Network Working Group V. Raisanen
Request for Comments: 3432 Nokia
Category: Standards Track G. Grotefeld
Motorola
A. Morton
AT&T Labs
November 2002
Network Working Group V. Raisanen
Request for Comments: 3432 Nokia
Category: Standards Track G. Grotefeld
Motorola
A. Morton
AT&T Labs
November 2002
Network performance measurement with periodic streams
周期流网络性能测量
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 (2002). All Rights Reserved.
版权所有（C）互联网协会（2002年）。版权所有。
Abstract
摘要
This memo describes a periodic sampling method and relevant metrics for assessing the performance of IP networks. First, the memo motivates periodic sampling and addresses the question of its value as an alternative to the Poisson sampling described in RFC 2330. The benefits include applicability to active and passive measurements, simulation of constant bit rate (CBR) traffic (typical of multimedia communication, or nearly CBR, as found with voice activity detection), and several instances in which analysis can be simplified. The sampling method avoids predictability by mandating random start times and finite length tests. Following descriptions of the sampling method and sample metric parameters, measurement methods and errors are discussed. Finally, we give additional information on periodic measurements, including security considerations.
本备忘录描述了评估IP网络性能的定期抽样方法和相关指标。首先，备忘录激励定期抽样，并解决其价值问题，作为RFC 2330中所述泊松抽样的替代方案。其优点包括适用于主动和被动测量，模拟恒定比特率（CBR）流量（典型的多媒体通信，或接近CBR，如语音活动检测），以及可以简化分析的几个实例。抽样方法通过强制随机开始时间和有限长度测试来避免可预测性。在描述采样方法和采样度量参数之后，讨论了测量方法和误差。最后，我们提供了有关定期测量的附加信息，包括安全考虑。
Table of Contents
目录
1. Conventions used in this document........................... 2
2. Introduction................................................ 3
2.1 Motivation.............................................. 3
3. Periodic Sampling Methodology............................... 4
4. Sample metrics for periodic streams......................... 5
4.1 Metric name............................................. 5
4.2 Metric parameters....................................... 5
4.3 High level description of the procedure to collect a
sample.................................................. 7
4.4 Discussion.............................................. 8
4.5 Additional Methodology Aspects.......................... 9
4.6 Errors and uncertainties................................ 9
4.7 Reporting............................................... 13
5. Additional discussion on periodic sampling.................. 14
5.1 Measurement applications................................ 15
5.2 Statistics calculable from one sample................... 18
5.3 Statistics calculable from multiple samples............. 18
5.4 Background conditions................................... 19
5.5 Considerations related to delay......................... 19
6. Security Considerations..................................... 19
6.1 Denial of Service Attacks............................... 19
6.2 User data confidentiality............................... 20
6.3 Interference with the metric............................ 20
7. IANA Considerations......................................... 20
8. Normative References........................................ 20
9. Informative References...................................... 21
10. Acknowledgments............................................. 21
11. Author's Addresses.......................................... 22
12. Full Copyright Statement.................................... 23
1. Conventions used in this document........................... 2
2. Introduction................................................ 3
2.1 Motivation.............................................. 3
3. Periodic Sampling Methodology............................... 4
4. Sample metrics for periodic streams......................... 5
4.1 Metric name............................................. 5
4.2 Metric parameters....................................... 5
4.3 High level description of the procedure to collect a
sample.................................................. 7
4.4 Discussion.............................................. 8
4.5 Additional Methodology Aspects.......................... 9
4.6 Errors and uncertainties................................ 9
4.7 Reporting............................................... 13
5. Additional discussion on periodic sampling.................. 14
5.1 Measurement applications................................ 15
5.2 Statistics calculable from one sample................... 18
5.3 Statistics calculable from multiple samples............. 18
5.4 Background conditions................................... 19
5.5 Considerations related to delay......................... 19
6. Security Considerations..................................... 19
6.1 Denial of Service Attacks............................... 19
6.2 User data confidentiality............................... 20
6.3 Interference with the metric............................ 20
7. IANA Considerations......................................... 20
8. Normative References........................................ 20
9. Informative References...................................... 21
10. Acknowledgments............................................. 21
11. Author's Addresses.......................................... 22
12. Full Copyright Statement.................................... 23
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 [2]. 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 that the results of measurements from two different implementations are comparable, and to note instances in which 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[2]中的描述进行解释。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。
This memo describes a sampling method and performance metrics relevant to certain applications of IP networks. The original driver for this work was Quality of Service of interactive periodic streams, such as multimedia conferencing over IP, but the idea of periodic sampling and measurement has wider applicability. Interactive multimedia traffic is used as an example below to illustrate the concept.
本备忘录描述了与IP网络特定应用相关的抽样方法和性能指标。这项工作最初的驱动因素是交互式周期流的服务质量，例如通过IP的多媒体会议，但周期性采样和测量的思想具有更广泛的适用性。下面以交互式多媒体通信为例来说明这一概念。
Transmitting equally sized packets (or mostly same-size packets) through a network at regular intervals simulates a constant bit-rate (CBR), or a nearly CBR multimedia bit stream. Hereafter, these packets are called periodic streams. Cases of "mostly same-size packets" may be found in applications that have multiple coding methods (e.g. digitally coded comfort noise during silence gaps in speech).
以固定间隔通过网络传输同等大小的数据包（或大部分相同大小的数据包）模拟恒定比特率（CBR）或接近CBR的多媒体比特流。此后，这些包被称为周期流。在采用多种编码方法的应用中，可能会出现“大小基本相同的数据包”的情况（例如，在语音沉默间隙期间，数字编码的舒适噪声）。
In the following sections, a sampling methodology and metrics are presented for periodic streams. The measurement results may be used in derivative metrics such as average and maximum delays. The memo seeks to formalize periodic stream measurements to achieve comparable results between independent implementations.
在以下部分中，将介绍周期流的采样方法和度量。测量结果可用于衍生指标，如平均和最大延迟。该备忘录试图将定期流测量形式化，以在独立实现之间获得可比较的结果。
As noted in the IPPM framework RFC 2330 [3], a sample metric using regularly spaced singleton tests has some limitations when considered from a general measurement point of view: only part of the network performance spectrum is sampled. However, some applications also sample this limited performance spectrum and their performance may be of critical interest.
如IPPM框架RFC 2330[3]中所述，当从一般测量角度考虑时，使用规则间隔单例测试的样本度量有一些局限性：仅对网络性能谱的一部分进行采样。然而，一些应用程序也会对这一有限的性能谱进行采样，它们的性能可能是至关重要的。
Periodic sampling is useful for the following reasons:
由于以下原因，定期采样非常有用：
* It is applicable to passive measurement, as well as active measurement.
* 它既适用于被动测量，也适用于主动测量。
* An active measurement can be configured to match the characteristics of media flows, and simplifies the estimation of application performance.
* 可以配置活动测量以匹配媒体流的特征，并简化对应用程序性能的估计。
* Measurements of many network impairments (e.g., delay variation, consecutive loss, reordering) are sensitive to the sampling frequency. When the impairments themselves are time-varying (and the variations are somewhat rare, yet important), a constant sampling frequency simplifies analysis.
