Network Working Group G. Almes
Request for Comments: 2681 S. Kalidindi
Category: Standards Track M. Zekauskas
Advanced Network & Services
September 1999
Network Working Group G. Almes
Request for Comments: 2681 S. Kalidindi
Category: Standards Track M. Zekauskas
Advanced Network & Services
September 1999
A Round-trip Delay Metric for IPPM
IPPM的往返延迟度量
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 (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
This memo defines a metric for round-trip delay of packets across Internet paths. It builds on notions introduced and discussed in the IPPM Framework document, RFC 2330 [1], and follows closely the corresponding metric for One-way Delay ("A One-way Delay Metric for IPPM") [2]; the reader is assumed to be familiar with those documents.
此备忘录定义了跨Internet路径的数据包往返延迟的度量。它以IPPM框架文件RFC 2330[1]中介绍和讨论的概念为基础，并严格遵循单向延迟的相应度量（“IPPM的单向延迟度量”）[2]；假定读者熟悉这些文档。
The memo was largely written by copying material from the One-way Delay metric. The intention is that, where the two metrics are similar, they will be described with similar or identical text, and that where the two metrics differ, new or modified text will be used.
这份备忘录主要是通过抄袭单向延迟指标的材料编写的。其目的是，在两个度量相似的情况下，将使用相似或相同的文本来描述它们，并且在两个度量不同的情况下，将使用新的或修改的文本。
This memo is intended to be parallel in structure to a future companion document for Packet Loss.
本备忘录旨在在结构上与未来关于数据包丢失的配套文件平行。
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 RFC 2119 [6]. Although 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 when 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RFC 2119[6]中所述进行解释。尽管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。它们用于确保两个不同实现的测量结果具有可比性，并用于记录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-Round-trip-Delay, will be introduced to measure a single observation of round-trip delay.
+ 将引入一种称为P型往返延迟的“单例”分析度量来测量往返延迟的单个观测值。
+ Using this singleton metric, a 'sample', called Type-P-Round-trip-Delay-Poisson-Stream, will be introduced to measure a sequence of singleton delays measured at times taken from a Poisson process.
+ 使用此单例度量，将引入称为类型-P-往返延迟-Poisson-Stream的“样本”，以测量在从Poisson过程中获取的时间测量的单例延迟序列。
+ 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“统计数据”。
This progression from singleton to sample to statistics, with clear separation among them, is important.
这种从单一样本到样本再到统计的过程，在它们之间有明确的分离，是很重要的。
Whenever a technical term from the IPPM Framework document is first used in this memo, it will be tagged with a trailing asterisk. For example, "term*" indicates that "term" is defined in the Framework.
本备忘录中首次使用IPPM框架文件中的技术术语时，将使用尾随星号进行标记。例如，“term*”表示框架中定义了“term”。
Round-trip delay of a Type-P* packet from a source host* to a destination host is useful for several reasons:
P型数据包从源主机*到目标主机*的往返延迟有以下几个原因：
+ Some applications do not perform well (or at all) if end-to-end delay between hosts is large relative to some threshold value.
+ 如果主机之间的端到端延迟相对于某个阈值较大，则某些应用程序的性能不好（或根本不好）。
+ Erratic variation in delay makes it difficult (or impossible) to support many interactive real-time applications.
+ 延迟的不稳定变化使得支持许多交互式实时应用程序变得困难（或不可能）。
+ The larger the value of delay, the more difficult it is for transport-layer protocols to sustain high bandwidths.
+ 延迟值越大，传输层协议就越难以维持高带宽。
+ The minimum value of this metric provides an indication of the delay due only to propagation and transmission delay.
+ 该度量的最小值提供仅由传播和传输延迟引起的延迟的指示。
+ The minimum value of this metric provides an indication of the delay that will likely be experienced when the path* traversed is lightly loaded.
+ 该度量的最小值提供了当路径*被轻装时可能经历的延迟指示。
+ Values of this metric above the minimum provide an indication of the congestion present in the path.
+ 此度量值高于最小值表示路径中存在的拥塞。
The measurement of round-trip delay instead of one-way delay has several weaknesses, summarized here:
往返延迟而非单向延迟的测量有几个缺点，总结如下：
+ The Internet path from a source to a destination may differ from the path from the destination back to the source ("asymmetric paths"), such that different sequences of routers are used for the forward and reverse paths. Therefore round-trip measurements actually measure the performance of two distinct paths together.
+ 从源到目的地的因特网路径可以不同于从目的地返回到源的路径（“非对称路径”），使得不同的路由器序列用于正向和反向路径。因此，往返测量实际上同时测量两条不同路径的性能。
+ Even when the two paths are symmetric, they may have radically different performance characteristics due to asymmetric queueing.
+ 即使这两条路径是对称的，由于非对称排队，它们也可能具有完全不同的性能特征。
+ Performance of an application may depend mostly on the performance in one direction.
+ 应用程序的性能可能主要取决于一个方向上的性能。
+ In quality-of-service (QoS) enabled networks, provisioning in one direction may be radically different than provisioning in the reverse direction, and thus the QoS guarantees differ.
+ 在支持服务质量（QoS）的网络中，一个方向的供应可能与反向的供应完全不同，因此QoS保证不同。
On the other hand, the measurement of round-trip delay has two specific advantages:
另一方面，往返延迟的测量有两个特定的优点：
+ Ease of deployment: unlike in one-way measurement, it is often possible to perform some form of round-trip delay measurement without installing measurement-specific software at the intended destination. A variety of approaches are well-known, including use of ICMP Echo or of TCP-based methodologies (similar to those outlined in "IPPM Metrics for Measuring Connectivity" [4]). However, some approaches may introduce greater uncertainty in the time for the destination to produce a response (see Section 2.7.3).
+ 易于部署：与单向测量不同，通常可以执行某种形式的往返延迟测量，而无需在预期目的地安装特定于测量的软件。各种方法是众所周知的，包括使用ICMP Echo或基于TCP的方法（类似于“IPPM度量连接性指标”[4]）。然而，一些方法可能会在目的地产生响应的时间上引入更大的不确定性（见第2.7.3节）。
+ Ease of interpretation: in some circumstances, the round-trip time is in fact the quantity of interest. Deducing the round-trip time from matching one-way measurements and an assumption of the destination processing time is less direct and potentially less accurate.
+ 易于解释：在某些情况下，往返时间实际上是兴趣的数量。从匹配的单向测量值和目的地处理时间的假设推断往返时间不太直接，并且可能不太准确。
Whenever a time (i.e., a moment in history) is mentioned here, it is understood to be measured in seconds (and fractions) relative to UTC.
