One document matched: draft-dicecco-vitcp-00.txt
Network Working Group S. DiCecco
Internet-Draft J. Williams
<draft-dicecco-vitcp-00.txt> GigaNet, Inc.
Expires January 2001 July 14, 2000
VI / TCP (Internet VI)
Status of this memo
This document is an Internet-Draft and is offered in full accordance
with all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
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The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
memo are to be interpreted as described in RFC2119.
Table of Contents
1 Abstract 2
2 Overview 3
2.1 VI Architectural Components 3
2.2 VI/TCP 4
2.2.1 Extensions to VI 4
2.2.2 VI/TCP Overview 4
2.2.2.1 Basic VI Components 4
2.2.2.2 Introduction to VI/TCP 5
2.2.2.2.1 VI/TCP Addressing 5
2.2.2.2.2 VI/TCP Connection Management 5
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2.2.2.2.3 VI/TCP Protocol Messaging 6
2.2.2.2.4 TCP/IP Options and VI/TCP 6
2.2.2.2.5 VI/TCP Retransmissions 6
2.2.2.2.6 Note on Outstanding RDMA Reads 7
3 The VI/TCP Protocol 7
3.1 VI/TCP Segment Header 8
3.2 VI/TCP Connection Establishment (CE) Header 12
3.3 VI/TCP RDMA Header 14
4 VI/TCP Connection Establishment 15
4.1 Basic Connection Establishment Timeline 15
4.2 Connection Establishment - Active 16
4.3 Connection Establishment - Passive 17
5 Security Considerations 18
6 References 18
7 Author's Addresses 19
1. Abstract
The Virtual Interface (VI) architecture [VIAR] describes a high
performance design for interfacing distributed applications to
accelerated protocol processing. VI seeks to improve the performance
of such applications by reducing the latency and overheads associated
with standard communications protocol stack processing. VI greatly
reduces the processing overhead associated with traditional network
architectures by providing applications a protected, directly
accessible interface to network hardware - a Virtual Interface.
This memo describes extensions to the VI Architecture designed to
facilitate operation over TCP/IP. These extensions take the form of
enhancements to the VI Provider Library API defined in the VI
Architecture Developer's Guide [VIDG], and a "VI Protocol" which
supports VI functionality during operation over TCP/IP.
The extensions to the VI Architecture which support operation over
TCP/IP are intended to be fully compliant with the VI Architecture
[VIAR] and its associated Developer's Guide [VIDG].
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2. Overview
This section contains a brief overview of VI components and a
functional overview of VI operation over TCP/IP
2.1. VI Architectural Components
VI is comprised of four architectural components - Virtual
Interfaces, Completion Queues, VI Providers, and VI Consumers.
Virtual Interfaces (VIs) are the mechanisms that allow VI Consumers
direct access to the data transfer services of VI Providers. VI
Consumers post data transfer requests, in the form of Descriptors,
directly to the VI Provider. Descriptors are structures that contain
the information necessary for the VI Provider to process the data
transfer (e.g.,data location). Descriptors are posted to Work Queues
(send and receive) associated with the VI. Facilities are provided to
signal VI Descriptor postings to the network adapter. Processing of
posted Descriptors is asynchronous and descriptors are marked when
processing completes. VI Consumers remove completed descriptors from
Work Queues for reuse in subsequent requests.
Completion Queues provide a facility whereby VI Consumers can create a
single point of notification for processing completed Descriptors.
Once a Work Queue is associated with a Completion Queue, handling of
all completions are handled via that Completions Queue.
The VI Provider consists of a physical network interface (NIC) and
driver functionality. The VI NIC implements the Virtual Interfaces and
Completion Queues, and directly performs data transfers. VI NIC
drivers provide the control and resource management functions to
maintain the VI between consumers and VI NICs.
VI Consumers are typically applications programs and their supporting
operating system functions. VI Consumers represent the users of a
Virtual Interface. Access to the Virtual Interface is through a
library referred to as the VI Provider Library [VIDG]. The VI Provider
Library provides an application programming interface for hardware
connection, endpoint creation and destruction, connection management,
memory handling, data transfer, queue management, informational
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queries, name services, and error handling.
2.2. VI/TCP
This section introduces the fundamentals of VI operation over TCP.
2.2.1. Extensions to VI
The proposed protocol supports the VI Architecture as currently
defined. In addition, the protocol supports certain enhancements to
VI. Extensions to the API defined in [VIDG] would be required to
exploit such enhancements. Proposed enhancements are as follows:
- Descriptor Flow Control: Transmit descriptors may be posted in
advance of the corresponding receive descriptors. The VI Provider will
supply flow control.