* 许多网络损伤的测量（例如延迟变化、连续丢失、重新排序）对采样频率敏感。当损伤本身是时变的（且变化有点罕见，但很重要）时，恒定的采样频率简化了分析。
* Frequency Domain analysis is simplified when the samples are equally spaced.
* 当样本间距相等时，频域分析简化。
Simulation of CBR flows with periodic streams encourages dense sampling of network performance, since typical multimedia flows have 10 to 100 packets in each second. Dense sampling permits the characterization of network phenomena with short duration.
由于典型的多媒体流每秒有10到100个数据包，因此使用周期流模拟CBR流有助于对网络性能进行密集采样。密集采样允许在短时间内表征网络现象。
The Framework RFC [3] points out the following potential problems with Periodic Sampling:
框架RFC[3]指出了定期采样的以下潜在问题：
1. The performance sampled may be synchronized with some other periodic behavior, or the samples may be anticipated and the results manipulated. Unpredictable sampling is preferred.
1. 采样的性能可能与其他一些周期性行为同步，或者可以预期样本并操纵结果。首选不可预测的采样。
2. Active measurements can cause congestion, and periodic sampling might drive congestion-aware senders into a synchronized state, producing atypical results.
2. 主动测量可能会导致拥塞，而定期采样可能会使拥塞感知发送方进入同步状态，从而产生非典型结果。
Poisson sampling produces an unbiased sample for the various IP performance metrics, yet there are situations where alternative sampling methods are advantageous (as discussed under Motivation).
泊松抽样为各种IP性能指标生成无偏样本，但在某些情况下，替代抽样方法是有利的（如激励下所述）。
We can prescribe periodic sampling methods that address the problems listed above. Predictability and some forms of synchronization can be mitigated through the use of random start times and limited stream duration over a test interval. The periodic sampling parameters produce bias, and judicious selection can produce a known bias of interest. The total traffic generated by this or any sampling method should be limited to avoid adverse affects on non-test traffic (packet size, packet rate, and sample duration and frequency should all be considered).
我们可以规定解决上述问题的定期抽样方法。通过在测试间隔内使用随机开始时间和有限的流持续时间，可以降低可预测性和某些形式的同步。周期性采样参数会产生偏差，而明智的选择会产生已知的感兴趣偏差。应限制此或任何取样方法产生的总流量，以避免对非测试流量产生不利影响（应考虑数据包大小、数据包速率以及取样持续时间和频率）。
The configuration parameters of periodic sampling are: + T, the beginning of a time interval where a periodic sample is desired. + dT, the duration of the interval for allowed sample start times. + T0, a time that MUST be selected at random from the interval [T, T+dT] to start generating packets and taking measurements. + Tf, a time, greater than T0, for stopping generation of packets for a sample (Tf may be relative to T0 if desired). + incT, the nominal duration of inter-packet interval, first bit to first bit.
周期性采样的配置参数为：+T，是需要周期性采样的时间间隔的开始dT，允许的采样开始时间间隔的持续时间+T0，必须从间隔[T，T+dT]中随机选择以开始生成数据包和进行测量的时间Tf，大于T0的时间，用于停止为样本生成数据包（如果需要，Tf可以相对于T0）。+incT，数据包间隔的标称持续时间，从第一位到第一位。
T0 may be drawn from a uniform distribution, or T0 = T + Unif(0,dT). Other distributions may also be appropriate. Start times in successive time intervals MUST use an independent value drawn from the distribution. In passive measurement, the arrival of user media flows may have sufficient randomness, or a randomized start time of the measurement during a flow may be needed to meet this requirement.
T0可以从均匀分布中得出，或者T0=T+Unif（0，dT）。其他分配也可能适用。连续时间间隔中的开始时间必须使用从分布中提取的独立值。在被动测量中，用户媒体流的到达可能具有足够的随机性，或者可能需要在流期间测量的随机开始时间来满足该要求。
When a mix of packet sizes is desired, passive measurements usually possess the sequence and statistics of sizes in actual use, while active measurements would need to reproduce the intended distribution of sizes.
当需要混合数据包大小时，被动测量通常具有实际使用中的大小顺序和统计信息，而主动测量则需要再现预期的大小分布。
The sample metric presented here is similar to the sample metric Type-P-One-way-Delay-Poisson-Stream presented in RFC 2679[4]. Singletons defined in [3] and [4] are applicable here.
此处给出的样本度量与RFC 2679[4]中给出的样本度量类型P-单向延迟-泊松流相似。[3]和[4]中定义的单例在此适用。
Type-P-One-way-Delay-Periodic-Stream
P型单向延迟周期流
These parameters apply in the following sub-sections (4.2.2, 4.2.3, and 4.2.4).
这些参数适用于以下小节（4.2.2、4.2.3和4.2.4）。
Parameters that each Singleton usually includes: + Src, the IP address of a host + Dst, the IP address of a host + IPV, the IP version (IPv4/IPv6) used in the measurement + dTloss, a time interval, the maximum waiting time for a packet before declaring it lost. + packet size p(j), the desired number of bytes in the Type-P packet, where j is the size index.
每个单例通常包括的参数：+Src、主机的IP地址+Dst、主机的IP地址+IPV、测量中使用的IP版本（IPv4/IPv6）+dTloss、时间间隔、数据包声明丢失前的最大等待时间数据包大小p（j），类型p数据包中所需的字节数，其中j是大小索引。
Optional parameters: + PktType, any additional qualifiers (transport address) + Tcons, a time interval for consolidating parameters collected at the measurement points.
可选参数：+PktType，任何附加限定符（传输地址）+Tcons，用于合并在测量点收集的参数的时间间隔。
While a number of applications will use one packet size (j = 1), other applications may use packets of different sizes (j > 1). Especially in cases of congestion, it may be useful to use packets smaller than the maximum or predominant size of packets in the periodic stream.
虽然许多应用程序将使用一个数据包大小（j=1），但其他应用程序可能使用不同大小的数据包（j>1）。特别是在拥塞的情况下，使用小于周期流中分组的最大或主要大小的分组可能是有用的。
A topology where Src and Dst are separate from the measurement points is assumed.
假设Src和Dst与测量点分离的拓扑。
Parameters that each Singleton usually includes: + Tstamp(Src)[i], for each packet [i], the time of the packet as measured at MP(Src)
每个单例通常包括的参数：+Tstamp（Src）[i]，对于每个数据包[i]，在MP（Src）处测量的数据包时间
Additional parameters: + PktID(Src) [i], for each packet [i], a unique identification or sequence number. + PktSi(Src) [i], for each packet [i], the actual packet size.
附加参数：+PktID（Src）[i]，对于每个数据包[i]，一个唯一标识或序列号PktSi（Src）[i]，对于每个数据包[i]，实际数据包大小。
Some applications may use packets of different sizes, either because of application requirements or in response to IP performance experienced.
有些应用程序可能会使用不同大小的数据包，这可能是因为应用程序的要求，也可能是为了响应IP性能。
+ Tstamp(Dst)[i], for each packet [i], the time of the packet as measured at MP(Dst) + PktID(Dst) [i], for each packet [i], a unique identification or sequence number. + PktSi(Dst) [i], for each packet [i], the actual packet size.
