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List:       sip-implementors
Subject:    Re: [Sip-implementors] is this a valid rtpmap attribute?
From:       "Dale Worley" <dworley () nortel ! com>
Date:       2009-05-26 18:42:06
Message-ID: 1243363326.3754.13.camel () victoria-pingtel-com ! us ! nortel ! com
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On Tue, 2009-05-26 at 09:21 +0300, Brocha Strous wrote:
> Is the following line valid:
> 
> a=rtpmap:101 telephone-event/000
> 
> What is the meaning of a 0 clock rate? And isn't it supposed to be a
> number? I tried to find somewhere a BNF specification for RTPMAP
> attribute lines but only found very general statements. What would be
> the correct way to parse a RTPMAP line into all its pieces that would
> account for the different syntaxes? Should the clock rate be treated
> as a string and not a number?

Looking at RFC 2833, especially section 3.5, the "rate" part of the
rtpmap specification means that the time units in the RTP
telephone-event packets are at that many per second.  E.g., the standard
value "8000" means that the timestamps are in units of 1/8000 second.

Given that, a rate value of zero is useless.

In your case, the standard value is 8000, and what we see is "000",
making it extremely likely that the line you see is a typo for

a=rtpmap:101 telephone-event/8000

Dale



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