每当这里提到一个时间（即历史上的一个时刻）时，它都被理解为以秒（和分数）为单位相对于UTC进行测量。
As described more fully in the Framework document, there are four distinct, but related notions of clock uncertainty:
正如框架文件中更全面地描述的，时钟不确定性有四个不同但相关的概念：
synchronization*
同步*
measures the extent to which two clocks agree on what time it is. For example, the clock on one host might be 5.4 msec ahead of the clock on a second host.
测量两个时钟在时间上的一致程度。例如，一台主机上的时钟可能比另一台主机上的时钟早5.4毫秒。
accuracy*
准确度*
measures the extent to which a given clock agrees with UTC. For example, the clock on a host might be 27.1 msec behind UTC.
测量给定时钟与UTC一致的程度。例如，主机上的时钟可能比UTC慢27.1毫秒。
resolution*
决议*
measures the precision of a given clock. For example, the clock on an old Unix host might tick only once every 10 msec, and thus have a resolution of only 10 msec.
测量给定时钟的精度。例如，旧Unix主机上的时钟可能仅每10毫秒滴答一次，因此分辨率仅为10毫秒。
skew*
歪斜*
measures the change of accuracy, or of synchronization, with time. For example, the clock on a given host might gain 1.3 msec per hour and thus be 27.1 msec behind UTC at one time and only 25.8 msec an hour later. In this case, we say that the clock of the given host has a skew of 1.3 msec per hour relative to UTC, which threatens accuracy. We might also speak of the skew of one clock relative to another clock, which threatens synchronization.
测量精度或同步度随时间的变化。例如，给定主机上的时钟可能每小时增加1.3毫秒，因此在某一时间比UTC慢27.1毫秒，而在一小时后仅为25.8毫秒。在这种情况下，我们说给定主机的时钟相对于UTC每小时有1.3毫秒的偏差，这威胁到准确性。我们也可以说一个时钟相对于另一个时钟的倾斜，这威胁到同步。
2.1. Metric Name:
2.1. 度量名称：
Type-P-Round-trip-Delay
P型往返延迟
2.2. Metric Parameters:
2.2. 公制参数：
+ 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
+ T, a time
+ T、 一段时间
2.3. Metric Units:
2.3. 公制单位：
The value of a Type-P-Round-trip-Delay is either a real number, or an undefined (informally, infinite) number of seconds.
P型往返延迟的值可以是实数，也可以是未定义的（非正式地说是无限的）秒数。
2.4. Definition:
2.4. 定义：
For a real number dT, >>the *Type-P-Round-trip-Delay* from Src to Dst at T is dT<< means that Src sent the first bit of a Type-P packet to Dst at wire-time* T, that Dst received that packet, then immediately sent a Type-P packet back to Src, and that Src received the last bit of that packet at wire-time T+dT.
对于实数dT，>>从Src到T的Dst的*Type-P-往返延迟*为dT<<意味着Src在连线时间*T将Type-P数据包的第一位发送到Dst，Dst接收到该数据包，然后立即将Type-P数据包发送回Src，并且Src在连线时间T+dT接收到该数据包的最后一位。
>>The *Type-P-Round-trip-Delay* from Src to Dst at T is undefined (informally, infinite)<< means that Src sent the first bit of a Type-P packet to Dst at wire-time T and that (either Dst did not receive the packet, Dst did not send a Type-P packet in response, or) Src did not receive that response packet.
>>从Src到T的Dst的*Type-P-往返延迟*未定义（非正式地说，无限）<<意味着Src在接线时间T向Dst发送了Type-P数据包的第一位，并且（Dst没有接收到数据包，Dst没有发送Type-P数据包作为响应，或者）Src没有接收到该响应数据包。
>>The *Type-P-Round-trip-Delay between Src and Dst at T<< means
either the *Type-P-Round-trip-Delay from Src to Dst at T or the
*Type-P-Round-trip-Delay from Dst to Src at T. When this notion is
used, it is understood to be specifically ambiguous which host acts
as Src and which as Dst. {Comment: This ambiguity will usually be a
small price to pay for being able to have one measurement, launched
from either Src or Dst, rather than having two measurements.}
>>The *Type-P-Round-trip-Delay between Src and Dst at T<< means
either the *Type-P-Round-trip-Delay from Src to Dst at T or the
*Type-P-Round-trip-Delay from Dst to Src at T. When this notion is
used, it is understood to be specifically ambiguous which host acts
as Src and which as Dst. {Comment: This ambiguity will usually be a
small price to pay for being able to have one measurement, launched
from either Src or Dst, rather than having two measurements.}
Suggestions for what to report along with metric values appear in Section 3.8 after a discussion of the metric, methodologies for measuring the metric, and error analysis.
在讨论度量、度量方法和误差分析后，第3.8节给出了报告内容和度量值的建议。
2.5. Discussion:
2.5. 讨论：
Type-P-Round-trip-Delay is a relatively simple analytic metric, and one that we believe will afford effective methods of measurement.
P型往返延迟是一个相对简单的分析指标，我们相信它将提供有效的测量方法。
The following issues are likely to come up in practice:
在实践中可能会出现以下问题：
+ The timestamp values (T) for the time at which delays are measured should be fairly accurate in order to draw meaningful conclusions about the state of the network at a given T. Therefore, Src should have an accurate knowledge of time-of-day. NTP [3] affords one way to achieve time accuracy to within several milliseconds. Depending on the NTP server, higher accuracy may be achieved, for example when NTP servers make use of GPS systems as a time source. Note that NTP will adjust the instrument's clock. If an adjustment is made between the time the initial timestamp is taken and the time the final timestamp is taken the adjustment will affect the uncertainty in the measured delay. This uncertainty must be accounted for in the instrument's calibration.
+ 测量延迟时间的时间戳值（T）应相当准确，以便得出关于给定T处网络状态的有意义结论。因此，Src应准确了解一天中的时间。NTP[3]提供了一种在几毫秒内实现时间精度的方法。根据NTP服务器的不同，可以实现更高的精度，例如，当NTP服务器使用GPS系统作为时间源时。请注意，NTP将调整仪器的时钟。如果在初始时间戳和最终时间戳之间进行调整，则调整将影响测量延迟的不确定性。该不确定度必须在仪器校准中考虑。
+ 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 [4], simple upper bounds (such as the 255 seconds theoretical upper bound on the lifetimes of IP packets [5]) 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[4]所指出的，可以使用简单的上界（例如IP数据包寿命的255秒理论上界[5]），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，对于这些指标的许多应用程序，将大延迟视为无限的危害可能为零或很小。例如，仅在RTT数倍之后到达的TCP数据包也可能丢失。}
+ If the packet is duplicated so that multiple non-corrupt instances of the response arrive back at the source, then the packet is counted as received, and the first instance to arrive back at the source determines the packet's round-trip delay.
