[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-stewart-tsvwg-sctp-ndata) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

Network Working Group                                         R. Stewart
Internet-Draft                                             Netflix, Inc.
Intended status: Standards Track                               M. Tuexen
Expires: January 7, 2016                Muenster Univ. of Appl. Sciences
                                                               S. Loreto
                                                                Ericsson
                                                           R. Seggelmann
                                     Metafinanz Informationssysteme GmbH
                                                            July 6, 2015


 Stream Schedulers and User Message Interleaving for the Stream Control
                         Transmission Protocol
                   draft-ietf-tsvwg-sctp-ndata-04.txt

Abstract

   The Stream Control Transmission Protocol (SCTP) is a message oriented
   transport protocol supporting arbitrary large user messages.
   However, the sender can not interleave different user messages which
   causes head of line blocking at the sender side.  To overcome this
   limitation, this document adds a new data chunk to SCTP.

   Whenever an SCTP sender is allowed to send a user data, it can
   possibly choose from multiple outgoing SCTP streams.  Multiple ways
   for this selection, called stream schedulers, are defined.  Some of
   them don't require the support of user message interleaving, some do.

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 January 7, 2016.







Stewart, et al.          Expires January 7, 2016                [Page 1]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  User Message Interleaving . . . . . . . . . . . . . . . . . .   4
     2.1.  The I-DATA Chunk supporting User Message Interleaving . .   4
     2.2.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   6
       2.2.1.  Negotiation . . . . . . . . . . . . . . . . . . . . .   6
       2.2.2.  Sender Side Considerations  . . . . . . . . . . . . .   6
       2.2.3.  Receiver Side Considerations  . . . . . . . . . . . .   7
     2.3.  Interaction with other SCTP Extensions  . . . . . . . . .   7
       2.3.1.  SCTP Partial Reliability Extension  . . . . . . . . .   7
       2.3.2.  SCTP Stream Reconfiguration Extension . . . . . . . .   8
   3.  Stream Schedulers . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Stream Scheduler without User Message Interleaving
           Support . . . . . . . . . . . . . . . . . . . . . . . . .   8
       3.1.1.  First Come First Serve (SCTP_SS_FCFS) . . . . . . . .   8
       3.1.2.  User Message Based Round Robin Scheduler (SCTP_SS_RR)   9
       3.1.3.  Packet Based Round Robin Scheduler (SCTP_SS_RR_PKT) .   9
       3.1.4.  Priority Based Scheduler (SCTP_SS_PRIO) . . . . . . .   9
       3.1.5.  Fair Bandwidth Scheduler (SCTP_SS_FB) . . . . . . . .   9
       3.1.6.  Weighted Fair Queueing Scheduler (SCTP_SS_WFQ)  . . .   9
     3.2.  Stream Scheduler with User Message Interleaving Support .   9
       3.2.1.  User Message Based Round Robin Scheduler
               (SCTP_SS_RR_INTER)  . . . . . . . . . . . . . . . . .   9
       3.2.2.  Packet Based Round Robin Scheduler
               (SCTP_SS_RR_PKT_INTER)  . . . . . . . . . . . . . . .   9
       3.2.3.  Priority Based Scheduler (SCTP_SS_PRIO_INTER) . . . .  10
       3.2.4.  Fair Bandwidth Scheduler (SCTP_SS_FB_INTER) . . . . .  10
       3.2.5.  Weighted Fair Queueing Scheduler (SCTP_SS_WFQ_INTER)   10
   4.  Socket API Considerations . . . . . . . . . . . . . . . . . .  10
     4.1.  SCTP_ASSOC_CHANGE Notification  . . . . . . . . . . . . .  10



Stewart, et al.          Expires January 7, 2016                [Page 2]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


     4.2.  Socket Options  . . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  Enable or Disable the Support of User Message
               Interleaving  . . . . . . . . . . . . . . . . . . . .  11
       4.2.2.  Get or Set the Stream Scheduler (SCTP_PLUGGABLE_SS) .  11
       4.2.3.  Get or Set the Stream Scheduler Parameter
               (SCTP_SS_VALUE) . . . . . . . . . . . . . . . . . . .  13
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

1.1.  Overview

   When SCTP [RFC4960] was initially designed it was mainly envisioned
   for transport of small signaling messages.  Late in the design stage
   it was decided to add support for fragmentation and reassembly of
   larger messages with the thought that someday Session Initiation
   Protocol (SIP) [RFC3261] style signaling messages may also need to
   use SCTP and a single MTU sized message would be too small.
   Unfortunately this design decision, though valid at the time, did not
   account for other applications which might send very large messages
   over SCTP.  When such large messages are now sent over SCTP a form of
   sender side head of line blocking becomes created within the
   protocol.  This head of line blocking is caused by the use of the
   Transmission Sequence Number (TSN) for two different purposes:

   1.  As an identifier for DATA chunks to provide a reliable transfer.

   2.  As an identifier for the sequence of fragments to allow
       reassembly.

   The protocol requires all fragments of a user message to have
   consecutive TSNs.  Therefore it is impossible for the sender to
   interleave different user messages.

