Subject: Re: [ippm] Question/comment on RFC5136

From: [email-masked]
Date: Mon, 09 Aug 2010 07:26:05 -0500 (CDT)

Remember, what we are talking about here is the IP capacity, not raw link capacity. So the definition includes the number of IP layer bits that can be transmitted by the source and received by the destination. Lots of things make this capacity smaller than the nominal link capacity measured at the physical layer. Some things that can reduce the IP layer capacity include: node backplane capcity, NIC implementation, queueing structure, buffer management, etc. etc. The notion of "middle-box" capacity is, in effect, included in the definition of IP capacity.

Regards,
Phil Chimento

Aug 9, 2010 12:00:47 AM, [email-masked] wrote:

Hi folks,

I'm reading RFC5136 "Defining Network Capacity", and I have some question/comment on it.

In section 2.1, the definition of link and path, it reads:

We then define a path P of length n as a series of
links (L1, L2, ..., Ln) connecting a sequence of nodes (N1, N2, ...,
Nn+1). A source S and destination D reside at N1 and Nn+1,
respectively.

I'm a bit confused by this definition,
it seems the middle-boxes (i.e., nodes N2, N3, ..., Nn) are not included (in this definition) in the path between N1 and Nn+1, is
this right?
it is very strange to me, because I remember we often mentioned "the middle-box in the path", does that means the middle-box should
be a part of the path?

Well, if the middle-boxes were part of the path, how about the "path capacity"?
In section 2.3.3, it specifies,

C(P,T,I) = min {1..n} {C(Ln,T,I)}

I think this should be updated, as

C(P,T,I) = min ( X, Y)
X = min {2..n} {C(Nn,T,I)}
Y = min {1..n} {C(Ln,T,I)}

Of course, we should additionally define the capacity of node (transmitting/receiving/forwarding aspect), I think that is necessary.
And there are also some other text need modification, such as IP-type-P Available Path Capacity.

For example, in the path between node A and B as follows,

A------link1------Router------link2------B

For some certain packet/traffic, if the capacity of link1 is 5G bps and the capacity of link2 is 3G bps, while the capacity of the
router is 2G bps, how much is the capacity of the path between A and B? I believe the capacity is 2G bps (the neckbottle is the
middle-box), but not 3G bps (as definition of RFC5136).

Since this is a very late comment (on a frozen RFC document), if you agree these are serious issues, I would submit a new draft, to
update this RFC.

Any thought?

Regards,
Xiangsong

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---

From: Xiangsong Cui <[email-masked]>
Date: Tue, 10 Aug 2010 09:27:07 +0800

Hi Phil,

Thank you for your quick feedback!

I do agree your statement about IP capacity, but I think that is a higher level concept, here I just want to talk about Path 
Capacity.
You said "The notion of "middle-box" capacity is, in effect, included in the definition of IP capacity.", my questions are:
Does the notion of "middle-box" capacity is included in the definition of Path Capacity? Should it be or not?

Additionally, I want to clarify my example, I also talked about IP capacity.

Node A sends IP packets to B at the rate of 5G bps, and all the packets are transferred by the router.
The router forwards the packets, but the rate exceeds its capacity, so unfortunately bit error happens in 60% packets, and what more 
unfortunately is, the error bit is in IP header checksum.
Node B receives packets from the router, it detects the IP header checksum errors, so the accepted IP flow rate is 2G bps (the 
capacity of the neckbottle, the router).

How should we say the capacity of the path between A and B?
I guess the capacity of the path is 2G bps, the invalid IP bandwidth is not our expected IP capacity (neither the link nor the 
path), right?

Thanks and regards
Xiangsong

----- Original Message ----- 
From: <[email-masked]>
To: <[email-masked]>
Cc: <[email-masked]>
Sent: Monday, August 09, 2010 8:26 PM
Subject: Re: [ippm] Question/comment on RFC5136

Remember, what we are talking about here is the IP capacity, not raw link capacity. So the definition includes the number of IP 
layer bits that can be transmitted by the source and received by the destination. Lots of things make this capacity smaller than the 
nominal link capacity measured at the physical layer. Some things that can reduce the IP layer capacity include: node backplane 
capcity, NIC implementation, queueing structure, buffer management, etc. etc. The notion of "middle-box" capacity is, in effect, 
included in the definition of IP capacity.

Regards,
Phil Chimento

  Hi folks,

  I'm a bit confused by this definition,
  it seems the middle-boxes (i.e., nodes N2, N3, ..., Nn) are not included (in this definition) in the path between N1 and Nn+1, is
  this right?
  it is very strange to me, because I remember we often mentioned "the middle-box in the path", does that means the middle-box 
should
  be a part of the path?

  C(P,T,I) = min ( X, Y)

  Of course, we should additionally define the capacity of node (transmitting/receiving/forwarding aspect), I think that is 
necessary.
  And there are also some other text need modification, such as IP-type-P Available Path Capacity.

  Since this is a very late comment (on a frozen RFC document), if you agree these are serious issues, I would submit a new draft, 
to
  update this RFC.

  Any thought?

  Regards,
  Xiangsong