draft-ietf-tsvwg-prsctp-03.txt   rfc3758.txt 
Network Working Group R. Stewart Network Working Group R. Stewart
Internet-Draft M. Ramalho Request for Comments: 3758 M. Ramalho
Expires: July 26, 2004 Cisco Systems, Inc. Category: Standards Track Cisco Systems, Inc.
Q. Xie Q. Xie
Motorola, Inc. Motorola, Inc.
M. Tuexen M. Tuexen
Univ. of Applied Sciences Muenster Univ. of Applied Sciences Muenster
P. Conrad P. Conrad
University of Delaware University of Delaware
January 26, 2004 May 2004
SCTP Partial Reliability Extension Stream Control Transmission Protocol (SCTP)
draft-ietf-tsvwg-prsctp-03.txt Partial Reliability Extension
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document specifies an Internet standards track protocol for the
all provisions of Section 10 of RFC2026. Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Internet-Drafts are working documents of the Internet Engineering Official Protocol Standards" (STD 1) for the standardization state
Task Force (IETF), its areas, and its working groups. Note that other and status of this protocol. Distribution of this memo is unlimited.
groups may also distribute working documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 26, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This memo describes an extension to the Stream Control Transmission This memo describes an extension to the Stream Control Transmission
Protocol (SCTP) RFC2960 [2] that allows an SCTP endpoint to signal to Protocol (SCTP) that allows an SCTP endpoint to signal to its peer
its peer that it should move the cumulative ack point forward. When that it should move the cumulative ack point forward. When both
both sides of an SCTP association support this extension, it can be sides of an SCTP association support this extension, it can be used
used by an SCTP implementation to provide partially reliable data by an SCTP implementation to provide partially reliable data
transmission service to an upper layer protocol. This memo describes transmission service to an upper layer protocol. This memo describes
(1) the protocol extensions, which consist of a new parameter for the protocol extensions, which consist of a new parameter for INIT
INIT and INIT ACK, and a new FORWARD TSN chunk type (2) one example and INIT ACK, and a new FORWARD TSN chunk type, and provides one
partially reliable service that can be provided to the upper layer example of a partially reliable service that can be provided to the
via this mechanism. upper layer via this mechanism.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Overview of Protocol Extensions . . . . . . . . . . . . . . 3 1.1. Overview of Protocol Extensions. . . . . . . . . . . . . 2
1.2 Overview of New Services Provided to the Upper Layer . . . . 3 1.2. Overview of New Services Provided to the Upper Layer . . 3
1.3 Benefits of PR-SCTP . . . . . . . . . . . . . . . . . . . . 4 1.3. Benefits of PR-SCTP . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Protocol Changes to support PR-SCTP . . . . . . . . . . . . 5 3. Protocol Changes to support PR-SCTP . . . . . . . . . . . . . 5
3.1 Forward-TSN-Supported Parameter For INIT and INIT ACK . . . 5 3.1. Forward-TSN-Supported Parameter For INIT and INIT ACK. . 5
3.2 Forward Cumulative TSN Chunk Definition (FORWARD TSN) . . . 6 3.2. Forward Cumulative TSN Chunk Definition (FORWARD TSN). . 5
3.3 Negotiation of Forward-TSN-Supported parameter . . . . . . . 7 3.3. Negotiation of Forward-TSN-Supported parameter . . . . . 7
3.3.1 Sending Forward-TSN-Supported param in INIT . . . . . . . . 7 3.3.1. Sending Forward-TSN-Supported param in INIT . . . 7
3.3.2 Receipt of Forward-TSN-Supported parameter in INIT or 3.3.2. Receipt of Forward-TSN-Supported parameter in
INIT-ACK . . . . . . . . . . . . . . . . . . . . . . . . . . 7 INIT or INIT-ACK. . . . . . . . . . . . . . . . . 7
3.3.3 Receipt of Op. Error for Forward-TSN-Supported Param . . . . 8 3.3.3. Receipt of Op. Error for Forward-TSN-Supported
3.4 Definition of "abandoned" in the context of PR-SCTP . . . . 8 Param . . . . . . . . . . . . . . . . . . . . . . 8
3.5 Sender Side Implementation of PR-SCTP . . . . . . . . . . . 9 3.4. Definition of "abandoned" in the context of PR-SCTP. . . 8
3.6 Receiver Side Implementation of PR-SCTP . . . . . . . . . . 12 3.5. Sender Side Implementation of PR-SCTP. . . . . . . . . . 9
4. Services provided by PR-SCTP to the upper layer . . . . . . 14 3.6. Receiver Side Implementation of PR-SCTP. . . . . . . . . 12
4.1 PR-SCTP Service Definition for "timed reliability" . . . . . 14 4. Services provided by PR-SCTP to the upper layer. . . . . . . . 14
4.2 PR-SCTP Association Establishment . . . . . . . . . . . . . 16 4.1. PR-SCTP Service Definition for "timed reliability" . . . 15
4.3 Guidelines for defining other PR-SCTP Services . . . . . . . 17 4.2. PR-SCTP Association Establishment. . . . . . . . . . . . 16
4.4 Usage Notes . . . . . . . . . . . . . . . . . . . . . . . . 18 4.3. Guidelines for defining other PR-SCTP Services . . . . . 17
5. Variables . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.4. Usage Notes. . . . . . . . . . . . . . . . . . . . . . . 19
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 19 5. Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . 19 6. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 19 7. Security Considerations. . . . . . . . . . . . . . . . . . . . 19
Normative references . . . . . . . . . . . . . . . . . . . . 19 8. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 20
Informational References . . . . . . . . . . . . . . . . . . 19 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20 9.1. Normative References . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . 22 9.2. Informative References . . . . . . . . . . . . . . . . . 20
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
11. Full Copyright Statement . . . . . . . . . . . . . . . . . . .
1. Introduction 1. Introduction
This memo describes an extension to the Stream Control Transmission This memo describes an extension to the Stream Control Transmission
Protocol (SCTP) RFC2960 [2] that allows an SCTP sender to signal to Protocol (SCTP) RFC2960 [2] that allows an SCTP sender to signal to
its peer that it should no longer expect to receive one or more DATA its peer that it should no longer expect to receive one or more DATA
chunks. chunks.
1.1 Overview of Protocol Extensions 1.1. Overview of Protocol Extensions
The protocol extension described in this document consists of two new The protocol extension described in this document consists of two new
elements: elements:
1. a single new parameter in the INIT/INIT-ACK exchange that 1. a single new parameter in the INIT/INIT-ACK exchange that
indicates whether the endpoint supports the extension indicates whether the endpoint supports the extension
2. a single new chunk type, FORWARD TSN, that indicates that the 2. a single new chunk type, FORWARD TSN, that indicates that the
receiver should move its cumulative ack point forward (possibly receiver should move its cumulative ack point forward (possibly
skipping past one or more DATA chunks that may not yet have been skipping past one or more DATA chunks that may not yet have been
received and/or acknowledged.) received and/or acknowledged.)
1.2 Overview of New Services Provided to the Upper Layer 1.2. Overview of New Services Provided to the Upper Layer
When this extension is supported by both sides of an SCTP When this extension is supported by both sides of an SCTP
association, it can be used to provide partially reliable transport association, it can be used to provide partially reliable transport
service over an SCTP association. We define partially reliable service over an SCTP association. We define partially reliable
transport service as a service that allows the user to specify, on a transport service as a service that allows the user to specify, on a
per message basis, the rules governing how persistent the transport per message basis, the rules governing how persistent the transport
service should be in attempting to send the message to the receiver. service should be in attempting to send the message to the receiver.
One example of partially reliable service is specified in this One example of partially reliable service is specified in this
document, namely a "timed reliability" service. This service allows document, namely a "timed reliability" service. This service allows
skipping to change at page 3, line 42 skipping to change at page 3, line 28
One example of partially reliable service is specified in this One example of partially reliable service is specified in this
document, namely a "timed reliability" service. This service allows document, namely a "timed reliability" service. This service allows
the service user to indicate a limit on the duration of time that the the service user to indicate a limit on the duration of time that the
sender should try to transmit/retransmit the message (this is a sender should try to transmit/retransmit the message (this is a
natural extension of the "lifetime" parameter already in the base natural extension of the "lifetime" parameter already in the base
protocol). protocol).
In addition to this example, we will also show that defining the In addition to this example, we will also show that defining the
semantics of a particular partially reliable service involves two semantics of a particular partially reliable service involves two
elements, namely: elements, namely:
1. how the service user indicates the level of reliability required 1. how the service user indicates the level of reliability required
for a particular message, and for a particular message, and
2. how the sender side implementation uses that reliability level to 2. how the sender side implementation uses that reliability level to
determine when to give up on further retransmissions of that determine when to give up on further retransmissions of that
message. message.
