Network Working Group R. Stewart Internet-Draft Netflix, Inc. Intended status: Standards Track M. Tuexen Expires: January 22, 2017 Muenster Univ. of Appl. Sciences S. Loreto Ericsson R. Seggelmann Metafinanz Informationssysteme GmbH July 21, 2016 Stream Schedulers and User Message Interleaving for the Stream Control Transmission Protocol draft-ietf-tsvwg-sctp-ndata-07.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 22, 2017. Stewart, et al. Expires January 22, 2017 [Page 1] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 Copyright Notice Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . 5 2. User Message Interleaving . . . . . . . . . . . . . . . . . . 5 2.1. The I-DATA Chunk supporting User Message Interleaving . . 5 2.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.1. Negotiation . . . . . . . . . . . . . . . . . . . . . 7 2.2.2. Sender Side Considerations . . . . . . . . . . . . . 8 2.2.3. Receiver Side Considerations . . . . . . . . . . . . 8 2.3. Interaction with other SCTP Extensions . . . . . . . . . 8 2.3.1. SCTP Partial Reliability Extension . . . . . . . . . 9 2.3.2. SCTP Stream Reconfiguration Extension . . . . . . . . 10 3. Stream Schedulers . . . . . . . . . . . . . . . . . . . . . . 10 3.1. First Come First Serve (SCTP_SS_FCFS) . . . . . . . . . . 10 3.2. Round Robin Scheduler (SCTP_SS_RR) . . . . . . . . . . . 11 3.3. Round Robin Scheduler per Packet (SCTP_SS_RR_PKT) . . . . 11 3.4. Priority Based Scheduler (SCTP_SS_PRIO) . . . . . . . . . 11 3.5. Fair Bandwidth Scheduler (SCTP_SS_FB) . . . . . . . . . . 11 3.6. Weighted Fair Queueing Scheduler (SCTP_SS_WFQ) . . . . . 11 4. Socket API Considerations . . . . . . . . . . . . . . . . . . 12 4.1. Exposition of the Stream Sequence Number (SSN) . . . . . 12 4.2. SCTP_ASSOC_CHANGE Notification . . . . . . . . . . . . . 12 4.3. Socket Options . . . . . . . . . . . . . . . . . . . . . 12 4.3.1. Enable or Disable the Support of User Message Interleaving (SCTP_INTERLEAVING_SUPPORTED) . . . . . 13 4.3.2. Get or Set the Stream Scheduler (SCTP_STREAM_SCHEDULER) . . . . . . . . . . . . . . . 14 4.3.3. Get or Set the Stream Scheduler Parameter (SCTP_STREAM_SCHEDULER_VALUE) . . . . . . . . . . . . 15 4.4. Explicit EOR Marking . . . . . . . . . . . . . . . . . . 15 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 Stewart, et al. Expires January 22, 2017 [Page 2] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction 1.1. Overview When SCTP [RFC4960] was initially designed it was mainly envisioned for the 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 three 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. 3. As a sequence number allowing to have up to 2**16 - 1 Stream Sequence Numbers (SSNs) outstanding. 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 also defines several stream schedulers for general SCTP associations. If support for user message interleaving has been negotiated, several more schedulers are available. The following Figure 1 illustrates the behaviour of a round robin stream scheduler using DATA chunks. Please note that the use of such an scheduler implies late TSN assignment but it can be used with an [RFC4960] compliant implementation not supporting user message interleaving. Stewart, et al. Expires January 22, 2017 [Page 3] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 +---+---+---+ | 0/0 |-+ +---+---+---+ | | +---+---+---+---+---+---+---+---+---+ +---+---+---+ +->|1/2|1/1|2/0|2/0|2/0|1/0|0/0|0/0|0/0| |1/2|1/1|1/0|--->|---|---|---|---|---|---|---|---|---| +---+---+---+ +->| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | +---+---+---+---+---+---+---+---+---+ +---+---+---+ | | 2/0 |-+ +---+---+---+ +-------+ +-------+ |SID/SSN| |SID/SSN| |-------| +-------+ | TSN | +-------+ Figure 1: Round Robin Scheduler without User Message Interleaving 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 having the same MID and ordering property. The TSN is used only for the reliable transfer in combination with SACK chunks. The MID is also used for ensuring ordered delivery, therefore replacing the stream sequence number. Therefore, the head of line blocking caused by the original design is avoided. The following Figure 2 illustrates the behaviour of an interleaving round robin stream scheduler using I-DATA chunks. Stewart, et al. Expires January 22, 2017 [Page 4] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 +---+---+---+ | 0/0 |-+ +---+---+---+ | | +-----+-----+-----+-----+-----+-----+-----+-----+-----+ +---+---+---+ +->|2/0/2|1/2/0|0/0/2|2/0/1|1/1/0|0/0/1|2/0/0|1/0/0|0/0/0| |1/2|1/1|1/0|--->|-----|-----|-----|-----|-----|-----|-----|-----|-----| +---+---+---+ +->| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | +-----+-----+-----+-----+-----+-----+-----+-----+-----+ +---+---+---+ | | 2/0 |-+ +---+---+---+ +-----------+ +-------+ |SID/MID/FSN| |SID/MID| |-----------| +-------+ | TSN | +-----------+ Figure 2: Round Robin Scheduler with User Message Interleaving 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. 