+ 如果数据包被复制，使得响应的多个未损坏实例返回到源，则数据包被计数为已接收，并且返回到源的第一个实例确定数据包的往返延迟。
+ If the packet is fragmented and if, for whatever reason, reassembly 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。
2.6. Methodologies:
2.6. 方法：
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）。
Generally, for a given Type-P, the methodology would proceed as follows:
一般而言，对于给定的P型，方法如下：
+ At the Src host, select Src and Dst IP addresses, and form a test packet of Type-P with these addresses. 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. The test packet must have some identifying information so that the response to it can be identified by Src when Src receives the response; one means to do this is by placing the timestamp generated just before sending the test packet in the packet itself.
+ 在Src主机上，选择Src和Dst IP地址，并使用这些地址形成类型为P的测试数据包。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。测试包必须有一些识别信息，以便当Src接收到响应时，Src能够识别对它的响应；实现这一点的一种方法是将在发送测试数据包之前生成的时间戳放在数据包本身中。
+ At the Dst host, arrange to receive and respond to the test packet. At the Src host, arrange to receive the corresponding response packet.
+ 在Dst主机上，安排接收和响应测试数据包。在Src主机上，安排接收相应的响应数据包。
+ At the Src host, take the initial timestamp and then send the prepared Type-P packet towards Dst. Note that the timestamp could be placed inside the packet, or kept separately as long as the packet contains a suitable identifier so the received timestamp can be compared with the send timestamp.
+ 在Src主机上，获取初始时间戳，然后向Dst发送准备好的Type-P数据包。注意，时间戳可以放在包内，或者只要包包含合适的标识符，就可以单独保存，以便可以将接收到的时间戳与发送时间戳进行比较。
+ If the packet arrives at Dst, send a corresponding response packet back from Dst to Src as soon as possible.
+ 如果数据包到达Dst，则尽快将相应的响应数据包从Dst发送回Src。
+ If the response packet arrives within a reasonable period of time, take the final timestamp as soon as possible upon the receipt of the packet. By subtracting the two timestamps, an estimate of round-trip delay can be computed. If the delay between the initial timestamp and the actual sending of the packet is known, then the estimate could be adjusted by subtracting this amount; uncertainty in this value must be taken into account in error analysis. Similarly, if the delay between the actual receipt of the response packet and final timestamp is known, then the estimate could be adjusted by subtracting this amount; uncertainty in this value must be taken into account in error analysis. See the next section, "Errors and Uncertainties", for a more detailed discussion.
+ 如果响应数据包在合理的时间段内到达，则在收到数据包后尽快获取最终时间戳。通过减去这两个时间戳，可以计算出往返延迟的估计值。如果初始时间戳和分组的实际发送之间的延迟是已知的，则可以通过减去该量来调整估计；误差分析中必须考虑该值的不确定性。类似地，如果响应分组的实际接收和最终时间戳之间的延迟是已知的，则可以通过减去该量来调整估计；误差分析中必须考虑该值的不确定性。有关更详细的讨论，请参见下一节“错误和不确定性”。
+ If the packet fails to arrive within a reasonable period of time, the round-trip delay is taken to be undefined (informally, infinite). Note that the threshold of 'reasonable' is a parameter of the methodology.
+ 如果数据包未能在合理的时间段内到达，则认为往返延迟是未定义的（非正式地说是无限的）。请注意，“合理”阈值是该方法的一个参数。
Issues such as the packet format and the means by which Dst knows when to expect the test packet are outside the scope of this document.
数据包格式和Dst知道何时期望测试数据包的方法等问题不在本文件范围内。
{Comment: Note that you cannot in general add two Type-P-One-way-Delay values (see [2]) to form a Type-P-Round-trip-Delay value. In order to form a Type-P-Round-trip-Delay value, the return packet must be triggered by the reception of a packet from Src.}
{注释：请注意，通常不能添加两个Type-P-One-way-Delay值（参见[2]）来形成Type-P-Round-trip-Delay值。为了形成Type-P-Round-trip-Delay值，必须通过从Src接收数据包来触发返回数据包。}
{Comment: "ping" would qualify as a round-trip measure under this definition, with a Type-P of ICMP echo request/reply with 60-byte packets. However, the uncertainties associated with a typical ping program must be analyzed as in the next section, including the type of reflecting point (a router may not handle an ICMP request in the fast path) and effects of load on the reflecting point.}
{注释：“ping”符合此定义下的往返测量，具有60字节数据包的ICMP回送请求/回复类型P。但是，与典型ping程序相关的不确定性必须在下一节中进行分析，包括反射点类型（路由器可能无法在快速路径中处理ICMP请求）以及负载对反射点的影响。}
2.7. Errors and Uncertainties:
2.7. 误差和不确定性：
The description of any specific measurement method should include an accounting and analysis of various sources of error or uncertainty. The Framework document provides general guidance on this point, but we note here the following specifics related to delay metrics:
任何特定测量方法的描述应包括对各种误差或不确定性来源的核算和分析。框架文件提供了关于这一点的一般指导，但我们注意到以下与延迟度量相关的细节：
+ Errors or uncertainties due to uncertainty in the clock of the Src host.
+ Src主机时钟不确定性导致的错误或不确定性。
+ Errors or uncertainties due to the difference between 'wire time' and 'host time'.
+ 由于“连线时间”和“主机时间”之间的差异而导致的错误或不确定性。
+ Errors or uncertainties due to time required by the Dst to receive the packet from the Src and send the corresponding response.
+ Dst从Src接收数据包并发送相应响应所需的时间导致的错误或不确定性。
In addition, the loss threshold may affect the results. Each of these are discussed in more detail below, along with a section ("Calibration") on accounting for these errors and uncertainties.
此外，损失阈值可能会影响结果。下面将详细讨论每一个问题，以及关于这些误差和不确定性的说明的一节（“校准”）。
The uncertainty in a measurement of round-trip delay is related, in part, to uncertainty in the clock of the Src host. In the following, we refer to the clock used to measure when the packet was sent from Src as the source clock, and we refer to the observed time when the packet was sent by the source as Tinitial, and the observed time when the packet was received by the source as Tfinal. Alluding to the notions of synchronization, accuracy, resolution, and skew mentioned in the Introduction, we note the following:
往返延迟测量的不确定性部分与Src主机时钟的不确定性有关。在下文中，我们将用于测量数据包何时从Src发送的时钟称为源时钟，将数据包何时由源发送的观测时间称为Tinitial，将数据包何时由源接收的观测时间称为Tfinal。关于引言中提到的同步、精度、分辨率和倾斜的概念，我们注意到以下几点：
+ While in one-way delay there is an issue of the synchronization of the source clock and the destination clock, in round-trip delay there is an (easier) issue of self-synchronization, as it were, between the source clock at the time the test packet is sent and the (same) source clock at the time the response packet is received. Theoretically a very severe case of skew could threaten this. In practice, the greater threat is anything that would cause a discontinuity in the source clock during the time between the taking of the initial and final timestamp. This might happen, for example, with certain implementations of NTP.
