Subject: [ippm] RFC3393 selection function question

From: "Perser, Jerry" <[email-masked]>
Date: Tue, 1 Apr 2003 13:04:42 -0800

I have a question about Type-P-One-way-ipdv selection function F.  In
section 2.2 it discuss a parameter "F, a selection function defining
unambiguously the two packets from the stream selected for the metric."

Can F be "two consecutively received packets?"  Looking at Figure 1 in
section 2.2, if packet P(j) is lost, is "ddT = dTk - dTi" still valid?

I can not think of a reason why not, but I wanted a second opinion.

Thanks in advance.

Jerry.

___________________________________________________________ 
Jerry Perser                         Spirent Communications
Director of Test Methodology         SmartBits Division 
Phone: 818.676.2320                  26750 Agoura Road 
Lab:   818.676.2337                  Calabasas, CA, 91302 
Cell:  818.292.6457                  Corp:  818.676.2300

_______________________________________________
ippm mailing list
[email-masked] 
https://www1.ietf.org/mailman/listinfo/ippm

---

From: Philip Chimento <[email-masked]>
Date: Tue, 01 Apr 2003 16:43:09 -0500

Hi Jerry: 
Well, yes and no. The idea was to give some flexibility to the 
definition so that groups such as the ITU that wanted to define IPDV as 
max_delay-min_delay might do so. So you could define a selection 
function that selects every 3rd packet. But the selection function, 
once chosen, is fixed. So in the case you bring up, if your selection 
function is contiguous packet pairs, then it is fixed and if you lose a 
packet, you lose 2 samples (see discussion of lost packets in the RFC). 
As the RFC says, you have to make explicit exactly what the selection 
function is so that anyone using your measurements knows exactly what 
they mean.

Regards, Phil Chimento 

-- 
Phil Chimento             Ericsson IPI
Phone: 240-314-3597	  7301 Calhoun Place
[email-masked]   Rockville, Md. 20855
-----------------------------------------------------

---

From: Al Morton <[email-masked]>
Date: Tue, 01 Apr 2003 17:02:22 -0500

I agree, Phil. Using "consecutive received packets"
would have variable pairings, depending on loss.
The selection function applies at the sending side,
is that correct?

Al

---

From: Philip Chimento <[email-masked]>
Date: Tue, 01 Apr 2003 17:06:57 -0500

Hi Al: Yes. That was the intent. Perhaps it should have been clearer. 
Regards, Phil