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I'm serving Images as part of my website for a long time now, but recently images became too slow on a certain ISP!

I'm hosting on DigitalOcean with a load balancer (with http2 rule) in front of multiple app server droplets using Nginx on Ubuntu, & images are being loaded from a database with acl on them when needed.

Here is the sample image (345 KB) I'm testing with, which loads very normally on 2 ISPs, but loads tooooo slow on a 3rd ISP as follows:

  • Vodafone ISP (3G)
    • Image load time: 0.8 S (Seconds)
    • ISP Speed test: 17 Mbps
  • Vodafone ISP (Adsl)
    • Image load time: 1 S
    • ISP Speed test: 11 Mbps
  • Orange ISP (Adsl)
    • Image load time: 2 S
    • ISP Speed test: 1.6 Mbps
  • We ISP (Adsl)
    • Image load time: 27 S
    • ISP Speed test: 3.5 Mbps

(note: these numbers are averages but almost consistent)

I know it is a very weird behavior, but it is consistent for several days now.

Question is how to start even debugging this issue to be able to fix it?!!

  • I think it is necessary to describe in more detail how you are performing these tests. Certainly you don’t have 4 ISPs hooked up that you have direct access to? That would mean these tests are on 4 different networks. All of which could have their own network and connectivity problems independent of the ISP. So please describe in detail how you know this is the ISP and not any number of other possible issues. As you have shown yourself, speedtests appear good. – Appleoddity Dec 25 '18 at 17:21
  • @Appleoddity, It just happens that I have currently access to these 4 different ISPs, the 3G on my own mobile & the other adsl ones are through 3 different routers that exists physically with me too & somehow they share the same physical copper Telephone line (I mean packaged together) .. & actually speed tests where taken just before testing the image, & also other images from other sites were loading fine at the same time ... Of course I'm not sure if it is an ISP problem or not, but this is the only difference I spotted so far! – Abdel Hady Dec 25 '18 at 17:34
  • I suspect the answer is to contact your ISP, let them know the problem, and ask them to diagnose it. – Tim Dec 25 '18 at 18:21
  • So you have one physical phone cable and three ADSL routers connected to it, each going to a different ISP? Then using the same computer, you connect in turn to the three different ADSL routers and perform the test? What about downloading images from other sites? Do you only experience this slowness on your own website? – Tommiie Dec 26 '18 at 19:54
  • @Tom photos from other sites load normally, only photos from my site are affected by this slowness on this ISP only! – Abdel Hady Dec 26 '18 at 20:16
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you must solve this through checking network ping time and trace between source and destination . first take a trace from your pc with low speed ISP internet link like this :

for example if your os is windows :

tracert www.yourwebsite.com 

and let the trace done completely until the hub number 30 for example . and take a pic from this .

then contact your hosting-provider and say them about this problem . after that if its needed they should take trace from server of your website to your low-speed isp IP .

then you have two directions of network trace and they can watch the problem clearly . if any hub has problem between source and destination they can fix it. sometimes its might be the ISP Caching system problem . so you can contact them and let them know about this problem.

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