Metrics and Methods for IP Capacity
draft-morton-ippm-capcity-metric-method-00

Abstract

This memo revisits the problem of Network Capacity metrics first examined in RFC 5136. The memo specifies a more practical Maximum IP-layer Capacity metric definition catering for measurement purposes, and outlines the corresponding methods of measurement.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14[RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on January 9, 2020.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Scope and Goals
• 3. Motivation
• 4. Metric Definitions
• 4.1. Formal Name
• 4.2. Parameters
• 4.3. Metric Definitions
• 4.4. Related Round-Trip Delay and Loss Definitions
• 4.5. Discussion
• 4.6. Reporting the Metric
• 5. Method of Measurement
• 5.1. Load Rate Adjustment Algorithm (from udpst)
• 6. Reporting
• 7. Security Considerations
• 8. IANA Considerations
• 9. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

The IETF's efforts to define Network and Bulk Transport Capacity have been chartered and progressed for over twenty years. Over that time, the performance community has seen development of Informative definitions in RFC 3148 for Framework for Bulk Transport Capacity (BTC), RFC 5136 for Network Capacity and Maximum IP-layer Capacity, and the Experimental metric definitions and methods in [RFC8337], Model-Based Metrics for BTC.

This memo recognizes the importance of a definition of a Maximum IP-layer Capacity Metric at this time, a definition that is both practical and effective for the performance community's needs, including Internet users. The metric definition is intended for Active Methods of Measurement [RFC7799], and a method of measurement is included here.

The most direct active measurement of IP-layer Capacity would use IP packets, but in practice a transport header is needed to traverse address and port translators. UDP offeres the most direct assessment possibility, and in the [copycat][copycat] measurement study to investigate whether UDP is viable as a general Internet transport protocol, the authors found that a high percentage of paths tested support UDP transport. A number of liaisons have been exchanged on this topic [ refs to ITU-T SG12, ETSI STQ, BBF liaisons ], discussing the laboratory and field tests that support the UDP-based approach to IP-layer Capacity measurement.

This memo also recognizes the many updates to the IP Performance Metrics Framework [RFC2330] published over twenty years, and makes use of [RFC7312] for Advanced Stream and Sampling Framework, and RFC 8468 [RFC8468]IPv4, IPv6, and IPv4-IPv6 Coexistence Updates.

NOTE: The text contains Author comments, in brackets [RG: , acm: ]

2. Scope and Goals

The scope of this memo is to define a metric and corresponding method to unambiguously perform Active measurements of Maximum IP-Layer Capacity.

The main goal is to harmonize the specified metric and method across the industry, and this memo is the vehicle through which working group (and eventually, IETF) consensus will be captured and communicated to achieve broad agreement, and possibly changes in other Standards Development Organizations (SDO).

A local goal is provide efficient test procedures where possible, and to recommend reporting with additional interpretation of the results. Also, to foster the development of protocol support for this metric and method of measurement.

3. Motivation

As with any problem that has been worked for many years in various SDOs without any special attempts at coordination, various solutions for metrics and methods have emerged.

There are five factors that have changed (or begun to change) in the last 5 years, and the presence of any one of them on the path requires features in the measurement design to account for the changes:

1. Internet access is no longer the bottleneck for many users
2. Both speed and latency are important to user's satisfaction
3. UDP's growing role in Transport, in areas where TCP once dominated.
4. Content and applications moving closer to users.
5. Possibly less traffic crossing ISP gateways in future.

4. Metric Definitions

This section sets requirements for the following components to support the Maximum IP-layer Capacity Metric.

4.1. Formal Name

Type-P-Max-IP-Capacity, or informally called Maximum IP-layer Capacity.

Note that Type-P depends on the chosen method.

4.2. Parameters

This section lists the REQUIRED input factors to specify a Route metric.