Note that other than the fact that the FORWARD-TSN chunk is required, Note that other than the fact that the FORWARD-TSN chunk is required,
neither of these two elements impacts the "on-the-wire" protocol; neither of these two elements impacts the "on-the-wire" protocol;
only the API, and the sender side implementation is affected by the only the API and the sender side implementation are affected by the
way in which the service is defined to the upper layer. Therefore, way in which the service is defined to the upper layer. Therefore,
in principle, it is feasible to implement many varieties of partially in principle, it is feasible to implement many varieties of partially
reliable services in a particular SCTP implementation without reliable services in a particular SCTP implementation without
changing the on-the-wire protocol. Also, the SCTP receiver does not changing the on-the-wire protocol. Also, the SCTP receiver does not
necessarily need to know which semantics of partially reliable necessarily need to know which semantics of partially reliable
service are being used by the sender, since the receiver's only role service are being used by the sender, since the receiver's only role
is to correctly interpret FORWARD TSN chunks, thereby skipping past is to correctly interpret FORWARD TSN chunks, thereby skipping past
messages that the sender has decided to no longer transmit (or messages that the sender has decided to no longer transmit (or
retransmit). retransmit).
Nevertheless, it is recommended that a limited number of standard Nevertheless, it is recommended that a limited number of standard
definitions of partially reliable services be standardized by the definitions of partially reliable services be standardized by the
IETF so that the designers of IETF application layer protocols can IETF so that the designers of IETF application layer protocols can
match the requirements of their upper layer protocols to standard match the requirements of their upper layer protocols to standard
service definitions provided by a particular SCTP implementation. service definitions provided by a particular SCTP implementation.
One such definition, "timed reliability" is included in this One such definition, "timed reliability", is included in this
document. Given the extensions proposed in this document, other document. Given the extensions proposed in this document, other
definitions may be standardized as the need arises without further definitions may be standardized as the need arises without further
changes to the on-the-wire protocol. changes to the on-the-wire protocol.
1.3 Benefits of PR-SCTP 1.3. Benefits of PR-SCTP
Hereafter, we use the notation "Partial Reliable Stream Control Hereafter, we use the notation "Partial Reliable Stream Control
Transmission Protocol (PR-SCTP)" to refer to the SCTP protocol Transmission Protocol (PR-SCTP)" to refer to the SCTP protocol,
extended as defined in this document. extended as defined in this document.
The following are some of the advantages for integrating partially The following are some of the advantages for integrating partially
reliable data service into SCTP, i.e., benefits of PR-SCTP: reliable data service into SCTP, i.e., benefits of PR-SCTP:
1. Some application layer protocols may benefit from being able to 1. Some application layer protocols may benefit from being able to
use a single SCTP association to carry both reliable content, -- use a single SCTP association to carry both reliable content, --
such as text pages, billing and accounting information, setup such as text pages, billing and accounting information, setup
signaling -- and unreliable content, e.g. state that is highly signaling -- and unreliable content, e.g., state that is highly
sensitive to timeliness, where generating a new packet is more sensitive to timeliness, where generating a new packet is more
advantageous than transmitting an old one [3]. advantageous than transmitting an old one [3].
2. Partially reliable data traffic carried by PR-SCTP will enjoy the 2. Partially reliable data traffic carried by PR-SCTP will enjoy the
same communication failure detection and protection capabilities same communication failure detection and protection capabilities
as the normal reliable SCTP data traffic does. This includes the as the normal reliable SCTP data traffic does. This includes the
ability to: - quickly detect a failed destination address; - ability to quickly detect a failed destination address, fail-over
fail-over to an alternate destination address, and; - be notified to an alternate destination address, and be notified if the data
if the data receiver becomes unreachable. receiver becomes unreachable.
3. In addition to providing unordered unreliable data transfer as
UDP does, PR-SCTP can provide ordered unreliable data transfer 3. In addition to providing unordered, unreliable data transfer as
UDP does, PR-SCTP can provide ordered, unreliable data transfer
service. service.
4. PR-SCTP employs the same congestion control and congestion 4. PR-SCTP employs the same congestion control and congestion
avoidance for all data traffic, whether reliable or partially avoidance for all data traffic, whether reliable or partially
reliable - this is very desirable since SCTP enforces reliable - this is very desirable since SCTP enforces TCP-
TCP-friendliness (unlike UDP.) friendliness (unlike UDP.)
5. Because of the chunk bundling function of SCTP, reliable and 5. Because of the chunk bundling function of SCTP, reliable and
unreliable messages can be multiplexed over a single PR-SCTP unreliable messages can be multiplexed over a single PR-SCTP
association. Therefore, the number of IP datagrams (and hence association. Therefore, the number of IP datagrams (and hence the
the network overhead) can be reduced versus having to send these network overhead) can be reduced instead of having to send these
different types of data using separate protocols. Additionally, different types of data using separate protocols. Additionally,
this multiplexing allows for port savings versus using different this multiplexing allows for port savings versus using different
ports for reliable and unreliable connections. ports for reliable and unreliable connections.
2. Conventions 2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in they appear in this document, are to be interpreted as described in
RFC2119 [1]. BCP 14, RFC 2119 [1].
Comparisons and arithmetic on Transport Sequence Numbers (TSNs) are Comparisons and arithmetic on Transport Sequence Numbers (TSNs) are
governed by the rules in Section 1.6 of RFC2960 [2]. governed by the rules in Section 1.6 of RFC2960 [2].
3. Protocol Changes to support PR-SCTP 3. Protocol Changes to support PR-SCTP
3.1 Forward-TSN-Supported Parameter For INIT and INIT ACK 3.1. Forward-TSN-Supported Parameter For INIT and INIT ACK
The following new OPTIONAL parameter is added to the INIT and INIT The following new OPTIONAL parameter is added to the INIT and INIT
ACK chunks. ACK chunks.
Parameter Name Status Type Value Parameter Name Status Type Value
------------------------------------------------------------- -------------------------------------------------------------
Forward-TSN-Suppored OPTIONAL 49152 (0xC000) Forward-TSN-Supported OPTIONAL 49152 (0xC000)
At the initialization of the association, the sender of the INIT or At the initialization of the association, the sender of the INIT or
INIT ACK chunk MAY include this OPTIONAL parameter to inform its peer INIT ACK chunk MAY include this OPTIONAL parameter to inform its peer
that it is able to support the Forward TSN chunk (see Section 3.3 for that it is able to support the Forward TSN chunk (see Section 3.3 for
further details). The format of this parameter is defined as follows: further details). The format of this parameter is defined as
follows:
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 49152 | Parameter Length = 4 | | Parameter Type = 49152 | Parameter Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 bit u_int Type: 16 bit u_int
49152, indicating Forward-TSN-Supported parameter 49152, indicating Forward-TSN-Supported parameter
Length: 16 bit u_int Length: 16 bit u_int
Indicates the size of the parameter i.e., 4. Indicates the size of the parameter, i.e., 4.
3.2 Forward Cumulative TSN Chunk Definition (FORWARD TSN) 3.2 Forward Cumulative TSN Chunk Definition (FORWARD TSN)
The following new chunk type is defined: The following new chunk type is defined:
Chunk Type Chunk Name Chunk Type Chunk Name
------------------------------------------------------ ------------------------------------------------------
192 (0xC0) Forward Cumulative TSN (FORWARD TSN) 192 (0xC0) Forward Cumulative TSN (FORWARD TSN)
This chunk shall be used by the data sender to inform the data This chunk shall be used by the data sender to inform the data
receiver to adjust its cumulative received TSN point forward because receiver to adjust its cumulative received TSN point forward because
some missing TSNs are associated with data chunks that SHOULD NOT be some missing TSNs are associated with data chunks that SHOULD NOT be
transmitted or retransmitted by the sender. transmitted or retransmitted by the sender.
Forward Cumulative TSN chunk has the following format: Forward Cumulative TSN chunk has the following format:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 6, line 43 skipping to change at page 6, line 34
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: Chunk Flags:
Set to all zeros on transmit and ignored on receipt. Set to all zeros on transmit and ignored on receipt.
New Cumulative TSN: 32 bit u_int New Cumulative TSN: 32 bit u_int
This indicates the new cumulative TSN to the data receiver. Upon This indicates the new cumulative TSN to the data receiver. Upon
the reception of this value, the data receiver MUST consider the reception of this value, the data receiver MUST consider
any missing TSNs earlier than or equal to this value as received any missing TSNs earlier than or equal to this value as received,
and stop reporting them as gaps in any subsequent SACKs. and stop reporting them as gaps in any subsequent SACKs.
Stream-N: 16 bit u_int Stream-N: 16 bit u_int
This field holds a stream number that was skipped by this This field holds a stream number that was skipped by this
FWD-TSN. FWD-TSN.