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 3 shows the new I-DATA chunk allowing user messages interleaving. Stewart, et al. Expires January 22, 2017 [Page 5] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 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 3: I-DATA chunk format The only differences between the I-DATA chunk in Figure 3 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). 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]. The new fields are: 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 for each outgoing stream, one for ordered messages, one for unordered messages. 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 Stewart, et al. Expires January 22, 2017 [Page 6] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 stream in flight. Please note that the MID is in "network byte order", a.k.a. Big Endian. 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. Note that in this case, this field is NOT touched by an SCTP implementation; therefore, its byte order is not necessarily in network byte order. The upper layer is responsible for any byte order conversions to this field, similar to the PPID of DATA chunks. 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 stack MUST know the application has indicated its choice in wanting to use the extension. Stewart, et al. Expires January 22, 2017 [Page 7] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 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 '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 implies the late assignment of the actual TSN to any chunk being sent. Each I-DATA chunk uses a single TSN. This way messages from other streams may be interleaved with the fragmented message. Please note that this is the only form of interleaving support. For example, it is not possible to interleave multiple ordered or unordered user messages from the same stream. The sender MUST NOT be fragmenting more than one user message in any given stream at any time. At any time, a sender MAY fragment multiple user message, each of them on different streams. The sender MUST assign TSN's in a way that the receiver can make progress. One way to achieve this is to assign the later fragments of a user message a higher TSN and send out the TSNs in sequence. 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. The receiver MUST NOT make any assumption about the TSN assignments of the sender. Note that a non-fragmented message is indicated by the fact that both the 'E' and 'B' bits are set. An ordered or unordered fragmented message is thus identified by 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. Stewart, et al. Expires January 22, 2017 [Page 8] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 2.3.1. SCTP Partial Reliability Extension When the SCTP extension defined in [RFC3758] is used in combination with the user message interleaving extension, the new I-FORWARD-TSN chunk MUST be used instead of the FORWARD-TSN chunk. The difference between the FORWARD-TSN and the I-FORWARD-TSN chunk is that the 16-bit Stream Sequence Number (SSN) has been replaced by the 32-bit Message Identifier (MID) and the largest skipped MID can also be provided for unordered messages. Therefore the principle applied to ordered message when using FORWARD-TSN chunks is applied to ordered and unordered messages when using I-FORWARD-TSN chunks. 