Network Working Group                                         T. Mizrahi
Internet-Draft                                                   Marvell
Intended status: Informational                               G. Fioccola
Expires: September 6, 2017                                Telecom Italia
                                                                 M. Chen
                                                                L. Zheng
                                                     Huawei Technologies
                                                               G. Mirsky
                                                           March 5, 2017


    Passive Performance Monitoring using a Multiplexed Marking Field
          draft-mizrahi-ippm-multiplexed-alternate-marking-01

Abstract

   This memo introduces a marking method that uses a single marking bit,
   or two marking values, and allows accurate loss and delay
   measurement.

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
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   This Internet-Draft will expire on September 6, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Alternate Marking using a Multiplexed Marking Bit . . . . . .   4
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Timing and Synchronization Aspects  . . . . . . . . . . .   5
   4.  Alternate Marking using Two Multiplexed Marking Values  . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Alternate marking, defined in [I-D.ietf-ippm-alt-mark], is a method
   for measuring packet loss, packet delay, and packet delay variation.
   Typical delay measurement protocols require the two measurement
   points (MPs) to exchange timestamped test packets.  In contrast, the
   alternate marking method does not require control packets to be
   exchanged.  Instead, every data packet carries a color indicator,
   which divides the traffic into consecutive blocks of packets.

   The color indicator may either be a single-bit binary indication, or
   a two reserved values of a larger field, such as an IPv6 Flow Label
   or an MPLS Label.  Throughout the rest of the document it is assumed
   that the color indication is a single-bit field, unless specified
   otherwise.  The color value is toggled periodically, as illustrated
   in Figure 1.














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   A: packet with color 0
   B: packet with color 1

   Packets      AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
      Time   ---------------------------------------------------------->
               |          |          |          |          |
               | Block 1  | Block 2  | Block 3  | Block 4  | Block 5 ...
               |          |          |          |          |
   Color        0000000000 1111111111 0000000000 1111111111 0000000000

     Figure 1: Alternate marking: packets are monitored on a per-color
                                  basis.

   Alternate marking is used between two MPs, the initiating MP, and the
   monitoring MP.  The initiating MP incorporates the marking field into
   en-route packets, allowing the monitoring MP to use the marking field
   in order to bind each packet to the corresponding block.

   Each of the MPs maintains two counters, one per color.  At the end of
   each block the counter values can be collected by a central
   management system, and analyzed; the packet loss can be computed by
   comparing the counter values of the two MPs.

   When using alternate marking delay measurement can be performed in
   one of three ways (as per [I-D.ietf-ippm-alt-mark]):

   o  Single marking: the first packet of each block is used by both MPs
      as a reference for delay measurement.  The timestamp of this
      packet is measured by the two measurement points, and can be
      collected by the mangement system from each of the measurement
      points, which can compute the path delay by comparing the two
      timestamps.  The drawback of this approach is that it is not
      accurate when packets arrive out-of-order, as the two measurement
      may have a different view of which packet was the first in the
      block.

   o  Average delay: each of the MPs computes the average packet
      timestamp of each block.  The management system can then compute
      the delay by comparing the average times of the two MPs.  The
      drawback of this approach is that it may be computationally heavy,
      or difficult to implement at the data plane.

   o  Double marking: each packet uses two marking bits.  One bit is
      used as a color indicator, and one is used as a timestamping
      indicator.  This method resolves the drawbacks raised for the two
      previous methods, at the expense of an extra bit in the packet
      header.




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   The double marking method allows for accurate measurement without
   incurring expensive computational load.  However, in some cases
   allocating two bits for passive measurement is not possible.  For
   example, if alternate marking is implemented over IPv4, allocating 2
   marking bits in the IPv4 header is challenging, as every bit in the
   20-octet header is costly; one of the possible approaches discussed
   in [I-D.ietf-ippm-alt-mark] is reserve one or two bits from the DSCP
   field for remarking.  In this case every marking bit comes at the
   expense of reducing the DSCP range by a factor of two.

   This memo extends the marking method of [I-D.ietf-ippm-alt-mark].
   The method introduced in this document uses a single marking bit in
   the packet header, while providing the advantages of the double
   marking method.  In a nutshell, the color indicator and the timestamp
   indicator are multiplexed into a single bit.  There is an underlying
   assumption that the two MPs that take part in the measurement are
   time-synchronized.

2.  Terminology

2.1.  Requirements Language

   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 [RFC2119].

