Space Shuttle Displays Go Glass 164
cloudscout writes: "NASA has finally decided to bring the space shuttle up to date with a 'glass cockpit.' Until now, the space shuttle cockpit has used a system of gauges and dials designed in the early 70's.
They now have full-color computer displays and controls. Pictures and details are available in this article at WESH Channel 2000. So how long until someone ports MAME to this thing?" Can anyone shed light on what sort of operating system will drive all those screens?
plexiglass (Score:1)
Microsoft Space Shuttle (TM) (Score:3)
NASA Administrator: "Sure, we want a calendar and a phone list in Atlantis -- but what about videos and MP3s??"
NASA Worker: "Uhh, I'll get right on that."
NASA Administrator: "Can you put in that paperclip thing too?"
- Cam MacLeod
-1:redundant (Score:1)
Why retrofit these things? (Score:4)
There are five computers- with tape drives! The tapes aren't big enough to hold everything, so there are seperate tapes for take-off, landing, orbit, etc. The tapes need to be changed by hand on the first four machines. The fifth machine is permanently running the emergency landing routine. If one of the first four computers disagrees with the others, it is shut down. If the shuttle is ever down to two computers, the fifth machine kicks in and takes the next available landing window- with or without anyone onboard. It's never happened.
I always assumed the reason that the system never got updated was because they were planning on replacing the shuttles soon. Makes you wonder how confident NASA is about the X-33.
(This information is a few years old. Anyone know if NASA has upgraded the computers yet?)
The Display (Score:2)
The shuttle requirements are high; they need a mission critical OS with real time performance for *many* of the systems. Good for QNX, bad for M$.
It's a case of both security through obscurity and the government not wanting to be known for publically endorsing one vendor over another. (What would be the impact if we heard that the government started using linux or microsoft over QNX?)
More cost cutting (Score:4)
BSoD in Space (Score:2)
Must be linux (Score:1)
Segfault
segfault@bellatlantic.net [mailto]
Is this really a good thing? (Score:1)
Does this really bring so much new funtionality that the risk is worth taking?
Shuttle still has core memory? (Score:1)
I also remember that the shuttle was apparently running on Z80 clones. Forget WinCE, they're still on CPM.... (which is more advanced that what runs under Win98).
Karen
MAME? (Score:1)
Re:Why retrofit these things? (Score:1)
Re:BSoD in Space (Score:1)
Can't believe they've had laptops up there without experiencing that beautiful blue screen at least once...
Re: (Score:1)
Re:Why retrofit these things? (Score:1)
~luge
Hmmm... (Score:3)
I'm just speculating, mind you. They could use Windows or DOS or something like that...and get all sorts of fun errors.
Life Support has caused an illegal operation and will be shut down.
c:\>Close bay doors
Bad command or file name.
c:\>Close "bay doors"
Too many parameters.
c:\>Close (bay doors)
Error reading bay doors.
Abort, Retry, Ignore?
[astronaut clicks on "Extend Landing Gear"]
Not enough memory to complete this operation. Close some programs and try again.
Oh dear....
Re:BSoD in Space (Score:1)
They're running... OI-27!!!!... ? (Score:2)
Now, I don't know exactly what it means.. but oh well. Maybe they just loaded one of the crays on there.. hehe.
Re:Is this really a good thing? (Score:1)
~luge
Re:Why retrofit these things? (Score:1)
Nope. The video in the link says that the glass cockpit is just one of the updates to make the shuttles last for another 20 years (been about 20 already).
Maybe they will build a new shuttle in the meantime, but the ones we have now (Atlantis, Columbia...) will stay in service.
Spyky
ShuttleOS: 1 bug in 420,000 lines (Score:5)
They Write the Right Stuff [fastcompany.com]
There have been 17 bugs total in the last 11 OS revisions of the Shuttle code, approximately 420,000 lines delivered each time.
Good luck. (Score:1)
Re:the real issue is... (Score:1)
Re:BSoD in Space (Score:1)
That would suck for Bill Gates if the astronauts aboard one of these shuttles die because of a computer malfunction. But, then again, he has more money than God. So, it wouldn't matter much, anyway.
Re:Shuttle still has core memory? (Score:2)
Re:Microsoft Space Shuttle (TM) (Score:1)
;)
Operating Systems in Space! (Score:2)
I work on military aircraft avionics, which are (theoretically speaking) not really a lot different than space navigation systems. Right now most of our aircraft are still using 60's and 70's technology in the avionics systems.
