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Network Working Group                                         R. Stewart
Internet-Draft                                       Cisco Systems, Inc.
Expires: August 26, 2003                                      C. Bestler
                                                              Consultant
                                                                  J. Jim
                                                               Microsoft
                                                              S. Ganguly
                                                       Iomega Corp, Inc.
                                                                 H. Shah
                                                       Intel Corporation
                                                              V. Kashyap
                                                                     IBM
                                                       February 25, 2003


    Stream Control Transmission Protocol (SCTP) Remote Direct Memory
          Access (RDMA) Direct Data Placement (DDP) Adaptation
                     draft-stewart-rddp-sctp-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 26, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes a method to adapt Direct Data Placement (DDP)



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   and Remote Direct Memory Access (RDMA) to Stream Control Transmission
   Protocol (SCTP) RFC2960 [2] using a generic description found in
   [RDMA-Draft] [4] and [DDP-Draft] [3].

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1 Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2 Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Data Formats . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.1 Adaptation Layer Indicator . . . . . . . . . . . . . . . . . .  4
   2.2 Payload Protocol Identifier  . . . . . . . . . . . . . . . . .  4
   3.  SCTP Endpoints . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.1 Adaptation Layer Indication Restriction  . . . . . . . . . . .  6
   3.2 Multihoming Implications . . . . . . . . . . . . . . . . . . .  6
   4.  Number of Streams  . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Sequenced Unordered Operation  . . . . . . . . . . . . . . . .  9
   7.  Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.1 Association Initialization . . . . . . . . . . . . . . . . . . 10
   7.2 Stream Reset . . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.3 Chunk Bundling . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.4 STag Validation  . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 12
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
       References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
       Intellectual Property and Copyright Statements . . . . . . . . 17






















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1. Introduction

   This document describes a method to adapt Direct Data Placement (DDP)
   and Remote Direct Memory Access (RDMA) to Stream Control Transmission
   Protocol (SCTP) RFC2960 [2] using a generic description found in
   [RDMA-Draft] [4] and [DDP-Draft] [3] This adaptation provides a
   method for two peers to know that each side is performing DDP or RDMA
   thus enabling hardware acceleration if available.

   Some implementations may include this adaptation layer within their
   SCTP implementations to obtain maximum performance but the behavior
   of SCTP will be unaffected.  In order to accomplish this we specify
   the use of the new adaptation layer indication as defined in
   [ADDIP-Draft] [6]

1.1 Definitions

   DDP stream - A bi-directional pair of SCTP streams which have the
      same SCTP Stream identifier.

   RDMA - Remote Direct Memory Access.

   RNIC - RDMA Network Interface Card.

   SCTP association - A protocol relationship between two SCTP
      endpoints.  An SCTP association supports multiple SCTP streams.

   SCTP endpoint - The logical sender/receiver of SCTP packets.  On a
      multi-homed host, an SCTP endpoint is represented to its peers as
      a combination of a set of eligible destination transport addresses
      to which SCTP packets can be sent and a set of eligible source
      transport addresses from which SCTP packets can be received.

   SCTP Stream - A uni-directional logical channel established from one
      to another associated SCTP endpoint.  An SCTP Stream is used to
      form one direction of a DDP stream.


1.2 Conventions

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
   they appear in this document, are to be interpreted as described in
   RFC2119 [1].







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2. Data Formats

2.1 Adaptation Layer Indicator

   This mapping places an entire SCTP association into a specific DDP
   mode: DDP or DDP+RDMA.  It is presumed that the handling of incoming
   data chunks for DDP enabled associations is sufficiently different
   than for routine SCTP associations that it is undesirable to mix DDP
   and non-DDP streams in a single association.  An application that
   needs to mix DDP and non-DDP traffic must use use more than a single
   association.

   We define a adaptation indication which MUST appear in the INIT or
   INIT-ACK with the following format as defined in [ADDIP-Draft] [6]

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Type =0xC006           |    Length = Variable          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Adaptation Indication                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Adaptation Indication:

   The following values are defined for DDP in this document:

       DDP                        - 0x00000001
       DDP+RDMA                   - 0x00000002


   The DDP implementation MAY require that all associations for a given
   SCTP endpoint be placed in the same mode.

