[Planetlab-users] question about packet loss

[Andy Bavier]

Hi,

Did you try it on some beta nodes?  It should be OK on them.  You can
get a list of beta nodes by logging into the PL web site and clicking
the Node Groups link.

Andy

On 8/8/08, Daekyeong Moon <dkmoon at cs.berkeley.edu> wrote:
> Hi Andy,
>
> Thanks.
> I tried on the same nodes with the toy udp sender/receiver, but it
> seems that I still have the issue.
> One interesting thing is such loss always starts from the sequence
> number 60.
> (As you can see in the program I sent you, the dumb toy program has
> nothing to do with the seq 60)
>
> (28 byte udp/ip header + 4 byte payload) / 1ms = 32KBps = 256Kbps
> I believe this is not much bw usage. Right?
>
>
> 57 4
> 58 4
> 59 4
> 797 4
> 798 4
> 799 4
>
>
> 57 4
> 58 4
> 59 4
> 469 4
> 470 4
> 471 4
>
>
> 57 4
> 58 4
> 59 4
> 1404 4
> 1405 4
> 1406 4
>
>
>
> Thanks,
>
> DK
>
>
> On Aug 8, 2008, at 8:52 AM, Andy Bavier wrote:
>
>> Hi,
>>
>> Ok I see what you mean. I believe the cause is a problem with the way
>> that the bandwidth limiter is configured on the nodes, and is fixed in
>> the software update running on the beta nodes. Can you try your test
>> on these nodes and see if it works as expected?
>>
>> Cheers
>> Andy
>>
>> On 8/8/08, Daekyeong Moon <dkmoon at cs.berkeley.edu> wrote:
>>> Hi Andy,
>>>
>>> Yeah, all nodes are planetlab nodes.
>>>
>>> Unfortunately, it does not always happen, and thus difficult to
>>> reproduce manually.
>>>
>>> Then, I'm wondering what if the receiver is highly overloaded.
>>> (say, w
>>> command show around 8.0)
>>> Can it drop packets for a long time? (e.g., more than a second)
>>>
>>> I did another very simple experiment.
>>> I used 216.165.109.79 as the receiver and 216.165.109.81 as the
>>> sender.
>>> (I guess they're on the same network.)
>>>
>>> The load average of the receiver was around 8, and the receiver
>>> dropped about 700 packets out of 6000, when the sender injected a 4
>>> byte udp packet every ms.
>>> Especially, it dropped consecutive packets. Here's a log snippet from
>>> the receiver.
>>> The first column is the seq number and the second one is the received
>>> payload size.
>>>
>>> ...
>>> 58 4
>>> 59 4
>>> 770 4  (big gap occurs here!! what happened!?)
>>> 771 4
>>> 772 4
>>> ...
>>>
>>> I wiresharked on the sender node and I could see the missing sequence
>>> numbers.
>>> (For some reason, wireshark on the receiver node didn't show packets
>>> at all)
>>>
>>> This is normal despite the same network?
>>>
>>> This experiment is fortunately reproduciable at this moment.
>>> The program I used is fairly simple udp server/client program with
>>> just 88 LOC.
>>> If you need it, I can send it to you (not to this group)
>>>
>>>
>>> Thanks,
>>>
>>> DK
>>>
>>>
>>> On Aug 7, 2008, at 11:46 PM, Andy Bavier wrote:
>>>
>>>> Hi,
>>>>
>>>> In your experiment, are both the sender *and* receiver PlanetLab
>>>> nodes?  If so, can you retry your experiment with only the sender or
>>>> receiver being a PL node?  I would expect the packet loss to occur
>>>> on
>>>> the sending side, since PL doesn't do any limiting of receive
>>>> bandwidth.
>>>>
>>>> If you can give me a way of reproducing your problem on some nodes,
>>>> I'll look into it more closely.
>>>>
>>>> Andy
>>>>
>>>> On Fri, Aug 8, 2008 at 8:02 AM, Daekyeong Moon
>>>> <dkmoon at cs.berkeley.edu> wrote:
>>>>> Hi,
>>>>>
>>>>> I'm seeing weird udp loss.
>>>>> I'm replaying traffic traces from some Internet application.
>>>>> The replayer is a very simple udp application injecting packets
>>>>> from a pcap
>>>>> file according to the packet interval recorded in the file.
>>>>>
>>>>> Each sender generates at most 50 udp packets per second for 2
>>>>> minutes, and
>>>>> each packet is 300 bytes on average.
>>>>> So, each sender consumes about 120Kbps, which is not much.
>>>>>
>>>>> A receiver receives packets from 7 senders (approximately 840Kbps),
>>>>> and
>>>>> reports timestamp using SO_TIMESTAMP.
>>>>> But, I found that the receiver sometimes doesn't receive any packet
>>>>> for more
>>>>> than 10 seconds.
>>>>> (select() call with 10 second timeout also fires.)
>>>>>
>>>>> Since, the traces don't have such big gap and the receiver receives
>>>>> from the
>>>>> 7 senders, this is quite abnormal.
>>>>> I repeated 200 times with random planet lab nodes in the US, and I
>>>>> don't
>>>>> think it's the issue of particular nodes.
>>>>>
>>>>> I'm just guessing it could be related to the receiver's bandwidth
>>>>> limitation.
>>>>> (e.g. dropping all packets until the next time window if bandwidth
>>>>> usage in
>>>>> a certain time window exceeds the Shared BW limit)
>>>>>
>>>>> Anybody experienced the same issue?
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> DK
>>>>>
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>>>>>
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