Anyway, in a system with a glass cockpit, they will usually have a separate computer for every main function (navigation, guidance, heading, etc), and each computer will run on its own custom hardware. Software usually comes from dozens of banks of ROM chips. Although, if this system is still being designed from scratch, or was recently, then I don't see why they wouldn't use some sort of small RAID arrangement. If it even runs an OS (at least, how *we* define OS), chances are it will be very low level, and custom-coded by either NASA or a high-profile aviation company like Lockheed. Remember, custom (and very expensive) hardwear.
If they *were* to run a PC-type OS in this glass cockpit, I forsee them choosing either MS-DOS, (hey, it's been proven stable) or some Unix variant or clone known to be very stable (BSD?).
I'm almost certain they aren't going with Linux because don't you think they would have announced it by now? I mean, Open Source == Publicity these days.
And to you guys worring about Wince... 1) NASA is not really that stupid and I doubt it could handle shuttle avionics anyway 2) There are always two or three backup systems for every major system.
NOTE: This is all pure speculation which therefore means that it will probably be moderated down as flamebait.
Re:BSoD in Space (Score:2)
Anyhow, I was watching the NASA channel -- I don't remember the official name -- a few months back. It's cool -- just old tapes of missions, and a bunch of live broadcasts, too. So I'm watching this live broadcast of a recent mission. It's really cool -- you can see a map showing where the shuttle is in relation to the globe, as well as the latitude and longitude, as well as a camera shot from the shuttle. There was some other stuff, too. The screen was all divided up like Bloomberg.
Oh, and you can hear all of the radio transmissions, too. So I hear a woman on the shuttle say something about a computer problem, and could Mission Control help her out? She describes the problem to MC, and a tech helps out. She reads off the message on the screen, as well as on a printout. It's a BSOD. MC chuckles, and you can hear laughter in the background, and MC says to reboot the computer.
Now, because I have a wicked poor memory, could somebody validate this?
Anyhow, the point is this: God help them all if they're upgrading and still running Windows.
-Waldo
Re:-1:redundant (Score:1)
Re:Why retrofit these things? (Score:1)
Re:Why retrofit these things? (Score:1)
Retrofiting accomplishes all of the following tasks:
1. More press coverage.
2. Provides a back-up if the new vehicles don't work right at first.
3. Provides additional payload capacity.
Besides, what are we gonna use after we wreck the X-33s blowing up a giant asteroid on a collision course with Earth.
--
Re:the real issue is... (Score:1)
Re:Good luck. (Score:1)
Re:BSoD in Space (Score:2)
They are not dead yet, so whatever they are using must be working.
Star trek (Score:1)
Re:Is this really a good thing? (Score:1)
Slightly out of date info (Score:3)
~luge
Re:Why retrofit these things? (Score:2)
Re:Why retrofit these things? (Score:3)
The problem with hard drives is their fragility. They are too sensitive to vibration and hostile environmental conditions. Tape drives have been successfully flying on spacecraft for decades.
The Space Station was using radiation hardened 80386 chips the last time I checked.
Re:BSoD in Space (Score:1)
Think Not!
Ever notice the life support clauses in most comercial compilers for non-realtime OS's?
the usual line in most microsoft end user agreements :
The SOFTWARE PRODUCT is not fault-tolerant and is not designed, manufactured, or intended for use or resale as on-line control equipment in hazardous environments requiring fail-safe performance, such as in the operation of nuclear facilities, aircraft navigation or communication systems, air traffic control, direct life support machines, or weapons systems, in which the failure of the SOFTWARE PRODUCT could lead directly to death, personal injury, or severe physical or environmental damage.
Just do a search of the MS site for "life support". That one was ripped from the IE 4 end user agreement [microsoft.com].
Sorry no wince powered porn sites for NASA...
TastesLikeHerringFlavoredChicken
Well... (Score:1)
But then again, I also think the space program hasn't acomplished anything big enough to justify the billions spent on it. And why does everyone assume that all of us hackers/nerds are into sci-fi (or anything to do with space for that matter)? Ugh.
Re:Shuttle still has core memory? (Score:1)
Always a Good thing? (Score:1)
Given radiation and other space born anomolies, don't these upgrades create another occasion for something to go wrong?
