Watching TNG again I realized that some subspace transmissions are occurring in real-time, but some reports require significant time to be delivered.

The odd thing is that this doesn't seem to be related to distance. Is it just a tool used by the screen-writers, or is there some explanation?

  • 2
    Do you have examples? Besides Voyager, I can only recall subspace communications being real-time. – user1027 Apr 11 '11 at 20:31
  • @Keen I will try to look up the specific episode, but in TNG in the first season Picard had a discussion with Riker about informing the Starfleet and claiming that the transmission will reach Starfleet in one day. – Let_Me_Be Apr 11 '11 at 20:37

Real World Answer:

The discrepancies are a series of continuity errors.

In-Setting Answer:

Several issues here.

  1. Relay stations have limited bandwidth.
  2. Subspace communications have limited range.
  3. Subspace communications have a known finite speed, TNG WF 9.9997
  4. Not all communications are the same distance.
  5. There are multiple bands.
  6. Weak signal strategems seem to work with subspace communications fairly normally.

We know about subspace communications relays because of a rather fun TNG episode (Aquiel). We see a relay station. Its role is discussed in episode, as well. Suffice it to say, it's a standard relay technique. Routing through a relay net takes some time, but often allows faster communications once the routing is established. As an example, it often takes several seconds to establish a route on the internet, but once established, the individual packets take a few dozens of milliseconds to travel that route. While the relay has a huge bandwith, it's presumable that those relays also have massive amounts of use.

We know that the individual communications have limited ranges because of both the inverse-square law, and the existence of subspace relay stations. We know the inverse square law applies because it is inherent to the nature of a wave in a 3-dimensional medium.

We know subspace communications have a finite speed because the episodes imply so, and the TNG Tech Manual says so (p. 111). There are times when it's taken significant lag to cover a certain distance in both directions. We also know that it travels in a wave.

We also see many of the communications with higher command being to local bases, not all the way back to SFHQ. Communications with the local base almost never show lag.

The various bands of subspace have different propagation speeds; Paris mentions this in at least one episode of Voyager. If maximum frequency correlates also to propagation speed, then the various bands also have different data rates.

We see and hear various radio-centric strategies for bosting long range communications, and they tend to match real-world radio modes... boosting signal power, moving out of the line of interference, multiple antenna interferometry, signal amplifiers, digital reconstruction. It's safe also to presume that frequency division of a digital signal can be used to make a borderline signal readable at range by sample averaging, albeit sacrificing bandwith.

It's safe to presume that this all adds up to being able to, in certain conditions, get a high-speed comm link, while in others, having to use slower and more relay-based bands for slower comm. We can also make a supposition that the relays pretty much always use the fastest bands from relay to relay.

It's not a large stretch to assume that the faster bands also require more energy; this would mean that the best communications are going to be, in most ship's cases, limited mostly by the ship and its nearest subspace relay.

Also note that communications lags really don't get noticed until they exceed 0.5 sec, since it's pretty typical for people to take over a second to begin to respond, and even a 1 sec delay isn't one that many people would notice in a conversation they are merely observing.

Fanon Notes

FASA's Star Trek RPG noted Subspace Radio at WF25 (which would be on the TOS/OCU scale).

The rec.arts.startrek.tech list's Warp Velocities FAQ (by Joshua Bell) lists WF9.9997 on the TNG/MCU scale, citing the TNG Tech Manual; that's ~198696 C, or roughly warp 58 on the old scale.


If I remember correctly there is something about subspace relays. Generally in TNG long range communications is faster than light.

Signals sent in the subspace realm travel faster-than-light (FTL). Over vast distances, such signals will eventually emerge into normal space, dropping to very slow light speed, which would make interstellar communications very nearly impossible. Subspace relays solve this problem by receiving FTL subspace communications before they emerge into normal space and retransmitting them in subspace at higher energies, allowing the signal to travel further in subspace, and to arrive at its final destination much faster, than it could without the relay.

It seems that when there are no subspace relays around (or some problem with them) it could too long to transmit or receive a message. In addition some anomalies with subspace can mess with real time communications.

When message sent in subspace it would appear real-time. Also if I get this correctly if the distance is too far away there would be some lag even if the message travels faster than light.

  • Why wouldn't every ship have its own built-in subspace relay? – Jack B Nimble Apr 15 '11 at 17:22
  • Because relay should be as far away as possible but not as far that the signal will degrade. – Sinan Apr 15 '11 at 21:49
  • @jack relays are big suckers, and yes, each ship has one, but it needs to hook into the network if the ship gets too far away (this network is other ships, starbases, freestanding relays, and each additional relay boosts the signal, keeping it from degrading all the way) – dkuntz2 Apr 18 '11 at 22:43

There's also the possibility that lower-priority messages are sent in a way more analagous to e-mail than a phone call.

High priority messages go through immediately, or there's possibly a different band for them to travel on, whilst lower-priority messages go out in regular bursts, delivered to mail queues.

Consider this: Real-time video conferencing requires a significant amount of bandwidth, and has to be transmitted in real-time. Video messages can be compressed, sent in parts, and otherwise made more bandwidth-considerate.

It's entirely possible that, the further from Earth and the center of the Federation you get, the worse the subspace relay infrastructure is. There must be a bandwidth limit somewhere, and if you're making two-way video calls every time you think you've left the oven on, that Starship 10 parsecs away may not have enough open bandwidth to place its distress call.


I always thought the request to communicate traveled slowly because it had to go via regular-speed communication.

The request would say "please communicate with me at FTL frequency 123, encryption code delta".

Once both sides are on the same FTL frequency, communication is instantaneous.

This is why Picard says "connect me to Starfleet and route it to my ready room" in the middle of a show, but then communicate real-time once the connection has been made.

Phil Farrand's Nitpickers' Guide mentions a specific example.

Of course, my explanation means that no one has kept open an FTL "out of band" frequency, which seems inefficient.

  • 3
    That seems like a stretch. A more mundane explanation for Picard's command is that's how most VIPs handle calls: "Doris, can you get me Bob from accounting? I'll take it in my office." Important people don't make calls themselves. – user366 Apr 12 '11 at 17:37
  • @MarkTrapp yeah - I can't imagine Picard sitting listening to StarFleet hold muzak while waiting for the Admiral's staff to locate and patch him through ;) although, with the computer's voice command system and its ability to patch communication direct to an individual, why doesn't the computer do the work of the operator instead of clumsy ol' Worf? – HorusKol Apr 12 '11 at 23:23
  • @HorusKol - well, maybe the admiral is sleeping/in the toilet/having an important meeting. The computer cannot explain why Picard want to talk to him, is it urgent, etc, etc... – SWeko Apr 13 '11 at 9:30
  • @SWeko - fair nuff :) – HorusKol Apr 13 '11 at 12:13
  • Define regular speed? – Pioneer Jul 26 '15 at 18:14

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