+ 虽然在单向延迟中存在源时钟和目标时钟的同步问题，但在往返延迟中，在发送测试数据包时的源时钟和接收响应数据包时的（相同）源时钟之间存在（更容易）的自同步问题。理论上，一个非常严重的歪斜案例可能会威胁到这一点。实际上，更大的威胁是在获取初始时间戳和最终时间戳之间的时间内可能导致源时钟中断的任何情况。例如，在某些NTP实现中可能会发生这种情况。
+ The accuracy of a clock is important only in identifying the time at which a given delay was measured. Accuracy, per se, has no importance to the accuracy of the measurement of delay.
+ 时钟的准确性仅在确定测量给定延迟的时间时才重要。准确度本身对延迟测量的准确度并不重要。
+ The resolution of a clock adds to uncertainty about any time measured with it. Thus, if the source clock has a resolution of 10 msec, then this adds 10 msec of uncertainty to any time value measured with it. We will denote the resolution of the source clock as Rsource.
+ 时钟的分辨率增加了用它测量的任何时间的不确定性。因此，如果源时钟的分辨率为10毫秒，则这会给用它测量的任何时间值增加10毫秒的不确定性。我们将源时钟的分辨率表示为Rsource。
Taking these items together, we note that naive computation Tfinal-Tinitial will be off by 2*Rsource.
将这些项放在一起，我们注意到naive计算Tfinal Tinitial将被2*Rsource关闭。
As we have defined round-trip delay, we would like to measure the time between when the test packet leaves the network interface of Src and when the corresponding response packet (completely) arrives at the network interface of Src, and we refer to these as "wire times". If the timings are themselves performed by software on Src, however, then this software can only directly measure the time between when Src grabs a timestamp just prior to sending the test packet and when it grabs a timestamp just after having received the response packet, and we refer to these two points as "host times".
正如我们定义的往返延迟，我们希望测量测试数据包离开Src网络接口和相应响应数据包（完全）到达Src网络接口之间的时间，我们称之为“连线时间”。但是，如果计时本身由Src上的软件执行，则该软件只能直接测量Src在发送测试数据包之前获取时间戳和在接收到响应数据包之后获取时间戳之间的时间，我们将这两点称为“主机时间”。
Another contributor to this problem is time spent at Dst between the receipt there of the test packet and the sending of the response packet. Ideally, this time is zero; it is explored further in the next section.
这个问题的另一个原因是在Dst接收测试数据包和发送响应数据包之间花费的时间。理想情况下，这个时间是零；下一节将进一步探讨这一点。
To the extent that the difference between wire time and host time is accurately known, this knowledge can be used to correct for host time measurements and the corrected value more accurately estimates the desired (wire time) metric.
在准确知道导线时间和主机时间之间的差异的情况下，此知识可用于校正主机时间测量值，且校正值可更准确地估计所需（导线时间）度量。
To the extent, however, that the difference between wire time and host time is uncertain, this uncertainty must be accounted for in an analysis of a given measurement method. We denote by Hinitial an upper bound on the uncertainty in the difference between wire time and host time on the Src host in sending the test packet, and similarly define Hfinal for the difference on the Src host in receiving the response packet. We then note that these problems introduce a total uncertainty of Hinitial + Hfinal. This estimate of total wire-vs-host uncertainty should be included in the error/uncertainty analysis of any measurement implementation.
然而，在一定程度上，导线时间和主机时间之间的差异是不确定的，在分析给定测量方法时必须考虑这种不确定性。我们通过Hinitial表示发送测试数据包时Src主机上的连线时间和主机时间之差的不确定性的上限，并且类似地定义了接收响应数据包时Src主机上的差异的Hfinal。然后我们注意到，这些问题引入了Hinital+Hfinal的总不确定性。在任何测量实施的误差/不确定度分析中，应包括导线与主机总不确定度的估计值。
Any time spent by the destination host in receiving and recognizing the packet from Src, and then producing and sending the corresponding response adds additional error and uncertainty to the round-trip delay measurement. The error equals the difference between the wire
目的主机从Src接收和识别数据包，然后生成和发送相应响应所花费的任何时间都会增加往返延迟测量的额外误差和不确定性。误差等于导线之间的差值
time the first bit of the packet is received by Dst and the wire time the first bit of the response is sent by Dst. To the extent that this difference is accurately known, this knowledge can be used to correct the desired metric. To the extent, however, that this difference is uncertain, this uncertainty must be accounted for in the error analysis of a measurement implementation. We denote this uncertainty by Hrefl. This estimate of uncertainty should be included in the error/uncertainty analysis of any measurement implementation.
Dst接收数据包的第一位的时间和Dst发送响应的第一位的连线时间。在准确知道这种差异的情况下，可以使用这种知识来修正所需的度量。然而，如果这种差异是不确定的，则必须在测量实施的误差分析中考虑这种不确定性。我们用Hrefl表示这种不确定性。任何测量实施的误差/不确定度分析中应包括该不确定度估计。
Generally, the measured values can be decomposed as follows:
通常，测量值可分解如下：
measured value = true value + systematic error + random error
measured value = true value + systematic error + random error
If the systematic error (the constant bias in measured values) can be determined, it can be compensated for in the reported results.
