Network Working Group C. Demichelis
Request for Comments: 3393 Telecomitalia Lab
Category: Standards Track P. Chimento
Ericsson IPI
November 2002
Network Working Group C. Demichelis
Request for Comments: 3393 Telecomitalia Lab
Category: Standards Track P. Chimento
Ericsson IPI
November 2002
IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)
IP性能指标（IPPM）的IP数据包延迟变化指标
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2002). All Rights Reserved.
版权所有（C）互联网协会（2002年）。版权所有。
Abstract
摘要
This document refers to a metric for variation in delay of packets across Internet paths. The metric is based on the difference in the One-Way-Delay of selected packets. This difference in delay is called "IP Packet Delay Variation (ipdv)".
本文档涉及互联网路径上数据包延迟变化的度量。该度量基于所选数据包的单向延迟差异。这种延迟差异称为“IP数据包延迟变化（ipdv）”。
The metric is valid for measurements between two hosts both in the case that they have synchronized clocks and in the case that they are not synchronized. We discuss both in this document.
该度量对于两台主机之间的测量有效，无论是在它们具有同步时钟的情况下还是在它们不同步的情况下。我们在本文件中讨论这两个问题。
Table of Contents
目录
1 Introduction..................................................... 2
1.1 Terminology.................................................. 3
1.2 Definition................................................... 3
1.3 Motivation................................................... 4
1.4 General Issues Regarding Time................................ 5
2 A singleton definition of a One-way-ipdv metric.................. 5
2.1 Metric name.................................................. 6
2.2 Metric parameters............................................ 6
2.3 Metric unit.................................................. 6
2.4 Definition................................................... 6
2.5 Discussion................................................... 7
2.6 Methodologies................................................ 9
2.7 Errors and Uncertainties.....................................10
1 Introduction..................................................... 2
1.1 Terminology.................................................. 3
1.2 Definition................................................... 3
1.3 Motivation................................................... 4
1.4 General Issues Regarding Time................................ 5
2 A singleton definition of a One-way-ipdv metric.................. 5
2.1 Metric name.................................................. 6
2.2 Metric parameters............................................ 6
2.3 Metric unit.................................................. 6
2.4 Definition................................................... 6
2.5 Discussion................................................... 7
2.6 Methodologies................................................ 9
2.7 Errors and Uncertainties.....................................10
2.7.1 Errors/Uncertainties related to Clocks.................11
2.7.2 Errors/uncertainties related to Wire-time vs Host-time.12
3 Definitions for Samples of One-way-ipdv..........................12
3.1 Metric name..................................................12
3.2 Parameters...................................................12
3.3 Metric Units.................................................13
3.4 Definition...................................................13
3.5 Discussion...................................................13
3.6 Methodology..................................................14
3.7 Errors and uncertainties.....................................14
4 Statistics for One-way-ipdv......................................14
4.1 Lost Packets and ipdv statistics.............................15
4.2 Distribution of One-way-ipdv values..........................15
4.3 Type-P-One-way-ipdv-percentile...............................16
4.4 Type-P-One-way-ipdv-inverse-percentile.......................16
4.5 Type-P-One-way-ipdv-jitter...................................16
4.6 Type-P-One-way-peak-to-peak-ipdv.............................16
5 Discussion of clock synchronization..............................17
5.1 Effects of synchronization errors............................17
5.2 Estimating the skew of unsynchronized clocks.................18
6 Security Considerations..........................................18
6.1 Denial of service............................................18
6.2 Privacy/Confidentiality......................................18
6.3 Integrity....................................................19
7 Acknowledgments..................................................19
8 References.......................................................19
8.1 Normative References........................................19
8.2 Informational References....................................19
9 Authors' Addresses...............................................20
10 Full Copyright Statement........................................21
2.7.1 Errors/Uncertainties related to Clocks.................11
2.7.2 Errors/uncertainties related to Wire-time vs Host-time.12
3 Definitions for Samples of One-way-ipdv..........................12
3.1 Metric name..................................................12
3.2 Parameters...................................................12
3.3 Metric Units.................................................13
3.4 Definition...................................................13
3.5 Discussion...................................................13
3.6 Methodology..................................................14
3.7 Errors and uncertainties.....................................14
4 Statistics for One-way-ipdv......................................14
4.1 Lost Packets and ipdv statistics.............................15
4.2 Distribution of One-way-ipdv values..........................15
4.3 Type-P-One-way-ipdv-percentile...............................16
4.4 Type-P-One-way-ipdv-inverse-percentile.......................16
4.5 Type-P-One-way-ipdv-jitter...................................16
4.6 Type-P-One-way-peak-to-peak-ipdv.............................16
5 Discussion of clock synchronization..............................17
5.1 Effects of synchronization errors............................17
5.2 Estimating the skew of unsynchronized clocks.................18
6 Security Considerations..........................................18
6.1 Denial of service............................................18
6.2 Privacy/Confidentiality......................................18
6.3 Integrity....................................................19
7 Acknowledgments..................................................19
8 References.......................................................19
8.1 Normative References........................................19
8.2 Informational References....................................19
9 Authors' Addresses...............................................20
10 Full Copyright Statement........................................21
This memo defines a metric for the variation in delay of packets that flow from one host to another through an IP path. It is based on "A One-Way-Delay metric for IPPM", RFC 2679 [2] and part of the text in this memo is taken directly from that document; the reader is assumed to be familiar with that document.
此备忘录定义了通过IP路径从一个主机流向另一个主机的数据包延迟变化的度量。它基于“IPPM的单向延迟度量”，RFC 2679[2]，本备忘录中的部分文本直接取自该文件；假定读者熟悉该文档。
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 BCP 14, RFC 2119 [3]. Although BCP 14, RFC 2119 was written with protocols in mind, the key words are used in this document for similar reasons. They are used to ensure the results of measurements from two different implementations are comparable and to note instances where an implementation could perturb the network.
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照BCP 14、RFC 2119[3]中所述进行解释。尽管BCP 14、RFC 2119在编写时考虑了协议，但出于类似的原因，本文档中使用了关键词。它们用于确保两种不同实现的测量结果具有可比性，并用于说明实现可能干扰网络的实例。
The structure of the memo is as follows:
备忘录的结构如下：
+ A 'singleton' analytic metric, called Type-P-One-way-ipdv, will be introduced to define a single instance of an ipdv measurement.
+ 将引入称为Type-P-One-way-ipdv的“单例”分析度量，以定义ipdv度量的单个实例。
+ Using this singleton metric, a 'sample', called Type-P-one-way-ipdv-Poisson-stream, will be introduced to make it possible to compute the statistics of sequences of ipdv measurements.
+ 使用此单例度量，将引入称为Type-P-one-way-ipdv-Poisson-stream的“样本”，以使计算ipdv测量序列的统计信息成为可能。
+ Using this sample, several 'statistics' of the sample will be defined and discussed
+ 使用此样本，将定义和讨论样本的几个“统计信息”
The variation in packet delay is sometimes called "jitter". This term, however, causes confusion because it is used in different ways by different groups of people.
数据包延迟的变化有时称为“抖动”。然而，这个术语会引起混淆，因为不同的人群以不同的方式使用它。
"Jitter" commonly has two meanings: The first meaning is the variation of a signal with respect to some clock signal, where the arrival time of the signal is expected to coincide with the arrival of the clock signal. This meaning is used with reference to synchronous signals and might be used to measure the quality of circuit emulation, for example. There is also a metric called "wander" used in this context.