Stream Sequence-N: 16 bit u_int Stream Sequence-N: 16 bit u_int
This field holds the sequence number associated with the stream This field holds the sequence number associated with the stream
that was skipped. The stream sequence field holds the largest stream that was skipped. The stream sequence field holds the largest
sequence number in this stream being skipped. The receiver of stream sequence number in this stream being skipped. The receiver
the FWD-TSN's can use the Stream-N and Stream Sequence-N fields of the FWD-TSN's can use the Stream-N and Stream Sequence-N fields
to enable delivery of any stranded TSN's that remain on the stream to enable delivery of any stranded TSN's that remain on the stream
re-ordering queues. This field MUST NOT report TSN's corresponding re-ordering queues. This field MUST NOT report TSN's corresponding
to DATA chunk that are marked as unordered. For ordered DATA to DATA chunks that are marked as unordered. For ordered DATA
chunks this field MUST be filled in. chunks this field MUST be filled in.
3.3 Negotiation of Forward-TSN-Supported parameter 3.3. Negotiation of Forward-TSN-Supported parameter
3.3.1 Sending Forward-TSN-Supported param in INIT 3.3.1. Sending Forward-TSN-Supported param in INIT
If an SCTP endpoint supports the FORWARD TSN chunk, then any time it If an SCTP endpoint supports the FORWARD TSN chunk, then any time it
sends an INIT during association establishment, it MAY include the sends an INIT during association establishment, it MAY include the
Forward-TSN-supported parameter in the INIT chunk to indicate this Forward-TSN-supported parameter in the INIT chunk to indicate this
fact to its peer. fact to its peer.
Note that if the endpoint chooses NOT to include the parameter, then Note that if the endpoint chooses NOT to include the parameter, then
at no time during the life of the association can it send or process at no time during the life of the association can it send or process
a FORWARD TSN. It MUST instead act as if it does NOT support the a FORWARD TSN. It MUST instead act as if it does NOT support the
FORWARD TSN chunk returning an ERROR to the peer upon receipt of any FORWARD TSN chunk, returning an ERROR to the peer upon receipt of any
FORWARD TSN. FORWARD TSN.
3.3.2 Receipt of Forward-TSN-Supported parameter in INIT or INIT-ACK 3.3.2. Receipt of Forward-TSN-Supported parameter in INIT or INIT-ACK
When a receiver of an INIT detects a Forward-TSN-Supported parameter, When a receiver of an INIT detects a Forward-TSN-Supported parameter
and does not support the Forward-TSN chunk type, the receiver MUST and does not support the Forward-TSN chunk type, the receiver MUST
follow the rules defined in Section 3.3.3 of RFC2960 [2]. follow the rules defined in Section 3.3.3 of RFC2960 [2].
When a receiver of an INIT-ACK detects a Forward-TSN-Supported When a receiver of an INIT-ACK detects a Forward-TSN-Supported
parameter, and does not support the Forward-TSN chunk type, the parameter and it does not support the Forward-TSN chunk type, the
receiver MUST follow the rules defined in Section 3.3.3 of RFC2960 receiver MUST follow the rules defined in Section 3.3.3 of RFC2960
[2]. [2].
When a receiver of an INIT detects a Forward-TSN-Supported parameter, When a receiver of an INIT detects a Forward-TSN-Supported parameter
and does support the Forward-TSN chunk type, the receiver MAY respond and it does support the Forward-TSN chunk type, the receiver MAY
with a Forward-TSN-supported parameter in the INIT-ACK chunk. respond with a Forward-TSN-supported parameter in the INIT-ACK chunk.
Note that if the endpoint chooses NOT to include the parameter, then Note that if the endpoint chooses NOT to include the parameter, then
at no time during the life of the association can it send or process at no time during the life of the association can it send or process
a FORWARD TSN. It MUST instead act as if it does NOT support the a FORWARD TSN. It MUST instead act as if it does NOT support the
FORWARD TSN chunk returning an ERROR to the peer upon receipt of any FORWARD TSN chunk, returning an ERROR to the peer upon receipt of any
FORWARD TSN. FORWARD TSN.
When an endpoint that supports the FORWARD TSN chunk receives an INIT When an endpoint that supports the FORWARD TSN chunk receives an INIT
that does not contain the Forward-TSN-Supported Parameter, that that does not contain the Forward-TSN-Supported Parameter, that
endpoint: endpoint:
o MAY include the Forward-TSN-Supported parameter in the INIT-ACK, o MAY include the Forward-TSN-Supported parameter in the INIT-ACK,
o SHOULD record the fact that the peer does not support the FORWARD o SHOULD record the fact that the peer does not support the FORWARD
TSN chunk, TSN chunk,
o MUST NOT send a FORWARD TSN chunk at any time during the o MUST NOT send a FORWARD TSN chunk at any time during the
associations life, associations life,
o SHOULD inform the upper layer, if the upper layer has requested o SHOULD inform the upper layer if the upper layer has requested
such notification. such notification.
3.3.3 Receipt of Op. Error for Forward-TSN-Supported Param 3.3.3. Receipt of Op. Error for Forward-TSN-Supported Param
When an SCTP endpoint that desires to use the FORWARD TSN chunk When an SCTP endpoint that desires to use the FORWARD TSN chunk
feature for partially reliable data transfer receives an operational feature for partially reliable data transfer receives an operational
error from the remote endpoint (either bundled with the COOKIE or as error from the remote endpoint (either bundled with the COOKIE or as
an unrecognized parameter in the INIT-ACK), indicating that the an unrecognized parameter in the INIT-ACK), indicating that the
remote endpoint does not recognize the Forward-TSN-Supported remote endpoint does not recognize the Forward-TSN-Supported
parameter, the local endpoint SHOULD inform its upper layer of the parameter, the local endpoint SHOULD inform its upper layer of the
remote endpoint's inability to support partially reliable data remote endpoint's inability to support partially reliable data
transfer. transfer.
The local endpoint may then choose to either: The local endpoint may then choose to either:
1) end the initiation process (in cases where the initiation
process has already ended the endpoint may need to send an ABORT), 1) end the initiation process (in cases where the initiation process
in consideration of the peer's inability to supply the requested has already ended, the endpoint may need to send an ABORT) in
consideration of the peer's inability to supply the requested
features for the new association, or features for the new association, or
2) continue the initiation process (in cases where the initiation 2) continue the initiation process (in cases where the initiation
process has already completed the endpoint MUST just mark the process has already completed, the endpoint MUST just mark the
association as not supporting partial reliability), but with the association as not supporting partial reliability), but with the
understanding that partially reliable data transmission is not understanding that partially reliable data transmission is not
supported. In this case, the endpoint receiving the operational supported. In this case, the endpoint receiving the operational
error SHOULD note that the FORWARD TSN chunk is not supported, and error SHOULD note that the FORWARD TSN chunk is not supported, and
MUST NOT transmit a FORWARD TSN chunk at any time during the life MUST NOT transmit a FORWARD TSN chunk at any time during the life
of the association. of the association.
3.4 Definition of "abandoned" in the context of PR-SCTP 3.4. Definition of "abandoned" in the context of PR-SCTP
At some point, a sending PR-SCTP implementation MAY determine that a At some point, a sending PR-SCTP implementation MAY determine that a
particular data chunk SHOULD NOT be transmitted or retransmitted particular data chunk SHOULD NOT be transmitted or retransmitted
further, in accordance with the rules governing some particular further, in accordance with the rules governing some particular PR-
PR-SCTP service definition (such as the definition of "timed SCTP service definition (such as the definition of "timed
reliability" in Section 4.1.) For purposes of this document, we reliability" in Section 4.1.) For purposes of this document, we
define the term "abandoned" to refer to any data chunk about which define the term "abandoned" to refer to any data chunk about which
the SCTP sender has made this determination. the SCTP sender has made this determination.
Each PR-SCTP service defines the rules for determining when a TSN is Each PR-SCTP service defines the rules for determining when a TSN is
"abandoned", and accordingly, the rules that govern how, whether, and "abandoned", and accordingly, the rules that govern how, whether, and
when to "abandon" a TSN may vary from one service definition to when to "abandon" a TSN may vary from one service definition to
another. However, the rules governing the actions taken when a TSN another. However, the rules governing the actions taken when a TSN
is "abandoned" do NOT vary between service definitions; these rules is "abandoned" do NOT vary between service definitions; these rules
are included in Section 3.5. are included in Section 3.5.
3.5 Sender Side Implementation of PR-SCTP 3.5. Sender Side Implementation of PR-SCTP
The sender side implementation of PR-SCTP is identical to that of the The sender side implementation of PR-SCTP is identical to that of the
base SCTP protocol, except for: base SCTP protocol, except for:
o actions a sending side PR-SCTP implementation must take when a TSN o actions a sending side PR-SCTP implementation must take when a TSN
is "abandoned" (as per the rules of whatever PR-SCTP service is "abandoned" (as per the rules of whatever PR-SCTP service
definition is in effect) definition is in effect)
o special actions that a PR-SCTP implementation must take upon o special actions that a PR-SCTP implementation must take upon
receipt of SACK receipt of SACK
o rules governing generation of FORWARD TSN chunks. o rules governing the generation of FORWARD TSN chunks.
