[asterisk-dev] zaptel timer for sip to iax proxy

Mark Spowage spowage at gmail.com
Mon Nov 10 07:35:24 CST 2008

clue #3

when gtalk is not loaded (gtalk/jabber ) then it is fine. Using Echo
on the remote asterisk, a sip phone will proxy via the embedded board. perfect

so ? somehow gtalk is stomping on iax.. ha ha that's cute.

more news to come i guess,though i dont relish ripping into the code.

perhaps backing off from 1.6 to 1.4 is worth a try now.


On Mon, Nov 10, 2008 at 7:07 AM, Mark Spowage <spowage at gmail.com> wrote:
> clue #2
> The first test today was to replace the embedded asterisk side with
> a pc, and test with the Echo command. Voila, no problem.
> Interesting, this problem came about after adding gtalk to the embedded
> asterisk :)..
> Gtalk from embedded to embedded is just fine, however embedded
> to asterisk (gateway) via iax is choppy. Simple divide and conquer.
> Well perhaps back off on gtalk for a start.  Why the embedded board
> chops up iax and not gtalk is peculiar.
> Any suggestions are welcome.
> For now i will remove gtalk.. and try to doctor iax.
> Though now i am considering investing time in gtalk to do without iax,
>  now that should shake a few trees in the jungle :)
> Why hang on to iax if gtalk can be made to deal with multiple inbound calls ?
> On Mon, Nov 10, 2008 at 5:44 AM, Tim Panton <thp at westhawk.co.uk> wrote:
>> On 10 Nov 2008, at 04:56, Mark Spowage wrote:
>>> if just ONE sip phone is proxied , will IAX get choppy without a
>>> zaptel timer ?
>>> tests here at times are ok and other times often choppy
>>> a zaptel timer seems to be required for trunking, but why bother for
>>> just a few channels, a major effort
>>> to get zaptel and a timer integrated,as well as more memory for an
>>> embedded machine short on memory.
>>> now if trunking is not used, then why would iax be choppy for serving
>>> as a sip proxy or bridge between sip phones ?
>>> a zaptel timer is on the main iax server side, but NOT on the
>>> embedded side
>>> gtalk never sounds choppy , so what is iax all chopped out about ?
>>> ast 1.6 & 1.4 both sound ok at times and choppy at times as well
>>> currently 1.6 is on the embedded side and 1.4 on the server.. perhaps
>>> they both need to be the same version
>>> is this some kind of iax circus ? :)  help ! sinking in the iax
>>> choppy sea
>>> playing musiconhold from either side can come in chopped as well,
>>> where as gtalk is always smooth..
>>> grief !
>> Mark, I think we need some more context to help answer properly.
>> In the meanwhile here is my understanding of the situation....
>> chan_iax (and most of asterisk) is externally clocked, i.e. if it is
>> bridging a pair of
>> channels then receiving an inbound voice frame will cause a voice
>> frame to
>> be sent out of the other end of the bridge. This works pretty well in
>> cases where
>> the incoming audio is being sampled (and sent) at a constant rate.
>> There are a number of places where this won't work - e.g. meetme, where
>> there isn't a single channel to use as a clock (each channel will
>> drift slightly
>> wrt the others), in this case Asterisk derives timing from the kernel,
>> either
>> via a real telephony device (e.g. a PRI card) or from a kernel resource
>> (timers etc) via zap_dummy.
>> IAX trunking is another of these examples - audio from several channels
>> need to be put into a single packet, so asterisk uses the kernel timer
>> to decide when to send a packet. (Note this is _not_ the same as
>> just using IAX to connect to a ITSP, IAX trunking tries to save on
>> headers
>> by multiplexing several calls into a single packet).
>> I'm guessing what you are seeing is the difference in timing in the
>> softphone
>> you are using - The IAX one is probably not using the local audio
>> hardware to
>> generate the timing, whereas the Gtalk one is.
>> Might that make sense ?
>> If not, give us some more clues ;-)
>> T.
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