   The local interface MAY allow the ULP to accept only requests to
   establish an association in a specified mode.

2.2 Payload Protocol Identifier

   SCTP provides for delivery of user data messages.  Each user message
   consists of a length, the data bytes and a Payload Protocol
   Identifier.  The DDP SCTP adaptation uses two different Payload
   Protocol Identifiers.








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   Payload Protocol Identifier:

   The following value are defined for DDP in this document:

       DDP Message                - 0x00000001
       Adaptation Layer Control   - 0x00000002


   DDP Messages are as defined in [DDP-Draft].  Adaptation Layer Control
   messages are defined in this document.


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Function Code                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Function Data (Dependent on Function Code)          |
   |                         ...                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following function code values are defined for DDP in
   this document:

       DDP Stream Reset           - 0x00000001


   A DDP Stream Reset message MUST be presented to the SCTP layer with a
   Payload Protocol Identifer of one and a length of 4 bytes (i.e.  the
   Function Code 0x00000001 with no Function dependant data).





















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3. SCTP Endpoints

3.1 Adaptation Layer Indication Restriction

   The local interface MUST allow the ULP to specify an SCTP endpoint to
   use a specific Adaptation Indication.  It MAY require the ULP to do
   so.

   Once an endpoint decides on its acceptable Adaptation Indication(s),
   it SHOULD terminate all requests to establish an association with any
   different Adaptation Indication.

   An SCTP implementation MAY choose to accept association requests for
   a given SCTP endpoint only until one association for the endpoint has
   been established.  At that point it MAY choose to restrict all
   further associations for the same endpoint to use the same Adaptation
   Indication.

3.2 Multihoming Implications

   SCTP allows an SCTP endpoint to be associated with multiple IP
   addresses, potentially representing different interface devices.
   Distribution of the logic for a single DDP stream across multiple
   input devices can be very undesirable, resulting in complex cache
   coherency challenges.  Therefore the local interface MAY restrict
   DDP-enabled SCTP endpoints to a single IP address, or to a set of IP
   addresses that are all assigned to the same input device ("RNIC").

   The default binding of a DDP enabled SCTP endpoint SHOULD NOT cover
   more than a single IP address unless doing so results in no
   additional bus traffic or duplication of memory registration
   resources.  This will frequently result in a different default than
   for SCTP endpoints that are not DDP enabled.

   Even when multi-homing is supported, ULPs are cautioned that they
   SHOULD NOT use ULP control of the source address in attempt to
   load-balance a stream across multiple paths.  A receiving DDP/SCTP
   implementation that chooses to support multi-homing SHOULD optimize
   its design on the assumption that multi-homing will be used for
   network fault tolerance, and not to load-balance between paths.  This
   is consistent with recomended SCTP practices.










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4. Number of Streams

   DDP Streams are bidirectional.  They are always composed by pairing
   the inbound and outbound SCTP streams with the same SCTP Stream
   Identifier.

   DDP should request the maximum it will wish to use from SCTP.  DDP
   Streams cannot be used without prior pre-posting of receive
   operations and/or enabling of STags.  Therefore DDP will be able to
   initialize each stream on an "as needed" basis.

   This mapping uses an SCTP association to carry one or more DDP
   Steams.  Each DDP Stream will be mapped to a pair of SCTP streams
   with the same SCTP stream number.  DDP MUST initialize all of its
   SCTP associations with the same number of inbound and outbound
   streams.



































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5. Fragmentation

   A DDP/SCTP Receiver already must deal with fragementation at both the
   IP and DDP Layers.  Therefore the sending DDP layer MUST disable SCTP
   layer segmenting of data chunks.  If the DDP layer presents messages
   that are too large, the result will be IP fragmentation.  While SCTP
   layer fragmentation is theoretically preferable, virtually all
   fragmentation will be done at the DDP layer.  Because SCTP layer
   fragmentation would only be invoked under corner conditions, its
   benefits do not justify the complexity of its inclusion.

   When disabling SCTP fragmentation, SCTP will reject messages that are
   known to be larger than the MTU size.  This means that the DDP layer
   MUST be prepared to handle this error case.





































