4 ms·

This is a problem that most people don't understand. The wireless at our office has 256mb/s over 802.11ac but the wireless hardware adds about 5 to 15ms of late

This is a problem that most people don't understand. The wireless at our office has 256mb/s over 802.11ac but the wireless hardware adds about 5 to 15ms of latency over the gigabit ethernet. For gaming this is death were it's not bandwidth that kills you, it's latency. I wonder how this could work in the "internet of tubes" analogy to explain to people?

jacquesm 12y ago
Well... how to make this visible? If you imagine a tube that is just wide enough to contain a single marble and you fill that tube with marbles all the way then you can also image that if you push one new marble in on one end instantaneously another one will pop out the far end. It's almost as if the marble you put in came out the other end. So even though the electron (the marble) moved very slowly the signal propagated extremely fast. Wireless hardware shares a chunk of the spectrum, much like cell phones share a chunk of the spectrum. So a node is not always transmitting the way a full-duplex ethernet connection is. Your packets wait for their slot to open up and then they are transmitted. The same happens on the way back. So the throughput can be extremely high but the latency can be murderous at the same time. And that's assuming the packet made it in one piece and did not have to be re-transmitted, in which case the lag will be even longer. I hope that explains it clearly enough.
- seacious 12y ago
  A slight nitpick that I mention only because I just learned this recently. The marble on the other end wouldn't come out instantaneously. Time it would take after starting to push the new marble in for the marble on the other side to start coming out is determined by speed of the pressure wave that would propogate through the marbles. You can see a really cool demonstration of this principle here: http://a.gifb.in/092011/1317143770_slinky_dropped_in_slowmotion.gif http://a.gifb.in/092011/1317143770_slinky_dropped_in_slowmot...
  - taejo 12y ago
    > speed of the pressure wave that would propogate through the marbles IOW, if it's not clear, the speed of sound in glass (assuming the marbles are made of glass).
- foobarian 12y ago
  In Boston I could tell people that no matter how many cars you add to the train, taking the T from Harvard Sq to Park will always take 10 minutes.
Jtsummers 12y ago
If you just mean explaining latency and not the difference between ethernet and wireless there are lots of physical instances of latency. You want hot water from the tap. If you haven't used it in a while or have poorly insulated pipes it could take seconds or even minutes before hot water starts flowing through the tap after you've turned the knob. Traffic. While a section of highway (say a 3 lane x 40' section) may see 30 cars every minute, a particular car that just started 60 miles away and traveling at 60mph is still going to take an hour to arrive. Even though tons of other traffic is going through constantly the particular vehicle (message) is still in transit. Echos are probably easy to explain this with, and are directly analogous to the sort of ping-pong, back-and-forth that network communication uses. You shout out a message and it can only travel at the speed of sound. It'll take seconds to cross the ravine and the same time to return to you. Shout 10 messages and 10 messages return in the same order all delayed by the same amount.
- justincormack 12y ago
  Or thunder vs lightning
  - Jtsummers 12y ago
    I had that and about 10 other examples (supersonic aircraft, hearing a car before it passes through your field of view, etc.). They were eaten by an accidental command-w. I have a number of technical friends, but also a lot of non-technical friends. Being a nerd, however, I tend to bring up technical topics amongst my non-technical friends more often than is fair. I've found that many of our CS topics (networking, OS, performance, security, etc.) have good physical analogs to at least convey a 10,000' view. Often (like latency) there are some almost perfect analogies that everyone has experienced or witnessed. I'm not turning them into programmers, but they'll understand the terms better.
swinglock 12y ago
The ISPs knows people don't know and takes advantage of this. http://www.youtube.com/watch?v=lehhEW6iuF8 http://www.youtube.com/watch?v=lehhEW6iuF8
zhemao 12y ago
> I wonder how this could work in the "internet of tubes" analogy to explain to people? Pretty simple. Water takes time to flow from one end of the pipe to the other. If you are trying to fill a huge tank, doesn't really matter how long it takes the water to get to you. If you are trying to fill a hundred tiny cups, it does matter because you are shutting the tap off and on again pretty frequently.
wisty 12y ago
Latency is tube length, bandwidth is tube width.
dm2 12y ago
Latency is time taken to travel the distance (between the client and server). Look at http://eyes.nasa.gov/dsn/dsn.html http://eyes.nasa.gov/dsn/dsn.html, for Voyager the latency would be 0.74 days. For the Mars Reconnaissance Orbiter it would be 6.6 minutes. Someday people might play live action video games with someone on Mars with very little latency, but right now it's not even theoretical without a wormhole through space/time.

