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Versions: 00 01 02 03 04                                 Standards Track
          draft-ietf-ippm-rfc8889bis                                    
Network Working Group                                   G. Fioccola, Ed.
Internet-Draft                                       Huawei Technologies
Obsoletes: 8889 (if approved)                                M. Cociglio
Intended status: Standards Track                          Telecom Italia
Expires: October 7, 2022                                        A. Sapio
                                                       Intel Corporation
                                                                R. Sisto
                                                   Politecnico di Torino
                                                                 T. Zhou
                                                     Huawei Technologies
                                                           April 5, 2022


                  Multipoint Alternate-Marking Method
                      draft-fioccola-rfc8889bis-04

Abstract

   This document generalizes and expands Alternate-Marking methodology
   to measure any kind of unicast flow whose packets can follow several
   different paths in the network -- in wider terms, a multipoint-to-
   multipoint network.  For this reason, the technique here described is
   called "Multipoint Alternate Marking".  This document obsoletes
   [RFC8889].

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/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 7, 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Correlation with RFC 5644 . . . . . . . . . . . . . . . .   6
   3.  Flow Classification . . . . . . . . . . . . . . . . . . . . .   6
   4.  Extension of the Method to Multipoint Flows . . . . . . . . .   9
     4.1.  Monitoring Network  . . . . . . . . . . . . . . . . . . .   9
     4.2.  Network Packet Loss . . . . . . . . . . . . . . . . . . .  10
   5.  Network Clustering  . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Algorithm for Clusters Partition  . . . . . . . . . . . .  12
   6.  Multipoint Packet Loss Measurement  . . . . . . . . . . . . .  16
   7.  Multipoint Delay and Delay Variation  . . . . . . . . . . . .  16
     7.1.  Delay Measurements on a Multipoint-Paths Basis  . . . . .  17
       7.1.1.  Single-Marking Measurement  . . . . . . . . . . . . .  17
     7.2.  Delay Measurements on a Single-Packet Basis . . . . . . .  17
       7.2.1.  Single- and Double-Marking Measurement  . . . . . . .  17
       7.2.2.  Hashing Selection Method  . . . . . . . . . . . . . .  18
   8.  Synchronization and Timing  . . . . . . . . . . . . . . . . .  19
   9.  Results of the Multipoint Alternate Marking Experiment  . . .  21
   10. A Closed-Loop Performance-Management Approach . . . . . . . .  21
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  23
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  23
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     15.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  Changes Log  . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   The Alternate-Marking method, as described in
   [I-D.fioccola-rfc8321bis], is applicable to a point-to-point path.
   The extension proposed in this document applies to the most general




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   case of a multipoint-to-multipoint path and enables flexible and
   adaptive performance measurements in a managed network.

   The Alternate-Marking methodology described in
   [I-D.fioccola-rfc8321bis] allows the synchronization of the
   measurements at different points by dividing the packet flow into
   batches.  So it is possible to get coherent counters and show what is
   happening in every marking period for each monitored flow.  The
   monitoring parameters are the packet counter and timestamps of a flow
   for each marking period.  Note that additional details about the
   applicability of the Alternate-Marking methodology are described in
   [I-D.fioccola-rfc8321bis] while implementation details can be found
   in the paper "AM-PM: Efficient Network Telemetry using Alternate
   Marking" [IEEE-Network-PNPM].

   There are some applications of the Alternate-Marking method where
   there are a lot of monitored flows and nodes.  Multipoint Alternate
   Marking aims to reduce these values and makes the performance
   monitoring more flexible in case a detailed analysis is not needed.
   For instance, by considering n measurement points and m monitored
   flows, the order of magnitude of the packet counters for each time
   interval is n*m*2 (1 per color).  The number of measurement points
   and monitored flows may vary and depends on the portion of the
   network we are monitoring (core network, metro network, access
   network) and the granularity (for each service, each customer).  So
   if both n and m are high values, the packet counters increase a lot,
   and Multipoint Alternate Marking offers a tool to control these
   parameters.

   The approach presented in this document is applied only to unicast
   flows and not to multicast.  Broadcast, Unknown Unicast, and
   Multicast (BUM) traffic is not considered here, because traffic
   replication is not covered by the Multipoint Alternate-Marking
   method.  Furthermore, it can be applicable to anycast flows, and
   Equal-Cost Multipath (ECMP) paths can also be easily monitored with
   this technique.

   [I-D.fioccola-rfc8321bis] applies to point-to-point unicast flows and
   BUM traffic.  For BUM traffic, the basic method of
   [I-D.fioccola-rfc8321bis] can easily be applied link by link and
   therefore split the multicast flow tree distribution into separate
   unicast point-to-point links.  While this document and its Clustered
   Alternate-Marking method is valid for multipoint-to-multipoint
   unicast flows, anycast, and ECMP flows.

   Therefore, the Alternate-Marking method can be extended to any kind
   of multipoint-to-multipoint paths, and the network-clustering
   approach presented in this document is the formalization of how to



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   implement this property and allow a flexible and optimized
   performance measurement support for network management in every
   situation.

   Without network clustering, it is possible to apply Alternate Marking
   only for all the network or per single flow.  Instead, with network
   clustering, it is possible to use the partition of the network into
   clusters at different levels in order to provide the needed degree of
   detail.  In some circumstances, it is possible to monitor a
   multipoint network by monitoring the network clusters, without
   examining in depth.  In case of problems (packet loss is measured or
   the delay is too high), the filtering criteria could be enhanced in
   order to perform a detailed analysis by using a different combination
   of clusters up to a per-flow measurement as described in
   [I-D.fioccola-rfc8321bis].