“抖动”通常有两种含义：第一种含义是信号相对于某个时钟信号的变化，其中信号的到达时间预计与时钟信号的到达时间一致。这一含义用于参考同步信号，例如，可用于测量电路仿真的质量。在此上下文中还使用了一个称为“漫游”的度量。
The second meaning has to do with the variation of a metric (e.g., delay) with respect to some reference metric (e.g., average delay or minimum delay). This meaning is frequently used by computer scientists and frequently (but not always) refers to variation in delay.
第二种含义与度量（例如，延迟）相对于某些参考度量（例如，平均延迟或最小延迟）的变化有关。这个意思经常被计算机科学家使用，经常（但不总是）指延迟的变化。
In this document we will avoid the term "jitter" whenever possible and stick to delay variation which is more precise.
在本文件中，我们将尽可能避免术语“抖动”，并坚持更精确的延迟变化。
A definition of the IP Packet Delay Variation (ipdv) can be given for packets inside a stream of packets.
可以为分组流内的分组给出IP分组延迟变化（ipdv）的定义。
The ipdv of a pair of packets within a stream of packets is defined for a selected pair of packets in the stream going from measurement point MP1 to measurement point MP2.
为从测量点MP1到测量点MP2的流中的选定分组对定义分组流中分组对的ipdv。
The ipdv is the difference between the one-way-delay of the selected packets.
ipdv是所选数据包的单向延迟之间的差值。
One important use of delay variation is the sizing of play-out buffers for applications requiring the regular delivery of packets (for example, voice or video play-out). What is normally important in this case is the maximum delay variation, which is used to size play-out buffers for such applications [7]. Other uses of a delay variation metric are, for example, to determine the dynamics of queues within a network (or router) where the changes in delay variation can be linked to changes in the queue length process at a given link or a combination of links.
延迟变化的一个重要用途是为需要定期传送数据包（例如，语音或视频播放）的应用程序调整播放缓冲区的大小。在这种情况下，通常重要的是最大延迟变化，它用于调整此类应用程序的播放缓冲区大小[7]。延迟变化度量的其他用途是，例如，确定网络（或路由器）内队列的动态，其中延迟变化的变化可以链接到给定链路或链路组合处队列长度过程的变化。
In addition, this type of metric is particularly robust with respect to differences and variations of the clocks of the two hosts. This allows the use of the metric even if the two hosts that support the measurement points are not synchronized. In the latter case indications of reciprocal skew of the clocks can be derived from the measurement and corrections are possible. The related precision is often comparable with the one that can be achieved with synchronized clocks, being of the same order of magnitude of synchronization errors. This will be discussed below.
此外，这种类型的度量对于两个主机的时钟的差异和变化特别稳健。这样，即使支持测量点的两台主机不同步，也可以使用度量。在后一种情况下，可以从测量中得出时钟倒数偏差的指示，并且可以进行校正。相关精度通常与同步时钟可达到的精度相当，同步误差的数量级相同。这将在下文讨论。
The scope of this document is to provide a way to measure the ipdv delivered on a path. Our goal is to provide a metric which can be parameterized so that it can be used for various purposes. Any report of the metric MUST include all the parameters associated with it so that the conditions and meaning of the metric can be determined exactly. Since the metric does not represent a value judgment (i.e., define "good" and "bad"), we specifically do not specify particular values of the metrics that IP networks must meet.
本文档的范围是提供一种测量路径上交付的ipdv的方法。我们的目标是提供一个可以参数化的度量，以便它可以用于各种目的。任何度量报告必须包括与其相关的所有参数，以便能够准确确定度量的条件和含义。由于该指标不代表价值判断（即定义“好”和“坏”），因此我们特别不指定IP网络必须满足的指标的特定值。
The flexibility of the metric can be viewed as a disadvantage but there are some arguments for making it flexible. First, though there are some uses of ipdv mentioned above, to some degree the uses of ipdv are still a research topic and some room should be left for experimentation. Secondly, there are different views in the community of what precisely the definition should be (e.g., [8],[9],[10]). The idea here is to parameterize the definition, rather than write a different document for each proposed definition. As long as all the parameters are reported, it will be clear what is meant by a particular use of ipdv. All the remarks in the document hold, no matter which parameters are chosen.
指标的灵活性可以被视为一个缺点，但有一些理由认为它是灵活的。首先，尽管上面提到了ipdv的一些用途，但在某种程度上，ipdv的用途仍然是一个研究课题，应该留出一些实验空间。第二，社会上对定义的确切含义有不同的看法（例如，[8]、[9]、[10]）。这里的想法是参数化定义，而不是为每个建议的定义编写不同的文档。只要报告了所有参数，就很清楚ipdv的特定用途是什么意思。无论选择哪个参数，文档中的所有备注都有效。
Everything contained in Section 2.2. of [2] applies also in this case.
第2.2节中包含的所有内容。第[2]条的规定也适用于这种情况。
To summarize: As in [1] we define "skew" as the first derivative of the offset of a clock with respect to "true time" and define "drift" as the second derivative of the offset of a clock with respect to "true time".
总结：如[1]中所述，我们将“偏斜”定义为时钟偏移量相对于“真实时间”的一阶导数，将“漂移”定义为时钟偏移量相对于“真实时间”的二阶导数。
From there, we can construct "relative skew" and "relative drift" for two clocks C1 and C2 with respect to one another. These are natural extensions of the basic framework definitions of these quantities:
从那里，我们可以构造两个时钟C1和C2相对于彼此的“相对倾斜”和“相对漂移”。这些是这些量的基本框架定义的自然延伸：
+ Relative offset = difference in clock times
+ 相对偏移=时钟时间差
+ Relative skew = first derivative of the difference in clock times
+ 相对偏差=时钟时间差的一阶导数
+ Relative drift = second derivative of the difference in clock times
+ 相对漂移=时钟时间差的二阶导数
NOTE: The drift of a clock, as it is above defined over a long period must have an average value that tends to zero while the period becomes large since the frequency of the clock has a finite (and small) range. In order to underline the order of magnitude of this effect,it is considered that the maximum range of drift for commercial crystals is about 50 part per million (ppm). Since it is mainly connected with variations in operating temperature (from 0 to 70 degrees Celsius), it is expected that a host will have a nearly constant temperature during its operation period, and variations in temperature, even if quick, could be less than one Celsius per second, and range in the order of a few degrees. The total range of the drift is usually related to variations from 0 to 70 Celsius. These are important points for evaluation of precision of ipdv measurements, as will be seen below.
注：由于时钟的频率范围有限（且很小），如上所述，时钟在长时间内的漂移必须具有一个趋于零的平均值，而该周期变大。为了强调这种效应的数量级，认为商业晶体的最大漂移范围约为百万分之五十（ppm）。由于它主要与工作温度的变化（从0到70摄氏度）有关，因此预计主机在其工作期间的温度将接近恒定，并且温度变化（即使很快）也可能低于每秒1摄氏度，范围在几摄氏度左右。漂移的总范围通常与0到70摄氏度的变化有关。这些是ipdv测量精度评估的要点，如下所示。
The purpose of the singleton metric is to define what a single instance of an ipdv measurement is. Note that it can only be statistically significant in combination with other instances. It is not intended to be meaningful as a singleton, in the sense of being able to draw inferences from it.
单例度量的目的是定义ipdv度量的单个实例是什么。请注意，它仅在与其他实例结合时具有统计显著性。从能够从中得出推论的意义上讲，它并不是作为一个单身汉有意义的。
This definition makes use of the corresponding definition of type-P-One-Way-Delay metric [2]. This section makes use of those parts of the One-Way-Delay Draft that directly apply to the One-Way-ipdv metric, or makes direct references to that Draft.