If I recall correctly (IIRC), nearly half episodes on Star Trek: The Next Generation were based on problems that could have been avoided with analogue equipment. So there.
Soldier(R)
Portrait of the '96 shuttle programming team (Score:1)
This article "They Write the Right Stuff [fastcompany.com]" appeared in the December 1996 issue of Fast Company. It paints an interesting picture of the requirements and culture of NASA's on-board shuttle programming team (circa 1996.)
The article's main trope pits the discipline and insanely controlled, methodical management of the team and its product against the stereotype of the undisciplined, unruly geeks pounding mountain dews and hammering out bug-riddled code at all hours.
It's still worth a look, though.
Re:Why retrofit these things? (Score:1)
Re:Is this really a good thing? (Score:1)
Or am I the only geek that read more than the summary of the reports [nasa.gov] released on the loss...
TastesLikeHerringFlavoredChicken
If its not broken dont fix(break) it (Score:1)
The last thing NASA needs right now is another goof-up. The money involved in deploying systems like this plus the training for the crew must have hurt on their shrinking budget.
What OS? (Score:5)
The avionics biz is very conservative when it comes to items that relate to safety. The primary and secondary displays have to be so safe, bug free, and have such a small memory space that they don't use an operating system such as windows, *nix, or DOS. It is strictly bare metal programming. In the boxes that I work on, having 500k of ram to work with is a luxury item.
The graphics are usually handled by seperate chip with a dedicated graphics engine embedded into it. The main processor and graphics chip usually communicate via shared memory locations and the commands don't get any more complicated than "draw blue circle at location x,y with radius r" and many of the items come predrawn.
Re:Why retrofit these things? (Score:1)
The STS was originally intended to be a 'space truck' each orbiter doing maybe 10+ missions a year. When it became clear that was an absolutely unrealistic number, the story was switched that the Shuttle was in fact a test-bed for the technologies that would make the second-generation shuttle the real space-truck.
The VentureStar, the vehicle the X-33 is a technology demonstrator for, will be built and owned commercially, not by NASA. NASA will purchase cargo-space on the new vehicle, but they will actually be owned by Lockmart (Lockheed-Martin) or whoever else decides to build them.
The MEDS upgrade is a logical next step in maintaining the shuttle until a replacement launcher is available. It will reduce maintenance costs, increase performance, increase safety, and make the shuttle fleet better vehicles overall until it is retired.
Shuttle GPC Operating Systems (Score:5)
Re:Why retrofit these things? (Score:1)
Computers (Score:2)
Old news (Score:1)
Quake? What are you thinking? (Score:1)
the weight -- and more links/pics (Score:3)
The part I found amazing was that, in this conversion, the shuttle cockpit lost 25 pounds of weight. Now, CRT's aren't the lightest thing in the world, so those old dials and guages must have been pretty heavy
======
Webmasters: get a Free Palm Pilot [jackpot.com] for referring 25 signups (Web-based games).
========
Re:IIS/ISS (Score:1)
OSS + SPACE? (Score:2)
Go ahead, prove me wrong...
The Mars lander was fine. (Score:1)
MS Shuttle (Score:1)
One of your applications has violated system integrity.
Please shut down all systems and restart Shuttle.
[OK][Help]
(Original message source: Shoei, RoI, 1994)
Re:OSS + SPACE? (Score:2)
Do you believe it would be possible to have an open source software project that could be successfully and without any problems or risks utilized for a space station?
Use DOS. (Score:2)
DOS is stable, and well known. You design these displays with either IR touch or resistive touch.
The reason for IR or resistive is it can handle gloved hands and the calibration is not effected by temperature or vibartions as much as accoustic or capacitance.
The reason for DOS, is it may have bugs, but everyone knows the bugs and all the tools for it is well developed and stable.
Using touch screens allow you to reduce the area needed for controls.
Re:Star trek (Score:2)
Why would NASA want a shuttle named 'Enterprise' when they already *have* one?
NASA's first Shuttle was the Enterprise (OV-101). It was an experimental orbiter, and was used in various atmospheric flight tests in the 1970's. Unfortunately, it was retired before it ever flew in space but it did provide valuable information during it's lifetime. (The first shuttle that made it into space was Columbia, in 1981. Enterprise last flew on October 26, 1977.)
You can find a really nice picture of the Enterprise here [nasa.gov].
-- Give him Head? Be a Beacon?
