Network Working Group G. Almes
Request for Comments: 2680 S. Kalidindi
Category: Standards Track M. Zekauskas
Advanced Network & Services
September 1999
Network Working Group G. Almes
Request for Comments: 2680 S. Kalidindi
Category: Standards Track M. Zekauskas
Advanced Network & Services
September 1999
A One-way Packet Loss Metric for IPPM
IPPM的单向丢包度量
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 one-way packet loss across Internet paths. It builds on notions introduced and discussed in the IPPM Framework document, RFC 2330 [1]; the reader is assumed to be familiar with that document.
此备忘录定义了跨Internet路径的单向数据包丢失的度量。它以IPPM框架文件RFC 2330[1]中介绍和讨论的概念为基础；假定读者熟悉该文档。
This memo is intended to be parallel in structure to a companion document for One-way Delay ("A One-way Delay Metric for IPPM") [2]; the reader is assumed to be familiar with that document.
本备忘录旨在在结构上与单向延迟（“IPPM单向延迟度量”）的配套文件平行[2]；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 RFC 2119 [5]. 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[5]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-One-way-Loss, is introduced to measure a single observation of packet transmission or loss.
+ 引入了一种称为Type-P-One-way-Loss的“单例”分析度量来测量分组传输或丢失的单个观测值。
+ Using this singleton metric, a 'sample', called Type-P-One-way-Loss-Poisson-Stream, is introduced to measure a sequence of singleton transmissions and/or losses measured at times taken from a Poisson process.
+ 使用此单例度量，引入称为Type-P-One-way-Loss-Poisson-Stream的“样本”，以测量单例传输序列和/或在从Poisson过程中获取的时间测量的损耗。
+ Using this sample, several 'statistics' of the sample are defined and discussed.
+ 使用该样本，定义并讨论了样本的几个“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”。
1.1. Motivation:
1.1. 动机：
Understanding one-way packet loss of Type-P* packets from a source host* to a destination host is useful for several reasons:
了解从源主机*到目标主机*的P*型数据包的单向数据包丢失是有用的，原因如下：
+ Some applications do not perform well (or at all) if end-to-end loss between hosts is large relative to some threshold value.
+ 如果主机之间的端到端损失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）。
+ Excessive packet loss may make it difficult to support certain real-time applications (where the precise threshold of "excessive" depends on the application).
+ 过度的数据包丢失可能使支持某些实时应用程序变得困难（其中“过度”的精确阈值取决于应用程序）。
+ The larger the value of packet loss, the more difficult it is for transport-layer protocols to sustain high bandwidths.
+ 数据包丢失的值越大，传输层协议就越难以维持高带宽。
+ The sensitivity of real-time applications and of transport-layer protocols to loss become especially important when very large delay-bandwidth products must be supported.
+ 当必须支持非常大的延迟带宽产品时，实时应用程序和传输层协议对丢失的敏感性变得尤为重要。
The measurement of one-way loss instead of round-trip loss is motivated by the following factors:
测量单向损耗而非往返损耗的原因如下：
+ In today's Internet, the path from a source to a destination may be different than 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. Measuring each path independently highlights the performance difference between the two paths which may traverse different Internet service providers, and even radically different types of networks (for example, research versus commodity networks, or ATM versus packet-over-SONET).
+ 在今天的互联网中，从源到目的地的路径可能不同于从目的地返回到源的路径（“非对称路径”），因此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。独立测量每条路径突出了两条路径之间的性能差异，这两条路径可能穿越不同的互联网服务提供商，甚至是完全不同类型的网络（例如，研究网络与商品网络，或ATM与SONET上的数据包）。
+ 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. For example, a file transfer using TCP may depend more on the performance in the direction that data flows, rather than the direction in which acknowledgements travel.
+ 应用程序的性能可能主要取决于一个方向上的性能。例如，使用TCP的文件传输可能更依赖于数据流方向的性能，而不是确认的传输方向。
+ 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. Measuring the paths independently allows the verification of both guarantees.
+ 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。独立测量路径可以验证两种保证。
It is outside the scope of this document to say precisely how loss metrics would be applied to specific problems.
准确说明损失指标如何应用于具体问题超出了本文件的范围。
{Comment: the terminology below differs from that defined by ITU-T
documents (e.g., G.810, "Definitions and terminology for
synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
performance"), but is consistent with the IPPM Framework document.