如果可以确定系统误差（测量值中的恒定偏差），则可以在报告的结果中对其进行补偿。
reported value = measured value - systematic error
报告值=测量值-系统误差
therefore
因此
reported value = true value + random error
报告值=真实值+随机误差
The goal of calibration is to determine the systematic and random error generated by the instruments themselves in as much detail as possible. At a minimum, a bound ("e") should be found such that the reported value is in the range (true value - e) to (true value + e) at least 95 percent of the time. We call "e" the calibration error for the measurements. It represents the degree to which the values produced by the measurement instrument are repeatable; that is, how closely an actual delay of 30 ms is reported as 30 ms. {Comment: 95 percent was chosen because (1) some confidence level is desirable to be able to remove outliers, which will be found in measuring any physical property; and (2) a particular confidence level should be specified so that the results of independent implementations can be compared.}
校准的目的是尽可能详细地确定仪器本身产生的系统和随机误差。至少应找到一个界限（“e”），以便报告的值至少在95%的时间内处于（真值-e）到（真值+e）的范围内。我们称“e”为测量的校准误差。它表示测量仪器产生的值可重复的程度；也就是说，30毫秒的实际延迟被报告为30毫秒的程度。{注释：选择95%是因为（1）需要某种置信水平来消除异常值，这将在测量任何物理特性时发现；（2）应指定特定的置信水平，以便可以比较独立实现的结果。}
From the discussion in the previous three sections, the error in measurements could be bounded by determining all the individual uncertainties, and adding them together to form
根据前三节中的讨论，测量误差可以通过确定所有单独的不确定度，并将它们相加形成
2*Rsource + Hinitial + Hfinal + Hrefl.
2*Rsource+Hinitial+Hfinal+Hrefl。
However, reasonable bounds on both the clock-related uncertainty captured by the first term and the host-related uncertainty captured by the last three terms should be possible by careful design techniques and calibrating the instruments using a known, isolated, network in a lab.
然而，通过仔细的设计技术和在实验室中使用已知、隔离的网络校准仪器，第一项捕获的时钟相关不确定度和最后三项捕获的主机相关不确定度的合理界限应是可能的。
The host-related uncertainties, Hinitial + Hfinal + Hrefl, could be bounded by connecting two instruments back-to-back with a high-speed serial link or isolated LAN segment. In this case, repeated measurements are measuring the same round-trip delay.
主机相关不确定性Hinitial+Hfinal+Hrefl可通过使用高速串行链路或隔离LAN段背靠背连接两台仪器来限定。在这种情况下，重复测量测量的是相同的往返延迟。
If the test packets are small, such a network connection has a minimal delay that may be approximated by zero. The measured delay therefore contains only systematic and random error in the instrumentation. The "average value" of repeated measurements is the systematic error, and the variation is the random error.
如果测试数据包很小，则这种网络连接具有可近似为零的最小延迟。因此，测量的延迟仅包含仪器中的系统和随机误差。重复测量的“平均值”是系统误差，变化是随机误差。
One way to compute the systematic error, and the random error to a 95% confidence is to repeat the experiment many times - at least hundreds of tests. The systematic error would then be the median. The random error could then be found by removing the systematic error from the measured values. The 95% confidence interval would be the range from the 2.5th percentile to the 97.5th percentile of these deviations from the true value. The calibration error "e" could then be taken to be the largest absolute value of these two numbers, plus the clock-related uncertainty. {Comment: as described, this bound is relatively loose since the uncertainties are added, and the absolute value of the largest deviation is used. As long as the resulting value is not a significant fraction of the measured values, it is a reasonable bound. If the resulting value is a significant fraction of the measured values, then more exact methods will be needed to compute the calibration error.}
计算系统误差和95%置信度的随机误差的一种方法是重复实验多次——至少数百次测试。系统误差即为中位数。然后，可以通过从测量值中去除系统误差来发现随机误差。95%的置信区间是这些偏离真实值的2.5%到97.5%之间的范围。然后，校准误差“e”可被视为这两个数字的最大绝对值，加上与时钟相关的不确定度。{注释：如上所述，由于添加了不确定度，该界限相对宽松，并且使用了最大偏差的绝对值。只要结果值不是测量值的重要部分，它就是一个合理的界限。如果结果值是测量值的重要部分，则更精确的定义为需要使用方法来计算校准误差。}
Note that random error is a function of measurement load. For example, if many paths will be measured by one instrument, this might increase interrupts, process scheduling, and disk I/O (for example, recording the measurements), all of which may increase the random error in measured singletons. Therefore, in addition to minimal load measurements to find the systematic error, calibration measurements should be performed with the same measurement load that the instruments will see in the field.
请注意，随机误差是测量负载的函数。例如，如果一台仪器将测量多条路径，这可能会增加中断、进程调度和磁盘I/O（例如，记录测量），所有这些都可能会增加测量单例中的随机误差。因此，除了最小负载测量以发现系统误差外，还应使用仪器在现场看到的相同测量负载进行校准测量。
We wish to reiterate that this statistical treatment refers to the calibration of the instrument; it is used to "calibrate the meter stick" and say how well the meter stick reflects reality.
我们希望重申，这种统计处理是指仪器的校准；它用于“校准仪表杆”，并说明仪表杆反映现实的程度。
In addition to calibrating the instruments for finite delay, two checks should be made to ensure that packets reported as losses were really lost. First, the threshold for loss should be verified. In particular, ensure the "reasonable" threshold is reasonable: that it is very unlikely a packet will arrive after the threshold value, and therefore the number of packets lost over an interval is not sensitive to the error bound on measurements. Second, consider the possibility that a packet arrives at the network interface, but is lost due to congestion on that interface or to other resource exhaustion (e.g. buffers) in the instrument.
除了为有限延迟校准仪器外，还应进行两次检查，以确保报告为丢失的数据包确实丢失。首先，应验证损失阈值。特别是，确保“合理”阈值是合理的：数据包不太可能在阈值之后到达，因此在一段时间间隔内丢失的数据包数量对测量值上的错误界限不敏感。其次，考虑数据包到达网络接口的可能性，但是由于该接口上的拥塞或该仪器中的其他资源耗尽（例如缓冲器）而丢失。
2.8. Reporting the Metric:
2.8. 报告指标：
The calibration and context in which the metric is measured MUST be carefully considered, and SHOULD always be reported along with metric results. We now present four items to consider: the Type-P of test packets, the threshold of infinite delay (if any), error calibration, and the path traversed by the test packets. This list is not exhaustive; any additional information that could be useful in interpreting applications of the metrics should also be reported.
必须仔细考虑测量公制的校准和环境，并应始终与公制结果一起报告。现在，我们提出了四个需要考虑的项目：测试数据包的类型P、无限延迟阈值（如果有）、错误校准和测试数据包通过的路径。这份清单并非详尽无遗；还应报告在解释指标应用时可能有用的任何其他信息。
As noted in the Framework document [1], the value of the metric may depend on the type of IP packets used to make the measurement, or "type-P". The value of Type-P-Round-trip-Delay could change if the protocol (UDP or TCP), port number, size, or arrangement for special treatment (e.g., IP precedence or RSVP) changes. The exact Type-P used to make the measurements MUST be accurately reported.