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6. Sequenced Unordered Operation

   Each DDP Segment MUST be encoded within a single Data Chunk, along
   with a DDP Stream Sequence Number (DDP-SSN), as follows:


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  DDP Stream Sequence Number   |         DDP Segment           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                      DDP Segment Continues                    |
   |                         ...                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The DDP Stream Sequence Number represented the sequence of DDP
   segments sent for this DDP stream from one end.  It is initialized to
   1 when a DDP Stream is initialized or reset.  It wraps to zero after
   65535.

   DDP MUST use the Unordered option on all Data Chunks (U Flag set to
   one).  Each DDP segment within an SCTP Data Chunk may be placed
   immediately upon receipt from the SCTP layer.

   A DDP segment is not deliverable until after it has been placed and
   all prior DDP Segments for the same DDP stream have been delivered.

   Because DDP employs unordered SCTP delivery, the receiver MUST NOT
   rely upon the SCTP Transmission Sequence Number (TSN) to imply
   ordering of DDP Segments.  The fact that the SCTP Data Chunk for a
   DDP Segment is prior the cumulative ack point does not guarantee that
   all prior DDP segments have been placed.  The SCTP sender is not
   obligated to transmit unordered Data Chunks in the order presented.

   Note that no special logic is required on either end if the the
   maximum number of in-flight messages is less than 32768.  No special
   DDP logic is required if the sending SCTP accepts no more than 32767
   Data Chunks for a single stream without assigning SSNs.

   If SCTP does accept more than 32768 Data chunks for a single stream
   without assigning SSNs,  the sending DDP must simply refrain from
   sending more than 32767 DDP Segments for a single stream without
   acknowledgement.  Note that it MUST NOT rely upon ULP flow control
   for this purpose.  Typical ULP flow control will deal exclusively
   with tagged messages, not with DDP segments.





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7. Procedures

7.1 Association Initialization

   At the startup of an association, an endpoint wishing to perform DDP,
   RDMA, or DDP+RDMA placement MUST include an adaptation layer
   indication in its INIT or INIT-ACK (as defined in Section 2.1.  After
   the exchange of the initial first two SCTP chunks (INIT and
   INIT-ACK), an endpoint MUST verify and inspect the adaptation
   indication and compare it to the following table to determine proper
   action.

        Indication |           Action
          type     |

   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                   | This indicates that the peer DOES NOT
       NONE        | support ANY DDP or RDMA adaptation and thus
                   | RDMA and DDP procedures MUST NOT be
                   | performed upon this association.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                   | This indicates that the peer DOES support
       DDP         | DDP (but not RDMA). Procedures outlined in
                   | [DDP-Draft] MUST be followed.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                   | This indicates that the peer supports BOTH
      DDP+RDMA     | RDMA and DDP. If the receiving endpoint
                   | indicated the same, then the procedures in
                   | both [RDMA-Draft] and [DDP-Draft]
                   | MUST be followed. If the local endpoint
                   | only indicated DDP, then ONLY the
                   | procedures in [DDP-Draft] MUST be followed.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                   | This indicates that the peer DOES NOT
     ANY-OTHER     | support ANY DDP or RDMA adaptation and thus
     Indication    | RDMA and DDP procedures MUST NOT be
                   | performed upon this association.

   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


7.2 Stream Reset

   DDP [DDP-Draft] requires that a DDP Stream be aborted upon certain
   error conditions such as receiving an untagged message which the
   receiving side ULP had not enabled the reception of.

   When a DDP stream is aborted, no further incoming packets will be



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   accepted for that stream until the stream is re-established.  Many
   ULPs will maintain a session by re-establishing the DDP stream after
   such a termination.

   Once a DDP Stream is declared to be aborted all DDP Messages on that
   stream MUST be discarded.  Placement MUST NOT be performed.  DDP
   Messages MUST NOT be delivered to the ULP.  New DDP Messages from the
   ULP MUST NOT be accepted.

   The aborted state MUST continue until a DDP Stream Reset Message is
   received.  When this packet is received, the inbound SCTP stream will
   be re-enabled for normal handling of DDP Messages.

