Defining Network Capacity
draft-ietf-ippm-bw-capacity-05

[Ballot comment]
> 2.3.4.  Definition: IP-type-P Link Usage
>
> The average usage of a link L, Used(L,T,I), is the actual number of
> ...
> The information
> transmitted across the link can be generated by any source, including
> those who may not be directly attached to either side of the link.
> In addition, each information flow from these sources may share any
> number (from one to n) of links in the overall path between S and D.

Why is the last sentence included? For measuring usage of L, it does
not matter.

[Ballot discuss]
This is a great document, I enjoyed reading it, and will probably employ it in my own work.

I do have a few issues, however:

> 2.3.3.  Definition: IP-type-P Path Capacity
>
> Using our definition for link capacity, we can then extend this
> notion to an entire path, such that the IP layer path capacity simply
> becomes that of the link with the smallest capacity along that path.
>
> C(P,T,I) = min {1..n} {C(Ln,T,I)}
>
> The previous definitions specify the number of IP layer bits that can
> be transmitted across a link or path should the resource be free of
> any congestion.  It represents the full capacity available for
> traffic between the source and destination.  Determining how much
> capacity is available for use on a congested link is potentially much
> more useful.  However, in order to define the available capacity we
> must first specify how much is being used.
>
> ...
> 2.3.7.  Definition: IP-type-P Available Path Capacity
>
> Using our definition for IP layer available link capacity, we can
> then extend this notion to an entire path, such that the IP layer
> available path capacity simply becomes that of the link with the
> smallest available capacity along that path.
>
> AvailCap(P,T,I) = min {1..n} {AvailCap(Ln,T,I)}

These definitions assume that the path capacity is only related to the capacity over each link. However, forwarding capacity of the routers in between will also have a significant impact, unless the routers are capable of forwarding at full line rate under all conditions (packet size, filters applied, IP version, going out from same or different line
card, etc)

Note that you could simply rule this out of scope, but if so, at least the document should be explicit about this limitation.

[Ballot discuss]
The authors clarify that IP options and all forms of IP packets are to be included in the calculations but, don't discuss the fact that frequently option packets and other "probing"  application packets (ICMP, traceroute) actually traverse a different forwarding path than other IP packets. Thus, by lumping them all together and counting them as if they are the same data may be erroneous. More text would be advised.

NOTE: given new text to be added by authors, I am clearing my discuss

[Ballot discuss]
The authors clarify that IP options and all forms of IP packets are to be included in the calculations but, don't discuss the fact that frequently option packets and other "probing"  application packets (ICMP, traceroute) actually traverse a different forwarding path than other IP packets. Thus, by lumping them all together and counting them as if they are the same data may be erroneous. More text would be advised.

[Ballot discuss]
This is a great document, I enjoyed reading it, and will probably employ it in my own work.

I do have a few issues, however:

> 2.3.3.  Definition: IP-type-P Path Capacity
>
> Using our definition for link capacity, we can then extend this
> notion to an entire path, such that the IP layer path capacity simply
> becomes that of the link with the smallest capacity along that path.
>
> C(P,T,I) = min {1..n} {C(Ln,T,I)}
>
> The previous definitions specify the number of IP layer bits that can
> be transmitted across a link or path should the resource be free of
> any congestion.  It represents the full capacity available for
> traffic between the source and destination.  Determining how much
> capacity is available for use on a congested link is potentially much
> more useful.  However, in order to define the available capacity we
> must first specify how much is being used.
>
> ...
> 2.3.7.  Definition: IP-type-P Available Path Capacity
>
> Using our definition for IP layer available link capacity, we can
> then extend this notion to an entire path, such that the IP layer
> available path capacity simply becomes that of the link with the
> smallest available capacity along that path.
>
> AvailCap(P,T,I) = min {1..n} {AvailCap(Ln,T,I)}

These definitions assume that the path capacity is only related to the capacity over each link. However, forwarding capacity of the routers in between will also have a significant impact, unless the routers are capable of forwarding at full line rate under all conditions (packet size, filters applied, IP version, going out from same or different line
card, etc)

Note that you could simply rule this out of scope, but if so, at least the document should be explicit about this limitation.

> 2.3.4.  Definition: IP-type-P Link Usage
>
> The average usage of a link L, Used(L,T,I), is the actual number of
> ...
> The information
> transmitted across the link can be generated by any source, including
> those who may not be directly attached to either side of the link.
> In addition, each information flow from these sources may share any
> number (from one to n) of links in the overall path between S and D.

Why is the last sentence included? For measuring usage of L, it does
not matter.

PROTO Write-up

(1.a) Who is the Document Shepherd for this document? Has the
Document Shepherd personally reviewed this version of the
document and, in particular, does he or she believe this
version is ready for forwarding to the IESG for publication?

Matt Zekauskas  is the document shepherd.
I have personally reviewed this version of the document, and feel
this version is ready to forward to the IESG for publication.

(1.b) Has the document had adequate review both from key WG members
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any concerns about the depth or breadth of the reviews that
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Yes. We have even have comments from another AD.

(1.c) Does the Document Shepherd have concerns that the document
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AAA, internationalization, or XML?

No.

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I have no specific concerns or issues with this document that the
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No IPR disclosure related to this document has been filed.

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This document requests nothing of IANA, and says so.

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There are no formal language fragments in this document.

(1.k) The IESG approval announcement includes a Document
Announcement Write-Up. Please provide such a Document
Announcement Write-Up. [detail elided--mjz]

Technical Summary

Measuring network 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, to provide a
common framework for the discussion and analysis of a diverse set
of current and future measurement and estimation techniques.


Working Group Summary

The working group has supported the document through the last
five revisions, and it has been uncontroversial.

Document Quality
The document has been given thorough review by the group over its
revisions, and in particular Joseph Kopena and Dan Romanescu have
given thorough reviews improving document quality.

Personnel
Document Shepherd: Matt Zekauskas
Responsible Area Director: Lars Eggert