Additional Policies for the Partial Reliability Extension of the Stream Control Transmission Protocol
draft-ietf-tsvwg-sctp-prpolicies-02
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| Document | Type | Active Internet-Draft (tsvwg WG) | |
|---|---|---|---|
| Authors | Michael Tüxen , Robin Seggelmann , Randall R. Stewart , Salvatore Loreto | ||
| Last updated | 2014-04-08 | ||
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draft-ietf-tsvwg-sctp-prpolicies-02
Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Appl. Sciences
Intended status: Informational R. Seggelmann
Expires: October 10, 2014 T-Systems International GmbH
R. Stewart
Adara Networks
S. Loreto
Ericsson
April 8, 2014
Additional Policies for the Partial Reliability Extension of the Stream
Control Transmission Protocol
draft-ietf-tsvwg-sctp-prpolicies-02.txt
Abstract
This document defines policies for the Partial Reliability Extension
of the Stream Control Transmission Protocol (PR-SCTP) allowing to
limit the number of retransmissions or to prioritize user messages
for more efficient send buffer usage.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 10, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Additional PR-SCTP Policies . . . . . . . . . . . . . . . . . 3
2.1. Limited Retransmissions Policy . . . . . . . . . . . . . 3
2.2. Priority Policy . . . . . . . . . . . . . . . . . . . . . 3
3. Socket API Considerations . . . . . . . . . . . . . . . . . . 3
3.1. Data Types . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Support for Added PR-SCTP Policies . . . . . . . . . . . 4
3.3. Socket Option for Getting the PR-SCTP Status
(SCTP_PR_STATUS) . . . . . . . . . . . . . . . . . . . . 4
3.4. Socket Option for Getting and Setting the PR-SCTP Support
(SCTP_PR_SUPPORTED) . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The SCTP Partial Reliability Extension (PR-SCTP) defined in [RFC3758]
provides a generic method for senders to abandon user messages. The
decision to abandon a user message is sender side only and the exact
condition is called a PR-SCTP policy. [RFC3758] also defines one
particular PR-SCTP policy, called Timed Reliability. This allows the
sender to specify a timeout for a user message after which the SCTP
stack abandons the user message.
This document specifies two additional PR-SCTP policies:
Limited Retransmission Policy: Allows to limit the number of
retransmissions.
Priority Policy: Allows to discard lower priority messages if space
for higher priority messages is needed in the send buffer.
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2. Additional PR-SCTP Policies
This section defined two new PR-SCTP policies, one in each
subsection.
2.1. Limited Retransmissions Policy
Using the Limited Retransmission Policy allows the sender of a user
message to specify an upper limit for the number of retransmissions
for each DATA chunk of the given user messages. The sender must
abandon a user message if the number of retransmissions of any of the
DATA chunks of the user message would exceed the provided limit.
Please note that the number of retransmissions includes the fast and
the timer based retransmissions.
Limiting the number of retransmissions to 0 is allowed. This will
result in abandoning the message when it would get retransmitted for
the first time. The use of this setting provides a service similar
to UDP, which also does not send any retransmissions either.
The Limited Retransmissions Policy is used for data channels in the
WebRTC protocol stack.
2.2. Priority Policy
Using the Priority Policy allows the sender of a user message to
specify a priority. When storing a user message in the send buffer
while there is not enough available space, the SCTP stack may abandon
other user messages with a priority lower than the provided one. The
algorithm for selecting the message being abandoned is implementation
specific.
After lower priority messages have been abandoned high priority
messages can be transferred without blocking the send call (if used
in blocking mode) or failing the send call (if used in non-blocking
mode).
The Priority Policy can be used in the IPFIX protocol stack. See
[RFC7011] for more information.
3. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is
extended to support the newly defined PR-SCTP policies and to provide
some statistical information.
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3.1. Data Types
This section uses data types from [IEEE.1003-1G.1997]: uintN_t means
an unsigned integer of exactly N bits (e.g. uint16_t). This is the
same as in [RFC6458]
3.2. Support for Added PR-SCTP Policies
As defined in [RFC6458], the PR-SCTP policy is specified and
configured by using the following sctp_prinfo structure:
struct sctp_prinfo {
uint16_t pr_policy;
uint32_t pr_value;
};
When the Limited Retransmission Policy described in Section 2.1 is
used, pr_policy has the value SCTP_PR_SCTP_RTX and the number of
retransmissions is given in pr_value.
For using the Priority Policy described in Section 2.2, pr_policy has
the value SCTP_PR_SCTP_PRIO. The priority is given in pr_value. The
value of zero is the highest priority and larger numbers in pr_value
denote lower priorities.
