9
1
This seems like a simple question, but I can't find a definitive answer for it. I have four devices connected to a Gigabit switch as in this diagram:
Can I get the full GBit bandwidth from A-B simultaneously as C-D are maxing out their link? Or, in general, do they "share" the bandwidth through the switch?
Sam
Posted 2015-02-03T18:59:48.070
Reputation: 93
6
With a well-designed Ethernet switch, it's possible to get the full port speed into each port and the full port speed out each port, all simultaneously (switch ports are full-duplex).
A switch designed to guarantee it can do this will be marketed has having an aggregate throughput of:
2 * (#-of-ports) * (speed-per-port)
This is sort of double-counting because the data going out any given port must have come in some other port, but this double-counting has become a de facto industry standard marketing practice.
So in your example of a 4-port Gigabit Ethernet switch, it would be marketed as having 8Gbps of bandwidth.
Unfortunately, it wouldn't surprise me if most 4-8 port GigE switches are cheap consumer crap that can't do that and thus wouldn't be marketed as such.
Spiff
Posted 2015-02-03T18:59:48.070
Reputation: 84 656
3Switches have a maximum throughput for the switch. This is how fast the switch can process the data passing through it. This number is dependant on the switch make/model specifically, which you have not included in your question. Having said that, what makes you think it wouldn't work? What problem are you encountering exactly? – Ƭᴇcʜιᴇ007 – 2015-02-03T19:04:06.333
1@Techie007, I specifically didn't include the model of my switch, as I'd like to know the generic "theoretical" answer. That said, I don't see a maximum throughput rating in its spec sheet. It does list "Filtering/Forwarding Rate: 1000Mbps/1,488,000pps", but its unclear to me what that means. – Sam – 2015-02-03T19:35:20.727
1"This seems like a simple question..." -- It's not. There are many performance factors, including switch implementations, i.e. store-and-forward versus cut-through. http://www.dlink.com/uk/en/support/faq/switches/layer-3-gigabit/dgs-series/what-is-the-difference-between-store-and-forward-switching-and-cut-through-switching – sawdust – 2015-02-03T20:25:47.887
The simple answer is that you can get all of the computers talking at gigabit speeds without any slowdowns IF the switch is capable. – MonkeyZeus – 2015-02-03T20:52:14.983
@sawdust, I get that there are many factors (hardware, OS/software, settings, etc) that go into what is actually achievable in the real world. I just need to know if the "gigabit" in "gigabit Ethernet switch" generally refers to total capacity, or per-node. It sounds like the answer is the latter. – Sam – 2015-02-03T21:57:27.147
Gigabit switch refers to the capacity it can handle on any single port. The switch is guaranteeing that you will achieve gigabit speeds on at least one cable coming out of that switch. I am not sure if there are abusive switch companies that would give you a 2-port switch, call it gigabit, and each line can only handle .5 gigabit simultaneously but that is a discussion for another day. – MonkeyZeus – 2015-02-04T14:45:18.297