+ Tstamp（Dst）[i]，对于每个数据包[i]，在MP（Dst）+PktID（Dst）[i]处测量的数据包时间，对于每个数据包[i]，唯一标识或序列号PktSi（Dst）[i]，对于每个数据包[i]，实际数据包大小。
Optional parameters: + dTstop, a time interval, used to add to time Tf to determine when to stop collecting metrics for a sample + PktStatus [i], for each packet [i], the status of the packet received. Possible status includes OK, packet header corrupt, packet payload corrupt, duplicate, fragment. The criteria to determine the status MUST be specified, if used.
可选参数：+dTstop，一个时间间隔，用于添加到时间Tf，以确定何时停止收集样本+PktStatus[i]的度量，对于每个数据包[i]，接收数据包的状态。可能的状态包括OK、数据包标头损坏、数据包有效负载损坏、重复、碎片。必须指定确定状态的标准（如果使用）。
4.2.4 Sample Metrics resulting from combining parameters at MP(Src) and MP(Dst)
4.2.4 组合MP（Src）和MP（Dst）处的参数得出的样本度量
Using the parameters above, a delay singleton would be calculated as follows:
使用上述参数，将按如下方式计算延迟单例：
+ Delay [i], for each packet [i], the time interval Delay[i] = Tstamp(Dst)[i] - Tstamp(Src)[i]
+ 延迟[i]，对于每个分组[i]，时间间隔延迟[i]=Tstamp（Dst）[i]-Tstamp（Src）[i]
For the following conditions, it will not be possible to compute delay singletons:
对于以下情况，将无法计算延迟单例：
Spurious: There will be no Tstamp(Src)[i] time Not received: There will be no Tstamp (Dst) [i] Corrupt packet header: There will be no Tstamp (Dst) [i] Duplicate: Only the first non-corrupt copy of the packet received at Dst should have Delay [i] computed.
伪：不会有Tstamp（Src）[i]未接收时间：不会有Tstamp（Dst）[i]损坏的数据包头：不会有Tstamp（Dst）[i]重复：只有在Dst接收的数据包的第一个非损坏副本应计算延迟[i]。
A sample metric for average delay is as follows
平均延迟的样本度量如下所示
AveDelay = (1/N)Sum(from i=1 to N, Delay[i])
AveDelay = (1/N)Sum(from i=1 to N, Delay[i])
assuming all packets i= 1 through N have valid singletons.
假设所有数据包i=1到N都有有效的单例。
A delay variation [5] singleton can also be computed:
还可以计算延迟变化[5]单态：
+ IPDV[i], for each packet [i] except the first one, delay variation between successive packets would be calculated as
+ IPDV[i]，对于除第一个包之外的每个包[i]，连续包之间的延迟变化将计算为
IPDV[i] = Delay[i] - Delay [i-1]
IPDV[i]=延迟[i]-延迟[i-1]
IPDV[i] may be negative, zero, or positive. Delay singletons for packets i and i-1 must be calculable or IPDV[i] is undefined.
IPDV[i]可以是负的、零的或正的。数据包i和i-1的延迟单例必须是可计算的，或者IPDV[i]未定义。
An example metric for the IPDV sample is the range:
IPDV样本的一个示例度量是范围：
RangeIPDV = max(IPDV[]) - min(IPDV[])
RangeIPDV = max(IPDV[]) - min(IPDV[])
Beginning on or after time T0, Type-P packets are generated by Src and sent to Dst until time Tf is reached with a nominal interval between the first bit of successive packets of incT, as measured at MP(Src). incT may be nominal due to a number of reasons: variation in packet generation at Src, clock issues (see section 4.6), etc. MP(Src) records the parameters above only for packets with timestamps between and including T0 and Tf having the required Src, Dst, and any other qualifiers. MP (Dst) also records for packets with time stamps between T0 and (Tf + dTstop).
从时间T0开始或之后，Src生成P型数据包并发送到Dst，直到达到时间Tf，incT连续数据包的第一位之间的标称间隔，如在MP（Src）处测量的。incT可能是名义上的，原因有很多：Src处数据包生成的变化、时钟问题（见第4.6节）等。MP（Src）仅记录时间戳介于T0和Tf之间且具有所需Src、Dst和任何其他限定符的数据包的上述参数。MP（Dst）还记录时间戳介于T0和（Tf+dTstop）之间的数据包。
Optionally at a time Tf + Tcons (but eventually in all cases), the data from MP(Src) and MP(Dst) are consolidated to derive the sample metric results. To prevent stopping data collection too soon, dTcons should be greater than or equal to dTstop. Conversely, to keep data collection reasonably efficient, dTstop should be some reasonable time interval (seconds/minutes/hours), even if dTloss is infinite or extremely long.
可选地，在Tf+Tcons（但最终在所有情况下）时，来自MP（Src）和MP（Dst）的数据被合并以导出样本度量结果。为防止过早停止数据采集，dTcons应大于或等于dTstop。相反，为了保持数据收集的合理效率，dTstop应该是一个合理的时间间隔（秒/分钟/小时），即使dTloss是无限的或非常长。
This sampling methodology is intended to quantify the delays and the delay variation as experienced by multimedia streams of an application. Due to the definitions of these metrics, packet loss status is also recorded. The nominal interval between packets assesses network performance variations on a specific time scale.
此采样方法旨在量化应用程序的多媒体流所经历的延迟和延迟变化。根据这些指标的定义，还将记录数据包丢失状态。数据包之间的标称间隔评估特定时间尺度上的网络性能变化。
There are a number of factors that should be taken into account when collecting a sample metric of Type-P-One-way-Delay-Periodic-Stream.
在收集P-单向延迟-周期流类型的样本度量时，应考虑许多因素。
+ The interval T0 to Tf should be specified to cover a long enough time interval to represent a reasonable use of the application under test, yet not excessively long in the same context (e.g. phone calls last longer than 100ms, but less than one week).
+ 间隔T0到Tf的规定应涵盖足够长的时间间隔，以表示被测应用程序的合理使用，但在同一上下文中不应过长（例如，电话呼叫持续时间超过100ms，但不超过一周）。
+ The nominal interval between packets (incT) and the packet size(s) (p(j)) should not define an equivalent bit rate that exceeds the capacity of the egress port of Src, the ingress port of Dst, or the capacity of the intervening network(s), if known. There may be exceptional cases to test the response of the application to overload conditions in the transport networks, but these cases should be strictly controlled.
+ 分组之间的标称间隔（incT）和分组大小（p（j））不应定义超过Src的出口端口、Dst的入口端口或介入网络（如果已知）容量的等效比特率。可能存在测试应用程序对传输网络中过载条件的响应的例外情况，但应严格控制这些情况。
+ Real delay values will be positive. Therefore, it does not make sense to report a negative value as a real delay. However, an individual zero or negative delay value might be useful as part of a stream when trying to discover a distribution of the delay errors.
+ 实际延迟值将为正值。因此，将负值报告为实际延迟是没有意义的。然而，当试图发现延迟错误的分布时，作为流的一部分，单个零或负延迟值可能是有用的。
+ Depending on measurement topology, delay values may be as low as 100 usec to 10 msec, whereby it may be important for Src and Dst to synchronize very closely. GPS systems afford one way to achieve synchronization to within several 10s of usec. Ordinary application of NTP may allow synchronization to within several msec, but this depends on the stability and symmetry of delay properties among the NTP agents used, and this delay is what we are trying to measure.