   This document describes a new Data chunk called I-DATA.  This chunk
   incorporates all the flags and fields except the Stream Sequence
   Number (SSN) and properties of the current SCTP Data chunk but also
   adds two new fields in its chunk header, the Fragment Sequence Number
   (FSN) and the Message Identifier (MID).  Then the FSN is only used
   for reassembling all fragments with the same MID and the TSN only for
   the reliability.  The MID is also used for ensuring ordered delivery,




Stewart, et al.          Expires January 7, 2016                [Page 3]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


   therefore replacing the stream sequence number.  Therefore, the head
   of line blocking caused by the original design is avoided.

   The support of the I-DATA chunk is negotiated during the association
   setup using the Supported Extensions Parameter as defined in
   [RFC5061].  If I-DATA support has been negotiated for an association
   I-DATA chunks are used for all user-messages and no DATA chunks.  It
   should be noted, that an SCTP implementation needs to support the
   coexistence of associations using DATA chunks and associations using
   I-DATA chunks.

   This document also defines several stream schedulers for general SCTP
   associations.  If I-DATA support has been negotiated, several more
   schedulers are available.

1.2.  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].

2.  User Message Interleaving

   The interleaving of user messages is required for WebRTC Datachannels
   as specified in [I-D.ietf-rtcweb-data-channel].

2.1.  The I-DATA Chunk supporting User Message Interleaving

   The following Figure 1 shows the new I-DATA chunk allowing user
   messages interleaving.





















Stewart, et al.          Expires January 7, 2016                [Page 4]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type = 64   |  Res  |I|U|B|E|           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              TSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Stream Identifier      |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Identifier                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Payload Protocol Identifier / Fragment Sequence Number     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                           User Data                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: I-DATA chunk format

   The only differences between the I-DATA chunk in Figure 1 and the
   DATA chunk defined in [RFC4960] and [RFC7053] is the addition of the
   new Message Identifier (MID) and Fragment Sequence Number (FSN) and
   the removal of the Stream Sequence Number (SSN).  However, the lower
   16-bit of the MID can be used as the SSN if necessary.  The length of
   the I-DATA chunk header is 20 bytes, which is 4 bytes more than the
   length of the DATA chunk header defined in [RFC4960].

   Reserved: 16 bits (unsigned integer)
      This field is reserved.  It MUST be set to 0 by the sender and
      MUST be ignored by the receiver.

   Message Identifier (MID): 32 bits (unsigned integer)
      The MID is the same for all fragments of a user message, it is
      used to determine which fragments (enumerated by the FSN) belong
      to the same user message.  For ordered user messages, the MID is
      also used by the SCTP receiver to deliver the user messages in the
      correct order to the upper layer (similar to the SSN of the DATA
      chunk defined in [RFC4960]).  The sender uses two counters, one
      for ordered messages, one for unordered messages, for each
      outgoing streams.  All counters are independent and initially 0.
      They are incremented by 1 for each user message.  Please note that
      the serial number arithmetic defined in [RFC1982] using
      SERIAL_BITS = 32 applies.  Therefore the sender MUST NOT have more
      than 2**31 - 1 ordered messages for each outgoing stream in flight
      and MUST NOT have more than 2**31 - 1 unordered messages for each
      outgoing stream in flight.  Please note that the MID is in
      "network byte order", a.k.a.  Big Endian.



Stewart, et al.          Expires January 7, 2016                [Page 5]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


   Payload Protocol Identifier (PPID) / Fragment Sequence Number (FSN):
   32 bits (unsigned integer)
      If the B bit is set, this field contains the PPID of the user
      message.  In this case the FSN is implicitly considered to be 0.
      If the B bit is not set, this field contains the FSN.  The FSN is
      used to enumerate all fragments of a single user message, starting
      from 0 and incremented by 1.  The last fragment of a message MUST
      have the 'E' bit set.  Note that the FSN MAY wrap completely
      multiple times allowing arbitrary large user messages.  For the
      FSN the serial number arithmetic defined in [RFC1982] applies with
      SERIAL_BITS = 32.  Therefore a sender MUST NOT have more than
      2**31 - 1 fragments of a single user message in flight.  Please
      note that the FSN is in "network byte order", a.k.a.  Big Endian.

