[Asterisk-Users] Codecs and bandwidth

[Tim Pushor]

I've seen several references to 'simplex' ulaw using 64k + overhead and 
'duplex' ulaw using 64k+overhead+64k+overhead (I wished that site was up).

Coming from this page: 
http://voip-info.org/tiki-index.php?page=Bandwidth+consumption, the 
following line strikes me:

(from near the top of the page) ... So even if one voice call sets up 
two 64 Kbit RTP streams over UDP over IP over Ethernet...

Also, other pages from the wiki seem to talk about this as well when 
computing bandwidth.

Is it because there are 2 RTP streams that don't know anything about 
each other, hence the 2x64k? Why would ISDN be any different?

Thanks,
Tim

BTW I am assuming that this has very little to do with the D channel in 
ISDN since the call has already been setup via SIP ..

Wiley Siler wrote:

>I assume ISDN accomplishes this since the PRI is set to use channel 24
>for signaling.  Your 64K channels is data and the control overhead is
>sent on the signaling channel.
>
>Actually, everything I have seen is around 80K full duplex for a uLaw
>channel with overhead.  That is point to point...
>
>W
>
>
>
>-----Original Message-----
>From: asterisk-users-bounces at lists.digium.com
>[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Tim Pushor
>Sent: Monday, July 18, 2005 9:22 AM
>To: Asterisk Users Mailing List - Non-Commercial Discussion
>Subject: [Asterisk-Users] Codecs and bandwidth
>
>Hi Friends,
>
>Something I'd like to shed some light on if possible - how is it that a 
>single ISDN conversation only uses 64K for bidirectional communication 
>(using ulaw, correct?), but on several occasions now have seen 
>references to ulaw voip conversations using 64K per side of the 
>conversation, plus packet overhead 
>(http://www.zytrax.com/tech/protocols/voip_rates.htm - seems to be down 
>now - plus other references) for a total of over 128K per ulaw 'full 
>duplex' voice conversation?
>
>Thanks
>Tim
>
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