   This approach fits very well with the Closed-Loop Network and
   Software-Defined Network (SDN) paradigm, where the SDN orchestrator
   and the SDN controllers are the brains of the network and can manage
   flow control to the switches and routers and, in the same way, can
   calibrate the performance measurements depending on the desired
   accuracy.  An SDN controller application can orchestrate how
   accurately the network performance monitoring is set up by applying
   the Multipoint Alternate Marking as described in this document.

   It is important to underline that, as an extension of
   [I-D.fioccola-rfc8321bis], this is a methodology document, so the
   mechanism that can be used to transmit the counters and the
   timestamps is out of scope here, and the implementation is open.
   Several options are possible -- e.g., see "Enhanced Alternate Marking
   Method" [I-D.zhou-ippm-enhanced-alternate-marking].

   This document assumes that the blocks are created according to a
   fixed timer as per [I-D.fioccola-rfc8321bis].  Switching after a
   fixed number of packets is possible but it is out of scope here.

   Note that the fragmented packets case can be managed with the
   Alternate-Marking methodology.  The same considerations of
   [I-D.fioccola-rfc8321bis] apply also in the case of Multipoint
   Alternate Marking.  As defined in [I-D.fioccola-rfc8321bis] the
   marking node MUST mark all the fragments except in the case of
   fragmentation within the network domain, in that event it is
   suggested to mark only the first fragment.








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1.1.  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.

2.  Terminology

   The definitions of the basic terms are identical to those found in
   Alternate Marking [I-D.fioccola-rfc8321bis].  It is to be remembered
   that [I-D.fioccola-rfc8321bis] is valid for point-to-point unicast
   flows and BUM traffic.

   The important new terms that need to be explained are listed below:

      Multipoint Alternate Marking: Extension to
      [I-D.fioccola-rfc8321bis], valid for multipoint-to-multipoint
      unicast flows, anycast, and ECMP flows.  It can also be referred
      to as Clustered Alternate Marking.

      Flow definition: The concept of flow is generalized in this
      document.  The identification fields are selected without any
      constraints and, in general, the flow can be a multipoint-to-
      multipoint flow, as a result of aggregate point-to-point flows.

      Monitoring Network: Identified with the nodes of the network that
      are the measurement points (MPs) and the links that are the
      connections between MPs.  The monitoring network graph depends on
      the flow definition, so it can represent a specific flow or the
      entire network topology as aggregate of all the flows.

      Cluster: Smallest identifiable subnetwork of the entire monitoring
      network graph that still satisfies the condition that the number
      of packets that go in is the same as the number that go out.

      Multipoint metrics: Packet loss, delay and delay variation are
      extended to the case of multipoint flows.  It is possible to
      compute these metrics on the basis of multipoint paths in order to
      associate the measurements to a cluster, a combination of
      clusters, or the entire monitored network.  For delay and delay
      variation, it is also possible to define the metrics on a single-
      packet basis, and it means that the multipoint path is used to
      easily couple packets between input and output nodes of a
      multipoint path.





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   The next section highlights the correlation with the terms used in
   RFC 5644 [RFC5644].

2.1.  Correlation with RFC 5644

   RFC 5644 [RFC5644] is limited to active measurements using a single
   source packet or stream.  Its scope is also limited to observations
   of corresponding packets along the path (spatial metric) and at one
   or more destinations (one-to-group) along the path.

   Instead, the scope of this memo is to define multiparty metrics for
   passive and hybrid measurements in a group-to-group topology with
   multiple sources and destinations.

   RFC 5644 [RFC5644] introduces metric names that can be reused here
   but have to be extended and rephrased to be applied to the Alternate-
   Marking schema:

   a.  the multiparty metrics are not only one-to-group metrics but can
       be also group-to-group metrics;

   b.  the spatial metrics, used for measuring the performance of
       segments of a source to destination path, are applied here to
       group-to-group segments (called clusters).

3.  Flow Classification

   A unicast flow is identified by all the packets having a set of
   common characteristics.  This definition is inspired by RFC 7011
   [RFC7011].

   As an example, by considering a flow as all the packets sharing the
   same source IP address or the same destination IP address, it is easy
   to understand that the resulting pattern will not be a point-to-point
   connection, but a point-to-multipoint or multipoint-to-point
   connection.

   In general, a flow can be defined by a set of selection rules used to
   match a subset of the packets processed by the network device.  These
   rules specify a set of Layer 3 and Layer 4 header fields
   (identification fields) and the relative values that must be found in
   matching packets.

   The choice of the identification fields directly affects the type of
   paths that the flow would follow in the network.  In fact, it is
   possible to relate a set of identification fields with the pattern of
   the resulting graphs, as listed in Figure 1.




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   A TCP 5-tuple usually identifies flows following either a single path
   or a point-to-point multipath (in the case of load balancing).  On
   the contrary, a single source address selects aggregate flows
   following a point-to-multipoint, while a multipoint-to-point can be
   the result of a matching on a single destination address.  In the
   case where a selection rule and its reverse are used for
   bidirectional measurements, they can correspond to a point-to-
   multipoint in one direction and a multipoint-to-point in the opposite
   direction.

   So the flows to be monitored are selected into the monitoring points
   using packet selection rules, which can also change the pattern of
   the monitored network.

