Internet Engineering Task Force (IETF) T. Phelan
Request for Comments: 6773 Sonus
Updates: 4340, 5762 G. Fairhurst
Category: Standards Track University of Aberdeen
ISSN: 2070-1721 C. Perkins
University of Glasgow
November 2012
Internet Engineering Task Force (IETF) T. Phelan
Request for Comments: 6773 Sonus
Updates: 4340, 5762 G. Fairhurst
Category: Standards Track University of Aberdeen
ISSN: 2070-1721 C. Perkins
University of Glasgow
November 2012
DCCP-UDP: A Datagram Congestion Control Protocol UDP Encapsulation for NAT Traversal
DCCP-UDP：一种用于NAT穿越的数据报拥塞控制协议UDP封装
Abstract
摘要
This document specifies an alternative encapsulation of the Datagram Congestion Control Protocol (DCCP), referred to as DCCP-UDP. This encapsulation allows DCCP to be carried through the current generation of Network Address Translation (NAT) middleboxes without modification of those middleboxes. This document also updates the Session Description Protocol (SDP) information for DCCP defined in RFC 5762.
本文档指定了数据报拥塞控制协议（DCCP）的另一种封装，称为DCCP-UDP。这种封装允许DCCP在当前一代网络地址转换（NAT）中间盒中进行，而无需修改这些中间盒。本文档还更新了RFC 5762中定义的DCCP的会话描述协议（SDP）信息。
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/rfc6773.
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/rfc6773.
Copyright Notice
版权公告
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. DCCP-UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. The UDP Header . . . . . . . . . . . . . . . . . . . . . . 5
3.2. The DCCP Generic Header . . . . . . . . . . . . . . . . . 5
3.3. DCCP-UDP Checksum Procedures . . . . . . . . . . . . . . . 6
3.3.1. Partial Checksums and the Minimum Checksum
Coverage Feature . . . . . . . . . . . . . . . . . . . 7
3.4. Network-Layer Options . . . . . . . . . . . . . . . . . . 8
3.5. Explicit Congestion Notification . . . . . . . . . . . . . 8
3.6. ICMP Handling for Messages Relating to DCCP-UDP . . . . . 8
3.7. Path Maximum Transmission Unit Discovery . . . . . . . . . 9
3.8. Usage of the UDP Port by DCCP-UDP . . . . . . . . . . . . 9
3.9. Service Codes and the DCCP Port Registry . . . . . . . . . 11
4. DCCP-UDP and Higher-Layer Protocols . . . . . . . . . . . . . 11
5.1. Protocol Identification . . . . . . . . . . . . . . . . . 12
5.2. Signalling Encapsulated DCCP Ports . . . . . . . . . . . . 13
5.3. Connection Management . . . . . . . . . . . . . . . . . . 14
5.4. Negotiating the DCCP-UDP Encapsulation versus Native
DCCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.5. Example of SDP Use . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. UDP Port Allocation . . . . . . . . . . . . . . . . . . . 17
7.2. DCCP Reset . . . . . . . . . . . . . . . . . . . . . . . . 17
7.3. SDP Attribute Allocation . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. DCCP-UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. The UDP Header . . . . . . . . . . . . . . . . . . . . . . 5
3.2. The DCCP Generic Header . . . . . . . . . . . . . . . . . 5
3.3. DCCP-UDP Checksum Procedures . . . . . . . . . . . . . . . 6
3.3.1. Partial Checksums and the Minimum Checksum
Coverage Feature . . . . . . . . . . . . . . . . . . . 7
3.4. Network-Layer Options . . . . . . . . . . . . . . . . . . 8
3.5. Explicit Congestion Notification . . . . . . . . . . . . . 8
3.6. ICMP Handling for Messages Relating to DCCP-UDP . . . . . 8
3.7. Path Maximum Transmission Unit Discovery . . . . . . . . . 9
3.8. Usage of the UDP Port by DCCP-UDP . . . . . . . . . . . . 9
3.9. Service Codes and the DCCP Port Registry . . . . . . . . . 11
4. DCCP-UDP and Higher-Layer Protocols . . . . . . . . . . . . . 11
5.1. Protocol Identification . . . . . . . . . . . . . . . . . 12
5.2. Signalling Encapsulated DCCP Ports . . . . . . . . . . . . 13
5.3. Connection Management . . . . . . . . . . . . . . . . . . 14
5.4. Negotiating the DCCP-UDP Encapsulation versus Native
DCCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.5. Example of SDP Use . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. UDP Port Allocation . . . . . . . . . . . . . . . . . . . 17
7.2. DCCP Reset . . . . . . . . . . . . . . . . . . . . . . . . 17
7.3. SDP Attribute Allocation . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
The Datagram Congestion Control Protocol (DCCP) [RFC4340] is a transport-layer protocol that provides upper layers with the ability to use non-reliable congestion-controlled flows. The current specification for DCCP [RFC4340] specifies a direct native encapsulation in IPv4 or IPv6 packets.
数据报拥塞控制协议（DCCP）[RFC4340]是一种传输层协议，它为上层提供了使用非可靠拥塞控制流的能力。DCCP[RFC4340]的当前规范指定了IPv4或IPv6数据包中的直接本机封装。
DCCP support has been specified for devices that use Network Address Translation (NAT) or Network Address and Port Translation (NAPT) [RFC5597]. However, there is a significant installed base of NAT/ NAPT devices that do not support [RFC5597]. It is therefore useful to have an encapsulation for DCCP that is compatible with this installed base of NAT/NAPT devices that support [RFC4787] but do not support [RFC5597]. This document specifies that encapsulation, which is referred to as DCCP-UDP. For convenience, the standard encapsulation for DCCP [RFC4340] (including [RFC5596] as required) is referred to as DCCP-STD.
已为使用网络地址转换（NAT）或网络地址和端口转换（NAPT）[RFC5597]的设备指定了DCCP支持。但是，有大量NAT/NAPT设备的安装基础不支持[RFC5597]。因此，DCCP封装与支持[RFC4787]但不支持[RFC5597]的NAT/NAPT设备安装群兼容是非常有用的。本文档指定封装，即DCCP-UDP。为方便起见，DCCP[RFC4340]（根据需要包括[RFC5596]）的标准封装称为DCCP-STD。
The encapsulation described in this document may also be used as a transition mechanism to enable support for DCCP in devices that support UDP but do not yet natively support DCCP. This also allows the DCCP transport to be implemented within an application using DCCP-UDP.
本文档中描述的封装也可用作转换机制，以便在支持UDP但本机不支持DCCP的设备中支持DCCP。这还允许使用DCCP-UDP在应用程序内实现DCCP传输。
This document also updates the SDP specification for DCCP [RFC5762] to convey the encapsulation type. In this respect only, it updates the method in [RFC5762].
本文件还更新了DCCP[RFC5762]的SDP规范，以传达封装类型。仅在这方面，它更新了[RFC5762]中的方法。
The DCCP-UDP encapsulation specified in this document supports all of the features contained in DCCP-STD, but with limited functionality for partial checksums.
本文档中指定的DCCP-UDP封装支持DCCP-STD中包含的所有功能，但部分校验和的功能有限。
Network optimisations for DCCP-STP and UDP may need to be updated to allow these optimisations to take advantage of DCCP-UDP. Encapsulation with an additional UDP protocol header can complicate or prevent inspection of DCCP header fields by equipment along the network path in the case where multiple DCCP connections share the same UDP 4-tuple, for example, routers that wish to identify DCCP ports to perform Equal-Cost Multi-Path (ECMP) routing, network devices that wish to inspect DCCP ports to inform algorithms for sharing the network load across multiple links, firewalls that wish to inspect DCCP ports and service codes to inform algorithms that implement access rules, media gateways that inspect SDP information to derive characteristics of the transport and session, etc.
