[Planetlab-users] question about packet loss

[Daekyeong Moon]

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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