Subject: [ippm] TWAMP Session-Reflector port negotiation

From: "Walt Steverson" <[email-masked]>
Date: Wed, 2 May 2007 14:56:36 -0500

Is there any provision for the Control-Client to request that the
Session-Reflector send/receive test traffic on a specific port?

Looking at section 3.5 of the draft, it seems odd that a
Session-Sender can have one IP address and port number for sending
test packets and another IP address and port number for receiving test
packets.  That makes it seem like you could have two separate devices
(one for sending and one for receiving) playing a single
Session-Sender role?  Why not use the Receiver address and port in the
TWAMP Request-Session message to request that the Session-Reflector
listen for test packets and generate responses using that address and
port?  If the Session-Reflector is unable to use that IP address
and/or port then it can reject the session.  If the Receiver port is
set to zero then the Server sends back an Accept-Session message just
like the draft states today with the port that the Session-Reflector
will use.  If the Receiver address is not set then treat it just like
the draft states today.

Thoughts? Comments?

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From: Al Morton <[email-masked]>
Date: Fri, 04 May 2007 10:59:06 -0400

Hi Walt,

Thanks for your questions, very good ones.
see below,
Al

>Session-Reflector send/receive test traffic on a specific port?

The way our text reads now, it appears to me the answer is no.

However, the current TWAMP usage may be a change from OWAMP when
the Conf-Sender and Conf-Receiver are set to zero.  I read in OWAMP,
section 3.5:

         ...                        If Conf-Receiver is not set,
    Receiver Port is the UDP port OWAMP-Test to which packets are
    requested to be sent.

So, it appears that OWAMP has this ability. And if the Sender Port and
Receiver Ports are likely to be the same in common use of TWAMP,
then we're losing the opportunity to suggest the receiving port
at the Session-Reflector.

Of course, the requested port may already be in use, so we
need to see how to recover from that error:

  - "Accept" Field of the Accept Session message is set to 5 (reject
    due to temporary resource constraints)

  - "Accept" Field of the Accept Session message is set to <new value>
    meaning requested port unavailable, send TWAMP-test packets to
    the port in the Port field.

Need to think about this some more, discuss with co-authors...

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