Internet Engineering Task Force (IETF) M. Tuexen
Request for Comments: 7053 I. Ruengeler
Updates: 4960 Muenster Univ. of Appl. Sciences
Category: Standards Track R. Stewart
ISSN: 2070-1721 Adara Networks
November 2013
Internet Engineering Task Force (IETF) M. Tuexen
Request for Comments: 7053 I. Ruengeler
Updates: 4960 Muenster Univ. of Appl. Sciences
Category: Standards Track R. Stewart
ISSN: 2070-1721 Adara Networks
November 2013
SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol
流控制传输协议的SACK-立即扩展
Abstract
摘要
This document updates RFC 4960 by defining a method for the sender of a DATA chunk to indicate that the corresponding Selective Acknowledgment (SACK) chunk should be sent back immediately and should not be delayed. It is done by specifying a bit in the DATA chunk header, called the (I)mmediate bit, which can get set by either the Stream Control Transmission Protocol (SCTP) implementation or the application using an SCTP stack. Since unknown flags in chunk headers are ignored by SCTP implementations, this extension does not introduce any interoperability problems.
本文档通过为数据块的发送方定义一种方法来更新RFC 4960，以指示应立即发送回相应的选择性确认（SACK）块，且不应延迟。这是通过在数据块头中指定一个位来完成的，称为（I）mmediate位，它可以通过流控制传输协议（SCTP）实现或使用SCTP堆栈的应用程序来设置。由于SCTP实现会忽略块头中的未知标志，因此此扩展不会引入任何互操作性问题。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7053.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc7053.
Copyright Notice
版权公告
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2013 IETF信托基金和确定为文件作者的人员。版权所有。
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.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The (I)mmediate Bit in the DATA Chunk Header . . . . . . . . . 3
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Triggering at the Application Level . . . . . . . . . . . . 4
4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Sender-Side Considerations . . . . . . . . . . . . . . . . 5
5.2. Receiver Side Considerations . . . . . . . . . . . . . . . 5
6. Interoperability Considerations . . . . . . . . . . . . . . . . 5
7. Socket API Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . . 7
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The (I)mmediate Bit in the DATA Chunk Header . . . . . . . . . 3
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Triggering at the Application Level . . . . . . . . . . . . 4
4.2. Triggering at the SCTP Level . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Sender-Side Considerations . . . . . . . . . . . . . . . . 5
5.2. Receiver Side Considerations . . . . . . . . . . . . . . . 5
6. Interoperability Considerations . . . . . . . . . . . . . . . . 5
7. Socket API Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . . 7
According to [RFC4960], the receiver of a DATA chunk should use delayed SACKs. This delay is completely controlled by the receiver of the DATA chunk and remains the default behavior.
根据[RFC4960]，数据块的接收器应该使用延迟SACK。此延迟完全由数据块的接收者控制，并保持默认行为。
In specific situations, the delaying of SACKs results in reduced performance of the protocol:
在特定情况下，SACK延迟会导致协议性能降低：
1. If such a situation can be detected by the receiver, the corresponding SACK can be sent immediately. For example, [RFC4960] recommends immediately sending the SACK if the receiver has detected message loss or message duplication.
1. 如果接收方能够检测到这种情况，则可以立即发送相应的SACK。例如，[RFC4960]建议在接收方检测到消息丢失或消息重复时立即发送SACK。
2. However, if the situation can only be detected by the sender of the DATA chunk, [RFC4960] provides no method of avoiding a delay in sending the SACK. Examples of these situations include ones that require interaction with the application (e.g., applications using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones that can be detected by the SCTP stack itself (e.g., closing the association, hitting window limits, or resetting streams, see Section 4.2).
2. 但是，如果这种情况只能由数据块的发送方检测到，[RFC4960]没有提供避免发送SACK时出现延迟的方法。这些情况的示例包括需要与应用程序交互的情况（例如，使用SCTP_SENDER_DRY_事件的应用程序，参见第4.1节）和SCTP堆栈本身可以检测到的情况（例如，关闭关联、达到窗口限制或重设流，参见第4.2节）。
To overcome the limitation described in the second case, this document describes a simple extension of the SCTP DATA chunk by defining a new flag, the "I bit". By setting this bit, the sender of a DATA chunk indicates that the corresponding SACK chunk should not be delayed.
To overcome the limitation described in the second case, this document describes a simple extension of the SCTP DATA chunk by defining a new flag, the "I bit". By setting this bit, the sender of a DATA chunk indicates that the corresponding SACK chunk should not be delayed.translate error, please retry
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].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
Figure 1 shows the extended DATA chunk.