In general, these differences derive from the different backgrounds;
the ITU-T documents historically have a telephony origin, while the
authors of this document (and the Framework) have a computer systems
background. Although the terms defined below have no direct
equivalent in the ITU-T definitions, after our definitions we will
provide a rough mapping. However, note one potential confusion: our
definition of "clock" is the computer operating systems definition
denoting a time-of-day clock, while the ITU-T definition of clock
denotes a frequency reference.}
{Comment: the terminology below differs from that defined by ITU-T
documents (e.g., G.810, "Definitions and terminology for
synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
performance"), but is consistent with the IPPM Framework document.
In general, these differences derive from the different backgrounds;
the ITU-T documents historically have a telephony origin, while the
authors of this document (and the Framework) have a computer systems
background. Although the terms defined below have no direct
equivalent in the ITU-T definitions, after our definitions we will
provide a rough mapping. However, note one potential confusion: our
definition of "clock" is the computer operating systems definition
denoting a time-of-day clock, while the ITU-T definition of clock
denotes a frequency reference.}
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*
Synchronization 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. {Comment: A rough ITU-T equivalent is "time error".}
同步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。{注释：粗略的ITU-T等价物是“时间错误”。}
accuracy*
准确度*
Accuracy 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. {Comment: A rough ITU-T equivalent is "time error from UTC".}
精度度量给定时钟与UTC一致的程度。例如，主机上的时钟可能比UTC慢27.1毫秒。{注释：粗略的ITU-T等价物是“UTC时间错误”。}
resolution*
决议*
Resolution measures the precision of a given clock. For example, the clock on an old Unix host might advance only once every 10 msec, and thus have a resolution of only 10 msec. {Comment: A very rough ITU-T equivalent is "sampling period".}
分辨率测量给定时钟的精度。例如，旧Unix主机上的时钟可能仅每10毫秒前进一次，因此分辨率仅为10毫秒。{注释：一个非常粗略的ITU-T等价物是“采样周期”。}
skew*
歪斜*
Skew 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. {Comment: A rough ITU-T equivalent is "time drift".}
倾斜测量精度或同步随时间的变化。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。{注释：粗略的ITU-T等价物是“时间漂移”。}
2.1. Metric Name:
2.1. 度量名称：
Type-P-One-way-Packet-Loss
P型单向丢包
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-One-way-Packet-Loss is either a zero (signifying successful transmission of the packet) or a one (signifying loss).
P型单向分组丢失的值是零（表示分组成功传输）或一（表示丢失）。
2.4. Definition:
2.4. 定义：
>>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 0<< means that Src sent the first bit of a Type-P packet to Dst at wire-time* T and that Dst received that packet.
>>在T从Src到Dst的*Type-P-One-way-Packet-Loss*为0<<意味着Src在连线时间*T将P型数据包的第一位发送到Dst，并且Dst接收到该数据包。
>>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 1<< means that Src sent the first bit of a type-P packet to Dst at wire-time T and that Dst did not receive that packet.
>>T处从Src到Dst的*Type-P-One-way-Packet-Loss*为1<<意味着Src在连线时间T将P型数据包的第一位发送到Dst，而Dst没有接收到该数据包。
2.5. Discussion:
2.5. 讨论：
Thus, Type-P-One-way-Packet-Loss is 0 exactly when Type-P-One-way-Delay is a finite value, and it is 1 exactly when Type-P-One-way-Delay is undefined.
因此，当Type-P-One-way-Delay为有限值时，Type-P-One-way-Packet-Loss精确为0，当Type-P-One-way-Delay未定义时，Type-P-One-way-Delay精确为1。
The following issues are likely to come up in practice:
在实践中可能会出现以下问题：
+ A given methodology will have to include a way to distinguish between a packet loss and a very large (but finite) delay. As noted by Mahdavi and Paxson [3], simple upper bounds (such as the 255 seconds theoretical upper bound on the lifetimes of IP packets [4]) 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, there may be no harm in treating a large delay as packet loss. An audio playback packet, for example, that arrives only after the playback point may as well have been lost.}
+ 给定的方法必须包括区分数据包丢失和非常大（但有限）延迟的方法。正如Mahdavi和Paxson[3]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[4]），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：注意，对于这些度量的许多应用程序，将大延迟视为数据包丢失可能没有害处。例如，仅在播放点之后到达的音频播放数据包也可能丢失。}
+ If the packet arrives, but is corrupted, then it is counted as lost. {Comment: one is tempted to count the packet as received since corruption and packet loss are related but distinct phenomena. If the IP header is corrupted, however, one cannot be sure about the source or destination IP addresses and is thus on shaky grounds about knowing that the corrupted received packet corresponds to a given sent test packet. Similarly, if other parts of the packet needed by the methodology to know that the corrupted received packet corresponds to a given sent test packet, then such a packet would have to be counted as lost. Counting these packets as lost but packet with corruption in other parts of the packet as not lost would be inconsistent.}
+ 如果数据包到达，但已损坏，则视为丢失。{注释：由于损坏和数据包丢失是相关但不同的现象，人们很容易将数据包计算为已接收数据包。但是，如果IP头已损坏，则无法确定源或目标IP地址，因此无法确定已损坏的接收数据包是否对应于给定的已发送测试数据包。类似地，如果该方法需要数据包的其他部分知道损坏的接收数据包对应于给定的发送测试数据包，则该数据包必须被计为丢失。将这些数据包计为丢失，但将数据包其他部分损坏的数据包计为未丢失将不一致。}
+ 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.