Re:Shuttle GPC Operating Systems (Score:2)
I spent years writing telemetry processor software for NASA ground stations, including software to support the Shuttle. You have to have a basic knowledge of Shuttle computer systems to understand how the telemetry is structured.
Re:Good luck. (Score:1)
Re:Is this really a good thing? (Score:2)
Re:the weight -- and more links/pics (Score:2)
not a huge suprise (Score:3)
Too bad the industry-at-large refuses to be as thorough as NASA.
Common sense time. (Score:2)
Nothing short of a custum, proprietary OS is going to run all that equipment. Proprietary, embedded, real-time OS. AtlantOS or something, or maybe DOScovery.
Gee, if they WERE using Linux, they'd have to release their code modifications, for the rest of us to install on our space shuttles.
Keep in mind that the new control systems have probably been in design for at least 5 years. What I'm getting at is that they're not going to design a bunch of custom hardware, then apply the latest kernel patch from kernel.org and then launch it. The OS was likely designed the same time as the hardware (only FOR that hardware, strangely enough) and probably has been rigorously tested and debugged for several years without any major changes. Just guessing, but it sounds similar to logic.
It's all about $ (Score:1)
Re: Why retrofit these things? (Score:5)
Think about it. How many other computer systems can you think of that have been running for the last twenty years? How many other systems have had the tens of thousands of hours of testing and, even more importantly, have worked flawlessly every time? The shuttle computers work. They have never failed in flight, period. Some new system? Hah. We all know how solid most applications are today. The above jokes about running CE on this shuttle show that for sure. ;-) The shuttle today does fundamentally the same thing it did twenty years ago; the calculations needed for launch and landing haven't changed. So why replace the most tested piece of code in the world with something new? Would you like to ride in the first flight with brand new software? Thought not.
Next question: So then why upgrade the displays? Partly it's economic - those bulky old dials weigh a lot, and it's still ten kilobucks a pound to LEO. Beyond that, the interface can be made far better and more adaptable than anything you can do with gauges and switches in hardware. Anything that can be done to make the pilot's life easier is a net win. They way they did it, they basically put in a new system which takes the data and runs the displays, leaving the main computers pretty much untouched, running the same ol' rock-solid code.
Another point about the backup system. As Detritus posted elsewhere, the four main machines all run a program called PASS, the Primary Avionic Software System , while the fifth computer runs BFS, the Backup Flight System. These two programs were written by completely independent groups of programmers. To this day, no one who has worked on one of them is allowed to ever see the code for the other. They're completely indepentent. The idea behind this is called "diverse design". The more dissimilar two systems are, the more improbably it becomes that both will fail at the same time. They originally wanted to have totally different hardware for the backup too, but that was nixed to save on costs. Lastly, the backup system most certainly doesn't kick in automatically, under any circumstances. It's the mission commander's call, whether to hit the big red button on the control stick or not. (And yes, it actually is a big red button.) The designers judged that it was better to keep a human in charge than blindly trust the software.
Computers in Spaceflight: The NASA Experience (Score:3)
Also see CACM Volume 27, Issue 9 (September 1984) for an interesting article on Shuttle software.
Re:Good luck. (Score:1)
Re:Common sense time. (Score:1)
Houston, we got a problem (Score:3)
Re:What OS? (Score:1)
darpa? (Score:1)
News for Nerds, right? So if like high-tech, go check out what DARPA [darpa.mil] is currently funding. Remember, high risk, but the potential for high paybacks. For HMD resolutions check out this project [darpa.mil].
Hmmm, just had an interesting thought. DARPA played a major role in the development of the internet. DARPA obviously also funds other seriously high-tech projects. Why isn't there more DARPA stories posted here? Perhaps it is time to change to the more politically correct name, ARPA? Note to some ppl, DARPA and ARPA are the same, only the name has been changed to appease the political gods of funding.
Side note, I don't know why the DARPA web site wants to give me cookies some of the time.
Re:It's all about $ (Score:2)
So, yes, in the end, it's all about cash. I'm just convinced that in the general case cash is being spent improperly.
Re:Good luck. (Score:3)
Spacecraft navigation is the descendant of aircraft navigation which descended from the navigation of wooden ships. That is why they still use knots, feet and nautical miles.
