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Versions: 00

Internet-Draft                                                 T. Talpey
Internet-Draft                                              J. Pinkerton
Updates: 5040, 7306 (if approved)                              Microsoft
Intended status: Standards Track
Expires: August 22, 2016                               February 19, 2016


                       RDMA Durable Write Commit
                      draft-talpey-rdma-commit-00

Abstract

   This document specifies extensions to RDMA protocols to provide
   capabilities in support of enhanced remotely-directed data
   consistency.  The extensions include a new operation supporting
   remote commitment to durability of remotely-managed buffers, which
   can provide enhanced guarantees and improve performance for low-
   latency storage applications.  In addition to, and in support of
   these, extensions to local behaviors are described, which may be used
   to guide implementation, and to ease adoption.  This document would
   extend the IETF Remote Direct Memory Access Protocol (RDMAP),
   RFC5040, and RDMA Protocol Extensions, RFC7306.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 22, 2016.






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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   7
       2.1.1.  Non-Requirements  . . . . . . . . . . . . . . . . . .   9
     2.2.  Additional Semantics  . . . . . . . . . . . . . . . . . .  10
   3.  Proposed Extensions . . . . . . . . . . . . . . . . . . . . .  11
     3.1.  Local Extensions  . . . . . . . . . . . . . . . . . . . .  11
       3.1.1.  Registration Semantics  . . . . . . . . . . . . . . .  11
       3.1.2.  Completion Semantics  . . . . . . . . . . . . . . . .  12
       3.1.3.  Platform Semantics  . . . . . . . . . . . . . . . . .  12
     3.2.  RDMAP Extensions  . . . . . . . . . . . . . . . . . . . .  12
       3.2.1.  RDMA Commit Request Header Format . . . . . . . . . .  15
       3.2.2.  RDMA Commit Response Header Format  . . . . . . . . .  16
       3.2.3.  Ordering  . . . . . . . . . . . . . . . . . . . . . .  16
       3.2.4.  Atomicity . . . . . . . . . . . . . . . . . . . . . .  17
       3.2.5.  Discovery of RDMAP Extensions . . . . . . . . . . . .  17
   4.  Ordering and Completions Table  . . . . . . . . . . . . . . .  18
   5.  Error Processing  . . . . . . . . . . . . . . . . . . . . . .  18
     5.1.  Errors Detected at the Local Peer . . . . . . . . . . . .  18
     5.2.  Errors Detected at the Remote Peer  . . . . . . . . . . .  19
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  21
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
   Appendix A.  DDP Segment Formats for RDMA Extensions  . . . . . .  22
     A.1.  DDP Segment for RDMA Commit Request . . . . . . . . . . .  22
     A.2.  DDP Segment for RDMA Commit Response  . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24



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1.  Introduction

   The RDMA Protocol (RDMAP) [RFC5040] and RDMA Protocol Extensions
   (RDMAPEXT) [RFC7306] provide capabilities for secure, zero copy data
   communications that preserve memory protection semantics, enabling
   more efficient network protocol implementations.  The RDMA Protocol
   is part of the iWARP family of specifications which also include the
   Direct Data Placement Protocol (DDP) [RFC5041], and others as
   described in the relevant documents.  For additional background on
   RDMA Protocol applicability, see "Applicability of Remote Direct
   Memory Access Protocol (RDMA) and Direct Data Placement Protocol
   (DDP)" RFC5045 [RFC5045].

   RDMA protocols are enjoying good success in improving the performance
   of remote storage access, and have been well-suited to semantics and
   latencies of existing storage solutions.  However, new storage
   solutions are emerging with much lower latencies, driving new
   workloads and new performance requirements.  Also, storage
   programming paradigms SNIANVM [SNIANVM] are driving new requirements
   of the remote storage layers, in addition to driving down latency
   tolerances.  Overcoming these latencies, and providing the means to
   achieve durability without invoking upper layers and remote CPUs for
   each such request, are the motivators for the extensions proposed by
   this document.

   This document specifies the following extensions to the RDMA Protocol
   (RDMAP) and its local memory ecosystem:

   o  RDMA Commit - support for RDMA requests and responses with
      enhanced placement semantics.

   o  Enhanced memory registration semantics in support of durability.

   The extensions defined in this document do not require the RDMAP
   version to change.

1.1.  Glossary

   This document is an extension of RFC 5040 and RFC 7306, and key words
   are additionally defined in the glossaries of the referenced
   documents.

   The following additional terms are defined in this document.

   Commit:  The placement of data into storage referenced by a target
      Tagged Buffer in a durable fashion.





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   Durability:  The property that data is present and remains stable
      after recovery from a power failure or other fatal error in an
      upper layer or hardware. <https://en.wikipedia.org/wiki/
      Durability_(database_systems)>, <https://en.wikipedia.org/wiki/
      Disk_buffer#Cache_control_from_the_host>[SCSI],

2.  Problem Statement

   RDMA is widely deployed in support of storage and shared memory over
   increasingly low-latency and high-bandwidth networks.  The state of
   the art today yields end-to-end network latencies on the order of one
   to two microseconds for message transfer, and bandwidths exceeding 40
   gigabit/s.  These bandwidths are expected to increase over time, with
   latencies decreasing as a direct result.

