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Thread: How to get that gigabit?

  1. #1
    Join Date
    Apr 2005
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    Kaunas, Lithuania
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    How to get that gigabit?

    I have a few PCs at home connected to a LAN. I want to upgrade the LAN to gigabit. I bought an Intel Pro/1000MT dual port server adapter (I have to use dual port NIC in my main PC because it does not have a free slot for another NIC). My laptop has Realtek 8169 gigabit NIC. I connect then with a crossover cable and try to transfer a file. I get ~20MB/s. Tried to transfer a file from a ramdisk on my laptop to a ramdisk on main PC - the speed remains the same). Cable is Cat 5e and is 3 meters long. Oh, I tries to connect laptop and main PC to a gigabit switch - speed is the same.

    How could I improve the speed?

    Operating system on both PCs is WinXP Pro.

  2. #2
    Join Date
    Apr 2002
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    NC
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    Something is not right here...

    Gigabit uses all 4 pairs of wires. IF you connect using a standard pin out for a crossover cable you will only use two pair. If you only see 20MB it sounds like they are not set to full duplex. All things beign equal you should get about 40MB over the 2 pairs.

    Standard 568-B pin 568-A pin out for a crossover cable only use cables 1 and 3 2 and 6 with wires 4,5,7 and 8 the same on both ends. This won't work for gigabit. Since you don't mention you made the cable or talk about pin outs, it is difficult to say.
    Are you using the crossover cable connected to the switch when you connect both machines to the gigabit switch up or are you using two different straight through cables? Have you looked at the pin outs for both cables?

    The steps you describe above don't add up. If both machines show a connection established at gigabit speeds connected to the switch there could be other limiting factors. Gigabit speeds require gigabit processors. Messing with the default advanced settings of the network adapter will cause issues as well.

    I think the missing piece may be the cables themselves and a misconfiguration of the tcp/ip settings for the cards.

  3. #3
    Join Date
    Nov 2003
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    399
    Gigabit ethernet uses whats known as dual-duplex transmission a normal cat5e wired patch cable (not crossover cable) should be able to connect two NICs together or NIC to switch. This is because during auto-negotiation one NIC becomes a master and the other a slave to accomidate timing as well data is sent in both directions on each pair (dual-duplex). Just my theory hehe never tested it.
    but anyway here is the pin out for 1000 baseT crossover..


    Pin # Signal Conductor Color Code Pin # Signal Conductor Color Code
    1 BI_DA+ white/green 1 BI_DA+ white/orange
    2 BI_DA- green 2 BI_DA- orange
    3 BI_DB+ white/orange 3 BI_DB+ white/green
    4 BI_DC+ blue 4 BI_DC+ white/brown
    5 BI_DC- white/blue 5 BI_DC- brown
    6 BI_DB- orange 6 BI_DB- green
    7 BI_DD+ white/brown 7 BI_DD+ blue
    8 BI_DD- brown 8 BI_DD- white/blue
    Last edited by juniper; 08-07-2006 at 09:15 AM.
    Everything I write is just my opinion so dont hold me liable.

  4. #4
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    The CPU in the main PC is AMD Athlon XP 3200+, laptop has AMD Turion64 1.6GHz.

    The crossover cable I used is "verified for gigabit ethernet" (or so is written on the cable itself). When connecting to a switch I used a "straight" cable. Results are the same. The max speed I got was ~24MB/s

    Yes, in the past I have changed TCP/IP settings to improve internet speed. What they should be for gigabit ethernet?

    I measured the speed using PCATTCP program http://www.pcausa.com/Utilities/ttcpdown1.htm

  5. #5
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    No idea what your settings should be generically speaking. But Speed and Duplex should be auto. This may help you further diagnose the issue. I would simply uninstall the NIC and reboot. Default settings will be fine for gigabit.

    I would look at the wires of the cable at both ends and post the colors 1-8 on both sides. If the cable says it is a gigabit crossover cable it should be pinned right. Worth checking though. Since you get the problem with and without the switch, it is probably not the switch. It is either a configuration error or a cable problem. Mixing cable pinouts can cause the issue.

    Your far below what it should be so it has nothing to do with tweaking. Default settings should be much faster.

  6. #6
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    For connecting to a switch, I used "normal" cables where all pins are assigned straigth (1-1, 2-2, 3-3...).
    While thinking about it, I came upon an idea - maybe my software firewall (agnitum outpost) slows the connection down? It is installed on both the main PC and the laptop. Any idea how I could test it while not having to uninstall the firewall on both computers (maybe a loopback speed test would show it)?
    My settings for the NIC that goes to the LAN are default. It is default on both the main PC and the laptop.

  7. #7
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    Nov 2003
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    Real time Virus scanners will slow it way down also especialy if scanning in both directions
    Everything I write is just my opinion so dont hold me liable.

