Subject: RE: [ipfix] Lost Flow Records - Synch Message

From: "MEYER,JEFFREY D (HP-Cupertino,ex1)" <[email-masked]>
Date: Tue, 20 May 2003 17:44:43 -0700

Sebastian,

  I completely agree that template refreshment is unnecessary in a TCP (or
SCTP) context.

  In UDP, I'd still propose that the use of a Pull model as I suggested in
an earlier e-mail is more effective than periodic retransmissions of
templates.

Regards,

  Jeff Meyer

-----Original Message-----
From: Sebastian Zander [mailto:[email-masked]]
Sent: Monday, May 19, 2003 11:22 PM
To: [email-masked]
Subject: Re: [ipfix] Lost Flow Records - Synch Message

Periodic refreshment of templates is in my opinion pointless when a
reliable connection-oriented transport is used. Either the transport
is working (the refreshment just wastes bandwidth) or it fails in
which case the sender (exporter) knows that it fails and can act
accordingly (such as failover and send the templates to the new
collector). In this case periodic refreshment just adds unecessary
complexity to the exporter.

For UDP it is necessary if there are no ACKs from collector to exporter.
Periodic refreshments are basically forward error correction. If there
would be application layer ACKs anyway (to achieve application layer
reliability as explained by other people on the list) why have periodic
template refreshments at all?

Just my 0.02 cents on the periodic refreshment discussion,

Sebastian

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From: Sebastian Zander <[email-masked]>
Date: Wed, 21 May 2003 04:55:42 +0200

Hi Jeff,

> an earlier e-mail is more effective than periodic retransmissions of

I also think that Pull mode is more effective (in my view ACKs + retransmissions
are some sort of Pull mode). Because I believe that there is not a constant
loss rate but loss is rather bursty. So optimizing the refresh interval for
the worst case might result in long periods where redundant data is sent without
making use of it.

If the protocol is unreliable (no ACKs) your proposal is IMO a better
alternative to periodic refreshments. Anyway it is an alternative to be
considered. Some nice properties of your proposal: the collector would not
need to contact the exporter it could contact some other box which has the
templates and the exporter could itself retrieve the templates from that other
box at startup (i don't know if that would be feasible for a router though).

If the collector can retrieve templates from another box other than the exporter
a clear distinction of template IDs and flow IDs is required (an issue raised
by Tal recently). Which is also good IMO.

Cheers,

Sebastian

-- 
Sebastian Zander                         E-mail: [email-masked]
Fraunhofer FOKUS / METEOR                Tel: +49-30-3463-7287
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