+ 根据测量拓扑，延迟值可能低至100 usec至10 ms，因此Src和Dst必须非常紧密地同步。GPS系统提供了一种在usec数10秒内实现同步的方法。NTP的普通应用可能允许同步在几毫秒内，但这取决于所用NTP代理之间延迟特性的稳定性和对称性，我们正试图测量这种延迟。
+ A given methodology will have to include a way to determine whether a packet was lost or whether delay is merely very large (and the packet is yet to arrive at Dst). The global metric parameter dTloss defines a time interval such that delays larger than dTloss are interpreted as losses. {Comment: For many applications, the treatment of a large delay as infinite/loss will be inconsequential. A TCP data packet, for example, that arrives only after several multiples of the usual RTT may as well have been lost.}
+ 给定的方法必须包括确定数据包是否丢失或延迟是否非常大（数据包尚未到达Dst）的方法。全局度量参数dTloss定义了一个时间间隔，使得大于dTloss的延迟被解释为损失。{注释：对于许多应用程序，将大延迟视为无限/丢失是无关紧要的。例如，只有在通常RTT的几倍之后才到达的TCP数据包也可能丢失。}
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 description of any specific measurement method should include an accounting and analysis of various sources of error or uncertainty. The Framework RFC [3] provides general guidance on this point, but we note here the following specifics related to periodic streams and 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RFC[3]提供了关于这一点的一般指导，但我们注意到以下与周期流和延迟度量相关的细节：
+ Error due to variation of incT. The reasons for this can be uneven process scheduling, possibly due to CPU load.
+ 因增量变化引起的错误。造成这种情况的原因可能是进程调度不均匀，可能是由于CPU负载。
+ Errors or uncertainties due to uncertainties in the clocks of the MP(Src) and MP(Dst) measurement points.
+ 由于MP（Src）和MP（Dst）测量点时钟的不确定性而产生的误差或不确定性。
+ 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。
The uncertainty in a measurement of one-way delay is related, in part, to uncertainties in the clocks of MP(Src) and MP(Dst). In the following, we refer to the clock used to measure when the packet was measured at MP(Src) as the MP(Src) clock and we refer to the clock used to measure when the packet was received at MP(Dst) as the MP(Dst) clock. Alluding to the notions of synchronization, accuracy, resolution, and skew, we note the following:
单向延迟测量的不确定度部分与MP（Src）和MP（Dst）时钟的不确定度有关。在下文中，我们将用于测量数据包何时在MP（Src）测量的时钟称为MP（Src）时钟，并将用于测量数据包何时在MP（Dst）接收的时钟称为MP（Dst）时钟。关于同步、精度、分辨率和倾斜的概念，我们注意到以下几点：
+ Any error in the synchronization between the MP(Src) clock and the MP(Dst) clock will contribute to error in the delay measurement. We say that the MP(Src) clock and the MP(Dst) clock have a synchronization error of Tsynch if the MP(Src) clock is Tsynch ahead of the MP(Dst) clock. Thus, if we know the value of Tsynch exactly, we could correct for clock synchronization by adding Tsynch to the uncorrected value of Tstamp(Dst)[i] - Tstamp(Src) [i].
+ MP（Src）时钟和MP（Dst）时钟之间的任何同步错误都将导致延迟测量错误。我们说，如果MP（Src）时钟比MP（Dst）时钟早于Tsynch，则MP（Src）时钟和MP（Dst）时钟具有Tsynch的同步错误。因此，如果我们准确地知道Tsynch的值，我们可以通过将Tsynch添加到Tstamp（Dst）[i]-Tstamp（Src）[i]的未校正值来校正时钟同步。
+ The resolution of a clock adds to uncertainty about any time measured with it. Thus, if the MP(Src) 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 and the MP(Dst) clock as ResMP(Src) and ResMP(Dst), respectively.
+ 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MP（Src）时钟的分辨率为10毫秒，则这会给使用它测量的任何时间值增加10毫秒的不确定性。我们将源时钟和MP（Dst）时钟的分辨率分别表示为ResMP（Src）和ResMP（Dst）。
+ The skew of a clock is not so much an additional issue as it is a realization of the fact that Tsynch is itself a function of time. Thus, if we attempt to measure or to bound Tsynch, this measurement or calculation must be repeated periodically. Over some periods of time, this function can be approximated as a linear function plus some higher order terms; in these cases, one option is to use knowledge of the linear component to correct the clock. Using this correction, the residual Tsynch is made smaller, but remains a source of uncertainty that must be accounted for. We use the function Esynch(t) to denote an upper bound on the uncertainty in synchronization. Thus, |Tsynch(t)| <= Esynch(t).
+ 时钟的偏移与其说是一个额外的问题，不如说是一个认识到Tsynch本身就是时间的函数这一事实的问题。因此，如果我们试图测量或绑定Tsynch，则必须定期重复此测量或计算。在一段时间内，该函数可以近似为线性函数加上一些高阶项；在这些情况下，一种选择是使用线性组件的知识来校正时钟。使用此校正，剩余Tsynch变小，但仍然是必须考虑的不确定性来源。我们使用函数Esynch（t）来表示同步中不确定性的上界。因此，| Tsynch（t）|<=Esynch（t）。
Taking these items together, we note that naive computation Tstamp(Dst)[i] - Tstamp(Src) [i] will be off by Tsynch(t) +/- (ResMP(SRc) + ResMP(Dst)). Using the notion of Esynch(t), we note that these clock-related problems introduce a total uncertainty of Esynch(t)+ Rsource + Rdest. This estimate of total clock-related uncertainty should be included in the error/uncertainty analysis of any measurement implementation.
把这些项放在一起，我们注意到原始计算Tstamp（Dst）[i]-Tstamp（Src）[i]将由Tsynch（t）+/-（ResMP（Src）+ResMP（Dst）关闭。使用Esynch（t）的概念，我们注意到这些与时钟相关的问题引入了Esynch（t）+Rsource+Rdest的总体不确定性。任何测量实施的误差/不确定度分析中都应包括与时钟相关的总不确定度的估计值。
We would like to measure the time between when a packet is measured and time-stamped at MP(Src) and when it arrives and is time-stamped at MP(Dst); we refer to these as "wire times." However, if timestamps are applied by software on Src and Dst, then this software can only directly measure the time between when Src generates the packet just prior to sending the test packet and when Dst has started to process the packet after having received the test packet; we refer to these two points as "host times".
我们想测量一个包在MP（Src）被测量和时间戳之间的时间，以及它到达MP（Dst）并在MP（Dst）被时间戳之间的时间；我们将其称为“连线时间”。然而，如果软件在Src和Dst上应用时间戳，则该软件只能直接测量Src在发送测试数据包之前生成数据包与Dst在收到测试数据包之后开始处理数据包之间的时间；我们将这两点称为“主办时间”。
To the extent that the difference between wire time and host time is accurately known, this knowledge can be used to correct for wire time measurements. The corrected value more accurately estimates the desired (host time) metric, and visa-versa.
