Subject: RE: One-way delay/vs round-trip delay

From: KERBERENES Jacques CNET/DAC/LAN <[email-masked]>
Date: Mon, 6 Dec 1999 16:30:22 +0100

HI all,

My understanding of the IPPM work is that the RFCs is Standards tracks.
Thus, one (end user, ISP/NSP) can choose to implement them or not. Althought
I don't participate to IPPM WG I have got all the mailing-list archives. I
have often read funnies exchanges  and in my mind I has been very confussed
: who tell the true ? 
Now my opinion is the following and has become very simple. When I am in my
garden I need different tools to do different things. Monitoring the
Internet is certaintly a more difficult issue. But the problem is the same :
what do you want to do ? One-way delay and  packet loss is very useful in
some situations, and round-trip measureaments is only what we need for other
purposes. For example FT hosts a Surveyor's boxe to monitor the oversea
links because the traffic is assymetric. I am also trying to host other
Surveyor's boxes for some of our domestic links , because since the King
LouisXIV France is a very centralized  and the traffic is also assymetric
between Paris an other towns in the country. But we also intend to use
two-way probes for monitoring our backbone and customers backbones. So where
is the problem : use the appropriate tools where there are needed, and use
cheaper tools when this is only what we need.

Jacques

> ----------
> De : 	Vern Paxson[SMTP:[email-masked]]
> Date :	Saturday, December 04, 1999 8:08 AM
> A :	Glossbrenner, Kenneth C.
> Cc :	IETF IPPM (E-mail); Annie Gravey (E-mail); Neal B. Seitz (E-mail)
> Objet :	Re: One-way delay
> 
> Also, one of the goals for IPPM metrics is that when possible they should
> be composable.  As you can in principle derive round-trip delay from two
> one-way delay measurements, this in a sense makes a one-way delay metric
> more fundamental than a round-trip delay metric.  The fact that the
> composition
> is not in practice trivial (i.e., just adding the two measurements gets
> you
> the wrong answer, since there's some additional delay at the far end
> turning
> around the packet) is a feature, because it highlights that a round-trip
> measurement is not simply a network measurement but also measures
> something
> about the end host.
> 
> 		Vern
>