IPPM Working Group                                             G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Informational                              W. Lingqiang
Expires: January 3, 2019                                         G. Zhui
                                                         ZTE Corporation
                                                            July 2, 2018

             Hybrid Two-Step Performance Measurement Method


   Development of, and advancements in, automation of network operations
   brought new requirements for measurement methodology.  Among them is
   the ability to collect instant network state as the packet being
   processed by the networking elements along its path through the
   domain.  This document introduces a new hybrid measurement method,
   referred to as hybrid two-step, as it separates the act of measuring
   and/or calculating performance metric from the act of collecting and
   transporting network state.

Status of This Memo

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   This Internet-Draft will expire on January 3, 2019.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Problem Overview  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Successful resolution of challenges of automated network operation,
   as part of, for example, overall service orchestration or data center
   operation, relies on a timely collection of accurate information that
   reflects the state of network elements on an unprecedented scale.
   Because performing the analysis and act upon the collected
   information requires considerable computing and storage resources,
   the network state information is unlikely to be processed by network
   elements themselves but will be relayed into the data storage
   facilities, e.g. data lakes.  The process of producing, collecting
   network state information also referred in this document as network
   telemetry, and transporting it for post-processing should work
   equally well with data flows or injected in the network test packets.
   RFC 7799 [RFC7799] describes a combination of elements of passive and
   active measurement as a hybrid measurement.

   Several technical methods have been proposed to enable collection of
   network state information instantaneous to the packet processing,
   among them [P4.INT] and [I-D.ietf-ippm-ioam-data].

   This document introduces Hybrid Two-Step (HTS) as a new hybrid
   measurement method that separates measuring or calculating
   performance metric from the collecting and transporting this
   information.  The Hybrid Two-Step method extends the two-step mode of

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   Residence Time Measurement (RTM) defined in [RFC8169] to on-path
   network state collection and transport.

2.  Conventions used in this document

2.1.  Terminology

   RTM Residence Time Measurement

   ECMP Equal Cost Multipath

   MTU Maximum Transmission Unit

   HTS Hybrid Two-Step

   Network telemetry - the process of collecting and reporting of
   network state

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

3.  Problem Overview

   Performance measurements are meant to provide data that characterize
   conditions experienced by traffic flows in the network and possibly
   trigger operational changes (e.g. - re-route of flows, or changes in
   resource allocations).  Changes to a network are determined based on
   the performance metric information available at the time that a
   change is to be made.  The correctness of this determination is based
   on the quality of the collected metrics data.  The quality of
   collected measurement data is defined is defined by:

   o  the resolution and accuracy of each measurement;

   o  predictability of both the time at which each measurement is made
      and the timeliness of measurement collection data delivery for

   Consider the case of delay measurement that relies on collecting time
   of packet arrival at the ingress interface and time of the packet
   transmission at egress interface.  The method may be to record a
   local clock value on receiving the first octet of an affected message
   at the device ingress, and again to record the clock value on sending

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   the first byte of the same message at the device egress.  In this
   ideal case, the difference between the two recorded clock times
   corresponds to the time that the message spent in traversing the
   device.  In practice, the times actually recorded can differ from the
   ideal case by any fixed amount and a correction may then be applied
   to compute the same time difference taking into account the known
   fixed time associated with the actual measurement.  In this way, the
   resulting time difference reflects any variable delay associated with

   Depending on the implementation, it may be a challenge to compute the
   difference between message arrival and departure times and - on the
   fly - add the necessary residence time information to the same
   message.  And that task may become even more challenging if the
   packet is encrypted.  Implementations SHOULD NOT record a message
   departure time that may be significantly inaccurate in an effort to
   include a correlated/computed delay value, in the same message, as a
   result of estimating the departure time while including any variable
   time component (such as that associated with buffering and queuing of
   messages).  A similar problem may cause a lower quality of, for
   example, information that characterizes utilization of the egress
   interface.  If unable to obtain the data consistently, without
   variable delays for additional processing, information may not
   accurately reflect the state at the egress interface.  To mitigate
   this problem [RFC8169] defined RTM two-step mode.

