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Author Topic: Packet Loss Confusion  (Read 2388 times)

artturnip

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Packet Loss Confusion
« on: July 17, 2015, 04:08:11 PM »

Hi everyone, I was wondering if anyone could clear up some confusion I have regarding UDP packet loss.

Scenario: I rent a VPS from OVH and run a VOIP server on it. Recently there's been a fairly high (10%) rate of packet loss for all users so I came to the conclusion that it was server side.

After contacting OVH with iperfs as proof, they sent the following message:

Quote
Hi

Thank you for providing me with the information, however your test is based on the UDP protocol.

UDP uses a simple connectionless transmission model with a minimum of protocol mechanism. It has no handshaking dialogues, and thus exposes any unreliability of the underlying network protocol to the user's program. There is no guarantee of delivery, ordering, or duplicate protection.

Under UDP there can be packet loss, this is why TCP is used.

My MTR doesn't indicate any packet loss over 20 packets:

Start: Fri Jul 17 15:32:50 2015
HOST:                             Loss%   Snt   Last   Avg  Best  Wrst StDev
  1.|-- balance-5418               0.0%    20    0.3   0.3   0.2   0.4   0.0
  2.|-- host81-148-128-1.in-addr.  0.0%    20   10.3  25.1   9.5 144.8  35.3
  3.|-- 213.120.182.141            0.0%    20    9.7  26.4   9.5 161.3  40.6
  4.|-- 213.120.161.82             0.0%    20   10.9  22.4  10.1 148.1  33.7
  5.|-- 31.55.164.55               0.0%    20   10.4  23.5   9.9 111.3  30.7
  6.|-- 31.55.164.107              0.0%    20   10.8  17.2  10.2  63.8  16.7
  7.|-- acc1-10GigE-0-2-0-13.bm.2  0.0%    20   16.1  17.7  16.1  33.6   4.0
  8.|-- core1-te0-15-0-17.ilford.  0.0%    20   19.5  20.7  16.5  53.3   8.0
  9.|-- peer6-te0-10-0-14.telehou  0.0%    20   18.0  20.8  17.4  75.9  13.0
 10.|-- ???                       100.0    20    0.0   0.0   0.0   0.0   0.0
 11.|-- gra-g1-a9.fr.eu            0.0%    20   21.1  27.8  20.4  88.5  17.7
 12.|-- rbx-s9-a9.fr.eu            0.0%    20   20.6  29.4  20.3 111.5  25.7
 13.|-- 136.ip-5-196-17.eu         0.0%    20   22.0  31.9  21.4 115.3  24.3
 14.|-- [my domain]        0.0%    20   25.2  36.6  20.8 158.8  37.7


The iperf which you have sent shows the bandwidth at 100 Mbits/sec. For me there isn't any issues regarding bandwidth nore packet loss on the server.

Surely if there's UDP packet loss then that's an issue and should be sorted out rather than basically saying "use TCP"?
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burakkucat

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Re: Packet Loss Confusion
« Reply #1 on: July 17, 2015, 06:07:46 PM »

Surely if there's UDP packet loss then that's an issue and should be sorted out rather than basically saying "use TCP"?

No, sorry, UDP can be totally lossy (100% loss) because that is how the protocol was designed. If a high degree of lossless delivery is required, then TCP would be more appropriate.
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Weaver

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Re: Packet Loss Confusion
« Reply #2 on: July 17, 2015, 11:08:50 PM »

timing: But saying something like “packet loss just happens” isn't good enough, whether tcp or udp or sctp or rtp or whatever you like. If something is dropping packets then the same thing could happen to tcp packets meaning horrific slowness, high costs and bad jitter on a tcp connection and tcp can't completely cover that up.
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artturnip

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Re: Packet Loss Confusion
« Reply #3 on: July 17, 2015, 11:25:35 PM »

Surely if there's UDP packet loss then that's an issue and should be sorted out rather than basically saying "use TCP"?

No, sorry, UDP can be totally lossy (100% loss) because that is how the protocol was designed. If a high degree of lossless delivery is required, then TCP would be more appropriate.

So why do VOIP applications use UDP over TCP? I can't choose which protocol to use for Teamspeak (the VOIP application mentioned) and so UDP is all I have.

Most online games requiring low latency also use UDP and on my home internet this isn't a problem so surely the problem doesn't lie with UDP but with the underlying packet loss?
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artturnip

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Re: Packet Loss Confusion
« Reply #4 on: July 17, 2015, 11:28:13 PM »

timing: But saying something like “packet loss just happens” isn't good enough, whether tcp or udp or sctp or rtp or whatever you like. If something is dropping packets then the same thing could happen to tcp packets meaning horrific slowness, high costs and bad jitter on a tcp connection and tcp can't completely cover that up.

It seemed as if I was being told that I've just to put up with packet loss.. AFAIK packet loss is considered to be detrimental to any internet connection - Even in small amounts.
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Weaver

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Re: Packet Loss Confusion
« Reply #5 on: July 18, 2015, 12:15:08 AM »

@artturnip -exactly. You were being fed something that while true is irrelevant. Saying we have a crap service so here's how to partially work around it is ridiculous. You should simply walk away.

I don't know if UKServers (http://www.virtualnames.co.uk/web_hosting.php) can do what you need, but I’ve been with them for well over ten years and think they're fantastic.
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