该定义利用了P型单向延迟度量的相应定义[2]。本节使用了单向延迟草案中直接适用于单向ipdv指标的部分，或直接引用该草案。
Type-P-One-way-ipdv
P型单向ipdv
+ Src, the IP address of a host
+ Src，主机的IP地址
+ Dst, the IP address of a host
+ Dst，主机的IP地址
+ T1, a time
+ T1，一次
+ T2, a time
+ T2，一次
+ L, a packet length in bits. The packets of a Type P packet stream from which the singleton ipdv metric is taken MUST all be of the same length.
+ 五十、 以位为单位的数据包长度。从中获取singleton ipdv度量的P类型数据包流的数据包必须具有相同的长度。
+ F, a selection function defining unambiguously the two packets from the stream selected for the metric.
+ F、 一个选择函数，明确定义为度量选择的流中的两个数据包。
+ I1,I2, times which mark that beginning and ending of the interval in which the packet stream from which the singleton measurement is taken occurs.
+ I1，I2，表示进行单例测量的数据包流发生的时间间隔的开始和结束的时间。
+ P, the specification of the packet type, over and above the source and destination addresses
+ P、 在源地址和目标地址之上的数据包类型规范
The value of a Type-P-One-way-ipdv is either a real number of seconds (positive, zero or negative) or an undefined number of seconds.
P-One-way-ipdv类型的值为实秒数（正、零或负）或未定义的秒数。
We are given a Type P packet stream and I1 and I2 such that the first Type P packet to pass measurement point MP1 after I1 is given index 0 and the last Type P packet to pass measurement point MP1 before I2 is given the highest index number.
我们被赋予一个P型分组流和I1和I2，使得在I1之后通过测量点MP1的第一个P型分组被赋予索引0，在I2之前通过测量点MP1的最后一个P型分组被赋予最高的索引号。
Type-P-One-way-ipdv is defined for two packets from Src to Dst selected by the selection function F, as the difference between the value of the type-P-One-way-delay from Src to Dst at T2 and the value
P-One-way-ipdv类型定义为选择函数F选择的从Src到Dst的两个数据包，作为T2处从Src到Dst的P-One-way-delay类型的值与值之间的差值
of the type-P-One-Way-Delay from Src to Dst at T1. T1 is the wire-time at which Scr sent the first bit of the first packet, and T2 is the wire-time at which Src sent the first bit of the second packet. This metric is derived from the One-Way-Delay metric.
在T1从Src到Dst的P型单向延迟。T1是Scr发送第一个数据包的第一位的连线时间，T2是Src发送第二个数据包的第一位的连线时间。此度量源自单向延迟度量。
Therefore, for a real number ddT "The type-P-one-way-ipdv from Src to Dst at T1, T2 is ddT" means that Src sent two packets, the first at wire-time T1 (first bit), and the second at wire-time T2 (first bit) and the packets were received by Dst at wire-time dT1+T1 (last bit of the first packet), and at wire-time dT2+T2 (last bit of the second packet), and that dT2-dT1=ddT.
因此，对于实数ddT，“T1时从Src到Dst的P型单向ipdv，T2为ddT”意味着Src发送两个数据包，第一个在线路时间T1（第一位），第二个在线路时间T2（第一位），Dst在线路时间dT1+T1（第一个数据包的最后一位）和线路时间dT2+T2接收数据包（第二个数据包的最后一位），并且该dT2-dT1=ddT。
"The type-P-one-way-ipdv from Src to Dst at T1,T2 is undefined" means that Src sent the first bit of a packet at T1 and the first bit of a second packet at T2 and that Dst did not receive one or both packets.
“未定义从Src到T1、T2的Dst的类型-P-单向-ipdv”指Src在T1发送数据包的第一位，在T2发送第二数据包的第一位，Dst未接收一个或两个数据包。
Figure 1 illustrates this definition. Suppose that packets P(i) and P(k) are selected.
图1说明了这个定义。假设选择了分组P（i）和P（k）。
I1 P(i) P(j) P(k) I2
I1 P(i) P(j) P(k) I2
MP1 |--------------------------------------------------------------|
|\ |\ |\
| \ | \ | \
| \ | \ | \
| \ | \ | \
|dTi \ |dTj \ |dTk \
|<--->v |<--->v |<--->v
MP1 |--------------------------------------------------------------|
|\ |\ |\
| \ | \ | \
| \ | \ | \
| \ | \ | \
|dTi \ |dTj \ |dTk \
|<--->v |<--->v |<--->v
MP2 |--------------------------------------------------------------|
MP2 |--------------------------------------------------------------|
I1 P(i) P(j) P(k) I2
I1 P(i) P(j) P(k) I2
Figure 1: Illustration of the definition
图1：定义说明
Then ddT = dTk - dTi as defined above.
然后ddT=dTk-如上定义的dTi。
This metric definition depends on a stream of Type-P-One-Way-Delay packets that have been measured. In general this can be a stream of two or more packets, delimited by the interval endpoints I1 and I2. There must be a stream of at least two packets in order for a singleton ipdv measurement to take place. The purpose of the selection function is to specify exactly which two packets from the stream are to be used for the singleton measurement. Note that the
此度量定义取决于已测量的P型单向延迟数据包流。通常，这可以是两个或更多数据包的流，由间隔端点I1和I2分隔。必须有至少两个数据包的流才能进行单态ipdv测量。选择函数的目的是精确指定流中的哪两个数据包将用于单例测量。请注意
selection function may involve observing the one-way-delay of all the Type P packets of the stream in the specified interval. Examples of a selection function are:
选择功能可涉及在指定间隔内观察流的所有P类型分组的单向延迟。选择函数的示例包括：
+ Consecutive Type-P packets within the specified interval
+ 指定间隔内的连续Type-P数据包
+ Type-P packets with specified indices within the specified interval
+ 在指定间隔内具有指定索引的Type-P数据包
+ Type-P packets with the min and max one-way-delays within the specified interval
+ 在指定间隔内具有最小和最大单向延迟的Type-P数据包
+ Type-P packets with specified indices from the set of all defined (i.e., non-infinite) one-way-delays Type-P packets within the specified interval.
+ 具有来自所有定义（即，非无限）单向集的指定索引的P型数据包在指定间隔内延迟P型数据包。
The following practical issues have to be considered:
必须考虑以下实际问题：
+ Being a differential measurement, this metric is less sensitive to clock synchronization problems. This issue will be more carefully examined in section 5 of this memo. It is pointed out that, if the relative clock conditions change in time, the accuracy of the measurement will depend on the time interval I2-I1 and the magnitude of possible errors will be discussed below.
+ 作为一种差分测量，该度量对时钟同步问题不太敏感。本备忘录第5节将更仔细地研究这一问题。需要指出的是，如果相对时钟条件随时间变化，测量精度将取决于时间间隔I2-I1，下面将讨论可能误差的大小。
+ A given methodology will have to include a way to determine whether a delay value is infinite or whether it is merely very large (and the packet is yet to arrive at Dst). As noted by Mahdavi and Paxson, simple upper bounds (such as the 255 seconds theoretical upper bound on the lifetimes of IP packets [Postel: RFC 791]) could be used, but good engineering, including an understanding of packet lifetimes, will be needed in practice. Comment: Note that, for many applications of these metrics, the harm in treating a large delay as infinite might be zero or very small. A TCP data packet, for example, that arrives only after several multiples of the RTT may as well have been lost.