   In storage, another trend is emerging - greatly reduced latency of
   persistently storing data blocks.  While best-of-class Hard Disk
   Drives (HDDs) have delivered latencies of several milliseconds for
   many years, Solid State Disks (SSDs) have improved this by one to two
   orders of magnitude.  Technologies such as NVM Express NVMe [1] yield
   even higher-performing results by eliminating the traditional storage
   interconnect.  The latest technologies providing memory-based
   persistence, such as Nonvolatile Memory DIMM NVDIMM [2], places
   storage-like semantics directly on the memory bus, reducing latency
   to less than a microsecond and bandwidth to potentially many tens of
   gigabyte/s.  [supporting data to be added]

   RDMA protocols, in turn, are used for many storage protocols,
   including NFS/RDMA RFC5661 [RFC5661] RFC5666 [RFC5666] RFC5667
   [RFC5667], SMB Direct MS-SMB2 [SMB3] MS-SMBD [SMBDirect] and iSER
   RFC7145 [RFC7145], to name just a few.  These protocols allow storage
   and computing peers to take full advantage of these highly performant
   networks and storage technologies to achieve remarkable throughput,
   while minimizing the CPU overhead needed to drive their workloads.
   This leaves more computing resources available for the applications,
   which in turn can scale to even greater levels.  Within the context
   of Cloud-based environments, and through scale-out approaches, this
   can directly reduce the number of servers that need to be deployed,
   making such attributes compelling.

   However, limiting factors come into play when deploying ultra-low
   latency storage in such environments:

   o  The latency of the fabric, and of the necessary RDMA message
      exchanges to ensure reliable transfer is now higher than that of
      the storage itself.





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   o  The requirement that storage be resilient to failure requires that
      multiple copies be committed in multiple locations across the
      fabric, adding extra hops which increase the latency and computing
      demand placed on implementing the resiliency.

   o  Processing is required at the receiver in order to ensure that the
      storage data has reached a persistent state, and acknowledge the
      transfer so that the sender can proceed.

   o  Typical latency optimizations, such as polling a receive memory
      location for a key that determines when the data arrives, can
      create both correctness and security issues because the buffer may
      not remain stable after the application determines that the IO has
      completed.  This is of particular concern in security conscious
      environments.

   The first issue is fundamental, and due to the nature of serial,
   shared communication channels, presents challenges that are not
   easily bypassed.  Therefore, an RDMA solution which reduces the
   exchanges which encounter such latencies is highly desirable.

   The second issue requires that outbound transfers be made as
   efficient as possible, so that replication of data can be done with
   minimal overhead and delay (latency).  A reliable "push" RDMA
   transfer method is highly suited to this.

   The third issue requires that the transfer be performed without an
   upper-layer exchange required.  Within security contraints, RDMA
   transfers arbitrated only by lower layers into well-defined and pre-
   advertised buffers present an ideal solution.

   The fourth issue requires significant CPU activity, consuming power
   and valuable resources, and additionally is not guaranteed by the
   RDMA protocols, which make no guarantee of the order in which
   received data is placed or becomes visible; such guarantees are made
   only after signaling a completion to upper layers.

   The RDMAP and DDP protocols, together, provide data transfer
   semantics with certain consistency guarantees to both the sender and
   receiver.  Delivery of data transferred by these protocols is said to
   have been Placed in destination buffers upon Completion of specific
   operations.  In general, these guarantees are limited to the
   visibility of the transferred data within the hardware domain of the
   receiver (data sink).  Significantly, the guarantees do not
   necessarily extend to the actual storage of the data in memory cells,
   nor do they convey any guarantee of durability, that is, that the
   data may not be present after a catastrophic failure such as power




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   loss.  These guarantees may be provided by upper layers, such as the
   ones mentioned.

   The NFSv4.1 and iSER protocols are, respectively, file and block
   oriented, and have been used extensively for providing access to hard
   disk and solid state flash drive media.  Such devices incur certain
   latencies in their operation, from the millisecond-order rotational
   and seek delays of rotating disk hardware, or the 100-microsecond-
   order erase/write and translation layers of solid state flash.  These
   file and block protocols have benefited from the increased bandwidth,
   lower latency, and markedly lower CPU overhead of RDMA to provide
   excellent performance for such media, approximately 30-50
   microseconds for 4KB writes in leading implementations.

   These protocols employ a "pull" model for write: the client, or
   initiator, sends an upper layer write request which contains a
   reference to the data to be written.  The upper layer protocols
   encode this as one or more memory regions.  The server, or target,
   then prepares the request for local write execution, and "pulls" the
   data with an RDMA Read.  After processing the write, a response is
   returned.  There are therefore two or more roundtrips on the RDMA
   network in processing the request.  This is desirable for several
   reasons, as described in the relevant specifications, but it incurs
   latency.  However, since as mentioned the network latency has been so
   much less than the storage processing, this has been a sound
   approach.

