[Asterisk-Dev] Jitter Buffer
Chris Wilson
chris at netservers.co.uk
Mon Jan 19 11:12:46 MST 2004
Hi all,
I've done a bit of searching in the Asterisk source and on Google, and it
seems to me that either there is no jitter buffer for SIP, or I can't find
it. However, there is a jitter buffer for IAX 1 and 2.
I'm running SIP (phones don't support IAX) over a wireless network shared
with data traffic, which causes some increase in jitter when large volumes
of data are transferred. Would it be useful to have a SIP jitter buffer,
is it something I could add, and would Digium be interested?
Could it be abstracted out of the IAX 1/2 jitter buffer code, which seems
to be roughly duplicated between the two modules? If so, does anyone have
any hints on what sort of interface I should provide to it, and where I
should put my source file?
Is there an Asterisk hacker's guide to explain how Asterisk does memory
allocation, callbacks, etc. and standards for data types, or should I just
try to copy what's present as best I can?
Is anyone willing to help me test and debug this?
Cisco VoIP phones seem to have particularly good handling of jitter and
packet loss. For example, I deliberately created 10% packet loss, and the
perceived call quality (to me) was about 99%. At 20% packet loss it was
about 90%. Budgetone phones seem to handle this very badly in my
experience, with every packet lost (or late) generating an annoying click
and a gap in sound. Can anyone else confirm or deny?
Can anyone point me to a standard for how reconstruction of lost packets
should be done, so I can look at implementing it for the jitter buffer?
Cheers, Chris.
--
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/ __/ / ,__(_)_ | Chris Wilson -- UNIX Firewall Lead Developer |
/ (_ ,\/ _/ /_ \ | NetServers.co.uk http://www.netservers.co.uk |
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