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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 5476

   PSAMP working group
   Internet Draft                                EDITOR:     B. Claise
   draft-ietf-psamp-protocol-09.txt                 Cisco Systems, Inc.
   Intended status: Proposed Standard                December 10th 2007
   Expires: June 2008
 
 
              Packet Sampling (PSAMP) Protocol Specifications
 
 
 Status of this Memo
 
   By submitting this Internet-Draft, each author represents that
   any applicable patent or other IPR claims of which he or she is
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   This Internet-Draft will expire on June, 2008.
 
 Copyright Notice
 
   Copyright (C) The IETF Trust (2007).
 
 Abstract
 
   This document specifies the export of packet information from a
   PSAMP Exporting Process to a PSAMP Collecting Process.  For export
   of packet information the IP Flow Information eXport (IPFIX)
   protocol is used, as both the IPFIX and PSAMP architecture match
   very well and the means provided by the IPFIX protocol are
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   sufficient.  The document specifies in detail how the IPFIX protocol
   is used for PSAMP export of packet information.
 
  Conventions used in this document
 
   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].
 
  Table of Contents
 
     1. Introduction.................................................3
     2. PSAMP Documents Overview.....................................3
     3. Terminology..................................................4
      3.1 IPFIX Terminology..........................................4
      3.2 PSAMP Terminology..........................................5
     3.2.1   Packet Streams and Packet Content.......................5
     3.2.2   Selection Process.......................................6
     3.2.3   Reporting...............................................7
     3.2.4   Metering Process........................................8
     3.2.5   Exporting Process.......................................8
     3.2.6   PSAMP Device............................................8
     3.2.7   Collector...............................................8
     3.2.8   Selection Methods.......................................8
      3.3 IPFIX and PSAMP Terminology Comparison....................11
     3.3.1   IPFIX and PSAMP Processes..............................11
     3.3.2   Packet Report, Packet Interpretation, and Data Record..11
     4. Differences between PSAMP and IPFIX.........................12
      4.1 Architecture Point of View................................12
      4.2 Protocol Point of View....................................13
      4.3 Information Model Point of View...........................14
     5. PSAMP Requirements versus the IPFIX Solution................14
      5.1 High Level View of the Integration........................15
     6. Using the IPFIX Protocol for PSAMP..........................16
      6.1 Selector ID...............................................16
      6.2 The Selection Sequence ID.................................16
      6.3 The Exporting Process.....................................17
      6.4 Packet Report.............................................17
     6.4.1   Basic Packet Report....................................17
     6.4.2   Extended Packet Report.................................20
      6.5 Report Interpretation.....................................21
     6.5.1   Selection Sequence Report Interpretation...............21
     6.5.2   Selector Report Interpretation.........................23
     6.5.2.1  Systematic Count-Based Sampling.......................24
     6.5.2.2  Systematic Time-Based Sampling........................25
     6.5.2.3  Random n-out-of-N Sampling............................26
     6.5.2.4  Uniform Probabilistic Sampling........................27
     6.5.2.5  Property Match Filtering..............................29
 
 
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     6.5.2.6  Hash-Based Filtering..................................30
     6.5.2.7  Other Selection Methods...............................34
     6.5.3   Selection Sequence Statistics Report Interpretation....34
     6.5.4   Accuracy Report Interpretation.........................36
     7. Security Considerations.....................................39
     8. IANA Considerations.........................................40
      8.1 IPFIX Related Considerations..............................40
      8.2 PSAMP Related Considerations..............................40
     9. References..................................................40
      9.1 Normative References......................................40
      9.2 Informative References....................................41
     10. Acknowledgments............................................41
     11. Intellectual Property Statement............................42
     12. Copyright Statement........................................42
     13. Disclaimer.................................................43
 
 
 1.    Introduction
 
   The name PSAMP is a contraction of the phrase Packet SAMPling.  The
   word "sampling" captures the idea that only a subset of all packets
   passing a network element will be selected for reporting.  PSAMP
   selection operations include random selection, deterministic
   selection, and deterministic approximations to random selection
   (hash-based selection).
 
   The IP Flow information export (IPFIX) protocol specified in [IPFIX-
   PROTO] exports IP traffic information [IPFIX-INFO] observed at
   network devices.  This matches the general protocol requirements
   outlined in the PSAMP framework [PSAMP-FMWK].  However, there are
   some architectural differences between IPFIX and PSAMP in the
   requirements for an export protocol.  While the IPFIX architecture
   [IPFIX-ARCH] is focused on gathering and exporting IP traffic flow
   information, the focus of the PSAMP framework [PSAMP-FMWK] is on
   exporting information on individual packets.  This basic difference
   and a set of derived differences in protocol requirements are
   outlined in Section 4.  Despite these differences, the IPFIX protocol
   is well suited as PSAMP protocol.  Section 5 specifies how the IPFIX
   protocol is used for the export of packet samples.  Required
   extensions of the IPFIX information model are specified in the PSAMP
   information model [PSAMP-INFO].
 
