Gigabit Ethernet: Dude, Where's My Bandwidth?

Features
By Don Woligroski
published

Testing-Cabling Factors

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.

Don Woligroski
125 Comments Comment from the forums
  • gwiz1987
    why is the RAM-to-RAM network max speed on the graph 111.2 when u state 111.4? typo?
    Reply
  • drtebi
    Interesting article, thank you. I wonder how a hardware based RAID 5 would perform on a gigabit network compared to a RAID 1?
    Reply
  • 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
    Reply
  • jankee
    The article does not make any sense and created from an rookie. Remember you will not see a big difference when transfer small amount of data due to some transfer negotiating between network. Try to transfer some 8GB file or folder across, you then see the difference. The same concept like you are trying to race between a honda civic and a ferrari just in a distance of 20 feet away.

    Hope this is cleared out.
    Reply
  • spectrewind
    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.
    Reply
  • IronRyan21
    There is a common misconception out there that gigabit networks require Category 5e class cable, but actually, even the older Cat 5 cable is gigabit-capable.

    Really? I thought Cat 5 wasn't gigabit capable? In fact cat 6 was the only way to go gigabit.
    Reply
  • cg0def
    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.
    Reply
  • MartenKL
    Gbit is actually 10^9 bits per second, ie about 119 MB/s.
    Reply
  • flinxsl
    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.
    Reply
  • jankee
    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.

    Reply