可能需要更新DCCP-STP和UDP的网络优化，以允许这些优化利用DCCP-UDP。在多个DCCP连接共享同一UDP 4元组的情况下，使用附加UDP协议头进行封装可能会使网络路径上的设备检查DCCP头字段变得复杂或无法进行检查，例如，希望识别DCCP端口以执行等成本多路径（ECMP）路由的路由器，希望检查DCCP端口以通知跨多条链路共享网络负载的算法的网络设备、希望检查DCCP端口的防火墙和用于通知实现访问规则的算法的服务代码、检查SDP信息以导出传输和会话特征的媒体网关等。
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。
The basic approach is to insert a UDP [RFC0768] header between the IP header and the DCCP packet. Note that this is not a tunneling approach. The IP addresses of the communicating end systems are carried in the IP header. The method does not embed additional IP addresses.
基本方法是在IP报头和DCCP数据包之间插入UDP[RFC0768]报头。请注意，这不是隧道方法。通信终端系统的IP地址在IP报头中携带。该方法不嵌入其他IP地址。
The method is designed to support use when these addresses are modified by a device that implements NAT/NAPT. A NAT translates the IP addresses, which impacts the transport-layer checksum. A NAPT device may also translate the port values (usually the source port). In both cases, the outer transport header that includes these values would need to be updated by the NAT/NAPT.
该方法旨在支持在实现NAT/NAPT的设备修改这些地址时使用。NAT转换IP地址，这会影响传输层校验和。NAPT设备还可以转换端口值（通常是源端口）。在这两种情况下，NAT/NAPT都需要更新包含这些值的外部传输头。
A device offering or using DCCP services via DCCP-UDP encapsulation listens on a UDP port (default port, 6511) or may bind to a specified port utilising out-of-band signalling, such as the Session Description Protocol (SDP). The DCCP-UDP server accepts incoming packets over the UDP transport and passes the received packets to the DCCP protocol module, after removing the UDP encapsulation.
通过DCCP-UDP封装提供或使用DCCP服务的设备侦听UDP端口（默认端口，6511），或者可以利用带外信令（如会话描述协议（SDP））绑定到指定端口。DCCP-UDP服务器通过UDP传输接受传入的数据包，并在移除UDP封装后将接收到的数据包传递给DCCP协议模块。
A DCCP implementation endpoint may simultaneously provide services over any or all combinations of DCCP-STD and/or DCCP-UDP encapsulations with IPv4 and/or IPv6.
DCCP实现端点可以同时通过DCCP-STD和/或DCCP-UDP封装与IPv4和/或IPv6的任何或所有组合提供服务。
The basic format of a DCCP-UDP packet is:
DCCP-UDP数据包的基本格式为：
+-----------------------------------+
| IP Header (IPv4 or IPv6) | Variable length
+-----------------------------------+
| UDP Header | 8 bytes
+-----------------------------------+
| DCCP Generic Header | 12 or 16 bytes
+-----------------------------------+
| Additional (type-specific) Fields | Variable length (could be 0)
+-----------------------------------+
| DCCP Options | Variable length (could be 0)
+-----------------------------------+
| Application Data Area | Variable length (could be 0)
+-----------------------------------+
+-----------------------------------+
| IP Header (IPv4 or IPv6) | Variable length
+-----------------------------------+
| UDP Header | 8 bytes
+-----------------------------------+
| DCCP Generic Header | 12 or 16 bytes
+-----------------------------------+
| Additional (type-specific) Fields | Variable length (could be 0)
+-----------------------------------+
| DCCP Options | Variable length (could be 0)
+-----------------------------------+
| Application Data Area | Variable length (could be 0)
+-----------------------------------+
Section 3.8 describes usage of UDP ports. This includes implementation of a DCCP-UDP encapsulation service as a daemon that listens on a well-known port, allowing multiplexing of different DCCP applications over the same port.
第3.8节介绍UDP端口的使用。这包括将DCCP-UDP封装服务实现为在已知端口上侦听的守护进程，允许在同一端口上多路复用不同的DCCP应用程序。
The format of the UDP header is specified in [RFC0768]:
UDP标头的格式在[RFC0768]中指定：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For DCCP-UDP, the fields are interpreted as follows:
对于DCCP-UDP，字段解释如下：
Source and Dest(ination) Ports: 16 bits each
源端口和目标端口：每个端口16位
These fields identify the UDP ports on which the source and destination (respectively) of the packet are listening for incoming DCCP-UDP packets. The UDP port values do not identify the DCCP source and destination ports.
这些字段标识数据包的源和目标（分别）正在侦听传入DCCP-UDP数据包的UDP端口。UDP端口值不标识DCCP源端口和目标端口。
Length: 16 bits
长度：16位
This field is the length of the UDP datagram, including the UDP header and the payload (for DCCP-UDP, the payload is a DCCP-UDP datagram).
此字段是UDP数据报的长度，包括UDP报头和有效负载（对于DCCP-UDP，有效负载是DCCP-UDP数据报）。
Checksum: 16 bits
校验和：16位
This field is the Internet checksum of a network-layer pseudoheader and Length bytes of the UDP packet [RFC0768]. The UDP checksum MUST NOT be zero for a UDP packet that carries DCCP-UDP.
此字段是网络层伪报头和UDP数据包[RFC0768]长度字节的Internet校验和。对于承载DCCP-UDP的UDP数据包，UDP校验和不得为零。
The DCCP Generic Header [RFC4340] takes two forms, one with long sequence numbers (48 bits) and the other with short sequence numbers (24 bits).
DCCP通用头[RFC4340]有两种形式，一种是长序列号（48位），另一种是短序列号（24位）。
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Offset | CCVal | CsCov | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |X| | .
| Res | Type |=| Reserved | Sequence Number (high bits) .
| | |1| | .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (low bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Offset | CCVal | CsCov | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |X| | .
| Res | Type |=| Reserved | Sequence Number (high bits) .
| | |1| | .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (low bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Generic DCCP Header with Long Sequence Numbers [RFC4340]
具有长序列号的通用DCCP头[RFC4340]
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Offset | CCVal | CsCov | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |X| |
| Res | Type |=| Sequence Number (low bits) |
| | |0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Offset | CCVal | CsCov | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |X| |
| Res | Type |=| Sequence Number (low bits) |
| | |0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Generic DCCP Header with Short Sequence Numbers [RFC4340]
具有短序列号的通用DCCP头[RFC4340]
All generic header fields, except for the Checksum field, have the meaning specified in [RFC4340], updated by [RFC5596].
除校验和字段外，所有通用标题字段均具有[RFC4340]中规定的含义，并由[RFC5596]更新。
Section 3.8 describes how a DCCP-UDP implementation treats UDP and DCCP ports.
第3.8节描述了DCCP-UDP实现如何处理UDP和DCCP端口。
DCCP-UDP employs a checksum at the UDP level and eliminates the use of the DCCP checksum. This approach was chosen to enable use of current NAT/NATP traversal methods developed for UDP. Such methods will generally be unaware whether DCCP is being encapsulated and hence do not update the inner checksum in the DCCP header. Standard DCCP requires protection of the DCCP header fields; this justifies any processing overhead incurred from calculating the UDP checksum.