只要准确知道导线时间和主机时间之间的差异，就可以使用这些知识来校正导线时间测量值。修正值更准确地估计所需（主机时间）度量，反之亦然。
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 Hsource an upper bound on the uncertainty in the difference between wire time of MP(Src) and host time on the Src host, and similarly define Hdest for the difference between the host time on the Dst host and the wire time of MP(Dst). We then note that these problems introduce a total uncertainty of Hsource+Hdest. 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。我们用Hsource表示MP（Src）的连线时间与Src主机上的主机时间之差的不确定性上限，并且类似地定义了Dst主机上的主机时间与MP（Dst）的连线时间之差的Hdest。然后我们注意到，这些问题引入了Hsource+Hdest的总体不确定性。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。
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 due to reasons discussed in [4], briefly summarized as (1) some confidence level is desirable to be able to remove outliers, which will be found in measuring any physical property; (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毫秒的实际延迟报告为30毫秒。{注释：选择95%是因为[4]中讨论的原因，简要总结为：（1）需要一定的置信水平，以便能够消除在测量任何物理特性时会发现的异常值；（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 two sections, the error in measurements could be bounded by determining all the individual uncertainties, and adding them together to form:
根据前两节中的讨论，测量误差可通过确定所有单个不确定度并将其相加形成：
Esynch(t) + ResMP(Src) + ResMP(Dst) + Hsource + Hdest
Esynch(t) + ResMP(Src) + ResMP(Dst) + Hsource + Hdest
However, reasonable bounds on both the clock-related uncertainty captured by the first three terms and the host-related uncertainty captured by the last two terms should be possible by careful design techniques and calibrating the instruments using a known, isolated, network in a lab.
然而，通过仔细设计技术和在实验室中使用已知的隔离网络校准仪器，前三项捕获的时钟相关不确定度和后两项捕获的主机相关不确定度的合理界限应是可能的。
For example, the clock-related uncertainties are greatly reduced through the use of a GPS time source. The sum of Esynch(t) + ResMP(Src) + ResMP(Dst) is small, and is also bounded for the duration of the measurement because of the global time source. The host-related uncertainties, Hsource + Hdest, could be bounded by
例如，通过使用GPS时间源，大大降低了与时钟相关的不确定性。Esynch（t）+ResMP（Src）+ResMP（Dst）之和很小，并且由于全局时间源的原因，在测量期间也是有界的。与主机相关的不确定性Hsource+Hdest可由
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 one-way delay.
使用高速串行链路或隔离LAN段背靠背连接两台仪器。在这种情况下，重复测量是测量相同的单向延迟。
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. 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.}
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。计算系统误差和随机误差的一种方法是将实验重复多次，至少数百次，置信度为95%。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。
The nominal interval between packets, incT, can vary during either active or passive measurements. In passive measurement, packet headers may include a timestamp applied prior to most of the protocol stack, and the actual sending time may vary due to processor scheduling. For example, H.323 systems are required to have packets ready for the network stack within 5 ms of their ideal time. There may be additional variation from the network between the Src and the
在主动或被动测量期间，数据包之间的标称间隔incT可能会变化。在被动测量中，分组报头可包括在大多数协议栈之前应用的时间戳，并且实际发送时间可因处理器调度而变化。例如，H.323系统需要在理想时间的5毫秒内为网络堆栈准备好数据包。Src和Src之间的网络可能存在其他变化
MP(Src). Active measurement systems may encounter similar errors, but to a lesser extent. These errors must be accounted for in some types of analysis.
MP（Src）。主动测量系统可能会遇到类似的误差，但误差较小。在某些类型的分析中必须考虑这些错误。
The calibration and context in which the method is used MUST be carefully considered, and SHOULD always be reported along with metric results. We next present five items to consider: the Type-P of test packets, the threshold of delay equivalent to loss, error calibration, the path traversed by the test packets, and background conditions at Src, Dst, and the intervening networks during a sample. This list is not exhaustive; any additional information that could be useful in interpreting applications of the metrics should also be reported.
必须仔细考虑使用该方法的校准和环境，并且应始终与度量结果一起报告。接下来，我们将介绍五个需要考虑的项目：测试数据包的类型P、等效于丢失的延迟阈值、错误校准、测试数据包穿过的路径以及采样期间Src、Dst和干预网络的背景条件。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 [3], the value of a metric may depend on the type of IP packets used to make the measurement, or "type-P". The value of Type-P-One-way-Periodic-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 reported.
如框架文件[3]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-单向周期性延迟的值可能会发生变化。必须报告用于进行测量的准确P型。
In addition, the threshold for delay equivalent to loss (or methodology to determine this threshold) MUST be reported.
此外，必须报告相当于损失的延迟阈值（或确定该阈值的方法）。
+ If the systematic error can be determined, it SHOULD be removed from the measured values. + 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.) + 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.
+ 如果可以确定系统误差，应将其从测量值中删除您还应报告校准误差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）。如果可能，应报告由于测量仪器上的资源耗尽导致有限延迟的测试数据包丢失的情况。
The path traversed by the packets 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 packets on short or stable paths. If Type-P includes the record route (or loose-source route) option in the IP header, and the
如果可能的话，应该报告数据包经过的路径。通常，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型分组，可以知道精确路径。如果Type-P在IP标头中包含记录路由（或松散源路由）选项，则
path is short enough, and all routers on the path support record (or loose-source) route, then the path will be precisely recorded.
路径足够短，并且路径上的所有路由器都支持记录（或松散源代码）路由，那么路径将被精确记录。
This may be 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.
这可能是不切实际的，因为路线必须足够短。许多路由器不支持（或未配置）记录路由，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。
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 one commercial setup, a Src on one NAP can reach a Dst on another NAP by either of several different backbone networks.}
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，在一个商业设置中，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。}
Fig.1 illustrates measurements on multiple protocol levels that are relevant to this memo. The user's focus is on transport quality evaluation from the application point of view. However, to properly separate the quality contribution of the operating system and codec on packet voice, for example, it is beneficial to be able to measure quality at the IP level [6]. Link layer monitoring provides a way of accounting for link layer characteristics such as bit error rates.
图1说明了与本备忘录相关的多个协议级别的测量。用户的重点是从应用的角度对运输质量进行评估。然而，为了正确区分操作系统和编解码器对分组语音的质量贡献，例如，能够在IP级别测量质量是有益的[6]。链路层监控提供了一种计算链路层特性（如误码率）的方法。
---------------
| application |
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| transport | <--
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| network | <--
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| link | <--
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| physical |
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| application |
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| transport | <--
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| network | <--
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| link | <--
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| physical |
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Fig. 1: Different possibilities for performing measurements: a protocol view. Above, "application" refers to all layers above L4 and is not used in the OSI sense.
图1：执行测量的不同可能性：协议视图。上面，“应用程序”指L4以上的所有层，不在OSI意义上使用。
In general, the results of measurements may be influenced by individual application requirements/responses related to the following issues:
通常，测量结果可能会受到与以下问题相关的个别应用要求/响应的影响：
+ Lost packets: Applications may have varying tolerance to lost packets. Another consideration is the distribution of lost packets (i.e. random or bursty).