2.2.  Procedures

   This subsection describes how the support of the I-DATA chunk is
   negotiated and how the I-DATA chunk is used by the sender and
   receiver.

2.2.1.  Negotiation

   A sender MUST NOT send a I-DATA chunk unless both peers have
   indicated its support of the I-DATA chunk type within the Supported
   Extensions Parameter as defined in [RFC5061].  If I-DATA support has
   been negotiated on an association, I-DATA chunks MUST be used for all
   user messages and DATA-chunk MUST NOT be used.  If I-DATA support has
   not been negotiated on an association, DATA chunks MUST be used for
   all user messages and I-DATA chunks MUST NOT be used.

   A sender MUST NOT use the I-DATA chunk unless the user has requested
   that use (e.g. via the socket API, see Section 4).  This constraint
   is made since usage of this chunk requires that the application be
   willing to interleave messages upon reception within an association.
   This is not the default choice within the socket API (see [RFC6458])
   thus the user MUST indicate support to the protocol of the reception
   of completely interleaved messages.  Note that for stacks that do not
   implement [RFC6458] they may use other methods to indicate
   interleaved message support and thus enable the usage of the I-DATA
   chunk, the key is that the the stack MUST know the application has
   indicated its choice in wanting to use the extension.

2.2.2.  Sender Side Considerations

   Sender side usage of the I-DATA chunk is quite simple.  Instead of
   using the TSN for fragmentation purposes, the sender uses the new FSN
   field to indicate which fragment number is being sent.  The first
   fragment MUST have the 'B' bit set.  The last fragment MUST have the



Stewart, et al.          Expires January 7, 2016                [Page 6]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


   'E' bit set.  All other fragments MUST NOT have the 'B' or 'E' bit
   set.  All other properties of the existing SCTP DATA chunk also apply
   to the I-DATA chunk, i.e. congestion control as well as receiver
   window conditions MUST be observed as defined in [RFC4960].

   Note that the usage of this chunk should also imply late binding of
   the actual TSN to any chunk being sent.  This way other messages from
   other streams may be interleaved with the fragmented message.

   The sender MUST NOT have more than one ordered fragmented message
   being produced in any one stream.  The sender MUST NOT have more than
   one un-ordered fragmented message being produced in any one stream.
   The sender MAY have one ordered and one unordered fragmented message
   being produced within a single stream.  At any time multiple streams
   MAY be producing an ordered or unordered fragmented message.

2.2.3.  Receiver Side Considerations

   Upon reception of an SCTP packet containing a I-DATA chunk if the
   message needs to be reassembled, then the receiver MUST use the FSN
   for reassembly of the message and not the TSN.  Note that a non-
   fragmented messages is indicated by the fact that both the 'E' and
   'B' bits are set.  An ordered or unordered fragmented message is thus
   identified with any message not having both bits set.

2.3.  Interaction with other SCTP Extensions

   The usage of the I-DATA chunk might interfere with other SCTP
   extensions.  Future SCTP extensions MUST describe if and how they
   interfere with the usage of I-DATA chunks.  For the SCTP extensions
   already defined when this document was published, the details are
   given in the following subsections.

2.3.1.  SCTP Partial Reliability Extension

   When the SCTP extension defined in [RFC3758] is used, the the I-
   FORWARD-TSN chunk MUST be used instead of the FORWARD-TSN chunk.  The
   only difference is that the 16-bit Stream Sequence Number (SSN) has
   been replaced by the 32-bit Message Identifier (MID).












Stewart, et al.          Expires January 7, 2016                [Page 7]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type = 194  | Flags = 0x00  |      Length = Variable        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       New Cumulative TSN                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Stream 1          |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Identifier 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Stream N          |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Identifier N                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: I-FORWARD-TSN chunk format

2.3.2.  SCTP Stream Reconfiguration Extension

   When an association resets the SSN using the SCTP extension defined
   in [RFC6525], the two counters (one for the ordered messages, one for
   the unordered messages) used for the MID MUST be reset to 0
   correspondingly.