• Src, the address of a host (such as the globally routable IP address).
• Dst, the address of a host (such as the globally routable IP address).
• i, the limit on the number of Hops a specific packet may visit as it traverses from the host at Src to the host at Dst (such as the TTL or Hop Limit).
• MaxHops, the maximum value of i used, (i=1,2,3,...MaxHops).
• T, the time at the start of measurement interval
• I, the duration of measurement interval
• dt, the duration of N equal sub-intervals in I
• Ts, the host time of a transmitted test packet as measured at MP(Src), meaning Measurement Point at the Source.
• Ta, the host time of a test packet's *arrival* as measured at MP(Dst), assigned to packets that arrive within a "reasonable" time (see parameter below).
• Tmax, a maximum waiting time for test packets to arrive at the destination, set sufficiently long to disambiguate packets with long delays from packets that are discarded (lost), such that the distribution of one-way delay is not truncated.
• F, the number of different flows synthesized by the method.
• flow, the stream of packets with the same n-tuple of designated header fields that (when held constant) result in identical treatment in a multi-path decision (such as the decision taken in load balancing). Note: The IPv6 flow label MAY be included in the flow definition when routers have complied with [RFC6438] guidelines at the Tunnel End Points (TEP), and the source of the measurement is a TEP.
• Type-P, the complete description of the packets for which this assessment applies (including the flow-defining fields). Note that the UDP transport layer is one requirement specified below.
• PM, a list of fundamental metrics, such as loss, delay, and reordering, and corresponding Target performance threshold. At least one fundamental metric and Target performance threshold MUST be supplied (such as One-way IP Packet Loss [RFC7680] equal to zero).

4.3. Metric Definitions

This section defines the REQUIRED aspects of the measureable Maximum IP-layer Capacity metric (unless otherwise indicated) for measurements between specified Source and Destination hosts:

Define the IP-layer capacity, Maximum_C(T,I,PM), to be the maximum number of IP-layer bits (including header and data fields) that can be transmitted from the Src host and correctly received by the Dst host during one contiguous sub-interval, dt in length, during the interval [T, T+I], and where the packet count of that single sub-interval dtn in [T, T+I] indicates the maximum number of IP-layer bits n0[dtn-1,dtn] which was captured as part of all packet counts n for all dt in [T, T+I]. The interval dt SHOULD be set to a natural number m so that T+I = T + m*dt with dtn - dtn-1 = dt and with 0 < n <= m. Parameter PM represents the other performance metrics [see section Related Round-Trip Delay and Loss Definitions below] and their measurement results for the maximum IP-layer capacity. At least one target performance threshold MUST be defined. If more than one target performance threshold is defined, then the sub-interval with maximum number of bits transmitted MUST meet all the target performance thresholds.

[RG: this requires more explanation. Do you mean that all results must hit the target performance level? Or is a one / two / k times hit out of x trials [T, T+I] a criterium indicating that a target has been reached? Or do you look for the maximum capacity without packet loss and queuing or added RTD latency, respectively? acm: I think I've clarified this in the text above... ]

Mathematically, this definition can be represented as:

                        max  ( n0[dtn-1,dtn] )
                       [T,T+I]
  Maximum_C(T,I,PM) = -------------------------
                                 dt
 where:
    T                                      T+I
    _________________________________________
    |   |   |   |   |   |   |   |   |   |   |
dtn=0   1   2   3   4   5   6   7   8   9   m=10

Equation for Maximum Capacity

• n0 is the total number of IP-layer header and payload bits that can be transmitted in Standard Formed packets from the Src host and correctly received by the Dst host during one contiguous sub-interval, dt in length, during the interval [T, T+I],
• Maximum _C(T,I,PM) corresponds to the maximum value of n0 measured in any sub-interval ending at dtn (meaning T + n*dt), divided by the constant length of all sub-intervals, dt.
• all sub-intervals SHOULD be of equal duration. Choosing dt as non-overlapping consecutive time intervals allows for a simple implementation. [RG: a sliding window of dt has its charme too, why exclude it? acm: seems less practical for real-time feedback.]
• [acm: I think this is a discussion point, not essential to the definition] If traffic conditioning applies along a path for which Maximum _C(T,I,PM) is to be determined, different values for dt SHOULD be picked and measurements be executed during multiple intervals [T, T+I]. Any single interval dt SHOULD be chosen so that is an integer multiple of increasing values k times serialisation delay of a path MTU at the physical interface speed where traffic conditioning is expected. This should avoid taking configured burst tolerance singletons as a valid Maximum _C(T,I,PM) result.
• The bandwidth of the physical interface of the measurement device must be higher than that of the interface whose Maximum _C(T,I,PM) is to be measured.

In this definition, the m sub-intervals can be viewed as trials when the Src host varies the transmitted packet rate, searching for the maximum n0 that meets the PM criteria measured at the Dst host in a test of duration, I. When the transmitted packet rate is held constant at the Src host, the m sub-intervals may also be viewed as trials to evaluate the stability of n0 and metric(s) in the PM list over all dt-length intervals in I.