图1显示了扩展数据块。
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 = 0 | Res |I|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier | Stream Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 = 0 | Res |I|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier | Stream Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended DATA chunk format
图1：扩展数据块格式
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.
图1中的数据块与[RFC4960]中定义的数据块之间的唯一区别是在数据块头的flags字段中添加了I位。
[RFC4960] defines the Reserved field and specifies that these bits should be set to 0 by the sender and ignored by the receiver.
[RFC4960]定义保留字段并指定发送方应将这些位设置为0，接收方应忽略这些位。
The setting of the I bit can either be triggered by the application using SCTP or by the SCTP stack itself. The following two subsections provide a non-exhaustive list of examples of how the I bit may be set.
I位的设置可以由使用SCTP的应用程序触发，也可以由SCTP堆栈本身触发。以下两小节提供了如何设置I位的示例的非详尽列表。
One example of a situation in which it may be desirable for an application to trigger the setting of the I bit involves the SCTP_SENDER_DRY_EVENT in the SCTP socket API [RFC6458]. Upper layers of SCTP that use the socket API as defined in [RFC6458] may subscribe to the SCTP_SENDER_DRY_EVENT to be notified as soon as no user data is outstanding. To avoid an unnecessary delay, the application can request that the I bit be set 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; this is possible using the extension of the socket API described in Section 7.
应用程序可能需要触发I位设置的情况的一个示例涉及SCTP套接字API[RFC6458]中的SCTP_SENDER_DRY_事件。使用[RFC6458]中定义的套接字API的SCTP上层可以订阅SCTP_SENDER_DRY_事件，以便在没有未处理的用户数据时立即收到通知。为了避免不必要的延迟，应用程序可以请求在等待事件之前发送最后一条用户消息时设置I位。这导致设置与用户消息相对应的最后数据块的I位；这可以通过使用第7节中描述的套接字API的扩展来实现。
There are also situations in which the SCTP implementation can set the I bit without interacting with the upper layer.
还有一些情况下，SCTP实现可以在不与上层交互的情况下设置I位。
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-lived associations.
如果关联处于SHUTDOWN-PENDING状态，则设置I位会减少繁忙服务器处理短期关联的同时关联数。
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.
另一种情况是，数据块的发送填充了拥塞或接收器窗口。在这些情况下，设置I位可以提高传输的吞吐量。
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 that require that there be no outstanding DATA chunks.
如果SCTP关联支持[RFC6525]中定义的SCTP流重新配置扩展，则当存在需要没有未完成数据块的未决重新配置请求时，可以通过设置I位来提高性能。
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 why the sender has set the I bit is irrelevant to the receiver.
每当数据块的发送方可以从相应的SACK块被毫不延迟地发送回来中获益时，发送方可以在数据块头中设置I位。请注意，发送方设置I位的原因与接收方无关。
Reasons for setting the I bit include, but are not limited to (see Section 4 for the benefits):
设置I位的原因包括但不限于（好处见第4节）：
o The application requests to set the I bit of the last DATA chunk of a user message when providing the user message to the SCTP implementation (see Section 7).
o 当向SCTP实现提供用户消息时，应用程序请求设置用户消息最后一个数据块的I位（参见第7节）。
o The sender is in the SHUTDOWN-PENDING state.
o 发送方处于关闭挂起状态。
o The sending of a DATA chunk fills the congestion or receiver window.
o 数据块的发送填充拥塞或接收器窗口。
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].
o 如果关联支持[RFC6525]中定义的流重新配置扩展，则发送传出SSN重置请求参数或SSN/TSN重置请求参数将挂起。
Upon receipt 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, i.e., the receiver SHOULD immediately respond with the corresponding SACK chunk.
在接收到包含设置了I位的数据块的SCTP数据包时，接收方不应延迟发送相应的SACK数据块，即，接收方应立即响应相应的SACK数据块。
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.
根据[RFC4960]，设置了I位的数据块的接收器在不支持本文档中描述的扩展时应忽略该位。由于数据块的发送方能够处理这种情况，因此不需要协商对本文档中描述的功能的支持。
This section describes how the socket API defined in [RFC6458] is extended to provide a way for the application to set the I bit.
本节介绍如何扩展[RFC6458]中定义的套接字API，以便为应用程序提供设置I位的方法。
Please note that this section is informational only.
请注意，本节仅供参考。
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.
需要扩展基于[RFC6458]的套接字API实现，以允许应用程序在发送每个用户消息时设置最后一个数据块的I位。
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 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.