如框架文件[1]中所述，度量值可能取决于用于进行测量的IP数据包的类型，或“type-P”。如果协议（UDP或TCP）、端口号、大小或特殊处理安排（如IP优先级或RSVP）发生变化，则P型往返延迟的值可能会发生变化。必须准确报告用于进行测量的准确P型。
In addition, the threshold (or methodology to distinguish) between a large finite delay and loss MUST be reported.
此外，必须报告大型有限延迟和损失之间的阈值（或区分方法）。
+ If the systematic error can be determined, it SHOULD be removed from the measured values.
+ 如果可以确定系统误差，应将其从测量值中删除。
+ You SHOULD also report the calibration error, e, such that the true value is the reported value plus or minus e, with 95% confidence (see the last section.)
+ 还应报告校准误差e，以便真实值为报告值加上或减去e，置信度为95%（见最后一节）
+ If possible, the conditions under which a test packet with finite delay is reported as lost due to resource exhaustion on the measurement instrument SHOULD be reported.
+ 如果可能，应报告由于测量仪器上的资源耗尽而导致具有有限延迟的测试数据包丢失的情况。
Finally, the path traversed by the packet SHOULD be reported, if possible. In general it is impractical to know the precise path a given packet takes through the network. The precise path may be known for certain Type-P on short or stable paths. For example, if Type-P includes the record route (or loose-source route) option in the IP header, and the path is short enough, and all routers* on the path support record (or loose-source) route, and the Dst host copies the path from Src to Dst into the corresponding reply packet, then the path will be precisely recorded. This is impractical because the route must be short enough, many routers do not support (or are not configured for) record route, and use of this feature would often artificially worsen the performance observed by removing the packet from common-case processing. However, partial information is still valuable context. For example, if a host can choose between two links* (and hence two separate routes from Src to Dst), then the initial link used is valuable context. {Comment: For example, with Merit's NetNow setup, a Src on one NAP can reach a Dst on another NAP by either of several different backbone networks.}
最后，如果可能的话，应该报告数据包经过的路径。一般来说，要知道给定数据包通过网络的精确路径是不切实际的。对于短路径或稳定路径上的某些P型，可能已知精确路径。例如，如果Type-P在IP报头中包括记录路由（或松散源路由）选项，并且路径足够短，并且路径上的所有路由器*都支持记录（或松散源）路由，并且Dst主机将从Src到Dst的路径复制到相应的应答包中，则将精确地记录该路径。这是不切实际的，因为路由必须足够短，许多路由器不支持（或未配置）记录路由，并且使用此功能通常会人为地降低从常见情况处理中删除数据包所观察到的性能。然而，部分信息仍然是有价值的。例如，如果主机可以在两条链路*（以及从Src到Dst的两条独立路由）之间进行选择，则使用的初始链路是有价值的上下文。{注释：例如，使用Merit的NetNow设置，一个NAP上的Src可以通过几个不同的主干网络之一到达另一个NAP上的Dst。}
Given the singleton metric Type-P-Round-trip-Delay, we now define one particular sample of such singletons. The idea of the sample is to select a particular binding of the parameters Src, Dst, and Type-P, then define a sample of values of parameter T. The means for defining the values of T is to select a beginning time T0, a final time Tf, and an average rate lambda, then define a pseudo-random Poisson process of rate lambda, whose values fall between T0 and Tf. The time interval between successive values of T will then average 1/lambda.
考虑到单例度量类型-P-往返延迟，我们现在定义了此类单例的一个特定样本。样本的思想是选择参数Src、Dst和Type-P的特定绑定，然后定义参数T值的样本。定义T值的方法是选择开始时间T0、最终时间Tf和平均速率lambda，然后定义速率lambda的伪随机泊松过程，其值介于T0和Tf之间。随后，T连续值之间的时间间隔将平均为1/lambda。
{Comment: Note that Poisson sampling is only one way of defining a sample. Poisson has the advantage of limiting bias, but other methods of sampling might be appropriate for different situations. We encourage others who find such appropriate cases to use this general framework and submit their sampling method for standardization.}
{注释：请注意，泊松抽样只是定义样本的一种方式。泊松抽样具有限制偏差的优势，但其他抽样方法可能适用于不同的情况。我们鼓励发现此类适当情况的其他人使用此通用框架，并将其抽样方法提交标准化。}
3.1. Metric Name:
3.1. 度量名称：
Type-P-Round-trip-Delay-Poisson-Stream
P型往返延迟泊松流
3.2. Metric Parameters:
3.2. 公制参数：
+ 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
3.3. Metric Units:
3.3. 公制单位：
A sequence of pairs; the elements of each pair are:
成对的序列；每对的元素包括：
+ T, a time, and
+ T、 一次，和
+ dT, either a real number or an undefined number of seconds.
+ dT，一个实数或未定义的秒数。
The values of T in the sequence are monotonic increasing. Note that T would be a valid parameter to Type-P-Round-trip-Delay, and that dT would be a valid value of Type-P-Round-trip-Delay.
序列中T的值是单调递增的。请注意，T将是P型往返延迟的有效参数，dT将是P型往返延迟的有效值。
3.4. Definition:
3.4. 定义：
Given T0, Tf, and lambda, we compute a pseudo-random Poisson process beginning at or before T0, with average arrival rate lambda, and ending at or after Tf. Those time values greater than or equal to T0 and less than or equal to Tf are then selected. At each of the times in this process, we obtain the value of Type-P-Round-trip-Delay at this time. The value of the sample is the sequence made up of the resulting <time, delay> pairs. If there are no such pairs, the sequence is of length zero and the sample is said to be empty.
给定T0、Tf和lambda，我们计算一个伪随机泊松过程，从T0开始或之前，平均到达率lambda，到Tf结束或之后。然后选择大于或等于T0且小于或等于Tf的时间值。在这个过程中的每一次，我们都会得到此时的P型往返延迟值。样本值是由结果<时间，延迟>对组成的序列。如果没有这样的对，序列的长度为零，样本称为空。
3.5. Discussion:
3.5. 讨论：
The reader should be familiar with the in-depth discussion of Poisson sampling in the Framework document [1], which includes methods to compute and verify the pseudo-random Poisson process.
读者应熟悉框架文件[1]中对泊松抽样的深入讨论，其中包括计算和验证伪随机泊松过程的方法。
We specifically do not constrain the value of lambda, except to note the extremes. If the rate is too large, then the measurement traffic will perturb the network, and itself cause congestion. If the rate is too small, then you might not capture interesting network behavior. {Comment: We expect to document our experiences with, and suggestions for, lambda elsewhere, culminating in a "best current practices" document.}
我们特别不限制lambda的值，只注意极端情况。如果速率太大，那么测量流量将干扰网络，并且本身会导致拥塞。如果速率太小，则可能无法捕获有趣的网络行为。{评论：我们希望记录我们在其他地方与lambda合作的经验和建议，最终形成一份“当前最佳实践”文件。}
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.