- Security Field: A security field is contained in the
Connect Request and Connect Accept PDUs. Use of this field is to be
defined.
- Attribute Negotiation: VI Architecture requires that incoming
connection establishment attempts be rejected unless the calling and
called VI Attributes match (e.g., Maximum Transfer Unit Size). The
protocol permits downward negotiation of MTU sizes.
2.2.2. VI/TCP Overview
This Section provides an overview of how the components of a
Virtual Interface are created, managed, and destroyed, and also
introduces the data transfer models.
2.2.2.1. Basic VI Components
Operations on basic VI architectural components remain largely
unchanged with VI/TCP. VI functionality is invoked by a VI Consumer
through the API defined in [VIDG]. Access to a VI NIC is achieved by
opening a handle to the driver representing the NIC. This handle is
used in subsequent operations. All memory used in data transfer is
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"registered" with the VI Provider. Memory handles are used to identify
the region and to qualify virtual memory addresses. VIs are created by
the VI Provider upon request by the VI Consumer. Connections are not
established by creation of a VI and no data transfer can occur until
the VI is connected to another. VI Work Queues may be associated with
Completion Queues to provide a single handling point for completed VI
Descriptors. VI provides a connection-oriented data transfer service.
Newly created VIs are not pre-associated with other VIs; a VI must be
explicitly connected to another to enter its data transfer phase. VI
provides two types of data transfers - traditional Send/Receive, and
Remote Direct Memory Access (RDMA).
2.2.2.2. Introduction to VI/TCP
This Section serves as an introduction to VI operation over
TCP/IP.
2.2.2.2.1. VI/TCP Addressing
The VI Architecture defines a generic "VI Network Address" format
consisting of an "address" portion and a "discriminator" portion. When
operating VI/TCP, the address portion contains an IP address and the
discriminator is per the VI Architecture [VIAR]. One transport layer
port is reserved for passive connection establishment. All incoming VI
connections are through this port and VI applications distinguish
themselves by the VI Network Address discriminator. For active
connection establishment, multiple transport layer ports are used.
2.2.2.2.2. VI/TCP Connection Management
With VI/TCP, all VI connections are implemented over an underlying
TCP connection. The VI/TCP connection establishment process requires
an underlying TCP connection over which VI/TCP protocol may be
exchanged. VI connections have a one-to-one correspondence with TCP
connections. This is referred to as the VI/TCP connection. When a VI
connection is closed, the underlying TCP connection must be closed.
Similarly, when a TCP connection is closed, the associated VI
connection must be closed. VI Provider's handling VIP_Connect Request
primitives [VIDG], first request TCP establish its connection and then
perform VI/TCP protocol messaging over this underlying connection. VI
Providers must have
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accepted an underlying TCP connection before the associated VI
connection is accepted. VI/TCP Provider's MUST check that
address/handles are valid for the underlying connection. From the
perspective of a VI/TCP Provider, TCP connection setup is an atomic
operation that either succeeds or fails. If the operation succeeds, VI
connection establishment is initiated; otherwise, the VI connection is
rejected.
2.2.2.2.3. VI/TCP Protocol Messaging
VI/TCP functionality is invoked by a VI Consumer through the API
defined in [VIDG]. The VI Provider supplies this functionality. The
VI Provider, through use of the VI Protocol, supports this VI/TCP
functionality. The VI Protocol defines "messages" to implement VI
these functions (e.g., connections establishment). Typically, there is
one message per Transmit Descriptor. Each message has a type (e.g.,
RDMA Write).
VI messages are divided into "segments". These segments are sent, in
order, over the associated TCP connection. It is recommended, but not
required, that there be exactly zero or one VI segment for each TCP
segment and that VI segments not be fragmented to span multiple TCP
segments. All segments for one VI message will be transmitted before
the next message is started. An exception is provided in that RDMA
Read Response segments may be interleaved with segments of any message
type other than another RDMA Read Response.
2.2.2.2.4. TCP/IP Options and VI/TCP
It is strongly recommended that TCP connections supporting VI/TCP
implement the timestamp option for PAWS (protection against wrapped
sequence numbers) as defined in RFC1323, TCP Extensions for High
Performance [PAWS].
2.2.2.2.5. VI/TCP Retransmissions
VI/TCP will retransmit dropped segments, as required. It is
recommended that retransmitted segments contain the same data as the
original dropped segment. In certain circumstances, this will not be
possible without undue burden on an implementation. The following
exceptions are
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noted:
- The "RX Descriptors Posted" field of the protocol's "VI Segment
Header" may contain the current value instead of the value at the time
of its original posting. Senders must not assume that this value has
actually been received since there are no facilities for determining
which of the two values has been received from the acknowledgement.