+ 丢失的数据包：应用程序可能对丢失的数据包有不同的容忍度。另一个考虑因素是丢失数据包的分布（即随机或突发）。
+ Long delays: Many applications will consider packets delayed longer than a certain value to be equivalent to lost packets (i.e. real time applications). + Duplicate packets: Some applications may be perturbed if duplicate packets are received. + Reordering: Some applications may be perturbed if packets arrive out of sequence. This may be in addition to the possibility of exceeding the "long" delay threshold as a result of being out of sequence. + Corrupt packet header: Most applications will probably treat a packet with a corrupt header as equivalent to a lost packet. + Corrupt packet payload: Some applications (e.g. digital voice codecs) may accept corrupt packet payload. In some cases, the packet payload may contain application specific forward error correction (FEC) that can compensate for some level of corruption. + Spurious packet: Dst may receive spurious packets (i.e. packets that are not sent by the Src as part of the metric). Many applications may be perturbed by spurious packets.
+ 长延迟：许多应用程序将考虑比某个值延迟更长的分组，以等同于丢失的分组（即实时应用）。重复数据包：如果接收到重复数据包，某些应用程序可能会受到干扰重新排序：如果数据包不按顺序到达，某些应用程序可能会受到干扰。除此之外，由于顺序错误，可能会超过“长”延迟阈值损坏的数据包标头：大多数应用程序可能会将具有损坏标头的数据包视为等同于丢失的数据包损坏的数据包负载：某些应用程序（如数字语音编解码器）可能接受损坏的数据包负载。在某些情况下，数据包有效载荷可能包含特定于应用程序的前向纠错（FEC），该前向纠错可以补偿某种程度的损坏虚假数据包：Dst可能接收虚假数据包（即Src未作为度量的一部分发送的数据包）。许多应用程序可能会受到虚假数据包的干扰。
Depending, e.g., on the observed protocol level, some issues listed above may be indistinguishable from others by the application, it may be important to preserve the distinction for the operators of Src, Dst, and/or the intermediate network(s).
例如，根据观察到的协议级别，上面列出的一些问题可能无法通过应用程序与其他问题区分开来，保持Src、Dst和/或中间网络运营商之间的区别可能很重要。
This sampling method provides a way to perform measurements irrespective of the possible QoS mechanisms utilized in the IP network. As an example, for a QoS mechanism without hard guarantees, measurements may be used to ascertain that the "best" class gets the service that has been promised for the traffic class in question. Moreover, an operator could study the quality of a cheap, low-guarantee service implemented using possible slack bandwidth in other classes. Such measurements could be made either in studying the feasibility of a new service, or on a regular basis.
该采样方法提供了一种执行测量的方法，而与IP网络中使用的可能QoS机制无关。例如，对于没有硬保证的QoS机制，可以使用测量来确定“最佳”类获得所讨论的业务类所承诺的服务。此外，运营商可以研究使用其他类别中可能的空闲带宽实现的廉价、低保证服务的质量。这些测量可以在研究新服务的可行性时进行，也可以定期进行。
IP delivery service measurements have been discussed within the International Telecommunications Union (ITU). A framework for IP service level measurements (with references to the framework for IP performance [3]) that is intended to be suitable for service planning has been approved as I.380 [7]. ITU-T Recommendation I.380 covers abstract definitions of performance metrics. This memo describes a method that is useful, both for service planning and end-user testing purposes, in both active and passive measurements.
国际电信联盟（ITU）讨论了IP交付服务测量。旨在适用于服务规划的IP服务水平测量框架（参考IP性能框架[3]）已被批准为I.380[7]。ITU-T建议I.380涵盖了性能指标的抽象定义。本备忘录描述了一种在主动和被动测量中对服务规划和最终用户测试都有用的方法。
Delay measurements can be one-way [3,4], paired one-way, or round-trip [8]. Accordingly, the measurements may be performed either with synchronized or unsynchronized Src/Dst host clocks. Different possibilities are listed below.
延迟测量可以是单向[3,4]、成对单向或往返[8]。因此，可以使用同步或非同步Src/Dst主机时钟执行测量。下面列出了不同的可能性。
The reference measurement setup for all measurement types is shown in Fig. 2.
所有测量类型的参考测量设置如图2所示。
----------------< IP >--------------------
| | | |
------- ------- -------- --------
| Src | | MP | | MP | | Dst |
------- |(Src)| |(Dst) | --------
------- --------
----------------< IP >--------------------
| | | |
------- ------- -------- --------
| Src | | MP | | MP | | Dst |
------- |(Src)| |(Dst) | --------
------- --------
Fig. 2: Example measurement setup.
图2：测量设置示例。
An example of the use of the method is a setup with a source host (Src), a destination host (Dst), and corresponding measurement points (MP(Src) and MP(Dst)) as shown in Figure 2. Separate equipment for measurement points may be used if having Src and/or Dst conduct the measurement may significantly affect the delay performance to be measured. MP(Src) should be placed/measured close to the egress point of packets from Src. MP(Dst) should be placed/measure close to the ingress point of packets for Dst. "Close" is defined as a distance sufficiently small so that application-level performance characteristics measured (such as delay) can be expected to follow the corresponding performance characteristic between Src and Dst to an adequate accuracy. The basic principle here is that measurement results between MP(Src) and MP(Dst) should be the same as for a measurement between Src and Dst, within the general error margin target of the measurement (e.g., < 1 ms; number of lost packets is the same). If this is not possible, the difference between MP-MP measurement and Src-Dst measurement should preferably be systematic.
该方法的一个使用示例是一个带有源主机（Src）、目标主机（Dst）和相应测量点（MP（Src）和MP（Dst））的设置，如图2所示。如果由Src和/或Dst进行测量可能会显著影响待测量的延迟性能，则可使用单独的测量点设备。MP（Src）应放置/测量在Src数据包出口点附近。MP（Dst）应放置/测量在靠近Dst数据包入口点的位置。“关闭”定义为足够小的距离，以便测量的应用程序级性能特性（如延迟）可以预期遵循Src和Dst之间的相应性能特性，达到足够的精度。这里的基本原则是，MP（Src）和MP（Dst）之间的测量结果应与Src和Dst之间的测量结果相同，在测量的一般误差范围内（例如，<1 ms；丢失的数据包数相同）。如果不可能，MP-MP测量和Src Dst测量之间的差异最好是系统性的。
The test setup just described fulfills two important criteria:
刚才描述的测试设置满足两个重要标准：
1) The test is made with realistic stream metrics, emulating - for example - a full-duplex Voice over IP (VoIP) call.
1) 该测试使用真实的流指标进行，模拟（例如）全双工IP语音（VoIP）呼叫。
2) Either one-way or round-trip characteristics may be obtained.
2) 可获得单向或往返特性。
It is also possible to have intermediate measurement points between MP(Src) and MP(Dst), but that is beyond the scope of this document.
也可以在MP（Src）和MP（Dst）之间设置中间测量点，但这超出了本文件的范围。
In the interests of specifying metrics that are as generally applicable as possible, application-level measurements based on one-way delays are used in the example metrics. The implication of application-level measurement for bi-directional applications, such as interactive multimedia conferencing, is discussed below.
为了指定尽可能普遍适用的度量，在示例度量中使用基于单向延迟的应用程序级度量。下面讨论双向应用程序（如交互式多媒体会议）的应用程序级度量的含义。
Performing a single one-way measurement only yields information on network behavior in one direction. Moreover, the stream at the network transport level does not emulate accurately a full-duplex multimedia connection.