DCCP-UDP在UDP级别使用校验和，并消除了DCCP校验和的使用。选择这种方法是为了能够使用为UDP开发的当前NAT/NATP遍历方法。此类方法通常不知道是否正在封装DCCP，因此不会更新DCCP头中的内部校验和。标准DCCP要求保护DCCP头字段；这证明了计算UDP校验和所产生的任何处理开销是合理的。
In addition, UDP NAT traversal does not support partial checksums. Although this is still permitted end-to-end in the encapsulated DCCP datagram, links along the path will treat these as UDP packets and can not enable special partial checksum processing.
此外，UDP NAT遍历不支持部分校验和。尽管这在封装的DCCP数据报中仍然允许端到端，但沿路径的链路将这些数据包视为UDP数据包，并且无法启用特殊的部分校验和处理。
DCCP-UDP does not update or modify the operation of UDP. The UDP transport protocol is used in the following way:
DCCP-UDP不更新或修改UDP的操作。UDP传输协议的使用方式如下：
For DCCP-UDP, the function of the DCCP Checksum field is performed by the UDP Checksum field. On transmission, the DCCP Checksum field SHOULD be set to zero. On receipt, the DCCP Checksum field MUST be ignored.
对于DCCP-UDP，DCCP校验和字段的功能由UDP校验和字段执行。传输时，DCCP校验和字段应设置为零。收到时，必须忽略DCCP校验和字段。
The UDP checksum MUST NOT be zero for a UDP packet that is sent using DCCP-UDP. If the received UDP Checksum field is zero, the packet MUST be dropped.
对于使用DCCP-UDP发送的UDP数据包，UDP校验和不得为零。如果收到的UDP校验和字段为零，则必须丢弃数据包。
If the UDP Length field of a received packet is less than 20 (the UDP header length and minimum DCCP-UDP header length), the packet MUST be dropped.
如果接收数据包的UDP长度字段小于20（UDP标头长度和最小DCCP-UDP标头长度），则必须丢弃该数据包。
If the UDP Checksum field, computed using standard UDP methods, is invalid, the received packet MUST be dropped.
如果使用标准UDP方法计算的UDP校验和字段无效，则必须丢弃接收的数据包。
If the UDP Length field in a received packet is less than the length of the UDP header plus the entire DCCP-UDP header (including the generic header and type-specific fields and options, if present) or if the UDP Length field is greater than the length of the packet from the beginning of the UDP header to the end of the packet, the packet MUST be dropped.
如果接收到的数据包中的UDP长度字段小于UDP报头的长度加上整个DCCP-UDP报头（包括通用报头和特定类型的字段和选项，如果存在），或者如果UDP长度字段大于从UDP报头开始到数据包结束的数据包长度，包必须被丢弃。
This document requires the UDP checksum to be enabled when using DCCP-UDP. This checksum provides coverage of the entire encapsulated DCCP datagram.
本文档要求在使用DCCP-UDP时启用UDP校验和。该校验和提供了整个封装DCCP数据报的覆盖范围。
DCCP-UDP supports the syntax of partial checksums. It also supports negotiation of the Minimum Checksum Coverage feature and settings of the CsCov field. However, the UDP Checksum field in DCCP-UDP always covers the entire DCCP datagram, and the DCCP checksum is ignored on receipt. An application that enables the partial checksums feature in the DCCP module will therefore experience a service that is functionally identical to using full DCCP checksum coverage. This is also the service that the application would have received if it had used a network path that did not provide optimised processing for DCCP partial checksums.
DCCP-UDP支持部分校验和的语法。它还支持最小校验和覆盖特性的协商和CsCov字段的设置。但是，DCCP-UDP中的UDP校验和字段始终覆盖整个DCCP数据报，并且在接收时忽略DCCP校验和。因此，在DCCP模块中启用部分校验和功能的应用程序将体验到功能上与使用完整DCCP校验和覆盖相同的服务。如果应用程序使用的网络路径没有为DCCP部分校验和提供优化处理，则它也会收到此服务。
A DCCP-UDP implementation MAY transfer network-layer options intended for DCCP to the network-layer header of the encapsulating UDP packet.
DCCP-UDP实现可以将用于DCCP的网络层选项传输到封装UDP数据包的网络层报头。
A DCCP-UDP endpoint that receives IP-options for the encapsulating UDP packet MAY forward these to the DCCP protocol module. If the endpoint forwards a specific network-layer option to the DCCP module, it MUST also forward all subsequent packets with this option. Consistent forwarding is essential for correct operation of many end-to-end options.
接收封装UDP数据包的IP选项的DCCP-UDP端点可以将这些选项转发给DCCP协议模块。如果端点将特定的网络层选项转发给DCCP模块，则它还必须使用此选项转发所有后续数据包。一致的转发对于许多端到端选项的正确操作至关重要。
A DCCP-UDP endpoint SHOULD follow the procedures of DCCP-STD in [RFC4340], Section 12 by setting the Explicit Congestion Notification (ECN) in the IP headers of outgoing packets and examining the values received in the ECN fields of incoming IP packets, relaying any packet markings to the DCCP module.
DCCP-UDP端点应遵循[RFC4340]第12节中DCCP-STD的程序，在传出数据包的IP报头中设置显式拥塞通知（ECN），并检查传入IP数据包的ECN字段中接收到的值，将任何数据包标记中继到DCCP模块。
Implementations that do not support ECN MUST follow the procedures of DCCP-STD in [RFC4340], Section 12.1 with regard to implementations that are not ECN capable.
不支持ECN的实施必须遵循[RFC4340]第12.1节中关于不支持ECN的实施的DCCP-STD程序。
To allow ICMP messages to be demultiplexed by the receiving endpoint, part of the original packet that resulted in the message is included in the payload of the ICMP error message. The receiving endpoint can therefore use this information to associate the ICMP error with the transport protocol instance that resulted in the ICMP message. When DCCP-UDP is used, the error message and the payload of the ICMP error message relate to the UDP transport.
为了允许接收端点对ICMP消息进行解复用，产生该消息的原始数据包的一部分包含在ICMP错误消息的有效负载中。因此，接收端点可以使用此信息将ICMP错误与导致ICMP消息的传输协议实例相关联。使用DCCP-UDP时，错误消息和ICMP错误消息的有效负载与UDP传输有关。
DCCP-UDP endpoints SHOULD forward ICMP messages relating to a UDP packet that carries a DCCP-UDP to the DCCP module. This may imply translation of the payload of the ICMP message into a form that is recognised by the DCCP stack. [RFC5927] describes precautions that are desirable before TCP acts on the receipt of an ICMP message. Similar precautions are desirable prior to forwarding by DCCP-UDP to the DCCP module.
DCCP-UDP端点应将与承载DCCP-UDP的UDP数据包相关的ICMP消息转发到DCCP模块。这可能意味着将ICMP消息的有效负载转换为DCCP堆栈可以识别的形式。[RFC5927]描述了TCP在接收ICMP消息之前需要采取的预防措施。在通过DCCP-UDP转发到DCCP模块之前，需要采取类似的预防措施。
The minimal length ICMP error message generated in response to processing a UDP datagram only identifies the UDP source port and UDP destination port. This ICMP message does not carry sufficient information to discover the encapsulated DCCP Port values. A DCCP-
为响应处理UDP数据报而生成的最小长度ICMP错误消息仅标识UDP源端口和UDP目标端口。此ICMP消息未包含足够的信息，无法发现封装的DCCP端口值。DCCP-
UDP endpoint that supports multiple DCCP connections over the same pair of UDP ports (see Section 3.8) may not therefore be able to associate an ICMP message with a unique DCCP-UDP connection.