- Retransmission is required, but data access results in an access
violation and retransmission cannot occur.
- Retransmission is required, but cannot occur because the VI/TCP
connection has been closed.
If a VI NIC is unable to retransmit original data, it may pad and
should set the "Transmit Error" bit in the "Type" field of the "VI
Segment Header".
2.2.2.2.6. Note on Outstanding RDMA Reads
For each RDMA Read Request received, memory allocated for the
request must be held until the response is acknowledged. The number of
outstanding RDMA Reads must be limited to control resource exhaustion.
Discarding excessive RDMA Reads pending completions of outstanding
requests does not seem viable in the absence of a deadlock avoidance
mechanism. It is proposed that the VI Protocol be extended to provide
negotiation of the number of outstanding RDMA Reads during connection
establishment. This number would represent a per VI limit and the
negotiated value would remain for the lifetime of the VI/TCP
connection.
3. The VI/TCP Protocol
This section provides the VI/TCP protocol data unit formats. All
multibyte formats are to be represented in network byte order (i.e.,
big-endian). Each VI/TCP PDU contains a VI Segment Header. Optionally,
an RDMA Header or CE (connection establishment) Header may be present.
The VI/TCP Segment Header provides sufficient features to support non-
RDMA send/receives. The RDMA Header must be included for RDMA
transfers. The CE Header must be included for connection
establishment. Encapsulations are as follows:
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| Lower Layer Headers |
+----------------------------------------+
| IP Header |
+----------------------------------------+
| TCP Header |
+----------------------------------------+
| VI/TCP Segment Header |
+----------------------------------------+
| (optional) VI/TCP RDMA or CE Header |
+----------------------------------------+
| VI/TCP Consumer's Data |
3.1. VI/TCP Segment Header
The VI/TCP Segment Header is defined as follows.
| Byte 0 | Byte 1 | Byte 2 | Byte 3 |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
| Version | Type/Flags | Segment Length |
+---------------+---------------+---------------+---------------+
| Data Offset |
+---------------+---------------+---------------+---------------+
| Immediate Data |
+---------------+---------------+---------------+---------------+
| Message Number |
+---------------+---------------+---------------+---------------+
| Message ACK |
+---------------+---------------+---------------+---------------+
| Rx Descriptors Posted | Remote Error Code |
+---------------+---------------+---------------+---------------+
| VI/TCP User Data |
| |
Version
This is an 8-bit field indicating the VI/TCP version.
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Type/Flags
Type is a 5-bit field indicating the packet type. Valid message types
are:
- Send
- RDMA Read Request
- RDMA Read Response
- RDMA Write
- NOP
- Connect Request
- Connect Accept
- Connect Reject
- Connect No Match
Flags is a 3-bit field defined as follows:
- BIT 1 : Immediate Data Valid
As defined by the VI Architecture [VIAR]
- BIT 2 : End of Message
Indicates the current segment is the last of a message
- BIT 3 : Transmit Error
Indicates either transmit length or protection error
Segment Length
Segment Length is a 16-bit field containing the length of the VI/TCP
segment including the VI/TCP Segment Header
Data Offset
For the initial segment of any message, this 32-bit field will contain
zero. For subsequent segments, it will contain the number of bytes
already transferred for this message in prior segments. Only segment
payload is included in this count; headers are specifically not
included.
Immediate Data
May hold 32-bits of optional user data as described by the VI
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Architecture [VIAR].
Message Number
Messages are sequentially number by the VI/TCP Provider. The initial
Message Number may be varied by an implementation. For RDMA Read
Responses, Message Number carries the message number of the
corresponding RDMA Read Request. Any two segments with the same type
are part of the same message if and only if their message numbers are
equal. Segments within a message may be processed out of order.
Reordering messages is not supported.
Rx Descriptors Posted
Indicates the number of receive Descriptors, modulo 2^16, that have
been posted during the lifetime of the VI/TCP connection. If
Descriptor flow control is in effect, the VI/TCP provider must delay
any transmission which would consume receive Descriptors until receive
descriptors complete and become available.
Notes on NOP
NOPs are used to send a Message ACK when a VI has no data to transmit.
