Subject: Multiplexing Scheme for RTP-Flows between Access Routers

From: Michael Menth <[email-masked]>
Date: Fri, 10 Mar 2000 11:11:59 +0100

Hello,

I would like to report on the results of our investigations on
multiplexing voice over IP using the RTP protocol suite.

The efficiency of multiplexing depends highly on the multiplexing
delay M: The longer the time for multiplexing is, the more packets
can be multiplexed and the more overhead is avoided. The maximum
allowed value for the (multiplexing and queuing) delay D  in the
mobile communication area is not fixed yet. It comes additional 
to the end-to-end delay of voice connections, therefore, it must be 
kept small. At the moment, values between 0.5 msec and 6 msec are 
discussed in 3GPP.

We assumed that the resulting RTP-flow is policed individually in a
strict QoS-IP network like in Integrated Services. Studies for D=1
msec have shown that the connection identifier (CID, maximum 256)
is too small to reach a good multiplexing gain for a single
RTP-connection. Consequently, to yield a good bandwidth
exploitation, either more than one RTP flows must be bundled
to one flow and be policed or spaced on a per flow basis or more 
than 1 octet should be spent in a general multiplexing framework 
for the CID value.

The paper contains several performance investigation on VoIP and
will be published at the "ITC Specialist Seminar on Mobile Systems
and Mobility", March 22 - 24, 2000, Lillehammer, Norway. It can be
downloaded from:

http://www-info3.informatik.uni-wuerzburg.de/staff/menth/Publications/

Best Regards,

   Michael

-- 
Dipl.-Inform. Michael Menth
University of Wuerzburg, Institute of Computer Science
Am Hubland, D-97074 Wuerzburg, Germany, room A212
phone: (+49)-931/888-6644, fax: (+49)-931/888-6632
e-mail: [email-masked]
WWW: http://www-info3.informatik.uni-wuerzburg.de/~menth