   Today, a new class of Storage Class Memory is emerging, in the form
   of Non-Volatile DIMM and NVM Express devices, among others.  These
   devices are characterized by further reduced latencies, in the 10-
   microsecond-order range for NVMe, and sub-microsecond for NVDIMM.
   The 30-50 microsecond write latencies of the above file and block
   protocols are therefore from one to two orders of magnitude larger
   than the storage media!  The client/server processing model of
   traditional storage protocols are no longer amortizable at an
   acceptable level into the overall latency of storage access, due to
   their requiring request/response communication, CPU processing by the
   both server and client (or target and initiator), and the interrupts
   to signal such requests.

   Another important property of certain such devices is the requirement
   for explicitly requesting that the data written to them be made
   durable.  Because durability requires that data be committed to
   memory cells, it is a relatively expensive operation in time (and
   power), and in order to maintain the highest device throughput and
   most efficient operation, the "commit" operation is explicit.  When
   the data is written by an application on the local platform, this
   responsibility naturally falls to that application (and the CPU on



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   which it runs).  However, when data is written by current RDMA
   protocols, no such semantic is provided.  As a result, upper layer
   stacks, and the target CPU, must be invoked to perform it, adding
   overhead and latency that is now highly undesirable.

   When such devices are deployed as the remote server, or target,
   storage, and when such a durability can be requested and guaranteed
   remotely, a new transfer model can be considered.  Instead of relying
   on the server, or target, to perform requested processing and to
   reply after the data is durably stored, it becomes desirable for the
   client, or initiator, to perform these operations itself.  By
   altering the transfer models to support a "push mode", that is, by
   allowing the requestor to push data with RDMA Write and subsequently
   make it durable, a full round trip can be eliminated from the
   operation.  Additionally, the signaling, and processing overheads at
   the remote peer (server or target) can be eliminated.  This becomes
   an extremely compelling latency advantage.

   Together the above discussion argues for a new transfer model
   supporting remote durability guarantees, provided by the RDMA
   transport, and used directly by upper layers on a data source, to
   control durable storage of data on a remote data sink without
   requiring its remote interaction.  Existing, or new, upper layers can
   use such a model in several ways, and evolutionary steps to support
   durability guarantees without required protocol changes are explored
   in the remainder of this document.

   Note that is intended that the requirements and concept of these
   extensions can be applied to any similar RDMA protocol, and that a
   compatible remote durability model can be applied broadly.

2.1.  Requirements

   The fundamental new requirement for extending RDMA protocols is to
   define the property of _durability_. This new property drives the
   operations to extend Placement as defined in existing RDMA protocols.
   When Placed, these protocols require only that the data be visible
   consistently to both the platform on which the buffer resides, and to
   remote peers across the network via RDMA.  In modern hardware
   designs, this buffer can reside in memory, or also in cache, if that
   cache is part of the hardware consistency domain.  Many designs use
   such caches extensively to improve performance of local access.

   Durability, by contrast, requires that the data not only be
   consistently visible, it further requires that the buffer contents be
   preserved across catastrophic failures.  While it is possible for
   caches to be durable, they are typically not.  Efficient designs, in
   fact, lead many implementations to make them volatile.  In these



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   designs, an explicit flush operation, often followed by an explicit
   commit, is required to provide this guarantee.

   For the RDMA protocol to remotely provide durability guarantees, the
   new requirement is mandatory.  Note that this does not imply support
   for durability by the RDMA hardware implementation itself; it is
   entirely acceptable for the RDMA implementation to request durability
   from another subsystem, for example, by requesting that the CPU
   perform the flush and commit.  But, in an ideal implementation, the
   RDMA implementation will be able to act as a master and provide these
   services without further work requests.  Note, it is possible that
   different buffers will require different durability processing, for
   example one buffer may reside in persistent memory, while another may
   place its durable blocks in a persistent storage device.  Many such
   memory-addressable designs are entering the market, from NVDIMM to
   NVMe and even to SSDs and hard drives.

   Therefore, any local memory registration primitive will be enhanced
   to specify an optional durability attribute, along with any local
   information required to achieve it.  These attributes remain local -
   like existing local memory registration, the region is fully
   described by a { handle, offset, length } descriptor, and such
   aspects of the local physical address, memory type, protection
   (remote read, remote write, protection key), etc are not instantiated
   in the protocol.  The RDMA implementation maintains these, and
   strictly performs processing based on them, but they are not known to
   the peer, and therefore are not a matter for the protocol.

   Note, additionally, that by describing durability only through the
   presence of an optional durability attribute, it is possible to
   describe regions as both durable and non-durable, in order to enable
   efficient processing.  When commit is remotely requested of a non-
   durable region, the result is not required to be that the data is
   durable.  This can be used by upper layers to enable bulk-type
   processing with low overhead, by assigning specific durability
   through use of the Steering Tag.

   The intention is that if the underlying region is marked as non-
   volatile, the placement of data into it is also non-volatile (i.e.
   any volatile buffering between the network and the underlying storage
   has been flushed).

   To enable the maximum generality, the commit operation is specified
   to act on a list of { handle, offset, length } regions.  The
   requirement is that each byte of each specified region be made
   durable before the response to the commit is generated.  However,
   depending on the implementation, other bytes in other regions may be
   made durable as part of processing any commit.  Any data in any



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   buffer destined for persistent, durable storage, may become durable
   at any time, even if not requested explicitly.  For example, a simple
   and stateless approach would be for all data be flushed and
   committed, system-wide.  A possibly more efficient implementation
   might track previously written bytes, or blocks with "dirty" bytes,
   and commit only those.  Either result provides the required
   guarantee.  The length of the region list, and the maximum amount of
   data that can be made durable in a single request, are implementation
   dependent and its protocol expression is to be described.