  8. #8
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    I do not use real time antiviruses.

    And I think I found the problem. I did a loopback speed test with firewall and got ~40MB/s. Did a loopback speed test with firewall uninstalled and got ~160MB/s. This is on my laptop. I will try to test the speed with firewall uninstalled on my main PC (I have a hardware firewall to protect me from the internet, but it does not block ads)

  9. #9
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    Try using some other firewall software rrather than getting rid of it completely.
    "Nuclear war can ruin your whole compile."
    -- Karl Lehenbauer

  10. #10
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    I use a hardware firewall now, the software one is just for ad blocking (because all incoming packets to blocked ports are dropped on the way to my main PC).

  11. #11
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    Update: I uninstalled the software firewall. I also built a new PC and installed a gigabit card (D-Link DGE-528T. I installed WinXP pro on that PC too.

    Loopback tests:

    Main PC: 50MB/s
    Laptop: 150MB/s
    PC#2: 120MB/

    That's OK.

    It gets more interesting when I try to measure network speed.
    Main PC->laptop :38MB/s
    laptop->main PC: 26MB/s
    Main PC->PC#2: 36MB/s
    PC#2->Main PC: 25MB/s
    laptop<->PC#2: 26MB/s

    One more strange thing: the CPU usage on all PC's does not exceed 40% while transferring (it was 100% when I used software firewall). But where is the speed?

    All cables are cat 5e, straight; all 3 PCs are plugged to a D-Link DGS-1005D switch.

  12. #12
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    Nov 2003
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    Hmm what kind of HD's is in those 3 computers? I think your hitting its maximum sustained data transfer rate.
    Everything I write is just my opinion so dont hold me liable.

  13. #13
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    In the main PC there is a Maxtor Atlas 15K2 36GB SCSI drive, laptop has Samsung 5400RPM 80GB drive, PC#2 has Seagate 320GB 7200RPM IDE drive.

    But that's not the problem. pcattcp, the program that I use for testing, tests data transfer rate from CPU to CPU (that is it generates something and sends it, hard drive is not used).

  14. #14
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    Nov 2003
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    Nevermind I dont think its your hard drives hehe, Forgot about this please look up in google "Tcp1323Opts" your TCP window size is prolly the issue.

    This is not easy to explain and pretty much I suxxors at math hehe and Im not about to read this stuff again cause it fries my brain LOL! anyway read on TCP congestion control / window size they will need increased to do high speed data transfers. Also the buffers in your switch probably are not sufficient for large transfers as well. There are also times that 100Mb is faster then 1Gb due to TCP slow start and congestion control, Think I posted it in here like two or three years ago when I was reading this stuff.
    Last edited by juniper; 09-12-2006 at 11:55 AM.
    Everything I write is just my opinion so dont hold me liable.

  15. #15
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    Kaunas, Lithuania
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    I changed the network card for PC#2 to Intel PRO/1000 GT desktop adapter. Now I get something like that:

    Small buffers (8KB):
    Main PC->PC#2 : 25MB/s
    PC#2->Main PC: 29MB/s

    The CPU usage on main PC does not exceed

    Big buffers: (100KB)
    Main PC->PC#2: 50MB/s
    PC#2->Main PC: 72MB/s

    The CPU usage on main PC rarely exceeds 55% (while sending)
    On PC#2 it does not exceed 20% even while sending at 72MB/s.
    A buffer is what the program (pcattcp) sends at a time.

    If I transfer a file using netbios then the speed is about 30MB/s.
    Last edited by Pentium100; 09-15-2006 at 12:54 AM. Reason: I forgot to include the CPU usage...

  16. #16
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    Apr 2005
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    I noticed a strange thing.

    If I open Control Panel->Administrative tools->Performance and select TCP->segments sent, received/s, then if I send 1.5MB buffers (using pcattcp), the numbers are like this:

    Main PC->PC#2

    On main PC:

    Segments received/s : ~3600
    Segments sent/s : ~3600

    On PC#2:

    Segments received/s : ~34000
    Segments sent/s : ~3600

    Speed: ~36MB/s

    BTW, both NICs support offloading TCP/IP checksum calculations and TCP segmentation.

    If I send 1.5MB buffers from PC#2 to main PC then the numbers are like this:

    On main PC:

    Segments received/s : ~52000
    Segments sent/s : ~2200

    On PC#2:

    Segments received/s : ~2200
    Segments sent/s : ~2300

    Speed: ~72MB/s


    So, main PC sends more packets per second even on slower speed? Why?

    TCP settings are the same for both PCs:
    TCP Receive Window: 321600
    Window Scaling: Yes
    Time Stamping: Yes
    Selective Acks: Yes
    Path MTU Discovery: Yes
    Black Hole Detection: No
    Max. Duplicate ACKs: 2

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