Re: Comparing two pcap files for latency

[jobhunts02 () aol com]

Since it is my H.263 video that Is being 
corrupted, is there a similar way to 
analyze H.263 streams?


On Feb 1, 2011, at 11:22 AM, Martin Visser <martinvisser99 () gmail com> wrote:

> All streaming media protocols need to deal with latency (or delay),
> but more importantly variation in latency (or jitter). (Or as you put
> it, fluctuation of latency). They accomplish this by having a jitter
> buffer. When you start a stream, the receiver will buffer a certain
> amount of data before playing it out. That way, if packets are delay,
> a little, the receiver has something to play while it waits for the
> outstanding data.
>
> As such, absolute latency isn't  important Provided that the buffer is
> large enough to accommodate for the maximum jitter, it will always
> have something to play. The receiver can wait as long it likes for the
> first packet, as long as it doesn't start playing until it has enough
> to accomodate with the variation in delay. Wireshark can show jitter
> if the stream is carried inside RTP. Just look in Telephony:RTP. If
> Jitter is exceeding your buffer size you have a problem.
>
>
>
> Regards, Martin
>
> MartinVisser99 () gmail com
>
>
>
> On 2 February 2011 04:03,  <jobhunts02 () aol com> wrote:
> > The reason I want this information is that I am streaming video over a communications link and am getting poor 
> > quality video.  I used the program TPCAT and found that no packets are being lost.  I assume that the poor video 
> > must be due to latency.  I'd like to look at the total latency from source to destination and see if it fluctuates.  
> > If it does, I will then see if there is a backlog in Linux on either end or in the link.  TPCAT is supposed to be 
> > able to measure latency but it stops responding when there are large numbers of packets like in a video stream.  The 
> > author told me this is a known issue.  I was hoping there might be an alternative tool to measure latency similar to 
> > TPCAT that compares pcap files for latency.
> >
> >
> > On Jan 31, 2011, at 4:44 PM, Guy Harris <guy () alum mit edu> wrote:
> >
> > > On Jan 31, 2011, at 3:20 PM, Martin Visser wrote:
> > >
> > > > As Guy has said, you can't use the absolute times unless you can
> > > > ensure the machines at each end are millisecond synchronized.
> > >
> > > ...and that the time stamps given to transmitted and received packets correspond to the times you're interested in. 
> > >  If you care *only* about transit time on the network - e.g., the time from the point at which the first bit of the 
> > > packet is put onto the first network hop and the time at which the last bit of the packet is received from the last 
> > > network hop - then those time stamps almost certainly do *not* correspond to the times you're interested in.  If 
> > > you care about latency *including network stack latency*, it might be better, although the time stamp applied to 
> > > outgoing packets is probably later than the time at which the outgoing packet was initially handed to the network 
> > > stack, and the time stamp applied to incoming packets is probably earlier than the time at which the incoming 
> > > packet was handed up from the network stack.
> > >
> > > =
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