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Versions: (draft-tuexen-tsvwg-sctp-prpolicies) 00 01 02 03 04 05 06 07 RFC 7496

Network Working Group                                          M. Tuexen
Internet-Draft                          Muenster Univ. of Appl. Sciences
Intended status: Informational                             R. Seggelmann
Expires: July 26, 2014                      T-Systems International GmbH
                                                              R. Stewart
                                                          Adara Networks
                                                               S. Loreto
                                                                Ericsson
                                                        January 22, 2014


Additional Policies for the Partial Reliability Extension of the Stream
                     Control Transmission Protocol
                draft-ietf-tsvwg-sctp-prpolicies-01.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
   working documents as Internet-Drafts.  The list of current Internet-
   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 July 26, 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
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .   3
   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  . . . . . . . . . . .   4
     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  . . . . . . . . . . . . . . . . .   6
   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.






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1.2.  Data Types

   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 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
   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.  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.

   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.



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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:

   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;
     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_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 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 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.







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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.

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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