 
 2.    PSAMP Documents Overview
 
   [PSAMP-FMWK]: "A Framework for Packet Selection and Reporting",
   describes the PSAMP framework for network elements to select subsets
 
 
 
 
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   of packets by statistical and other methods, and to export a stream
   of reports on the selected packets to a collector.
 
   [PSAMP-TECH]: "Sampling and Filtering Techniques for IP Packet
   Selection", describes the set of packet selection techniques
   supported by PSAMP.
 
   This document: "Packet Sampling (PSAMP) Protocol Specifications"
   specifies the export of packet information from a PSAMP Exporting
   Process to a PSAMP Collecting Process.
 
   [PSAMP-INFO]: "Information Model for Packet Sampling Exports" defines
   an information and data model for PSAMP.
 
 
 3.    Terminology
 
   As the IPFIX export protocol is used to export the PSAMP information,
   the relevant IPFIX terminology from [IPFIX-PROTO] is copied over in
   this document.  All terms defined in this section have their first
   letter capitalized when used in this document.  The terminology
   summary table in section 3.1 gives a quick overview of the
   relationships between the different IPFIX terms.  The PSAMP
   terminology defined here is fully consistent with all terms listed in
   [PSAMP-TECH] and [PSAMP-FMWK] but only definitions that are relevant
   to the PSAMP protocol appear here.   Section 5.4 applies the PSAMP
   terminology to the IPFIX protocol terminology.
 
 3.1     IPFIX Terminology
 
   IPFIX-specific terminology used in this document is defined in
   section 2 of [IPFIX-PROTO].  The only exceptions are the Metering
   Process, Exporting Process, and the Collector terms, which are
   defined more precisely in the PSAMP terminology section. As in
   [IPFIX-PROTO], these IPFIX-specific terms have the first letter of a
   word capitalized when used in this document.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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    +------------------+---------------------------------------------+
    |                  |                 contents                    |
    |                  +--------------------+------------------------+
    |       Set        |      Template      |         record         |
    +------------------+--------------------+------------------------+
    |     Data Set     |          /         |     Data Record(s)     |
    +------------------+--------------------+------------------------+
    |   Template Set   | Template Record(s) |           /            |
    +------------------+--------------------+------------------------+
    | Options Template | Options Template   |           /            |
    |       Set        | Record(s)          |                        |
    +------------------+--------------------+------------------------+
               Figure A: Terminology Summary Table
 
 3.2      PSAMP Terminology
 
   The PSAMP terminology section has been copied over from [PSAMP-TECH].
 
 
 3.2.1    Packet Streams and Packet Content
 
   Observed Packet Stream
 
   The Observed Packet Stream is the set of all packets observed at the
   Observation Point.
 
   Packet Stream
 
   A Packet Stream denotes a subset of the Observed Packet Stream that
   flows past some specified point within the Selection Process.
   An example of a Packet Stream is the output of the Selection Process.
   Note that packets selected from a stream, e.g. by Sampling, do not
   necessarily possess a property by which they can be distinguished
   from packets that have not been selected.  For this reason the term
   "stream" is favored over "flow", which is defined as set of packets
   with common properties [RFC3917].
 
   Packet Content
 
   The Packet Content denotes the union of the packet header (which
   includes link layer, network layer and other encapsulation headers)
   and the packet payload.  Note that, depending on the Observation
   Point, the link layer information might not be available.
 
 
 
 
 
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 3.2.2   Selection Process
 
   Selection Process
 
   A Selection Process takes the Observed Packet Stream as its input and
   selects a subset of that stream as its output.
 
   Selection State
 
   A Selection Process may maintain state information for use by the
   Selection Process.  At a given time, the Selection State may depend
   on packets observed at and before that time, and other variables.
   Examples include:
 
       (i)   sequence numbers of packets at the input of Selectors;
 
       (ii)  a timestamp of observation of the packet at the
             Observation Point;
 
       (iii) iterators for pseudorandom number generators;
 
       (iv)  hash values calculated during selection;
 
       (v)   indicators of whether the packet was selected by a
             given Selector.
 
   Selection Processes may change portions of the Selection State as a
   result of processing a packet.  Selection state for a packet is to
   reflect the state after processing the packet.
 
   Selector
 
   A Selector defines the action of a Selection Process on a single
   packet of its input.  If selected, the packet becomes an element of
   the output Packet Stream.
 
   The Selector can make use of the following information in determining
   whether a packet is selected:
 
       (i)  the Packet Content;
 
       (ii) information derived from the packet's treatment at the
            Observation Point;
 
       (iii) any selection state that may be maintained by the
             Selection Process.
 