3.  Stream Schedulers

   This section defines several stream schedulers.  The stream
   schedulers which can be used even without the user message
   interleaving support as defined in Section 2 are described in
   Section 3.1.  In Section 3.2 stream schedulers requiring user message
   interleaving defined in Section 2 are described.

3.1.  Stream Scheduler without User Message Interleaving Support

3.1.1.  First Come First Serve (SCTP_SS_FCFS)

   The simple first-come, first-serve scheduler of user messages is
   used.  It just passes through the messages in the order in which they
   have been delivered by the application.  No modification of the order
   is done at all.







Stewart, et al.          Expires January 7, 2016                [Page 8]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


3.1.2.  User Message Based Round Robin Scheduler (SCTP_SS_RR)

   This scheduler provides a fair scheduling based on the number of user
   messages by cycling around non-empty stream queues.

3.1.3.  Packet Based Round Robin Scheduler (SCTP_SS_RR_PKT)

   This is a round-robin scheduler but only bundles user messages of the
   same stream in one packet.  This minimizes head-of-line blocking when
   a packet is lost because only a single stream is affected.

3.1.4.  Priority Based Scheduler (SCTP_SS_PRIO)

   Scheduling of user messages with strict priorities is used.  The
   priority is configurable per outgoing SCTP stream.  Streams having a
   higher priority will be scheduled first and when multiple streams
   have the same priority, the default scheduling should be used for
   them.

3.1.5.  Fair Bandwidth Scheduler (SCTP_SS_FB)

   A fair bandwidth distribution between the streams is used.  This
   scheduler considers the lengths of the messages of each stream and
   schedules them in a certain way to maintain an equal bandwidth for
   all streams.

3.1.6.  Weighted Fair Queueing Scheduler (SCTP_SS_WFQ)

   A weighted fair queueing scheduler between the streams is used.  The
   weight is configurable per outgoing SCTP stream.  This scheduler
   considers the lengths of the messages of each stream and schedules
   them in a certain way to use the bandwidth according to the given
   weights.

3.2.  Stream Scheduler with User Message Interleaving Support

3.2.1.  User Message Based Round Robin Scheduler (SCTP_SS_RR_INTER)

   This scheduler is similar to the one described in Section 3.1.2, but
   based on I-DATA chunks instead of user messages.

3.2.2.  Packet Based Round Robin Scheduler (SCTP_SS_RR_PKT_INTER)

   This scheduler is similar to the one described in Section 3.1.3, but
   based on I-DATA chunks instead of user messages.






Stewart, et al.          Expires January 7, 2016                [Page 9]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


3.2.3.  Priority Based Scheduler (SCTP_SS_PRIO_INTER)

   This scheduler is similar to the one described in Section 3.1.4, but
   based on I-DATA chunks instead of user messages.

3.2.4.  Fair Bandwidth Scheduler (SCTP_SS_FB_INTER)

   This scheduler is similar to the one described in Section 3.1.5, but
   based on I-DATA chunks instead of user messages.

3.2.5.  Weighted Fair Queueing Scheduler (SCTP_SS_WFQ_INTER)

   This scheduler is similar to the one described in Section 3.1.6, but
   based on I-DATA chunks instead of user messages.  This scheduler is
   used for WebRTC Datachannels as specified in
   [I-D.ietf-rtcweb-data-channel].

4.  Socket API Considerations

   This section describes how the socket API defined in [RFC6458] is
   extended to allow applications to use the extension described in this
   document.

   Please note that this section is informational only.

4.1.  SCTP_ASSOC_CHANGE Notification

   When an SCTP_ASSOC_CHANGE notification is delivered indicating a
   sac_state of SCTP_COMM_UP or SCTP_RESTART for an SCTP association
   where both peers support the I-DATA chunk,
   SCTP_ASSOC_SUPPORTS_INTERLEAVING should be listen in the sac_info
   field.

4.2.  Socket Options

   +-----------------------------+-------------------------+-----+-----+
   | option name                 | data type               | get | set |
   +-----------------------------+-------------------------+-----+-----+
   | SCTP_INTERLEAVING_SUPPORTED | struct sctp_assoc_value |  X  |  X  |
   | SCTP_PLUGGABLE_SS           | struct sctp_assoc_value |  X  |  X  |
   | SCTP_SS_VALUE               | struct                  |  X  |  X  |
   |                             | sctp_stream_value       |     |     |
   +-----------------------------+-------------------------+-----+-----+








Stewart, et al.          Expires January 7, 2016               [Page 10]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


4.2.1.  Enable or Disable the Support of User Message Interleaving

   This socket option allows the enabling or disabling of the
   negotiation of user message interleaving support for future
   associations.  For existing associations it allows to query whether
   user message interleaving support was negotiated or not on a
   particular association.