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. {Comment: there is, of course, no claim that real Internet traffic arrives according to a Poisson arrival process.} The Poisson process is used to schedule the delay measurements. The test packets will generally not arrive at Dst according to a Poisson distribution, nor will response packets arrive at Src according to a Poisson distribution, since they are influenced by the network.
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。{注释：当然，没有人声称真正的互联网流量是根据泊松到达过程到达的。}泊松过程用于安排延迟测量。测试数据包通常不会根据泊松分布到达Dst，响应数据包也不会根据泊松分布到达Src，因为它们受到网络的影响。
All the singleton Type-P-Round-trip-Delay metrics in the sequence will have the same values of Src, Dst, and Type-P.
序列中的所有单例P型往返延迟度量将具有相同的Src、Dst和P型值。
Note also that, given one sample that runs from T0 to Tf, and given new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the subsequence of the given sample whose time values fall between T0' and Tf' are also a valid Type-P-Round-trip-Delay-Poisson-Stream sample.
还要注意，给定一个从T0运行到Tf的样本，并且给定新的时间值T0'和Tf'，使得T0<=T0'<=Tf'<=Tf'，其时间值介于T0'和Tf'之间的给定样本的子序列也是有效的P型往返延迟泊松流样本。
3.6. Methodologies:
3.6. 方法：
The methodologies follow directly from:
这些方法直接来自：
+ the selection of specific times, using the specified Poisson arrival process, and
+ 使用指定的泊松到达过程选择特定时间，以及
+ the methodologies discussion already given for the singleton Type-P-Round-trip-Delay metric.
+ 已经给出了单例类型P往返延迟度量的方法论讨论。
Care must, of course, be given to correctly handle out-of-order arrival of test or response packets; it is possible that the Src could send one test packet at TS[i], then send a second test packet (later) at TS[i+1], and it could receive the second response packet at TR[i+1], and then receive the first response packet (later) at TR[i].
当然，必须注意正确处理无序到达的测试或响应数据包；Src可能在TS[i]发送一个测试包，然后在TS[i+1]发送第二个测试包（稍后），并且可能在TR[i+1]接收第二个响应包，然后在TR[i]接收第一个响应包（稍后）。
3.7. Errors and Uncertainties:
3.7. 误差和不确定性：
In addition to sources of errors and uncertainties associated with methods employed to measure the singleton values that make up the sample, care must be given to analyze the accuracy of the Poisson process with respect to the wire-times of the sending of the test packets. Problems with this process could be caused by several
除了与用于测量构成样本的单态值的方法相关的误差和不确定性来源外，还必须注意分析与发送测试数据包的连线时间有关的泊松过程的准确性。此过程中的问题可能由以下几个原因引起
things, including problems with the pseudo-random number techniques used to generate the Poisson arrival process, or with jitter in the value of Hinitial (mentioned above as uncertainty in the singleton delay metric). The Framework document shows how to use the Anderson-Darling test to verify the accuracy of a Poisson process over small time frames. {Comment: The goal is to ensure that test packets are sent "close enough" to a Poisson schedule, and avoid periodic behavior.}
事情，包括用于生成泊松到达过程的伪随机数技术的问题，或Hinitial值的抖动（上文提到的单态延迟度量中的不确定性）。框架文档展示了如何使用Anderson-Darling检验在小时间范围内验证泊松过程的准确性。{注释：目标是确保发送的测试数据包“足够接近”泊松计划，并避免周期性行为。}
3.8. Reporting the Metric:
3.8. 报告指标：
You MUST report the calibration and context for the underlying singletons along with the stream. (See "Reporting the metric" for Type-P-Round-trip-Delay.)
您必须随流报告基础单例的校准和上下文。（关于P型往返延迟，请参见“报告度量”。）
Given the sample metric Type-P-Round-trip-Delay-Poisson-Stream, we now offer several statistics of that sample. These statistics are offered mostly to be illustrative of what could be done.
给定样本度量类型P-往返延迟泊松流，我们现在提供该样本的几种统计信息。提供这些统计数据主要是为了说明可以做些什么。
Given a Type-P-Round-trip-Delay-Poisson-Stream and a percent X between 0% and 100%, the Xth percentile of all the dT values in the Stream. In computing this percentile, undefined values are treated as infinitely large. Note that this means that the percentile could thus be undefined (informally, infinite). In addition, the Type-P-Round-trip-Delay-Percentile is undefined if the sample is empty.
给定P型往返延迟泊松流和0%到100%之间的百分比X，流中所有dT值的第X个百分位。在计算该百分位数时，未定义的值被视为无穷大。请注意，这意味着百分位数可能因此未定义（非正式地说是无限的）。此外，如果样本为空，则P型往返延迟百分比未定义。
Example: suppose we take a sample and the results are:
示例：假设我们抽取一个样本，结果如下：
Stream1 = <
<T1, 100 msec>
<T2, 110 msec>
<T3, undefined>
<T4, 90 msec>
<T5, 500 msec>
>
Stream1 = <
<T1, 100 msec>
<T2, 110 msec>
<T3, undefined>
<T4, 90 msec>
<T5, 500 msec>
>
Then the 50th percentile would be 110 msec, since 90 msec and 100 msec are smaller and 110 msec and 'undefined' are larger.
那么第50个百分位是110毫秒，因为90毫秒和100毫秒更小，110毫秒和“未定义”更大。
Note that if the possibility that a packet with finite delay is reported as lost is significant, then a high percentile (90th or 95th) might be reported as infinite instead of finite.
注意，如果具有有限延迟的数据包被报告为丢失的可能性很大，那么高百分位（第90或95位）可能被报告为无限而不是有限。
Given a Type-P-Round-trip-Delay-Poisson-Stream, the median of all the dT values in the Stream. In computing the median, undefined values are treated as infinitely large. As with Type-P-Round-trip-Delay-Percentile, Type-P-Round-trip-Delay-Median is undefined if the sample is empty.
给定一个P型往返延迟泊松流，流中所有dT值的中值。在计算中值时，未定义的值被视为无穷大。与P型往返延迟百分比一样，如果样本为空，则P型往返延迟中值未定义。
As noted in the Framework document, the median differs from the 50th percentile only when the sample contains an even number of values, in which case the mean of the two central values is used.
