Subject: [Tsvwg] Cumulative TSN within SCTP Socket API

From: "Douglas Otis" <[email-masked]>
Date: Fri, 28 Dec 2001 13:16:39 -0800

Direct Data Placement DDP for SCTP

DDP will likely be used as an auxiliary mode of operation within a Stream
for many protocols once assisted by NIC based hardware.  One example may be
command/response sent using sequential delivery but data transfers using the
DDP mode.  The Stream would act to bind this related information while also
offering concurrency.  As such, the DDP mode should carry the minimum
information to support DDP, an OFFSET.

As the DDP is Unordered for immediate delivery carrying an OFFSET added by
ULP fragmentation, the technique suggested is to create a signal on the last
chunk using a different PPI type, or flag if SCTP is modified, to mark the
last chunk in a sequence.  The ULP would hold this signal until the TSN of
the marked chunk was equal to or less than the cumulative TSN of the
Association.  The possible signal categories being Synchronize and Release.
Release would be used to invalidate further use of the present receive
vector whereas Synchronize would only indicate completion of the message and
continued use of the vector is expected.  For this to function with the
Socket specification, Cumulative TSN will need adding.  This appears to be
an oversight as most applications to date use the sequential mode of
operation and this use has not become apparent.  SSN is invalid for
Unordered Data Chunks, so if fragmentation is to take place at the ULP to
include such things as OFFSET, then the ability to monitor the cumulative
TSN is important to qualify a completed message.

Doug

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