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<p class=MsoNormal>Hi<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’m trying to ensure optimal bandwidth usage for our
VoIP solution. The last mile link to the customer is ATM.<o:p></o:p></p>
<p class=MsoNormal>I have done some calculations, and unless I’m missing something
here it seems 1 voice packet will always be split across two ATM cells. I’m
not finding a good doc that can break this down into detail.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Voice usage per packet:<o:p></o:p></p>
<p class=MsoNormal>Codec: G729a, using 20ms sample size, 20 byte payload = 20
bytes.<o:p></o:p></p>
<p class=MsoNormal>Layer3: IP/RTP/UDP header = 40 bytes<br>
Bandwidth required = at least 60 byte packet.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>ATM Cell: 53 bytes – 5 overhead – 8 AAL trailer<o:p></o:p></p>
<p class=MsoNormal>Bandwidth available = at most 40 bytes.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>My first question is: How does the Cisco voice bandwidth
calculator fit G729 on 10ms or 20ms or 30ms payload into 1 Cell? Do they assume
cRTP is enabled?<o:p></o:p></p>
<p class=MsoNormal>Then, I’m not finding a good doc on how to effectively
calculate bandwidth usage for cRTP across ATM. Configuring it via a virtual–template
interface seems straight forward though.<br>
Lastly, if I manage to get a G729 packet squeezed into 1 cell, apart from the
obvious save in bandwidth consumption, should there be any other improvement in
the solution as a whole?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Regards,<o:p></o:p></p>
<p class=MsoNormal>kris <o:p></o:p></p>
<p class=MsoNormal><span lang=EN style='font-size:8.0pt;font-family:"Arial","sans-serif"'>"Morality
is moral only when it is voluntary." Lincoln Steffens</span><span
style='font-size:8.0pt'><o:p></o:p></span></p>
<p class=MsoNormal><o:p> </o:p></p>
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