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

From: "Patrik Arlos" <[email-masked]>
Date: Thu, 23 Jun 2005 10:11:59 +0200

Hi Phil,

With IP Layer Link Capacity are you referring to the capacity seen on the
Network to Link-Layer and Link to Network-Layer interfaces? Or do you mean
the Transport-Network, Network-Transport interfaces? I would argue for the
later, since this will be the capacity seen by the higher layers and
eventually the user/application. Using such a definition would simplify the
definition of capacity on other layers. 

Regarding utilization, at least on Ethernet the utilization is also based on
the frame rate. Small frames fill the link, but only use ~75% of the
bit-capacity. Will we not see the same from the higher layers, as the
payload size varies compared the headers introduced? If so, the utilization
cannot be based only on the bit count. 

/Patrik

Patrik Arlos
Tech. Lic Telecommunications systems
PhD Candidate Telecommunications
Blekinge Institute of Technology
School of Engineering, Telecommunications Group
371 79  KARLSKRONA
SWEDEN
+46 (0)455 385654 Office
+46 (0)733 800312 Mobile

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From: Joseph Ishac <[email-masked]>
Date: Thu, 23 Jun 2005 12:36:38 -0400

> definition of capacity on other layers. 

We mean IP Layer as in the definition of IP layer bits, which is the IP
header plus payload (regardless of content).  I'm not sure I understand
your definition though.

> cannot be based only on the bit count. 

The utilization is a fraction that is based on both the capacity (C())
and usage (Used()).  It is not based of the nominal capacity of the
link.  So, the Ethernet framing overhead will affect the value of C().
We actually have a small bit talking to this in section 3.

-Joseph

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From: Joseph Ishac <[email-masked]>
Date: Wed, 29 Jun 2005 15:28:15 -0400

Thanks to all who have commented thus far on the capacity draft.  In
addition to the notes sent to the list, we have received some feedback
directly.  I am going to try and summarize some of the more major issues
that resulted from those discussions.

Recently, another WG experimented with breaking down the issues into
individual threads.  That seemed to work well, so I'm going to attempt
and employ the same technique for this draft.

1. Correctly received bits

The current draft states that only correctly received bits at the
destination will be counted towards the IP Layer Link Capacity.  Our
intent was to exclude bits that could not be properly handled at the
IP layer (and thus reduces the capacity seen at that layer).  

Thus errors at the lower layers and packets that fail validation of the
IP header (RFC 1812 for version 4) would not be counted.  We did not
intend that to imply that all bits in the IP packet would need to be
"correct" as we are not concerned with what happens at the higher layers.

Currently we plan on making the above clearer in the draft, and I
believe that would satisfy most who have commented on this issue.

-Joseph