执行单个单向测量只能产生一个方向上的网络行为信息。此外，网络传输级别的流不能准确模拟全双工多媒体连接。
Paired one way delay refers to two multimedia streams: Src to Dst and Dst to Src for the same Src and Dst. By way of example, for some applications, the delay performance of each one way path is more important than the round trip delay. This is the case for delay-limited signals such as VoIP. Possible reasons for the difference between one-way delays is different routing of streams from Src to Dst vs. Dst to Src.
成对单向延迟是指两个多媒体流：Src到Dst和Dst到Src，用于相同的Src和Dst。举例来说，对于某些应用，每条单向路径的延迟性能比往返延迟更重要。这是延迟受限信号（如VoIP）的情况。单向延迟之间差异的可能原因是从Src到Dst的流路由与从Dst到Src的流路由不同。
For example, a paired one way measurement may show that Src to Dst has an average delay of 30ms, while Dst to Src has an average delay of 120ms. To a round trip delay measurement, this example would look like an average of 150ms delay. Without the knowledge of the asymmetry, we might miss a problem that the application at either end may have with delays averaging more than 100ms.
例如，配对单向测量可能显示Src到Dst的平均延迟为30ms，而Dst到Src的平均延迟为120ms。对于往返延迟测量，此示例的平均延迟为150ms。如果不知道这种不对称性，我们可能会忽略一个问题，即两端的应用程序可能存在平均延迟超过100ms的问题。
Moreover, paired one way delay measurement emulates a full-duplex VoIP call more accurately than a single one-way measurement only.
此外，配对单向延迟测量比仅单向测量更准确地模拟全双工VoIP呼叫。
From the point of view of periodic multimedia streams, round-trip measurements have two advantages: they avoid the need of host clock synchronization and they allow for a simulation of full-duplex communication. The former aspect means that a measurement is easily performed, since no special equipment or NTP setup is needed. The latter property means that measurement streams are transmitted in both directions. Thus, the measurement provides information on quality of service as experienced by two-way applications.
从周期性多媒体流的角度来看，往返测量有两个优点：它们避免了主机时钟同步的需要，并且允许模拟全双工通信。前一方面意味着测量很容易进行，因为不需要特殊设备或NTP设置。后一个属性意味着测量流在两个方向上传输。因此，度量提供了双向应用程序体验的服务质量信息。
The downsides of round-trip measurement are the need for more bandwidth than a one-way test and more complex accounting of packet loss. Moreover, the stream that is returning towards the original sender may be more bursty than the one on the first "leg" of the
往返测量的缺点是需要比单向测试更多的带宽和更复杂的数据包丢失计算。此外，返回到原始发送方的流可能比第一个“分支”上的流更具突发性
round-trip journey. The last issue, however, means in practice that the returning stream may experience worse QoS than the out-going one, and the performance estimates thus obtained are pessimistic ones. The possibility of asymmetric routing and queuing must be taken into account during an analysis of the results.
往返旅行。然而，最后一个问题在实践中意味着返回流可能比输出流经历更差的QoS，并且由此获得的性能估计是悲观的。在分析结果时，必须考虑不对称路由和排队的可能性。
Note that with suitable arrangements, round-trip measurements may be performed using paired one way measurements.
注意，在适当的安排下，可使用成对的单向测量进行往返测量。
Some statistics may be particularly relevant to applications simulated by periodic streams, such as the range of delay values recorded during the sample.
一些统计数据可能与周期流模拟的应用程序特别相关，例如采样期间记录的延迟值范围。
For example, a sample metric generates 100 packets at MP(Src) with the following measurements at MP(Dst):
例如，样本度量在MP（Src）生成100个数据包，并在MP（Dst）进行以下测量：
+ 80 packets received with delay [i] <= 20 ms
+ 8 packets received with delay [i] > 20 ms
+ 5 packets received with corrupt packet headers
+ 4 packets from MP(Src) with no matching packet recorded at
MP(Dst) (effectively lost)
+ 3 packets received with corrupt packet payload and delay
[i] <= 20 ms
+ 2 packets that duplicate one of the 80 packets received correctly
as indicated in the first item
+ 80 packets received with delay [i] <= 20 ms
+ 8 packets received with delay [i] > 20 ms
+ 5 packets received with corrupt packet headers
+ 4 packets from MP(Src) with no matching packet recorded at
MP(Dst) (effectively lost)
+ 3 packets received with corrupt packet payload and delay
[i] <= 20 ms
+ 2 packets that duplicate one of the 80 packets received correctly
as indicated in the first item
For this example, packets are considered acceptable if they are received with less than or equal to 20ms delays and without corrupt packet headers or packet payload. In this case, the percentage of acceptable packets is 80/100 = 80%.
对于该示例，如果接收到的数据包延迟小于或等于20ms，并且没有损坏的数据包头或数据包有效负载，则认为这些数据包是可接受的。在这种情况下，可接受分组的百分比为80/100＝80%。
For a different application that will accept packets with corrupt packet payload and no delay bounds (so long as the packet is received), the percentage of acceptable packets is (80+8+3)/100 = 91%.
对于将接受数据包有效负载损坏且无延迟边界的数据包的不同应用程序（只要接收到数据包），可接受数据包的百分比为（80+8+3）/100=91%。
There may be value in running multiple tests using this method to collect a "sample of samples". For example, it may be more appropriate to simulate 1,000 two-minute VoIP calls rather than a single 2,000 minute call. When considering a collection of multiple samples, issues like the interval between samples (e.g. minutes, hours), composition of samples (e.g. equal Tf-T0 duration, different
使用此方法运行多个测试以收集“样本样本”可能有价值。例如，模拟1000个两分钟的VoIP呼叫可能比模拟一个2000分钟的呼叫更合适。当考虑多个样本的采集时，样本之间的间隔（例如分钟、小时）、样本组成（例如相同的Tf-T0持续时间、不同的
packet sizes), and network considerations (e.g. run different samples over different intervening link-host combinations) should be taken into account. For items like the interval between samples, the usage pattern for the application of interest should be considered.
数据包大小）和网络注意事项（例如，在不同的中间链路-主机组合上运行不同的样本）应予以考虑。对于样本之间的间隔等项目，应考虑相关应用的使用模式。
When computing statistics for multiple samples, more general statistics (e.g. median, percentile, etc.) may have relevance with a larger number of packets.
当计算多个样本的统计数据时，更一般的统计数据（例如中位数、百分位数等）可能与更多的数据包相关。
In many cases, the results may be influenced by conditions at Src, Dst, and/or any intervening networks. Factors that may affect the results include: traffic levels and/or bursts during the sample, link and/or host failures, etc. Information about the background conditions may only be available by external means (e.g. phone calls, television) and may only become available days after samples are taken.
在许多情况下，结果可能受到Src、Dst和/或任何干预网络条件的影响。可能影响结果的因素包括：采样期间的流量水平和/或突发、链路和/或主机故障等。有关背景条件的信息可能只能通过外部手段（如电话、电视）获得，并且可能仅在采样后几天才可用。
For interactive multimedia sessions, end-to-end delay is an important factor. Too large a delay reduces the quality of the multimedia session as perceived by the participants. One approach for managing end-to-end delays on an Internet path involving heterogeneous link layer technologies is to use per-domain delay quotas (e.g. 50 ms for a particular IP domain). However, this scheme has clear inefficiencies, and can over-constrain the problem of achieving some end-to-end delay objective. A more flexible implementation ought to address issues like the possibility of asymmetric delays on paths, and sensitivity of an application to delay variations in a given domain. There are several alternatives as to the delay statistic one ought to use in managing end-to-end QoS. This question, although very interesting, is not within the scope of this memo and is not discussed further here.