   User message interleaving is disabled per default.

   This socket option uses IPPROTO_SCTP as its level and
   SCTP_INTERLEAVING_SUPPORTED as its name.  It can be used with
   getsockopt() and setsockopt().  The socket option value uses the
   following structure defined in [RFC6458]:

   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 user message
      interleaving whereas a value of 0 encodes the disabling of user
      message interleaving.

   sctp_opt_info() needs to be extended to support
   SCTP_INTERLEAVING_SUPPORTED.

   An application using user message interleaving should also set the
   fragment interleave level to 2.  This allows the reception from
   multiple streams simultaneously.  Failure to set this option can
   possibly lead to application deadlock.

4.2.2.  Get or Set the Stream Scheduler (SCTP_PLUGGABLE_SS)

   A stream scheduler can be selected with the SCTP_PLUGGABLE_SS option
   for setsockopt().  The struct sctp_assoc_value is used to specify the
   association for which the scheduler should be changed and the value
   of the desired algorithm.

   The definition of struct sctp_assoc_value is the same as in
   [RFC6458]:




Stewart, et al.          Expires January 7, 2016               [Page 11]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


   struct sctp_assoc_value {
     sctp_assoc_t assoc_id;
     uint32_t assoc_value;
   };

   assoc_id:  Holds the identifier for the association of which the
      scheduler should be changed.  The special
      SCTP_{FUTURE|CURRENT|ALL}_ASSOC can also be used.  This parameter
      is ignored for one-to-one style sockets.

   assoc_value:  This specifies which scheduler is used.  The following
      constants can be used:

      SCTP_SS_DEFAULT:  The default scheduler used by the SCTP
         implementation.  Typical values are SCTP_SS_FCFS or SCTP_SS_RR.

      SCTP_SS_FCFS:  Use the scheduler specified in Section 3.1.1.

      SCTP_SS_RR:  Use the scheduler specified in Section 3.1.2.

      SCTP_SS_RR_PKT:  Use the scheduler specified in Section 3.1.3.

      SCTP_SS_PRIO:  Use the scheduler specified in Section 3.1.4.  The
         priority can be assigned with the sctp_stream_value struct.
         The higher the assigned value, the lower the priority, that is
         the default value 0 is the highest priority and therefore the
         default scheduling will be used if no priorities have been
         assigned.

      SCTP_SS_FB:  Use the scheduler specified in Section 3.1.5.

      SCTP_SS_WFQ:  Use the scheduler specified in Section 3.1.6.  The
         weight can be assigned with the sctp_stream_value struct.

      SCTP_SS_RR_INTER:  Use the scheduler specified in Section 3.2.1.

      SCTP_SS_RR_PKT_INTER:  Use the scheduler specified in
         Section 3.2.2.

      SCTP_SS_PRIO_inter:  Use the scheduler specified in Section 3.2.3.
         The priority can be assigned with the sctp_stream_value struct.
         The higher the assigned value, the lower the priority, that is
         the default value 0 is the highest priority and therefore the
         default scheduling will be used if no priorities have been
         assigned.

      SCTP_SS_FB_INTER:  Use the scheduler specified in Section 3.2.4.




Stewart, et al.          Expires January 7, 2016               [Page 12]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


      SCTP_SS_WFQ_INTER:  Use the scheduler specified in Section 3.2.5.
         The weight can be assigned with the sctp_stream_value struct.

4.2.3.  Get or Set the Stream Scheduler Parameter (SCTP_SS_VALUE)

   Some schedulers require additional information to be set for single
   streams as shown in the following table:

                +----------------------+-----------------+
                | name                 | per stream info |
                +----------------------+-----------------+
                | SCTP_SS_DEFAULT      |        no       |
                | SCTP_SS_FCFS         |        no       |
                | SCTP_SS_RR           |        no       |
                | SCTP_SS_RR_PKT       |        no       |
                | SCTP_SS_PRIO         |       yes       |
                | SCTP_SS_FB           |        no       |
                | SCTP_SS_WFQ          |       yes       |
                | SCTP_SS_RR_INTER     |        no       |
                | SCTP_SS_RR_PKT_INTER |        no       |
                | SCTP_SS_PRIO_INTER   |       yes       |
                | SCTP_SS_FB_INTER     |        no       |
                | SCTP_SS_WFQ_INTER    |       yes       |
                +----------------------+-----------------+