I've wondered how we could switch to metric units for the operation and navigation of aircraft without killing thousands of people in the process. Everyone is used to "500 knots at 35,000 feet", and the air traffic control system is built around those units. How do we seamlessly change that to metric units? Plus the pilots have the old units deeply embedded in their brains. They know that the stall speed of their plane is 100 knots, the fuel consumption of the engine is 10 gallons/hour and many other important facts in the old units.
I'd rather not have glass... (Score:3)
Then there's the electrical system that's needed to drive such as system. What if the electrical system for the gauges were to lose power? No gauges? There should at least be backup analog gauges for some vital system gauges.
What they should also try to develop that would be better than CRTs though not as good as analogs would be some kind of flexible durable flat panel display. Something like the surface of those plastic mouse pads. You could bend it, press on it, and it would not cause significant damage. Even better still, make it so that the display is not a general purpose display, but pre-configured display that changes depending on electrical current/voltage like the analog gauges. But it would have advantage over the analog gauges because it would not have any moving parts. To get an idea of what I'm talking about, imagine those Duracell battery testers used as gauges. I mean, wouldn't that fairly resistant to all kinds of adverse conditions and abuse? And if you make them like "skins" that you could just snap in place, then you could easily carry redundant gauges because they would be very light!
Come on, they could do better than that! Or am I just completely wrong on this?!
Re:The Display (Score:1)
Re:OSS + SPACE? (Score:2)
I don't see why these processes couldn't be implemented in OSS work. They already are, in part. The "many eyes" principle ensures rigourous code checking.
The reason open software still tends to be buggy (at least compared to the space shuttle software) is partially the lack of a coherent plan for the software before writing begins. Most OSS projects start life as a small chunk of sloppy code that is interesting enough to attract the attention of other developers. Consider what would happen if, instead, a project began life as a high-level spec, and the specs were filled out through an open-source process before coding began. This could produce very sophisticated code quite quickly. It requires pretty good organization, though.
Interestingly, most large OSS projects use CVS repositories and bug-tracking software, which fill the role of the code and error databases mentioned in the article. So it would seem that the only thing standing between OSS and this kind of sophistication is the need for a coherent and detailed design for the software before coding starts.
That said, I doubt that this process would ever generate anything much more creative than a hardware driver. The Shuttle Group programmers themselves admit that the all-important process stifles creativity. If you think about it, considering the level of specification they've been given, their end-product is really little more than a device driver for the entire space shuttle. You would be hard-pressed to write something requiring real innovation this way. If you tried, you'd probably find that you spend the same amount of effort making the spec book for the software, which would end up with subtle bugs in the spec due to the evolutionary nature of the project, which would then get translated directly into software bugs in the code. Oh well...
The shuttle can't land by itself (Score:1)
Re:What OS? (Score:1)
Re:The shuttle can't land by itself (Score:4)
The astronauts objected to the computer being able to deploy the gear automatically, and this was given to them by the software people as a meaningless victory in their fight against the full automation of the shuttle.
The concern the astronauts claimed was that if a computer glitch caused the gear to deploy while in orbit, the result would be a loss-of-vehicle scenario.
The software is capable of handling every aspect of a shuttle landing except for the landing gear itself.
An interesting side note, if the gear aren't deploying within a half a second or so of the deploy switch being pressed, there are pyrotechnic charges that deploy the gear by force. As far as I know, they haven't been needed yet, but I imagine it'd be quite a sensation...
Mission control at Houston (Score:2)
----
Re:not a huge suprise (Score:1)
Hacking ISS (Score:1)
insert "buhaha...buhahah"
B
The PDP-11, of course (Score:1)
Believe it or not, but the PDP/LSI-11 series of computer is still in use in sheet metal and other factory floors even today. The damn thing is a workhorse which lives in production even after the death of Digital -- long after DEC stopped supporting the hardware.
Not that this diminishes the value of your point.
Re:I'd rather not have glass... (Score:2)
It occurs to me that CRT's would be far BETTER for high stress environments, simply due to the removal of moving parts.
Doug
OS? Reliability and more... (Score:2)
Well, I've seen a few 'comical' posts about this story, so I just have to weigh in. I'm an Aerospace Engineer, and I have friends who are 'Aviation Computer Scientists'. That means that they program the computers that run airplanes.
Observation 1. The 'glass cockpit' displays in airplanes (and, presumably the Space Shuttle) do not run off the shelf operating systems. They are custom, proprietary operating systems written specifically for what they do. They have no need to use a general purpose OS, when what they need above all else is rock solid stability for just a few functions. One of my old college buddies is even working on the code for the 'operating system' of the new space station.
