5 ms·

> QoS (Quality of Service) can help, but only if it is applied at every router the traffic for a call goes through. You really only need it on routers where a

by zrm 10y ago

> QoS (Quality of Service) can help, but only if it is applied at every router the traffic for a call goes through. You really only need it on routers where a bottleneck is. If a router is forwarding 100% of packets immediately there is nothing for QoS to do. In practice what this means is that the most important place to have it is at the border where you go from high bandwidth LAN to lower bandwidth internet. In particular if you control a router there, make sure it knows to limit traffic to what the next hop link speed actually is. In will often see the link as gigabit ethernet even if it's slower than that and then forward all traffic when you really want it to be the device that chooses which traffic gets dropped. Unfortunately if your ISP supports burst bandwidth it's not always easy to get it right without breaking that.

MandieD 10y ago
QoS depends on tagging (DSCP), and if one of the routers along the way doesn't support it or isn't configured for it, those tags are often dropped - or at least that's what I've seen in our company's network.
- jlgaddis 10y ago
  Like so many other things in tech, "it depends". Network gear can be configured to treat frames/packets in various ways -- leave the ToS/DSCP bits alone, strip them out, or remark them. At the edge of a network, it's common to mark them. In the core of a network, you'll usually leave them alone (but honor them). On connections to third-parties (such as ISPs), it's not unusual for them to strip your QoS markings -- unless you're paying extra for them not to. For a random packet that leaves your home network and hits the Internet (even VoIP traffic), I'd be surprised if it ends up at its destination with those same QoS bits set. Like zrm said, though, if there's no congestion on links, prioritizing traffic typically isn't going to do you much good. It's only when there's contention that moving packets to the front of the line helps out.
  - AstralStorm 10y ago
    Except Internet routing is not smart, the routers cannot send you through a low bandwidth but uncontested and low latency pipe when your packets are unmarked because you didn't pay a premium for a peering agreement. It actually can hurt the Internet performance as a whole, as the tiny VoIP packets prevent Jumbo throughput ones from working really well. It takes just one bad hop to ruin latency.
    - jlgaddis 10y ago
      Sure they can, especially on MPLS circuits sold for exactly this reason -- and with SLA commitments to deliver packets w/ specific markings within specific parameters (i.e. up to 5 Mbps of traffic marked ef will have maximum latency of 30 ms between A-Z). Not on your home Internet connection, perhaps, but if you're a company and you want guaranteed performance levels (i.e. for VoIP traffic), you can certainly get it.

by zrm 10y ago

MandieD 10y ago

QoS depends on tagging (DSCP), and if one of the routers along the way doesn't support it or isn't configured for it, those tags are often dropped - or at least that's what I've seen in our company's network.

jlgaddis 10y ago
Like so many other things in tech, "it depends". Network gear can be configured to treat frames/packets in various ways -- leave the ToS/DSCP bits alone, strip them out, or remark them. At the edge of a network, it's common to mark them. In the core of a network, you'll usually leave them alone (but honor them). On connections to third-parties (such as ISPs), it's not unusual for them to strip your QoS markings -- unless you're paying extra for them not to. For a random packet that leaves your home network and hits the Internet (even VoIP traffic), I'd be surprised if it ends up at its destination with those same QoS bits set. Like zrm said, though, if there's no congestion on links, prioritizing traffic typically isn't going to do you much good. It's only when there's contention that moving packets to the front of the line helps out.
- AstralStorm 10y ago
  Except Internet routing is not smart, the routers cannot send you through a low bandwidth but uncontested and low latency pipe when your packets are unmarked because you didn't pay a premium for a peering agreement. It actually can hurt the Internet performance as a whole, as the tiny VoIP packets prevent Jumbo throughput ones from working really well. It takes just one bad hop to ruin latency.
  - jlgaddis 10y ago
    Sure they can, especially on MPLS circuits sold for exactly this reason -- and with SLA commitments to deliver packets w/ specific markings within specific parameters (i.e. up to 5 Mbps of traffic marked ef will have maximum latency of 30 ms between A-Z). Not on your home Internet connection, perhaps, but if you're a company and you want guaranteed performance levels (i.e. for VoIP traffic), you can certainly get it.