   Another challenge associated with methods that collect network state
   information into the actual data packet is the risk to exceed the
   Maximum Transmission Unit (MTU) size, particularly if the packet
   traverses overlay domains or VPNs.  Since the fragmentation is not
   available at the transport network, operators may have to reduce MTU
   size advertised to client layer or risk missing network state data
   for the part, most probably the latter part, of the path.

4.  Theory of Operation

   The HTS method consists of the two phases:

   o  performing a measurement or obtaining network state information,
      one or more than one type, on a node;

   o  collecting and transporting the measurement.

   HTS uses HTS Control message to define types of measurement or
   network state data collection requested from a node.  HTS Control
   message may be inserted into the data packet, as meta-data or shim,
   or be transmitted in a specially constructed test packet.

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   To collect measurement and network state data from the nodes HTS
   method uses the follow-up packet.  The node that creates the HTS
   Control message also originates the HTS follow-up packet.  The
   follow-up packet contains characteristic information, copied from the
   data packet, sufficient for participating nodes to associate it with
   the original packet.  The exact composition of the characteristic
   information is specific for each transport network and its definition
   is outside the scope of this document.  The follow-up packet also
   uses the same encapsulation as the data packet.  If not payload but
   only network information used to load-balance flows in equal cost
   multipath (ECMP), use of the network encapsulation identical to the
   data packet should guarantee that the follow-up packet remains in-
   band, i.e. traverses the same set of network elements, with the
   original data packet.  Only one outstanding follow-up packet may be
   on the node for the given path.  That means that if the node receives
   HTS Control message for the flow on which it still waits for the
   follow-up packet to the previous HTS Control message, the node will
   originate the follow-up packet to transport the former set of the
   network state data and transmit it before it transmits the follow-up
   packet with the latest set of network state information.

5.  IANA Considerations

   This document doesn't have any IANA requirements.  The section may be
   deleted before the publication.

6.  Security Considerations

   Nodes that practice HTS method are presumed to share a trust model
   that depends on the existence of a trusted relationship among nodes.
   This is necessary as these nodes are expected to correctly modify the
   specific content of the data in the follow-up packet, and the degree
   to which HTS measurement is useful for network operation depends on
   this ability.  In practice, this means that those portions of
   messages that contain the network state data cannot be covered by
   either confidentiality or integrity protection.  Though there are
   methods that make it possible in theory to provide either or both
   such protections and still allow for intermediate nodes to make
   detectable but authenticated modifications, such methods do not seem
   practical at present, particularly for protocols that used to measure
   latency and/or jitter.

   The ability to potentially authenticate and/or encrypt the network
   state data for scenarios both with and without the participation of
   intermediate nodes that participate in HTS measurement is left for
   further study.

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   While it is possible for a supposed compromised node to intercept and
   modify the network state information in the follow-up packet, this is
   an issue that exists for nodes in general - for any and all data that
   may be carried over the particular networking technology - and is
   therefore the basis for an additional presumed trust model associated
   with an existing network.

7.  Acknowledgments


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
              "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
              data-03 (work in progress), June 2018.

   [P4.INT]   "In-band Network Telemetry (INT)", P4.org Specification,
              October 2017.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC8169]  Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
              and A. Vainshtein, "Residence Time Measurement in MPLS
              Networks", RFC 8169, DOI 10.17487/RFC8169, May 2017,

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Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com

   Wang Lingqiang
   ZTE Corporation
   No 19 ,East Huayuan Road
   Beijing   100191

   Phone: +86 10 82963945
   Email: wang.lingqiang@zte.com.cn

   Guo Zhui
   ZTE Corporation
   No 19 ,East Huayuan Road
   Beijing   100191

   Phone: +86 10 82963945
   Email: guo.zhui@zte.com.cn

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