Subject: [ipfix-protocol] PROTO-31 - Sequence Number

From: Stewart Bryant <[email-masked]>
Date: Mon, 22 Nov 2004 15:37:04 +0000

PROTO-31 The "Sequence Number" and "Source ID" treatment in case of
multiple streams in SCTP is not well described. For example, in case
the Templates are sent to one stream and the flow records to another
one, what should the "Sequence Number"? What should the collector
do?

I propose that when IPFIX uses multiple streams a separate
Sequence Number space MUST be used for each stream.

I also note that we need to call out that this is modulo
arithmetic.

Therefore the following text in Section 7.1

Sequence Number
    Incremental sequence counter of all IPFIX Messages sent from
    the current Observation Domain by the Exporting Process.
    This value SHOULD be used by the Collecting Process to
    identify whether any IPFIX Messages have been missed.

should be changed to:

Sequence Number
    Incremental sequence counter modulo 2^32 of all IPFIX
    Messages sent on this stream from the current Observation
    Domain by the Exporting Process. This value SHOULD be used
    by the Collecting Process to identify whether any IPFIX
    Messages have been missed.

However it might be more useful if we were to track the number of
records sent rather than the number of IPFIX Messages. We could
do this by making the sequence number be the sequence number of
the first record in the IPFIX Message, and instead of incrementing
it by one on each message, increasing it by the number of
records in the Message. This gives the number of records lost per
template in cases when a single template is sent per stream.

Thus the definition then becomes:

Sequence Number
    The total number of IPFIX data records received on this stream
    prior to the receipt of this IPFIX Message modulo 2^32. This
    value SHOULD be used by the Collecting Process to identify
    whether any data records have been missed in that stream.

- Stewart

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