   The commit operation is specified to return a status, which may be
   zero on success but may take other values to be determined.  Several
   possibilities present themselves.  The commit operation may fail to
   make the data durable, perhaps due to a hardware failure, or a change
   in device capability (device read-only, device wear, etc).  The data,
   however, may not have been lost and is still present in the buffer.
   Or, the device may support an integrity check, similar to modern
   error checking memory or media error detection on hard drive
   surfaces, and its status is returned.  Or, the request may exceed
   device limits in size or even transient attribute such as temporary
   media failure.  The behavior of the device itself is beyond the scope
   of this specification.

   Because the commit involves processing on the local platform and the
   actual device, it is expected to take a certain time to be performed.
   For this reason, the commit operation is required to be defined as a
   "queued" operation on the RDMA device, and therefore also the
   protocol.  The RDMA protocol supports RDMA Read and Atomic in such a
   fashion.  The iWARP family defines a "queue number" with queue-
   specific processing that is naturally suited for this.  Queuing
   provides a convenient means for supporting ordering among other
   operations, and for flow control.  Flow control for RDMA Reads and
   Atomics share incoming and outgoing crediting depths ("IRD/ORD");
   commit will either share these, or define their own separate values.

2.1.1.  Non-Requirements

   The protocol does not include a "RDMA Write with durability", that
   is, a modifier on the existing RDMA Write operation.  While it might
   seem a logical approach, several issues become apparent:

      The existing RDMA Write operation is unacknowledged at the RDMA
      layer.  Requiring it to provide an indication of remote durability
      would require it to have an acknowledgement, which would be an
      undesirable extension to the operation.

      Such an operation would require flow control and therefore also
      buffering on the responding peer.  Existing RDMA Write semantics



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      are not flow controlled and as tagged transfers are by design
      zero-copy i.e. unbuffered.  Requiring these would introduce
      potential pipeline stalls and increase implementation complexity
      in a critical performance path.

      The operation at the initiator would stall until the
      acknowledgement of completion, significantly changing the semantic
      of the existing operation, and complicating software by blocking
      the send work queue.  As each operation would be self-describing
      with respect to durability, individual operations would therefore
      block with differing semantics.

      Even for the possibly-common case of commiting after every write,
      it is highly undesirable to impose new optional semantics on an
      existing operation.  And, the same result can be achieved by
      sending the commit in the same network packet, and since the RDMA
      Write is unacknowledged while the commit is always replied-to, no
      additional overhead is imposed on the combined exchange.

   [Further expand on the undesirable nature of such a change.]

2.2.  Additional Semantics

   Ordering w.r.t.  RDMA Write, receives, RDMA Read, other commits.
   Also, ensure ordering ensures similar remote semantics to local

   The commit operation is ordered with respect to certain other
   operations, and it may be advantageous to combine certain actions
   into the same request, or requests with specific ordering to the
   commit.  Examples to be discussed include:

      Additional optional payload to be placed and made durable in an
      atomic fashion after the requested commit.  A small (64 bit)
      payload, sent in the same, or other single, request, and aligned
      such that it can be made durable in a single hardware operation,
      can be used to satisfy the "log update" scenario (describe this in
      more detail).

      Immediate data to be optionally provided in a completion to an
      upper layer on the remote peer.  Such an indication can be used to
      signal the upper layer that certain data has been placed in the
      peer's buffer, and has been made available durably.

      Remote invalidation, as optionally performed by existing RDMA
      protocols for other operations.

      Upper Layer message, an optional full message to be provided in a
      completion after the commit.



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      Integrity check for committed data, which could take the form of a
      value to be verified before returning, or a value computed and
      returned which the initiator can use to verify.  Specification of
      the checksum or hash algorithm, or its negotiation by an upper
      layer, will be necessary if adopted.

3.  Proposed Extensions

   The extensions in this document fall into two categories:

   o  Local behavior extensions

   o  Protocol extensions

   These categories are described, and may be implemented, separately.

3.1.  Local Extensions

   Here discuss memory registration, new memory and protection
   attributes, and applicability to both remote and "local" (receives).

3.1.1.  Registration Semantics

   New platform-specific attributes to RDMA registration, allows them to
   be processed at the server *only* without client knowledge, or
   protocol exposure.  No client knowledge - ensures future interop

   New local PM memory registration example:

      Register(region[], PMType, mode) -> Handle



         PMType includes type of PM i.e. plain RAM, or "commit
         required", or PCIe-resident, or any other local platform-
         specific processing

         Mode includes disposition of data Read and/or write e.g.
         Cacheable after operation (needed by CPU on data sink)

   Handle is processed in receiving NIC during RDMA operation to
   specified region, under control of original Mode.

   Also consider whether potential "integrity check" behavior can be
   made per-region.  If so, piggybacking it on the registration enables
   selecting the integrity hash, and making its processing optional and
   straightforward.