In detail, these exceptions are as follows: In detail, these exceptions are as follows:
A1) The sender maintains an "Advanced.Peer.Ack.Point" for each peer A1) The sender maintains an "Advanced.Peer.Ack.Point" for each peer
to track a theoretical cumulative TSN point of the peer (Note, to track a theoretical cumulative TSN point of the peer (Note,
this is a _new_ protocol variable and its value is NOT necessarily this is a _new_ protocol variable and its value is NOT
the same as the SCTP "Cumulative TSN Ack Point" as defined in necessarily the same as the SCTP "Cumulative TSN Ack Point" as
Section 1.4 of RFC2960 [2]) and discussed throughout that defined in Section 1.4 of RFC 2960 [2], and as discussed
document. throughout that document.)
A2) From time to time, as governed by the rules of a particular
PR-SCTP service definition (see Section 4), the SCTP data sender A2) From time to time, as governed by the rules of a particular PR-
may make a determination that a particular data chunk that has SCTP service definition (see Section 4), the SCTP data sender may
make a determination that a particular data chunk that has
already been assigned a TSN SHOULD be "abandoned". already been assigned a TSN SHOULD be "abandoned".
When a data chunk is "abandoned", the sender MUST treat the data When a data chunk is "abandoned", the sender MUST treat the data
chunk as being finally acked and no longer outstanding. chunk as being finally acked and no longer outstanding.
The sender MUST NOT credit an "abandoned" data chunk to the The sender MUST NOT credit an "abandoned" data chunk to the
partial_bytes_acked as defined in Section 7.2.2 of RFC2960 [2], partial_bytes_acked as defined in Section 7.2.2 of RFC2960 [2],
and MUST NOT advance the cwnd based on this "abandoned" data and MUST NOT advance the cwnd based on this "abandoned" data
chunk. chunk.
A3) When a TSN is "abandoned", if it is part of a fragmented message, A3) When a TSN is "abandoned", if it is part of a fragmented message,
all other TSN's within that fragmented message MUST be abandoned all other TSN's within that fragmented message MUST be abandoned
at the same time. at the same time.
A4) Whenever the data sender receives a SACK from the data receiver, A4) Whenever the data sender receives a SACK from the data receiver,
it MUST first process the SACK using the normal procedures as it MUST first process the SACK using the normal procedures as
defined in Section 6.2.1 of RFC2960 [2]. defined in Section 6.2.1 of RFC2960 [2].
The data sender MUST then perform the following additional steps : The data sender MUST then perform the following additional steps :
C1) Let SackCumAck be the Cumulative TSN ACK carried in the C1) Let SackCumAck be the Cumulative TSN ACK carried in the
received SACK. received SACK.
If (Advanced.Peer.Ack.Point < SackCumAck), then update If (Advanced.Peer.Ack.Point < SackCumAck), then update
skipping to change at page 10, line 10 skipping to change at page 10, line 12
it MUST first process the SACK using the normal procedures as it MUST first process the SACK using the normal procedures as
defined in Section 6.2.1 of RFC2960 [2]. defined in Section 6.2.1 of RFC2960 [2].
The data sender MUST then perform the following additional steps : The data sender MUST then perform the following additional steps :
C1) Let SackCumAck be the Cumulative TSN ACK carried in the C1) Let SackCumAck be the Cumulative TSN ACK carried in the
received SACK. received SACK.
If (Advanced.Peer.Ack.Point < SackCumAck), then update If (Advanced.Peer.Ack.Point < SackCumAck), then update
Advanced.Peer.Ack.Point to be equal to SackCumAck. Advanced.Peer.Ack.Point to be equal to SackCumAck.
C2) Try to further advance the "Advanced.Peer.Ack.Point" locally, C2) Try to further advance the "Advanced.Peer.Ack.Point" locally,
that is, to move "Advanced.Peer.Ack.Point" up as long as the that is, to move "Advanced.Peer.Ack.Point" up as long as the
chunk next in the out-queue space is marked as "abandoned" as chunk next in the out-queue space is marked as "abandoned",
shown in the following example: as shown in the following example:
Assuming that a SACK arrived with the Cumulative TSN ACK = Assuming that a SACK arrived with the Cumulative TSN ACK =
102 and the Advanced.Peer.Ack.Point is updated to this 102 and the Advanced.Peer.Ack.Point is updated to this
value: value:
out-queue at the end of ==> out-queue after Adv.Ack.Point out-queue at the end of ==> out-queue after Adv.Ack.Point
normal SACK processing local advancement normal SACK processing local advancement
... ... ... ...
Adv.Ack.Pt-> 102 acked 102 acked Adv.Ack.Pt-> 102 acked 102 acked
skipping to change at page 10, line 32 skipping to change at page 10, line 35
... ... ... ...
Adv.Ack.Pt-> 102 acked 102 acked Adv.Ack.Pt-> 102 acked 102 acked
103 abandoned 103 abandoned 103 abandoned 103 abandoned
104 abandoned Adv.Ack.P-> 104 abandoned 104 abandoned Adv.Ack.P-> 104 abandoned
105 105 105 105
106 acked 106 acked 106 acked 106 acked
... ... ... ...
In this example, the data sender successfully advanced the In this example, the data sender successfully advanced the
"Advanced.Peer.Ack.Point" from 102 to 104 locally. "Advanced.Peer.Ack.Point" from 102 to 104 locally.
C3) If, after step C1 and C2, the "Advanced.Peer.Ack.Point" is C3) If, after step C1 and C2, the "Advanced.Peer.Ack.Point" is
greater than the Cumulative TSN ACK carried in the received greater than the Cumulative TSN ACK carried in the received
SACK, the data sender MUST send the data receiver a FORWARD TSN SACK, the data sender MUST send the data receiver a FORWARD
chunk containing the latest value of the TSN chunk containing the latest value of the
"Advanced.Peer.Ack.Point". Note that the sender MAY delay the "Advanced.Peer.Ack.Point". Note that the sender MAY delay
sending of a FORWARD TSN as defined in rule F2 below. the sending of a FORWARD TSN as defined in rule F2 below.
IMPLEMENTATION NOTE: It is an implemenation decision as to IMPLEMENTATION NOTE: It is an implementation decision as to
which destination address is to be sent to, the only which destination address it is to be sent to, the only
restriction being that the address MUST be one that is restriction being that the address MUST be one that is
CONFIRMED. CONFIRMED.
C4) For each "abandoned" TSN the sender of the FORWARD TSN MUST
C4) For each "abandoned" TSN, the sender of the FORWARD TSN MUST
determine if the chunk has a valid stream and sequence number determine if the chunk has a valid stream and sequence number
(i.e., it was ordered). If the chunk has a valid stream and (i.e., it was ordered). If the chunk has a valid stream and
sequence number the sender MUST include the stream and sequence sequence number, the sender MUST include the stream and
number in the FORWARD TSN. This information will enable the sequence number in the FORWARD TSN. This information will
receiver to easily find any stranded TSN's waiting on stream enable the receiver to easily find any stranded TSN's waiting
reorder queues. Each stream SHOULD only be reported once; this on stream reorder queues. Each stream SHOULD only be
means that if multiple abandoned messages occur in the same reported once; this means that if multiple abandoned messages
stream then only the highest abandoned stream sequence number occur in the same stream, then only the highest abandoned
is reported. If the total size of the FORWARD TSN does NOT fit stream sequence number is reported. If the total size of the
in a single MTU then the sender of the FORWARD TSN SHOULD lower FORWARD TSN does NOT fit in a single MTU, then the sender of
the Advanced.Peer.Ack.Point to the last TSN that will fit in a the FORWARD TSN SHOULD lower the Advanced.Peer.Ack.Point to
single MTU. the last TSN that will fit in a single MTU.
C5) If a FORWARD TSN is sent, the sender MUST assure that at least
one T3-rtx timer is running. C5) If a FORWARD TSN is sent, the sender MUST assure that at
IMPLEMENTATION NOTE: Any destination's timer may be used for least one T3-rtx timer is running. IMPLEMENTATION NOTE: Any
the purposes of rule C5. destination's timer may be used for the purposes of rule C5.
A5) Any time the T3-rtx timer expires, on any destination, the sender A5) Any time the T3-rtx timer expires, on any destination, the sender
SHOULD try to advance the "Advanced.Peer.Ack.Point" by following SHOULD try to advance the "Advanced.Peer.Ack.Point" by following
the procedures outlined in C2 - C5. the procedures outlined in C2 - C5.
The following additional rules govern the generation of FORWARD TSN The following additional rules govern the generation of FORWARD TSN
chunks: chunks:
F1) An endpoint MUST NOT use the FORWARD TSN for any purposes other F1) An endpoint MUST NOT use the FORWARD TSN for any purposes other
than circumstances described in this document. than circumstances described in this document.