The following table summarizes the possible parameter settings
defined in [RFC6458] and this document:
+-------------------+---------------------------+---------------+
| pr_policy | pr_value | Specification |
+-------------------+---------------------------+---------------+
| SCTP_PR_SCTP_NONE | Ignored | [RFC6458] |
| SCTP_PR_SCTP_TTL | Lifetime in ms | [RFC6458] |
| SCTP_PR_SCTP_RTX | Number of retransmissions | Section 2.1 |
| SCTP_PR_SCTP_PRIO | Priority | Section 2.2 |
+-------------------+---------------------------+---------------+
3.3. Socket Option for Getting the PR-SCTP Status (SCTP_PR_STATUS)
This socket option uses IPPROTO_SCTP as its level and SCTP_PR_STATUS
as its name. It can only be used with getsockopt(), but not with
setsockopt(). The socket option value uses the following structure:
struct sctp_prstatus {
sctp_assoc_t sprstat_assoc_id;
uint64_t sprstat_abandoned_unsent;
uint64_t sprstat_abandoned_sent;
};
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sprstat_assoc_id: This parameter is ignored for one-to-one style
sockets. For one-to-many style sockets this parameter indicates
for which association the user wants the information. It is an
error to use SCTP_{CURRENT|ALL|FUTURE}_ASSOC in sprstat_assoc_id.
sprstat_abandoned_unsent: The number of user messages which have
been abandoned, before any part of the user message could be sent.
sprstat_abandoned_sent: The number of user messages which have been
abandoned, after a part of the user message has been sent.
There are separate counters for unsent and sent user messages because
the SCTP_SEND_FAILED_EVENT supports a similar differentiation.
Please note that an abandoned large user message requiring an SCTP
level fragmentation is reported in the sprstat_abandoned_sent counter
as soon as at least one fragment of it has been sent. Therefore each
abandoned user message is either counted in sprstat_abandoned_unsent
or sprstat_abandoned_sent.
If more detailed information about abandoned user messages is
required, the subscription to the SCTP_SEND_FAILED_EVENT is
recommended.
sctp_opt_info() needs to be extended to support SCTP_PR_STATUS.
3.4. Socket Option for Getting and Setting the PR-SCTP Support
(SCTP_PR_SUPPORTED)
This socket option allows the enabling or disabling of the
negotiation of PR-SCTP support for future associations. For existing
associations it allows to query whether PR-SCTP support was
negotiated or not on particular associations.
Whether PR-SCTP is enabled or not per default is implementation
specific.
This socket option uses IPPROTO_SCTP as its level and
SCTP_PR_SUPPORTED as its name. It can be used with getsockopt() and
setsockopt(). The socket option value uses the following structure
defined in [RFC6458]:
struct sctp_assoc_value {
sctp_assoc_t assoc_id;
uint32_t assoc_value;
};
assoc_id: This parameter is ignored for one-to-one style sockets.
For one-to-many style sockets, this parameter indicates upon which
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association the user is performing an action. The special
sctp_assoc_t SCTP_FUTURE_ASSOC can also be used, it is an error to
use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.
assoc_value: A non-zero value encodes the enabling of PR-SCTP
whereas a value of 0 encodes the disabling of PR-SCTP.
sctp_opt_info() needs to be extended to support SCTP_PR_SUPPORTED.
4. IANA Considerations
This document requires no actions from IANA.
5. Security Considerations
This document does not add any additional security considerations in
addition to the ones given in [RFC4960], [RFC3758], and [RFC6458].
6. Acknowledgments
The authors wish to thank Karen Egede Nielsen, Ka-Cheong Poon, Irene
Ruengeler, Jamal Hadi Salim, and Vlad Yasevich for their invaluable
comments.
7. References
7.1. Normative References
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
7.2. Informative References
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011.
[RFC7011] Claise, B., Trammell, B., and P. Aitken, "Specification of
the IP Flow Information Export (IPFIX) Protocol for the
Exchange of Flow Information", STD 77, RFC 7011, September
2013.
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[IEEE.1003-1G.1997]
Institute of Electrical and Electronics Engineers,
"Protocol Independent Interfaces", IEEE Standard 1003.1G,
March 1997.
Authors' Addresses
Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
48565 Steinfurt
DE
Email: tuexen@fh-muenster.de
Robin Seggelmann
T-Systems International GmbH
Fasanenweg 5
70771 Leinfelden-Echterdingen
DE
Email: robin.seggelmann@t-systems.com
Randall R. Stewart
Adara Networks
Chapin, SC 29036
US
Email: randall@lakerest.net
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
FI
Email: Salvatore.Loreto@ericsson.com
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