Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Appl. Sciences
Intended status: Standards Track R. Seggelmann
Expires: August 11, 2015 T-Systems International GmbH
R. Stewart
Netflix, Inc.
S. Loreto
Ericsson
February 7, 2015
Additional Policies for the Partial Reliability Extension of the Stream
Control Transmission Protocol
draft-ietf-tsvwg-sctp-prpolicies-07.txt
Abstract
This document defines two additional 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
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This Internet-Draft will expire on August 11, 2015.
Copyright Notice
Copyright (c) 2015 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
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Additional PR-SCTP Policies . . . . . . . . . . . . . . . . . 3
3.1. Limited Retransmissions Policy . . . . . . . . . . . . . 3
3.2. Priority Policy . . . . . . . . . . . . . . . . . . . . . 3
4. Socket API Considerations . . . . . . . . . . . . . . . . . . 4
4.1. Data Types . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Support for Added PR-SCTP Policies . . . . . . . . . . . 4
4.3. Socket Option for Getting the Stream Specific PR-SCTP
Status (SCTP_PR_STREAM_STATUS) . . . . . 5
4.4. Socket Option for Getting the Association Specific PR-
SCTP Status (SCTP_PR_ASSOC_STATUS) . . . 6
4.5. Socket Option for Getting and Setting the PR-SCTP Support
(SCTP_PR_SUPPORTED) . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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] refers to them as
'PR-SCTP Services'). [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 the following two additional PR-SCTP
policies:
Limited Retransmission Policy: Allows to limit the number of
retransmissions.
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Priority Policy: Allows to discard lower priority messages if space
for higher priority messages is needed in the send buffer.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Additional PR-SCTP Policies
This section defines two new PR-SCTP policies, one in each
subsection.
Please note that it is REQUIRED to implement [RFC3758], if you want
to implement these additional policies. However, these additional
policies are OPTIONAL when implementing [RFC3758].
3.1. 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. The
sender MUST perform all other actions required for processing the
retransmission event, such as adapting the congestion window and the
retransmission timeout. Please note that the number of
retransmissions includes both fast and timer-based retransmissions.
The sender MAY limit the number of retransmissions to 0. 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 perform any retransmissions.
Please note that using this policy does not affect the handling of
the thresholds 'Association.Max.Retrans' and 'Path.Max.Retrans' as
specified in Section 8 of [RFC4960].
The WebRTC protocol stack (see [I-D.ietf-rtcweb-data-channel]), is an
example of where the Limited Retransmissions Policy is used.
3.2. 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 at the
sender side MAY abandon other user message(s) of the same SCTP
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association (with the same or a different stream) with a priority
lower than the provided one. User messages sent reliable are
considered having a priority higher than all messages sent with the
Priority Policy. The algorithm for selecting the message(s) being
abandoned is implementation specific.
After lower priority messages have been abandoned high priority
messages can be transferred without the send call blocking (if used
in blocking mode) or the send call failing (if used in non-blocking
mode).
The IPFIX protocol stack (see [RFC7011]) is an example of where the
Priority Policy can be used. Template records would be sent with
full reliability, while billing, security-related, and other
monitoring flow records would be sent using the Priority Policy with
varying priority. The priority of security related flow-records
would be chosen higher than the the priority of monitoring flow
records.
4. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is
extended to support the newly defined PR-SCTP policies, to provide
some statistical information and to control the negotiation of the
PR-SCTP extension during the SCTP association setup.
Please note that this section is informational only.
4.1. 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].
4.2. 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 3.1 is
used, pr_policy has the value SCTP_PR_SCTP_RTX and the number of
retransmissions is given in pr_value.
