Internet DRAFT - draft-tuexen-tsvwg-sctp-prpolicies
draft-tuexen-tsvwg-sctp-prpolicies
Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Appl. Sciences
Intended status: Informational R. Seggelmann
Expires: April 23, 2014 T-Systems International GmbH
R. Stewart
Adara Networks
S. Loreto
Ericsson
October 20, 2013
Additional Policies for the Partial Delivery Extension of the Stream
Control Transmission Protocol
draft-tuexen-tsvwg-sctp-prpolicies-03.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
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This Internet-Draft will expire on April 23, 2014.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Data Types . . . . . . . . . . . . . . . . . . . . . . . 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. Support for Added PR-SCTP Policies . . . . . . . . . . . 3
3.2. Socket Option for Getting the PR-SCTP Status
(SCTP_PR_STATUS) . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
1.1. Overview
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.
1.2. Data Types
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This documents uses data types from Draft 6.6 (March 1997) of POSIX
1003.1g: uintN_t means an unsigned integer of exactly N bits (e.g.
uint16_t). This is the same as in [RFC6458]
2. Additional PR-SCTP Policies
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
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
RTCWeb 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.
After lower priority messages have been abandoned high priority
messages can be transferred without blocking the send() call.
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.
Please note that this section is informational only.
3.1. 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:
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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 |
+-------------------+---------------------------+---------------+
3.2. 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;
uint32_t sprstat_abandoned_unsent;
uint32_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_abandoned_unsent: The number of user messages which have
been abandoned, before any part of the user message could be sent.
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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 messages 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 messages 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.
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 Irene Ruengeler, Jamal Hadi Salim, and Vlad
Yasevich for there 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.
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[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.
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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