nifty features like, just one prominent example, time-stamping (or time
management in general): Pre-calculate the route of an aircraft carrier,
feed it to multiple sims in advance and the ship will show up on every
of the participating machines exactly at the desired position exactly in
the desired moment.
> This is not a feature to be hacked into FG as an add-on, no, HLA is
bringing this to you at no additional cost. Think of the same for AI
aircraft or cloud positions.
>
Agree with the first part about hacking, but disagree with the second idea
of "cost"
HLA is a follow-on to DIS and SimNet developed by DARPA and would require
either an extensive rewrite of FG to be HLA (Stanag 4603)
compliant or a wrapper function, In addition, there is a thing called
Run-Time Infrastructure (RTI) that handles the federates interfaces
Excerpt from an old MIT/Mitre paper on the topic:
4.2.2 RTI Transportation Requirements One design goal for the RTI is for
the implementation to be independent of communication infrastructure.
While the initial implementation is focussed on supporting an IP-multicast
network environment, it is clear that as the RTI matures it should support
other environments. Two such environments to consider are ATM (without IP)
and shared (or reflective) memory systems. ATM is a rapidly maturing
technology that can provide high bandwidth, but presents a very different
notion of multicast than IP. Shared memory systems can achieve very high
effective bandwidth between tightly coupled systems, but limits the
geographic range that such a system can span.
To address these example communication systems, and to enable the
exploitation of other systems, the RTI depends upon an abstraction of
"distributed simulation services." These services include:
* Best-effort point-to-point messaging. [e.g., UDP/IP].
* Best-effort point-to-multipoint messaging. [e.g., UDP/IP].
* Reliable point-to-point messaging. Message service built on [e.g.,
TCP/IP].
* Reliable point-to-multipoint messaging. [RMP]
* Reliable point-to-point stream. [e.g., TCP/IP].
* Fragmentation/reassembly of large messages. [e.g., >65k bytes]
* Get number of multicast groups available.
* Join a multicast group.
* Leave a multicast group.
* Resource reservation. [e.g., RSVP API.]
* Scope. Specify the extent of distribution of a message. [e.g., IP
time-to-live]
* Priority. Set priority for message delivery. [e.g., ATM cell priority]
* Map name to address.
> I think it's worth to keep this in mind,
>
Maybe something along the lines of an "HLA-lite". From Durk's suggestion,
and the excerpt above it sounds like the multiplayer server might function
in the manner of an RTI for a limited set of object model types ( unless
we want to include submarines, tanks, bad guys, etc, etc... ;-) )
However, a quick search indicates there is an open source HLA on sourceforge
License is Apache License V2.0, no idea how that compare to GPL or LGPL,
but might be worth a look-see. Whatever, it is going to take time and
effort (cost) to make FG compliant amd/or turn the multi-player server
into an RTI clone or "play-alike". And perhaps it would add a bit of
formalism to the FG development track. :-)
John
> Martin.
> --
> Unix _IS_ user friendly - it's just selective about who its friends are
!
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