hub at the center of the cylinder or one of the tunnel entrances around its edge. The empty space in the middle of the cylinder was full of containers in free fall and I had to consciously keep myself from cringing as they flew overhead with quiet rushes of air. I felt like a mouse in a warehouse, scampering to avoid being crushed by the frenetic, incomprehensible activity going on overhead.
Merral was watching me. 'Impressive, ay?' she asked.
'Impressive isn't the word. I can't believe you let those things go in free fall.'
She laughed. 'It looks like disaster in motion, doesn't it? Actually it's very safe. There are eight hundred sixty- one trajectories. Whenever one is in use, all the intersecting flight paths are locked out until the container is down and clear of its destination.'
I looked up at the graceful, ponderous, hundred-thousand-tonne aerial ballet. It wasn't that I doubted her, but it was hard to shake the feeling all those containers were going to fall on me as soon as God cut the strings.
Our destination was a cargo box, but this one had doors and large windows cut in the sides. Powerful lights were mounted flush with the walls. Jocelyn thumbed a door open and waved us in. 'We use this for troubleshooting and inspections. It carries everything we need, and we don't have to shut down a tunnel to use it.'
Inside the container was mostly empty space. There were doors and windows in the floor and ceiling as well as the walls and all the surfaces were padded and well equipped with handholds. Strap down chairs with mounts that locked into the handholds were set up beside the forward windows. A quarter of the bottom rear was given over to a series of cabinets that housed batteries, switches and various tool chests. Beneath the forward window there was a spartan control board with a compact data terminal as well as various buttons, gauges and comm gear. Beside it was a small keypad. I recognized it at once from the tranship operations manual. It was the container's shipping control panel, a duplicate of the one mounted on the outside.
I walked over and examined the panel. When Jocelyn joined me, I asked, 'This contains the tranship codes?'
'Not just the codes, everything about the shipment. The freight manifest, maximum and minimum allowable temperatures, power requirements, loading parameters, whether the container is pressure sealed, center of mass, priority level, customs codes, COD status and charges. Everything.' She tapped a few keys and cryptic data slid over the small screen inset on the panel. PRI, COD, KPA, BOT, and others along with numbers that didn't mean anything to me. I did recognize two codes. SRC and DST indicated the container's source and destination-both were rack addresses in the up-axis hub.
I tapped a few keys and managed to bring up the DST code. 'Can you set this up to go anywhere?' I asked Merral.
'Anywhere on Tiamat. The lockouts don't allow us to be loaded for an offworld destination. This container isn't vacc sealed. I'll set it for the outbound receiving racks at the down-axis hub with a routing override so we get tunnel nineteen. That'll take us right through Tiamat.'
It was better than I'd hoped for. 'Can you try TMU19J234C?' I asked.
She looked at me with the half accusing 'How do you know what that means?' look that's usually reserved for medical patients who show their doctor some basic piece of medical knowledge. Specialists hate it when you trespass on their specialty. It makes them less special. Nevertheless, she thumbed the pad to authorize the change and punched in the destination code. After a couple of seconds the screen displayed accepted, then reverted to DST: TMU19J234C.
'This transaction is now logged in the transport net, correct?' I asked.
Merral nodded, adjusting the restraining straps that held her in her seat. She motioned for me to do the same.
'Is there any way to circumvent that?' I asked, fumbling with the belts.
'How do you mean?'
'Can you enter destinations into this panel without having the system become aware of it.'
'It could be done. You'd have to block the scan transceiver and trick the panel into thinking it had transmitted the change and received a valid authorization verification. It wouldn't be easy, we use dynamic encryption. Why would you want to?' She reached over and helped me get buckled in.
'A smuggler might change an onworld destination for an offworld destination, or perhaps just make a shipment the system isn't aware of.'
'I see what you're getting at, but you misunderstand me. If you prevent the panel from talking to the net, the net will just ignore it. It won't get sent anywhere. There's a lot of ways to break the system, but once it's broken it won't work properly.'
'I don't follow.'
'Look, the system is vulnerable to tampering and there's no way to avoid that. Rather than try to make it tamper-proof we've made it fail-safe. Getting a container to move involves a series of steps, with our control procedures built into the chain. If any link is broken the system flashes us a trouble warning and won't move the container.'
'And the data in the panel itself is all self-encrypted so you need a Port Authority ident to change it, correct?'
Merral warmed to her topic. She obviously enjoyed having someone show an interest in her work. It probably didn't happen too often. 'Not quite. The source address is always locked so we can back-trace a shipment, nobody can change that. When the shipment arrives and is accepted, the destination address is copied to the source so the container can be sent out again. Manifest, COD charges and destination are set by the shipper and then locked when the PA verifies and seals the shipment. The user functions-like humidity, temperature and all that-can either be set and locked or left open at the shipper's discretion in case they need adjustment in transit.'
'So you can't change the source or the destination in transit unless you have a Port Authority ident.'
'Not even if you do have a PA ident. Once a setting is locked, it can't be changed until the receiver accepts the shipment and signs off with us. The system only lets that happen at the destination address.'
'What if you hacked it, opened the box and modified the software?'
'All you'd do is cause a self-encryption verification failure. The system would halt the container at the next control point and drop a trouble flag.'
'What if I supplied my own panel that allowed in-transit re-routing?'
'It still wouldn't work. Firstly, it would fail PA verification at the point of shipping. Second, the tranship net and the panel would disagree on the destination as soon as you modified it. The net would halt the container and you'd get another flag. It's fail-safe.'
Fail-safe. It's a one-word lie. Nothing built by humans is fail-safe. I knew someone was playing games with the tranship net. What Merral was really telling me was that I needed to look for hackers in the net's high-level control software or corruption at the Port Authority itself. I didn't tell her that: she might be the one I was looking for.
Instead I offered a compliment. 'Sounds like you're pretty secure. I've seen banks with looser systems.' I meant it too. I didn't mention that I'd seen banks with looser systems because I'd gone in to investigate the frauds that had occurred at them.
'You've got to understand, there are better than two million containers in the system. Every day we move thirty thousand of them through Tiamat. The cargo value in just one of those can get into the tens of millions of crowns. We can't just lose track of one.' There was pride in her voice. She was a hands-on technocrat and the tranship system was her baby.
The conversation was interrupted by the arrival of the conveyor crane. The rollers on the container rack slid us into the jaws of the waiting cradle. I felt like Captain Nemo being attacked by a giant squid. There was a clang as the locking dogs engaged and then we were on our way, swaying gently in the minuscule gravity field. The crane loaded us onto the roller rails at the end of our row of container racks. The cradle disconnected and the crane swung away. The rollers began spinning and our container moved off.
I watched out the windows like a kid on a train for the first time. There was a double jolt as we were loaded onto a sorter, then a gentle surge as we launched into free fall. I watched in fascination as we soared past the tops of the container racks. We spun slowly and I got a revolving view of the entire, bustling hub. To my surprise we didn't come within a hundred meters of another container. What looked like near misses from below were a trick of perspective. There was all sorts of room.