   Composite Selector
 
 
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   A Composite Selector is an ordered composition of Selectors, in which
   the output Packet Stream issuing from one Selector forms the input
   Packet Stream to the succeeding Selector.
 
   Primitive Selector
 
   A Selector is primitive if it is not a Composite Selector.
 
   Selector ID
 
   The Selector ID is the unique ID identifying a Primitive Selector.
   The ID is unique within the Observation Domain.
 
   Selection Sequence
 
   From all the packets observed at an Observation Point, only a few
   packets are selected by one or more Selectors.  The Selection
   Sequence is a unique value per Observation Domain describing the
   Observation Point and the Selector IDs through which the packets are
   selected.
 
 
 3.2.3   Reporting
 
   Packet Reports
 
   Packet Reports comprise a configurable subset of a packet's input to
   the Selection Process, including the Packet Content, information
   relating to its treatment (for example, the output interface), and
   its associated selection state (for example, a hash of the Packet
   Content).
 
   Report Interpretation
 
   Report Interpretation comprises subsidiary information, relating to
   one or more packets, that are used for interpretation of their Packet
   Reports.  Examples include configuration parameters of the Selection
   Process.
 
   Report Stream
 
   The Report Stream is the output of a Metering Process, comprising two
   distinguished types of information: Packet Reports, and Report
   Interpretation.
 
 
 
 
 
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 3.2.4   Metering Process
 
   Metering Process
 
   A Metering Process selects packets from the Observed Packet Stream
   using a Selection Process, and produces as output a Report Stream
   concerning the selected packets.  The PSAMP Metering Process can be
   viewed as analogous to the IPFIX metering process [IPFIX-PROTO],
   which produces flow records as its output.
 
 
 3.2.5   Exporting Process
 
   Exporting Process
 
   An Exporting Process sends, in the form of Export Packets, the output
   of one or more Metering Processes to one or more Collectors.
 
   Export Packet
 
   An Export Packet is a combination of Report Interpretation(s) and/or
   one or more Packet Reports that are bundled by the Exporting Process
   into a Export Packet for exporting to a Collector.
 
 3.2.6   PSAMP Device
 
   PSAMP Device
 
   A PSAMP Device is a device hosting at least an Observation Point, a
   Selection Process and an Exporting Process.  Typically, corresponding
   Observation Point(s), Selection Process(es) and Exporting Process(es)
   are co-located at this device, for example at a router.
 
 
 
 3.2.7   Collector
 
   Collector
 
   A Collector receives a Report Stream exported by one or more
   Exporting Processes. In some cases, the host of the Metering and/or
   Exporting Processes may also serve as the Collector.
 
 
 3.2.8   Selection Methods
 
 
 
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   Filtering
 
   A filter is a Selector that selects a packet deterministically based
   on the Packet Content, or its treatment, or functions of these
   occurring in the Selection State.  Examples include property match
   Filtering, and Hash-based Selection.
 
   Sampling
 
   A Selector that is not a filter is called a Sampling operation.  This
   reflects the intuitive notion that if the selection of a packet
   cannot be determined from its content alone, there must be some type
   of Sampling taking place.
 
   Content-independent Sampling
 
   A Sampling operation that does not use Packet Content (or quantities
   derived from it) as the basis for selection is called a Content-
   independent Sampling operation.  Examples include systematic
   Sampling, and uniform pseudorandom Sampling driven by a pseudorandom
   number whose generation is independent of Packet Content.  Note that
   in Content-independent Sampling it is not necessary to access the
   Packet Content in order to make the selection decision.
 
   Content-dependent Sampling
 
   A Sampling operation where selection is dependent on Packet Content
   is called a Content-dependent Sampling operation.  Examples include
   pseudorandom selection according to a probability that depends on the
   contents of a packet field.  Note that this is not a filter, because
   the selection is not deterministic.
 
   Hash Domain
 
   A subset of the Packet Content and the packet treatment, viewed as an
   N-bit string for some positive integer N.
 
   Hash Range
 
   A set of M-bit strings for some positive integer M that define the
   range of values the result of the hash operation can take.
 
   Hash Function
 
   A deterministic map from the Hash Domain into the Hash Range.
 
   Hash Selection Range
 
 
 
 
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   A subset of the Hash Range.  The packet is selected if the action of
   the Hash Function on the Hash Domain for the packet yields a result
   in the Hash Selection Range.
 
   Hash-based Selection
 
   Filtering specified by a Hash Domain, a Hash Function, a Hash Range
   and a Hash Selection Range.
 
   Approximative Selection
 
   Selectors in any of the above categories may be approximated by
   operations in the same or another category for the purposes of
   implementation.  For example, uniform pseudorandom Sampling may be
   approximated by Hash-based Selection, using a suitable Hash Function
   and Hash Domain.  In this case, the closeness of the approximation
   depends on the choice of Hash Function and Hash Domain.
 