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   Any other per-region durability processing to be explored.

3.1.2.  Completion Semantics

   Transparency is possible when upper layer provides Completions (e.g.
   messages or immediate data)

   Commit to durability can be piggybacked by data sink upon signaling.
   Upper layer may not need to explicitly Commit in this case, which of
   course are dependent on upper layer and workload.

   Can apply this concept to RDMA Write with Immediate Or ...ordinary
   receives.  Strong possibilities exist - explore here.

   Ordering of operations is critical: Such RDMA Writes cannot be
   allowed to "pass" durability.  Therefore, protocol implications may
   also exist.

   Discuss optional behaviors explored in prior section, and whether/how
   they generate completions.

3.1.3.  Platform Semantics

   Writethrough behavior on durable regions and reasons for same.
   Consider requiring/recommending a local writethrough behavior on any
   durable region, to support a nonblocking hurry-up to avoid future
   stalls on a subsequent cache flush, prior to a commit.  Also, it
   would enhance durability.

   PCI extension to support Commit Allow NIC to provide durability
   directly and efficiently To Memory, CPU, PCI Root, PM device, PCIe
   device, ... Avoids CPU interaction Supports strong data consistency
   model Performs equivalent of: CLFLUSHOPT (region list) PCOMMIT Or if
   NIC is on memory bus or within CPU complex... Other possibilities
   exist

3.2.  RDMAP Extensions

   This document defines a new RDMA operation, "RDMA Commit".  The wire-
   related aspects of the proposed protocol are discussed in this
   section.

   This section and the ones following present one possible approach
   toward defining the wire protocol defined by the above discussion.
   The definitions are included for initial discussion and do not
   comprise a complete specification.  Certain additional protocol
   features of any potential new extension, such as any associated




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   Immediate Data, Solicited Events, Remote Invalidation, ULP Message
   inclusion, etc, are left to a later version.

   For reference, Figure 1 depicts the format of the DDP Control and
   RDMAP Control Fields, in the style and convention of RFC 5040 and
   RFC7306:

   The DDP Control Field consists of the T (Tagged), L (Last), Resrv,
   and DV (DDP protocol Version) fields RFC 5041.  The RDMAP Control
   Field consists of the RV (RDMA Version), Rsv, and Opcode fields RFC
   5040.

   This specification adds values for the RDMA Opcode field to those
   specified in RFC 5040.  Table 1 defines the new values of the RDMA
   Opcode field that are used for the RDMA Messages defined in this
   specification.

   As shown in Table 1, STag (Steering Tag) and Tagged Offset are valid
   only for certain RDMA Messages defined in this specification.
   Table 1 also shows the appropriate Queue Number for each Opcode.

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |T|L| Resrv | DV| RV|R|  Opcode |
                                   | | |       |   |   |s|         |
                                   | | |       |   |   |v|         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Invalidate STag                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 1: DDP Control and RDMAP Control Fields

   All RDMA Messages defined in this specification MUST carry the
   following values:

   o  The RDMA Version (RV) field: 01b.

   o  Opcode field: Set to one of the values in Table 1.

   o  Invalidate STag: Set to zero, or optionally to non-zero by the
      sender, processed by the receiver.

   Note: N/A in the table below means Not Applicable







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   -------+-----------+-------+------+-------+-----------+--------------
   RDMA   | Message   | Tagged| STag | Queue | Invalidate| Message
   Opcode | Type      | Flag  | and  | Number| STag      | Length
          |           |       | TO   |       |           | Communicated
          |           |       |      |       |           | between DDP
          |           |       |      |       |           | and RDMAP
   -------+-----------+-------+------+-------+-----------+--------------
   -------+-----------+-------------------------------------------------
   01100b | RDMA      |  0    |  N/A |  1    |  opt      |  Yes
          | Commit    |       |      |       |           |
          | Request   |       |      |       |           |
   -------+-----------+-------------------------------------------------
   01101b | RDMA      |  0    |  N/A |  3    |  N/A      |  Yes
          | Commit    |       |      |       |           |
          | Response  |       |      |       |           |
   -------+-----------+-------------------------------------------------

               Table 1: Additional RDMA Usage of DDP Fields

   This extension adds RDMAP use of Queue Number 1 for Untagged Buffers
   for issuing RDMA Commit Requests, and use of Queue Number 3 for
   Untagged Buffers for tracking RDMA Commit Responses.

   All other DDP and RDMAP Control Fields are set as described in RFC
   5040 and RFC 7306.

   Table 2 defines which RDMA Headers are used on each new RDMA Message
   and which new RDMA Messages are allowed to carry ULP payload.

   -------+-----------+-------------------+-------------------------
   RDMA   | Message   | RDMA Header Used  | ULP Message allowed in
   Message| Type      |                   | the RDMA Message
   OpCode |           |                   |
          |           |                   |
   -------+-----------+-------------------+-------------------------
   -------+-----------+-------------------+-------------------------
   01100b | RDMA      | None              | TBD
          | Commit    |                   |
          | Request   |                   |
   -------+-----------+-------------------+-------------------------
   01101b | RDMA      | None              | No
          | Commit    |                   |
          | Response  |                   |
   -------+-----------+---------------------------------------------

                     Table 2: RDMA Message Definitions

   Further discussion.