2.2.  Abbreviations

   MP         Measurement Point

   MPLS       Multiprotocol Label Switching

   DSCP       Differentiated Services Code Point

   LSP       Label Switched Path

   SFL       Synonymous Flow Label [I-D.bryant-mpls-sfl-framework]

3.  Alternate Marking using a Multiplexed Marking Bit

3.1.  Overview

   This section introduces a method that uses a single marking bit that
   serves two purposes: a color indicator, and a timestamp indicator.
   The double marking method that was discussed in the previous section
   uses two 1-bit values: a color indicator C, and a timestamp indicator
   T.  The multiplexed marking bit, denoted by M, is an exclusive or
   between these two values: M = C XOR T.



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   An example of the use of the multiplexed marking bit is depicted in
   Figure 2.  The example considers two routers, R1 and R2, that use the
   multiplexed bit method to measure traffic from R1 to R2.  In each
   block R1 designates one of the packets for delay measurement.  In
   each of these designated packets the value of the multiplexed bit is
   reversed compared to the other packets in the same block, allowing R2
   to distinguish the designated packets from the other packets.


   A: packet with color 0
   B: packet with color 1

   Packets      AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
      Time   ---------------------------------------------------------->
               |          |          |          |          |
               | Block 1  | Block 2  | Block 3  | Block 4  | Block 5 ...
               |          |          |          |          |
   Color        0000000000 1111111111 0000000000 1111111111 0000000000
                    ^          ^          ^           ^        ^
     Packets        |          |          |           |        |
     marked for     |          |          |           |        |
     timestamping   |          |          |           |        |
                    v          v          v           v        v
   Muxed bit    0000100000 1111011111 0000100000 1111101111 0001000000


             Figure 2: Alternate marking with multiplexed bit.

3.2.  Timing and Synchronization Aspects

   It is assumed that all MPs are synchronized to a common reference
   time with an accuracy of +/- A/2.  Thus, the difference between the
   clock values of any two MPs is bounded by A.  Clocks can be
   synchronized for example using NTP [RFC5905], PTP [IEEE1588], or by
   other means.  The common reference time is used for dividing the time
   domain into equal-sized measurement periods, such that all packets
   forwarded during a measurement period have the same color, and
   consecutive periods have alternating colors.

   The single marking bit incorporates two multiplexed values.  From the
   monitoring MP's perspective, the two values are Time-Division
   Multiplexed (TDM), as depicted in Figure 3.  It is assumed that the
   start time of every measurement period is known to both the
   initiating MP and the monitoring MP.  If the measurement period is L,
   then during the first and the last L/4 time units of each block the
   marking bit is interpreted by the monitoring MP as a color indicator.
   During the middle part of the block, the marking bit is interpreted
   as a timestamp indicator; if the value of this bit is different than



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   the color value, the corresponding packet is used as a reference for
   delay measurement.


                 +--- Beginning of measurement period
                 |
                 v

    ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
                 |<======================================>|
                 |                   L                    |
       <========>|<========><==================><========>|<========>
           L/4       L/4            L/2             L/4       L/4

       <===================><==================><===================>
           Detect color     Detect timestamping      Detect color
             change              indication            change

    Figure 3: Multiplexed marking field interpretation at the receiving
                            measurement point.

   In order to prevent ambiguity in the receiver's interpretation of the
   marking field, the initiating MP is permitted to set the timestamp
   indication only during a specific interval, as depicted in Figure 4.
   Since the receiver is willing to receive the timestamp indication
   during the middle L/2 time units of the block, the sender refrains
   from sending the timestamp indication during a guardband interval of
   d time units at the beginning and end of the L/2-period.


                 +--- Beginning of measurement period
                 |
                 v

    ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
                 |<======================================>|
                 |                   L                    |
       <========>|<========>|<================>|<========>|
           L/4       L/4    |       L/2        |    L/4
                         <=>|<=>            <=>|<=>
                          d   d              d   d
                                <==========>
                                permissible
                                timestamping
                                indication
                                interval

                       Figure 4: A time domain view.



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   The guardband d is given by d = A + D_max - D_min, where A is the
   clock accuracy, D_max is an upper bound on the network delay between
   the MPs, and D_min is a lower bound on the delay.  It is
   straightforward from Figure 4 that d < L/4 must be satisfied.  The
   latter implies a minimal requirement on the synchronization accuracy.

