LWN: Comments on "Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)"

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

pirx3 — Mon, 20 Apr 2009 19:36:52 +0000

RTPS is multicast, not broadcast.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

bvdm — Sun, 19 Apr 2009 17:20:43 +0000

DDS's Real-time Publish-Subscribe (RTPS) protocol is only specified for UDP for a good reason, it is a broadcast protocol. Sure you can run the higher layers over TCP, which is what OpenDDS does (they actually use CORBA on top of), but then you lose interoperability.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

pflugstad — Sun, 19 Apr 2009 17:02:10 +0000

I know what DDS is, and BTW I'm pretty sure you can run it over TCP if you so desire (although how you can do QoS with TCP in the mix I don't know). My point was to note that DDS is an open spec with at least one FOSS implementation (thanks for the pointer to the Prismtech impl), contrary to xarma's comment.

And all of this misses the point of the original article - integrating RTI's proprietary DDS implementation with the NSA created SELinux. This makes DDS in general (and RTI's implementation in particular) more appealing to the DoD/Navy, since it can probably now be used in more security restricted (e.g. MLS) environments. So the point of the other part of my comment was to provide readers with some motivation for this integration beyond the obvious.

Bringing up competing technologies (AMQP) is irrelevant in this context, since as you point out, they have different use cases (although I'd guess you could make DDS work in a generic manner fairly easily).

I'd love to see any (either) of the open DDS implementations do a similar integration and give RTI some competition (or at least get the wire-level interoperability solved). I kinda doubt it's gonna happen though, as it seems like something you really would want a company behind. Maybe the ACE/TAO/OCI guys will do it.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

bvdm — Sun, 19 Apr 2009 16:12:07 +0000

DDS is a UDP-based, publish-subscribe only protocol.

AMQP is generic messaging queuing middleware.

Different use cases.

If anyone is interested in DDS, Prismtech has (most) of their implementation under the LPGL. http://www.opensplice.com/

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

xarma — Sun, 19 Apr 2009 09:34:56 +0000

Concerning the OpenDDS implementation, it is not interoperable with other DDS implementation:

From the FAQ Here : http://www.opendds.org/faq.html

Q:
Is OpenDDS interoperable with other DDS implementations?
A:
Currently no. OpenDDS currently doesn't have an implementation of RTPS (Real Time Publish-Subscribe) transport layer required for interoperability.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

pflugstad — Sun, 19 Apr 2009 03:50:20 +0000

Huh? DDS is a spec available from Object Management Group.

RTI is just the main mover behind it. There is an open source implementation (OpenDDS).

The US DoD (the Navy mainly I think) is very interested in DDS, so integrating it into SELinux is a nice check-box item for the DDS supporters.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

ms — Sat, 18 Apr 2009 20:44:20 +0000

AMQP is the open protocol. See www.amqp.org
OpenAMQ is _an_ implementation of it. There are several of them, including one by Red Hat (qpid), and another by LShift (lshift.net) (www.rabbitmq.com) which has recently made it into Debian and Ubuntu. There are other non-free implementations available too.

Real-Time Messaging Middleware Integrated with Secure Linux (Embedded.com)

xarma — Sat, 18 Apr 2009 20:13:04 +0000

This is about Publish Subscribe:
http://en.wikipedia.org/wiki/Publish/subscribe

There are other options to this proprietary technology:
- Epics: http://aps.anl.gov/epics/
- OpenAMQ http://www.openamq.org/