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3.2.1.  RDMA Commit Request Header Format

   The RDMA Commit Request Message makes use of the DDP Untagged Buffer
   Model.  RDMA Commit Request messages MUST use the same Queue Number
   as RDMA Read Requests and RDMA Extensions Atomic Operation Requests
   (QN=1).  Reusing the same queue number for RMDA Commit Requests
   allows the operations to reuse the same infrastructure (e.g.
   Outbound and Inbound RDMA Read Queue Depth (ORD/IRD) flow control) as
   that defined for RDMA Read Requests.

   The RDMA Commit Request Message carries an RDMA Commit header that
   describes the ULP Buffer address in the Responder's memory.  The RDMA
   Write Request header immediately follows the DDP header.  The RDMAP
   layer passes an RDMAP Control Field to the DDP layer.  Figure 2
   depicts the RDMA Commit Request Header that is used for all RDMA
   Commit Request Messages:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Request Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Data Sink STag                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Data Sink Length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Data Sink Tagged Offset                   |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: RDMA Commit Request Header

   Request Identifier: 32 bits.  The Request Identifier specifies a
      number that is used to identify the RDMA Commit Request Message.
      The value used in this field is selected by the RNIC that sends
      the message, and it is reflected back to the Local Peer in the
      RDMA Commit Response message.  N.B.  Is this field really useful
      to the RNIC, or does ordering suffice???

   Data Sink STag: 32 bits  The Data Sink STag identifies the Remote
      Peer's Tagged Buffer targeted by the RDMA Commit Request.  The
      Data Sink STag is associated with the RDMAP Stream through a
      mechanism that is outside the scope of the RDMAP specification.

   Data Sink Tagged Offset: 64 bits  The Data Sink Tagged Offset
      specifies the starting offset, in octets, from the base of the
      Remote Peer's Tagged Buffer targeted by the RDMA Commit Request.



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   ...  Additional region identifiers to be committed in processing the
      RDMA Commit Request, and/or upper layer message to be passed to
      upper layer after commit completion (TBD).

3.2.2.  RDMA Commit Response Header Format

   The RDMA Commit Response Message makes use of the DDP Untagged Buffer
   Model.  RDMA Commit Response messages MUST use the same Queue Number
   as RDMA Extensions Atomic Operation Responses (QN=3).  The RDMAP
   layer passes the following payload to the DDP layer on Queue Number
   3.

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Original Request Identifier                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Status                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: RDMA Commit Response Header

   Original Request Identifier: 32 bits.  The Original Request
      Identifier is set to the value specified in the Request Identifier
      field that was originally provided in the corresponding RDMA
      Commit Request Message.  N.B. ditto previous question.

   Status: 32 bits.  Zero if the RDMA Commit was successfully processed,
      or any other value if not.

3.2.3.  Ordering

   Ordering and completion rules for RDMA Commit Request are similar to
   those for an Atomic operation as described in section 5 of RFC 7306.
   The queue number field of the RDMA Commit Request for the DDP layer
   MUST be 1, and the RDMA Commit Response for the DDP layer MUST be 3.

   There are no ordering requirements for the placement of the data to
   be committed, nor are there any requirements for the order in which
   the data is made durable.  Data received by prior operations (e.g.
   RDMA Write) MAY be submitted for placement at any time, and
   durability MAY occur before the commit is requested.  Data committed
   after placement MAY become durable at any time, in the course of
   operation of the persistency management of the storage device, or by
   other actions resulting in durability.  Any data specified by the
   commit operation, in any case, MUST be made durable before successful
   return of the commit.






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3.2.4.  Atomicity

   There are no atomicity guarantees provided on the Responder's node by
   the RDMA Commit Operation with respect to any other operations.
   While the Completion of the RDMA Commit Operation ensures that the
   requested data was placed and committed to the target Tagged Buffer,
   other operations might have also placed or fetched overlapping data.
   The upper layer is responsible for arbitrating any shared access.

   (To discuss) The commit operation provides an optional block of data
   which is committed to a specified region after the successful
   completion of the requested commit.  This specified region MAY be
   constrained in size and alignment by the implementation, and the
   implementation MUST fail the operation and send a terminate message
   if the subsequent commit cannot be performed atomically.  The
   implementation MUST NOT perform the subsequent commit if an error
   occurred on the requested commit, and SHOULD return a non-zero status
   indicating the error.

   (Sidebar) It would be useful to make a statement about other RDMA
   Commit to the target buffer and RDMA Read from the target buffer on
   the same connection.  Use of QN 1 for these operations provides
   ordering guarantees which imply that they will "work" (see #7 below).
   NOTE: this does not, however, extend to RDMA Write, which is not
   sequenced nor does it employ a DDP QN.

3.2.5.  Discovery of RDMAP Extensions

   As for RFC 7306, explicit negotiation by the RDMAP peers of the
   extensions covered by this document is not required.  Instead, it is
   RECOMMENDED that RDMA applications and/or ULPs negotiate any use of
   these extensions at the application or ULP level.  The definition of
   such application-specific mechanisms is outside the scope of this
   specification.  For backward compatibility, existing applications
   and/or ULPs should not assume that these extensions are supported.