   Note that, more generally, the flow can be defined at different
   levels based on the potential encapsulation, and additional
   conditions that are not in the packet header can also be included as
   part of matching criteria.

   The Alternate-Marking method is applicable only to a single path (and
   partially to a one-to-one multipath), so the extension proposed in
   this document is suitable also for the most general case of
   multipoint-to-multipoint, which embraces all the other patterns of
   Figure 1.


          point-to-point single path
              +------+      +------+      +------+
          ---<>  R1  <>----<>  R2  <>----<>  R3  <>---
              +------+      +------+      +------+


          point-to-point multipath
                           +------+
                          <>  R2  <>
                         / +------+ \
                        /            \
              +------+ /              \ +------+
          ---<>  R1  <>                <>  R4  <>---
              +------+ \              / +------+
                        \            /
                         \ +------+ /
                          <>  R3  <>
                           +------+


          point-to-multipoint
                                      +------+



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                                     <>  R4  <>---
                                    / +------+
                          +------+ /
                         <>  R2  <>
                        / +------+ \
              +------+ /            \ +------+
          ---<>  R1  <>              <>  R5  <>---
              +------+ \              +------+
                        \ +------+
                         <>  R3  <>
                          +------+ \
                                    \ +------+
                                     <>  R6  <>---
                                      +------+


          multipoint-to-point
              +------+
          ---<>  R1  <>
              +------+ \
                        \ +------+
                        <>  R4  <>
                        / +------+ \
              +------+ /            \ +------+
          ---<>  R2  <>              <>  R6  <>---
              +------+              / +------+
                          +------+ /
                         <>  R5  <>
                        / +------+
              +------+ /
          ---<>  R3  <>
              +------+


          multipoint-to-multipoint
              +------+                +------+
          ---<>  R1  <>              <>  R6  <>---
              +------+ \            / +------+
                        \ +------+ /
                         <>  R4  <>
                          +------+ \
              +------+              \ +------+
          ---<>  R2  <>             <>  R7  <>---
              +------+ \            / +------+
                        \ +------+ /
                         <>  R5  <>
                        / +------+ \
              +------+ /            \ +------+



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          ---<>  R3  <>              <>  R8  <>---
              +------+                +------+


                       Figure 1: Flow Classification

   The case of unicast flow is considered in Figure 1.  The anycast flow
   is also in scope, because there is no replication and only a single
   node from the anycast group receives the traffic, so it can be viewed
   as a special case of unicast flow.  Furthermore, an ECMP flow is in
   scope by definition, since it is a point-to-multipoint unicast flow.

4.  Extension of the Method to Multipoint Flows

   By using the Alternate-Marking method, only point-to-point paths can
   be monitored.  To have an IP (TCP/UDP) flow that follows a point-to-
   point path, in general we have to define, with a specific value, 5
   identification fields (IP Source, IP Destination, Transport Protocol,
   Source Port, Destination Port).

   Multipoint Alternate Marking enables the performance measurement for
   multipoint flows selected by identification fields without any
   constraints (even the entire network production traffic).  It is also
   possible to use multiple marking points for the same monitored flow.

4.1.  Monitoring Network

   The monitoring network is deduced from the production network by
   identifying the nodes of the graph that are the measurement points,
   and the links that are the connections between measurement points.

   There are some techniques that can help with the building of the
   monitoring network (as an example, see [I-D.ietf-ippm-route]).  In
   general, there are different options: the monitoring network can be
   obtained by considering all the possible paths for the traffic or
   periodically checking the traffic (e.g. daily, weekly, monthly) and
   updating the graph as appropriate, but this is up to the Network
   Management System (NMS) configuration.

   So a graph model of the monitoring network can be built according to
   the Alternate-Marking method: the monitored interfaces and links are
   identified.  Only the measurement points and links where the traffic
   has flowed have to be represented in the graph.

   Figure 2 shows a simple example of a monitoring network graph:






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                                                    +------+
                                                   <>  R6  <>---
                                                  / +------+
                           +------+     +------+ /
                          <>  R2  <>---<>  R4  <>
                         / +------+ \   +------+ \
                        /            \            \ +------+
              +------+ /   +------+   \ +------+   <>  R7  <>---
          ---<>  R1  <>---<>  R3  <>---<>  R5  <>   +------+
              +------+ \   +------+ \   +------+ \
                        \            \            \ +------+
                         \            \            <>  R8  <>---
                          \            \            +------+
                           \            \
                            \            \ +------+
                             \            <>  R9  <>---
                              \            +------+
                               \
                                \ +------+
                                 <>  R10 <>---
                                  +------+


                    Figure 2: Monitoring Network Graph

   Each monitoring point is characterized by the packet counter that
   refers only to a marking period of the monitored flow.  Also, it is
   assumed that there be a monitoring point at all possible egress
   points of the multipoint monitored network.

   The same is also applicable for the delay, but it will be described
   in the following sections.

   The rest of the document assumes that the traffic is going from left
   to right in order to simplify the explanation.  But the analysis done
   for one direction applies equally to all directions.

4.2.  Network Packet Loss

   Since all the packets of the considered flow leaving the network have
   previously entered the network, the number of packets counted by all
   the input nodes is always greater than, or equal to, the number of
   packets counted by all the output nodes.  Non-initial fragments are
   not considered here.