   Population
 
   A Population is a Packet Stream, or a subset of a Packet Stream.  A
   Population can be considered as a base set from which packets are
   selected.  An example is all packets in the Observed Packet Stream
   that are observed within some specified time interval.
 
   Population Size
 
   The Population Size is the number of all packets in the Population.
 
   Sample Size
 
   The number of packets selected from the Population by a Selector.
 
   Configured Selection Fraction
 
   The Configured Selection Fraction is the ratio of the number of
   packets selected by a Selector from an input Population, to the
   Population Size, as based on the configured selection parameters.
 
   Attained Selection Fraction
 
   The Attained Selection Fraction is the actual ratio of the
   number of packets selected by a Selector from an input
   Population, to the Population Size.  For some Sampling methods the
   Attained Selection Fraction can differ from the Configured Selection
   Fraction due to, for example, the inherent statistical variability in
   Sampling decisions of probabilistic Sampling and Hash-based
   Selection.  Nevertheless, for large Population Sizes and properly
 
 
 
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   configured Selectors, the Attained Selection Fraction usually
   approaches the Configured Selection Fraction.
 
 3.3      IPFIX and PSAMP Terminology Comparison
 
   The PSAMP terminology has been specified with an IPFIX background, as
   PSAMP and IPFIX have similar terms.  However, this section clarifies
   the terms between the IPFIX and PSAMP terminology.
 
 3.3.1   IPFIX and PSAMP Processes
 
   The figure B indicates the sequence of the processes (Metering and
   Exporting) within the PSAMP Device.
 
              +------------------+
              | Metering Process |
              | +-----------+    |     +-----------+
    Observed  | | Selection |    |     | Exporting |
    Packet--->| | Process   |--------->| Process   |--->Collector
    Stream    | +-----------+    |     +-----------+
              +------------------+
 
       Figure B: PSAMP Processes
 
 
   The Selection Process, which takes an Observed Packet Stream as its
   input, is an integral part of the Metering Process.  The Selection
   Process chooses which packets from its input packet stream will be
   reported on by the rest of the Metering Process.  Note that a
   "Process" is not necessarily implemented as a separate CPU thread.
 
 
 3.3.2   Packet Report, Packet Interpretation, and Data Record
 
   The PSAMP terminology speaks of Packet Report and Packet
   Interpretation, while the IPFIX terminology speaks of Data Record and
   (Option) Template Record.  The PSAMP Packet Report, which comprises
   information about the observed packet, can be viewed as analogous to
   the IPFIX Data Record defined by a Template Record.  The PSAMP Packet
   Interpretation, which comprises subsidiary information used for the
   interpretation of the Packet Reports, can be viewed as analogous to
   the IPFIX Data Record defined by an Option Template Record.
 
 
 
 
 
 
 
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 4.    Differences between PSAMP and IPFIX
 
   The output of the IPFIX working group relevant for this draft is
   structured into three documents:
      - IP Flow information architecture [IPFIX-ARCH]
      - IPFIX protocol specifications [IPFIX-PROTO]
      - IP Flow information export information model [IPFIX-INFO]
 
   In the following sections we investigate the differences between
   IPFIX and PSAMP for each of those aspects.
 
 4.1      Architecture Point of View
 
   Traffic Flow measurement as described in the IPFIX requirements
   [RFC3917] and the IPFIX architecture [IPFIX-ARCH] can be separated
   into two stages: packet processing and Flow processing.
   Figure C illustrates these stages.
 
   In stage 1, all processing steps act on packets.  Packets are
   captured, time stamped, selected by one or more selection steps and
   finally forwarded to packet classification that maps packets to
   Flows.  The packets selection steps may include Filtering and
   Sampling functions.
 
   In stage 2, all processing steps act on Flows.  After packets are
   classified (mapped to Flows), Flows are generated (or updated if they
   exist already).  Flow generation and update steps may be performed
   repeatedly for aggregating Flows.  Finally, Flows are exported.
 
   Packet Sampling as described in the PSAMP framework [PSAMP-FMWK]
   covers only stage 1 of the IPFIX architecture with the packet
   classification replaced by packet record export.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
 
 
      IPFIX architecture                       PSAMP framework
 
 
        packet header                           packet header
          capturing     \                         capturing
              |          |                            |
         timestamping    |                       timestamping
              |          |                            |
              v          |                            v
      +------>+          |  stage 1:          +------>+
      |       |           > packet            |       |
      |    packet        |  processing        |    packet
      |   selection      |                    |   selection
      |       |          |                    |       |
      +-------+          |                    +-------+
              |          |                            |
              v          |                            v
           packet       /                       packet record
        classification  \                          export
              |          |
              v          |
      +------>+          |
      |       |          |
      | Flow generation  |
      |   and update     |  stage 2:
      |       |           > Flow
      |       v          |  processing
      |     Flow         |
      |   selection      |
      |       |          |
      +-------+          |
              |          |
              v          |
         Flow Record    /
           export
 
       Figure C: Comparison of IPFIX architecture and PSAMP framework
 
 4.2      Protocol Point of View
 
   Concerning the protocol, the major difference between IPFIX and PSAMP
   is that the IPFIX protocol exports Flow Records while the PSAMP
   protocol exports Packet Records.  From a pure export point of view,
   IPFIX will not distinguish a Flow Record composed of several packets
   aggregated together, from a Flow Record composed of a single packet.
 