+ 如果数据包沿着路径（一个或多个路径）复制，以便多个未损坏的副本到达目的地，则该数据包被视为已接收。
+ 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, one possible methodology would proceed as follows:
通常，对于给定的P型，一种可能的方法如下：
+ Arrange that Src and Dst have clocks that are synchronized with each other. The degree of synchronization is a parameter of the methodology, and depends on the threshold used to determine loss (see below).
+ 安排Src和Dst具有相互同步的时钟。同步程度是该方法的一个参数，取决于用于确定损失的阈值（见下文）。
+ At the Src host, select Src and Dst IP addresses, and form a test packet of Type-P with these addresses.
+ 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。
+ At the Dst host, arrange to receive the packet.
+ 在Dst主机上，安排接收数据包。
+ At the Src host, place a timestamp in the prepared Type-P packet, and send it towards Dst.
+ 在Src主机上，在准备好的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, the one-way packet-loss is taken to be zero.
+ 如果数据包在合理的时间段内到达，则单向数据包丢失被视为零。
+ If the packet fails to arrive within a reasonable period of time, the one-way packet-loss is taken to be one. Note that the threshold of "reasonable" here is a parameter of the methodology.
+ 如果数据包未能在合理的时间段内到达，则单向数据包丢失被视为1。请注意，此处的“合理”阈值是该方法的一个参数。
{Comment: The definition of reasonable is intentionally vague, and is intended to indicate a value "Th" so large that any value in the closed interval [Th-delta, Th+delta] is an equivalent threshold for loss. Here, delta encompasses all error in clock synchronization along the measured path. If there is a single value after which the packet must be counted as lost, then we reintroduce the need for a degree of clock synchronization similar to that needed for one-way delay. Therefore, if a measure of packet loss parameterized by a specific non-huge "reasonable" time-out value is needed, one can always measure one-way delay and see what percentage of packets from a given stream exceed a given time-out value.}
{注释：合理的定义故意含糊不清，目的是表示一个值“Th”，该值太大，以至于闭合区间内的任何值[Th delta，Th+delta]是丢失的等效阈值。此处，增量包含沿测量路径的时钟同步中的所有错误。如果存在一个值，在该值之后，数据包必须被计为丢失，则我们重新引入时钟同步度的需要，类似于单向延迟所需的时钟同步度。因此，如果数据包丢失的测量值如果需要一个特定的非巨大的“合理”超时值来计量，则可以始终测量单向延迟，并查看来自给定流的数据包超过给定超时值的百分比。}
Issues such as the packet format, the means by which Dst knows when to expect the test packet, and the means by which Src and Dst are synchronized are outside the scope of this document. {Comment: We plan to document elsewhere our own work in describing such more detailed implementation techniques and we encourage others to as well.}
数据包格式、Dst知道何时期望测试数据包的方法以及Src和Dst同步的方法等问题不在本文件的范围内。{评论：我们计划在其他地方记录我们自己在描述这种更详细的实现技术方面的工作，我们鼓励其他人也这样做。}
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.
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。框架文件就这一点提供了一般性指导。
For loss, there are three sources of error:
对于损失，有三个错误来源：
+ Synchronization between clocks on Src and Dst.
+ Src和Dst上时钟之间的同步。
+ The packet-loss threshold (which is related to the synchronization between clocks).
+ 数据包丢失阈值（与时钟之间的同步有关）。
+ Resource limits in the network interface or software on the receiving instrument.
+ 接收仪器网络接口或软件中的资源限制。
The first two sources are interrelated and could result in a test packet with finite delay being reported as lost. Type-P-One-way-Packet-Loss is 0 if the test packet does not arrive, or if it does arrive and the difference between Src timestamp and Dst timestamp is greater than the "reasonable period of time", or loss threshold. If the clocks are not sufficiently synchronized, the loss threshold may not be "reasonable" - the packet may take much less time to arrive than its Src timestamp indicates. Similarly, if the loss threshold is set too low, then many packets may be counted as lost. The loss threshold must be high enough, and the clocks synchronized well enough so that a packet that arrives is rarely counted as lost. (See the discussions in the previous two sections.)
