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.
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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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