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Testing-Cabling Factors

Gigabit Ethernet: Dude, Where's My Bandwidth?
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With our tests delivering performance so close to ideal, we’re probably not going to see any appreciable differences when we change a few cable variables. But we wanted to try it anyway just for curiosity’s sake, mostly to see if it would bring our results any closer to the theoretical performance speed limit.

We did four tests:

Test 1: Default
In this test, we used two 25 ft. cables, each running from one computer to a gigabit switch. We left the cables as they sat, running right beside power cables and power bars.

Test 2: Remove Power Cable Interference
This time, we used the same 25 ft. Cat 5e cables as in the first test, but we moved the network cable as far as possible from power cables and power bars.

Test 3: Shorten Cable length from 50 ft. to 28 ft.
In this test, we removed one of the 25 ft. cables and replaced it with a 3 ft. Cat 5e cable.

Test 4: Replace Cat 5e cables with Cat 6 cables
In this final test, we replaced the 28 ft. Cat 5e cables with 28 ft. Cat 6 cables.

In short, our cable testing didn't show us a lot of difference anywhere, but we did learn a few things:

Test 2: Running Cables Close to Power Cables:
In a small LAN setup like ours, our tests showed you don't have too much to worry about if you have to run your network cable close to a power bar or two. While it's not ideal, it's probably not going to have an appreciable effect on network speeds. Having said that, it should be avoided if possible, and you should keep in mind that these results were taken from a small home network.

Test 3: Shorter Cable Length
This wasn't much of a test, but was just something we tried to see if there was an appreciable difference. We have to remember that when replacing the 25 ft. cable with a three ft. cable that any difference we might see is not necessarily a result of the shorter distance, but may indicate a cable problem. In any case, we didn't really see any differences of note in most tests, although we did see an abnormal jump in performance between the client-to-server C: drive file copy.

Test 4: Cat 6 Cables vs. Cat 5e Cables
Once again, we didn't see much difference here at all. Since we're dealing with 28 ft. of length, we might see a difference over longer cabling. But as long as the cables are in good shape, it looks like Cat 5e cables will work just as well in a home gigabit network with 50 ft. of cable between the peers.

It's also interesting to note that these cabling variables had absolutely no effect on transferring data from one RAM drive to another. Clearly, something else in the system is bottlenecking network performance at the magic 111 MB/s number; as we mentioned, there is some network overhead to be expected so this result is perfectly acceptable.

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Top Comments
  • 19 Hide
    SpadeM , June 22, 2009 9:00 AM
    For all tech people out there, the title of the article should have been a dead give away
    Quote:
    Gigabit Ethernet: Dude, Where's My Bandwidth?
    about the technical aspect of this piece. Sure they could have used a server platform with a server os, SSD's and ram disks, and why not some tech language what most people don't understand. But, as the titles states in a very suggestive way, this article is for people that have simple questions and seek simple answers.

    I'm ok with this piece, it isn't and injustice or it isn't wrong in any way IF you look at who it is addressed to. Remember the KISS rule guys.
  • 19 Hide
    flinxsl , June 22, 2009 7:37 AM
    do you have any engineers on your staff that understand how this stuff works?? when you transfer some bits of data over a network, you don't just shoot the bits directly, they are sent in something called packets. Each packet contains control bits as overhead, which count toward the 125 Mbps limit, but don't count as data bits.

    11% loss due to negotiation and overhead on a network link is about ballpark for a home test.
  • 12 Hide
    cg0def , June 22, 2009 7:25 AM
    why didn't you test SSD performance? It's quite a hot topic and I'm sure a lot of people would like to know if it will in fact improve network performance. I can venture a guess but it'll be entirely theoretical.
Other Comments
  • -5 Hide
    gwiz1987 , June 22, 2009 6:28 AM
    why is the RAM-to-RAM network max speed on the graph 111.2 when u state 111.4? typo?
  • 5 Hide
    drtebi , June 22, 2009 6:29 AM
    Interesting article, thank you. I wonder how a hardware based RAID 5 would perform on a gigabit network compared to a RAID 1?
  • 5 Hide
    Anonymous , June 22, 2009 6:55 AM
    Hello

    Thanks for the article. But I would like to ask how is the transfer speed measured. If it is just the (size of the file)/(a time needed for a tranfer) you are probably comsuming all the bandwith, beacuse you have to count in all the control part of the data packet (ethernet header, IP headrer, TCP header...)

    Blake
  • 12 Hide
    spectrewind , June 22, 2009 7:14 AM
    Don Woligroski has some incorrect information, which invalidates this whole article. He should be writing about hard drives and mainboard bus information transfers. This article is entirely misleading.

    For example: "Cat 5e cables are only certified for 100 ft. lengths"
    This is incorrect. 100 meters (or 328 feet) maximum official segment length.

    Did I miss the section on MTU and data frame sizes. Segment? Jumbo frames? 1500 vs. 9000 for consumer devices? Fragmentation? TIA/EIA? These words and terms should have occurred in this article, but were omitted.

    Worthless writing. THG *used* to be better than this.
  • 12 Hide
    cg0def , June 22, 2009 7:25 AM
    why didn't you test SSD performance? It's quite a hot topic and I'm sure a lot of people would like to know if it will in fact improve network performance. I can venture a guess but it'll be entirely theoretical.
  • 8 Hide
    MartenKL , June 22, 2009 7:34 AM
    Gbit is actually 10^9 bits per second, ie about 119 MB/s.
  • 19 Hide
    flinxsl , June 22, 2009 7:37 AM
    do you have any engineers on your staff that understand how this stuff works?? when you transfer some bits of data over a network, you don't just shoot the bits directly, they are sent in something called packets. Each packet contains control bits as overhead, which count toward the 125 Mbps limit, but don't count as data bits.

