[cisco-voip] Weird Conference Voice Quality

[Wes Sisk]

Vandy,

If audio coming from the source device to the conference device has large,
irregular jitter, then everyone listening to the conference will be
affected.

Simple way to test this out:
setup conference with remote users and 1 central user.
have all remote users go on "mute" (no RTP stream generated on mute)
have central user speak.
How is voice quality?

Now, have everyone except 1 remote user go on mute.
How is voice quality?

We need to make sure those streams coming from the remote sites are "good"
with very low jitter as the 6608 uses a static dejitter buffer in contrast
with most ipphones and gateways which use dynamic jitter buffers.  This
makes fragmentation critical on the WAN links.

CSCdx78486 6608 configured as CFB has a static jitter buffer, needs adaptive
Problem Description:  Voice quality suffers with choppiness when conference
particants are located across low speed links and the device providing for
conferencing is the 6608.

Workaround:  None

/Wes

> -----Original Message-----
> From: cisco-voip-bounces at puck.nether.net
> [mailto:cisco-voip-bounces at puck.nether.net]On Behalf Of Vandy Hamidi
> Sent: Wednesday, July 21, 2004 11:30 PM
> To: cisco-voip at puck.nether.net
> Subject: [cisco-voip] Weird Conference Voice Quality
>
>
> Hey guys,
> I'm having a weird problem that isn't making sense
>
> I have a 6608-T1 blade in my main office performing conferencing for
> most of the remote offices in the company.  I know, not recommended, but
> read on.
>
> All the offices are connected Hub/Spoke to the main office and I have
> QOS setup (supposedly correctly) on my wan links and call quality is
> great.  I've tested the QOS by maxing out the line during voice calls.
>
> We've been receiving user complaints of voice quality problems.  Cutting
> out, delays, overall chopping communication.  All these complaints are
> when they are on conference calls.
>
> We've performed testing and during high wan usage the conference call
> quality becomes horrible to/from the remote sites and sometimes for all
> users for example I'll have a hard time understanding a conference
> attendee in my own office.
> We're able to reproduce with windows copies during conference calls.
>
> 1) Why is the voice quality ok with phone to phone calls, but become
> horrible during a conference call.
> 2) Does the 6608-T1 blade change/alter the QOS/TOS bits on the packets?
> 3) Why would this issue affect local attendee conference quality when
> everyone is connected to the same switch where the 6608 blade is.
>
> TIA,
>
> 	-=Vandy=-
>
>
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