对于交互式多媒体会话，端到端延迟是一个重要因素。延迟太大会降低参与者感知到的多媒体会话的质量。管理涉及异构链路层技术的Internet路径上的端到端延迟的一种方法是使用每个域的延迟配额（例如，特定IP域为50毫秒）。然而，该方案具有明显的低效性，并且可以过度约束实现某些端到端延迟目标的问题。更灵活的实现应该解决诸如路径上不对称延迟的可能性以及应用程序对给定域中延迟变化的敏感性等问题。对于管理端到端QoS时应该使用的延迟统计，有几种选择。这个问题虽然很有趣，但不在本备忘录的范围内，此处不再进一步讨论。
This method generates a periodic stream of packets from one host (Src) to another host (Dst) through intervening networks. This method could be abused for denial of service attacks directed at Dst and/or the intervening network(s).
该方法通过中间网络生成从一个主机（Src）到另一个主机（Dst）的周期性数据包流。针对Dst和/或介入网络的拒绝服务攻击可能会滥用此方法。
Administrators of Src, Dst, and the intervening network(s) should establish bilateral or multi-lateral agreements regarding the timing, size, and frequency of collection of sample metrics. Use of this
Src、Dst和干预网络的管理员应就样本指标收集的时间、规模和频率建立双边或多边协议。使用这个
method in excess of the terms agreed between the participants may be cause for immediate rejection, discard of packets, or other escalation procedures defined between the affected parties.
超出参与者之间约定条款的方法可能会导致立即拒绝、丢弃数据包或受影响方之间定义的其他升级程序。
Active use of this method generates packets for a sample, rather than taking samples based on user data, and does not threaten user data confidentiality. Passive measurement must restrict attention to the headers of interest. Since user payloads may be temporarily stored for length analysis, suitable precautions MUST be taken to keep this information safe and confidential.
主动使用此方法会为样本生成数据包，而不是基于用户数据采集样本，并且不会威胁用户数据的机密性。被动测量必须将注意力限制在感兴趣的标题上。由于用户有效载荷可能会临时存储以进行长度分析，因此必须采取适当的预防措施以确保该信息的安全和保密。
It may be possible to identify that a certain packet or stream of packets is part of a sample. With that knowledge at Dst and/or the intervening networks, it is possible to change the processing of the packets (e.g. increasing or decreasing delay) that may distort the measured performance. It may also be possible to generate additional packets that appear to be part of the sample metric. These additional packets are likely to perturb the results of the sample measurement.
可以识别特定分组或分组流是样本的一部分。利用Dst和/或介入网络处的该知识，可以改变分组的处理（例如，增加或减少延迟），这可能会扭曲所测量的性能。还可以生成似乎是样本度量的一部分的附加数据包。这些额外的数据包可能会干扰样本测量的结果。
To discourage the kind of interference mentioned above, packet interference checks, such as cryptographic hash, MAY be used.
为了阻止上述类型的干扰，可以使用分组干扰检查，例如加密散列。
Since this method and metric do not define a protocol or well-known values, there are no IANA considerations in this memo.
由于此方法和指标未定义协议或已知值，因此本备忘录中没有IANA注意事项。
[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996.
[1] Bradner，S.，“互联网标准过程——第3版”，BCP 9，RFC 2026，1996年10月。
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[3] Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
[3] Paxson，V.，Almes，G.，Mahdavi，J.和M.Mathis，“IP性能度量框架”，RFC 2330，1998年5月。
[4] Almes, G., Kalidindi, S. and M. Zekauskas, "A one-way delay metric for IPPM", RFC 2679, September 1999.
[4] Almes，G.，Kalidini，S.和M.Zekauskas，“IPPM的单向延迟度量”，RFC 2679，1999年9月。
[5] Demichelis, C. and P. Chimento, "IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)", RFC 3393, November 2002.
[5] Demichelis，C.和P.Chimento，“IP性能度量的IP数据包延迟变化度量（IPPM）”，RFC 3393，2002年11月。
[6] "End-to-end Quality of Service in TIPHON systems; Part 5: Quality of Service (QoS) measurement methodologies", ETSI TS 101 329-5 V1.1.2, January 2002.
[6] “TIPHON系统中的端到端服务质量；第5部分：服务质量（QoS）测量方法”，ETSI TS 101 329-5 V1.1.22002年1月。
[7] International Telecommunications Union, "Internet protocol data communication service _ IP packet transfer and availability performance parameters", Telecommunications Sector Recommendation I.380 (re-numbered Y.1540), February 1999.
[7] 国际电信联盟，“因特网协议数据通信服务——IP分组传输和可用性性能参数”，电信部门建议I.380（重新编号为Y.1540），1999年2月。
[8] Almes, G., Kalidindi, S. and M. Zekauskas, "A round-trip delay metric for IPPM", RFC 2681, September 1999.
[8] Almes，G.，Kalidini，S.和M.Zekauskas，“IPPM的往返延迟度量”，RFC 2681，1999年9月。
The authors wish to thank the chairs of the IPPM WG (Matt Zekauskas and Merike Kaeo) for comments that have made the present document more clear and focused. Howard Stanislevic and Will Leland have also presented useful comments and questions. We also gratefully acknowledge Henk Uijterwaal's continued challenge to develop the motivation for this method. The authors have built on the substantial foundation laid by the authors of the framework for IP performance [3].
作者希望感谢IPPM工作组主席（Matt Zekauskas和Merike Kaeo）的评论，这些评论使本文件更加清晰和集中。Howard Stanislevic和Will Leland也提出了有用的评论和问题。我们也非常感谢Henk Uijterwaal继续挑战开发这种方法的动机。作者已经建立了由IP性能框架的作者奠定的坚实基础〔3〕。
Vilho Raisanen Nokia Networks P.O. Box 300 FIN-00045 Nokia Group Finland
Vilho Raisanen诺基亚网络邮政信箱300 FIN-00045诺基亚集团芬兰
Phone: +358 7180 8000
Fax: +358 9 4376 6852
EMail: Vilho.Raisanen@nokia.com
Phone: +358 7180 8000
Fax: +358 9 4376 6852
EMail: Vilho.Raisanen@nokia.com
Glenn Grotefeld Motorola, Inc. 1501 W. Shure Drive, MS 2F1 Arlington Heights, IL 60004 USA
Glenn Grotefeld Motorola，Inc.美国伊利诺伊州阿灵顿高地舒尔大道西1501号，邮编：60004
Phone: +1 847 435-0730
Fax: +1 847 632-6800
EMail: g.grotefeld@motorola.com
Phone: +1 847 435-0730
Fax: +1 847 632-6800
EMail: g.grotefeld@motorola.com
Al Morton AT&T Labs Room D3 - 3C06 200 Laurel Ave. South Middletown, NJ 07748 USA
美国新泽西州南米德尔顿劳雷尔大道200号艾尔莫顿AT&T实验室D3-3C06室，邮编07748
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EMail: acmorton@att.com
Phone: +1 732 420 1571
Fax: +1 732 368 1192
EMail: acmorton@att.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。