当使用SCTP_sendv（）或sendmsg（）时，可以通过在struct SCTP_sndinfo结构的snd_flags字段中立即设置一个名为SCTP_SACK_的标志来实现。如果在调用sctp_send（）、sctp_sendx（）或sendmsg（）时使用不推荐的结构sctp_sndrcvinfo结构，则可以在sinfo_flags字段中设置sctp_SACK_立即标记。使用不推荐使用的函数sctp_sendmsg（）时，可以在flags参数中使用sctp_SACK_立即标记。
Following the chunk flag registration procedure defined in [RFC6096], IANA has registered a new bit, the I bit, for the DATA chunk.
按照[RFC6096]中定义的块标志注册过程，IANA为数据块注册了一个新位，即I位。
The "Chunk Flags" registry for SCTP has been updated as described in the following table.
SCTP的“区块标志”注册表已按下表所述更新。
DATA Chunk Flags
数据块标志
+------------------+-----------------+-----------+
| Chunk Flag Value | Chunk Flag Name | Reference |
+------------------+-----------------+-----------+
| 0x01 | E bit | [RFC4960] |
| 0x02 | B bit | [RFC4960] |
| 0x04 | U bit | [RFC4960] |
| 0x08 | I bit | [RFC7053] |
| 0x10 | Unassigned | |
| 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+
+------------------+-----------------+-----------+
| Chunk Flag Value | Chunk Flag Name | Reference |
+------------------+-----------------+-----------+
| 0x01 | E bit | [RFC4960] |
| 0x02 | B bit | [RFC4960] |
| 0x04 | U bit | [RFC4960] |
| 0x08 | I bit | [RFC7053] |
| 0x10 | Unassigned | |
| 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+
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 received packet containing DATA chunks. 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 simplest SACK chunk (no gap reports, no duplicate TSNs), since in cases of packet drops or reordering in the network a SACK chunk would be sent immediately anyway. Therefore, this does not introduce a significant additional processing cost on the receiver side. This also does not result in more traffic in the network, because a receiver sending a SACK for every packet is already permitted.
有关SCTP的一般安全注意事项，请参见[RFC4960]。此外，恶意发送方可以强制其对等方为每个接收到的包含数据块的数据包（而不是每个其他接收到的包含数据块的数据包）发送包含SACK块的数据包。这可能会影响网络，导致在网络或对等方上发送更多的数据包，因为数据包的生成和发送有一些处理成本。然而，额外的数据包只能包含最简单的SACK块（没有间隙报告，没有重复的TSN），因为在网络中数据包丢失或重新排序的情况下，SACK块无论如何都会立即发送。因此，这不会在接收器侧引入显著的额外处理成本。这也不会导致网络中的流量增加，因为已经允许接收器为每个数据包发送SACK。
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.
作者希望感谢马克·奥尔曼、布赖恩·比杜洛克、大卫·布莱克、安娜·布伦斯特伦、戈里·费尔赫斯特、贾纳丹·艾扬格、卡昌潘和迈克尔·韦尔兹尔的宝贵评论。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007.
[RFC4960]Stewart，R.，“流控制传输协议”，RFC 49602007年9月。
[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission Protocol (SCTP) Chunk Flags Registration", RFC 6096, January 2011.
[RFC6096]Tuexen，M.和R.Stewart，“流控制传输协议（SCTP）块标志注册”，RFC 60962011年1月。
[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.
[RFC6458]Stewart，R.，Tuexen，M.，Poon，K.，Lei，P.，和V.Yasevich，“流控制传输协议（SCTP）的套接字API扩展”，RFC 6458，2011年12月。
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control Transmission Protocol (SCTP) Stream Reconfiguration", RFC 6525, February 2012.
[RFC6525]Stewart，R.，Tuexen，M.，和P.Lei，“流控制传输协议（SCTP）流重新配置”，RFC 65252012年2月。
Authors' Addresses
作者地址
Michael Tuexen Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt DE
米迦勒TuxEN明斯特应用科学大学StigalddSTR。斯坦福德德39 48565
EMail: tuexen@fh-muenster.de
EMail: tuexen@fh-muenster.de
Irene Ruengeler Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt DE
明斯特应用科技大学斯坦福德德39 48565
EMail: i.ruengeler@fh-muenster.de
EMail: i.ruengeler@fh-muenster.de
Randall R. Stewart Adara Networks Chapin, SC 29036 US
Randall R.Stewart Adara Networks Chapin，SC 29036美国
EMail: randall@lakerest.net
EMail: randall@lakerest.net