   In the case of no packet loss occurring in the marking period, if all
   the input and output points of the network domain to be monitored are
   measurement points, the sum of the number of packets on all the



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   ingress interfaces equals the number on egress interfaces for the
   monitored flow.  In this circumstance, if no packet loss occurs, the
   intermediate measurement points only have the task of splitting the
   measurement.

   It is possible to define the Network Packet Loss of one monitored
   flow for a single period.  In a packet network, the number of lost
   packets is the number of packets counted by the input nodes minus the
   number of packets counted by the output nodes.  This is true for
   every packet flow in each marking period.

   The monitored network packet loss with n input nodes and m output
   nodes is given by:

   PL = (PI1 + PI2 +...+ PIn) - (PO1 + PO2 +...+ POm)

   where:

   PL is the network packet loss (number of lost packets)

   PIi is the number of packets flowed through the i-th input node in
   this period

   POj is the number of packets flowed through the j-th output node in
   this period

   The equation is applied on a per-time-interval basis and a per-flow
   basis:

      The reference interval is the Alternate-Marking period, as defined
      in [I-D.fioccola-rfc8321bis].

      The flow definition is generalized here.  Indeed, as described
      before, a multipoint packet flow is considered, and the
      identification fields can be selected without any constraints.

5.  Network Clustering

   The previous equation of Section 4.2 can determine the number of
   packets lost globally in the monitored network, exploiting only the
   data provided by the counters in the input and output nodes.

   In addition, it is also possible to leverage the data provided by the
   other counters in the network to converge on the smallest
   identifiable subnetworks where the losses occur.  These subnetworks
   are named "clusters".





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   A cluster graph is a subnetwork of the entire monitoring network
   graph that still satisfies the packet loss equation (introduced in
   the previous section), where PL in this case is the number of packets
   lost in the cluster.  As for the entire monitoring network graph, the
   cluster is defined on a per-flow basis.

   For this reason, a cluster should contain all the arcs emanating from
   its input nodes and all the arcs terminating at its output nodes.
   This ensures that we can count all the packets (and only those)
   exiting an input node again at the output node, whatever path they
   follow.

   In a completely monitored unidirectional network (a network where
   every network interface is monitored), each network device
   corresponds to a cluster, and each physical link corresponds to two
   clusters (one for each device).

   Clusters can have different sizes depending on the flow-filtering
   criteria adopted.

   Moreover, sometimes clusters can be optionally simplified.  For
   example, when two monitored interfaces are divided by a single router
   (one is the input interface, the other is the output interface, and
   the router has only these two interfaces), instead of counting
   exactly twice, upon entering and leaving, it is possible to consider
   a single measurement point.  In this case, we do not care about the
   internal packet loss of the router.

   It is worth highlighting that it might also be convenient to define
   clusters based on the topological information so that they are
   applicable to all the possible flows in the monitored network.

5.1.  Algorithm for Clusters Partition

   A simple algorithm can be applied in order to split our monitoring
   network into clusters.  This can be done for each direction
   separately.  The clusters partition is based on the monitoring
   network graph, which can be valid for a specific flow or can also be
   general and valid for the entire network topology.

   It is a two-step algorithm:

   o  Group the links where there is the same starting node;

   o  Join the grouped links with at least one ending node in common.

   Considering that the links are unidirectional, the first step implies
   listing all the links as connections between two nodes and grouping



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   the different links if they have the same starting node.  Note that
   it is possible to start from any link, and the procedure will work.
   Following this classification, the second step implies eventually
   joining the groups classified in the first step by looking at the
   ending nodes.  If different groups have at least one common ending
   node, they are put together and belong to the same set.  After the
   application of the two steps of the algorithm, each one of the
   composed sets of links, together with the endpoint nodes, constitutes
   a cluster.

   In our monitoring network graph example, it is possible to identify
   the clusters partition by applying this two-step algorithm.

   The first step identifies the following groups:

   1.  Group 1: (R1-R2), (R1-R3), (R1-R10)

   2.  Group 2: (R2-R4), (R2-R5)

   3.  Group 3: (R3-R5), (R3-R9)

   4.  Group 4: (R4-R6), (R4-R7)

   5.  Group 5: (R5-R8)

   And then, the second step builds the clusters partition (in
   particular, we can underline that Groups 2 and 3 connect together,
   since R5 is in common):

   1.  Cluster 1: (R1-R2), (R1-R3), (R1-R10)

   2.  Cluster 2: (R2-R4), (R2-R5), (R3-R5), (R3-R9)

   3.  Cluster 3: (R4-R6), (R4-R7)

   4.  Cluster 4: (R5-R8)

   The flow direction here considered is from left to right.  For the
   opposite direction, the same reasoning can be applied, and in this
   example, you get the same clusters partition.

   In the end, the following 4 clusters are obtained:


          Cluster 1
                           +------+
                          <>  R2  <>---
                         / +------+



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                        /
              +------+ /   +------+
          ---<>  R1  <>---<>  R3  <>---
              +------+ \   +------+
                        \
                         \
                          \
                           \
                            \
                             \
                              \
                               \
                                \ +------+
                                 <>  R10 <>---
                                  +------+


          Cluster 2
              +------+     +------+
          ---<>  R2  <>---<>  R4  <>---
              +------+ \   +------+
                        \
              +------+   \ +------+
          ---<>  R3  <>---<>  R5  <>---
              +------+ \   +------+
                        \
                         \
                          \
                           \
                            \ +------+
                             <>  R9  <>---
                              +------+


          Cluster 3
                          +------+
                         <>  R6  <>---
                        / +------+
              +------+ /
          ---<>  R4  <>
              +------+ \
                        \ +------+
                         <>  R7  <>---
                          +------+


          Cluster 4
              +------+



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          ---<>  R5  <>
              +------+ \
                        \ +------+
                         <>  R8  <>---
                          +------+


                        Figure 3: Clusters Example

   There are clusters with more than two nodes as well as two-node
   clusters.  In the two-node clusters, the loss is on the link (Cluster
   4).  In more-than-two-node clusters, the loss is on the cluster, but
   we cannot know in which link (Cluster 1, 2, or 3).