    11% loss due to negotiation and overhead on a network link is about ballpark for a home test.
  • 6 Hide
    jankee , June 22, 2009 7:41 AM
    After carefully read the article. I believe this is not a tech review, just a concern from a newbie because he does not understand much about all external factor of data transfer. All his simple thought is 1000 is ten time of 100 Mbs and expect have to be 10 time faster.

    Anyway, many difference factors will affect the transfer speed. The most accurate test need to use Ram Drive and have to use powerful machines to illuminate the machine bottle neck factor out.

  • 0 Hide
    jankee , June 22, 2009 7:43 AM
    Correction: "eliminate" (sorry)
  • 8 Hide
    MartenKL , June 22, 2009 7:46 AM
    Cat 5e is actually a newer standard than the aging Cat 6 standard. Cat 6a however is a relatively new standard that I would recommend, it does support 10Gb/s networks as well.
  • 0 Hide
    Anonymous , June 22, 2009 8:04 AM
    First of all, gigabit ethernet uses entirely different addressing and encoding from 100-meg, and overhead is one heck of a lot greater than that.
    First of all, there's the 10b/8b encoding, so an 8-bit byte is encoded to a 10-bit unit. Then there's a concept of invariable frame sizes, whereit might be possible that a TCP/IP packet spans two frames, filling 100% of the first and 1% of the second, it means 50.5% efficiency. Third, every frame is payload only in part, rest is taken up by header information, footer and CRC. It's not much, perhaps about 5% of the frame, but it can get noticeable.
    First, you have to divide by 10, not by 8, to get the speed in bytes/second (ie. 100 MB/s, not 125 MB/s).
    Second, if you transmit a lot of inefficient frames (networking programs aren't exactly frugal about bandwidth when they have gigabit ethernet, and next to none are actually optimized in any way for it), you might lose up to half of the bandwidth.
    Third, when you factor in the frame level overhead, you might end up with maybe 40-45 MB/s of the promised 100 MB/s...

    Fortunately, a lot of these issues can be resolved by optimizing software and firmware to take advantage of the available bandwidth and idiosyncracies of gigabit ethernet.
  • 1 Hide
    MartenKL , June 22, 2009 8:14 AM
    Ok my bad, this article is not for Tomshardware it is not meant for people that understand networking or maybe even computers. Pass this article on to another site with more "normal" visitors.

    Testing with a different file for ram to ram then used in the other tests really show the errors in these tests.
  • 0 Hide
    cyberkuberiah , June 22, 2009 8:29 AM
    this is why i am a regular reader here at tom's .
  • -1 Hide
    apache_lives , June 22, 2009 8:50 AM
    What i want to see is the effect of jumboframe packets and hdd allocation unit size (or stripe size) and its effects on network transfers since the packets etc transfer differently across the network cable - benchmarks?
  • 19 Hide
    SpadeM , June 22, 2009 9:00 AM
    For all tech people out there, the title of the article should have been a dead give away
    Quote:
    Gigabit Ethernet: Dude, Where's My Bandwidth?
    about the technical aspect of this piece. Sure they could have used a server platform with a server os, SSD's and ram disks, and why not some tech language what most people don't understand. But, as the titles states in a very suggestive way, this article is for people that have simple questions and seek simple answers.

    I'm ok with this piece, it isn't and injustice or it isn't wrong in any way IF you look at who it is addressed to. Remember the KISS rule guys.
  • -3 Hide
    Psycomo , June 22, 2009 9:31 AM
    Technically you could see a 10 fold increase in thruput. A 100Mb/s network is capable of 12.5MB/s thruput. A 1Gb/s network has a thruput of 128MB/s. So therefore 100Mb/s(12.5MB/s) x 10 = 1Gb/s(128MB/s). Of course this takes in to account an optimal or perfect network invironement, one with a single user and a sata based SSD that can push that amount of data on the read/write. Your typical magnetic based HDD running at 7200 RPM will be hard pressed to push more then 100MB/s on the write which is going to be your data bottle neck as you can only push data as fast as it can be written. Of course even at that speed you are around an 8x improvement in thruput. You will also lose bandwith with overhead alone of roughly 10%(on this I could be mistaken). Again this all takes into account a perfect environement to test in.
  • 6 Hide
    thexder1 , June 22, 2009 9:33 AM
    First of all I would like to point out to IronRyan21 that the actual Gigabit ethernet standard is for Cat5. Second I would have preferred to see more through tests done as the "50 ft" of cable used is a very short run for ethernet since the maximum length is actually 100 meters or 328 Ft as spectrewind pointed out. In a home you probably will not see runs much over 50 Ft but the setup used in the article was actually 2 x 25 Ft runs. If the tests were done closer to the maximum length you would then see a much bigger difference when changes were made to how the cable was run and the cable itself. I would want the article to be redone with runs of 50, 100, 200, and 300 Ft to see if the conclusions were correct or if they only apply to very short runs. I would have also liked to have seen testing on the throughput difference using jumbo frames as well as different file sizes.

    I think the RAM disk was a good idea to do a maximum throughput test in using real world data copies but that was the only good thing about the article that I can see.
  • 3 Hide
    zetone , June 22, 2009 9:51 AM
    @all complaining about the technical aspects of this article: I think the target audience is NOT network administrators.

    One the other hand is is worth mentioning, that transfer speed over gigabit network from disk to disk, depends on the files size transferred and number of files transferred.

    It's one thing to copy over network a 4 gig file. And is totally different to copy 40k+ files totalizing 4 gigs. For the latest scenario, performance will take another hit due to increased I/O overhead @ disk level.
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