Latency Envelope


    When transferring large amounts of data, care must be taken to ensure that the transmitted data and the received data are identical.  At less than astronomical distances, this usually means a handshake mechanism that occasionally ensures that data transfer is proceeding without corruption.  In the case of the extreme latencies incurred by space travel, transit time between data nodes can vary from seconds to days or longer depending on the distance involved.  Because of this, there is a practical limit to the amount of bandwidth available at any given astronomical distance between any two nodes.  Within the data trader community, this is known as the “latency envelope.”  For most practical purposes, this envelope is set to one hour (approx. 1,200 GigaMeters or 0.04 Parsecs).  While one way transmission is possible even at extreme latency, handshake is impractical which makes the transfer difficult to confirm.  Beyond one hour of latency, large data transfers are rarely attempted, even via laser-comm tight beam.


    Excerpted With Permission


    Data Trader’s Handbook


    Copyright 3250, Interstellar Data Trader Guild


    As they exited the Reggie, they could see the derelict Data Ark through the main viewport of the shuttle.  Still relatively close, they would have no problem covering the short distance in the small shuttle.  The Reggie, her engines continuing to spool up, rapidly shrank until she was invisible to the naked eye.


    Ollu expertly piloted the shuttle towards the ship.  Leo was startled to see that she was flying using manual controls.  While Leo knew how to fly a shuttle, he always used the automated systems.  As he looked out the window again, he realized that the ship’s running lights were on and the boat lock had a flashing green light around it.


    “Hey, the docking systems are up!”


    Ollu just grinned.  “Sure, why do things the hard way?  After we brought up the reactors I ran a full system boot.  All the automated systems should be back up by now.”


    Leo still looked glum.  “If only we had the trading systems up, we could sync with the Reggie before she leaves.”


    Ollu was still grinning.  “Well, you better get busy.  You’ve got about an hour before the Reggie hits the latency envelope.”


    Leo just shook his head.  “No way to bootstrap the system.  All the memory cores are gone.  If I had a couple dozen cores I could at least to a prelim sync, but not without the cores.”


    As the shuttle passed through the GTE barrier of the boat deck, Ollu pivoted the ship and brought it to a perfect halt on the pad.  As she shut systems down she looked back at Leo.  “Why don’t you check replicator bay four?”


    “Sorry?”


    “Replicator bay four, that’s where I ran the memory core build program.”


    “Wait, what?”


    Now both Ramona and Ollu were looking at him again.  Ollu repeated her instructions like she was talking to a child.  “Bay Four.”  She held up four fingers, just in case he didn’t know what four meant.  She made a shooing motion with her hand.  “Now git.  Fifty eight minutes.”


    Leo flew out of the shuttle and down the corridor with Ramona close behind.  He wasn’t exactly sure, but he thought bay four was down there and to the left.  Luckily, his memory was correct and he found the large door with the number 4 painted on it where he had remembered it.  Entering the extremely large compartment, he was shocked to find a pile of memory cores.  They were neatly stacked up in the output area.  The automated system had made at least a hundred of them but the output area was filling up and the system would have to halt soon.


    “Grab one of those lift carts.  Take the first batch and I’ll grab the second.  We’ll go back to the main DC we looked at before.  I left the backup power running so we should be able to bootstrap the system.”


    The carts were easy to manage.  They were powered and designed to haul much heavier loads than memory cores.  However, they weren’t quick.  Leo fretted all the way up to the data center they had inspected on their first visit.


    Leo was relieved to find that the DC was still powered up.  The backup fusion bottle was running and the indicator lights were green.  If they could bootstrap the system, they could do a data sync with the Reggie before she got too far away.


    “OK you take cabinet one and I’ll take cabinet two.  Twenty four modules per cabinet.  That should get us enough memory to bootstrap.   We can keep adding memory as we go.”


    Adding the memory cores only took a few minutes.  They were designed to be easy to maintain and they simply snapped into the sockets provided.  The console was a different story.


    “Dammit, they pulled the main memory core.  We can’t bootstrap it.”


    Ramona was looking at where the memory core for the console was supposed to go.  “Isn’t this another Elmo console?”


    “Yeah, of course.  The whole ship will be the same.  Makes maintenance easier.”


    Reading on this site? This novel is published elsewhere. Support the author by seeking out the original.


    “What about the backup?”


    “The backup?”


    “You said these consoles have backups.”


    “Oh, damn..   I completely forgot.”  Leo opened the case and looked into the bowels of the machine.  “Crap, this one doesn’t have a backup installed.”  Leo thought for a second.  “Oh, shit!  I still have the one from engineering!”  Rummaging around in the pouch he still wore he found the memory module he had removed from the engineering console that morning.  “Here goes nothing.”  Leo hit a few keys on the console and recycled the system.


    After a few seconds, the console started to come up.  “Oh yeah!!  It’s working!”  Leo furiously typed on the console for a steady minute.  “OK, we have a bootstrap here.  The system is starting to come up.  Oh man, this is slow.  It has to decompress this massive backup before it can do anything.”


    Slowly, the system was able to restore running state from the compressed backup.  Once the main memory was again populated, things got moving faster.


    “Bringing up data transfer subsystem.”


    Ramona looked puzzled.  “Why that one?”


    “It’s the most automated.  If we can sync with Reggie it will automatically sync all data transfer jobs in memory, starting with those that have the closest point of delivery.  It’s our fastest way of making some guilders.”


    “Right.  Delivering the mail.”


    “Yeah.”


    Leo watched the status indicators crawl along.  “Yes!!  Handshake!  We have handshake with Reggie!!”


    “What does that mean?”