F2) The data sender SHOULD always attempt to bundle an outgoing F2) The data sender SHOULD always attempt to bundle an outgoing
FORWARD TSN with outbound DATA chunks for efficiency. FORWARD TSN with outbound DATA chunks for efficiency.
A sender MAY even choose to delay the sending of the FORWARD TSN A sender MAY even choose to delay the sending of the FORWARD TSN
in the hope of bundling it with an outbound DATA chunk. in the hope of bundling it with an outbound DATA chunk.
IMPLEMENTATION NOTE: An implementation may wish to limit the IMPLEMENTATION NOTE: An implementation may wish to limit the
number of duplicate FORWARD TSN chunks it sends by either only number of duplicate FORWARD TSN chunks it sends by either only
sending a duplicate FORWARD TSN every other SACK or waiting a full sending a duplicate FORWARD TSN every other SACK or waiting a
RTT before sending a duplicate FORWARD TSN. full RTT before sending a duplicate FORWARD TSN.
IMPLEMENTATION NOTE: An implementation may allow the maximum
delay for generating a FORWARD TSN to be configured either
statically or dynamically in order to meet the specific timing
requirements of the protocol being carried, but see the next
rule:
IMPLEMENTATION NOTE: An implementation may allow the maximum delay
for generating a FORWARD TSN to be configured either statically or
dynamically in order to meet the specific timing requirements of
the protocol being carried, but see the next rule:
F3) Any delay applied to the sending of FORWARD TSN chunk SHOULD NOT F3) Any delay applied to the sending of FORWARD TSN chunk SHOULD NOT
exceed 200ms and MUST NOT exceed 500ms. In other words an exceed 200ms and MUST NOT exceed 500ms. In other words, an
implementation MAY lower this value below 500ms but MUST NOT raise implementation MAY lower this value below 500ms but MUST NOT
it above 500ms. raise it above 500ms.
NOTE: Delaying the sending of FORWARD TSN chunks may cause delays NOTE: Delaying the sending of FORWARD TSN chunks may cause delays
in the receiver's ability to deliver other data being held at the in the receiver's ability to deliver other data being held at the
receiver for re-ordering. The values of 200ms and 500ms match the receiver for re-ordering. The values of 200ms and 500ms match
required values for the delayed acknowledgement in RFC2960 [2] the required values for the delayed acknowledgement in RFC 2960
since delaying a FORWARD TSN has the same consequences but in the [2] since delaying a FORWARD TSN has the same consequences but in
reverse direction. the reverse direction.
F4) The detection criterion for out-of-order SACKs MUST remain the F4) The detection criterion for out-of-order SACKs MUST remain the
same as stated in RFC2960, that is, a SACK is only considered same as stated in RFC2960, that is, a SACK is only considered
out-of-order if the Cumulative TSN ACK carried in the SACK is out-of-order if the Cumulative TSN ACK carried in the SACK is
earlier than that of the previous received SACK (i.e., the earlier than that of the previous received SACK (i.e., the
comparison MUST NOT be made against "Advanced.Peer.Ack.Point"). comparison MUST NOT be made against "Advanced.Peer.Ack.Point").
F5) If the decision to "abandon" a chunk is made, no matter how such F5) If the decision to "abandon" a chunk is made, no matter how such
a decision is made, the appropriate congestion adjustment MUST be a decision is made, the appropriate congestion adjustment MUST be
made as specified in RFC2960 if the chunk would have been marked made as specified in RFC2960 if the chunk would have been marked
for retransmission later (e.g. either by T3-Timeout or by Fast for retransmission later (e.g., either by T3-Timeout or by Fast
Retransmit). Retransmit).
3.6 Receiver Side Implementation of PR-SCTP 3.6. Receiver Side Implementation of PR-SCTP
The receiver side implementation of PR-SCTP at an SCTP endpoint A is The receiver side implementation of PR-SCTP at an SCTP endpoint A is
capable of supporting any PR-SCTP service definition used by the capable of supporting any PR-SCTP service definition used by the
sender at endpoint B, even if that service definition is not sender at endpoint B, even if that service definition is not
supported by the sending side functionality of host A. All that is supported by the sending side functionality of host A. All that is
necessary is that the receiving side correctly handle the necessary is that the receiving side correctly handle the Forward-
Forward-TSN-Supported parameter as specified in Section 3.3, and TSN-Supported parameter as specified in Section 3.3, and correctly
correctly handle the receipt of FORWARD TSN chunks as specified handle the receipt of FORWARD TSN chunks as specified below.
below.
DATA chunk arrival at a PR-SCTP receiver proceeds exactly as for DATA DATA chunk arrival at a PR-SCTP receiver proceeds exactly as for DATA
chunk arrival at a base protocol SCTP receiver---that is, the chunk arrival at a base protocol SCTP receiver---that is, the
receiver MUST perform the same TSN handling including duplicate receiver MUST perform the same TSN handling, including duplicate
detection, gap detection, SACK generation, cumulative TSN detection, gap detection, SACK generation, cumulative TSN
advancement, etc. as defined in RFC2960 [2]---with the following advancement, etc. as defined in RFC2960 [2]---with the following
exceptions and additions. exceptions and additions.
When a FORWARD TSN chunk arrives, the data receiver MUST first update When a FORWARD TSN chunk arrives, the data receiver MUST first update
its cumulative TSN point to the value carried in the FORWARD TSN its cumulative TSN point to the value carried in the FORWARD TSN
chunk, and then MUST further advance its cumulative TSN point locally chunk, and then MUST further advance its cumulative TSN point locally
if possible, as shown by the following example: if possible, as shown by the following example:
Assuming that the new cumulative TSN carried in the arrived Assuming that the new cumulative TSN carried in the arrived
FORWARD TSN is 103: FORWARD TSN is 103:
in-queue before processing in-queue after processing the in-queue before processing in-queue after processing
the FORWARD TSN ==> the FORWARD TSN and further the FORWARD TSN ==> the FORWARD TSN and further
advancement advancement
cum.TSN.Pt-> 102 received 102 -- cum.TSN.Pt-> 102 received 102 --
103 missing 103 -- 103 missing 103 --
104 received 104 -- 104 received 104 --
105 received cum.TSN.Pt-> 105 received 105 received cum.TSN.Pt-> 105 received
106 missing 106 missing 106 missing 106 missing
107 received 107 received 107 received 107 received
... ... ... ...
In this example, the receiver's cumulative TSN point is first In this example, the receiver's cumulative TSN point is first
updated to 103 and then further advanced to 105. updated to 103 and then further advanced to 105.
skipping to change at page 13, line 13 skipping to change at page 13, line 20
... ... ... ...
In this example, the receiver's cumulative TSN point is first In this example, the receiver's cumulative TSN point is first
updated to 103 and then further advanced to 105. updated to 103 and then further advanced to 105.
After the above processing, the data receiver MUST stop reporting any After the above processing, the data receiver MUST stop reporting any
missing TSNs earlier than or equal to the new cumulative TSN point. missing TSNs earlier than or equal to the new cumulative TSN point.
Note, if the "New Cumulative TSN" value carried in the arrived Note, if the "New Cumulative TSN" value carried in the arrived
FORWARD TSN chunk is found to be behind or at the current cumulative FORWARD TSN chunk is found to be behind or at the current cumulative
TSN point, the data receiver MUST treat this FORWARD TSN as TSN point, the data receiver MUST treat this FORWARD TSN as out-of-
out-of-date and MUST NOT update its Cumulative TSN. The receiver date and MUST NOT update its Cumulative TSN. The receiver SHOULD
SHOULD send a SACK to its peer (the sender of the FORWARD TSN) since send a SACK to its peer (the sender of the FORWARD TSN) since such a
such a duplicate may indicate the previous SACK was lost in the duplicate may indicate the previous SACK was lost in the network.
network.
Any time a FORWARD TSN chunk arrives, for the purposes of sending a Any time a FORWARD TSN chunk arrives, for the purposes of sending a
SACK, the receiver MUST follow the same rules as if a DATA chunk had SACK, the receiver MUST follow the same rules as if a DATA chunk had
been received (i.e., follow the delayed sack rules specified in been received (i.e., follow the delayed sack rules specified in RFC
RFC2960 [2] section 6.2). 2960 [2] section 6.2).
Whenever a DATA chunk arrives with the 'U' bit set to '0' (indicating Whenever a DATA chunk arrives with the 'U' bit set to '0' (indicating
ordered delivery) and is out of order, the receiver must hold the ordered delivery) and is out of order, the receiver must hold the
chunk for reordering. Since it is possible with PR-SCTP that a DATA chunk for reordering. Since it is possible with PR-SCTP that a DATA
chunk being waited upon will not be retransmitted, special actions chunk being waited upon will not be retransmitted, special actions
will need to be taken upon the arrival of a FORWARD TSN. will need to be taken upon the arrival of a FORWARD TSN.