因此，在同一对UDP端口上支持多个DCCP连接的UDP端点（参见第3.8节）可能无法将ICMP消息与唯一的DCCP-UDP连接相关联。
DCCP-UDP implementations MUST follow DCCP-STD [RFC4340], Section 14 with regard to determining the maximum packet size and the use of Path Maximum Transmission Unit Discovery (PMTUD). This requires the processing of ICMP Destination Unreachable messages with a code that indicates that an unfragmentable packet was too large to be forwarded (a "Datagram Too Big" message), as defined in RFC 4340.
DCCP-UDP实现必须遵循DCCP-STD[RFC4340]第14节关于确定最大数据包大小和使用路径最大传输单元发现（PMTUD）的规定。这需要处理ICMP目的地不可到达的消息，其代码指示不可分割的数据包太大而无法转发（“数据报太大”消息），如RFC 4340中所定义。
An effect of encapsulation is to incur additional datagram overhead. This will reduce the Maximum Packet Size (MPS) at the DCCP level.
封装的一个效果是产生额外的数据报开销。这将减少DCCP级别的最大数据包大小（MPS）。
A DCCP-UDP server (that is, an initially passive endpoint that wishes to receive DCCP-Request packets [RFC4340] over DCCP-UDP) listens for connections on one or more UDP ports. UDP port number 6511 has been allocated as the default listening UDP port for a DCCP-UDP server. Some NAT/NAPT topologies may require using a non-default listening port.
DCCP-UDP服务器（即希望通过DCCP-UDP接收DCCP请求数据包[RFC4340]的初始被动端点）侦听一个或多个UDP端口上的连接。UDP端口号6511已分配为DCCP-UDP服务器的默认侦听UDP端口。某些NAT/NAPT拓扑可能需要使用非默认侦听端口。
The purpose of this IANA-assigned port is for the operating system or a framework to receive and process DCCP-UDP datagrams for delivery to the DCCP module (e.g., to support a system-wide DCCP-UDP daemon serving multiple DCCP applications or a DCCP-UDP server placed behind a firewall).
此IANA分配的端口用于操作系统或框架接收和处理DCCP-UDP数据报，以传送到DCCP模块（例如，支持服务于多个DCCP应用程序的系统范围DCCP-UDP守护程序或防火墙后面的DCCP-UDP服务器）。
An application-specific implementation SHOULD use an ephemeral port and advertise this port using outside means, e.g., SDP. This method of implementation SHOULD NOT use the IANA-assigned port to listen for incoming DCCP-UDP packets.
特定于应用程序的实现应使用临时端口，并使用外部手段（如SDP）公布此端口。此实现方法不应使用IANA分配的端口侦听传入的DCCP-UDP数据包。
A DCCP-UDP client provides UDP source and destination ports as well as DCCP source and destination ports at connection initiation time. A client SHOULD ensure that each DCCP connection maps to a single DCCP-UDP connection by setting the UDP source port. Choosing a distinct UDP source port for each distinct DCCP connection ensures that UDP-based flow identifiers differ whenever DCCP-based flow identifiers differ. Specifically, two connections with different <source IP address, source DCCP port, destination IP address, destination DCCP port> DCCP 4-tuples will have different <source IP address, source UDP port, destination IP address, destination UDP port> UDP 4-tuples.
DCCP-UDP客户端在连接启动时提供UDP源端口和目标端口以及DCCP源端口和目标端口。客户端应通过设置UDP源端口确保每个DCCP连接映射到单个DCCP-UDP连接。为每个不同的DCCP连接选择不同的UDP源端口可确保基于UDP的流标识符在基于DCCP的流标识符不同时也不同。具体而言，具有不同<源IP地址、源DCCP端口、目标IP地址、目标DCCP端口>DCCP 4元组的两个连接将具有不同的<源IP地址、源UDP端口、目标IP地址、目标UDP端口>UDP 4元组。
A DCCP-UDP server SHOULD accept datagrams from any UDP source port. There is a risk that the same DCCP source port number could be used by two endpoints, each behind a NAPT. A DCCP-UDP server MUST therefore demultiplex a DCCP-UDP flow using both the UDP source and destination port numbers and the encapsulated DCCP ports. This ensures than an active DCCP connection is uniquely identified by the 6-tuple <source IP address, source UDP port, source DCCP port, destination IP address, destination UDP port, destination DCCP port>. (The active state of a DCCP connection is defined in Section 3.8: a DCCP connection becomes active following transmission of a DCCP-Request and becomes inactive after sending a DCCP-Close.)
DCCP-UDP服务器应接受来自任何UDP源端口的数据报。存在一种风险，即相同的DCCP源端口号可能被两个端点使用，每个端点位于NAPT后面。因此，DCCP-UDP服务器必须使用UDP源和目标端口号以及封装的DCCP端口对DCCP-UDP流进行解复用。这确保了活动DCCP连接由6元组唯一标识<源IP地址、源UDP端口、源DCCP端口、目标IP地址、目标UDP端口、目标DCCP端口>。（第3.8节定义了DCCP连接的活动状态：DCCP连接在传输DCCP请求后变为活动状态，在发送DCCP关闭后变为非活动状态。）
This demultiplexing at a DCCP-UDP endpoint occurs in two stages:
DCCP-UDP端点处的解复用分两个阶段进行：
1. In the first stage, DCCP-UDP packets are demultiplexed using the UDP 4-tuple: <source IP address, source UDP port, destination IP address, destination UDP port>.
1. 在第一阶段，使用UDP 4元组对DCCP-UDP数据包进行解复用：<源IP地址、源UDP端口、目标IP地址、目标UDP端口>。
2. In the second stage, a receiving endpoint MUST ensure that two independent DCCP connections that were multiplexed to the same UDP 4-tuple are not associated with the same connection in the DCCP module. The endpoint therefore needs to keep state for the set of active DCCP-UDP endpoints using each combination of a UDP 4-tuple: <source IP address, source UDP port, destination IP address, destination UDP port>. Two DCCP endpoint methods are specified. A DCCP-UDP implementation MUST implement exactly one of these:
2. 在第二阶段，接收端点必须确保多路复用到同一UDP 4元组的两个独立DCCP连接不与DCCP模块中的同一连接相关联。因此，端点需要使用UDP 4元组的每个组合来保持活动DCCP-UDP端点集的状态：<源IP地址、源UDP端口、目标IP地址、目标UDP端口>。指定了两种DCCP端点方法。DCCP-UDP实现必须正好实现以下其中一项：
* The DCCP server may accept only one active 6-tuple at any one time for a given UDP 4-tuple. In this method, DCCP-UDP packets that do not match an active 6-tuple MUST NOT be passed to the DCCP module and the DCCP Server SHOULD send a DCCP-Reset with Reset Code 12, "Encapsulated Port Reuse". An endpoint that receives a DCCP-Reset with this reset code will clear its connection state but MAY immediately try again using a different 4-tuple. This provides protection should the same UDP 4-tuple be re-used by multiple DCCP connections, ensuring that only one DCCP connection is established at one time.