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 Identifier | Reserved |U| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Stream Identifier | Reserved |U| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: I-FORWARD-TSN chunk format The relevant new fields are: Stream Identifier (SID): 16-bits (unsigned integer) This field holds the stream number this entry refers to. Reserved: 15 bits This field is reserved. It MUST be set to 0 by the sender and MUST be ignored by the receiver. U bit: 1 bit The U bit specifies if the Message Identifier of this entry refers unordered messages (U bit is set) or ordered messages (U bit is not set). Message Identifier (MID): 32 bits (unsigned integer) Stewart, et al. Expires January 22, 2017 [Page 9] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 This field holds the largest Message Identifier for ordered or unordered messages indicated by the U-bit that was skipped for the stream specified by the Stream Identifier. For ordered messages this is similar to the FORWARD-TSN chunk, just replacing the 16-bit SSN by the 32-bit MID. The FORWARD-TSN chunk MUST be used in combination with the DATA chunk and MUST NOT be used in combination with the I-DATA chunk. The I- FORWARD-TSN chunk MUST be used in combination with the I-DATA chunk and MUST NOT be used in combination with the DATA chunk. Support for the I-FORWARD-TSN chunk is negotiated during the SCTP association setup via the Supported Extensions Parameter as defined in [RFC5061]. Only if both end points support the I-DATA chunk and the I-FORWARD-TSN chunk, the partial reliability extension can be used in combination with user message interleaving. 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. Since most schedulers, especially all schedulers when supporting user message interleaving, require late TSN assignment, it should be noted that the implementation of [RFC6525] needs to handle this. 3. Stream Schedulers This section defines several stream schedulers. The streams schedulers may behave differently depending on whether user message interleaving has been negotiated for the association or not. The set of schedulers being implemented is implementation dependent. 3.1. 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. The usage of user message interleaving does not affect the sending of the chunks, except that I-DATA chunks are used instead of DATA chunks. Stewart, et al. Expires January 22, 2017 [Page 10] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 3.2. Round Robin Scheduler (SCTP_SS_RR) When not using user message interleaving, this scheduler provides a fair scheduling based on the number of user messages by cycling around non-empty stream queues. When using user message interleaving, this scheduler provides a fair scheduling based on the number of I-DATA chunks by cycling around non-empty stream queues. 3.3. Round Robin Scheduler per Packet (SCTP_SS_RR_PKT) This is a round-robin scheduler but bundles only DATA or I-DATA chunks referring to the same stream in a packet. This minimizes head-of-line blocking when a packet is lost because only a single stream is affected. 3.4. 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 scheduling between them is implementation specific. When using user message interleaving, the sending of lower priority user messages will not block the sending of higher priority user messages. 3.5. 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. The details are implementation specific. Using user message interleaving allows for a better realization of the fair bandwidth usage. 3.6. 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. The details are implementation specific. Using user message interleaving allows for a better realization of the bandwidth usage according to the given weights. This scheduler in combination with user message interleaving is used for WebRTC Datachannels as specified in [I-D.ietf-rtcweb-data-channel]. Stewart, et al. Expires January 22, 2017 [Page 11] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 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. Exposition of the Stream Sequence Number (SSN) The socket API defined in [RFC6458] defines several structures in which the SSN of a received user message is exposed to the application. The list of these structures includes: struct sctp_sndrcvinfo Specified in Section 5.3.2 of [RFC6458] and being deprecated. struct sctp_extrcvinfo Specified in Section 5.3.3 of [RFC6458] and being deprecated. struct sctp_rcvinfo Specified in Section 5.3.5 of [RFC6458]. If user message interleaving is used, the lower order 16 bits of the MID are used as the SSN when filling out these structures. 4.2. 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 listed in the sac_info field. 