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can a x86 PC saturate a gigabit ethernet link
I am looking at doing some testing on gigabit ethernet links and need a way
to saturate the link. On the hardware side I can buy optical or electrical gigabit Ethernet cards but what sort of hardware is required to get a full 1 Gigabit per second out of a PCI card? Do I have to use a 64 bit PCI bus rather than a 32 bit one? I am guessing that the saturate a Gig E card on a 64 bit PCI slot the bus would have to do better than 16 Meg per second and on a 32 bit bus it would have to do better than about 23 Meg per second. Is this correct? Is the main question then what type of CPU you are running as to whether it can pump enough data out? I am looking at using the iperf package to generate the gig E data so I believe that my main problem is likely to be hardware firstly and software secondly. Does anyone have any experience with something like this? thankyou -- David To reply remove the dipthong before the @ |
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Under Windows XP on a 2.4Ghz P4 I can push about 600mbit of UDP traffic
through an Intel Pro/1000F card (in a 32-bit PCI slot). Under TCP it is obviously much worse due to the limitation of latency between any two hosts. However, this is using the standard frame size of 1500 bytes. For optimum gigabit performance you need to go to larger frame sizes (like ~9KB or even larger in some cases). If you are on a homogeneous network with only hosts speaking the larger frame size, then the increase in performance can be huge. Because of the low frame size of 1500 bytes, the card needs to send ~67 thousand packets/sec to saturate a gigabit connection. Imagine the receiving computer having to process an interrupt for every single packet... If you switch to so-called jumbo frames of 9KB, then you cut the number of packets needed by a factor of 6. The other factor to consider is the PCI bus the card is sitting on. The 33Mhz 32-bit PCI bus only has enough bandwidth to push about 1gbit/sec total, so filling a full-duplex connection is out of the question. You have a few options in this regard: a) Switch to 64-bit or 66Mhz (or both) PCI gigabit cards. Only a few server chipsets have that support, so on most off-the-shelf computers its not much of an option. b) The new Intel 875/865 chipsets have support for a seperate data-path to a built-in gigabit network interface. This is dedicated and seperate from the PCI bus, so you can get full-duplex gigabit performance without saturating the PCI bus. Now, adding this option is a manufacturer's decision, and so not all boards have this (in fact, I don't think I've seen any 865 [the lower end model] with them). In a lot of cases, it is apparently cheaper for manufactuers to put a seperate gigabit interface on the board (sitting on the PCI bus, unfortunately), so you have to read closely to make sure it is using Intel's dedicated interface. The good news is that there is a decent selection of high-end consumer boards that do have the dedicated gigabit interface. The only limiting factor is that all the boards I have seen only offer a copper gigabit interface. If you were interested in fiber, you'd have to get a media converter. "dpnsw" wrote in message ... I am looking at doing some testing on gigabit ethernet links and need a way to saturate the link. On the hardware side I can buy optical or electrical gigabit Ethernet cards but what sort of hardware is required to get a full 1 Gigabit per second out of a PCI card? Do I have to use a 64 bit PCI bus rather than a 32 bit one? I am guessing that the saturate a Gig E card on a 64 bit PCI slot the bus would have to do better than 16 Meg per second and on a 32 bit bus it would have to do better than about 23 Meg per second. Is this correct? Is the main question then what type of CPU you are running as to whether it can pump enough data out? I am looking at using the iperf package to generate the gig E data so I believe that my main problem is likely to be hardware firstly and software secondly. Does anyone have any experience with something like this? thankyou -- David To reply remove the dipthong before the @ |
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