   The DDP layer MAY send a DDP SCTP Stream Reset message in a Data
   Chunk to enable re-use of a Stream Identifier within an association
   for a new DDP Stream.  However, it SHOULD select a previously unused
   stream first, if one is available.

   The ability to re-use a Stream Identifier allows an SCTP association
   between two endpoints to remain open indefinitely.  Isolated ULP
   faults will only impact the ULP components using the faulted stream,
   not those merely sharing the same association.

7.3 Chunk Bundling

   SCTP allows multiple Data Chunks to be bundled in a single SCTP
   packet.  Data chunks containing untagged messages SHOULD NOT be
   delayed to facilitate bundling.  Data chunks containing tagged
   messages will generally be full sized, and hence not subject to
   bundling.  However partial size tagged messages MAY be delayed, as
   that they are frequently followed by a short untagged message.

7.4 STag Validation

   STag validation is to be performed on a per stream basis.  An
   integrated DDP/SCTP implementation MUST NOT enable an STag for an
   entire SCTP association merely because it is enabled for a single
   stream on that association.  The ULP MUST be able to control STag
   enabling on a per stream basis, without regard to which SCTP
   association each stream is a part of.











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8. IANA considerations

   This document defines two new Adaptation Layer Indication codepoints:


       DDP                         - 0x00000001
       DDP+RDMA                    - 0x00000002

   This document also defines two new Payload Protocol Identifier
   (PPIDs):

       DDP Message                - 0x00000001
       Adaptation Layer Control   - 0x00000002






































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9. Security Considerations

   Any direct placement of memory could pose a significant security risk
   if adequate local controls are not provided.  These threats should be
   addressed in the appropriate DDP [DDP-Draft] [3] or RDMA [RDMA-Draft]
   [4] drafts.  This document does not add any additional security risks
   over those found in RFC2960 [2].












































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10. Acknowledgments

   The authors would like to thank the following people that have
   provided comments and input Stephen Bailey, David Black, Douglas
   Otis, and Allyn Romanow.














































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References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
        H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
        "Stream Control Transmission Protocol", RFC 2960, October 2000.

   [3]  Culley, P., "Direct Data Placement over Reliable Transports",
        draft-shah-iwarp-ddp-00 (work in progress), September 2002.

   [4]  Recio, R., "An RDMA Protocol Specification",
        draft-recio-iwarp-rdma-01 (work in progress), November 2002.

   [5]  Stewart, R., "Sockets API Extensions for Stream Control
        Transmission Protocol", draft-ietf-tsvwg-sctpsocket-05 (work in
        progress), September 2002.

   [6]  Stewart, R., "Stream Control Transmission Protocol (SCTP)
        Dynamic Address  Reconfiguration",
        draft-ietf-tsvwg-addip-sctp-06 (work in progress), September
        2002.


Authors' Addresses

   Randall R. Stewart
   Cisco Systems, Inc.
   8725 West Higgins Road
   Suite 300
   Chicago, IL  60631
   USA

   Phone: +1-815-477-2127
   EMail: rrs@cisco.com


   Caitlin Bestler
   Consultant
   1241 W. North Shore
   # 2G
   Chicago, IL  60626
   USA

   Phone: +1-773-743-1594
   EMail: cait@asomi.com




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   Jim Pinkerton
   Microsoft


   Bellevue, Wa
   USA

   Phone: +1-xxx-xxx-xxx
   EMail: jpink@microsoft.com


   Sukanta Ganguly
   Iomega Corp, Inc.
   4435 Eastgate Mall
   Suite 300
   San Diego, CA  92121
   USA

   Phone: +1-858-795-7026
   EMail: ganguly@iomega.com


   Hemal V. Shah
   Intel Corporation
   Mailstop: PTL1
   1501 S. Mopac Expressway, #400
   Austin, TX  78746
   USA

   Phone: +1-512-732-3963
   EMail: hemal.shah@intel.com


   Vivek Kashyap
   IBM
   15450 SW Koll Parkway
   Beaverton, OR  57006
   USA

   Phone: +1-503-578-3422
   EMail: vivk@us.ibm.com










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Intellectual Property Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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