[VoiceOps] Question about Packet Jitter

[Schwarz, Albrecht (Albrecht)]

VoIP performance experts should be familiar with

- ITU-T Y.1541 concerning IPDV (IP packet delay variation = jitter); there are many sections on IPDV, particularily also on "aggregated PDV";

- IETF PMOL, ... IP performance metrics

- IETF AVT, ... RFC's for RTCP XR (RFC 3611, 5093) and ietf drafts on work in progress RTCP XR metrics

-Albrecht


 

> -----Original Message-----
> From: voiceops-bounces at voiceops.org 
> [mailto:voiceops-bounces at voiceops.org] On Behalf Of Jim Dalton
> Sent: Freitag, 29. Oktober 2010 14:15
> To: 'David Knell'; voiceops at voiceops.org
> Subject: Re: [VoiceOps] Question about Packet Jitter
> 
> > Jitter is an average measure of what's essentially noise (random 
> > variations in the arrival times of packets from a mean), and so I'd 
> > expect - for two jitter sources in series producing average 
> jitter of 
> > j1 and j2 respectively - the overall jitter to be sqrt(j1^2 + j2^2).
> > 
> > Intuitively, a packet which is late as a result of the first jitter 
> > source might then be further delayed or delivered early by 
> the second 
> > - so just summing the average jitter values isn't appropriate.
> > 
> > --Dave
> 
> [JD wrote:] Very good point.  The relationship of overall jitter to be
> sqrt(j1^2 + j2^2) makes sense.  However, I am having trouble 
> working through a proof of the math.  Any suggestions of a 
> reference on jitter that might address this?
> 
> Many thanks for your insight,
> 
> Jim D.
> 
> > -----Original Message-----
> > From: voiceops-bounces at voiceops.org [mailto:voiceops- 
> > bounces at voiceops.org] On Behalf Of David Knell
> > Sent: Friday, October 29, 2010 1:37 AM
> > To: voiceops at voiceops.org
> > Subject: Re: [VoiceOps] Question about Packet Jitter
> > 
> > On Thu, 2010-10-28 at 16:26 -0400, Scott Berkman wrote:
> > > The only portion missing is the jitter through the SBC 
> itself, which
> > really
> > > should be negligible.  Assuming that is 0, your equation 
> below would
> > be
> > > correct.
> > 
> > I think I'd disagree with this.  Jitter is an average measure of 
> > what's essentially noise (random variations in the arrival times of 
> > packets from a mean), and so I'd expect - for two jitter sources in 
> > series producing average jitter of j1 and j2 respectively - the 
> > overall jitter to be sqrt(j1^2 + j2^2).
> > 
> > Intuitively, a packet which is late as a result of the first jitter 
> > source might then be further delayed or delivered early by 
> the second 
> > - so just summing the average jitter values isn't appropriate.
> > 
> > --Dave
> > 
> > > -----Original Message-----
> > > From: voiceops-bounces at voiceops.org [mailto:voiceops-
> > bounces at voiceops.org]
> > > On Behalf Of Jim Dalton
> > > Sent: Thursday, October 28, 2010 8:34 AM
> > > To: voiceops at voiceops.org
> > > Subject: [VoiceOps] Question about Packet Jitter
> > >
> > > I have a question about calculating jitter.  Consider the call
> > diagram
> > > below.
> > > A SIP call flows from the source device to the Session Border
> > Controller
> > > (SBC)
> > > to the destination device.  All RTP packets are proxied 
> through the
> > SBC.
> > >
> > > +========+                    +=====+
> > +=============+
> > > | Source |  Ingress Call Leg  | SBC |  Egress Call Leg  | 
> > > | Destination
> > |
> > > | Device |------------------->|     |------------------>|   Device
> > |
> > > +========+                    +=====+
> > +=============+
> > >             Jitter Src to SBC
> > >           ------------------->
> > >
> > >                     Jitter Source to Destination
> > >           --------------------------------------------->
> > >
> > > If the packet jitter is known for the Ingress Call Leg from the
> > source to
> > > SBC and for end to end packet flow from the source to the
> > destination, is it
> > > possible to calculate jitter for the Egress Call Leg from 
> the SBC to
> > the
> > > destination device?
> > >
> > > I do not think the following relationship is accurate.
> > > (jitter Source to Destination) less (jitter Src to SBC) = (jitter 
> > > SBC
> > to
> > > Destination)
> > >
> > > Can anyone provide some guidance on this question?
> > >
> > > Thank you,
> > >
> > > Jim Dalton
> > > VoIP Least Cost Routing, Analysis, Billing
> > > 1.404.526.6053
> > > www.TransNexus.com
> > >
> > >
> > >
> > > _______________________________________________
> > > VoiceOps mailing list
> > > VoiceOps at voiceops.org
> > > https://puck.nether.net/mailman/listinfo/voiceops
> > >
> > >
> > > _______________________________________________
> > > VoiceOps mailing list
> > > VoiceOps at voiceops.org
> > > https://puck.nether.net/mailman/listinfo/voiceops
> > >
> > 
> > --
> > David Knell, Director, 3C Limited
> > T: +44 20 3298 2000
> > E: dave at 3c.co.uk
> > W: http://www.3c.co.uk
> > 
> > _______________________________________________
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> 
> 
> 
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