[cisco-voip] SIP phone jitter, how do I find the culprit?

[Jason Dance]

Hello all!

 

I am trying to work through a rather puzzling SIP issue on my CUCM 8.6
system at the moment.  We have 10 non cisco SIP phones connected to our
Call Manager, and we are experiencing a bit of jitter on certain
inbound/outbound external calls (there doesn't sem to be a clear pattern
though) and the audio on one side will sound robotic (we call it
autotuning).  

 

We use 2 x Cisco 2811 routers, one hosting a SIP trunk to our Telco
(runs CUBE, and has DSPs for codec translation), and the other is for a
ISDN PRI trunk (also have enough DSPs to cover the channels).  Calls
that hit the PRI trunk seem to do ok, so I think this is narrowed to a
SIP phone => CUCM => SIP trunk issue.  We use G.722/711 within the
region/device pool assigned to the phones and CUCM, and we also use
G.722/711 between the phones/CUCM and the region/device pool the CUBE is
assigned to.

 

For our switching infrastructure, we use 3750s for access layer with
fiber uplinks to our 6509 distribution/core switch.  The 2811s are
connected to the 6509.  Both sets of switches have QOS enabled, but I
profess that I do not understand it at all well enough to mentally
picture how it would affect traffic flows on this issue.

 

With the above in mind, I'd appreciate any suggestions on:

 

1.) Some good methods I could use to track down where the jitter delay
is being introduced.

2.) What path could I expect the SIP traffic to take? (I think the SIP
legs go like: SIP phone <=> CUCM <=> CUBE <=> SIP provider, but I am not
sure).

 

Thanks in advance,

Jason

 


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