   In the absence of application-specific negotiation of the features
   defined within this specification, the new operations can be
   attempted, and reported errors can be used to determine a remote
   peer's capabilities.  In the case of RDMA Commit, an operation to a
   previously Advertised buffer with remote write permission can be used
   to determine the peer's support.  A Remote Operation Error or
   Unexpected OpCode error will be reported by the remote peer if the
   Operation is not supported by the remote peer.







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4.  Ordering and Completions Table

   Table 3 summarizes the ordering relationships for the RDMA Commit
   operation from the standpoint of the Requester.  Note that in the
   table, Send Operation includes Send, Send with Invalidate, Send with
   Solicited Event, and Send with Solicited Event and Invalidate.  Also
   note that Immediate Operation includes Immediate Data and Immediate
   Data with Solicited Event.

   As for the prior section, the text below presents one possible
   approach, and is included in skeletal form to be filled-in when
   appropriate.

   Note: N/A in the table below means Not Applicable

   ----------+------------+-------------+-------------+-----------------
   First     | Second     | Placement   | Placement   | Ordering
   Operation | Operation  | Guarantee at| Guarantee at| Guarantee at
             |            | Remote Peer | Local Peer  | Remote Peer
   ----------+------------+-------------+-------------+-----------------
   RDMA      | TODO       | No Placement| N/A         | Completed in
   Commit    |            | Guarantee   |             | Order
             |            | between Foo |             |
             |            | and Bar     |             |
   ----------+------------+-------------+-------------+-----------------
   TODO      | RDMA       | No Placement| N/A         | TODO
             | Commit     | Guarantee   |             |
             |            | between Foo |             |
             |            | and Bar     |             |
   ----------+------------+-------------+-------------+-----------------
   TODO      | TODO       | Etc         | Etc         | Etc
   ----------+------------+-------------+-------------+-----------------
   ----------+------------+-------------+-------------+-----------------

                      Table 3: Ordering of Operations

5.  Error Processing

   In addition to error processing described in section 7 of RFC 5040
   and section 8 of RFC 7306, the following rules apply for the new RDMA
   Messages defined in this specification.

5.1.  Errors Detected at the Local Peer

   The Local Peer MUST send a Terminate Message for each of the
   following cases:





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   1.  For errors detected while creating a RDMA Commit Request or other
       reasons not directly associated with an incoming Message, the
       Terminate Message and Error code are sent instead of the Message.
       In this case, the Error Type and Error Code fields are included
       in the Terminate Message, but the Terminated DDP Header and
       Terminated RDMA Header fields are set to zero.

   2.  For errors detected on an incoming RDMA Commit Request or RDMA
       Commit Response, the Terminate Message is sent at the earliest
       possible opportunity, preferably in the next outgoing RDMA
       Message.  In this case, the Error Type, Error Code, and
       Terminated DDP Header fields are included in the Terminate
       Message, but the Terminated RDMA Header field is set to zero.

   3.  For errors detected in the processing of the RDMA Commit itself,
       that is, the act of making the data durable, no Terminate Message
       is generated.  Because the data is not lost, the connection MUST
       NOT terminate and the peer MUST inform the requester of the
       status, and allow the requester to perform further action, for
       instance, recovery.

5.2.  Errors Detected at the Remote Peer

   On incoming RDMA Commit Requests, the following MUST be validated:

   o  The DDP layer MUST validate all DDP Segment fields.

   The following additional validation MUST be performed:

   o  If the RDMA Commit cannot be satisfied, due to transient or
      permanent errors detected in the processing by the Responder, a
      status MUST be returned to the Requestor.  Valid status values are
      to be specified.

6.  IANA Considerations

   This document requests that IANA assign the following new operation
   codes in the "RDMAP Message Operation Codes" registry defined in
   section 3.4 of [RFC6580].

   0xC  RDMA Commit Request, this specification

   0xD  RDMA Commit Response, this specification

   Additionally, the name of the listed entry in "RDMAP DDP Untagged
   Queue Numbers" as defined in section 10.2 of [RFC7306] is requested
   to be updated as follows:




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   0x00000003 Queue 3  Modify name to "Atomic Response and RDMA Commit
      Response operations" and add reference to this specification

   Note to RFC Editor: this section may be edited and updated prior to
   publication as an RFC.

7.  Security Considerations

   This document specifies extensions to the RDMA Protocol specification
   in RFC 5040 and RDMA Protocol Extensions in RFC 7306, and as such the
   Security Considerations discussed in Section 8 of RFC 5040 and
   Section 9 of RFC 7306 apply.  In particular, RDMA Commit Operations
   use ULP Buffer addresses for the Remote Peer Buffer addressing used
   in RFC 5040 as required by the security model described in [RDMAP
   Security [RFC5042]].

   If the "push mode" transfer model discussed in section 2 is
   implemented by upper layers, new security considerations will be
   potentially introduced in those protocols, particularly on the
   server, or target, if the new memory regions are not carefully
   protected.  Therefore, for them to take full advantage of the
   extension defined in this document, additional security design is
   required in the implementation of those upper layers.  The facilities
   of RFC5042 [RFC5042] can provide the basis for any such design.