In particular, during processing of a FORWARD TSN, the receiver MUST In particular, during processing of a FORWARD TSN, the receiver MUST
use the stream sequence information to examine all of the listed use the stream sequence information to examine all of the listed
stream reordering queues, and immediately make available for delivery stream reordering queues, and immediately make available for delivery
stream sequence numbers earlier than or equal to the stream sequence stream sequence numbers earlier than or equal to the stream sequence
number listed inside the FORWARD TSN. Any such stranded data SHOULD number listed inside the FORWARD TSN. Any such stranded data SHOULD
be made immediately available to the upper layer application. be made immediately available to the upper layer application.
An application using PR-SCTP receiving data should be aware of An application using PR-SCTP receiving data should be aware of
possible missing messages. The stream sequence number can be used, in possible missing messages. The stream sequence number can be used,
such a case, to determine that an intervening message has been in such a case, to determine that an intervening message has been
skipped. When intervening messages are missing it is an application skipped. When intervening messages are missing, it is an application
decision to process the messages or to take some other corrective decision to process the messages or to take some other corrective
action. action.
After receiving and processing a FORWARD TSN, the data receiver MUST After receiving and processing a FORWARD TSN, the data receiver MUST
take cautions in updating its re-assembly queue. The receiver MUST take cautions in updating its re-assembly queue. The receiver MUST
remove any partially reassembled message which is still missing one remove any partially reassembled message, which is still missing one
or more TSNs earlier than or equal to the new cumulative TSN point. or more TSNs earlier than or equal to the new cumulative TSN point.
In the event that the receiver has invoked the partial delivery API a In the event that the receiver has invoked the partial delivery API,
notification SHOULD also be generated to inform the upper layer API a notification SHOULD also be generated to inform the upper layer API
that the message being partially delivered will NOT be completed. that the message being partially delivered will NOT be completed.
Note that after receiving a FORWARD TSN and updating the cumulative Note that after receiving a FORWARD TSN and updating the cumulative
acknowledgement point, if a TSN that was skipped does arrive (i.e. acknowledgement point, if a TSN that was skipped does arrive (i.e.,
due to network reordering) then the receiver will follow the normal due to network reordering), then the receiver will follow the normal
rules defined in RFC2960 [2] for handling duplicate data. This rules defined in RFC2960 [2] for handling duplicate data. This
implies that the receiver will drop the chunk and report it as a implies that the receiver will drop the chunk and report it as a
duplicate in the next outbound SACK chunk. duplicate in the next outbound SACK chunk.
4. Services provided by PR-SCTP to the upper layer 4. Services provided by PR-SCTP to the upper layer
As described in Section 1.2, it is feasible to implement a variety of As described in Section 1.2, it is feasible to implement a variety of
partially reliable transport services using the new protocol partially reliable transport services using the new protocol
mechanisms introduced in Section 3; introducing these new services mechanisms introduced in Section 3; introducing these new services
requires making changes only at the sending side API, and the sending requires making changes only at the sending side API, and the sending
side protocol implementation. Thus, there may be a temptation to side protocol implementation. Thus, there may be a temptation to
standardize only the protocol, and leave the service definition as standardize only the protocol, and leave the service definition as
"implementation specific" or leave it to be defined in "implementation specific" or leave it to be defined in
"informational" documents. "informational" documents.
However, for those who may wish to write IETF standards for upper However, for those who may wish to write IETF standards for upper
layer protocols implemented over PR-SCTP, it is important to be able layer protocols implemented over PR-SCTP, it is important to be able
to refer to a standard definition of services provided. Therefore, to refer to a standard definition of services provided. Therefore,
this section provides an example definitions of one such service, this section provides example definitions of one such service, while
while also providing guidelines for the definition of additional also providing guidelines for the definition of additional services
services as required. Each such service may be proposed as a as required. Each such service may be proposed as a separate new
separate new RFC. RFC.
Section 4 is organized as follows: Section 4 is organized as follows:
Section 4.1 provides the definition of one specific PR-SCTP
o Section 4.1 provides the definition of one specific PR-SCTP
service: timed reliability. service: timed reliability.
Section 4.2 describes how a particular PR-SCTP service definition
o Section 4.2 describes how a particular PR-SCTP service definition
is requested by the upper layer during association establishment, is requested by the upper layer during association establishment,
and how the upper layer is notified if that request cannot be and how the upper layer is notified if that request cannot be
satisfied. satisfied.
Section 4.3 then provides guidelines for the specification of
PR-SCTP services other then the one defined in this memo. o Section 4.3 then provides guidelines for the specification of PR-
Finally, Section 4.4 describes some additional usage notes that SCTP services other then the one defined in this memo.
o Finally, Section 4.4 describes some additional usage notes that
upper layer protocol designers and implementors may find helpful. upper layer protocol designers and implementors may find helpful.
4.1 PR-SCTP Service Definition for "timed reliability" 4.1. PR-SCTP Service Definition for "timed reliability"
The "timed reliability" service is a natural extension of the The "timed reliability" service is a natural extension of the
"lifetime" concept already present in the base SCTP protocol. "lifetime" concept already present in the base SCTP protocol.
When this service is requested for an SCTP association, it changes When this service is requested for an SCTP association, it changes
the meaning of the lifetime parameter specified in the SEND primitive the meaning of the lifetime parameter specified in the SEND primitive
(see Section 10.1, part (E) of RFC2960 [2]; note that the parameter (see Section 10.1, part (E) of RFC2960 [2]; note that the parameter
is spelled "life time" in that document.) is spelled "life time" in that document.)
In the base SCTP protocol, the lifetime parameter is used to avoid In the base SCTP protocol, the lifetime parameter is used to avoid
skipping to change at page 15, line 21 skipping to change at page 15, line 36
During episodes of congestion this is particularly unfortunate, as During episodes of congestion this is particularly unfortunate, as
retransmission wastes bandwidth that could have been used for other retransmission wastes bandwidth that could have been used for other
(non-lifetime expired) messages. (non-lifetime expired) messages.
When the "timed reliability" service is invoked, this latter When the "timed reliability" service is invoked, this latter
restriction is removed. Specifically, when the "timed reliability" restriction is removed. Specifically, when the "timed reliability"
service is in effect, the following rules govern all messages that service is in effect, the following rules govern all messages that
are sent with a lifetime parameter: are sent with a lifetime parameter:
TR1) If the lifetime parameter of a message is SCTP_LIFETIME_RELIABLE TR1) If the lifetime parameter of a message is SCTP_LIFETIME_RELIABLE
(or unspecified see Section 5) that message is treated as a normal (or unspecified see Section 5), that message is treated as a
reliable SCTP message, just as in the base SCTP protocol. normal reliable SCTP message, just as in the base SCTP protocol.
TR2) If the lifetime parameter is not SCTP_LIFETIME_RELIABLE (see TR2) If the lifetime parameter is not SCTP_LIFETIME_RELIABLE (see
Section 5), then the SCTP sender MUST treat the message just as if Section 5), then the SCTP sender MUST treat the message just as
it were a normal reliable SCTP message as long as the lifetime has if it were a normal reliable SCTP message, as long as the
not yet expired. lifetime has not yet expired.
TR3) Before assigning a TSN to any message, the SCTP sender MUST TR3) Before assigning a TSN to any message, the SCTP sender MUST
evaluate the lifetime of that message. If it is expired, the SCTP evaluate the lifetime of that message. If it is expired, the
sender MUST NOT assign a TSN to that message, but instead, SHOULD SCTP sender MUST NOT assign a TSN to that message, but instead,
issue a notification to the upper layer and abandon the message. SHOULD issue a notification to the upper layer and abandon the
message.
TR4) Before transmitting or retransmitting a message for which a TSN TR4) Before transmitting or retransmitting a message for which a TSN
is already assigned, the SCTP sender MUST evaluate the lifetime of is already assigned, the SCTP sender MUST evaluate the lifetime
the message. If the lifetime of the message is expired, the SCTP of the message. If the lifetime of the message is expired, the
sender MUST "abandon" the message, as per the rules specified in SCTP sender MUST "abandon" the message, as per the rules
Section 3.5 marking that TSN as eligible for forward TSN. Note specified in Section 3.5 marking that TSN as eligible for
that this meets the requirement G1 defined in Section 4.3 forward TSN. Note that this meets the requirement G1 defined in
IMPLEMENTATION NOTE: An implementation SHOULD delay TSN assignment Section 4.3. IMPLEMENTATION NOTE: An implementation SHOULD
as mentioned in RFC2960 [2] Section 10.1. In such a case the delay TSN assignment as mentioned in RFC 2960 [2] Section 10.1.
lifetime parameter should be checked BEFORE assigning a TSN thus In such a case, the lifetime parameter should be checked BEFORE
allowing a message to be abandoned without the need to send a assigning a TSN, thus allowing a message to be abandoned without
FORWARD TSN. the need to send a FORWARD TSN.