 
 
 
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   So the PSAMP export can be seen as special IPFIX Flow Record
   containing information about a single packet.
 
   All extensions of the IPFIX protocol that are required to satisfy the
   PSAMP requirements have already been incorporated in the IPFIX
   protocol [IPFIX-PROTO], which was developed in parallel with the
   PSAMP protocol.  An example is the need for a data type for protocol
   fields that have flexible length, such as an octet array.  This was
   added to the IPFIX protocol specification in order to meet the
   requirement of the PSAMP protocol to report content of captured
   packets, for example the first octets of a packet.
 
 4.3      Information Model Point of View
 
   From the information model point of view, the overlap between both
   the IPFIX and PSAMP protocols is quite large.  Most of the
   Information Elements in the IPFIX protocol are also relevant for
   exporting packet information, for example all fields reporting packet
   header properties.  Only a few Information Elements, such as
   observedFlowTotalCount (whose value will always be 1 for PSAMP) etc.,
   cannot be used in a meaningful way by the PSAMP protocol.  Also,
   IPFIX protocol requirements concerning stage 2 of figure C do not
   apply to the PSAMP metering process.
 
   Further required extensions apply to the information model.  Even if
   the IPFIX charter speaks of Sampling, no Sampling related Information
   Elements are specified in [IPFIX-INFO].  The task of specifying them
   was intentionally left for the PSAMP information model [PSAMP-INFO].
   A set of several additional fields is required for satisfying the
   requirements for the PSAMP information model [PSAMP-TECH].
 
   Exploiting the extensibility of the IPFIX information model, the
   required extension is covered by the PSAMP information model
   specified in [PSAMP-INFO].
 
 5.    PSAMP Requirements versus the IPFIX Solution
 
   In the "Generic Requirements for PSAMP" section, [PSAMP-FMWK]
   describes some requirements that affect directly the PSAMP export
   protocol.
 
   In the "Generic Selection Process Requirements" section, [PSAMP-FMWK]
   describes one requirement that, if not directly related to the export
   protocol, will put some constraints on it.  Parallel Measurements:
   multiple independent selection processes at the same entity.
 
   Finally, [PSAMP-FMWK] describes a series of requirements specifying
   the different Information Elements that MUST and SHOULD be reported
 
 
 
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   to the Collector.  Nevertheless IPFIX, being a generic export
   protocol, can export any Information Elements as long as they are
   described in the information model.  So these requirements are mainly
   targeted for the [PSAMP-INFO] document.
 
   The PSAMP protocol specifications meets almost all the protocol
   requirements stated in the PSAMP framework document [PSAMP-FMWK]:
 
       * Extensibility
       * Parallel selection processes
       * Encrypted packets
       * Indication of information loss
       * Accuracy
       * Privacy
       * Timeliness
       * Congestion avoidance
       * Secure export
       * Export rate limit
       * Microsecond timestamp resolution
 
   The only requirement that is not met is Export Packet compression.
   With the choice of IPFIX as PSAMP export protocol, the export packet
   compression option mentioned in the section 8.5 of the framework
   document [PSAMP-FMWK] is not addressed.
 
 5.1     High Level View of the Integration
 
   The Template Record in the Template Set is used to describe the
   different PSAMP Information Elements that will be exported to the
   Collector.  The Collector decodes the Template Record in the Template
   Set and knows which Information Elements to expect when it receives
   the Data Records in the PSAMP Packet Report Data Set.   Typically, in
   the base level of the PSAMP functionality, the Template Set will
   contain the input sequence number, the packet fragment (some number
   of contiguous bytes from the start of the packet or from the start of
   the payload) and the Selection Sequence.
 
   The Options Template Record in the Options Template Set is used to
   describe the different PSAMP Information Elements that concern the
   Metering Process itself: Sampling and/or Filtering functions, and the
   associated parameters.  The Collector decodes the Options Template
   Records in the Option Template Set and knows which Information
   Elements to expect when it receives the Data Records in the PSAMP
   Report Interpretation Data Set.  Typically, the Options Template
   would contain the Selection Sequence, the Sampling or Filtering
   functions, and the Sampling or Filtering associated parameters.
 