   The algorithm, as applied in this example of a point-to-multipoint
   network, works for the more general case of multipoint-to-multipoint
   network in the same way.  It should be highlighted that for a
   multipoint-to-multipoint network the multiple sources MUST mark
   coherently the traffic and MUST be synchronized with all the other
   nodes according to the timing requirements detailed in Section 8.

   When the clusters partition is done, the calculation of packet loss,
   delay and delay variation can be made on a cluster basis.  Note that
   the packet counters for each marking period permit calculating the
   packet rate on a cluster basis, so Committed Information Rate (CIR)
   and Excess Information Rate (EIR) could also be deduced on a cluster
   basis.

   Obviously, by combining some clusters in a new connected subnetwork
   the packet-loss rule is still true.  So it is also possible to
   consider combinations of clusters if and where it suits.

   In this way, in a very large network, there is no need to configure
   detailed filter criteria to inspect the traffic.  It is possible to
   check a multipoint network and, in case of problems, go deep with a
   step-by-step cluster analysis, but only for the cluster or
   combination of clusters where the problem happens.

   In summary, once a flow is defined, the algorithm to build the
   clusters partition is based on topological information; therefore, it
   considers all the possible links and nodes crossed by the given flow,
   even if there is no traffic.  So, if the flow does not enter or
   traverse all the nodes, the counters have a non-zero value for the
   involved nodes and a zero value for the other nodes without traffic;
   but in the end, all the formulas are still valid.

   The algorithm described above network is an iterative clustering
   algorithm, but it is also possible to apply a recursive clustering



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   algorithm by using the node-node adjacency matrix representation
   [IEEE-ACM-ToN-MPNPM].

   The complete and mathematical analysis of the possible algorithms for
   clusters partition, including the considerations in terms of
   efficiency and a comparison between the different methods, is in the
   paper [IEEE-ACM-ToN-MPNPM].

6.  Multipoint Packet Loss Measurement

   The Network Packet Loss, defined in Section 4.2, valid for the an
   entire monitored flow, can easily be extended to each multipoint path
   (e.g., the whole multipoint network, a cluster, or a combination of
   clusters).  In this way it is possible to calculate Multipoint Packet
   Loss that is representative of a multipoint path.

   The same equation of Section 4.2 can be applied to a generic
   multipoint path like a cluster or a combination of clusters, where
   the number of packets are those entering and leaving the multipoint
   path.

   By applying the algorithm described in Section 5.1, it is possible to
   split the monitoring network into clusters.  Then, packet loss can be
   measured on a cluster basis for each single period by considering the
   counters of the input and output nodes that belong to the specific
   cluster.  This can be done for every packet flow in each marking
   period.

7.  Multipoint Delay and Delay Variation

   The same line of reasoning can be applied to delay and delay
   variation.  Similarly to the delay measurements defined in
   [I-D.fioccola-rfc8321bis], the marking batches anchor the samples to
   a particular period, and this is the time reference that can be used.
   It is important to highlight that both delay and delay-variation
   measurements make sense in a multipoint path.  The delay variation is
   calculated by considering the same packets selected for measuring the
   delay.

   In general, it is possible to perform delay and delay-variation
   measurements on the basis of multipoint paths or single packets:

   o  Delay measurements on the basis of multipoint paths mean that the
      delay value is representative of an entire multipoint path (e.g.,
      the whole multipoint network, a cluster, or a combination of
      clusters).





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   o  Delay measurements on a single-packet basis mean that you can use
      a multipoint path just to easily couple packets between input and
      output nodes of a multipoint path, as described in the following
      sections.

7.1.  Delay Measurements on a Multipoint-Paths Basis

7.1.1.  Single-Marking Measurement

   Mean delay and mean delay-variation measurements can also be
   generalized to the case of multipoint flows.  It is possible to
   compute the average one-way delay of packets in one block, a cluster,
   or the entire monitored network.

   The average latency can be measured as the difference between the
   weighted averages of the mean timestamps of the sets of output and
   input nodes.  This means that, in the calculation, it is possible to
   weigh the timestamps by considering the number of packets for each
   endpoints.

   Note that, since the one-way delay value is representative of a
   multipoint path, it is possible to calculate the two-way delay of a
   multipoint path by summing the one-way delays of the two directions,
   similarly to [I-D.fioccola-rfc8321bis].

7.2.  Delay Measurements on a Single-Packet Basis

7.2.1.  Single- and Double-Marking Measurement

   Delay and delay-variation measurements relative to only one picked
   packet per period (both single and double marked) can be performed in
   the multipoint scenario, with some limitations:

      Single marking based on the first/last packet of the interval
      would not work, because it would not be possible to agree on the
      first packet of the interval.

