[Lanforge] Jitter

[Rasmus Bauck]

>Rasmus Bauck wrote:
>>
>> I'm back from a week off, and straight on to a new challenge with the

>> LANforge software.
>>
>> We're trying to emulate a network with jitter problems, but we are
not 
>> sure if we are doing the setup process properly. It seems like all
the 
>> packages that experience jitter, will be delayed with the amount of 
>> time specified in the max_jitter parameter (i.e. it is acting more 
>> like a latency). Our endpoint decoder will accept up to 200 ms
jitter, 
>> before considering a packet as dropped. However, if we set max_jitter

>> to 1000 ms and force jitter to be applied to all packages, the only 
>> result is that the entire data stream is being delayed by 
>> approximately 1 second (max_jitter plus the unavoidable additional 
>> network latency).
>>
>> Are we doing something wrong here or is this a known problem with 
>> LANforge?
>>
>Jitter is just random latency. If you apply jitter to every packet, it 
>becomes similar to delay and actually
>decreases over-all jitter. My suggestion is to set jitter-frequency to 
>around 1-10% and jitter to around 500ms.
>
>This means that 1-10% of the packets will be delayed an additional 
>1-500ms. If you set the max jitter to only
>200, then very few of the packets will be delayed by a full 200ms.
>
>Please let me know if this provides more realistic jitter patterns for 
>your testing.
>
>Thanks,
>Ben

Hmm, I agree with most of what you are saying, but if we apply jitter to
100% of the packages, shouldn't they then all be delayed by a RANDOM
amount of ms (between 1 and max_jitter), and not all delayed by the
max_jitter? The behavior we want is similar to what you are describing
for your suggested settings, only we want it to apply to all packages.
Unfortunately, I haven't yet had time to do much more testing on whether
the results are more reasonable with your suggested settings, I'll get
back to it when I have time.

Another question, what distribution is used for the random jittering?
Uniform, normal, or any other distribution?

Thanks again, Ben!

Rasmus