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The test is that I'll pay more for my VoIP packets to get through right now than I will for my Netflix packets. My 2am download of Windows Update goes into the

The test is that I'll pay more for my VoIP packets to get through right now than I will for my Netflix packets. My 2am download of Windows Update goes into the bargain basement slow lane. Let anyone else go first, I don't care.

AnthonyMouse 13y ago
There isn't anyone to go first at 2AM. Nobody's packets are dropped at that time of day. The problem with QoS is that the window where it's actually useful is miniscule. If, on the one hand, it's 2AM and nobody is using the network, QoS does nothing because all the packets are delivered and none are dropped. On the other hand, if everybody is trying to watch the Superbowl at the same time and $STREAM_BPS * $NUM_USERS > $TOTAL_BANDWIDTH, QoS can't save you. You have more time-sensitive traffic than you have pipe to put it in, so at least some of your customers are going to see choppy video (or no video). In the middle of that you have this tiny slice where the network is saturated "just right" for QoS to actually do something. You have only just enough bandwidth to handle all of the active streams, so that when some bursty thing (like loading a large web page) comes along, you can drop some packets from a stream and have just enough bandwidth available two seconds later to let the stream catch up before the client's buffer is exhausted. To skip to the punch line, that never happens. Networks that hit 100% utilization on a regular basis are under-provisioned. If you're at the point where QoS helps you do something, your network is broken, because tomorrow's peak usage could be higher than today's which means you needed to start upgrading yesterday. QoS on the Internet is useless. And that's before you get to the whole trouble with what to do about ssh tunnels and TLS connections and otherwise unclassifiable traffic.
- danielweber 13y ago
  I've helped plenty of clients where QoS changed their VoIP phones from "not working" to "working." You can push my Windows Update example to 6pm -- I still don't care at all how it runs. I'd tell my router to mark it as the least time-sensitive of any of my network connections.
  - AnthonyMouse 13y ago
    > I've helped plenty of clients where QoS changed their VoIP phones from "not working" to "working." Because QoS on a LAN is a different animal. A LAN will have multiple machines that each have a 100Mbps or faster connection to a shared router with a 100Mbps or slower link to the rest of the Internet. That means one person downloading anything will saturate the entire Internet connection. ISPs have the opposite topology: A bunch of users with e.g. 50Mbps connections that come together to share a multi-Gbps uplink. Regularly saturating the uplink in that context is Bad. It means customers aren't getting the speeds you sold them. There is also a difference between QoS and fairness. If you're using VOIP and I'm downloading something, the ISP should be dropping my packets before yours when we're on the same plan, but because of the quantity of traffic rather than the type. That pretty much exempts VoIP from being dropped, without doing any kind of DPI or traffic classification, based simply on how relatively little bandwidth it requires.

AnthonyMouse 13y ago

There isn't anyone to go first at 2AM. Nobody's packets are dropped at that time of day. The problem with QoS is that the window where it's actually useful is miniscule. If, on the one hand, it's 2AM and nobody is using the network, QoS does nothing because all the packets are delivered and none are dropped. On the other hand, if everybody is trying to watch the Superbowl at the same time and $STREAM_BPS * $NUM_USERS > $TOTAL_BANDWIDTH, QoS can't save you. You have more time-sensitive traffic than you have pipe to put it in, so at least some of your customers are going to see choppy video (or no video). In the middle of that you have this tiny slice where the network is saturated "just right" for QoS to actually do something. You have only just enough bandwidth to handle all of the active streams, so that when some bursty thing (like loading a large web page) comes along, you can drop some packets from a stream and have just enough bandwidth available two seconds later to let the stream catch up before the client's buffer is exhausted. To skip to the punch line, that never happens. Networks that hit 100% utilization on a regular basis are under-provisioned. If you're at the point where QoS helps you do something, your network is broken, because tomorrow's peak usage could be higher than today's which means you needed to start upgrading yesterday. QoS on the Internet is useless. And that's before you get to the whole trouble with what to do about ssh tunnels and TLS connections and otherwise unclassifiable traffic.

danielweber 13y ago
I've helped plenty of clients where QoS changed their VoIP phones from "not working" to "working." You can push my Windows Update example to 6pm -- I still don't care at all how it runs. I'd tell my router to mark it as the least time-sensitive of any of my network connections.
- AnthonyMouse 13y ago
  > I've helped plenty of clients where QoS changed their VoIP phones from "not working" to "working." Because QoS on a LAN is a different animal. A LAN will have multiple machines that each have a 100Mbps or faster connection to a shared router with a 100Mbps or slower link to the rest of the Internet. That means one person downloading anything will saturate the entire Internet connection. ISPs have the opposite topology: A bunch of users with e.g. 50Mbps connections that come together to share a multi-Gbps uplink. Regularly saturating the uplink in that context is Bad. It means customers aren't getting the speeds you sold them. There is also a difference between QoS and fairness. If you're using VOIP and I'm downloading something, the ISP should be dropping my packets before yours when we're on the same plan, but because of the quantity of traffic rather than the type. That pretty much exempts VoIP from being dropped, without doing any kind of DPI or traffic classification, based simply on how relatively little bandwidth it requires.