Subject: [ippm] TWAMP questions/comments

From: "Walt Steverson" <[email-masked]>
Date: Wed, 13 Jun 2007 15:14:50 -0500

I apologize for all these questions this late in the process but I
came late to the TWAMP party.

With the addition of Sender TTL to the test packets in the latest
draft the minimum unauthenticated test packet length is 41 octets not
40 octets.  If the Sender DSCP field is adopted it bumps it up to 42
octets.  The minimum authenticated/encrypted packet length should be
104 instead of 80 octets.

In authenticated mode why aren't both the Sequence Number and Sender
Sequence Number fields encrypted?  In encrypted mode why aren't all
the sequence numbers and timestamps encrypted instead of just the
first Sequence Number and Timestamp fields?

Should the authenticated/encrypted test packet be padded to a 16-byte
boundary after the Sender TTL?  If not then why is it padded at all?
It doesn't look like the Sender TTL will ever be encrypted so it
should only need a 3 octet MBZ field afterwards.

This may be a silly question at this point but does the Session-Sender
fill out the Sender Sequence Number, Sender Timestamp, Sender Error
Estimate when the test packet is generated? Or should it fill out the
Sequence Number, Timestamp, and Error Estimate field and the
Session-Reflector is responsible for copying the Sequence Number,
Timestamp, and Error Estimate into the Sender Sequence Number, Sender
Timestamp, and Sender Error Estimate, respectively?  I ask because the
following two paragraphs from section 4.2.1 seem unclear:

"Sequence Number is the sequence number of the test packet according
to its arrival at the Session-Reflector.  It starts with zero and is
incremented by one for each subsequent packet.  The Sequence Number
generated by the Session-Reflector is independent from the sequence
number of the arriving packets."

"Sender Sequence Number is a copy of the Sequence Number of the packet
transmitted by the Session-Sender that caused the Session-Reflector to
generate and send this test packet."

The paragraphs about Timestamp and Sender Timestamp have similar language.

Thanks for your help,
Walt

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