   This is achieved with the SCTP_SS_VALUE option and the corresponding
   struct sctp_stream_value.  The definition of struct sctp_stream_value
   is as follows:

   struct sctp_stream_value {
     sctp_assoc_t assoc_id;
     uint16_t stream_id;
     uint16_t stream_value;
   };

   assoc_id:  Holds the identifier for the association of which the
      scheduler should be changed.  The special
      SCTP_{FUTURE|CURRENT|ALL}_ASSOC can also be used.  This parameter
      is ignored for one-to-one style sockets.

   stream_id:  Holds the stream id for the stream for which additional
      information has to be provided.

   stream_value:  The meaning of this field depends on the scheduler
      specified.  It is ignored when the scheduler does not need
      additional information.





Stewart, et al.          Expires January 7, 2016               [Page 13]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


5.  IANA Considerations

   [NOTE to RFC-Editor:

      "RFCXXXX" is to be replaced by the RFC number you assign this
      document.

   ]

   [NOTE to RFC-Editor:

      The suggested values for the chunk type and the chunk flags are
      tentative and to be confirmed by IANA.

   ]

   This document (RFCXXXX) is the reference for all registrations
   described in this section.

   A new chunk type has to be assigned by IANA.  IANA should assign this
   value from the pool of chunks with the upper two bits set to '01'.
   This requires an additional line in the "Chunk Types" registry for
   SCTP:

            +----------+-------------------------+-----------+
            | ID Value | Chunk Type              | Reference |
            +----------+-------------------------+-----------+
            | 64       | New DATA chunk (I-DATA) | [RFCXXXX] |
            +----------+-------------------------+-----------+

   The registration table as defined in [RFC6096] for the chunk flags of
   this chunk type is initially given by the following table:

            +------------------+-----------------+-----------+
            | Chunk Flag Value | Chunk Flag Name | Reference |
            +------------------+-----------------+-----------+
            | 0x01             | E bit           | [RFCXXXX] |
            | 0x02             | B bit           | [RFCXXXX] |
            | 0x04             | U bit           | [RFCXXXX] |
            | 0x08             | I bit           | [RFCXXXX] |
            | 0x10             | Unassigned      |           |
            | 0x20             | Unassigned      |           |
            | 0x40             | Unassigned      |           |
            | 0x80             | Unassigned      |           |
            +------------------+-----------------+-----------+






Stewart, et al.          Expires January 7, 2016               [Page 14]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


6.  Security Considerations

   This document does not add any additional security considerations in
   addition to the ones given in [RFC4960] and [RFC6458].

7.  Acknowledgments

   The authors wish to thank Christer Holmberg, Karen E.  Egede Nielsen,
   Irene Ruengeler, and Lixia Zhang for her invaluable comments.

8.  References

8.1.  Normative References

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061, September
              2007.

   [RFC6096]  Tuexen, M. and R. Stewart, "Stream Control Transmission
              Protocol (SCTP) Chunk Flags Registration", RFC 6096,
              January 2011.

   [RFC6525]  Stewart, R., Tuexen, M., and P. Lei, "Stream Control
              Transmission Protocol (SCTP) Stream Reconfiguration", RFC
              6525, February 2012.

   [RFC7053]  Tuexen, M., Ruengeler, I., and R. Stewart, "SACK-
              IMMEDIATELY Extension for the Stream Control Transmission
              Protocol", RFC 7053, November 2013.








Stewart, et al.          Expires January 7, 2016               [Page 15]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


8.2.  Informative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [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, "WebRTC Data
              Channels", draft-ietf-rtcweb-data-channel-13 (work in
              progress), January 2015.

Authors' Addresses

   Randall R. Stewart
   Netflix, Inc.
   Chapin, SC  29036
   United States

   Email: randall@lakerest.net


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

   Email: tuexen@fh-muenster.de


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Salvatore.Loreto@ericsson.com









Stewart, et al.          Expires January 7, 2016               [Page 16]


Internet-Draft   Stream Schedulers and the I-DATA Chunk        July 2015


   Robin Seggelmann
   Metafinanz Informationssysteme GmbH
   Leopoldstrasse 146
   80804 Muenchen
   Germany

   Email: rfc@robin-seggelmann.com












































Stewart, et al.          Expires January 7, 2016               [Page 17]


Html markup produced by rfcmarkup 1.124, available from https://tools.ietf.org/tools/rfcmarkup/