Subject: Re: [NSIS] yet another attempted summary of fragmentation discussion

From: Bob Braden <[email-masked]>
Date: Thu, 19 Jun 2003 12:25:28 -0700 (PDT)

I don't get why an NSLP should be able to disable NTLP fragmentation.
What happens if the NSLP did disable it?  A message that exceeds the
local MTU must then be black-holed by the NTLP, since it cannot be
fragmented (I believe there was a consensus against IP fragmentation.)
That does not make sense.  If the NSLP want to avoid fragmentation, it
must itself make sure it sends messages smaller than the local MTU.
But if it does that, then any fragmentation mechanism in the NTLP won't
be invoked anyway, so there is no need to explicitly tell the NTLP not
to fragment.

What am I missing?

Bob Braden

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---

From: "Georgios Karagiannis" <[email-masked]>
Date: Fri, 20 Jun 2003 15:53:46 +0200

Hi Bob

In order to explain why, from my point of view,  it is important to have
the "Do fragmentation" bit I would  like to use the following figure.
* NF are NSIS Forwarders
* NF2, NF3, NF4 and NF5 are NF nodes belonging to a network that is manged
by one
administrator. These nodes can be optimally configured by the administrator.
* NF2 and NF5 are edge nodes; Moreover they are NTLP statefull and they can
also be seen
   as NSIS Initiators (NI);
* NF3 and NF4 are interior nodes. Moreover they are NTLP stateless nodes.
For definitions of these terms please see:
http://www.ietf.org/internet-drafts/draft-westberg-proposal-for-rsvpv2-nslp-
00.txt

|--------|      |--------|      |--------|     |--------|      |--------|
|-------|
|NSLP  |<->| NSLP |<->| NSLP |<->| NSLP |<->| NSLP |<->| NSLP|
|            |<->|            |<->|            |<->|           |<->|
|<->|           |
|            |      |            |      |            |      |           |
|            |      |           |
--------------------------------------------- ------- ------- ------- -----
|NTLP |<->| NTLP  |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP|
|           |<->|            |<-> |            |<->|            |<->|
|<->|           |
|-------|       |--------|      |--------|      |--------|     |--------|
|-------|
NF1             NF2             NF3           NF4             NF5
NF6
                    edge              interior       interior         edge

Suppose that the interior nodes of this core network have to support, in
comparison,
to the edge nodes, a very large  number of sessions (e.g., factor 100),
i.e.,  since they are interior
nodes of a big core network.

Thus the performance of the interior nodes, has to be optimized as much as
possible.
Note that the performance is in terms of processing delay and
scalability (i.e., performance remains almost the same even if  the number
of flows is increased).
The administrator will try to simplify the algorithms that are running on
the interior nodes
as much as possible by combinig the functionality that can be provided by
edge nodes
(could be complex) and the ability to configure optimally its network.
Now when this administrator will need to  use NSIS in its network will try
to minimize
the features that must be used by the NTLP interior nodes.
This applies to features such as fragmentation/reassembly but also flow
control and congestion control.
Please note that such features could be supported by the NF edge nodes.

Now in case of fragmentation/reassembly, the operator will configure the
network such that
it could be ensured that the NTLP packets sent by the NF edge nodes will not
be fragmeted by the
NTLP interior nodes.
In this situation the NSLP instance located at NF2 edge node will set the
"Do fragmentation" off.
In this situation the NF3 and NF4 nodes by only checking this "Do
fragmentation" bit will deduce that
no fragmentation and reassembly is needed. If this bit would not be there
then an additional
feature will be needed to decide if fragmentation and/or reassembly is
needed.
The NSLP instance located at NF5 can set the "Do fragmentation" bit to on.

Best Regards,
Georgios

----- Original Message -----
From: "Bob Braden" <[email-masked]>
To: <[email-masked]>; <[email-masked]>
Cc: <[email-masked]>
Sent: Thursday, June 19, 2003 9:25 PM
Subject: Re: [NSIS] yet another attempted summary of fragmentation
discussion