 
 
 
 
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   PSAMP requires all the different possibilities of the IPFIX protocol
   specifications [IPFIX-PROTO].  That is the 3 types of Set (Data Set,
   Template Set and Options Templates Set) with the 2 types of Templates
   Records (Template Record and Options Template Record), as described
   in the figure A.  As a consequence, PSAMP can't rely on a subset of
   the IPFIX protocol specifications described in [IPFIX-PROTO].   The
   entire IPFIX protocol specifications [IPFIX-PROTO] MUST be
   implemented for the PSAMP protocol.
 
 6.    Using the IPFIX Protocol for PSAMP
 
   In this section, we describe the usage of the IPFIX protocol for
   PSAMP.  We describe the record formats and the additional
   requirements that must be met.  PSAMP uses two different types of
   messages:
      - Packet Reports
      - Report Interpretation
 
   The format of Packet Reports is defined in IPFIX Template Records.
   The PSAMP data is transferred as Information Elements in IPFIX Data
   Records as described by the Template Record.  There are two different
   types of Packet Reports.  Basic Packet Reports contain only the basic
   Information Elements required for PSAMP reporting.  Extended Packet
   Reports MAY contain further Information Elements.
   The format of Report Interpretations is defined in IPFIX Option
   Template Record.  The Information Elements are transferred in IPFIX
   Data Records as described by the Option Template Record.  There are
   four different types of Report Interpretation messages:
      - Selection Sequence Report Interpretation
      - Selector Report Interpretation
      - Selection Sequence Statistics Report Interpretation
      - Accuracy Report Interpretation
   A description and examples about the usage of those reports is given
   below.
 
 6.1     Selector ID
 
   The Selector ID is the unique ID identifying a Primitive Selector.
   Each Primitive Selector MUST have a unique ID within the Observation
   Domain.  The Selector ID is represented by the selectorId Information
   Element [PSAMP-INFO].
 
 6.2     The Selection Sequence ID
 
   From all the packets observed at an Observation Point, a subset of
   packets is selected by one or more Selectors.  The Selection Sequence
   is the combination of an Observation Point and one or more
   Selector(s) through which the packets are selected. The Selection
   Sequence ID is a unique value representing that combination.  The
 
 
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   Selection Sequence ID is represented by the selectionSequenceId
   Information Element [PSAMP-INFO].
 
 6.3     The Exporting Process
 
   An Exporting Process MUST be able to limit the export rate according
   to a configurable value.  The Exporting Process MAY limit the export
   rate on a per Collecting Process basis.
 
 6.4     Packet Report
 
   For each Selection Sequence, for each selected packet, a Packet
   Report MUST be created.  The format of the Packet Report is specified
   in a Template Record contained in a Template Set.
 
   There are two types of Packet Report, as described in [PSAMP-FMWK]:
   the basic Packet Report and the extended Packet Report.
 
 6.4.1   Basic Packet Report
 
   For each selected packet, the Packet Report MUST contain the
   following information:
   - The selectionSequenceId Information Element
   If there is a digest function in the selection sequence, the Packet
   report MUST contain the hash value (digestHashValue Information
   Element) generated by the digest hash function for each selected
   packet.  If there is more than one digest function then each hash
   value MUST be included in the same order as they appear in the
   selection sequence.  If there are no digest functions in the
   selection sequence no element for the digest needs to be sent.
   - Some number of contiguous bytes from the start of the packet,
   including the packet header (which includes link layer, network layer
   and other encapsulation headers) and some subsequent bytes of the
   packet payload.  Alternatively, the number of contiguous bytes may
   start at the beginning of the payload.  The dataLinkFrameSection,
   mplsLabelStackSection, mplsPayloadPacketSection, ipPacketSection, and
   ipPayloadPacketSection PSAMP Information Elements are available for
   this use.  If one of those Information Elements that contain some
   number of contiguous bytes has got a content with an insufficient
   number of octets compared to its length specified in the Template,
   then this Information Element MUST be sent with a new Template using
   either a fixed length Information Element of the necessary size or a
   variable length Information Element.
 
   For each selected packet, the Packet Report SHOULD contain the
   following information:
   - the observationTimeMicroseconds Information Element
 
 
 
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   In the Packet Report, the PSAMP device MUST be capable of exporting
   the number of observed packets and the number of packets selected by
   each instance of its Primitive Selectors (as described by the non
   scope Information Elements of the Selection Sequence Statistics
   Report Interpretation) although it MAY be a configurable option not
   to include them.  If exported, the Attained Selection Fraction may
   be calculated precisely for the Observed Packet Stream.  The Packet
   Report MAY include only the final selector packetSelected, to act as
   an index for that selection sequence in the Selection Sequence
   Statistics Report Interpretation, which also allows the calculation
   of the Attained Selection Fraction.
 
