Additional Policies for the Partial Delivery Extension of the Stream Control Transmission Protocol
draft-tuexen-tsvwg-sctp-prpolicies-02

Network Working Group                                          S. Loreto
Internet-Draft                                                  Ericsson
Intended status: Informational                             R. Seggelmann
Expires: January 13, 2014                   T-Systems International GmbH
                                                              R. Stewart
                                                          Adara Networks
                                                               M. Tuexen
                                        Muenster Univ. of Appl. Sciences
                                                           July 12, 2013

  Additional Policies for the Partial Delivery Extension of the Stream
                     Control Transmission Protocol
               draft-tuexen-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

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   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 January 13, 2014.

Copyright Notice

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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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Additional PR-SCTP Policies . . . . . . . . . . . . . . . . .   2
     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_GET_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.

2.  Additional PR-SCTP Policies

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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.  See [I-D.ietf-rtcweb-data-channel] for more
   information.

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
   [RFC5101] 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_GET_PR_STATUS)

   This socket option uses IPPROTO_SCTP as its level, SCTP_GET_PR_STATUS
   as its name and 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_GET_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

   [RFC5101]  Claise, B., "Specification of the IP Flow Information
              Export (IPFIX) Protocol for the Exchange of IP Traffic
              Flow Information", RFC 5101, January 2008.

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   [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.

   [I-D.ietf-rtcweb-data-channel]
              Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb Data
              Channels", draft-ietf-rtcweb-data-channel-04 (work in
              progress), February 2013.

Authors' Addresses

   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   FI

   Email: Salvatore.Loreto@ericsson.com

   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

   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstrasse 39
   48565 Steinfurt
   DE

   Email: tuexen@fh-muenster.de

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