前两个源是相互关联的，可能导致有限延迟的测试数据包被报告为丢失。如果测试数据包没有到达，或者它确实到达并且Src时间戳和Dst时间戳之间的差值大于“合理时间段”或丢失阈值，则Type-P-One-way-Packet-Loss为0。如果时钟没有充分同步，丢失阈值可能不“合理”-数据包到达的时间可能比其Src时间戳指示的时间少得多。类似地，如果丢失阈值设置得太低，则许多数据包可能被视为丢失。丢失阈值必须足够高，并且时钟同步得足够好，以便到达的数据包很少被视为丢失。（请参阅前两节中的讨论。）
Since the sensitivity of packet loss measurement to lack of clock synchronization is less than for delay, we refer the reader to the treatment of synchronization errors in the One-way Delay metric [2] for more details.
由于分组丢失测量对缺少时钟同步的敏感性小于对延迟的敏感性，我们请读者参考单向延迟度量[2]中的同步错误处理以了解更多细节。
The last source of error, resource limits, cause the packet to be dropped by the measurement instrument, and counted as lost when in fact the network delivered the packet in reasonable time.
最后一个错误源，即资源限制，导致数据包被测量仪器丢弃，当网络在合理的时间内交付数据包时，被视为丢失。
The measurement instruments should be calibrated such that the loss threshold is reasonable for application of the metrics and the clocks are synchronized enough so the loss threshold remains reasonable.
应校准测量仪器，以确保损耗阈值适用于量度，且时钟足够同步，从而使损耗阈值保持合理。
In addition, the instruments should be checked to ensure the that the possibility a packet arrives at the network interface, but is lost due to congestion on the interface or to other resource exhaustion (e.g., buffers) on the instrument is low.
此外，应检查仪器，以确保数据包到达网络接口但由于接口拥塞或仪器上的其他资源耗尽（如缓冲区）而丢失的可能性较低。
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: Type-P of the test packets, the loss threshold, instrument 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P型、丢失阈值、仪器校准和测试数据包穿过的路径。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-One-way-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，则类型-P-单向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。
The threshold (or methodology to distinguish) between a large finite delay and loss MUST be reported.
必须报告大型有限延迟和损失之间的阈值（或区分方法）。
The degree of synchronization between the Src and Dst clocks MUST be reported. If possible, possibility that a test packet that arrives at the Dst network interface is reported as lost due to resource exhaustion on Dst SHOULD be reported.
必须报告Src和Dst时钟之间的同步程度。如果可能，应报告到达Dst网络接口的测试数据包由于Dst上的资源耗尽而丢失的可能性。
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. 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, 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,
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。如果Type-P在IP报头中包含记录路由（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，则将精确记录路径。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，
a Src on one NAP can reach a Dst on another NAP by either of several different backbone networks.}
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-One-way-Packet-Loss, 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.
给定单例度量Type-P-One-way-Packet-Loss，我们现在定义这样的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-One-way-Packet-Loss-Poisson-Stream
P型单向丢包泊松流
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
+ L, either a zero or a one
+ 五十、 要么是零，要么是一
The values of T in the sequence are monotonic increasing. Note that T would be a valid parameter to Type-P-One-way-Packet-Loss, and that L would be a valid value of Type-P-One-way-Packet-Loss.
序列中T的值是单调递增的。注意，T是Type-P-One-way-Packet-Loss的有效参数，L是Type-P-One-way-Packet-Loss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-One-way-Packet-Loss at this time. The value of the sample is the sequence made up of the resulting <time, loss> 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Type-P-One-way-Packet-Loss的值。样本值是由结果<时间，损失>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. The Poisson process is used to schedule the delay measurements. The test packets will generally not arrive at Dst 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。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，因为它们受到网络的影响。
{Comment: there is, of course, no claim that real Internet traffic arrives according to a Poisson arrival process.
{注释：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。
It is important to note that, in contrast to this metric, loss rates observed by transport connections do not reflect unbiased samples. For example, TCP transmissions both (1) occur in bursts, which can
需要注意的是，与此指标相反，传输连接观察到的损耗率并不反映无偏样本。例如，TCP传输都（1）以突发方式发生，这可能导致
induce loss due to the burst volume that would not otherwise have been observed, and (2) adapt their transmission rate in an attempt to minimize the loss rate observed by the connection.}
由于突发量而导致的损失（否则无法观察到），以及（2）调整其传输速率，以尽量减少连接观察到的损失率。}
All the singleton Type-P-One-way-Packet-Loss metrics in the sequence will have the same values of Src, Dst, and Type-P.
