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Re: reduce jitter in routed network for voip applications

2005-03-28 04:06:06
RTP is transparent at the transport layer. We analyse TCP and UDP:
TCP is connection oriented and so the communication begins with the
definition of a virtual circuit.
A virtual circuit is a temporary connection of sequence nodes with relative
reservation of bandwidth.
A connection oriented service gives the certainty that all information units
use the same nodes with a same medium latency.
Same latency maintains reduced the jitter.

UDP is connection less protocol and so routing and forwarding functions are
executed for any information unit in arrival to a node.
Information units with the same destination address can use different path
and so the latency can be different.
A variable delay increases the jitter.

I think that RTP should use a layer 4 connection oriented protocol (like
TCP) but without retransmissions of information units with excessive delay
or errors (like UDP).

What do you think about this?





----- Original Message ----- 
From: "Dean Anderson" <dean(_at_)av8(_dot_)com>
To: "Daniele Giordano" <d(_dot_)giordano(_at_)fastpiu(_dot_)it>
Cc: <ietf(_at_)ietf(_dot_)org>
Sent: Monday, March 28, 2005 2:00 AM
Subject: Re: reduce jitter in routed network for voip applications


On Sun, 27 Mar 2005, Daniele Giordano wrote:

voip applications use connectionless layer 4 protocols and this
increases
jitter. A layer 4 connection oriented protocol limits jitter but it must
not
use packet checks in voip applications.

Connection oriented protocols don't limit jitter. Jitter is the same no
matter what. However, a very late packet is discarded by a jitter buffer.
(you don't care what joe said 10 seconds ago--if it didn't get here in the
jitter buffer, its too late.)  But it would not be discarded by a
connection oriented protocol. You'd hear what joe said 10 seconds ago, and
then you would have to wait 10 seconds to hear what joe just said. This is
OK for streaming a song. Its not fine for two way voice.

Is there an intefrace between TCP and UDP? Isn't there a "TDP" (transfer
datagram protocol) that joins the two features?
What do you think about this?

Right protocol for the right purpose.  We already have RTSP for streaming,
and RTP for voip.

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