I have a small office. There are ~5 PCs connected via cable. There is 1 PC via WiFi, 3 VoIP phones and a bunch of cellphones connected via WiFi.

There is a Gigalan switch and a internet connection via a modem and router. The internet connection is 10 MB for download and 1MB for upload.

When an user is download a big file from the internet, all the others users cannot browse or cannot place calls. Or the calls have a big latency that makes them very low quality.

How do I diagnose where is the problem? A better switch would make things better? Or is it a problem with my router?

I can run a few tests using a linux box and come back with the results.


My hardware configuration (all home equipment, nothing fancy):

  • 1 gigalan switch
  • 1 cable modem (provided by my carrier)
  • 1 linksys router with public ip
  • 1 wifi access point (professional) connected to the switch.
  • 3 voip phones directly connected to the switch (no wifi here). each one to different ports on the switch.
  • ~5 PCs via ethernet and 1 via wifi.
  • I haven't set up any qos in the router or specific configuration.
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    Assuming the bottleneck is your Internet connection and you're trunking the VoIP lines to an outside gateway: you need to prioritize VoIP and reserve bandwidth for calls. Please add device details and configurations to your question for more detail. – Zac67 Nov 6 '17 at 22:06
  • Hi @Zac67, I've added a little more information, please tell me if that's what you were looking for. – Mauro Ciancio Nov 7 '17 at 11:57
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    Unfortunately, consumer equipment is off-topic here. You could try asking on Super User, Any of the QoS suggestions we make will require commercial grade equipment. – Ron Trunk Nov 7 '17 at 12:33

The problem is your download traffic is filling up your Internet link. Unless your ISP can prioritize VoIP traffic, there is little you can do. There is no configuration you can put on your equipment to fix this.

One option is to buy a much larger Internet connection (so your downloads don't saturate your link), or buy a service that lets you prioritize VoIP traffic.

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  • Actually, you can police inbound as well. TCP responds very well to delaying packets. – Ricky Beam Nov 7 '17 at 0:52
  • I suppose, but then you limit the download traffic all the time. My experience is it gives poor performance. – Ron Trunk Nov 7 '17 at 0:55
  • For Cisco IOS, the policy doesn't begin messing with traffic until thresholds are crossed (link at 80%, etc.) Depends on how you configure it. OP needs a dedicated voice-class that reserves enough bandwidth for voip to function (which is not much.) [given the very high likelihood of this being a "residential" cablemodem setup, the QoS capabilities will be nearly zero.] – Ricky Beam Nov 7 '17 at 1:08
  • Hi @RickyBeam, yes this is a residential cablemodem. Buying a better router or a better switch, would make things better? I'm not sure how to decide what I need. – Mauro Ciancio Nov 7 '17 at 12:06
  • @MauroCiancio You will need a commercial-grade router to implement any of the QoS recommendations. – Ron Trunk Nov 7 '17 at 12:34

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