[cisco-voip] Jitter Question

[Patrick Diener]

found also something to quote :-)

slide from "Implementing Cisco Quality of Service (QOS) v2.1" course...

Patrick

On 3/8/07, J. Oquendo <sil at infiltrated.net> wrote:
> Patrick Diener wrote:
> > bottom line:  jitter level should not be greater than 30 - 35ms...
> > unfortunately on a quick search on cisco.com I could not find any docu
> > to back that value...
> >
> I don't know where you got the 30-35ms range from so I quote again from
> the DQoS book:
>
> As per:
>
> Cisco DQOS Exam Certification Guide
> Wendell Odom and Michael J. Cavanaugh
> Copyright (c) 2004 Cisco Systems, Inc.
>
>
> ONE WAY DELAY BUDGET GUIDELINES
> *1-Way Delay (in ms) Description*
> 0–150 ITU G.114's recommended acceptable range
> 0–200 Cisco's recommended acceptable range
> 150–400 ITU G.114's recommended range for degraded service
> 400+ ITU G.114's range of unacceptable delay in all cases
>
> Some flows tolerate loss better than others do. For instance, the human
> ear can detect loss of
> only 10 ms of voice, but the listener can generally understand speech
> with such small loss. Cisco
> digital signal processors (DSPs) can predict the contents of lost voice
> packets, up to 30 ms when
> using the G.729 codec.
>
> Lost voice packets result in the receiver having a period of silence
> corresponding the
> length of voice payload inside the lost packet(s). With two consecutive
> G.729 packets
> lost, 40 ms of voice is lost; the G.729 codec cannot predict and
> generate replacement
> signals when more than 30 ms of consecutive voice is lost. A single lost
> G.729 packet
> would only cause a 20-ms break in the voice, which could be regenerated.
> So, a single
> lost packet is not perceived as loss in a G.729 call.
>
> No luck searching through the book on 35 ms or 35ms so I tried 40 ms & 40ms:
>
> Page 862
> Instantaneous buffer overrun occurs when a switch port TX queue fills
> for an instant
> causing packet loss, which can adversely affect real-time applications.
> In a VoIP
> conversation, for example, 40 ms of congestion causes an audible clip in the
> conversation.
>
> Page 82
> In Figure 1-23, the playout begins at the statically set playout delay
> interval—40 ms in this
> case—regardless of the arrival time of other packets. A 40-ms de-jitter
> playout delay allows
> jitter to occur—because we all know that jitter happens—so that the
> played-out voice can
> continue at a constant rate.
>
>
> --
> ====================================================
> J. Oquendo
> http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x1383A743
> sil . infiltrated @ net http://www.infiltrated.net
>
> The happiness of society is the end of government.
> John Adams
>
>
>
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