+ 给定的方法必须包括确定延迟值是无限大还是非常大（数据包尚未到达Dst）的方法。正如Mahdavi和Paxson所指出的，可以使用简单的上限（例如IP数据包寿命的255秒理论上限[Postel:RFC 791]），但在实践中需要良好的工程，包括对数据包寿命的理解。注释：请注意，对于这些度量的许多应用程序，将大延迟视为无限的危害可能为零或很小。例如，只有在多次RTT之后才到达的TCP数据包也可能丢失。
+ As with other 'type-P' metrics, the value of the metric may depend on such properties of the packet as protocol,(UDP or TCP) port number, size, and arrangement for special treatment (as with IP precedence or with RSVP).
+ 与其他“type-P”度量一样，度量的值可能取决于数据包的属性，如协议（UDP或TCP）端口号、大小和特殊处理的安排（如IP优先级或RSVP）。
+ ddT is derived from the start of the first bit out from a packet sent out by Src to the reception of the last bit received by Dst. Delay is correlated to the size of the packet. For this reason, the packet size is a parameter of the measurement and must be reported along with the measurement.
+ ddT从Src发送的数据包的第一位开始到Dst接收到的最后一位结束。延迟与数据包的大小相关。因此，数据包大小是测量的一个参数，必须随测量一起报告。
+ If the packet is duplicated along the path (or paths!) so that multiple non-corrupt copies arrive at the destination, then the packet is counted as received, and the first copy to arrive determines the packet's One-Way-Delay.
+ 如果数据包沿着路径（或多条路径！）复制，从而多个未损坏的副本到达目的地，则数据包被视为已接收，并且到达的第一个副本确定数据包的单向延迟。
+ If the packet is fragmented and if, for whatever reason, re-assembly does not occur, then the packet will be deemed lost.
+ 如果数据包被分割，并且无论出于何种原因，没有重新组装，那么数据包将被视为丢失。
In this document it is assumed that the Type-P packet stream is generated according to the Poisson sampling methodology described in [1].
在本文档中，假设根据[1]中描述的泊松抽样方法生成P型分组流。
The reason for Poisson sampling is that it ensures an unbiased and uniformly distributed sampling of times between I1 and I2. However, alternate sampling methodologies are possible. For example, continuous sampling of a constant bit rate stream (i.e., periodic packet transmission) is a possibility. However, in this case, one must be sure to avoid any "aliasing" effects that may occur with periodic samples.
泊松采样的原因是它确保了在I1和I2之间的时间的无偏和均匀分布采样。但是，也可以采用其他抽样方法。例如，恒定比特率流的连续采样（即，周期性分组传输）是一种可能性。但是，在这种情况下，必须确保避免周期性采样可能出现的任何“锯齿”效应。
As with other Type-P-* metrics, the detailed methodology will depend on the Type-P (e.g., protocol number, UDP/TCP port number, size, precedence).
与其他类型P-*指标一样，详细方法将取决于类型P（例如，协议号、UDP/TCP端口号、大小、优先级）。
The measurement methodology described in this section assumes the measurement and determination of ipdv in real-time as part of an active measurement. Note that this can equally well be done a posteriori, i.e., after the one-way-delay measurement is completed.
本节所述的测量方法假设实时测量和确定ipdv，作为主动测量的一部分。注意，这同样可以在后验阶段完成，即在单向延迟测量完成之后。
Generally, for a given Type-P, the methodology would proceed as follows: Note that this methodology is based on synchronized clocks. The need for synchronized clocks for Src and Dst will be discussed later.
通常，对于给定的P型，该方法将如下进行：注意，该方法基于同步时钟。Src和Dst对同步时钟的需求将在后面讨论。
+ Start after time I1. At the Src host, select Src and Dst IP addresses, and form test packets of Type-P with these addresses according to a given technique (e.g., the Poisson sampling technique). Any 'padding' portion of the packet needed only to make the test packet a given size should be filled with randomized bits to avoid a situation in which the measured delay is lower than it would otherwise be due to compression techniques along the path.
+ 在时间I1之后开始。在Src主机上，选择Src和Dst IP地址，并根据给定技术（例如，泊松抽样技术）使用这些地址形成P型测试数据包。数据包的任何“填充”部分仅用于使测试数据包达到给定大小，应使用随机位填充，以避免测量的延迟低于由于路径上的压缩技术而产生的延迟。
+ At the Dst host, arrange to receive the packets.
+ 在Dst主机上，安排接收数据包。
+ At the Src host, place a time stamp in the Type-P packet, and send it towards Dst.
+ 在Src主机上，在Type-P数据包中放置一个时间戳，并将其发送到Dst。
+ If the packet arrives within a reasonable period of time, take a time stamp as soon as possible upon the receipt of the packet. By subtracting the two time stamps, an estimate of One-Way-Delay can be computed.
+ 如果数据包在一段合理的时间内到达，则在收到数据包后尽快获取时间戳。通过减去两个时间戳，可以计算出单向延迟的估计值。
+ If the packet meets the selection function criterion for the first packet, record this first delay value. Otherwise, continue generating the Type-P packet stream as above until the criterion is met or I2, whichever comes first.
+ 如果数据包满足第一个数据包的选择功能标准，则记录该第一个延迟值。否则，继续如上所述生成Type-P分组流，直到满足标准或I2，以先到者为准。
+ At the Src host, packets continue to be generated according to the given methodology. The Src host places a time stamp in the Type-P packet, and send it towards Dst.
+ 在Src主机上，根据给定的方法继续生成数据包。Src主机在Type-P数据包中放置一个时间戳，并将其发送到Dst。
+ If the packet arrives within a reasonable period of time, take a time stamp as soon as possible upon the receipt of the packet. By subtracting the two time stamps, an estimate of One-Way-Delay can be computed.
+ 如果数据包在一段合理的时间内到达，则在收到数据包后尽快获取时间戳。通过减去两个时间戳，可以计算出单向延迟的估计值。
+ If the packet meets the criterion for the second packet, then by subtracting the first value of One-Way-Delay from the second value the ipdv value of the pair of packets is obtained. Otherwise, packets continue to be generated until the criterion for the second packet is fulfilled or I2, whichever comes first.
+ 如果分组满足第二分组的标准，则通过从第二值减去单向延迟的第一值，获得分组对的ipdv值。否则，数据包将继续生成，直到满足第二个数据包的标准或I2，以先到者为准。
+ If one or both packets fail to arrive within a reasonable period of time, the ipdv is taken to be undefined.
+ 如果一个或两个数据包未能在合理的时间段内到达，则认为ipdv未定义。
In the singleton metric of ipdv, factors that affect the measurement are the same as those affecting the One-Way-Delay measurement, even if, in this case, the influence is different.
在ipdv的单态度量中，影响测量的因素与影响单向延迟测量的因素相同，即使在这种情况下，影响不同。
The Framework document [1] provides general guidance on this point, but we note here the following specifics related to delay metrics:
框架文件[1]提供了关于这一点的一般指导，但我们在此注意到与延迟度量相关的以下细节：
+ Errors/uncertainties due to uncertainties in the clocks of the Src and Dst hosts.
+ Src和Dst主机时钟不确定性导致的错误/不确定性。
+ Errors/uncertainties due to the difference between 'wire time' and 'host time'.
+ 由于“接线时间”和“主机时间”之间的差异而产生的错误/不确定性。
Each of these errors is discussed in more detail in the following paragraphs.
