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We've got a slowish broadband non fibre connection c. 10mbps up, 1mbps down. It should be ok for everyday browsing for 1 or 2 people but we are trying to use it for 5 people at once all syncing large files in dropbox.

To make the matter worse although the speeds via speedtest.net are ok(ish) the ping is ofter high 100-300ms. Its not always like this, but quite often is. Any idea what could be causing this and how possibly to remedy it ?

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    Ping is just the amount of time between a packet send and packet received. This is added to by: the speed of light (travel time of packet) and the number of stops along the route. Open cmd and type tracert google.com, see how many stops your packet makes between your home and the destination. Each one of those stops adds some "processing" or "routing" time. Ping doesn't affect downloads or static activities much, and dynamic things like online games much more. – JaredT May 5 '16 at 19:59
  • Ping uses ICMP, and that is normally very low priority traffic. It is more likely to be queued or dropped in favor of "real" traffic. The times you see in ping do not match reality for things like TCP (e.g. HTTP) or UDP (e.g. VoIP). – Ron Maupin May 5 '16 at 20:06
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    What makes ping high, latency, ping is a way to measure the latency of a packet. The numbers you indicate (10mbps up, 1mbps down) have very little to do with latency, which is, "the delay before a transfer of data begins following an instruction for its transfer:". In 99/100 cases latency on a connection cannot be solved by the end user, that is because, the latency often is outside of their own local network. The fact it "does not always happen" indicates a problem by your ISP and/or one of their downstream partners. – Ramhound May 5 '16 at 20:44
  • What does dslreports.com/speedtest tell you for your latency numbers and bufferbloat grade? – Spiff May 6 '16 at 3:21
  • Have you configured your Dropbox to use LAN sync and make all the appropriate ports are opened? Port 17500. Dropbox still has to be involved for syncing files, but once verified by Dropbox the LAN sync is much faster. dropbox.com/en/help/137 – Sun May 10 '16 at 16:06
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When data flows over the internet, both the upload and download are used.

If you download something, everytime a series of packages has been download, an upload package is sent back to confirm that the download was okay. If you upload something, everytime a series of packages has been uploaded the client waits to receive the confirmation package that it downloads.

Even with fast download speeds, it can happen that the upload channel is full. If that happens, the download stalls because sending that confirmation package is stalled.

Because of this principle, whenever your connection is measured (ping) the same thing applies. You send your ping to the remote server, the server responds and your client waits for the confirmation package.

What happens in your case, is that the upload channel is constantly full, causing congestion. Due to the congestion, the connection becomes slow and pings drastically increase from say 10-50ms to 300ms and more.

The best way to combat your issue is either limiting the connection so the upload and download limits are never reached, or setup a Quality of Service which prioritizes certain packages over others (and usually also maintains an overall bandwidth limit.

EDIT: That being said, it should be noted that ping itself is the time it takes from a package to go from your computer to another one. Even with slow speeds, if the computer is closeby, the ping will be low, if the computer is far away, even with fast speeds, the ping will be high. But in your case, when sometimes the connection has a low ping while other times it has a very high ping, this is definitely due to congestion.

  • I think it is important to point out that, one could have extremely low ping, on a "slow" connection. Often the only difference between a 10mbps up and 1 mbps up connection, is the configuration of your connection, on their end. Case in point, 56k modem connections, didn't have high latency, they couldn't recieve large packets. If you sent a small packet, it would have been sent/recieved (realative) quickly. – Ramhound May 5 '16 at 20:48
  • @Ramhound good point. I've edited it in. :) tnx. – LPChip May 5 '16 at 21:00
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    Congestion doesn't cause huge latency spikes unless your router suffers from bufferbloat (an all-too-common bug). – Spiff May 6 '16 at 3:19

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