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This article seems on a first glance to be completely misunderstanding the nature of latency, confusing latency with the general notion of throughput.
Latency is not just "a measure of amount of time between the start of an action and its completion", it is specifically the amount of time that is unavoidably expended before transmission actually begins. To go along with the travel analogy, the jet plane may travel faster than a car once when both are in motion, and the jet plane may carry more. However, loading up luggage and passengers and starting up the vehicle will inevitably take longer for the jet plane than for the car; the amount of time it takes to prepare for the travel is the latency. -- Antaeus Feldspar 21:47, 5 Dec 2004 (UTC)
I agree with the article and disagree with defining Latency as the time for starting an action only. In telecommunication delay and latency are often used as synonyms, but most understood latency as the total sum of the end to end signal delay. Depending on the transmission system this could be defined and measured on a per packet base (equivalent to the airplane with it's passengers) or on a bit level (no boardening of passengers, each passenger would fly immediately in a single plane). -- Matthias, 7 Dec 2004
The definition of latency is more or less correct. It is the total time, including the startup time. The definition of throughput is not. Throughput is the amount of work done (e.g., bits transmitted over a network) in a given amount of time, not just the number of actions. In a computer network, sending data in large packets has a higher throughput than sending the same data in small packets, even though there are less actions (packets). This is both because of the lower number of overhead bits and because of reduced startup and queueing latency. If the data is streamed, propogation latency won't have much effect on throughput, but if the system waits for an acknowledgement after each packet before sending the next, high propagation latency will drastically reduce throughput. Errors that cause packets to be retransmitted also reduce throughput. --Rick Sidwell 05:51, 11 Dec 2004 (UTC)
I'm no expert on this, but the external link given in the article seems to agree with Antaeus. It does eventually mention overall latency, but focuses on minimal latency and refers to this simply as latency. Here's the definition given:
- "No matter how small the amount of data, for any particular network device there's always a minimum time that you can never beat. That's called the latency of the device."
Maybe this usage was chosen because the author wanted to compare networking methods in general, rather than their performance on a specific task. Does anyone have authoritative examples of contrasting usage? -- Avenue 23:22, 7 Jan 2005 (UTC)
Maybe the disputing sides will agree to accept this definition? If a zero-length message is considered, both definitions should mean the same.
Latency
The time taken to service a request or deliver a message which is independent of the size or nature of the operation. The latency of a message passing system is the minimum time to deliver a message, even one of zero length that does not have to leave the source processor. The latency of a file system is the time required to decode and execute a null operation.
Look at
http://www.nhse.org/NHSEreview/CMS/Chapter6.html
--[Grzesiek] 14:36, 31 Jan 2005 (UTC)
This article needs a complete rewrite.
There is also the article Comparison of latency and bandwidth.
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