Subject: RE: [ippm] I-D ACTION:draft-ietf-ippm-bw-capacity-00.txt

From: "Fardid, Reza" <[email-masked]>
Date: Tue, 21 Jun 2005 16:33:11 -0700

Hi Phil,

I have a couple of comments on this I-D on first glance:

1. Even though the goal is not to provide an exhaustive list of factors
that can reduce link and/or path capacity, an important factor worth
including is the impact of traffic policing and shaping on IP layer path
capacity.  SPs commonly use rate-limiting, e.g., in Metro Ethernet
networks, to either restrict the nominal physical link capacity (e.g.,
Ethernet over SONET) for a single customer or enforce traffic contracts
via sharing of link capacity among multiple customers (e.g., per VLAN).
Verification of path capacity can be challenging in such networks;

2. Bulk transfer capacity (BTC) is also relevant in the context of
end-to-end path capacity, even though its scope is limited as a TCP
throughput metric.  It might be useful to include it in the discussion
section.

A relevant reference is 

R. S. Prasad, M. Murray, C. Dovrolis and K. Claffy, "Bandwidth
estimation: metrics, measurement techniques and tools", IEEE Network,
Nov/Dec 2003, Vol 17, No. 6, pages 27-35.

Regards,
Reza Fardid

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Subject: [ippm] I-D ACTION:draft-ietf-ippm-bw-capacity-00.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the IP Performance Metrics Working Group of
the IETF.

	Title		: Defining Network Capacity
	Author(s)	: P. Chimento, J. Ishac
	Filename	: draft-ietf-ippm-bw-capacity-00.txt
	Pages		: 14
	Date		: 2005-6-21
	
   Measuring capacity is a task that sounds simple, but in reality can
   be quite complex.  In addition, the lack of a unified nomenclature on
   this subject makes it increasingly difficult to properly build, test,
   and use techniques and tools built around these constructs.  This
   document provides definitions for the terms 'Capacity' and 'Available
   Capacity' related to IP traffic traveling between a source and
   destination in an IP network.  By doing so, we hope to build a common
   language that can be used when discussing and analyzing a diverse set
   of current and future estimation techniques.

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From: [email-masked]
Date: Wed, 22 Jun 2005 21:44:40 -0400

Hi Reza: Thanks for your comments. Responses inline.

> Verification of path capacity can be challenging in such networks;

Yes, you are right  of course; a service provider can use shaping to 
limit apparent capacity of a logical link (like VLANs).  However, the 
definition tries to capture capacity (but does not say how to measure 
it), no matter how the nominal capacity is reduced or impaired (i.e. 
whether deliberately or not). We can add shaping (policing is another 
matter) to the list, but it will still be incomplete.

> throughput metric.  It might be useful to include it in the discussion

I am not sure how BTC is relevant here. We are not trying to do a 
survey of capacity-related metrics, but only trying to define what two 
quantities are (regardless of the transport layer protocol).

> Nov/Dec 2003, Vol 17, No. 6, pages 27-35.
Thanks for the reference.

Regards,
Phil Chimento