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Slow download speeds

If you experience slow downloads, it could be for many reasons. However, they can be different when you experience slow download speed from certain user(s) or when you get slow speeds downloading from every peer. Please try to download from or get filelist of several (at least 10) users before you go on. Note that this faq does NOT cover the case when your downloads won't start at all.

Slow downloads from certain user(s)

Reasons connections with some users may be too slow:

  1. The upload bandwidth of the peer you are downloading from is maxed out. Don't pay attention to the value of the Connection column in the user list: it is subjective and often not an accurate representation of the user's actual speed.
  2. The peer you are downloading from is too far from you (maybe on another continent) and too many hops are necessary to connect you to your peer.
    It is also possible that either your ISP or the other user's provider has limited overseas bandwitdh available.
    You can view your peer's country in Transfers area (provided the Guess user country from IP setting is enabled).
  3. The person who you are downloading from is using a bandwidth limiter. There are two types of limiting: client based or using a third-party program. So for particularly slow transfers (1 KiB/s or slower) from a certain user, abusive upload limiting may be to blame.
  4. The person who you are downloading from suffers from one or more constant speed problem described in the next section.

Solution: try to find more sources for your downloads:

Slow downloads from every user

Slow downloads within DC++ may be caused by the following:

  1. Bandwidth limiting is enabled for downloads. Make sure the limiter is disabled or set to a high enough value.
  2. Your Internet connection is shared with others on your LAN and they are using up all the available bandwidth. Tell them to knock it off. =) Also your connection speed to the gateway or router on your LAN can be slower than the available speed from your ISP. It could be for reasons like week signal strength on a wireless connection, broken/old network devices, etc... Try to do a file transfer test within your local network to be sure that it's fast enough.
  3. Your ISP may be limiting your P2P traffic via some method of packet shaping. Call up the ISP and inquire if they do anything with P2P traffic. You can try to connect to ADC hubs and test your downloads there. As ADC is a newer and more efficient DC protocol it can be still unknown to your ISP's throttling system. If the ISP does throttle you, then there is nothing much that can be done to increase the speeds. This is also common at Universities and at the workplace, and is the topic of another FAQ.
  4. You haven't set up your third party firewall or internet monitor software correctly. Some of these security applications may treat p2p transfer as a DDoS flood attempt and tries to defend your computer from it. Try to disable or even uninstall these applications temporarily and test your downloads again. If it helps refer the application's documentation how to make exception rules for DC++. If you have a router its also possible that it has some anti-DDoS or flood protection feature and it may enabled by default. Check the router's documentation or configuration page for a possible option of this kind.
  5. You need to optimize your operating system for your current connection speed. First, close all P2P applications. Next run the DSLReports TweakTest. Once you have optimized it, then run a speed test at DSLReports SpeedTest Page or at the nice looking SpeedTest.Net page (select a test site closest to your location for accurate results). This will give you a good idea what your maximum download and upload speeds are. If you're getting within 10% of your connection speed, that's the best you can get! If you are having trouble with your broadband connection, and it relates to packet loss, excessive latency, or Internet or ISP congestion, running the Line Quality Test may help find the cause (requires logon, free signup).
  6. Your Internet connection is DSL, cable, or satellite one with an asymmetrical connection speed, such as 768/128 Kib/s or 3.0 Mib/s / 256 Kib/s. On such connections, if you upload near the speed of your upload limit (16 KiB/s in the case of the 768/128 connection), it may affect the speeds of your downloads, no matter how much larger your download connection is. If this is happening, you can use the built-in transfer limiting function to set the maximum upload rate value slightly lower than your available upload speed (eg. to 15 or 14 KiB/s in the case above).

    If you aren't allowed to use upload limiting you can also experiment with changing the size of Socket Write Buffer in Experts Only panel of DC++ settings. It defaults to 8 KiB and you can try to change it to a smaller value. You should specify the value in bytes and you may have to try several values to test what size suits your connection best. Note that you should restart DC++ to changes take effect.

  7. The "QoS Packet Scheduler" is enabled in your Windows so you are not able to use some reserved bandwidth for download. Follow this guide to disable QoS in Windows XP or this one to disable QoS in Windows Vista, 7 or 8. Some routers also have QoS capabilities, but it shouldn't be enabled by default. Please consult your router's manual for more information.
  8. Your computer is infected with malicious software which altered the low level network settings of your operating system. This is common when your Windows become infected with spy/adware. Even they are disinfected, their destructive modifications usually still remain. You can follow the official guided help from Microsoft how to restore these settings here and here.