4.3. Socket Options +-----------------------------+-------------------------+-----+-----+ | option name | data type | get | set | +-----------------------------+-------------------------+-----+-----+ | SCTP_INTERLEAVING_SUPPORTED | struct sctp_assoc_value | X | X | | SCTP_STREAM_SCHEDULER | struct sctp_assoc_value | X | X | | SCTP_STREAM_SCHEDULER_VALUE | struct | X | X | | | sctp_stream_value | | | +-----------------------------+-------------------------+-----+-----+ Stewart, et al. Expires January 22, 2017 [Page 12] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 4.3.1. Enable or Disable the Support of User Message Interleaving (SCTP_INTERLEAVING_SUPPORTED) 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 by using the SCTP_FRAGMENT_INTERLEAVE socket option specified in Section 8.1.20 of [RFC6458]. This allows the interleaving of user messages from different streams. Please note that it does not allow the interleaving of ordered and unordered user messages on the same stream. Failure to set this option can possibly lead to application deadlock. Some implementations might therefore put some restrictions on setting combinations of these values. Stewart, et al. Expires January 22, 2017 [Page 13] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 4.3.2. Get or Set the Stream Scheduler (SCTP_STREAM_SCHEDULER) A stream scheduler can be selected with the SCTP_STREAM_SCHEDULER 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]: 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. SCTP_SS_RR: Use the scheduler specified in Section 3.2. SCTP_SS_RR_PKT: Use the scheduler specified in Section 3.3. SCTP_SS_PRIO: Use the scheduler specified in Section 3.4. 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 3.5. SCTP_SS_WFQ: Use the scheduler specified in Section 3.6. The weight can be assigned with the sctp_stream_value struct. Stewart, et al. Expires January 22, 2017 [Page 14] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 4.3.3. Get or Set the Stream Scheduler Parameter (SCTP_STREAM_SCHEDULER_VALUE) Some schedulers require additional information to be set for individual streams as shown in the following table: +-----------------+-----------------+ | name | per stream info | +-----------------+-----------------+ | SCTP_SS_DEFAULT | n/a | | 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 | +-----------------+-----------------+ This is achieved with the SCTP_STREAM_SCHEDULER_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. 4.4. Explicit EOR Marking Using explicit EOR marking for an SCTP association supporting user message interleaving allows the user to interleave the sending of user messages on different streams. Stewart, et al. Expires January 22, 2017 [Page 15] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 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 22, 2017 [Page 16] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 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, Marcelo Ricardo Leitner, Karen E. Egede Nielsen, Irene Ruengeler, Felix Weinrank, and Lixia Zhang for her invaluable comments. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 644334 (NEAT). The views expressed are solely those of the author(s). 8. References 8.1. Normative References [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, DOI 10.17487/RFC1982, August 1996, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, DOI 10.17487/RFC3758, May 2004, . [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", RFC 4960, DOI 10.17487/RFC4960, September 2007, . [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. Kozuka, "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", RFC 5061, DOI 10.17487/RFC5061, September 2007, . [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission Protocol (SCTP) Chunk Flags Registration", RFC 6096, DOI 10.17487/RFC6096, January 2011, . Stewart, et al. Expires January 22, 2017 [Page 17] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control Transmission Protocol (SCTP) Stream Reconfiguration", RFC 6525, DOI 10.17487/RFC6525, February 2012, . [RFC7053] Tuexen, M., Ruengeler, I., and R. Stewart, "SACK- IMMEDIATELY Extension for the Stream Control Transmission Protocol", RFC 7053, DOI 10.17487/RFC7053, November 2013, . 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, DOI 10.17487/RFC3261, 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, DOI 10.17487/RFC6458, 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 Stewart, et al. Expires January 22, 2017 [Page 18] Internet-Draft Stream Schedulers and the I-DATA Chunk July 2016 Salvatore Loreto Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: Salvatore.Loreto@ericsson.com Robin Seggelmann Metafinanz Informationssysteme GmbH Leopoldstrasse 146 80804 Muenchen Germany Email: rfc@robin-seggelmann.com Stewart, et al. Expires January 22, 2017 [Page 19]