--- 1/draft-ietf-tsvwg-sctp-sack-immediately-02.txt 2013-04-08 14:03:10.164124452 +0200 +++ 2/draft-ietf-tsvwg-sctp-sack-immediately-03.txt 2013-04-08 14:03:10.176124244 +0200 @@ -1,20 +1,20 @@ Network Working Group M. Tuexen Internet-Draft I. Ruengeler Updates: 4960 (if approved) Muenster Univ. of Appl. Sciences Intended status: Standards Track R. R. Stewart -Expires: September 17, 2013 Adara Networks - March 16, 2013 +Expires: October 10, 2013 Adara Networks + April 08, 2013 SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol - draft-ietf-tsvwg-sctp-sack-immediately-02.txt + draft-ietf-tsvwg-sctp-sack-immediately-03.txt Abstract This document updates RFC 4960 by defining a method for the sender of a DATA chunk to indicate that the corresponding SACK chunk should be sent back immediately and not be delayed. It is done by specifying a bit in the DATA chunk header, called the I-bit, which can get set either by the SCTP implementation or by the application using an SCTP stack. Since unknown flags in chunk headers are ignored by SCTP implementations, this extension does not introduce any @@ -28,21 +28,21 @@ 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 September 17, 2013. + This Internet-Draft will expire on October 10, 2013. Copyright Notice Copyright (c) 2013 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 @@ -52,33 +52,33 @@ the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. The I-bit in the DATA Chunk Header . . . . . . . . . . . . . 3 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. Triggering at the Application Level . . . . . . . . . . . 3 - 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 3 + 4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . 4 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Sender Side Considerations . . . . . . . . . . . . . . . 4 - 5.2. Receiver Side Considerations . . . . . . . . . . . . . . 4 + 5.2. Receiver Side Considerations . . . . . . . . . . . . . . 5 6. Interoperability Considerations . . . . . . . . . . . . . . . 5 7. Socket API Considerations . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 - 11.2. Informative References . . . . . . . . . . . . . . . . . 6 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 + 11.2. Informative References . . . . . . . . . . . . . . . . . 7 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction According to [RFC4960] the receiver of a DATA chunk should use delayed SACKs. This delaying is completely controlled by the receiver of the DATA chunk and remains the default behavior. In specific situations the delaying of SACKs results in reduced performance of the protocol. If such a situation can be detected by the receiver, the corresponding SACK can be sent immediately. For @@ -116,51 +116,60 @@ / User Data / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Extended DATA chunk format The only difference between the DATA chunk in Figure 1 and the DATA chunk defined in [RFC4960] is the addition of the I-bit in the flags field of the DATA chunk header. + This bit was Reserved in [RFC4960]. [RFC4960] specified that this + bit should be set to 0 by the sender and ignored by the receiver. + 4. Use Cases The setting of the I-bit can either be triggered by the application - using SCTP or by the SCTP stack itself. + using SCTP or by the SCTP stack itself. The following two + subsections provide a non-exhaustive list of examples. 4.1. Triggering at the Application Level - Upper layers of SCTP using the socket API as defined in [RFC6458] may - subscribe to the SCTP_SENDER_DRY_EVENT for getting a notification as - soon as no user data is outstanding anymore. To avoid an unnecessary - delay while waiting for such an event, the application might set the - I-Bit on the last DATA chunk sent before waiting for the event. This - enabling is possible using the extension of the socket API described - in Section 7. + One example of a situation in which it may be desirable for an + application to trigger setting of the I-bit involves the + SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers + of SCTP using the socket API as defined in [RFC6458] may subscribe to + the SCTP_SENDER_DRY_EVENT for getting a notification as soon as no + user data is outstanding anymore. To avoid an unnecessary delay + while waiting for such an event, the application can request the + setting of the I-Bit when sending the last user message before + waiting for the event. This results in setting the I-bit of the last + DATA chunk corresponding to the user message and is possible using + the extension of the socket API described in Section 7. 4.2. Triggering at the SCTP Level + There are also situations in which the SCTP implementation can set the I-bit without interacting with the upper layer. - If the association is in the SHUTDOWN-PENDING state, the I-bit should - be set. This reduces the number of simultaneous associations in case - of a busy server handling short living associations. + If the association is in the SHUTDOWN-PENDING state, setting the + I-bit reduces the number of simultaneous associations for a busy + server handling short living associations. Another case is where the sending of a DATA chunk fills the congestion or receiver window. Setting the I-bit in these cases improves the throughput of the transfer. If an SCTP association supports the SCTP Stream Reconfiguration extension defined in [RFC6525], the performance can be improved by setting the I-bit when there are pending reconfiguration requests - requiring no outstanding DATA chunks. + that require that there be no outstanding DATA chunks. 