* 对于给定的UDP 4元组，DCCP服务器一次只能接受一个活动的6元组。在此方法中，与活动6元组不匹配的DCCP-UDP数据包不得传递到DCCP模块，DCCP服务器应发送带有重置代码12“封装端口重用”的DCCP重置。使用此重置代码接收DCCP重置的端点将清除其连接状态，但可以立即使用不同的4元组重试。如果相同的UDP 4元组被多个DCCP连接重新使用，这将提供保护，确保一次只建立一个DCCP连接。
* The DCCP server may support multiple DCCP connections over the same UDP 4-tuple. In this method, the endpoint MUST then associate each 6-tuple with a single DCCP connection. If an endpoint is unable to demultiplex the 6-tuple (e.g., due to internal resource limits), it MUST discard DCCP-UDP packets that do not match an active 6-tuple instead of forwarding them to the DCCP module. The DCCP endpoint MAY send a DCCP-Reset
* DCCP服务器可以支持同一UDP 4元组上的多个DCCP连接。在此方法中，端点必须将每个6元组与单个DCCP连接相关联。如果端点无法将6元组解复用（例如，由于内部资源限制），则必须丢弃与活动6元组不匹配的DCCP-UDP数据包，而不是将其转发到DCCP模块。DCCP端点可以发送DCCP重置
with Reset Code 12, "Encapsulated Port Reuse", indicating the connection has been closed but may be retried using a different UDP 4-tuple.
使用重置代码12，“封装端口重用”，表示连接已关闭，但可以使用不同的UDP 4元组重试。
This section clarifies the usage of DCCP Service Codes and the registration of server ports by DCCP-UDP. The section is not intended to update the procedures for allocating Service Codes or server ports.
本节说明DCCP服务代码的使用以及DCCP-UDP对服务器端口的注册。本节不打算更新分配服务代码或服务器端口的过程。
There is one Service Code registry and one DCCP port registration that apply to all combinations of encapsulation and IP version. A DCCP Service Code specifies an application using DCCP regardless of the combination of DCCP encapsulation and IP version. An application may choose not to support some combinations of encapsulation and IP version, but its Service Code will remain registered for those combinations, and the Service Code must not be used by other applications. An application should not register different Service Codes for different combinations of encapsulation and IP version. [RFC5595] provides additional information about DCCP Service Codes.
有一个服务代码注册表和一个DCCP端口注册，适用于封装和IP版本的所有组合。DCCP服务代码指定使用DCCP的应用程序，而不考虑DCCP封装和IP版本的组合。应用程序可能会选择不支持封装和IP版本的某些组合，但其服务代码将保留这些组合的注册，并且服务代码不得被其他应用程序使用。应用程序不应为封装和IP版本的不同组合注册不同的服务代码。[RFC5595]提供了有关DCCP服务代码的附加信息。
Similarly, a DCCP port registration is applicable to all combinations of encapsulation and IP version. Again, an application may choose not to support some combinations of encapsulation and IP version on its registered DCCP port, although the port will remain registered for those combinations. Applications should not register different DCCP ports just for the purpose of using different combinations of encapsulation.
类似地，DCCP端口注册适用于封装和IP版本的所有组合。同样，应用程序可能会选择在其注册的DCCP端口上不支持封装和IP版本的某些组合，尽管该端口将保持这些组合的注册状态。应用程序不应该仅仅为了使用不同的封装组合而注册不同的DCCP端口。
The encapsulation of a higher-layer protocol within DCCP MUST be the same for both DCCP-STD and DCCP-UDP. Encapsulation of Datagram Transport Layer Security (DTLS) over DCCP is defined in [RFC5238] and RTP over DCCP is defined in [RFC5762]. This document therefore does not update these encapsulations when using DCCP-UDP.
对于DCCP-STD和DCCP-UDP，DCCP内的高层协议封装必须相同。[RFC5238]中定义了DCCP上的数据报传输层安全性（DTLS）封装，而[RFC5762]中定义了DCCP上的RTP。因此，本文档在使用DCCP-UDP时不会更新这些封装。
Applications often signal transport connection parameters through outside means, such as SDP. Applications that define such methods for DCCP MUST define how the DCCP encapsulation is chosen and MUST allow either encapsulation to be signalled. Where DCCP-STD and DCCP-UDP are both supported, DCCP-STD SHOULD be preferred.
应用程序通常通过外部手段（如SDP）向传输连接参数发送信号。为DCCP定义此类方法的应用程序必须定义如何选择DCCP封装，并且必须允许对任意一种封装发出信号。如果同时支持DCCP-STD和DCCP-UDP，则应首选DCCP-STD。
The Session Description Protocol (SDP) [RFC4566] and the offer/answer model [RFC3264] can be used to negotiate DCCP sessions, and [RFC5762]
会话描述协议（SDP）[RFC4566]和提供/应答模型[RFC3264]可用于协商DCCP会话，以及[RFC5762]
defines SDP extensions for signalling the use of an RTP session running over DCCP connections. However, since [RFC5762] predates this document, it does not define a mechanism for signalling that the DCCP-UDP encapsulation is to be used. This section updates [RFC5762] to describe how SDP can be used to signal RTP sessions running over the DCCP-UDP encapsulation.
定义SDP扩展，用于向通过DCCP连接运行的RTP会话的使用发送信号。但是，由于[RFC5762]早于本文档，因此它没有定义一种机制，用于发出使用DCCP-UDP封装的信号。本节更新了[RFC5762]，以描述如何使用SDP向通过DCCP-UDP封装运行的RTP会话发送信号。
The new SDP support specified in this section is expected to be useful when the offering party is on the public Internet or in the same private addressing realm as the answering party. In this case, the DCCP-UDP server has a public address. The client may either have a public address or be behind a NAT/NAPT. This scenario has the potential to be an important use case. Some other NAT/NAPT topologies may result in the advertised port being unreachable via the NAT/NAPT.
本节中指定的新SDP支持在提供方位于公共互联网上或与应答方位于同一个私有寻址域中时很有用。在这种情况下，DCCP-UDP服务器具有公共地址。客户机可以有公共地址，也可以在NAT/NAPT后面。这个场景有可能成为一个重要的用例。一些其他NAT/NAPT拓扑可能导致无法通过NAT/NAPT访问播发端口。
SDP uses a media ("m=") line to convey details of the media format and transport protocol used. The ABNF syntax [RFC5234] of a media line for DCCP is as follows (from [RFC4566]):
SDP使用媒体（“m=”）行传达所用媒体格式和传输协议的详细信息。DCCP介质线的ABNF语法[RFC5234]如下所示（来自[RFC4566]）：
media-field = %x6d "=" media SP port ["/" integer]
SP proto 1*(SP fmt) CRLF
media-field = %x6d "=" media SP port ["/" integer]
SP proto 1*(SP fmt) CRLF
The proto field denotes the transport protocol used for the media, while the port indicates the transport port to which the media is sent, following [RFC5762]. This document defines the following five values of the proto field to indicate media transported using DCCP-UDP encapsulation:
proto字段表示介质使用的传输协议，而端口表示介质发送到的传输端口，如下[RFC5762]。本文档定义了proto字段的以下五个值，以指示使用DCCP-UDP封装传输的媒体：
UDP/DCCP
UDP/DCCP
UDP/DCCP/RTP/AVP
UDP/DCCP/RTP/AVP
UDP/DCCP/RTP/SAVP
UDP/DCCP/RTP/SAVP
UDP/DCCP/RTP/AVPF
UDP/DCCP/RTP/AVPF
UDP/DCCP/RTP/SAVPF
UDP/DCCP/RTP/SAVPF
The "UDP/DCCP" protocol identifier is similar to the "DCCP" protocol identifier defined in [RFC5762] and denotes the DCCP transport protocol encapsulated in UDP, but not its upper-layer protocol.
