Brewster Rockit explains network latency.

Sunday's "Brewster Rockit" comic strip explained bandwidth vs. latency better than I've ever seen is some text books:

When I interview anyone for a technical position I always ask them to explain the difference between bandwidth and latency. It is an important concept, especially in today's networked world. Years ago most candidates didn't know the difference. Lately most candidates I interview know the difference, but have a difficult time putting it into words. Fewer can explain it in a mathematical or scientific way.

Latency is how long information takes to get from one place to another. Bandwidth is how much data per second is sent. Suppose you are querying a database that is very far away. The time it takes the query to go to the server and for the reply to come back could be very long (say, 1 second). If you do 1,000 database queries and each time wait for the query to complete before moving on to the next one, the task will take 1,000 seconds. If you increase the bandwidth between the two points the speed improvement will be nil or next to nil because the time it takes for the information to travel outweighs the transmission time. However if you send all your queries one after the next, without waiting for the replies, then wait and catch all the replies as they arrive, the entire list of 1,000 queries might happen in a matter of seconds. However, if you can't do the second query until you have information from the first query (say, the first query looks up a person's ID number and the second query uses the ID number as part of the query) you have to find some other optimization or you will simply have to wait 1,000 seconds for the entire process to run.

One situation I give the candidate is that they are dealing with a developer or manager that can't understand why doubling the bandwidth between the NYC office and Australia won't improve performance of a particular technical issue. Whether the candidate is a software developer, operations engineer/sysadmin, or desktop support engineer, there is a good chance they will find themselves in this situation. I roleplay as the person that needs the explanation and ask dumb questions. The candidate should be able to give a reasonable explanation in a couple minutes.

Maybe next time I should just ask them if they read Brewster Rockit.

Posted by Tom Limoncelli

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2 Comments | Leave a comment

To give a logistics example.

Courier is low latency, low bandwidth.
UPS (small truck) is low(ish) latency, medium bandwidth.
Semi tailor is medium latency, high bandwidth
Train is high latency, huge bandwidth.

Low latency and high bandwidth would be Superman picking up a truck and dropping it at your house. IE it doesn't exist in the logistics world.

In fact if you actually managed to use your bandwidth you will most likely increase latency because you will spend more time packing more into storage which will take time moving.

+1.

way too many people have confused bandwidth with speed. The bufferbloat problem is a fallout of that...

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