如框架文件所述，只有当样本包含偶数个值时，中位数才与第50百分位不同，在这种情况下，使用两个中心值的平均值。
Example: suppose we take a sample and the results are:
示例：假设我们抽取一个样本，结果如下：
Stream2 = <
<T1, 100 msec>
<T2, 110 msec>
<T3, undefined>
<T4, 90 msec>
>
Stream2 = <
<T1, 100 msec>
<T2, 110 msec>
<T3, undefined>
<T4, 90 msec>
>
Then the median would be 105 msec, the mean of 100 msec and 110 msec, the two central values.
然后中位数将是105毫秒，100毫秒和110毫秒的平均值，这两个中心值。
Given a Type-P-Round-trip-Delay-Poisson-Stream, the minimum of all the dT values in the Stream. In computing this, undefined values are treated as infinitely large. Note that this means that the minimum could thus be undefined (informally, infinite) if all the dT values are undefined. In addition, the Type-P-Round-trip-Delay-Minimum is undefined if the sample is empty.
给定一个P型往返延迟泊松流，流中所有dT值的最小值。在计算时，未定义的值被视为无穷大。注意，这意味着如果所有dT值都未定义，则最小值可能因此未定义（非正式地说，无限）。此外，如果样本为空，则P-往返-延迟-最小类型未定义。
In the above example, the minimum would be 90 msec.
在上述示例中，最小值为90毫秒。
Given a Type-P-Round-trip-Delay-Poisson-Stream and a time duration threshold, the fraction of all the dT values in the Stream less than or equal to the threshold. The result could be as low as 0% (if all the dT values exceed threshold) or as high as 100%. Type-P-Round-trip-Delay-Inverse-Percentile is undefined if the sample is empty.
给定P型往返延迟泊松流和持续时间阈值，流中所有dT值的分数小于或等于阈值。结果可能低至0%（如果所有dT值超过阈值），或高达100%。如果样本为空，则类型-P-往返-延迟-反向百分比未定义。
In the above example, the Inverse-Percentile of 103 msec would be 50%.
在上面的例子中，103毫秒的反百分位为50%。
Conducting Internet measurements raises both security and privacy concerns. This memo does not specify an implementation of the metrics, so it does not directly affect the security of the Internet nor of applications which run on the Internet. However, implementations of these metrics must be mindful of security and privacy concerns.
进行互联网测量会引起安全和隐私问题。此备忘录未指定指标的实现，因此它不会直接影响Internet或在Internet上运行的应用程序的安全性。然而，这些指标的实现必须考虑安全和隐私问题。
There are two types of security concerns: potential harm caused by the measurements, and potential harm to the measurements. The measurements could cause harm because they are active, and inject packets into the network. The measurement parameters MUST be carefully selected so that the measurements inject trivial amounts of additional traffic into the networks they measure. If they inject "too much" traffic, they can skew the results of the measurement, and in extreme cases cause congestion and denial of service.
存在两种类型的安全问题：由测量引起的潜在危害和对测量的潜在危害。这些测量可能会造成危害，因为它们处于活动状态，并将数据包注入网络。必须仔细选择测量参数，以便测量将少量的额外流量注入到它们测量的网络中。如果它们注入了“太多”的流量，它们可能会扭曲测量结果，在极端情况下会导致拥塞和拒绝服务。
The measurements themselves could be harmed by routers giving measurement traffic a different priority than "normal" traffic, or by an attacker injecting artificial measurement traffic. If routers can recognize measurement traffic and treat it separately, the measurements will not reflect actual user traffic. If an attacker injects artificial traffic that is accepted as legitimate, the loss rate will be artificially lowered. Therefore, the measurement methodologies SHOULD include appropriate techniques to reduce the probability measurement traffic can be distinguished from "normal" traffic. Authentication techniques, such as digital signatures, may be used where appropriate to guard against injected traffic attacks.
路由器赋予测量流量不同于“正常”流量的优先级，或者攻击者注入人工测量流量，可能会损害测量本身。如果路由器能够识别测量流量并单独处理，那么测量将不会反映实际的用户流量。如果攻击者注入被认为合法的人工流量，则损失率将被人为降低。因此，测量方法应包括适当的技术，以降低测量流量可与“正常”流量区分的概率。在适当的情况下，可以使用诸如数字签名之类的认证技术来防止注入流量攻击。
The privacy concerns of network measurement are limited by the active measurements described in this memo. Unlike passive measurements, there can be no release of existing user data.
网络测量的隐私问题受到本备忘录中所述的主动测量的限制。与被动测量不同，不能释放现有用户数据。
Special thanks are due to Vern Paxson and to Will Leland for several useful suggestions.
特别感谢Vern Paxson和Will Leland提出的一些有用的建议。
[1] Paxson, D., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
[1] Paxson，D.，Almes，G.，Mahdavi，J.和M.Mathis，“IP性能度量框架”，RFC 2330，1998年5月。
[2] Almes, G., Kalidindi,S. and M. Zekauskas, "A One-way Delay Metric for IPPM", RFC 2679, September 1999.
[2] Almes，G.，Kalidini，S.和M.Zekauskas，“IPPM的单向延迟度量”，RFC 2679，1999年9月。
[3] Mills, D., "Network Time Protocol (v3)", RFC 1305, April 1992.
[3] Mills，D.，“网络时间协议（v3）”，RFC13051992年4月。
[4] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring Connectivity", RFC 2678, September 1999.
[4] Mahdavi，J.和V.Paxson，“测量连接性的IPPM度量”，RFC 2678，1999年9月。
[5] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[5] Postel，J.，“互联网协议”，STD 5，RFC 7911981年9月。
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[6] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
Guy Almes Advanced Network & Services, Inc. 200 Business Park Drive Armonk, NY 10504 USA
Guy Almes Advanced Network&Services，Inc.美国纽约州阿蒙克商业园区大道200号，邮编10504
Phone: +1 914 765 1120
EMail: almes@advanced.org
Phone: +1 914 765 1120
EMail: almes@advanced.org
Sunil Kalidindi Advanced Network & Services, Inc. 200 Business Park Drive Armonk, NY 10504 USA
Sunil Kaliddi Advanced Network&Services，Inc.美国纽约州阿蒙克商业园区大道200号，邮编10504
Phone: +1 914 765 1128
EMail: kalidindi@advanced.org
Phone: +1 914 765 1128
EMail: kalidindi@advanced.org
Matthew J. Zekauskas Advanced Network & Services, Inc. 200 Business Park Drive Armonk, NY 10504 USA
Matthew J.Zekauskas Advanced Network&Services，Inc.美国纽约州阿蒙克商业园区大道200号，邮编10504
Phone: +1 914 765 1112
EMail: matt@advanced.org
Phone: +1 914 765 1112
EMail: matt@advanced.org
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Acknowledgement
确认
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