5. Procedures 5.1. Sender Side Considerations Whenever the sender of a DATA chunk can benefit from the corresponding SACK chunk being sent back without delay, the sender MAY set the I-bit in the DATA chunk header. Please note that it is irrelevant to the receiver why the sender has set the I-bit. @@ -178,21 +187,22 @@ o The sending of an Outgoing SSN Reset Request Parameter or an SSN/ TSN Reset Request Parameter is pending, if the association supports the Stream Reconfiguration extension defined in [RFC6525]. 5.2. Receiver Side Considerations On reception of an SCTP packet containing a DATA chunk with the I-bit set, the receiver SHOULD NOT delay the sending of the corresponding - SACK chunk and send it back immediately. + SACK chunk, i.e., the receiver SHOULD immediately respond with the + corresponding SACK chunk. 6. Interoperability Considerations According to [RFC4960] the receiver of a DATA chunk with the I-bit set should ignore this bit when it does not support the extension described in this document. Since the sender of the DATA chunk is able to handle this case, there is no requirement for negotiating the support of the feature described in this document. 7. Socket API Considerations @@ -203,59 +213,74 @@ Please note that this section is informational only. A socket API implementation based on [RFC6458] needs to be extended to allow the application to set the I-bit of the last DATA chunk when sending each user message. This can be done by setting a flag called SCTP_SACK_IMMEDIATELY in the snd_flags field of the struct sctp_sndinfo structure when using sctp_sendv() or sendmsg(). If the deprecated struct sctp_sndrcvinfo structure is used instead when calling sctp_send(), sctp_sendx(), or - sendmsg(), the SCTP_SACK_IMMEDIATELY flags can be set in the + sendmsg(), the SCTP_SACK_IMMEDIATELY flag can be set in the sinfo_flags field. When using the deprecated function sctp_sendmsg() the SCTP_SACK_IMMEDIATELY flag can be in the flags parameter. 8. IANA Considerations [NOTE to RFC-Editor: "RFCXXXX" is to be replaced by the RFC number you assign this document. ] - Following the chunk flag registration procedure defined in [RFC6096] + Following the chunk flag registration procedure defined in [RFC6096], IANA should register a new bit, the I-bit, for the DATA chunk. The - suggested value is 0x08. The reference for the new chunk flag in the - chunk flags table for the DATA chunk should be RFCXXXX. + suggested value is 0x08 and the reference should be RFCXXXX. + + This requires an update of the "DATA Chunk Flags" registry for SCTP: + + DATA Chunk Flags + + +------------------+-----------------+-----------+ + | Chunk Flag Value | Chunk Flag Name | Reference | + +------------------+-----------------+-----------+ + | 0x01 | E bit | [RFC4960] | + | 0x02 | B bit | [RFC4960] | + | 0x04 | U bit | [RFC4960] | + | 0x08 | I Bit | [RFCXXXX] | + | 0x10 | Unassigned | | + | 0x20 | Unassigned | | + | 0x40 | Unassigned | | + | 0x80 | Unassigned | | + +------------------+-----------------+-----------+ 9. Security Considerations - This document does not add any additional security considerations in - addition to the ones given in [RFC4960]. It should be noted that a - malicious sender can force its peer to send packets containing a SACK - chunk for each received packet containing DATA chunks instead of - every other. This could impact the network, resulting in more - packets sent on the network, or the peer because the generating and - sending of the packets has some processing cost. However, the - additional packets can only contain the most simplest SACK chunk (no - gap reports, no duplicate TSNs), since in case of packet drop or - reordering in the network a SACK chunk would be sent immediately - anyway. Therefore this does neither introduce a significant - additional processing cost on the receiver side nor does it cause - congestion on the network. + See [RFC4960] for general security considerations for SCTP. In + addition, a malicious sender can force its peer to send packets + containing a SACK chunk for each received packet containing DATA + chunks instead of every other. This could impact the network, + resulting in more packets sent on the network, or the peer because + the generating and sending of the packets has some processing cost. + However, the additional packets can only contain the most simplest + SACK chunk (no gap reports, no duplicate TSNs), since in case of + packet drop or reordering in the network a SACK chunk would be sent + immediately anyway. Therefore this does neither introduce a + significant additional processing cost on the receiver side nor does + it cause congestion on the network. 10. Acknowledgments - The authors wish to thank Mark Allmann, Brian Bidulock, Gorry - Fairhurst, Janardhan Iyengar, and Kacheong Poon for their invaluable - comments. + The authors wish to thank Mark Allmann, Brian Bidulock, David Black, + Anna Brunstrom, Gorry Fairhurst, Janardhan Iyengar, Kacheong Poon, + and Michael Welzl for their invaluable comments. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007.