[Planetlab-users] question about packet loss

Daekyeong Moon dkmoon at cs.berkeley.edu
Fri Aug 8 16:41:42 EDT 2008 

Hi Andy,

Sorry. I misunderstood.

I used planetlab3.csail.mit.edu as the receiver and  
hptest-1.cs.princeton.edu as the server.
I repeated 10 times, and it seems to work. Thanks!

Can you apply the fix to other regular nodes?
My experiment needs to randomly select 16 nodes every iteration. So, I  
need more nodes.

By the way, is there anyway to see and set my bandwidth limitation?
I'm wondering whether the net_max_rate (kbps) attribute can be set by  
a user.

Thanks again,

DK


On Aug 8, 2008, at 11:40 AM, Andy Bavier wrote:

> 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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