TR5) The sending SCTP MAY evaluate the lifetime of messages at TR5) The sending SCTP MAY evaluate the lifetime of messages at
anytime. Expired messages that have not been assigned a TSN MAY be anytime. Expired messages that have not been assigned a TSN MAY
handled as per rule TR3. Expired messages that HAVE been assigned be handled as per rule TR3. Expired messages that HAVE been
a TSN MAY be handled as per rule TR4. assigned a TSN MAY be handled as per rule TR4.
TR6) The sending application MUST NOT change the lifetime parameter TR6) The sending application MUST NOT change the lifetime parameter
once the message is passed to the sending SCTP. once the message is passed to the sending SCTP.
Implementation Note: Rules TR1 through TR4 are designed in such a way Implementation Note: Rules TR1 through TR4 are designed in such a way
as to avoid requiring the implementer to maintain a separate timer as to avoid requiring the implementer to maintain a separate timer
for each message; instead, the lifetime need only be evaluated at for each message; instead, the lifetime need only be evaluated at
points in the life of the message where actions are already being points in the life of the message where actions are already being
taken, such as TSN assignment, transmission, or expiration of a taken, such as TSN assignment, transmission, or expiration of a
retransmission timeout. Rule TR5 is intended to give the SCTP retransmission timeout. Rule TR5 is intended to give the SCTP
implementor flexibility to evaluate lifetime at any other convenient implementor flexibility to evaluate lifetime at any other convenient
opportunity, WITHOUT requiring that lifetime be evaluated immediately opportunity, WITHOUT requiring that lifetime be evaluated immediately
at the point in time where it expires. at the point in time where it expires.
4.2 PR-SCTP Association Establishment 4.2. PR-SCTP Association Establishment
An upper layer protocol (ULP) that uses PR-SCTP may need to know An upper layer protocol (ULP) that uses PR-SCTP may need to know
whether PR-SCTP can be supported on a given association. Therefore, whether PR-SCTP can be supported on a given association. Therefore,
the ULP needs to have some indication of whether the FORWARD-TSN the ULP needs to have some indication of whether the FORWARD-TSN
chunk is supported by its peer. chunk is supported by its peer.
Section 10.1 of RFC2960 [2] describes abstract primitives for the Section 10.1 of RFC2960 [2] describes abstract primitives for the
ULP-to-SCTP interface, while noting that "individual implementations ULP-to-SCTP interface, while noting that "individual implementations
must define their own exact format, and may provide combinations or must define their own exact format, and may provide combinations or
subsets of the basic functions in single calls." subsets of the basic functions in single calls."
In this section, we describe one additional return value that may be In this section, we describe one additional return value that may be
added to the ASSOCIATE primitive to allow an SCTP service user to added to the ASSOCIATE primitive to allow an SCTP service user to
indicate whether the FORWARD-TSN chunk is supported by its peer. indicate whether the FORWARD-TSN chunk is supported by its peer.
RFC2960 indicates that the ASSOCIATE primitive "allows the upper RFC2960 indicates that the ASSOCIATE primitive "allows the upper
layer to initiate an association to a specific peer endpoint". It is layer to initiate an association to a specific peer endpoint". It is
structured as follows: structured as follows:
Format: ASSOCIATE(local SCTP instance name, destination transport addr, Format: ASSOCIATE(local SCTP instance name, destination transport
outbound stream count) addr, outbound stream count)
-> association id [,destination transport addr list] -> association id [,destination transport addr list]
[,outbound stream count] [,outbound stream count]
This extension adds one new OPTIONAL return value, such that the new This extension adds one new OPTIONAL return value, such that the new
primitive reads as follows: primitive reads as follows:
Format: ASSOCIATE(local SCTP instance name, destination transport addr, Format: ASSOCIATE(local SCTP instance name, destination transport
outbound stream count ) addr, outbound stream count )
-> association id [,destination transport addr list] -> association id [,destination transport addr list]
[,outbound stream count] [,forward tsn supported] [,outbound stream count] [,forward tsn supported]
NOTE: As per RFC2960, if the ASSOCIATE primitive is implemented as a NOTE: As per RFC2960, if the ASSOCIATE primitive is implemented as a
non-blocking call, the new OPTIONAL return value shall be passed with non-blocking call, the new OPTIONAL return value shall be passed with
the association parameters using the COMMUNICATION UP notification. the association parameters using the COMMUNICATION UP notification.
The new OPTIONAL parameter "forward tsn supported" is a boolean flag: The new OPTIONAL parameter "forward tsn supported" is a boolean flag:
(0) false [default] indicates that FORWARD TSN is not enabled by both (0) false [default] indicates that FORWARD TSN is not enabled by both
skipping to change at page 17, line 7 skipping to change at page 17, line 26
[,outbound stream count] [,forward tsn supported] [,outbound stream count] [,forward tsn supported]
NOTE: As per RFC2960, if the ASSOCIATE primitive is implemented as a NOTE: As per RFC2960, if the ASSOCIATE primitive is implemented as a
non-blocking call, the new OPTIONAL return value shall be passed with non-blocking call, the new OPTIONAL return value shall be passed with
the association parameters using the COMMUNICATION UP notification. the association parameters using the COMMUNICATION UP notification.
The new OPTIONAL parameter "forward tsn supported" is a boolean flag: The new OPTIONAL parameter "forward tsn supported" is a boolean flag:
(0) false [default] indicates that FORWARD TSN is not enabled by both (0) false [default] indicates that FORWARD TSN is not enabled by both
endpoints. endpoints.
(1) true indicates that FORWARD TSN is enabled on both endpoints. (1) true indicates that FORWARD TSN is enabled on both endpoints.
We also add a new primitive to allow the user application to enable/ We also add a new primitive to allow the user application to enable/
disable the PR-SCTP service on its endpoint before an association is disable the PR-SCTP service on its endpoint before an association is
established. established.
Format: ENABLE_PRSCTP(local SCTP instance name, boolean enable) Format: ENABLE_PRSCTP(local SCTP instance name, boolean enable)
The boolean parameter enable if set to true will enable PR-SCTP upon The boolean parameter enable, if set to true, will enable PR-SCTP
future endpoint associations. If the boolean parameter is set to upon future endpoint associations. If the boolean parameter is set
false, then the local endpoint will not advertise support of PR-SCTP to false, then the local endpoint will not advertise support of PR-
and thus disable the feature on future associations. It is SCTP and thus disable the feature on future associations. It is
recommended that this option be disabled by default I.e. in order to recommended that this option be disabled by default, i.e., in order
enable PR-SCTP the user will need to call this API option with the to enable PR-SCTP, the user will need to call this API option with
enable flag set to "true". the enable flag set to "true".
4.3 Guidelines for defining other PR-SCTP Services 4.3. Guidelines for defining other PR-SCTP Services
Other PR-SCTP services may be defined and implemented as dictated by Other PR-SCTP services may be defined and implemented as dictated by
the needs of upper layer protocols. If such upper layer protocols the needs of upper layer protocols. If such upper layer protocols
are to be standardized and require some particular PR-SCTP service are to be standardized and require some particular PR-SCTP service
other than the one defined in this document (i.e., "timed other than the one defined in this document (i.e., "timed
reliability") then those additional PR-SCTP services should also be reliability"), then those additional PR-SCTP services should also be
specified and standardized in a new RFC. specified and standardized in a new RFC.
It is suggested that any such additional service definitions be It is suggested that any such additional service definitions be
modeled after the contents of Section 4.1 . In particular, the modeled after the contents of Section 4.1 . In particular, the
service definition should provide: service definition should provide:
1. A description of how the service user specifies any parameters 1. A description of how the service user specifies any parameters
that need to be associated with a particular message (and/or any that need to be associated with a particular message (and/or any
other communication that takes place between the application and other communication that takes place between the application and
the SCTP transport sender) that provides the SCTP transport the SCTP transport sender) that provides the SCTP transport sender
sender with the information needed to determine when to give up with the information needed to determine when to give up on
on transmission of a particular message. transmission of a particular message.
Preferably this description should reference the primitives in Preferably, this description should reference the primitives in
the abstract API provided in Section 10 of RFC2960 [2], the abstract API provided in Section 10 of RFC2960 [2],
indicating any: indicating any:
* changes to the interpretation of the existing parameters of * changes to the interpretation of the existing parameters of
existing primitives, existing primitives,
* additional parameters to be added to existing primitives
(these should be OPTIONAL, and default values should be * additional parameters to be added to existing primitives (these
indicated), should be OPTIONAL, and default values should be indicated),
* additional primitives that may be needed. * additional primitives that may be needed.
2. A description of the rules used by the sender side implementation 2. A description of the rules used by the sender side implementation
to determine when to give up on messages that have not yet been to determine when to give up on messages that have not yet been
assigned a TSN. This description should also indicate what assigned a TSN. This description should also indicate what
protocol events trigger the evaluation, and what actions to take protocol events trigger the evaluation, and what actions to take
(e.g. notifications.) (e.g., notifications.)