If a VI has data to transmit, the Rx Descriptors Posted number is
included in the transferred segments. However, if a transmitter is
idle, a NOP is utilized to permit conveyance of Rx Descriptors Posted
in the absence of use data message segments. Idle VI/TCP connections
that have an updated Rx Descriptors Posted value, must use NOP to
convey this information. NOPs should be sent whenever there have been
Rx Descriptors Posted since the last segment sent and the number of
unused credits falls below some threshold. Unused credits are the
number of Rx Descriptors of which the remote VI has been notified but
has not yet used. The threshold value should be set at the time of
connection establishment.
Message ACK
Message ACK is valid only for VI/TCP connections at the Reliable
Delivery Level [VIAR]. Message ACK is used in conjunction with Remote
Error Code to provide information relating to memory protection or VI
Descriptor errors and also to provide facilities for implementation
specific error handling. If the VI Error subfield of the Remote Error
Code
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(Remote Error Codes, next section) indicates "No Error", then Message
ACK contains the Message Number from the last VI Message received
without error. If VI Error is OTHER THAN "No Error", then Message ACK
contains the Message Number of the message segment in error. Message
ACK should not be indicated for messages until both message data has
been written to host memory and the doorbell has been rung. Message
ACKs may be included in any VI Message Segment including that of a NOP
message.
When a VI/TCP connection is supporting level Reliable Reception, the
Message ACK field must be valid and will be used determine when
transmit Descriptors will be completed. RDMA Reads are completed upon
receipt of a valid response. Message ACK are indicated for messages
received in error. In this case, the VI Error Type field of Remote
Error Code is set to reflect the appropriate VI error. Remote Error
Code is defined in the following paragraph. Message ACK is invalid on
subsequent messages.
When a VI/TCP connection is supporting level Reliable Delivery or
Unreliable Delivery, the contents of Message ACK are undefined and must
be ignored by a receiver.
Remote Error Code
Remote Error Code is comprised of two subfields - the VI Error Type,
and the IS Error Code. Both VI Error Type and IS Error Code apply to
VI message identified by the Message ACK field. These are defined in
the following paragraphs.
IS Error Code
IS Error Code is an Implementation Specific error code, its semantics
are implementation dependent and considered outside the scope of this
document. If the IS Error Code is set, Message ACK must be set to
indicate the VI Message on which the error occurred. Note that VI
errors (see next paragraph) and local errors need not be mutually
exclusive and this field may be used to provide supplemental status
information.
VI Error Type
VI Error Type indicates one of the following
- No Error
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- RDMA Memory Protection Error
- VI Descriptor Error
When a VI/TCP connection is supporting level Reliable Reception, the VI
Error Type field must be valid and is used to update the Status of the
VI Descriptor's Control Segment.
When a VI/TCP connection is supporting level Reliable Delivery or
Unreliable Delivery, VI Error Type shall indicate No Error and be
ignored by a receiver.
3.2. VI/TCP Connection Establishment (CE) Header
The VI/TCP CE Header is defined as follows.
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| Byte 0 | Byte 1 | Byte 2 | Byte 3 |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
| Calling Attributes | Calling Discriminator Length |
+---------------+---------------+---------------+---------------+
| MTU Size |
+---------------+---------------+---------------+---------------+
| |
+- -+
| |
+- Calling Discriminator -+
| |
+- -+
| |
+---------------+---------------+---------------+---------------+
| Calling RDMA Read Window | Called Discriminator Length |
+---------------+---------------+---------------+---------------+
| |
+- -+
| |
+- Called Discriminator -+
| |
+- -+
| |
+---------------+---------------+---------------+---------------+
| Security Information |
Calling Attributes
The Calling Attributes field contains the following flag bits
- Reliable : Reliable reception and delivery are merged
- RDMA Write Enable
- RDMA Read Enable
- Descriptor Flow Control Enabled
- Peer-to-peer Connection Establishment
Calling/Called Discriminator and Discriminator Lengths
These fields are as defined by the VI Architecture [VIAR]
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MTU Size
MTU Size is "proposed" in Connect Request PDUs and is considered an
"agreed" value in a Connect Accept. The agreed value must be the
lesser of the called/calling VI/TCP Provider's MTU capability.
Security Information
To be supplied. A VI/TCP Consumer may use this feature as an
additional basis for accepting or rejecting calls. This feature is
currently unsupported by the VI Architecture [VIAR] and the programming
API [VIDG]. Extensions to the API to expose this feature are to be
supplied.