      Double marking or multiplexed marking would work, but each
      measurement would only give information about the delay of a
      single path.  However, by repeating the measurement multiple
      times, it is possible to get information about all the paths in
      the multipoint flow.  This can be done in the case of a point-to-
      multipoint path, but it is more difficult to achieve in the case
      of a multipoint-to-multipoint path because of the multiple source
      routers.

   If we would perform a delay measurement for more than one picked
   packet in the same marking period, and especially if we want to get



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   delay measurements on a multipoint-to-multipoint basis, neither the
   single- nor the double-marking method is useful in the multipoint
   scenario, since they would not be representative of the entire flow.
   The packets can follow different paths with various delays, and in
   general it can be very difficult to recognize marked packets in a
   multipoint-to-multipoint path, especially in the case when there is
   more than one per period.

   A desirable option is to monitor simultaneously all the paths of a
   multipoint path in the same marking period; for this purpose, hashing
   can be used, as reported in the next section.

   Note that, since the one-way delay measurement is done on a single-
   packet basis, it is always possible to calculate the two-way delay
   but it is not immediate since it is necessary to couple the
   measurement on each single path with the opposite direction.  In this
   case the NMS can do the calculation.

7.2.2.  Hashing Selection Method

   RFCs 5474 [RFC5474] and 5475 [RFC5475] introduce sampling and
   filtering techniques for IP packet selection.

   The hash-based selection methodologies for delay measurement can work
   in a multipoint-to-multipoint path and MAY be used either coupled to
   mean delay or stand-alone.

   [I-D.mizrahi-ippm-marking] introduces how to use the hash method (RFC
   5474 [RFC5474] and RFC 5475 [RFC5475]) combined with the Alternate-
   Marking method for point-to-point flows.  It is also called Mixed
   Hashed Marking: the coupling of a marking method and hashing
   technique is very useful, because the marking batches anchor the
   samples selected with hashing, and this simplifies the correlation of
   the hashing packets along the path.

   It is possible to use a basic-hash or a dynamic-hash method.  One of
   the challenges of the basic approach is that the frequency of the
   sampled packets may vary considerably.  For this reason, the dynamic
   approach has been introduced for point-to-point flows in order to
   have the desired and almost fixed number of samples for each
   measurement period.  Using the hash-based sampling, the number of
   samples may vary a lot because it depends on the packet rate that is
   variable.  The dynamic approach helps to have an almost fixed number
   of samples for each marking period, and this is a better option for
   making regular measurements over time.  In the hash-based sampling,
   Alternate Marking is used to create periods, so that hash-based
   samples are divided into batches, which allows anchoring the selected
   samples to their period.  Moreover, in the dynamic hash-based



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   sampling, by dynamically adapting the length of the hash value, the
   number of samples is bounded in each marking period.

   In a multipoint environment, the hashing selection MAY be the
   solution for performing delay measurements on specific packets and
   overcoming the single- and double-marking limitations.

8.  Synchronization and Timing

   It is important to consider the timing aspects, since out-of-order
   packets happen and have to be handled as well, as described in
   [I-D.fioccola-rfc8321bis].

   However, in a multisource situation, an additional issue has to be
   considered.  With multipoint path, the egress nodes will receive
   alternate marked packets in random order from different ingress
   nodes, and this must not affect the measurement.

   So, if we analyze a multipoint-to-multipoint path with more than one
   marking node, it is important to recognize the reference measurement
   interval.  In general, the measurement interval for describing the
   results is the interval of the marking node that is more aligned with
   the start of the measurement, as reported in Figure 4.

   Note that the mark switching approach based on a fixed timer is
   considered in this document.


           time -> start         stop
           T(R1)   |-------------|
           T(R2)     |-------------|
           T(R3)        |------------|


                      Figure 4: Measurement Interval

   In Figure 4, it is assumed that the node with the earliest clock (R1)
   identifies the right starting and ending times of the measurement,
   but it is just an assumption, and other possibilities could occur.
   So, in this case, T(R1) is the measurement interval, and its
   recognition is essential in order to make comparisons with other
   active/passive/hybrid Packet Loss metrics.

   Regarding the timing constraints of the methodology,
   [I-D.fioccola-rfc8321bis] already describes two contributions that
   are taken into account: the clock error between network devices and
   the network delay between the measurement points.




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   When we expand to a multipoint environment, we have to consider that
   there are more marking nodes that mark the traffic based on
   synchronized clock time.  But, due to different synchronization
   issues that may happen, the marking batches can be of different
   lengths and with different offsets when they get mixed in a
   multipoint flow.  The additional gap that results between the sources
   can be incorporated into A, which is the maximum clock skew between
   the network devices, as already defined in [I-D.fioccola-rfc8321bis].


   ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
                |<======================================>|
                |                   L                    |
   ...=========>|<==================><==================>|<==========...
                |         L/2                L/2         |
                |<====>|                          |<====>|
                   d   |                          |   d
                       |<========================>|
                       available counting interval


                         Figure 5: Timing Aspects

   Moreover, it is assumed that each path of the multipoint flow can
   still be represented with a distinct normal distribution.  So, for
   the aggregate multipoint path, the combination of normal
   distributions result in a new normal distribution.  Under this
   assumption, the definition of the guard band d is still applicable as
   defined in [I-D.fioccola-rfc8321bis] and is given by:

   d = A + D_avg + 3*D_stddev,

   where A is the clock accuracy, D_avg is the average value of the
   network delay, and D_stddev is the standard deviation of the delay.