“UDP/DCCP”协议标识符类似于[RFC5762]中定义的“DCCP”协议标识符，表示封装在UDP中的DCCP传输协议，但不表示其上层协议。
The "UDP/DCCP/RTP/AVP" protocol identifier refers to RTP using the RTP Profile for Audio and Video Conferences with Minimal Control [RFC3551] running over the DCCP-UDP encapsulation.
“UDP/DCCP/RTP/AVP”协议标识符是指使用RTP配置文件的RTP，用于音频和视频会议，在DCCP-UDP封装上运行最小控制[RFC3551]。
The "UDP/DCCP/RTP/SAVP" protocol identifier refers to RTP using the Secure Real-time Transport Protocol [RFC3711] running over the DCCP-UDP encapsulation.
“UDP/DCCP/RTP/SAVP”协议标识符是指使用在DCCP-UDP封装上运行的安全实时传输协议[RFC3711]的RTP。
The "UDP/DCCP/RTP/AVPF" protocol identifier refers to RTP using the Extended RTP Profile for RTCP-based Feedback [RFC4585] running over the DCCP-UDP encapsulation.
“UDP/DCCP/RTP/AVPF”协议标识符是指使用扩展RTP配置文件的RTP，用于在DCCP-UDP封装上运行的基于RTCP的反馈[RFC4585]。
The "UDP/DCCP/RTP/SAVPF" protocol identifier refers to RTP using the Extended Secure RTP Profile for RTCP-based Feedback [RFC5124] running over the DCCP-UDP encapsulation.
“UDP/DCCP/RTP/SAVPF”协议标识符是指使用扩展安全RTP配置文件的RTP，用于在DCCP-UDP封装上运行的基于RTCP的反馈[RFC5124]。
The fmt value in the "m=" line is used as described in [RFC5762].
“m=”行中的fmt值按照[RFC5762]中的说明使用。
The port number specified in the "m=" line indicates the UDP port that is used for the DCCP-UDP encapsulation service. The DCCP port number MUST be sent using an associated "a=dccp-port:" attribute, as described in Section 5.2.
“m=”行中指定的端口号表示用于DCCP-UDP封装服务的UDP端口。DCCP端口号必须使用相关的“a=DCCP端口：”属性发送，如第5.2节所述。
The use of ports with DCCP-UDP encapsulation is described further in Section 3.8.
第3.8节将进一步介绍使用DCCP-UDP封装的端口。
When using DCCP-UDP, the UDP port used for the encapsulation is signalled using the SDP "m=" line. The DCCP ports MUST NOT be included in the "m=" line but are instead signalled using a new SDP attribute ("dccp-port") defined according to the following ABNF:
使用DCCP-UDP时，使用SDP“m=”行向用于封装的UDP端口发送信号。DCCP端口不得包含在“m=”行中，而是使用根据以下ABNF定义的新SDP属性（“DCCP端口”）发出信号：
dccp-port-attr = %x61 "=dccp-port:" dccp-port
dccp-port-attr = %x61 "=dccp-port:" dccp-port
dccp-port = 1*DIGIT
dccp-port = 1*DIGIT
where DIGIT is as defined in [RFC5234]. This is a media-level attribute that is not subject to the charset attribute. The "a=dccp-port:" attribute MUST be included when the protocol identifiers described in Section 5.1 are used.
其中数字如[RFC5234]中所定义。这是一个不受字符集属性约束的媒体级属性。使用第5.1节中描述的协议标识符时，必须包括“a=dccp端口：”属性。
The use of ports with DCCP-UDP encapsulation is described further in Section 3.8.
第3.8节将进一步介绍使用DCCP-UDP封装的端口。
o If the "a=rtcp:" attribute [RFC3605] is used, then the signalled port is the DCCP port used for RTCP.
o 如果使用了“a=rtcp:”属性[RFC3605]，则信号端口是用于rtcp的DCCP端口。
o If the "a=rtcp-mux" attribute [RFC5761] is negotiated, then RTP and RTCP are multiplexed onto a single DCCP port; otherwise, separate DCCP ports are used for RTP and RTCP [RFC5762].
o 如果协商“a=rtcp mux”属性[RFC5761]，则RTP和rtcp被多路复用到单个DCCP端口上；否则，RTP和RTCP使用单独的DCCP端口[RFC5762]。
NOTE: In each case, only a single UDP port is used for the DCCP-UDP encapsulation.
注意：在每种情况下，DCCP-UDP封装只使用一个UDP端口。
o If the "a=rtcp-mux" attribute is not present, then the second of the two demultiplexing methods described in Section 3.8 MUST be implemented; otherwise, the second DCCP connection for the RTCP flow will be rejected. For this reason, using "a=rtcp-mux" is RECOMMENDED when using RTP over DCCP-UDP.
o 如果“a=rtcp mux”属性不存在，则必须实施第3.8节中描述的两种解复用方法中的第二种；否则，RTCP流的第二个DCCP连接将被拒绝。因此，当通过DCCP-UDP使用RTP时，建议使用“a=rtcp mux”。
The "a=setup:" attribute is used in a manner compatible with [RFC5762], Section 5.3 to indicate which of the DCCP-UDP endpoints should initiate the DCCP-UDP connection establishment.
“a=setup:”属性以与[RFC5762]第5.3节兼容的方式使用，以指示哪个DCCP-UDP端点应启动DCCP-UDP连接建立。
An endpoint that supports both native DCCP and the DCCP-UDP encapsulation may wish to signal support for both options in an SDP offer, allowing the answering party the option of using native DCCP where possible, while falling back to the DCCP-UDP encapsulation otherwise.
同时支持本机DCCP和DCCP-UDP封装的端点可能希望在SDP提供中表示支持这两个选项，从而允许应答方在可能的情况下使用本机DCCP，而在其他情况下则返回到DCCP-UDP封装。
An approach to doing this might be to include candidates for the DCCP-UDP encapsulation and native DCCP into an Interactive Connectivity Establishment (ICE) [RFC5245] exchange. Since DCCP is connection-oriented, these candidates would need to be encoded into ICE in a manner analogous to TCP candidates defined in [RFC6544]. Both active and passive candidates could be supported for native DCCP and DCCP-UDP encapsulation, as may DCCP simultaneous-open candidates [RFC5596]. In choosing local preference values, it may make sense to prefer DCCP-UDP over native DCCP in cases where low connection setup time is important and to prioritise native DCCP in cases where low overhead is preferred (on the assumption that DCCP-UDP is more likely to work through legacy NAT but has higher overhead). The details of this encoding into ICE are left for future study.
实现这一点的一种方法可能是将DCCP-UDP封装和本机DCCP的候选项包含到交互式连接建立（ICE）[RFC5245]交换中。由于DCCP是面向连接的，因此这些候选者需要以类似于[RFC6544]中定义的TCP候选者的方式编码到ICE中。本机DCCP和DCCP-UDP封装可以支持主动候选和被动候选，DCCP同步开放候选[RFC5596]也可以支持。在选择本地首选项值时，在连接设置时间较短的情况下，优先选择DCCP-UDP而非本机DCCP可能是有意义的，在优先选择低开销的情况下，优先考虑本机DCCP（假设DCCP-UDP更有可能通过传统NAT工作，但开销较高）。这种编码到ICE中的细节留待将来研究。
While ICE is appropriate for selecting basic use of DCCP-UDP versus DCCP-STD, it may not be appropriate for negotiating different RTP profiles with each transport encapsulation. The SDP Capability Negotiation framework [RFC5939] may be more suitable. Section 3.7 of RFC 5939 specifies how to provide attributes and transport protocols as capabilities and negotiate them using the framework. The details of the use of SDP Capability Negotiation with DCCP are left for future study.
