Ping Spikes Every Few Seconds While Streaming Netflix

[nhille030]

Hi,

I found a lot of similar threads here, but none of them seems to solve or even address the exact same problem I'm facing.

When my girlfriend is streaming Netflix, I'm experiencing short ping spikes every few seconds. Normally, my ping to closely located servers is around 20ms, but every 3-6 seconds it goes up to 120-140ms for 1-2 seconds (see screenshot below). When she stops streaming, I'm immediately not getting any more spikes. I'm assuming Netflix is loading its videos in chunks of data every few seconds which causes the short latency increase, correct?

I have a wired connection to my router while my girlfriend is using WiFi. The ping tool in my router shows the exact same behavior as the one executed on my local machine.

I tried setting up simple QoS rules in my router, but that doesn't change anything, even if I give lowest priority (max. 20% of bandwith) to my girlfriend's device and highest priority to mine. I'm not a network guy, but I'm starting to think that QoS only affects bandwith, but not latency. Does that make any sense?

Is there anything else besides QoS that I could try to avoid these annoying ping spikes?

The problem only started a few days ago. Before that, I experienced no lags or ping spikes in online games whatsoever while Netflix was streaming. Could it be an issue on my ISP's end?

Thanks in advance!

 

[bill001g]

It does load the data in chunks.. most people do not notice since it seldom has any impact.

If you have a rather small internet connection it is much more visible. This is a problem called burst rate. Very advanced QoS has the ability to limit this since all rates are average rates but you can get the same average number transfer 100mbit/sec for 1 second and nothing for 9 seconds or transferring 10mbit for each of 10 seconds.

This is not that simple to fix. Your best option would be to try to see if there are setting on the netflix pc that can limit the transfer rates. If you were "uploading" video you have lots of control but when it is incoming ie "download" the ISP has already sent the data before your router can do anything. Most router QoS is upload limitations which is why you saw it have no effect.

Note if you really want to verify this is the problem load wireshark on the netflix pc and run a ping at the same time on that machine. You will actually see if the ping is coming back during bursts of data. Wireshark draws nice graphs if your want.........still that does not actually fix the problem.

 

[nhille030]

...

Thanks for your answer, that clears things up a bit. A few notes though:

• 
  ■ I usually have around 40-50 Mbit/s downstream and 6-8 Mbit/s upstream, shouldn't that be more than enough to play lag-free while streaming Netflix?
  ■ My router's QoS explicitly support downstream QoS, at least indirectly by prioritizing received packets according to the corresponding upload QoS rules (if I understand it correctly). I'm using Asuswrt-Merlin (v. 380.66) on an ASUS RT-N66U ("Dark Knight") router. So my general question remains: How exactly is ping/latency affected by the bandwith used at any point in time? Shouldn't limiting the bandwith somehow have a positive effect on latency?
  ■ Also, I'm still confused as to why this hasn't happened before. I just started getting ping spikes without having changed anything in my network configuration/setup. Doesn't that mean that it's probably an issue with my ISP?

I'll try investigating the problem further with wireshark, even though I'm already certain that the problem is caused by Netflix (or streaming in general). I think I'll also test it with Netflix set to lower quality and see if and how that affects the latency.

 

[bill001g]

There really is no such thing as downstream QoS what they are doing is trying to trick the end device. To really understand this you would need to study the concept of TCP window size.

But a overly simplistic example. Let say you have a application that tells the server please send me data at 100mbits/sec. And your internet connection is only 100mbits. Now you also have addition user traffic. The ISP can not fit it all in so it randomly send data but the 100mbit/sec application will still take all it can. What can your router possibly do the data from the other applications is gone or delayed.

So you limit it to say 20mbit/sec download from the offending application. The router of course continues to receive 100mbps of crap but it discards 80mbps of it and only delivers 20mbits of it to the end machine. At this point you fixed nothing. The hope is the end machine detects that it getting lots of lost data when it requests 100mbps and drops its request rate until it no longer see data loss.

This works for many things but bit torrent will actually open more streams when it gets data loss. Things like games send at a constant rate and can not be reduced. Netflix and youtube would have to reduce the resolution to actually reduce their rate.


Merlin has a lot of traffic monitors you might see something interesting in that. You could also try to factory reset your router and configure a very minimal setting...just IP addresses and WiFi settings. All the extra features put burden on the CPU. On routers newer than yours they have hardware NAT assist. They can easily run gbit internet connections. If you use any of the fancy feature it turns this off and uses the CPU which cuts the speed to about 250mbits.

You can try to limit the netflix machine to say 10mbps download and see what happens. Problem is the 10mbps is a average rate and you can not control the time the average is taken over. Things like 5 or 10seconds is actually a huge amount of time and you can still get big spikes of data. You can not change the average....unless you are really ambitious and modify the merlin firmware yourself.

You still maybe better off trying to limit the rates on the end machine running netflix. Setting a fixed limit in your router download QoS is kinda the same thing you just hope the machine responds to data loss.