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When using the Priority Policy described in Section 3.2, 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 3.1 |
| SCTP_PR_SCTP_PRIO | Priority | Section 3.2 |
+-------------------+---------------------------+---------------+
4.3. Socket Option for Getting the Stream Specific PR-SCTP Status
(SCTP_PR_STREAM_STATUS)
This socket option uses IPPROTO_SCTP as its level and
SCTP_PR_STREAM_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;
uint16_t sprstat_sid;
uint16_t sprstat_policy;
uint64_t sprstat_abandoned_unsent;
uint64_t sprstat_abandoned_sent;
};
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_sid: This parameter indicates for which outgoing SCTP stream
the user wants the information.
sprstat_policy: This parameter indicates for which PR-SCTP policy
the user wants the information. It is an error to use
SCTP_PR_SCTP_NONE in sprstat_policy. If SCTP_PR_SCTP_ALL is used,
the counters provided are aggregated over all supported policies.
sprstat_abandoned_unsent: The number of user messages which have
been abandoned using the policy specified in sprstat_policy on the
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stream specified in sprstat_sid for the association specified by
sprstat_assoc_id, before any part of the user message could be
sent.
sprstat_abandoned_sent: The number of user messages which have been
abandoned using the policy specified in sprstat_policy on the
stream specified in sprstat_sid for the association specified by
sprstat_assoc_id, 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. Please note that some implementations might choose not
to support this option, since it increases the resources needed for
an outgoing SCTP stream. For the same reasons, some implementations
might only support using SCTP_PR_SCTP_ALL in sprstat_policy.
sctp_opt_info() needs to be extended to support
SCTP_PR_STREAM_STATUS.
4.4. Socket Option for Getting the Association Specific PR-SCTP Status
(SCTP_PR_ASSOC_STATUS)
This socket option uses IPPROTO_SCTP as its level and
SCTP_PR_ASSOC_STATUS as its name. It can only be used with
getsockopt(), but not with setsockopt(). The socket option value
uses the same structure as described in Section 4.3:
struct sctp_prstatus {
sctp_assoc_t sprstat_assoc_id;
uint16_t sprstat_sid;
uint16_t sprstat_policy;
uint64_t sprstat_abandoned_unsent;
uint64_t sprstat_abandoned_sent;
};
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.
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sprstat_sid: This parameter is ignored.
sprstat_policy: This parameter indicates for which PR-SCTP policy
the user wants the information. It is an error to use
SCTP_PR_SCTP_NONE in sprstat_policy. If SCTP_PR_SCTP_ALL is used,
the counters provided are aggregated over all supported policies.
sprstat_abandoned_unsent: The number of user messages which have
been abandoned using the policy specified in sprstat_policy for
the association specified by sprstat_assoc_id, before any part of
the user message could be sent.
sprstat_abandoned_sent: The number of user messages which have been
abandoned using the policy specified in sprstat_policy for the
association specified by sprstat_assoc_id, 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 usage of the option described in Section 4.3 or the
subscription to the SCTP_SEND_FAILED_EVENT is recommended.
sctp_opt_info() needs to be extended to support SCTP_PR_ASSOC_STATUS.
4.5. 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 a particular association.
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]:
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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
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.
5. IANA Considerations
This document requires no actions from IANA.
6. Security Considerations
This document does not add any additional security considerations in
addition to the ones given in [RFC4960], [RFC3758], and [RFC6458].
As indicated in the Security Section of [RFC3758], transport layer
security in the form of TLS over SCTP (see [RFC3436]) can't be used
for PR-SCTP. However, DTLS over SCTP (see [RFC6083]) could be used
instead. If DTLS over SCTP as specified in [RFC6083] is used, the
security considerations of [RFC6083] do apply. It should also be
noted that using PR-SCTP for an SCTP association doesn't allow that
association to behave more aggressively than an SCTP association not
using PR-SCTP.
7. Acknowledgments
The authors wish to thank Benoit Claise, Spencer Dawkins, Stephen
Farrell, Gorry Fairhurst, Barry Leiba, Karen Egede Nielsen, Ka-Cheong
Poon, Dan Romascanu, Irene Ruengeler, Jamal Hadi Salim, Joseph
Salowey, Brian Trammell, and Vlad Yasevich for their invaluable
comments.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
8.2. Informative References
[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol",
RFC 3436, December 2002.
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083, January 2011.
[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.
[I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015.
[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
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Robin Seggelmann
T-Systems International GmbH
Fasanenweg 5
70771 Leinfelden-Echterdingen
DE
Email: rfc@robin-seggelmann.com
Randall R. Stewart
Netflix, Inc.
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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