   In addition to protection, in "push mode" the server or target will
   expose memory resources to the peer for potentially extended periods,
   and will allow the peer to perform remote durability requests which
   will necessarily consume shared resources, e.g. memory bandwidth,
   power, and memory itself.  It is recommended that the upper layers
   provide a means to gracefully adjust such resources, for example
   using upper layer callbacks, without resorting to revoking RDMA
   permissions, which would summarily close connections.  With the
   initiator applications relying on the protocol extension itself for
   managing their required durability, the lack of such an approach
   would lead to frequent recovery in low-resource situations,
   potentially opening a new threat to such applications.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.





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   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, DOI 10.17487/RFC5040, October
              2007, <http://www.rfc-editor.org/info/rfc5040>.

   [RFC5041]  Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
              Data Placement over Reliable Transports", RFC 5041,
              DOI 10.17487/RFC5041, October 2007,
              <http://www.rfc-editor.org/info/rfc5041>.

   [RFC5042]  Pinkerton, J. and E. Deleganes, "Direct Data Placement
              Protocol (DDP) / Remote Direct Memory Access Protocol
              (RDMAP) Security", RFC 5042, DOI 10.17487/RFC5042, October
              2007, <http://www.rfc-editor.org/info/rfc5042>.

   [RFC6580]  Ko, M. and D. Black, "IANA Registries for the Remote
              Direct Data Placement (RDDP) Protocols", RFC 6580,
              DOI 10.17487/RFC6580, April 2012,
              <http://www.rfc-editor.org/info/rfc6580>.

   [RFC7306]  Shah, H., Marti, F., Noureddine, W., Eiriksson, A., and R.
              Sharp, "Remote Direct Memory Access (RDMA) Protocol
              Extensions", RFC 7306, DOI 10.17487/RFC7306, June 2014,
              <http://www.rfc-editor.org/info/rfc7306>.

8.2.  Informative References

   [RFC5045]  Bestler, C., Ed. and L. Coene, "Applicability of Remote
              Direct Memory Access Protocol (RDMA) and Direct Data
              Placement (DDP)", RFC 5045, DOI 10.17487/RFC5045, October
              2007, <http://www.rfc-editor.org/info/rfc5045>.

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <http://www.rfc-editor.org/info/rfc5661>.

   [RFC5666]  Talpey, T. and B. Callaghan, "Remote Direct Memory Access
              Transport for Remote Procedure Call", RFC 5666,
              DOI 10.17487/RFC5666, January 2010,
              <http://www.rfc-editor.org/info/rfc5666>.

   [RFC5667]  Talpey, T. and B. Callaghan, "Network File System (NFS)
              Direct Data Placement", RFC 5667, DOI 10.17487/RFC5667,
              January 2010, <http://www.rfc-editor.org/info/rfc5667>.






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   [RFC7145]  Ko, M. and A. Nezhinsky, "Internet Small Computer System
              Interface (iSCSI) Extensions for the Remote Direct Memory
              Access (RDMA) Specification", RFC 7145,
              DOI 10.17487/RFC7145, April 2014,
              <http://www.rfc-editor.org/info/rfc7145>.

   [SCSI]     American National Standards Institute, "SCSI Primary
              Commands - 3 (SPC-3) (INCITS 408-2005)", May 2005.

   [SMB3]     Microsoft Corporation, "Server Message Block (SMB)
              Protocol Versions 2 and 3 (MS-SMB2)", October 2015.

   [SMBDirect]
              Microsoft Corporation, "SMB2 Remote Direct Memory Access
              (RDMA) Transport Protocol (MS-SMBD)", October 2015.

   [SNIANVM]  Storage Networking Industry Association NVM TWG, "SNIA NVM
              Programming Model v1.0", 2014.

8.3.  URIs

   [1] http://www.nvmexpress.org

   [2] http://www.jedec.org

Appendix A.  DDP Segment Formats for RDMA Extensions

   This appendix is for information only and is NOT part of the
   standard.  It simply depicts the DDP Segment format for each of the
   RDMA Messages defined in this specification.

A.1.  DDP Segment for RDMA Commit Request

   Figure 3 depicts an RDMA Commit Request, DDP Segment:

















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    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 Control | RDMA Control  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Reserved (Not Used)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            DDP (RDMA Commit Request) Queue Number             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        DDP (RDMA Commit Request) Message Sequence Number      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Request Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Data Sink STag                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Data Sink Length                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Data Sink Tagged Offset                     |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 3

A.2.  DDP Segment for RDMA Commit Response

   Figure 4 depicts an RDMA Commit Response, DDP Segment:

    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 Control | RDMA Control  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Reserved (Not Used)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              DDP (RDMA Commit Response) Queue Number          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       DDP (RDMA Commit Response) Message Sequence Number      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Original Request Identifier                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Status                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 4




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Authors' Addresses

   Tom Talpey
   Microsoft
   One Microsoft Way
   Redmond, WA  98052
   US

   Email: ttalpey@microsoft.com


   Jim Pinkerton
   Microsoft
   One Microsoft Way
   Redmond, WA  98052
   US

   Email: jpink@microsoft.com

































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