Problem Detail: I was preparing a presentation in work on GPON & other optical network technologies using documentation provided by a supplier, and the claim it made was “GPON networks have a capacity of up to 100Tbps”. Instantly that looked odd to me as I know the throughput of the most advanced version of InfiniBand only goes up to 280-290Gbps. I couldn’t find any evidence that supported the supplier’s claim, only turning up that the throughput of GPON was up to 2.5Gbps. The colleague who had been given the documentation I was working off said that the supplier had claimed that speed was independent of the devices on the network, and that it was limited only by the Optical Network Units (ONUs) and endpoint devices. That seems a bit ridiculous considering the “data” in an optical cable is a pulse of light. Light travels (in a vacuum) at c, so surely the speed of any fibre-optic network is close to c, and in the same way the speed of electromagnetic wave propagation down a wire is 66 – 99% the speed of light, but I’ve never heard a CAT5 manufacturer claim their cables can support those speeds. I brought it up with the supplier rep and he (derisively) let me know that “that’s the capacity, not the throughput”. I’m aware that to a lot of people the terms are interchangeable, but from a technical standpoint if throughput is the amount of data that can be sent over a network in a specified amount of time, what is capacity? It would seem like the “capacity” of an optical fibre is “1 flash of light” as that’s all it’s likely to hold. NB this question is about the science behind computer (or other data) networks, so I think it belongs here, despite references to particular hardware.
Asked By : leylandski
Answered By : D.W.
The easiest way to think about your situation is to just say that there is no such thing as “network capacity”. To my ears, the term “capacity” makes most sense for data at rest (e.g., storage media); “throughput” is about data in motion; and networks are about data in motion. I’m sure people have used the phrase “network capacity” to mean something specific, but it doesn’t appear that your salesperson isn’t using it that way, so I’d suggest you accept that this particular example of sales literature appears to be kinda meaningless and move on. (Not to mention that the clever use of “up to” makes their claim almost unfalsifiable.)
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Question Source : http://cs.stackexchange.com/questions/47275