    “It means that the two ships are talking.  That they recognize each other and are doing a sync.”  Leo continued to work on the console.   “OK buy side system coming up.”  More console work.  “Sell side.”


    Ramona was also studying the displays.  “Leo?  Shouldn’t our latency to Reggie be rising on this display?”


    “Yeah, they’re moving away from us.”


    “Well, it says latency is down to one minute.”


    “What?  How?”


    “They must have turned around.”


    “Oh, shit.”


    At about three seconds per gigameter, a sixty second delay meant that the Reggie was about twenty gigameters away.  While this was a massive distance on a planetary or even solar scale, it was tiny on an galactic scale.


    “Why are they coming back?”


    “I don’t know, but they’re helping us right now.  The closer they get, the tighter the sync will be.  Help me load more memory modules.  We may run out of storage if they get any closer.”


    As Leo and Ramona loaded the remaining modules into cabinets, Ollu arrived with another cart full of modules.  “OK, we have core bootstrap running and all the maintenance bots are up.  We’re in pretty good shape shipwise.”


    Leo was halfway down the first row of cabinets.  “Bring that cart over here, it looks like we are going to get more data from the Reggie than I thought.”


    “Why is that?”  Ollu wheeled the cart carefully down the narrow isle.


    “Because they’re coming back.”


    “Oh, shit.”


    Leo laughed despite the strain.  “That’s what I said.”


    Ramona finished with her cabinet.  “I think Gunny will try to board us.”


    “What?  That’s illegal.”


    “According to who?  Any Guild tribunal would be judged by his buddies, the masters.  Would they find him guilty?  Or themselves?”


    Leo paused in his work.  “No, that’s a good point.  They wouldn’t.”


    Ollu started on another cabinet.  “Well, they won’t shoot at us, I know that.”


    “Why is that?”


    “Because the Reggie isn’t armed and I took the armed cutters down for maintenance before I left.”


    “What?”


    “Well, I was afraid something like this might happen.  The Reggie only has two.  Simple enough to enter a maintenance order.  By now, they should both be in pieces in the maintenance bay.”


    “But they could print one out.”


    “Yeah, but that’s a thirty hour job, minimum.  By then, we will be FTL.”


    Ramona looked determined.  “Gunny will try to board us.  That’s what I would do.”


    Leo thought about it for a moment.  Gunny was used to getting his way and Thorsten wasn’t going to try and stop him.  However, he had been a trader for as long as Leo had been alive.  His much vaunted military service had been ages ago, when Gunny was eighteen.   He had only served in the Marines for eight years before getting medically discharged and eventually becoming a trader.  Leo wasn’t even sure if he had made Gunnery Sergeant or not.  “He’s a trader.   He will play the odds.”


    Ramona shook her head.  “It’s about mission.  Get the mission done.”


    Leo placed a hand on her arm.  “He’s been a trader way longer than he was a Marine.  We just need to make the operation too risky and he’ll back off.”


    “OK, how do we do that?”


    Ollu suddenly grinned.  “Variable thrust maneuvers.”


    Leo looked confused.  “Say what?”


    “Remember your flight training?  What was the most difficult docking maneuver you ever tried?”


    “Oh, yeah.  The faulty engine scenario.  The target ship kept making unpredictable course changes because they had a simulated engine control system failure.  I crashed that one like four times in the simulator.”


    “Exactly.”


    Leo scratched his head.  “So, we break our own engines?”


    Ollu punched his shoulder.  “Keep to trading kid.  No, we just program the ship to make random course and thrust changes.  Add enough variability and your docking maneuver gets tough.  Especially if we close the hard lock on the boat bay.  Those external lock points are small and hard to hit.”


    Ollu pulled out a data pad and started entering programming the guidance system.  Leo could hear but not really feel the engines come online.  Instead of the steady drone he was used to, they changed pitch up and down at odd intervals.  Occasionally, there was a slight vibration.


    Ramona was impressed.  “These trader ships have the best of everything don’t they?  Those compensators work amazingly well.”


    Leo was back at work installing memory modules.   “Let’s get this row finished.  That should give us enough capacity for a full sync.”


    “How long to full sync?”


    Leo consulted the console.  “I’d say another hour at this latency.  We’ve already got a good chunk of the data transfer queue.  We’re getting the open source libraries right now.  Latency is still dropping.  Down to just ten seconds.”


    “How long until they figure it out?”


    “Figure what out?”


    Ollu gave Leo yet another disbelieving stare.  “Come on Leo, you’re not dumb.  What happens next?”


    “What?   We finish sync and we go to FTL.”


    “No, they disable their systems to prevent us from pulling a full database.”


    “But, that’s illegal….”


    “Leo.”


    “OK, OK.”


    Ten minutes later, the console bleeped a warning.  “Handshake lost.”


    “Yeah, took them longer than I thought.”


    “It’s hard to turn that stuff off.  They’re designed to always stay on.”


    “Just cut power to the transmitters.  That’s what I would do.”


    “Might not occur to a trader.”


    “Fair enough.”  Ollu made a sweeping gesture to the other two.  “Let’s head up to the bridge.  If they do launch a boat we’ll need to use the guidance systems and sensors.”


    Leo went down to the replicator bay for another batch of modules.  Now that they had a working network, they could restore console functionality on the bridge once the modules were installed.  Each of the consoles only took two modules, so it would be much faster than the work in the DC.  Walking down to the bay by himself, he finally began to realize how alone they were.  The Data Ark was massive and normally held anywhere from fifteen hundred to two thousand crew members.  With only the three of them onboard the ship felt very large and empty.  What the hell are we doing?