以下段落将详细讨论这些错误中的每一个。
If, as a first approximation, the error that affects the first measurement of One-Way-Delay were the same as the one affecting the second measurement, they will cancel each other when calculating ipdv. The residual error related to clocks is the difference of the errors that are supposed to change from time T1, at which the first measurement is performed, to time T2 at which the second measurement is performed. Synchronization, skew, accuracy and resolution are here considered with the following notes:
作为第一近似值，如果影响单向延迟第一次测量的误差与影响第二次测量的误差相同，则在计算ipdv时，它们将相互抵消。与时钟相关的残余误差是假定从执行第一次测量的时间T1到执行第二次测量的时间T2变化的误差差。同步、倾斜、精度和分辨率在这里考虑，并注意以下事项：
+ Errors in synchronization between source and destination clocks contribute to errors in both of the delay measurements required for calculating ipdv.
+ 源时钟和目标时钟之间的同步错误会导致计算ipdv所需的两个延迟测量中的错误。
+ The effect of drift and skew errors on ipdv measurements can be quantified as follows: Suppose that the skew and drift functions are known. Assume first that the skew function is linear in time. Clock offset is then also a function of time and the error evolves as e(t) = K*t + O, where K is a constant and O is the offset at time 0. In this case, the error added to the subtraction of two different time stamps (t2 > t1) is e(t2)-e(t1) = K*(t2 - t1) which will be added to the time difference (t2 - t1). If the drift cannot be ignored, but we assume that the drift is a linear function of time, then the skew is given by s(t) = M*(t**2) + N*t + S0, where M and N are constants and S0 is the skew at time 0. The error added by the variable skew/drift process in this case becomes e(t) = O + s(t) and the error added to the difference in time stamps is e(t2)-e(t1) = N*(t2-t1) + M*{(t2-t1)**2}.
+ 漂移和偏斜误差对ipdv测量的影响可以量化如下：假设偏斜和偏斜函数已知。首先假设倾斜函数在时间上是线性的。然后，时钟偏移也是时间的函数，误差演变为e（t）=K*t+O，其中K是常数，O是时间0处的偏移。在这种情况下，加在两个不同时间戳（t2>t1）的减法上的误差是e（t2）-e（t1）=K*（t2-t1），这将被加在时间差（t2-t1）上。如果漂移不能忽略，但我们假设漂移是时间的线性函数，那么倾斜由s（t）=M*（t**2）+N*t+S0给出，其中M和N是常数，S0是时间0的倾斜。在这种情况下，由可变倾斜/漂移过程添加的误差变为e（t）=O+s（t），并且添加到时间戳差的误差为e（t2）-e（t1）=N*（t2-t1）+M*{（t2-t1）**2}。
It is the claim here (see remarks in section 1.3) that the effects of skew are rather small over the time scales that we are discussing here, since temperature variations in a system tend to be slow relative to packet inter-transmission times and the range of drift is so small.
这里的说法（见第1.3节中的备注）是，在我们这里讨论的时间尺度上，倾斜的影响相当小，因为系统中的温度变化相对于数据包间传输时间来说往往很慢，漂移范围很小。
+ As far as accuracy and resolution are concerned, what is noted in the one-way-delay document [2] in section 3.7.1, applies also in this case, with the further consideration, about resolution, that in this case the uncertainty introduced is two times the one of a single delay measurement. Errors introduced by these effects are often larger than the ones introduced by the drift.
+ 就精度和分辨率而言，第3.7.1节中单向延迟文件[2]中所述内容也适用于这种情况，并进一步考虑分辨率，即在这种情况下，引入的不确定度是单个延迟测量不确定度的两倍。这些效应引起的误差通常大于漂移引起的误差。
The content of sec. 3.7.2 of [2] applies also in this case, with the following further consideration: The difference between Host-time and Wire-time can be in general decomposed into two components, of which one is constant and the other is variable. Only the variable components will produce measurement errors, while the constant one will be canceled while calculating ipdv.
美国证券交易委员会的内容。[2]中的3.7.2也适用于这种情况，并进一步考虑以下因素：主机时间和接线时间之间的差异通常可分解为两个分量，其中一个是常数，另一个是变量。只有可变分量会产生测量误差，而恒定分量在计算ipdv时会被取消。
However, in most cases, the fixed and variable components are not known exactly.
然而，在大多数情况下，固定和可变组件并不确切。
The goal of the sample definition is to make it possible to compute the statistics of sequences of ipdv measurements. The singleton definition is applied to a stream of test packets generated according to a pseudo-random Poisson process with average arrival rate lambda. If necessary, the interval in which the stream is generated can be divided into sub-intervals on which the singleton definition of ipdv can be applied. The result of this is a sequence of ipdv measurements that can be analyzed by various statistical procedures.
样本定义的目标是使计算ipdv测量序列的统计信息成为可能。将单例定义应用于根据平均到达率λ的伪随机泊松过程生成的测试包流。如有必要，可以将生成流的间隔划分为子间隔，在子间隔上可以应用ipdv的单例定义。其结果是一系列ipdv测量，可通过各种统计程序进行分析。
Starting from the definition of the singleton metric of one-way-ipdv, we define a sample of such singletons. In the following, the two packets needed for a singleton measurement will be called a "pair".
从定义单向ipdv的单例度量开始，我们定义了这样一个单例的样本。在下文中，单例测量所需的两个数据包称为“对”。
Type-P-One-way-ipdv-Poisson-stream
类型-P-单向-ipdv-泊松流
+ Src, the IP address of a host
+ Src，主机的IP地址
+ Dst, the IP address of a host
+ Dst，主机的IP地址
+ T0, a time
+ T0，一次
+ Tf, a time
+ Tf，一次
+ lambda, a rate in reciprocal seconds
+ λ，以倒数秒为单位的速率
+ L, a packet length in bits. The packets of a Type P packet stream from which the sample ipdv metric is taken MUST all be of the same length.
+ 五十、 以位为单位的数据包长度。从中获取样本ipdv度量的P类型数据包流的数据包都必须具有相同的长度。
+ F, a selection function defining unambiguously the packets from the stream selected for the metric.
+ F、 一种选择函数，明确定义为度量选择的流中的数据包。
+ I(i),I(i+1), i >=0, pairs of times which mark the beginning and ending of the intervals in which the packet stream from which the measurement is taken occurs. I(0) >= T0 and assuming that n is the largest index, I(n) <= Tf.
+ I（I），I（I+1），I>=0，表示从中进行测量的分组流发生的间隔的开始和结束的成对时间。I（0）>=T0，假设n是最大的指数，I（n）<=Tf。
+ P, the specification of the packet type, over and above the source and destination addresses
+ P、 在源地址和目标地址之上的数据包类型规范
3.3. Metric Units:
3.3. 公制单位：
A sequence of triples whose elements are:
三元组序列，其元素为：
+ T1, T2,times
+ T1，T2，次
+ dT a real number or an undefined number of seconds
+ dT是实数还是未定义的秒数
A pseudo-random Poisson process is defined such that it begins at or before T0, with average arrival rate lambda, and ends at or after Tf. Those time values T(i) greater than or equal to T0 and less than or equal to Tf are then selected for packet generation times.
定义了一个伪随机泊松过程，使得它以平均到达率λ在T0或T0之前开始，并在Tf或之后结束。然后为分组生成时间选择那些大于或等于T0且小于或等于Tf的时间值T（i）。
Each packet falling within one of the sub-intervals I(i), I(i+1) is tested to determine whether it meets the criteria of the selection function F as the first or second of a packet pair needed to compute ipdv. The sub-intervals can be defined such that a sufficient number of singleton samples for valid statistical estimates can be obtained.
测试子间隔I（I）、I（I+1）之一内的每个分组，以确定其是否满足作为计算ipdv所需的分组对的第一个或第二个的选择函数F的标准。可以定义子区间，以便获得足够数量的单例样本用于有效的统计估计。
The triples defined above consist of the transmission times of the first and second packets of each singleton included in the sample, and the ipdv in seconds.