   All MPs must be synchronized to the same reference time with an
   accuracy of +/- L/8.  Depending on the system topology, in some
   systems the accuracy requirement will be even more stringent, subject
   to d < L/4.  Note that the accuracy requirement of the conventional
   alternate marking method [I-D.ietf-ippm-alt-mark] is +/- L/2, while
   the multiplexed marking method requires an accuracy of +/- L/8.

   Note that we assume that the middle L/2-period is designated as the
   timestamp indication period, allowing a sufficiently long guardband
   between the transitions.  However, a system may be configured to use
   a longer timestamp indication period or a shorter one, if it is
   guaranteed that the synchronization accuracy meets the guardband
   requirements (i.e., the constraints on d).

4.  Alternate Marking using Two Multiplexed Marking Values

   As mentioned above, the color indicator is not necessarily a single
   bit, but may be implemented by using two well-known values in one of
   the header fields.  For example, as defined in
   [I-D.bryant-mpls-rfc6374-sfl], two MPLS Label values can be used to
   indicate the two colors of a given LSP: the original Label value, and
   a Synonymous Flow Label (SFL) value.

   The bit multiplexing approach of Section 3 is applicable not only to
   single-bit color indicators, but also to two-value indicators;
   instead of using a single bit that is toggled between '0' and '1',
   two values of the indicator field, U and W, can be used in the same
   manner, allowing both loss and delay measurement to be performed
   using only two reserved values.  Thus, the multiplexing approach of
   Figure 2 can be illustrated more generally with two values, U and W,
   as depicted in Figure 5.














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   A: packet with color 0
   B: packet with color 1

   Packets      AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
      Time   ---------------------------------------------------------->
               |          |          |          |          |
               | Block 1  | Block 2  | Block 3  | Block 4  | Block 5 ...
               |          |          |          |          |
   Color        0000000000 1111111111 0000000000 1111111111 0000000000
                    ^          ^          ^           ^        ^
     Packets        |          |          |           |        |
     marked for     |          |          |           |        |
     timestamping   |          |          |           |        |
                    v          v          v           v        v
   Muxed        UUUUWUUUUU WWWWUWWWWW UUUUWUUUUU WWWWWUWWWW UUUWUUUUUU
   marking
   values

    Figure 5: Alternate marking with two multiplexed marking values, U
                                  and W.

5.  IANA Considerations

   This memo includes no requests from IANA.

6.  Security Considerations

   The security considerations of the alternate marking method are
   discussed in [I-D.ietf-ippm-alt-mark].  Specifically, the method that
   is defined in this document requires slightly more stringent
   synchronization than the conventional marking method, potentially
   making the method more vulnerable to attacks on the time
   synchronization protocol.  A detailed discussion about the threats
   against time protocols and how to mitigate them is presented in
   [RFC7384].

7.  References

7.1.  Normative References

   [I-D.ietf-ippm-alt-mark]
              Fioccola, G., Capello, A., Cociglio, M., Castaldelli, L.,
              Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate Marking method for passive performance
              monitoring", draft-ietf-ippm-alt-mark-04 (work in
              progress), March 2017.





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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

7.2.  Informative References

   [I-D.bryant-mpls-rfc6374-sfl]
              Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
              Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow
              Labels", draft-bryant-mpls-rfc6374-sfl-03 (work in
              progress), October 2016.

   [I-D.bryant-mpls-sfl-framework]
              Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
              and G. Mirsky, "Synonymous Flow Label Framework", draft-
              bryant-mpls-sfl-framework-02 (work in progress), October
              2016.

   [IEEE1588]
              IEEE, "IEEE 1588 Standard for a Precision Clock
              Synchronization Protocol for Networked Measurement and
              Control Systems Version 2", 2008.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <http://www.rfc-editor.org/info/rfc5905>.

   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
              Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
              October 2014, <http://www.rfc-editor.org/info/rfc7384>.

Authors' Addresses

   Tal Mizrahi
   Marvell
   6 Hamada st.
   Yokneam
   Israel

   Email: talmi@marvell.com









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   Giuseppe Fioccola
   Telecom Italia
   Via Reiss Romoli, 274
   Torino 10148
   Italy

   Email: giuseppe.fioccola@telecomitalia.it


   Mach(Guoyi) Chen
   Huawei Technologies

   Email: mach.chen@huawei.com


   Lianshu Zheng
   Huawei Technologies

   Email: vero.zheng@huawei.com


   Greg Mirsky
   USA

   Email: gregimirsky@gmail.com


























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