Subject: [Capwap] Issue 175: Retransmission clarification required

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Tue, 5 Aug 2008 10:04:51 -0700

The text from section 4.5.3 is unclear as to what happens when the
RetransmitInterval timer reaches half the EchoInterval. Should the
CAPWAP implementation no longer attempt to double the value, or stop
retransmitting. The text in question is:

<current text>
4.5.3.  Retransmissions
[...]
   After transmitting a Request message, the RetransmitInterval (see
   Section 4.7) timer and MaxRetransmit (see Section 4.8) variable are
   used to determine if the original Request message needs to be
   retransmitted.  The RetransmitInterval timer is used the first time
   the Request is retransmitted.  The timer is then doubled every
   subsequent time the same Request message is retransmitted, up to
   MaxRetransmit but no more than half the EchoInterval timer (see
   Section 4.7.7).  Response messages are not subject to these timers.
</current text>

I believe the original intent is that the implementation should
retransmit until MaxRetransmit has been reached, and not keep the
RetransmitInterval intact once it has reached half EchoInterval.

Further, section 4.4.1 describes how the CAPWAP Data Channel Keepalive
is retransmitted, specifically:

<current text>
4.4.1.  CAPWAP Data Channel Keepalive
[...]
   Upon receiving a CAPWAP Data Channel Keep Alive packet, the WTP
   cancels the DataChannelDeadInterval timer and resets the
   DataChannelKeepAlive timer.  The CAPWAP Data Channel Keep Alive
   packet is retransmitted by the WTP in the same manner as the CAPWAP
   control messages.  If the DataChannelDeadInterval timer expires, the
   WTP tears down the control DTLS session, and the data DTLS session if
   one existed.
</current text>

I think the second sentence could use a clarification and modified as
follows:

<new text>
   The CAPWAP Data Channel Keep Alive
   packet is retransmitted by the WTP in the same manner as the CAPWAP
   control messages, except the DataChannelKeepAlive timer is used in
lieu
   of the EchoInterval timer.
</new text>

Comments?
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