Myth: Glass displays are fragile. This is simply not true. The space shuttle has had glass displays since the first one, but there just weren't as many, and as prevalent as they are after this refurbishing. Glass displays can handle the 4 G's experienced by the shuttle just fine, as well as the vibration. For one, jet fighters have glass displays in them, and regularly handle worse G forces than the shuttle ever does.
Hopefully this clears it up a little more. Any questions, just post.
Re:not a huge suprise (Score:2)
Shuttle "Human Interface" at CHI 88 (Score:2)
Re:Why retrofit these things? (Score:3)
This isn't correct. There are two tape drives called Mass Memory Units (MMUs); each has an identical copy of the flight software, both PASS and BFS. The drives are physically separate units from the GPCs; for the sake of redundancy, they communicate across separate data buses. All five GPCs share the same two MMUs.
The tapes in the MMUs are large enough to hold all the flight software for the different phases of the mission. These separate programs are called "Ops modes". There is an ops mode for each mission phase: OPS 1 for Ascent, OPS 2 for Orbit, OPS 3 for Entry/Landing. There are some other modes, but these are the significant ones.
The tapes do not have to be changed during the mission, but an crew member must manually enter the command for the ops mode transitions. Within an ops mode, the flight software can make its own transitions between program phases -- these are called "major mode transitions" and don't require an access to the MMU.
I'm not a FSW expert, but I've spent the last two+ years writing GPC emulators, so I've become familiar with some of these concepts.
--Jim
Re: GPS for aviation (Score:3)
But there are a lot of other reasons why GPS isn't very good for aviation use:
GPS does not handle altitude very accurately.
GPS does not handle very high speeds all that well.
I imagine the GPS system would break down entirely when you reach a good percentage of the altitude of the GPS satellites themselves. Not so good for the shuttle. (Seeing as this is what the article is about...)
Here's a great URL for lots of info on how GPS works: http://www.trimble.com/gps/index.htm [trimble.com] (It uses Shockwave, but you can still view it without.) Here's another with lots of information about GPS units: http://joe.mehaffey.com/ [mehaffey.com]
-=-=-=-=-
Re:Common sense time. (Score:2)
More than likely, they picked something which was as simple in construction as possible, but still can get the job done, and then had their own people crawl over the architecture & source code with a fine-tooth comb. You'd better believe that they're not going to blindly trust a software company just because they SAY their code is mission-critical ready - they're going to want to look at the source code themselves.
Re:OSS + SPACE? (Score:2)
You could have a dedicated bunch of people who deliberately try and break any proposed system (including setting up hardware glitches, like cosmic rays or something).
Over time, the software would probably evolve into something quite robust.
Re:Common sense time. (Score:2)
(....pondering the previous statement)
Whatever they use, it's surely been in testing for years. I'm sure that the "booster O-ring bug" taught a hard lesson on cutting corners.
Linux is great, but it can't do everything. I still have to wipe my own ass.
error rate in Airbus fly-by-wire software (Score:2)
Airbus has taken the position that the computer, rather than the pilots, can fly the airplane better. In fact, the pilots cannot override the computer.
As a pilot and software engineer, I find the Airbus philosophy fundamentally flawed. I can think of a few incidents on Boeing aircraft that would have turned into an "everyone dead" senario on a fly-by-wire Airbus (A320/330/340). You won't catch me dead flying on or acting as Pilot In Command of an aircraft exhibiting the Airbus philosophy.
OK, French Persons, flame away. :-)
Re:OS? Reliability and more... (Score:2)
Yes, but they're bulky, heavy, use lots of power and generate lots of heat. Basically the worst possible thing to use on a spacecraft besides uninsulated O-rings... Why didn't they go with flat-panel (plasma or LCD) displays?
Your Working Boy,
Re:I'd rather not have glass... (Score:2)
I'd hate to see what happens when all those controls attempt to operate simultaneously.. Gives 'packet collision' a new image, eh? (and judging how cheap some of these airlines get you KNOW like Tower Air is gonna go for the daisy-chained Linksys hubs...)
(Token Ring and FDDI are far more suitable for realtime communications than CSMA/CD systems, particularly the interference-resistance of optical connections from FDDI... And hell, the French love AIX/IBM...)
Your Working Boy,