-----Original Message----- From: Pete Kruckenberg [mailto:pete@kruckenberg.com] Sent: Tuesday, May 29, 2001 12:10 PM To: nanog@merit.edu Subject: RE: QOS or more bandwidth
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Voice-over-IP benefits from statistical multiplexing as much, if not moreso, than any other application. A toll-quality voice call runs at ~5-6kbps (factoring silence suppression and RTP header compression) vs. 8kbps across compressed TDM.
Do you mean G.723.1? Let's put aside that some people do not consider G.723.1 to be toll-quality. Ignoring that, I would call your 5-6 kbps number to be compression rather than statistical multiplexing. The voice packets still come out periodically every 30ms or so. The only significant statistical multiplexing you get with voice is due to silence suppression. Also, how do you actually achieve 5-6 kbps when you consider the IP overhead? Prabhu ---------------------------------------------------------------------- Prabhu Kavi Phone: 1-978-264-4900 x125 Director, Adv. Prod. Planning Fax: 1-978-264-0671 Tenor Networks Email: prabhu_kavi@tenornetworks.com 100 Nagog Park WWW: www.tenornetworks.com Acton, MA 01720
On Tue, 29 May 2001, Kavi, Prabhu wrote:
Voice-over-IP benefits from statistical multiplexing as much, if not moreso, than any other application. A toll-quality voice call runs at ~5-6kbps (factoring silence suppression and RTP header compression) vs. 8kbps across compressed TDM.
Do you mean G.723.1? Let's put aside that some people do not consider G.723.1 to be toll-quality. Ignoring that, I would call your 5-6 kbps number to be compression rather than statistical multiplexing. The voice packets still come out periodically every 30ms or so. The only significant statistical multiplexing you get with voice is due to silence suppression.
Also, how do you actually achieve 5-6 kbps when you consider the IP overhead?
This was information that came back from one of our test networks, that I didn't participate in personally, so I may be speaking apples to oranges. I have done the theoretical numbers, an 8kbps raw stream takes ~21kbps without IP header compression (mostly because of the packet-per-30ms requirement). The numbers that came back from the test showed with RTP header compression (takes care of some of the IP header over head, at the cost of some CPU state-tracking) less than 8kbps. I was surprised. Maybe I should look into it further, but I had heard similar numbers in casual conversation with other people. Curious what others would consider 'typical' bit rate for a "toll-quality" (as far as the users are concerned) VoIP session, incorporating the various compressions and optimizations that are available. Pete.
participants (2)
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Kavi, Prabhu -
Pete Kruckenberg