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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: 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
   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 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
   (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.  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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