上面定义的三元组包括样本中每个单例的第一个和第二个数据包的传输时间，以及以秒为单位的ipdv。
Note first that, since a pseudo-random number sequence is employed, the sequence of times, and hence the value of the sample, is not fully specified. Pseudo-random number generators of good quality will be needed to achieve the desired qualities.
首先请注意，由于采用了伪随机数序列，因此没有完全指定时间序列以及样本值。需要质量良好的伪随机数生成器来实现所需的质量。
The sample is defined in terms of a Poisson process both to avoid the effects of self-synchronization and also capture a sample that is statistically as unbiased as possible. There is, of course, no claim that real Internet traffic arrives according to a Poisson arrival process.
根据泊松过程定义样本，以避免自同步的影响，并捕获统计上尽可能无偏的样本。当然，没有人声称真正的互联网流量是按照泊松到达过程到达的。
The sample metric can best be explained with a couple of examples: For the first example, assume that the selection function specifies the "non-infinite" max and min one-way-delays over each sub-interval. We can define contiguous sub-intervals of fixed specified length and produce a sequence each of whose elements is the triple <transmission time of the max delay packet, transmission time of the min delay packet, D(max)-D(min)> which is collected for each sub-interval. A second example is the selection function that specifies packets whose indices (sequence numbers) are just the integers below a certain bound. In this case, the sub-intervals are defined by the transmission times of the generated packets and the sequence produced is just <T(i), T(i+1), D(i+1)-D(i)> where D(i) denotes the one-way-delay of the ith packet of a stream.
示例度量可以用几个示例来最好地解释：对于第一个示例，假设选择函数指定每个子间隔上的“非无限”最大和最小单向延迟。我们可以定义固定指定长度的连续子间隔，并生成一个序列，其每个元素是为每个子间隔收集的三个<最大延迟数据包的传输时间，最小延迟数据包的传输时间，D（max）-D（min）>。第二个示例是选择函数，该函数指定其索引（序列号）仅为某个界限下的整数的数据包。在这种情况下，子间隔由生成的分组的传输时间定义，并且生成的序列正好<T（i），T（i+1），D（i+1）-D（i）>其中D（i）表示流的第i个分组的单向延迟。
This definition of the sample metric encompasses both the definition proposed in [9] and the one proposed in [10].
样本度量的定义包括[9]中提出的定义和[10]中提出的定义。
Since packets can be lost or duplicated or can arrive in a different order than the order sent, the pairs of test packets should be marked with a sequence number. For duplicated packets only the first received copy should be considered.
由于数据包可能丢失或重复，或者可能以与发送顺序不同的顺序到达，因此测试数据包对应标有序列号。对于重复的数据包，只应考虑第一个收到的副本。
Otherwise, the methodology is the same as for the singleton measurement, with the exception that the singleton measurement is repeated a number of times.
除此之外，该方法与单例测量方法相同，但单例测量重复多次。
The same considerations apply that have been made about the singleton metric. Additional error can be introduced by the pseudo-random Poisson process as discussed in [2]. Further considerations will be given in section 5.
同样的考虑也适用于单例度量。如[2]所述，伪随机泊松过程可能会引入额外的误差。第5节将给出进一步的考虑。
Some statistics are suggested which can provide useful information in analyzing the behavior of the packets flowing from Src to Dst. The statistics are assumed to be computed from an ipdv sample of reasonable size.
本文提出了一些统计数据，这些数据可以为分析从Src到Dst的数据包的行为提供有用的信息。假设统计数据是根据合理规模的ipdv样本计算得出的。
The purpose is not to define every possible statistic for ipdv, but ones which have been proposed or used.
目的不是定义ipdv的所有可能统计数据，而是已经提出或使用的统计数据。
The treatment of lost packets as having "infinite" or "undefined" delay complicates the derivation of statistics for ipdv. Specifically, when packets in the measurement sequence are lost, simple statistics such as sample mean cannot be computed. One possible approach to handling this problem is to reduce the event space by conditioning. That is, we consider conditional statistics; namely we estimate the mean ipdv (or other derivative statistic) conditioned on the event that selected packet pairs arrive at the destination (within the given timeout). While this itself is not without problems (what happens, for example, when every other packet is lost), it offers a way to make some (valid) statements about ipdv, at the same time avoiding events with undefined outcomes.
将丢失的数据包视为具有“无限”或“未定义”延迟，使ipdv统计数据的推导变得复杂。具体地说，当测量序列中的数据包丢失时，不能计算简单的统计数据，例如样本平均值。处理此问题的一种可能方法是通过调节减少事件空间。也就是说，我们考虑条件统计；也就是说，我们根据所选数据包对到达目的地（在给定超时内）的事件估计平均ipdv（或其他衍生统计）。虽然这本身并非没有问题（例如，当其他数据包丢失时会发生什么情况），但它提供了一种方法，可以对ipdv做出一些（有效）声明，同时避免发生结果未定义的事件。
In practical terms, what this means is throwing out the samples where one or both of the selected packets has an undefined delay. The sample space is reduced (conditioned) and we can compute the usual statistics, understanding that formally they are conditional.
实际上，这意味着在一个或两个选定数据包具有未定义延迟的情况下抛出样本。样本空间被缩减（条件化），我们可以计算通常的统计数据，理解它们在形式上是有条件的。
The one-way-ipdv values are limited by virtue of the fact that there are upper and lower bounds on the one-way-delay values. Specifically, one-way-delay is upper bounded by the value chosen as the maximum beyond which a packet is counted as lost. It is lower bounded by propagation, transmission and nodal transit delays assuming that there are no queues or variable nodal delays in the path. Denote the upper bound of one-way-delay by U and the lower bound by L and we see that one-way-ipdv can only take on values in the (open) interval (L-U, U-L).
单向ipdv值由于单向延迟值上有上界和下界而受到限制。具体地说，单向延迟的上限是被选为最大值的值，超过该值的数据包被视为丢失。假设路径中没有队列或可变节点延迟，则其下限由传播、传输和节点传输延迟决定。用U表示单向延迟的上界，用L表示下界，我们看到单向ipdv只能在（开放）区间（L-U，U-L）上取值。
In any finite interval, the one-way-delay can vary monotonically (non-increasing or non-decreasing) or of course it can vary in both directions in the interval, within the limits of the half-open interval [L,U). Accordingly, within that interval, the one-way-ipdv values can be positive, negative, or a mixture (including 0).
在任何有限区间内，单向延迟可以单调变化（非递增或非递减），当然也可以在区间内的两个方向上变化，在半开放区间[L，U]的限制范围内。因此，在该区间内，单向ipdv值可以是正的、负的或混合的（包括0）。
Since the range of values is limited, the one-way-ipdv cannot increase or decrease indefinitely. Suppose, for example, that the ipdv has a positive 'run' (i.e., a long sequence of positive values). At some point in this 'run', the positive values must approach 0 (or become negative) if the one-way-delay remains finite. Otherwise, the one-way-delay bounds would be violated. If such a run were to continue infinitely long, the sample mean (assuming no packets are lost) would approach 0 (because the one-way-ipdv values must approach 0). Note, however, that this says nothing about the shape of the
由于值的范围有限，单向ipdv不能无限增加或减少。例如，假设ipdv具有正“运行”（即，一长串正值）。在此“运行”中的某个点，如果单向延迟保持有限，则正值必须接近0（或变为负值）。否则，将违反单向延迟界限。如果这样的运行持续无限长，则样本平均值（假设没有数据包丢失）将接近0（因为单向ipdv值必须接近0）。但是，请注意，这并没有说明
distribution, or whether it is symmetric. Note further that over significant intervals, depending on the width of the interval [L,U), that the sample mean one-way-ipdv could be positive, negative or 0.