   The contiguous Information Elements (dataLinkFrameSection,
   mplsLabelStackSection, mplsPayloadPacketSection, ipPacketSection,
   and ipPayloadPacketSection) MAY be encoded with a fixed length field
   or with a variable sized field.  If one of these Information
   Elements is encoded with a fixed length field whose length is too
   long for the number of contiguous bytes in the selected packet,
   padding MUST NOT be used.  In this case, the Exporting Process MUST
   export the information either in a new Template Record with the
   correct fixed length field, or either in a new Template Record with
   a variable length field.
 
   Here is an example of a basic Packet Report, with a
   SelectionSequenceId value of 9 and dataLinkFrameSection
    Information Element of 12 bytes, 0x4500 005B A174 0000 FF11 832E,
   encoded with a fixed length field.
 
    IPFIX Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 2          |         Length = 24           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 260      |        Field Count = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   selectionSequenceId = 301   |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      digestHashValue = 326    |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   dataLinkFrameSection = 315  |        Field Length = 12      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |observationTimeMicroseconds=324|        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    The associated IPFIX Data Record:
 
 
 
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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 260        |           Length = 28         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               9                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         0x9123 0613                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         0x4500 005B                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         0xA174 0000                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         0xFF11 832E                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   observation time encoded as dateTimeSeconds [IPFIX-PROTO]   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
            Figure D: Example of a Basic Packet Report
 
   Here is an example of a basic Packet Report, with a
   SelectionSequenceId value of 9 and ipHeaderPacketSection Information
   Element of 12 bytes, 0x4500 005B A174 0000 FF11 832E, encoded with a
   variable sized field.
 
    IPFIX Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 2          |         Length = 16           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 261      |        Field Count = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    selectionSequenceId = 301  |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ipHeaderPacketSection = 313  |      Field Length = 65535     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    The associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 261        |           Length = 21         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               9                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
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   |  Length = 12  |                  0x4500 ...                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ...  005B   |                  0xA174 ...                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ...  0000   |                  0xFF11 ...                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ...  832E   |
   +-+-+-+-+-+-+-+-+
 
            Figure E: Example of a Basic Packet Report,
                      with a variable sized field
 
 
 6.4.2   Extended Packet Report
 
   Alternatively to the basic Packet Report, the extended Packet Report
   MAY contain other Information Elements related to the protocols used
   in the packet (such as source and destination IP addresses), related
   to the packet treatment (such as output interface, destination BGP
   autonomous system [RFC4271]), or related to the Selection State
   associated with the packet (such as timestamp, hash value).
 
   It is envisaged that selection of fields for extended Packet Reports
   may be used to reduce reporting bandwidth, in which case the option
   to report some number of contiguous bytes from the start of the
   packet, mandatory in the basic Packet Report, may not be exercised.
   In this case, the Packet Content MAY be omitted.  Note this
   configuration is quite similar to an IPFIX Device for which a
   Template Record containing information about a single packet is
   reported.
 
   Example of a detailed Extended Packet Report:
 
    IPFIX Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Set ID =  2        |           Length = 32         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Template ID = 261       |         Field Count = 6       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|  selectionSequenceId = 301  |         Field Length = 4      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|  sourceIPv4Address = 44     |         Field Length = 4      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0| destinationIPv4Address = 45 |         Field Length = 4      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
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    |0|    totalLengthIPv4 = 190    |         Field Length = 2      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|     tcpSourcePort = 182     |         Field Length = 2      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|  tcpDestinationPort = 183   |         Field Length = 2      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    The associated IPFIX Data Record:
 
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Set ID = 261        |            Length = 20        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               9                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           192.0.2.1                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          192.0.2.106                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                72             |                1372           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               80              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure F: Example of an Extended Packet Report
 
 
  6.5      Report Interpretation
 
   To make full sense of the Packet Reports there are a number of
   additional pieces of information that must be communicated to the
   Collector:
   - The details about which Selectors and Observation Points are being
   used within a Selection Sequences MUST be provided using the
   Selection Sequence Report Interpretation.
   - The configuration details of each Selector MUST be provided using
   the Selector Report Interpretation.
   - The Selector ID statistics MUST be provided using the Selection
   Sequence Statistics Report Interpretation.
   - The accuracies of the reported fields MUST be provided using the
   Accuracy Report Interpretation.
 
 
 6.5.1   Selection Sequence Report Interpretation
 
   Each Packet Report contains a selectionSequenceId Information Element
   that identifies the particular combination of Observation Point and
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   Selector(s) used for its selection.  For every selectionSequenceId
   Information Element in use, the PSAMP Device MUST export a Selection
   Sequence Report Interpretation using an Options Template with the
   following Information Elements:
 
    Scope:     selectionSequenceId
    Non-Scope: one Information Element representing
                   the Observation Point
               selectorId (one or more)
 
   An Information Element representing the Observation Point would
   typically be taken from the ingressInterface, egressInterface,
   lineCardId, exporterIPv4Address, exporterIPv6Address Information
   Elements (specified in [IPFIX-INFO]), but not limited to those: any
   Information Element specified in [IPFIX-INFO] or [PSAMP-INFO] can
   potentially be used.  In case of more complex Observation Points
   (such as a list of interfaces, a bus, etc..), a new Information
   Element describing the new type of Observation Point must be
   specified, along with an option template record describing it in more
   details (if necessary).
 
