Subject: [rddp] SCTP rwnd

From: Caitlin Bestler <[email-masked]>
Date: Tue, 23 Jul 2002 15:16:11 -0500

Assuming that an SCTP association is used for a single RDDP
connection, how should the receive window credits be
calculated?

In a purely layered implementation, the credits represent
the SCTP layer's buffering capacity. SCTP data chunks are
delivered to the SCTP's "ULP", RDDP. When it completes them
the count is returned to the available SCTP buffer capacity.

That works. And you *could* implement that way.

But the goal is allow the "ULP" to be implementable in
hardware. That means that the time it takes to empty the
SCTP layer buffer to an RDDP target buffer is totally
predictable, and several factors shorter than the round trip
time of the connection.

Rather than churning all of these calculations as though the
buffering at the two layers were totally distinct, would it
be acceptable to advertise the receive window credits based
upon the assumption that all received data chunks will have
a valid RDDP target buffer, and that the  transport layer
buffering was only required to the extent necessary to
validate an SCTP packet?

If RDDP's ULP is sending messages that will not have valid
receiving buffers the connection will be torn down anyway.
Is there any need to faithfully exchange SCTP layer buffer
credits? Could the receiver simply set the credits high,
knowing that if it receives a data chunk for which there is
no valid RDDP layer target that it will simply drop the
packet and break the connection?

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