[asterisk-users] jitterbuffer

[Tim Nelson]

----- "Jeff LaCoursiere" <jeff at jeff.net> wrote:
> On Thu, 8 Apr 2010, Tim Nelson wrote:
> 
> > ----- "Jeff LaCoursiere" <jeff at jeff.net> wrote:
> >> What is the consensus on using the 1.4 jitterbuffer?  Do most
> people
> >> enable it?
> >>
> >> We have a "PSTN" server that has our RBS T1 trunks in a central
> >> location,
> >> then have clients that connect via SIP to us for access to those
> >> trunks.
> >> Most of them are just fine, but lately we have a handful that are
> >> having
> >> latency and jitter issues.  I am hesitant to just turn on the
> jitter
> >> buffer in zapata.conf on the PSTN server for fear of impacting the
> >> clients
> >> that are "just fine".
> >>
> >> Should I be?
> >
> > I'm using the 1.4 jitterbuffer extensively as many of my customers
> have 
> > poor connectivity (lossy wireless, satellite, etc). It functions
> well, 
> > albeit keep in mind you'll likely need to do some fine tuning to get
> it 
> > just right.
> >
> 
> I guess that is part of my question - it would seem to me that
> "tuning" is 
> basically sizing the buffer, correct?  And that the tuning would be 
> different from client to client, as their latency/jitter needs will be
> 
> different.  How did you handle that aspect?  Did you just keep playing
> 
> until you found something that was a best fit for all clients?

The tuning is typically done at installation time to find a proper setting, then with a bit of headroom for those 'problem times'. I utilize the jitterbuffer on both SIP and IAX2 channels for both sides of the connection (our systems, and customer premise device).

> 
> I kind of understand that the dejitter must happen on the way "out" as
> the 
> data gets placed onto a zap channel, and that the other direction
> should 
> be dejittered at the customer's phone or adapter.  In our case this is
> 
> mainly Polycom IP 501s.  I suppose some amount of tuning there will
> help 
> what our client hears.
> 
> But the phones are on a 100mb LAN.  So would it be worthwhile to force
> a 
> jitterbuffer on chan_sip on the asterisk server sitting at the
> client's 
> location?

I would not think you'd need to worry about jitter on a "normal" 100mbit LAN unless there is heavy traffic or people are running their PC's through the phone (don't remember if the 501 has two ethernet ports...). Typically the quality issues are introduced on your WAN connectivity between the premise system and your hosted system aka 'The Big Internet'.

> 
> Sorry for trhe vague questions.  I think this would be a great topic
> for 
> someone's BLOG - I haven't found too much in the way of advice via
> Google 
> this morning.
> 

Working with the jitterbuffer and general quality tuning seems to be a bit of a black art, specifically over 'challenging' connectivity. Everyone has a blog these days(except me I suppose), you should post your findings to yours. :-) 

--Tim