3.2.1. VI/TCP RDMA Header
The VI/TCP RDMA Header is defined as follows.
| Byte 0 | Byte 1 | Byte 2 | Byte 3 |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
| |
+- RDMA Address -+
| |
+---------------+---------------+---------------+---------------+
| Registered Memory Handle |
+---------------+---------------+---------------+---------------+
| RDMA Length |
+---------------+---------------+---------------+---------------+
| |
| VI/TCP Consumer's Data |
| |
RDMA Address
The RDMA Address field contains the 64-bit data address of the first
data segment from the VI Descriptor
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Registered Memory Handle
The Registered Memory Handle field contains the Memory Handle returned
when the region of memory containing the data segment was registered
with the VI Provider. This is the same memory handle required by the
VI Descriptor.
RDMA Length
The RDMA Length field contains the length field from the VI Descriptor
that indicates the total number of bytes to be transferred across all
segments of a message.
4. VI/TCP Connection Establishment
This section contains the state machines governing VI/TCP
connection establishment. Both active and passive (e.g., listens)
scenarios are presented. For peer-to-peer connection establishment,
conflicts are resolved lexicographically on IP address. "Lower" (in
the lexicographic sense) IP addressed hosts concede to "higher"
addressed host during peer connection establishment and the process
reverts that of the active/passive case. Receiving a Connect No Match
VI/TCP packet type during peer connection establishment results it
repeated attempts for a period specified by the VI Consumer's
connection timeout value.
4.1. Basic Connection Establishment Timeline
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VIPL API [VIDG] | VI/TCP Protocol | VIPL API
------------------------------------------------------------------
| |
| | VipConnectWait
VipConnectRequest | | <-----------------
-----------------> | |
| setup TCP connection |
| |
| Connect Request |
| -------------------> | VipConnectWait(ret)
| | ----------------->
| | VipPostRecv
| | <-----------------
| | VipConnectAccept
| Connect Accept | <----------------
VipConnectReq (ret) | <------------------- |
<----------------- | or Connect Reject |
| or Connect No Match |
4.2. Connection Establishment - Active
The state machine governing active VI/TCP connection establishment
is as follows:
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+----------------+ (Legend: event - action)
| Disconnected | <--------------------------------<+
+----------------+ ^
| VipConnectRequest |
| - Setup TCP connection |
| |
\|/ |
+----------------+ TCP setup fail ^
+------>| Connecting +>--------------------------------->+
| +----------------+ ^
| TCP Closes | TCP connection established |
| - | - ConnectRequest |
| Reestablish \|/ |
| +----------------+ ConnectReject or Timeout ^
+------<| Pending Accept |>--------------------------------->+
+----------------+ - close TCP connect. ^
| |
| ConnectAccept |
\|/ |
+----------------+ Vip or TCP disconnect ^
| Connected |>--------------------------------->+
+----------------+ - close TCP connection
4.3. "Connection Establishment - Passive"
The state machine governing passive VI/TCP connection
establishment is as follows:
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+----------------+ +--------------+
| Listening on | ( Listen is implied by + Disconnected +
| VI/TCP Port | 1'st VipCreateVI ) +--------------+
+----------------+ ^
| |
| incoming TCP connection - Accept TCP connection |
| (Legend: event - action) |
\|/ |
+----------------+ Timeout - close TCP connection ^
| Incoming |---------------------------------------------->+
+----------------+ TCP connection closes ^
| |
| incoming Connect Request |
\|/ |
+----------------+ No Matching Discriminator ^
| Matching +---------------------------------------------->+
+----------------+ - Send Connect NoMatch; close TCP connection ^
| |
| Discriminator match |
\|/ |
+----------------+ ConnectReject - VipConnectReject, close TCP ^
| Pending Accept |---------------------------------------------->+
+----------------+ ^
| |
| VipConnectAccept - ConnectAccept |
\|/
+----------------+ Vip or TCP disconnect - close TCP connection ^
| Connected |---------------------------------------------->+
+----------------+
5. Security Considerations
No special security considerations exist at this time.
6. References
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[VIAR] "Virtual Interface Architecture Specification", Compaq
Computer Corp., Intel Corporation, Microsoft Corporation,
1997.
[VIDG] "Intel Virtual Interface (VI) Architecture Developer's
Guide", Intel Corporation, September 1998.
[PAWS] Jacobsen, Braden, Borman, "TCP Extensions for High
Performance", RFC 1323, May 1992.
7. Author's Addresses
Stephen DiCecco
James Williams
GigaNet, Inc.
Concord Office Center
2352 Main Street
Concord, Massachusetts 01742
978.461.0402 (tel)
978.461.0430 (fax)
www.giganet.com
Email:
sdicecco@giganet.com
jimw@giganet.com
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