分布，或是否对称。进一步注意，在有效间隔内，取决于间隔[L，U]的宽度，样本表示单向ipdv可能为正、负或0。
There are basically two ways to represent the distribution of values of an ipdv sample: an empirical pdf and an empirical cdf. The empirical pdf is most often represented as a histogram where the range of values of an ipdv sample is divided into bins of a given length and each bin contains the proportion of values falling between the two limits of the bin. (Sometimes instead the number of values falling between the two limits is used). The empirical cdf is simply the proportion of ipdv sample values less than a given value, for a sequence of values selected from the range of ipdv values.
基本上有两种方法来表示ipdv样本的值分布：经验pdf和经验cdf。经验pdf通常表示为直方图，其中ipdv样本的值范围划分为给定长度的箱子，每个箱子包含位于箱子两个极限之间的值的比例。（有时使用介于两个限值之间的值的数量）。对于从ipdv值范围中选择的一系列值，经验cdf只是ipdv样本值小于给定值的比例。
Given a Type-P One-Way-ipdv sample and a given percent X between 0% and 100%. The Xth percentile of all ipdv values is in the sample. Therefore, then 50th percentile is the median.
给定一个P型单向ipdv样本，且给定百分比X在0%和100%之间。所有ipdv值的第X个百分位在样本中。因此，第50百分位是中位数。
Given a Type-P-One-way-ipdv sample and a given value Y, the percent of ipdv sample values less than or equal to Y.
给定P型单向ipdv样本和给定值Y，ipdv样本值的百分比小于或等于Y。
Although the use of the term "jitter" is deprecated, we use it here following the authors in [8]. In that document, the selection function specifies that consecutive packets of the Type-P stream are to be selected for the packet pairs used in ipdv computation. They then take the absolute value of the ipdv values in the sample. The authors in [8] use the resulting sample to compare the behavior of two different scheduling algorithms.
虽然“抖动”一词的使用已被弃用，但我们在这里使用它是根据[8]中的作者。在该文档中，选择函数指定为ipdv计算中使用的分组对选择P类型流的连续分组。然后取样本中ipdv值的绝对值。[8]中的作者使用得到的样本来比较两种不同调度算法的行为。
An alternate, but related, way of computing an estimate of jitter is given in RFC 1889 [11]. The selection function there is implicitly consecutive packet pairs, and the "jitter estimate" is computed by taking the absolute values of the ipdv sequence (as defined in this document) and applying an exponential filter with parameter 1/16 to generate the estimate (i.e., j_new = 15/16* j_old + 1/16*j_new).
RFC 1889[11]中给出了计算抖动估计值的另一种相关方法。那里的选择函数是隐式连续的分组对，并且“抖动估计”是通过获取ipdv序列的绝对值（如本文中所定义）并应用具有参数1/16的指数滤波器来计算的，以生成估计（即，j_new＝15/16×j_old＋1/16×j_new）。
In this case, the selection function used in collecting the Type-P-One-Way-ipdv sample specifies that the first packet of each pair to be the packet with the maximum Type-P-One-Way-Delay in each subinterval and the second packet of each pair to be the packet with
在这种情况下，用于收集Type-P-One-Way-ipdv样本的选择函数指定每对的第一个分组为在每个子间隔中具有最大Type-P-One-Way-Delay的分组，并且每对的第二个分组为具有最大Type-P-One-Way-Delay的分组
the minimum Type-P-One-Way-Delay in each sub-interval. The resulting sequence of values is the peak-to-peak delay variation in each subinterval of the measurement interval.
每个子间隔中的最小P型单向延迟。结果值序列是测量间隔的每个子间隔中的峰-峰延迟变化。
This section gives some considerations about the need for having synchronized clocks at the source and destination, although in the case of unsynchronized clocks, data from the measurements themselves can be used to correct error. These considerations are given as a basis for discussion and they require further investigation.
本节给出了在源和目的地需要同步时钟的一些注意事项，尽管在非同步时钟的情况下，可以使用测量本身的数据来纠正错误。这些考虑作为讨论的基础，需要进一步调查。
Clock errors can be generated by two processes: the relative drift and the relative skew of two given clocks. We should note that drift is physically limited and so the total relative skew of two clocks can vary between an upper and a lower bound.
时钟误差可以由两个过程产生：两个给定时钟的相对漂移和相对倾斜。我们应该注意到漂移在物理上是有限的，因此两个时钟的总相对偏差可以在上限和下限之间变化。
Suppose then that we have a measurement between two systems such that the clocks in the source and destination systems have at time 0 a relative skew of s(0) and after a measurement interval T have skew s(T). We assume that the two clocks have an initial offset of O (that is letter O).
然后假设我们在两个系统之间进行测量，使得源系统和目标系统中的时钟在时间0时具有s（0）的相对偏斜，并且在测量间隔T之后具有偏斜s（T）。我们假设两个时钟的初始偏移量为O（即字母O）。
Now suppose that the packets travel from source to destination in constant time, in which case the ipdv is zero and the difference in the time stamps of the two clocks is actually just the relative offset of the clocks. Suppose further that at the beginning of the measurement interval the ipdv value is calculated from a packet pair and at the end of the measurement interval another ipdv value is calculated from another packet pair. Assume that the time interval covered by the first measurement is t1 and that the time interval covered by the second measurement is t2. Then
现在假设数据包以恒定时间从源传输到目的地，在这种情况下，ipdv为零，两个时钟的时间戳差实际上只是时钟的相对偏移量。进一步假设在测量间隔开始时，从分组对计算ipdv值，并且在测量间隔结束时，从另一分组对计算另一ipdv值。假设第一次测量覆盖的时间间隔为t1，第二次测量覆盖的时间间隔为t2。然后
ipdv1 = s(0)*t1 + t1*(s(T)-s(0))/T
ipdv1 = s(0)*t1 + t1*(s(T)-s(0))/T
ipdv2 = s(T)*t2 + t2*(s(T)-s(0))/T
ipdv2 = s(T)*t2 + t2*(s(T)-s(0))/T
assuming that the change in skew is linear in time. In most practical cases, it is claimed that the drift will be close to zero in which case the second (correction) term in the above equations disappears.
假设倾斜的变化在时间上是线性的。在大多数实际情况下，据称漂移将接近零，在这种情况下，上述方程中的第二项（校正）消失。
Note that in the above discussion, other errors, including the differences between host time and wire time, and externally-caused clock discontinuities (e.g., clock corrections) were ignored. Under these assumptions the maximum clock errors will be due to the maximum relative skew acting on the largest interval between packets.
请注意，在上述讨论中，忽略了其他错误，包括主机时间和线路时间之间的差异，以及外部引起的时钟不连续性（例如时钟校正）。在这些假设下，最大时钟误差将是由于作用于数据包之间最大间隔的最大相对偏斜造成的。
If the skew is linear (that is, if s(t) = S * t for constant S), the error in ipdv values will depend on the time between the packets used in calculating the value. If ti is the time between the packet pair, then let Ti denote the sample mean time between packets and the average skew is s(Ti) = S * Ti. In the event that the delays are constant, the skew parameter S can be estimated from the estimate Ti of the time between packets and the sample mean ipdv value. Under these assumptions, the ipdv values can be corrected by subtracting the estimated S * ti.
