Quick 1Gbit Ethernet question

[titanmiller]

If I have 100 computers with 10mbit/sec cards connected to a gigabit network, will a total network throughput of 1gigabit be possible, even if each computer can only recieve 10mbps?

 

[Ulfwald]

Nope, because your cards can only send at 10 mbit. The total speed of your network will be 10.

 

[ScottMac]

Actually this is the most common / normal setup in a business environment; the "Fat Pipe" inter-switch link. This is where a switch can actually do many-to-one and not suffer a performance hit.

As long as the aggregate input from all the 10meg ports do not exceed the bandwidth of the Gig link (assuming it is a gig-to-gig connection between devices), then it is "non-blocking"; there will always be a full bandwidth path for the traffic.

As already mentioned, each computer will still only be transmitting and receiving at 10Meg, but the inter-switch Gig link can handle 100 10meg connections blabbing at full tilt. Actually, it'd be a few more than that, because the 10meg links are going to be running at ~80+ percent, and the gig link will be running probably closer to ~95 percent.

Now, if the design is such that when the traffic gets across the GIg link, it all gets switched to a single port (like a server or Internet connection), then that would be your bottleneck ... unless that one link is as big as the aggregate bandwidth being directed through it (like another gig link to a gig NIC in the server that's fast enough to handle Gig traffic at Gig speeds).

It's easy to analogize it to water;if you feed a garden hose from 3" firehose, you still can only get a garden hose's throughput (ingore the pressure thing for now). If you feed a 3" fire hose with one garden hose, you still only get one garden hose's throughput, but the fire hose can carry the volume of a buncha garden hoses (like, maybe a hundred). Once you reach what would be the normal capacity for the firehose, that's all it can handle ... adding more garden hoses just means that some of the water from some of the garden hoses is going to be backed up (the "fat pipe" is full).

All of the above assumes "perfect" case scenarios. The transmission protocols may limit the actual throughput because of things like handshakes (SYN/ACK), or distance latencies (also associated with waiting for acknowledgements). Stack latency / processing (the time it takes to get information up and down the stack) may also limit the ultimate ability to get max throughput (associated with CPU, the NICs, the bus, the OS, cable quality, other concurrent processes, etc).

FWIW

Scott

 

[titanmiller]

Thanks both of you, great analogy Scott.