   As shown in Figure 5 and according to [I-D.fioccola-rfc8321bis], the
   condition that must be satisfied to enable the method to function
   properly is that the available counting interval must be > 0, and
   that means:

   L - 2d > 0.

   This formula needs to be verified for each measurement point on the
   multipoint path.

   Note that the timing considerations are valid for both packet loss
   and delay measurements.




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9.  Results of the Multipoint Alternate Marking Experiment

   The methodology described in the previous sections can be applied to
   various performance measurement problems, as also explained in
   [I-D.fioccola-rfc8321bis].

   Either one or two flag bits might be available for marking in
   different deployments:

      One flag: packet loss measurement SHOULD be done as described in
      Section 6 by applying the network clustering partition described
      in Section 5.  While delay measurement MAY be done according to
      the Mean delay calculation representative of the multipoint path,
      as described in Section 7.1.1.  Single-marking method based on the
      first/last packet of the interval cannot be applied, as mentioned
      in Section 7.2.1.

      Two flags: packet loss measurement SHOULD be done as described in
      Section 6 by applying the network clustering partition described
      in Section 5.  While delay measurement SHOULD be done on a single
      packet basis according to double-marking method Section 7.2.1.  In
      this case the Mean delay calculation (Section 7.1.1) MAY also be
      used as a representative value of a multipoint path.

      One flag and hash-based selection: packet loss measurement SHOULD
      be done as described in Section 6 by applying the network
      clustering partition described in Section 5.  Hash-based selection
      methodologies, introduced in Section 7.2.2, MAY be used for delay
      measurement.

   The experiment with Multipoint Alternate Marking methodologies
   confirmed the benefits of the Alternate Marking methodology described
   in [I-D.fioccola-rfc8321bis], as its extension to the general case of
   multipoint-to-multipoint scenarios.

   The Multipoint Alternate Marking Method is RECOMMENDED only for
   controlled domains, as per [I-D.fioccola-rfc8321bis].

10.  A Closed-Loop Performance-Management Approach

   The Multipoint Alternate-Marking framework that is introduced in this
   document adds flexibility to Performance Management (PM), because it
   can reduce the order of magnitude of the packet counters.  This
   allows an SDN orchestrator to supervise, control, and manage PM in
   large networks.

   The monitoring network can be considered as a whole or split into
   clusters that are the smallest subnetworks (group-to-group segments),



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   maintaining the packet-loss property for each subnetwork.  The
   clusters can also be combined in new, connected subnetworks at
   different levels, depending on the detail we want to achieve.

   An SDN controller or a Network Management System (NMS) can calibrate
   performance measurements, since they are aware of the network
   topology.  They can start without examining in depth.  In case of
   necessity (packet loss is measured or the delay is too high), the
   filtering criteria could be immediately reconfigured in order to
   perform a partition of the network by using clusters and/or different
   combinations of clusters.  In this way, the problem can be localized
   in a specific cluster or a single combination of clusters, and a more
   detailed analysis can be performed step by step by successive
   approximation up to a point-to-point flow detailed analysis.  This is
   the so-called "closed loop".

   This approach can be called "network zooming" and can be performed in
   two different ways:

   1) change the traffic filter and select more detailed flows;

   2) activate new measurement points by defining more specified
   clusters.

   The network-zooming approach implies that some filters or rules are
   changed and that therefore there is a transient time to wait once the
   new network configuration takes effect.  This time can be determined
   by the Network Orchestrator/Controller, based on the network
   conditions.

   For example, if the network zooming identifies the performance
   problem for the traffic coming from a specific source, we need to
   recognize the marked signal from this specific source node and its
   relative path.  For this purpose, we can activate all the available
   measurement points and better specify the flow filter criteria (i.e.,
   5-tuple).  As an alternative, it can be enough to select packets from
   the specific source for delay measurements; in this case, it is
   possible to apply the hashing technique, as mentioned in the previous
   sections.

   [I-D.song-opsawg-ifit-framework] defines an architecture where the
   centralized Data Collector and Network Management can apply the
   intelligent and flexible Alternate-Marking algorithm as previously
   described.

   As for [I-D.fioccola-rfc8321bis], it is possible to classify the
   traffic and mark a portion of the total traffic.  For each period,
   the packet rate and bandwidth are calculated from the number of



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   packets.  In this way, the network orchestrator becomes aware if the
   traffic rate surpasses limits.  In addition, more precision can be
   obtained by reducing the marking period; indeed, some implementations
   use a marking period of 1 sec or less.

   In addition, an SDN controller could also collect the measurement
   history.

   It is important to mention that the Multipoint Alternate Marking
   framework also helps Traffic Visualization.  Indeed, this methodology
   is very useful for identifying which path or cluster is crossed by
   the flow.

11.  Security Considerations

   This document specifies a method of performing measurements that does
   not directly affect Internet security or applications that run on the
   Internet.  However, implementation of this method must be mindful of
   security and privacy concerns, as explained in
   [I-D.fioccola-rfc8321bis].

12.  IANA Considerations

   This document has no IANA actions.

13.  Contributors

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

   Tal Mizrahi
   Huawei Technologies
   Email: tal.mizrahi.phd@gmail.com

   Xiao Min
   ZTE Corp.
   Email: xiao.min2@zte.com.cn

14.  Acknowledgements

   The authors would like to thank Martin Duke and Tommy Pauly for their
   assistance and their detailed and precious reviews.