如果歪斜是线性的（即，如果s（t）=s*t表示常数s），则ipdv值中的误差将取决于用于计算值的数据包之间的时间。如果ti是分组对之间的时间，那么让ti表示分组之间的样本平均时间，并且平均偏斜为s（ti）=s*ti。在延迟恒定的情况下，可以根据分组之间的时间的估计Ti和样本平均ipdv值来估计倾斜参数S。在这些假设下，可以通过减去估计的S*ti来校正ipdv值。
We observe that the displacement due to the skew does not change the shape of the distribution, and, for example the Standard Deviation remains the same. What introduces a distortion is the effect of the drift, also when the mean value of this effect is zero at the end of the measurement. The value of this distortion is limited to the effect of the total skew variation on the emission interval.
我们观察到，由于倾斜而产生的位移不会改变分布的形状，例如，标准偏差保持不变。引入失真的是漂移效应，在测量结束时，漂移效应的平均值为零时也是如此。该失真的值仅限于总倾斜变化对发射间隔的影响。
The one-way-ipdv metric has the same security properties as the one-way-delay metric [2], and thus they inherit the security considerations of that document. The reader should consult [2] for a more detailed treatment of security considerations. Nevertheless, there are a few things to highlight.
单向ipdv度量与单向延迟度量具有相同的安全属性[2]，因此它们继承了该文档的安全注意事项。读者应参考[2]了解安全注意事项的更详细处理方法。然而，有几件事需要强调。
It is still possible that there could be an attempt at a denial of service attack by sending many measurement packets into the network. In general, legitimate measurements must have their parameters carefully selected in order to avoid interfering with normal traffic.
仍有可能通过向网络发送许多测量数据包来尝试拒绝服务攻击。通常，合法测量必须仔细选择其参数，以避免干扰正常通信。
The packets contain no user information, and so privacy of user data is not a concern.
数据包不包含用户信息，因此用户数据的隐私不受关注。
There could also be attempts to disrupt measurements by diverting packets or corrupting them. To ensure that test packets are valid and have not been altered during transit, packet authentication and integrity checks may be used.
也可能有人试图通过转移数据包或破坏数据包来破坏测量。为确保测试数据包有效且在传输过程中未被更改，可使用数据包身份验证和完整性检查。
Thanks to Merike Kaeo, Al Morton and Henk Uiterwaal for catching mistakes and for clarifying re-wordings for this final document.
感谢Merike Kaeo、Al Morton和Henk Uiterwaal发现错误并澄清本最终文件的措辞。
A previous major revision of the document resulted from e-mail discussions with and suggestions from Mike Pierce, Ruediger Geib, Glenn Grotefeld, and Al Morton. For previous revisions of this document, discussions with Ruediger Geib, Matt Zekauskas and Andy Scherer were very helpful.
该文件之前的一次重大修订是通过与迈克·皮尔斯、鲁迪格·盖布、格伦·格罗特菲尔德和阿尔·莫顿的电子邮件讨论和建议而产生的。对于本文件之前的修订，与Ruediger Geib、Matt Zekauskas和Andy Scherer的讨论非常有用。
[1] Paxon, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, February 1998.
[1] Paxon，V.，Almes，G.，Mahdavi，J.和M.Mathis，“IP性能度量框架”，RFC 2330，1998年2月。
[2] Almes, G. and S. Kalidindisu, "A One-Way-Delay Metric for IPPM", RFC 2679, September 1999.
[2] Almes，G.和S.Kalidindisu，“IPPM的单向延迟度量”，RFC 2679，1999年9月。
[3] Bradner, S., "Key words for use in RFCs to indicate requirement levels", BCP 14, RFC 2119, March 1997.
[3] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[4] ITU-T Recommendation Y.1540 (formerly numbered I.380) "Internet Protocol Data Communication Service - IP Packet Transfer and Availability Performance Parameters", February 1999.
[4] ITU-T建议Y.1540（以前编号为I.380）“互联网协议数据通信服务——IP数据包传输和可用性性能参数”，1999年2月。
[5] Demichelis, Carlo - "Packet Delay Variation Comparison between ITU-T and IETF Draft Definitions" November 2000 (in the IPPM mail archives).
[5] Demichelis，Carlo—“ITU-T和IETF草案定义之间的数据包延迟变化比较”，2000年11月（在IPPM邮件档案中）。
[6] ITU-T Recommendation I.356 "B-ISDN ATM Layer Cell Transfer Performance".
[6] ITU-T建议I.356“B-ISDN ATM层信元传输性能”。
[7] S. Keshav - "An Engineering Approach to Computer Networking", Addison-Wesley 1997, ISBN 0-201-63442-2.
[7] S.Keshav-“计算机网络的工程方法”，Addison Wesley 1997，ISBN 0-201-63442-2。
[8] Jacobson, V., Nichols, K. and Poduri, K. "An Expedited Forwarding PHB", RFC 2598, June 1999.
[8] Jacobson，V.，Nichols，K.和Poduri，K.“快速转发PHB”，RFC 25981999年6月。
[9] ITU-T Draft Recommendation Y.1541 - "Internet Protocol Communication Service - IP Performance and Availability Objectives and Allocations", April 2000.
[9] ITU-T建议草案Y.1541——“互联网协议通信服务——IP性能和可用性目标及分配”，2000年4月。
[10] Demichelis, Carlo - "Improvement of the Instantaneous Packet Delay Variation (IPDV) Concept and Applications", World Telecommunications Congress 2000, 7-12 May 2000.
[10] Demichelis，Carlo—“瞬时分组延迟变化（IPDV）概念和应用的改进”，2000年世界电信大会，2000年5月7日至12日。
[11] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A transport protocol for real-time applications", RFC 1889, January 1996.
[11] Schulzrinne，H.，Casner，S.，Frederick，R.和V.Jacobson，“RTP：实时应用的传输协议”，RFC 1889，1996年1月。
Carlo Demichelis Telecomitalia Lab S.p.A Via G. Reiss Romoli 274 10148 - TORINO Italy
卡洛·德米切利斯意大利电信实验室S.p.A通过G.Reiss Romoli 274 10148-意大利都灵
Phone: +39 11 228 5057
Fax: +39 11 228 5069
EMail: carlo.demichelis@tilab.com
Phone: +39 11 228 5057
Fax: +39 11 228 5069
EMail: carlo.demichelis@tilab.com
Philip Chimento Ericsson IPI 7301 Calhoun Place Rockville, Maryland 20855 USA
Philip Chimento Ericsson IPI 7301美国马里兰州洛克维尔卡尔霍恩广场20855
Phone: +1-240-314-3597
EMail: chimento@torrentnet.com
Phone: +1-240-314-3597
EMail: chimento@torrentnet.com
Copyright (C) The Internet Society (2002). All Rights Reserved.
版权所有（C）互联网协会（2002年）。版权所有。
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
本文件及其译本可复制并提供给他人，对其进行评论或解释或协助其实施的衍生作品可全部或部分编制、复制、出版和分发，不受任何限制，前提是上述版权声明和本段包含在所有此类副本和衍生作品中。但是，不得以任何方式修改本文件本身，例如删除版权通知或对互联网协会或其他互联网组织的引用，除非出于制定互联网标准的需要，在这种情况下，必须遵循互联网标准过程中定义的版权程序，或根据需要将其翻译成英语以外的其他语言。
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
上述授予的有限许可是永久性的，互联网协会或其继承人或受让人不会撤销。
This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
本文件和其中包含的信息是按“原样”提供的，互联网协会和互联网工程任务组否认所有明示或暗示的保证，包括但不限于任何保证，即使用本文中的信息不会侵犯任何权利，或对适销性或特定用途适用性的任何默示保证。
Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。