Digital Logic

High Latency During BitTorrent Downloads

by on Jun.02, 2008, under Technology

No, I’m not talking about slow torrenting, I’m talking about what effect BitTorrent has on other applications and services on your network. George Ou has a very interesting article on how the BitTorrent protocol and its packet blasting nature can disrupt VoIP and online gaming protocols.

Since I have recently moved into a new house and have at least one roommate who frequently torrents large amounts of data, I’ve noticed this latency first hand, I’ll watch as my ping climbs to 900ms or higher and my Skype calls deteriorate into nothingness.

Enabling QoS on the router has almost no effect:

Now it is possible to solve this problem on the network level by prioritizing VoIP and gaming packets in the home DSL modem upload queue. Unfortunately, I don’t have administrative access to the modem and implementing VoIP or gaming prioritization on my home router seemed to have no effect.  Packets in the home router get forwarded as soon as they arrive with 100 Mbps Ethernet on both ends so there is nothing to reorder in the queue.  More advanced business-class routers like those from Cisco will allow you to configure the speed of the FastEthernet connection to match your DSL throughput so that the queue will migrate from the DSL modem to the router but this isn’t very practical for most people.

Very interesting read. Until a permanent solution is found, it looks like I’ll just be yelling at my roommates to turn off uTorrent.

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1 Comment for this entry

  • Jake Billo

    This problem is easily solved with a $70 WRT54GL and Tomato firmware. The layer 7 filtering is built right into the firmware and ensures that your roommates’ downloading of anime doesn’t interfere with your Skype calls. I’ve used this firsthand and capping the total download speed in combination with the QoS priority does what’s intended.

    In addition, it’s also worthwhile to set Skype and Xbox Live traffic to Premium status, since those services are definitely time sensitive and impacted by QoS to a fair degree.

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