虽然ICE适合选择DCCP-UDP和DCCP-STD的基本用途，但它可能不适合与每个传输封装协商不同的RTP配置文件。SDP能力协商框架[RFC5939]可能更合适。RFC 5939的第3.7节规定了如何提供属性和传输协议作为功能，并使用框架进行协商。与DCCP进行SDP能力协商的细节留待将来研究。
The example below shows an SDP offer, where an application signals support for DCCP-UDP:
下面的示例显示了SDP产品，其中应用程序发出支持DCCP-UDP的信号：
v=0
o=alice 1129377363 1 IN IP4 192.0.2.47
s=-
c=IN IP4 192.0.2.47
t=0 0
m=video 50234 UDP/DCCP/RTP/AVP 99
a=rtpmap:99 h261/90000
a=dccp-service-code:SC=x52545056
a=dccp-port:5004
a=rtcp:5005
a=setup:passive
a=connection:new
v=0
o=alice 1129377363 1 IN IP4 192.0.2.47
s=-
c=IN IP4 192.0.2.47
t=0 0
m=video 50234 UDP/DCCP/RTP/AVP 99
a=rtpmap:99 h261/90000
a=dccp-service-code:SC=x52545056
a=dccp-port:5004
a=rtcp:5005
a=setup:passive
a=connection:new
The answering party at 192.0.2.128 receives this offer and responds with the following answer:
192.0.2.128的应答方收到此报价并回复如下：
v=0
o=bob 1129377364 1 IN IP4 192.0.2.128
s=-
c=IN IP4 192.0.2.128
t=0 0
m=video 40123 UDP/DCCP/RTP/AVP 99
a=rtpmap:99 h261/90000
a=dccp-service-code:SC:RTPV
a=dccp-port:9
a=setup:active
a=connection:new
v=0
o=bob 1129377364 1 IN IP4 192.0.2.128
s=-
c=IN IP4 192.0.2.128
t=0 0
m=video 40123 UDP/DCCP/RTP/AVP 99
a=rtpmap:99 h261/90000
a=dccp-service-code:SC:RTPV
a=dccp-port:9
a=setup:active
a=connection:new
Note that the "m=" line in the answer includes the UDP port number of the encapsulation service. The DCCP service code is set to "RTPV", signalled using the "a=dccp-service-code" attribute [RFC5762]. The "a=dccp-port:" attribute in the answer is set to 9 (the discard port) in the usual manner for an active connection-oriented endpoint.
请注意，答案中的“m=”行包括封装服务的UDP端口号。DCCP服务代码设置为“RTPV”，使用“a=DCCP服务代码”属性[RFC5762]发出信号。答案中的“a=dccp port:”属性按面向活动连接端点的常用方式设置为9（丢弃端口）。
The answering party will then attempt to establish a DCCP-UDP connection to the offering party. The connection request will use an ephemeral DCCP source port and DCCP destination port 5004. The UDP packet encapsulating that request will have UDP source port 40123 and UDP destination port 50234.
然后，应答方将尝试与提供方建立DCCP-UDP连接。连接请求将使用短暂的DCCP源端口和DCCP目标端口5004。封装该请求的UDP数据包将具有UDP源端口40123和UDP目标端口50234。
DCCP-UDP provides all of the security risk-mitigation measures present in DCCP-STD and also all of the security risks. It does not maintain additional state at the encapsulation layer.
DCCP-UDP提供了DCCP-STD中存在的所有安全风险缓解措施以及所有安全风险。它不会在封装层保持额外的状态。
The tunnel encapsulation recommends processing of ICMP messages received for packets sent using DCCP-UDP and translation to allow use by DCCP. [RFC5927] describes precautions that are desirable before TCP acts on receipt of ICMP messages. Similar precautions are desirable for endpoints processing ICMP for DCCP-UDP. The purpose of DCCP-UDP is to allow DCCP to pass through NAT/NAPT devices; therefore, it exposes DCCP to the risks associated with passing through NAT devices. It does not create any new risks with regard to NAT/NAPT devices.
隧道封装建议对使用DCCP-UDP发送的数据包接收的ICMP消息进行处理，并进行翻译以允许DCCP使用。[RFC5927]描述了TCP在接收ICMP消息之前需要采取的预防措施。对于处理DCCP-UDP的ICMP的端点，也需要类似的预防措施。DCCP-UDP的目的是允许DCCP通过NAT/NAPT设备；因此，它使DCCP面临通过NAT设备的相关风险。它不会对NAT/NAPT设备产生任何新的风险。
DCCP-UDP may also allow DCCP applications to pass through existing firewall devices using rules for UDP, if the administrators of the devices so choose. A simple use may either allow all DCCP applications or allow none.
如果设备管理员选择，DCCP-UDP还可以允许DCCP应用程序使用UDP规则通过现有防火墙设备。简单的使用可以允许所有DCCP应用程序，也可以不允许任何应用程序。
A firewall that interprets this specification could inspect the encapsulated DCCP header to filter based on the inner DCCP header information. Full control of DCCP connections by applications will require enhancements to firewalls, as discussed in [RFC4340] and related RFCs (e.g., [RFC5595]).
解释此规范的防火墙可以检查封装的DCCP头，以便根据内部DCCP头信息进行过滤。如[RFC4340]和相关RFC（如[RFC5595]）中所述，应用程序对DCCP连接的完全控制需要对防火墙进行增强。
Datagram Transport Layer Security (DTLS) provides mechanisms that can be used to provide security protection for the encapsulated DCCP packets. DTLS may be used in two ways:
数据报传输层安全性（DTLS）提供了可用于为封装的DCCP数据包提供安全保护的机制。DTL可通过两种方式使用：
o Individual DCCP connections may be protected in the same way that DTLS is used with native DCCP [RFC5595]. This does not encrypt the UDP transport header added by DCCP-UDP.
o 单个DCCP连接的保护方式可能与DTL与本机DCCP一起使用的方式相同[RFC5595]。这不会加密DCCP-UDP添加的UDP传输头。
o This specification also permits the use of DTLS with the UDP transport that encapsulates DCCP packets. When DTLS is used at the encapsulation layer, this protects the DCCP headers. This prevents the headers from being inspected or updated by network middleboxes (such as firewalls and NAPT). It also eliminates the need for a separate DTLS handshake for each DCCP connection.
o 该规范还允许将DTL与封装DCCP数据包的UDP传输一起使用。当在封装层使用DTL时，这将保护DCCP头。这可以防止网络中间盒（如防火墙和NAPT）检查或更新头。它还消除了对每个DCCP连接进行单独DTLS握手的需要。
IANA has made the allocations described in the following sections.
