[Asterisk-Dev] How are IAX2 timestamps supposed to work?

[Derek Smithies]

Hi,
 When I was investigating the iax2 voip protocol, I found packet dumps the 
most useful thing to use.

 The latest windows version of ethereal had  a iax2 packet analyser built 
into it.

The timestamps are calculated from the start of call. A code analyssis 
will tell you the souce of the time value. From memory, it is the system 
clock.


> Firstly, non-voice frames get "artificial" timestamps that are offset from
> the last sent timestamp by 3ms.
I have a suspicion that 3ms offset was introduced for a reason. Which 
makes me wonder, could a malicous person create havoc by sending packets 
with bogus timestamps?


Derek.
================================================================================
 On Fri, 18 Jun 2004 steve at daviesfam.org wrote:

> 
> Hi,
> 
> Could someone who knows take a few minutes to explain in concept how 
> timestamps are supposed to work in IAX2?
> 
> The basic idea is clearly a "number of milliseconds since call start", but
> within that theory the practice is a bit more complicated:
> 
> Firstly, non-voice frames get "artificial" timestamps that are offset from
> the last sent timestamp by 3ms.
> 
> Secondly, timestamps have various sources - the system clock, somewhere 
> upstream, or counting audio samples.  Discontinuities seems quite 
> possible...
> 
> Thanks,
> Steve
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