Measurements according to these definitions SHALL use UDP transport layer. [RG: don't we need loss free transmission without added latency as criteria and add that UDP without closed loop flow control needs to be applied ? acm: I don't think we should require loss-free transmission, because most networks allow a small loss ratio which would likely appear to be zero loss in most trials. Methods may use feedback, let's talk about how to diffentiate from flow-control]

4.4. Related Round-Trip Delay and Loss Definitions

RTD[dtn-1,dtn] is defined as a sample of the [RFC2681] Round-trip Delay between the Src host and the Dst host over the interval [T,T+I]. The statistics used to to summarize RTD[dtn-1,dtn] MAY include the minimum, maximum, and mean.

RTL[dtn-1,dtn] is defined as a sample of the [RFC6673] Round-trip Loss between the Src host and the Dst host over the interval [T,T+I]. The statistics used to to summarize RTL[dtn-1,dtn] MAY include the lost packet count and the lost packet ratio.

4.5. Discussion

Depending on the

4.6. Reporting the Metric

@@@@ not yet addressed,

5. Method of Measurement

This section needs development, based on Annex A of Y.1540.

The duration of a test, I, MUST be constrained in a production network, since this is an active test method and it will likely cause congestion on the Src to Dst host path during a test.

Additional Test methods and configurations may be provided in this section, after review.

5.1. Load Rate Adjustment Algorithm (from udpst)

A table is pre-built defining all the offered load rates that will be supported (R1 – Rn, in ascending order). Each rate is defined as datagrams of size S, sent as a burst of count C, every time interval T. While it is advantageous to use datagrams of as large a size as possible, it may be prudent to use a slightly smaller maximum that allows for secondary protocol headers and/or tunneling without resulting in IP-layer fragmentation.

At the beginning of a test, the sender begins sending at rate R1 and the receiver starts a feedback timer at interval F (while awaiting inbound datagrams). As datagrams are received they are checked for sequence number anomalies (loss, out-of-order, duplication, etc.) and the delay variation is measured (one-way or round-trip). This information is accumulated until the feedback timer F expires and a status feedback message is sent from the receiver back to the sender, to communicate this information. The accumulated statistics are then reset by the receiver for the next feedback interval. As feedback messages are received back at the sender, they are evaluated to determine how to adjust the current offered load rate (Rx).

If the feedback indicates that there were no sequence number anomalies AND the delay variation was below the lower threshold, the offered load rate is increased. If congestion has not been confirmed up to this point, the offered load rate is increased by more than one rate (e.g., Rx+10). This allows the offered load to quickly reach a near-maximum rate. Conversely, if congestion has been previously confirmed, the offered load rate is only increased by one (Rx+1).

If the feedback indicates that sequence number anomalies were detected OR the delay variation was above the upper threshold, the offered load rate is decreased. If congestion has not been confirmed up to this point, the offered load rate is decreased by more than one rate (e.g., Rx-30). This allows the offered load to back off enough to compensate for the fast initial ramp-up. Conversely, if congestion has been previously confirmed, the offered load rate is only decreased by one (Rx-1).

If the feedback indicates that there were no sequence number anomalies AND the delay variation was above the lower threshold, but below the upper threshold, the offered load rate is not changed. This allows time for recent changes in the offered load rate to stabilize, and the feedback to represent current conditions more accurately.

Lastly, the method for confirming congestion is that there were sequence number anomalies OR the delay variation was above the upper threshold for two consecutive feedback intervals.

6. Reporting

This section needs development...

The following text TO BE REPLACED !!!!

=======================================

The results SHOULD be reported in the format of a table with a row for each of the tested frame sizes and Number of Flows. There SHOULD be columns for the frame size with number of flows, and for the resultant average frame count (or time) for each type of data stream tested.

The number of tests Averaged for the Benchmark, N, MUST be reported.

The Minimum, Maximum, and Standard Deviation across all complete tests SHOULD also be reported.

The Corrected DUT Restoration Time SHOULD also be reported, as applicable.

Static and configuration parameters:

Number of test repetitions, N

Minimum Step Size (during searches), in frames.

7. Security Considerations

Active metrics and measurements have a long history of security considerations [add references to LMAP Framework, etc.].

<There are certainly some new ones for Capacity testing>

8. IANA Considerations

This memo makes no requests of IANA.

9. Acknowledgements

Thanks to

10. References

10.1. Normative References

10.2. Informative References

Authors' Addresses