3. A description of the rules used by the sender side implementation 3. A description of the rules used by the sender side implementation
to determine when to give up on the transmission or to determine when to give up on the transmission or retransmission
retransmission of messages that have already been assigned a TSN, of messages that have already been assigned a TSN, and may have
and may have been transmitted and possibly retransmitted zero or been transmitted and possibly retransmitted zero or more times.
more times.
Items (2) and (3) in the list above should also indicate what Items (2) and (3) in the list above should also indicate what
protocol events trigger the evaluation, and what actions to take if protocol events trigger the evaluation, and what actions to take if
the determination is made that the sender should give up on the determination is made that the sender should give up on
transmitting the message (e.g. notifications to the ULP.) transmitting the message (e.g., notifications to the ULP.)
Note that in any PR-SCTP service, the following rule MUST be Note that in any PR-SCTP service, the following rule MUST be
specified to avoid a protocol deadlock: specified to avoid a protocol deadlock:
(G1) When the sender side implementation gives up on transmitting a (G1) When the sender side implementation gives up on transmitting a
message that has been assigned a TSN (i.e., when that message is message that has been assigned a TSN (i.e., when that message is
"abandoned", as defined in Section 3.4) the sender side MUST mark "abandoned", as defined in Section 3.4), the sender side MUST
that TSN as eligible for forward TSN, and the rules in Section 3.4 mark that TSN as eligible for forward TSN, and the rules in
regarding the sending of FORWARD TSN chunks MUST be followed. Section 3.4 regarding the sending of FORWARD TSN chunks MUST be
followed.
Finally, a PR-SCTP service definition should specify a "canonical Finally, a PR-SCTP service definition should specify a "canonical
service name" to uniquely identify the service, and distinguish it service name" to uniquely identify the service, and distinguish it
from other PR-SCTP services. This name can then be used in upper from other PR-SCTP services. This name can then be used in upper
layer protocol standards, to indicate which PR-SCTP service layer protocol standards to indicate which PR-SCTP service definition
definition is required by that upper layer protocol. It can also be is required by that upper layer protocol. It can also be used in the
used in the documentation of APIs of PR-SCTP implementations to documentation of APIs of PR-SCTP implementations to indicate how an
indicate how an upper layer indicates which definition of PR-SCTP upper layer indicates which definition of PR-SCTP service should
service should apply. The canonical service name for the PR-SCTP apply. The canonical service name for the PR-SCTP service defined in
service defined in Section 4.1 is "timed reliability". Section 4.1 is "timed reliability".
4.4 Usage Notes 4.4. Usage Notes
Detecting missing data in a PR-SCTP stream is useful for some Detecting missing data in a PR-SCTP stream is useful for some
applications (e.g. Fiber channel or SCSI over IP). With PR-SCTP this applications (e.g., Fibre channel or SCSI over IP). With PR-SCTP,
becomes possible - the upper layer simply needs to examine the stream this becomes possible - the upper layer simply needs to examine the
sequence number of the arrived user messages of that stream to detect stream sequence number of the arrived user messages of that stream to
any missing data. Note, this detection only works when all the detect any missing data. Note, this detection only works when all
messages on that stream are sent in order, i.e., the "U" bit is not the messages on that stream are sent in order, i.e., the "U" bit is
set. not set.
5. Variables 5. Variables
This section defines variables used throughout this document: This section defines variables used throughout this document:
SCTP_LIFETIME_RELIABLE - A user interface indication defined by an SCTP_LIFETIME_RELIABLE - A user interface indication defined by an
implementation and used to indicate when a message is to be implementation and used to indicate when a message is to be
considered fully reliable. considered fully reliable.
6. Acknowledgments 6. Acknowledgments
The authors would like to thank Brian Bidulock, Scott Bradner, Jon The authors would like to thank Brian Bidulock, Scott Bradner, Jon
Berger, Armando L. Caro Jr., John Loughney, Jon Peterson, Ivan Arias Berger, Armando L. Caro Jr., John Loughney, Jon Peterson, Ivan Arias
Rodriguez, Ian Rytina, Chip Sharp, and others for their comments. Rodriguez, Ian Rytina, Chip Sharp, and others for their comments.
7. Security Considerations 7. Security Considerations
This document does not introduce any new security concerns to SCTP This document does not introduce any new security concerns to SCTP
other than the ones already documented in RFC2960 [2]. In particular other than the ones already documented in RFC 2960 [2]. In
this document shares the same security issues as unordered data particular, this document shares the same security issues as
within RFC2960 [2] identified by RFC3436 [4]. An application using unordered data within RFC 2960 [2] identified by RFC 3436 [4]. An
the PR-SCTP extension should not use transport layer security; application using the PR-SCTP extension should not use transport
further details can be found in RFC3436 [4]. layer security; further details can be found in RFC 3436 [4].
Note that the ability to cause a message to be skipped (I.e: the Note that the ability to cause a message to be skipped (i.e, the
FORWARD TSN chunk) does not provide any new attack for a FORWARD TSN chunk) does not provide any new attack for a Man-In-the-
Man-In-the-Middle (MIM), since the MIM already is capable of changing Middle (MIM), since the MIM already is capable of changing and/or
and/or withholding data thus effectively skipping messages. However withholding data, thus effectively skipping messages. However, the
the FORWARD TSN chunk does provide a mechanism to make it easier for FORWARD TSN chunk does provide a mechanism to make it easier for a
a MIM to skip selective messages when the application has this MIM to skip selective messages when the application has this feature
feature enabled since the MIM would have less state to maintain. enabled since the MIM would have less state to maintain.
8. IANA Considerations 8. IANA Considerations
IANA is requested to assign one new chunk type to SCTP using "192" is IANA has assigned 192 as a new chunk type to SCTP.
recommended. An alternate number can be assigned as long as the two
upper bits are both set to one.
IANA is requested to assign one new parameter type code to SCTP using IANA has assigned 49152 as a new parameter type code to SCTP.
"49152" is recommended. An altenate number can be assigned as long as
the two upper bits are both set to one.
Normative references 9. References
9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, [2] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000. "Stream Control Transmission Protocol", RFC 2960, October 2000.
Informational References 9.2. Informative References
[3] Clark, D. and D. Tennenhouse, "Architectural Considerations for [3] Clark, D. and D. Tennenhouse, "Architectural Considerations for
a New Generation of Protocols", SIGCOMM 1990 pp. 200-208, a New Generation of Protocols", SIGCOMM 1990 pp. 200-208,
September 1990. September 1990.
[4] Jungmaier, A., Rescorla, E. and M. Tuexen, "TLS over SCTP", RFC [4] Jungmaier, A., Rescorla, E. and M. Tuexen, "Transport Layer
3436, December 2002. Security over Stream Control Transmission Protocol", RFC 3436,
December 2002.
Authors' Addresses 10. Authors' Addresses
Randall R. Stewart Randall R. Stewart
Cisco Systems, Inc. Cisco Systems, Inc.
8725 West Higgins Road 8725 West Higgins Road
Suite 300 Suite 300
Chicago, IL 60631 Chicago, IL 60631
USA USA
Phone: +1-815-477-2127 Phone: +1-815-477-2127
EMail: rrs@cisco.com EMail: rrs@cisco.com
skipping to change at page 21, line 4 skipping to change at page 21, line 29
Phone: +1-847-632-3028 Phone: +1-847-632-3028
EMail: qxie1@email.mot.com EMail: qxie1@email.mot.com
Michael Tuexen Michael Tuexen
Univ. of Applied Sciences Muenster Univ. of Applied Sciences Muenster
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
Germany Germany
EMail: tuexen@fh-muenster.de EMail: tuexen@fh-muenster.de
Phillip T. Conrad Phillip T. Conrad
University of Delaware University of Delaware
Department of Computer and Information Sciences Department of Computer and Information Sciences
Newark, DE 19716 Newark, DE 19716
US USA
Phone: +1 302 831 8622 Phone: +1 302 831 8622
EMail: conrad@acm.org EMail: conrad@acm.org
URI: http://www.cis.udel.edu/~pconrad URI: http://www.cis.udel.edu/~pconrad
Intellectual Property Statement 11. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it might or might not be available; nor does it represent that it has
has made any effort to identify any such rights. Information on the made any independent effort to identify any such rights. Information
IETF's procedures with respect to rights in standards-track and on the procedures with respect to rights in RFC documents can be
standards-related documentation can be found in BCP-11. Copies of found in BCP 78 and BCP 79.
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to Copies of IPR disclosures made to the IETF Secretariat and any
obtain a general license or permission for the use of such assurances of licenses to be made available, or the result of an
proprietary rights by implementors or users of this specification can attempt made to obtain a general license or permission for the use of
be obtained from the IETF Secretariat. such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF at ietf-
Director. ipr@ietf.org.
Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

This html diff was produced by rfcdiff 1.25, available from http://www.levkowetz.com/ietf/tools/rfcdiff/