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I have recently moved several hundred meters from my previous residence and I am now experiencing what seems to be, to me at least, some strange performance issues. I would like to know if there is anything I can do to improve things on my end. Alternatively, I would need "ammunition" for persuading my provider to fix the issue (the upload speed is not "guaranteed").

The facts are:

  • the connection is rated at 100 Mbps
  • my previous speeds were ~90 Mbps download and ~60 Mbps upload (with router)
  • my current speeds are ~90 Mbps download and ~0.5 Mbps upload (with router)
  • running without my router (a WRT54GCv3 from LinkSys) the download speed increases slightly (~93 Mbps) but the upload speed drops to ~10 Kbps
  • pinging and others drops about 25% of the packets without the router and about 5% with it
  • running (flash based) speed tests continuously (without my router) sometimes return download speeds as low as 8 Mbps and, once, as high as 112 Mbps.

The overall browsing experience seems more "choppy" but it obviously doesn't count as a fact.

I am particularly confused about the high download speed in the presence of so many dropped packets and the strange influence of the router.

Any ideas?


  • the ISP refused to acknowledge that this is an issue
  • neighbors claim good connection
  • the cable is CAT5e and it has what might be a failure point in the middle
  • the connection is 100 megabit Ethernet

My next step is to open the common box with the modem and routers, test my cable and replace it or add new plugs to ensure correct wiring.


The situation was resolved using a new Ethernet cable from the common box to my computer/router.

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Are you using the same or a different modem? A modem swap-out (with a known good unit) would be a reasonable experiment. – sawdust Jul 31 '12 at 21:30
@sawdust My end of the connection (router + PC) is exactly the same. I am using an integrated Realtek network card. – Andrei Jul 31 '12 at 21:41
@sawdust I don't have access to the fiber optics modem, it belongs to the ISP and is outside my apartment. – Andrei Jul 31 '12 at 22:08
You should probably ask for help from your provider directly. Even though speeds (and up time) are not guaranteed, there are reasonable expectations that need to be met. – sawdust Jul 31 '12 at 22:09
The ISP basically provides an ethernet connection from a central router/modem in my building and PPoE login details. The ISP is known for very good speeds and prices and good uptime. I never had any issues in the two years I've spent in my past residence. They are not known for good support. I am preparing myself for persuading them on the "reasonable expectations" you mention. – Andrei Jul 31 '12 at 22:20
up vote 3 down vote accepted

So you're in a different apartment of the same building, and now you're having problems? It could just be a problem with the Ethernet wiring to your new apartment. In fact, it seems HIGHLY likely to me that you're running 100BASE-TX and your transmit pair is patched wrong.

If I were you, I'd try a different Ethernet jack in the apartment (if you have more than one), or ask my next-door neighbor if I could run a test using their jack.

If you all connect to the same switch and can see your neighbors' machines, I'd try a performance test between your apartment and a neighbor's apartment and see if I see the same performance problem in that case (with no WAN link involved, just in-building Ethernet).

What Ethernet link speed is being autonegotiated? 100 megabit or gigabit?

If this is just 100 megabit Ethernet (100BASE-TX, two pairs of wires), it could be that your transmit pair is terminated incorrectly, so that your two transmit pins aren't actually patched into a twisted pair of conductors in the in-building cabling. That could be destroying your Tx signal integrity, causing high bit error rates (and thus high packet loss) on Tx, while not affecting Rx much.

If this is gigabit Ethernet (1000BASE-T), then it gets more complicated, because all 4 pairs are in use, and all 4 pairs are bi-directional. It's harder to see how this could be a wiring problem. However, if it's still somehow a wiring problem, and the problem happens to only be on one or both of the pairs that aren't used for 100BASE-TX, then you could possibly work around the problem by forcing your router (or your PC) to only negotiate 100 megabit.

Who owns the wiring? Your landlord, or your ISP? Who owns the switch that you connect to? If you can get the landlord to let you access the wiring closet, you could run some more, very useful tests by finding your port on the switch and seeing what performance you get right there directly connected to the switch while standing in the closet; changing out the patch cable for your port with a known good cable; and inspecting how the wires for your apartment's drop were terminated onto the back of the patch panel, looking for poor connections, incorrectly mated pairs, or rolled pairs. You could also look to see if the wiring from the patch panel to your apartment is at least CAT3 (voice grade, but still twisted pairs) for 100BASE-TX, or at least CAT5 for 1000BASE-T.

In your apartment, you could open up your Ethernet wall jack and look at how the cable was terminated there, looking again for loose connections, mis-matched pairs, rolled pairs, and the appropriate grade of wiring. Be sure to study up on EIA/TIA 568 pinouts (especially 568b, which seems to be the most common in the real world) so you don't make bad assumptions. Pin 3 and 6 are a pair, not 3&4. Also, pins 4 and 5 are pair, not 5&6.

You could also check with your landlord to try to get a sense of how the structured cabling is layed out / physically cable-routed through your building, to make sure the run between your apartment and whatever switch you connect to is no more than 100 meters of cable.

If you have access to a fancy cable tester, you could do some nifty quality tests on the cable. But beware of the simple/cheap pinout testers that only test the pinout; these can detect rolled pairs, but not mismatches where two pins that are supposed to be on the same twisted pair are not actually on the same twisted pair. I've seen plenty of questions here on SuperUser where someone thought their cable was fine because they'd used a pinout tester, and it ended up being wired where 3&4 and 5&6 were on twisted pairs together, instead of 3&6 and 4&5.

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