IANA进行了以下各节所述的分配。
IANA has allocated a UDP port (6511) for the DCCP-UDP service. This port is allocated for use by a transport service rather than an application. In this case, the name of the transport should explicitly appear in the registry. Use of this port is defined in Section 3.8
IANA已为DCCP-UDP服务分配了一个UDP端口（6511）。此端口分配给传输服务而不是应用程序使用。在这种情况下，传输的名称应显式显示在注册表中。第3.8节定义了该端口的使用
IANA has assigned a new DCCP reset code (12) in the DCCP Reset Codes Registry, with the short description "Encapsulated Port Reuse". This code applies to all DCCP congestion control IDs. Use of this reset code is defined in Section 3.8. Section 5.6 of [RFC4340] defines three "Data" bytes that are carried by a DCCP Reset. For this reset code, these are defined as follows:
IANA在DCCP重置代码注册表中分配了一个新的DCCP重置代码（12），简短描述为“封装端口重用”。此代码适用于所有DCCP拥塞控制ID。第3.8节定义了该重置代码的使用。[RFC4340]第5.6节定义了DCCP重置所携带的三个“数据”字节。对于该重置代码，其定义如下：
o Data byte 1: The DCCP Packet Type of the DCCP datagram that resulted in the error message.
o 数据字节1：导致错误消息的DCCP数据报的DCCP数据包类型。
o Data bytes 2 & 3: The encapsulated UDP source port from the DCCP-UDP datagram that triggered the ICMP message, in network order.
o 数据字节2和3：按网络顺序触发ICMP消息的DCCP-UDP数据报的封装UDP源端口。
IANA has allocated the following new SDP attribute ("att-field"):
IANA已分配以下新的SDP属性（“att字段”）：
Contact name: DCCP Working Group
联系人姓名：DCCP工作组
Attribute name: dccp-port
属性名称：dccp端口
Long-form attribute name in English: Encapsulated DCCP Port
英文长格式属性名称：封装的DCCP端口
Type of attribute: Media level only
属性类型：仅媒体级别
Subject to charset attribute? No
以字符集属性为准？不
Purpose of the attribute: See this document, Section 5.1
属性用途：见本文件第5.1节
Allowed attribute values: See this document, Section 5.1
允许的属性值：见本文件第5.1节
This document was produced by the DCCP WG. The following individuals contributed during the working group last call: Andrew Lentvorski, Lloyd Wood, Pasi Sarolahti, Gerrit Renker, Eddie Kohler, and Dan Wing.
本文件由DCCP工作组编制。以下个人在工作组最后一次电话会议期间作出了贡献：安德鲁·兰特沃斯基、劳埃德·伍德、帕西·萨罗拉蒂、格瑞特·伦克、埃迪·科勒和丹·荣格。
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980.
[RFC0768]Postel，J.，“用户数据报协议”，STD 6，RFC 768，1980年8月。
[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。
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, October 2003.
[RFC3605]Huitema，C.，“会话描述协议（SDP）中的实时控制协议（RTCP）属性”，RFC3605，2003年10月。
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
[RFC4340]Kohler，E.，Handley，M.和S.Floyd，“数据报拥塞控制协议（DCCP）”，RFC 43402006年3月。
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5234]Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，STD 68，RFC 5234，2008年1月。
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control Protocol (DCCP)", RFC 5762, April 2010.
[RFC5762]Perkins，C.，“RTP和数据报拥塞控制协议（DCCP）”，RFC 5762，2010年4月。
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002.
[RFC3264]Rosenberg，J.和H.Schulzrinne，“具有会话描述协议（SDP）的提供/应答模型”，RFC 3264，2002年6月。
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
[RFC3551]Schulzrinne，H.和S.Casner，“具有最小控制的音频和视频会议的RTP配置文件”，STD 65，RFC 3551，2003年7月。
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[RFC3711]Baugher，M.，McGrew，D.，Naslund，M.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 37112004年3月。
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC4566]Handley，M.，Jacobson，V.，和C.Perkins，“SDP：会话描述协议”，RFC4566，2006年7月。
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006.
[RFC4585]Ott，J.，Wenger，S.，Sato，N.，Burmeister，C.，和J.Rey，“基于实时传输控制协议（RTCP）的反馈（RTP/AVPF）的扩展RTP配置文件”，RFC 45852006年7月。
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, January 2007.
[RFC4787]Audet，F.和C.Jennings，“单播UDP的网络地址转换（NAT）行为要求”，BCP 127，RFC 4787，2007年1月。
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, February 2008.
[RFC5124]Ott，J.和E.Carrara，“基于实时传输控制协议（RTCP）的反馈扩展安全RTP配置文件（RTP/SAVPF）”，RFC 51242008年2月。
[RFC5238] Phelan, T., "Datagram Transport Layer Security (DTLS) over the Datagram Congestion Control Protocol (DCCP)", RFC 5238, May 2008.
[RFC5238]Phelan，T.，“数据报拥塞控制协议（DCCP）上的数据报传输层安全性（DTLS）”，RFC 5238，2008年5月。
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010.
[RFC5245]Rosenberg，J.，“交互式连接建立（ICE）：提供/应答协议的网络地址转换器（NAT）遍历协议”，RFC 52452010年4月。
[RFC5595] Fairhurst, G., "The Datagram Congestion Control Protocol (DCCP) Service Codes", RFC 5595, September 2009.
[RFC5595]Fairhurst，G.“数据报拥塞控制协议（DCCP）服务代码”，RFC5952009年9月。
[RFC5596] Fairhurst, G., "Datagram Congestion Control Protocol (DCCP) Simultaneous-Open Technique to Facilitate NAT/ Middlebox Traversal", RFC 5596, September 2009.
[RFC5596]Fairhurst，G.“数据报拥塞控制协议（DCCP）促进NAT/中间盒遍历的同时开放技术”，RFC 55962009年9月。
[RFC5597] Denis-Courmont, R., "Network Address Translation (NAT) Behavioral Requirements for the Datagram Congestion Control Protocol", BCP 150, RFC 5597, September 2009.
[RFC5597]Denis Courmont，R.，“数据报拥塞控制协议的网络地址转换（NAT）行为要求”，BCP 150，RFC 5597，2009年9月。
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, April 2010.
[RFC5761]Perkins，C.和M.Westerlund，“在单个端口上多路传输RTP数据和控制数据包”，RFC 5761，2010年4月。
[RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, July 2010.
[RFC5927]Gont，F.，“针对TCP的ICMP攻击”，RFC 5927，2010年7月。
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) Capability Negotiation", RFC 5939, September 2010.
[RFC5939]Andreasen，F.，“会话描述协议（SDP）能力协商”，RFC 59392010年9月。
[RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. B. Roach, "TCP Candidates with Interactive Connectivity Establishment (ICE)", RFC 6544, March 2012.
[RFC6544]Rosenberg，J.，Keranen，A.，Lowekamp，B.，和A.B.Roach，“具有交互式连接建立（ICE）的TCP候选者”，RFC 65442012年3月。
Authors' Addresses
作者地址
Tom Phelan Sonus Networks 7 Technology Dr. Westford, MA 01886 US
Tom Phelan Sonus Networks 7 Technology Westford博士，马萨诸塞州，美国01886
Phone: +1 978 614 8456
EMail: tphelan@sonusnet.com
Phone: +1 978 614 8456
EMail: tphelan@sonusnet.com
Godred Fairhurst University of Aberdeen School of Engineering Fraser Noble Building Aberdeen, Scotland AB24 3UE UK
GoRead FelHurt阿伯丁大学工程学院弗雷泽贵族大厦阿伯丁，苏格兰AB24 3UE英国
EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk
EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk
Colin Perkins University of Glasgow School of Computing Science Glasgow, Scotland G12 8QQ UK
柯林帕金斯格拉斯哥大学计算科学学院，格拉斯哥，苏格兰G128QQ英国
EMail: csp@csperkins.org
URI: http://csperkins.org/
EMail: csp@csperkins.org
URI: http://csperkins.org/