jacquesm 12y ago

Well... how to make this visible? If you imagine a tube that is just wide enough to contain a single marble and you fill that tube with marbles all the way then you can also image that if you push one new marble in on one end instantaneously another one will pop out the far end. It's almost as if the marble you put in came out the other end. So even though the electron (the marble) moved very slowly the signal propagated extremely fast. Wireless hardware shares a chunk of the spectrum, much like cell phones share a chunk of the spectrum. So a node is not always transmitting the way a full-duplex ethernet connection is. Your packets wait for their slot to open up and then they are transmitted. The same happens on the way back. So the throughput can be extremely high but the latency can be murderous at the same time. And that's assuming the packet made it in one piece and did not have to be re-transmitted, in which case the lag will be even longer. I hope that explains it clearly enough.

seacious 12y ago
A slight nitpick that I mention only because I just learned this recently. The marble on the other end wouldn't come out instantaneously. Time it would take after starting to push the new marble in for the marble on the other side to start coming out is determined by speed of the pressure wave that would propogate through the marbles. You can see a really cool demonstration of this principle here: http://a.gifb.in/092011/1317143770_slinky_dropped_in_slowmotion.gif http://a.gifb.in/092011/1317143770_slinky_dropped_in_slowmot...
- taejo 12y ago
  > speed of the pressure wave that would propogate through the marbles IOW, if it's not clear, the speed of sound in glass (assuming the marbles are made of glass).
foobarian 12y ago
In Boston I could tell people that no matter how many cars you add to the train, taking the T from Harvard Sq to Park will always take 10 minutes.

Jtsummers 12y ago

If you just mean explaining latency and not the difference between ethernet and wireless there are lots of physical instances of latency. You want hot water from the tap. If you haven't used it in a while or have poorly insulated pipes it could take seconds or even minutes before hot water starts flowing through the tap after you've turned the knob. Traffic. While a section of highway (say a 3 lane x 40' section) may see 30 cars every minute, a particular car that just started 60 miles away and traveling at 60mph is still going to take an hour to arrive. Even though tons of other traffic is going through constantly the particular vehicle (message) is still in transit. Echos are probably easy to explain this with, and are directly analogous to the sort of ping-pong, back-and-forth that network communication uses. You shout out a message and it can only travel at the speed of sound. It'll take seconds to cross the ravine and the same time to return to you. Shout 10 messages and 10 messages return in the same order all delayed by the same amount.

justincormack 12y ago
Or thunder vs lightning
- Jtsummers 12y ago
  I had that and about 10 other examples (supersonic aircraft, hearing a car before it passes through your field of view, etc.). They were eaten by an accidental command-w. I have a number of technical friends, but also a lot of non-technical friends. Being a nerd, however, I tend to bring up technical topics amongst my non-technical friends more often than is fair. I've found that many of our CS topics (networking, OS, performance, security, etc.) have good physical analogs to at least convey a 10,000' view. Often (like latency) there are some almost perfect analogies that everyone has experienced or witnessed. I'm not turning them into programmers, but they'll understand the terms better.

swinglock 12y ago

The ISPs knows people don't know and takes advantage of this. http://www.youtube.com/watch?v=lehhEW6iuF8 http://www.youtube.com/watch?v=lehhEW6iuF8

zhemao 12y ago

> I wonder how this could work in the "internet of tubes" analogy to explain to people? Pretty simple. Water takes time to flow from one end of the pipe to the other. If you are trying to fill a huge tank, doesn't really matter how long it takes the water to get to you. If you are trying to fill a hundred tiny cups, it does matter because you are shutting the tap off and on again pretty frequently.

wisty 12y ago

Latency is tube length, bandwidth is tube width.

dm2 12y ago

Latency is time taken to travel the distance (between the client and server). Look at http://eyes.nasa.gov/dsn/dsn.html http://eyes.nasa.gov/dsn/dsn.html, for Voyager the latency would be 0.74 days. For the Mars Reconnaissance Orbiter it would be 6.6 minutes. Someday people might play live action video games with someone on Mars with very little latency, but right now it's not even theoretical without a wormhole through space/time.