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15.  References

15.1.  Normative References

   [I-D.fioccola-rfc8321bis]
              Fioccola, G., Cociglio, M., Mirsky, G., Mizrahi, T., and
              T. Zhou, "Alternate-Marking Method", draft-fioccola-
              rfc8321bis-04 (work in progress), April 2022.

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

   [RFC5474]  Duffield, N., Ed., Chiou, D., Claise, B., Greenberg, A.,
              Grossglauser, M., and J. Rexford, "A Framework for Packet
              Selection and Reporting", RFC 5474, DOI 10.17487/RFC5474,
              March 2009, <https://www.rfc-editor.org/info/rfc5474>.

   [RFC5475]  Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.
              Raspall, "Sampling and Filtering Techniques for IP Packet
              Selection", RFC 5475, DOI 10.17487/RFC5475, March 2009,
              <https://www.rfc-editor.org/info/rfc5475>.

   [RFC5644]  Stephan, E., Liang, L., and A. Morton, "IP Performance
              Metrics (IPPM): Spatial and Multicast", RFC 5644,
              DOI 10.17487/RFC5644, October 2009,
              <https://www.rfc-editor.org/info/rfc5644>.

   [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>.

15.2.  Informative References

   [I-D.ietf-ippm-route]
              Alvarez-Hamelin, J. I., Morton, A., Fabini, J., Pignataro,
              C., and R. Geib, "Advanced Unidirectional Route Assessment
              (AURA)", draft-ietf-ippm-route-10 (work in progress),
              August 2020.

   [I-D.mizrahi-ippm-marking]
              Mizrahi, T., Fioccola, G., Cociglio, M., Chen, M., and G.
              Mirsky, "Marking Methods for Performance Measurement",
              draft-mizrahi-ippm-marking-00 (work in progress), October
              2021.





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   [I-D.song-opsawg-ifit-framework]
              Song, H., Qin, F., Chen, H., Jin, J., and J. Shin, "A
              Framework for In-situ Flow Information Telemetry", draft-
              song-opsawg-ifit-framework-17 (work in progress), February
              2022.

   [I-D.zhou-ippm-enhanced-alternate-marking]
              Zhou, T., Fioccola, G., Liu, Y., Cociglio, M., Lee, S.,
              and W. Li, "Enhanced Alternate Marking Method", draft-
              zhou-ippm-enhanced-alternate-marking-09 (work in
              progress), February 2022.

   [IEEE-ACM-ToN-MPNPM]
              IEEE/ACM TRANSACTION ON NETWORKING, "Multipoint Passive
              Monitoring in Packet Networks",
              DOI 10.1109/TNET.2019.2950157, 2019.

   [IEEE-Network-PNPM]
              IEEE Network, "AM-PM: Efficient Network Telemetry using
              Alternate Marking", DOI 10.1109/MNET.2019.1800152, 2019.

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,
              <https://www.rfc-editor.org/info/rfc7011>.

   [RFC8889]  Fioccola, G., Ed., Cociglio, M., Sapio, A., and R. Sisto,
              "Multipoint Alternate-Marking Method for Passive and
              Hybrid Performance Monitoring", RFC 8889,
              DOI 10.17487/RFC8889, August 2020,
              <https://www.rfc-editor.org/info/rfc8889>.

Appendix A.  Changes Log

   Changes from RFC 8889 include:

   o  Minor editorial changes

   o  Removed section on "Examples of application"

   Changes in v-(01) include:

   o  Considerations on BUM traffic

   o  Reference to RFC8321bis for the fragmentation part

   o  Revised section on "Delay Measurements on a Single-Packet Basis"



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   o  Revised section on "Timing Aspects"

   Changes in v-(02) include:

   o  Clarified the formula in the section on "Timing Aspects" to be
      aligned with RFC 8321

   o  Considerations on two-way delay measurements in both sections 8.1
      and 8.2 on delay measurements

   o  Clarified in section 4.1 on "Monitoring Network" that the
      description is done for one direction but it can easily be
      extended to all direction

   o  New section on "Results of the Multipoint Alternate Marking
      Experiment"

   Changes in v-(03) include:

   o  Moved and renamed section on "Timing Aspects" as "Synchronization
      and Timing"

   o  Renamed old section on "Multipoint Packet Loss" as "Network Packet
      Loss"

   o  New section on "Multipoint Packet Loss Measurement"

   o  Renamed section on "Multipoint Performance Measurement" as
      "Extension of the Method to Multipoint Flows"

   Changes in v-(04) include:

   o  Revised section 5.1 on "Algorithm for Clusters Partition"

Authors' Addresses

   Giuseppe Fioccola (editor)
   Huawei Technologies
   Riesstrasse, 25
   Munich  80992
   Germany

   Email: giuseppe.fioccola@huawei.com








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   Mauro Cociglio
   Telecom Italia
   Via Reiss Romoli, 274
   Torino  10148
   Italy

   Email: mauro.cociglio@telecomitalia.it


   Amedeo Sapio
   Intel Corporation
   4750 Patrick Henry Dr.
   Santa Clara, CA  95054
   USA

   Email: amedeo.sapio@intel.com


   Riccardo Sisto
   Politecnico di Torino
   Corso Duca degli Abruzzi, 24
   Torino  10129
   Italy

   Email: riccardo.sisto@polito.it


   Tianran Zhou
   Huawei Technologies
   156 Beiqing Rd.
   Beijing  100095
   China

   Email: zhoutianran@huawei.com

















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