序列中的所有单例Type-P-One-way-Packet-Loss度量将具有相同的Src、Dst和Type-P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-One-way-Packet-Loss-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型单向丢包泊松流样本。
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-One-way-Packet-Loss metric.
+ 已经给出了单例类型P单向丢包度量的方法论讨论。
Care must be given to correctly handle out-of-order arrival of test packets; it is possible that the Src could send one test packet at TS[i], then send a second one (later) at TS[i+1], while the Dst could receive the second test packet at TR[i+1], and then receive the first one (later) at TR[i].
必须注意正确处理无序到达的测试数据包；Src可能在TS[i]发送一个测试数据包，然后在TS[i+1]发送第二个（稍后），而Dst可能在TR[i+1]接收第二个测试数据包，然后在TR[i]接收第一个（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 arrival process of the wire-times of the sending of the test packets. Problems with this process could be caused by several things, including problems with the pseudo-random number techniques used to generate the Poisson arrival process. The Framework document shows how to use the Anderson-Darling test verify the accuracy of the Poisson process over small time frames. {Comment: The goal is to ensure that the test packets are sent "close enough" to a Poisson schedule, and avoid periodic behavior.}
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，还必须注意分析测试数据包发送线时间的泊松到达过程的准确性。这一过程的问题可能由多种因素引起，包括用于生成泊松到达过程的伪随机数技术的问题。框架文档展示了如何使用Anderson-Darling测试验证小时间范围内泊松过程的准确性。{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：
The calibration and context for the underlying singletons MUST be reported along with the stream. (See "Reporting the metric" for Type-P-One-way-Packet-Loss.)
底层单例的校准和上下文必须与流一起报告。（请参阅“报告度量”了解P型单向丢包。）
Given the sample metric Type-P-One-way-Packet-Loss-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-One-way-Packet-Loss-Poisson-Stream，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-One-way-Packet-Loss-Poisson-Stream, the average of all the L values in the Stream. In addition, the Type-P-One-way-Packet-Loss-Average is undefined if the sample is empty.
给定一个类型为P-单向-丢包-泊松-流，流中所有L值的平均值。此外，如果样本为空，则类型P-One-way-Packet-Loss-Average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, 0>
<T2, 0>
<T3, 1>
<T4, 0>
<T5, 0>
>
Stream1 = <
<T1, 0>
<T2, 0>
<T3, 1>
<T4, 0>
<T5, 0>
>
Then the average would be 0.2.
那么平均值是0.2。
Note that, since healthy Internet paths should be operating at loss rates below 1% (particularly if high delay-bandwidth products are to be sustained), the sample sizes needed might be larger than one would like. Thus, for example, if one wants to discriminate between various fractions of 1% over one-minute periods, then several hundred samples per minute might be needed. This would result in larger values of lambda than one would ordinarily want.
请注意，由于健康的Internet路径应以低于1%的丢失率运行（特别是如果要维持高延迟带宽产品），因此所需的样本量可能比人们希望的要大。因此，例如，如果想要在一分钟内区分1%的各种分数，那么每分钟可能需要几百个样本。这将导致lambda的值大于人们通常想要的值。
Note that although the loss threshold should be set such that any errors in loss are not significant, if the possibility that a packet which arrived is counted as lost due to resource exhaustion is significant compared to the loss rate of interest, Type-P-One-way-Packet-Loss-Average will be meaningless.
注意，尽管应将丢失阈值设置为使得丢失中的任何错误都不显著，但是如果由于资源耗尽而到达的分组被计为丢失的可能性与丢失利率相比是显著的，则Type-P-One-way-packet-loss-Average将是无意义的。
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。
Thanks are due to Matt Mathis for encouraging this work and for calling attention on so many occasions to the significance of packet loss.
感谢Matt Mathis鼓励这项工作，并多次提醒大家注意数据包丢失的重要性。
Thanks are due also to Vern Paxson for his valuable comments on early drafts, and to Garry Couch and Will Leland for several useful suggestions.
感谢Vern Paxson对早期草稿提出的宝贵意见，以及Garry Coach和Will Leland提出的一些有用建议。
[1] Paxson, V., Almes,G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
[1] Paxson，V.，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] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring Connectivity", RFC 2678, September 1999.
[3] Mahdavi，J.和V.Paxson，“测量连接性的IPPM度量”，RFC 2678，1999年9月。
[4] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[4] Postel，J.，“互联网协议”，STD 5，RFC 7911981年9月。
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[5] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[6] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996.
[6] Bradner，S.，“互联网标准过程——第3版”，BCP 9，RFC 2026，1996年10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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