   If the packets are selected by a Composite Selector, the Selection
   Sequence is composed of several Primitive Selectors.  In such a case,
   the Selection Sequence Report Interpretation MUST contain the list of
   all the Primitive Selector IDs in the Selection Sequence.  If
   multiple Selectors are contained in the Selection Sequence Report
   Interpretation, the selectorId's MUST be identified in the order they
   are used.
 
   Example of two Selection Sequences:
 
    Selection Sequence 7 (Filter->Sampling):
      ingressInterface    5
      selectorId          5 (Filter, match IPV4SourceAddress 192.0.2.1)
      selectorId         10 (Sampler, Random 1 out-of ten)
 
    Selection Sequence 9 (Sampling->Filtering):
      ingressInterface    5
      selectorId         10 (Sampler, Random 1 out-of ten)
      selectorId          5 (Filter, match IPV4SourceAddress 192.0.2.1)
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Set ID = 3           |          Length = 26          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 262      |         Field Count = 4       |
 
 
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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count =  1    |0|  selectionSequenceId = 301  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Scope 1 Length = 4      |0|     ingressInterface = 10   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Field Length = 4       |0|      selectorId = 300       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Field Length = 4       |0|      selectorId = 300       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Field Length = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   The associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Set ID = 262         |           Length = 36         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               7                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               5                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               5                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              10                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               9                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               5                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              10                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               5                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure G: Example of a Selection Sequence Report Interpretation
 
   Notes:
   * There are two Records here in the same Data Set.  Each record
   defines a different Selection Sequence.
   * If, for example, a different Selection Sequence is composed of
   three Selectors then a different Options Template with three
   selectorId Information Elements (instead of two) must be used.
 
 6.5.2   Selector Report Interpretation
 
   An IPFIX Data Record, defined by an Option Template Record, MUST be
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   used to send the configuration details of every Selector in use.  The
   Option Template Record MUST contain the selectorId Information
   Element as the Scope field and the SelectorAlgorithm Information
   Element followed by some specific configuration parameters:
 
    Scope:     selectorId
    Non-scope: selectorAlgorithm
               algorithm specific Information Elements
 
   The algorithm specific Information Elements are specified in the
   following subsections, depending on the selection method represented
   by the value of the selectorAlgorithm [PSAMP-INFO].
 
 6.5.2.1 Systematic Count-Based Sampling
 
   In systematic count-based Sampling, the start and stop triggers for
   the Sampling interval are defined in accordance with the spatial
   packet position (packet count) [PSAMP-TECH].
 
   The REQUIRED algorithm specific Information Elements in the case of
   systematic count-based Sampling are:
 
      samplingPacketInterval: number of packets selected in a row
      samplingPacketSpace:    number of packets between selections
 
 
   Example of a simple 1 out-of 10 systematic count-based Selector
   definition, where the samplingPacketInterval is 1 and the
   samplingPacketSpace is 9.
 
   IPFIX Options Template Record:
 
   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Set ID = 3           |          Length = 26          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID =  263     |         Field Count = 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Scope Field Count =  1     |0|       selectorId = 302      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 4       |0|   selectorAlgorithm = 304   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 1        |0|samplingPacketInterval = 305 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 1        |0|  samplingPacketSpace = 306  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
 
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   |       Field Length = 1        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Set ID = 263       |          Length = 11          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              15                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       1       |      1        |      9        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure H: Example of the Selector Report Interpretation,
                 For Systematic Count-Based Sampling
 
   Notes:
   * A selectorAlgorithm value of 1 represents systematic count-based
   Sampling.
   * samplingPacketInterval and samplingPacketSpace are of type
   unsigned32 but are compressed down to one octet here, as allowed by
   the IPFIX protocol specifications [IPFIX-PROTO].
 
 
 6.5.2.2 Systematic Time-Based Sampling
 
   In systematic time-based Sampling, the start and stop triggers are
   used to define the Sampling intervals [PSAMP-TECH].  The REQUIRED
   algorithm specific Information Elements in the case of systematic
   time-based Sampling are:
 
      samplingTimeInterval: time (in us) when packets are selected
      samplingTimeSpace:    time (in us) between selections
 
   Example of a 100 us out-of 1000 us systematic time-based Selector
   definition, where the samplingTimeInterval is 100 and the
   samplingTimeSpace is 900
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 3          |          Length = 26          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 264        |        Field Count = 4        |
 
 
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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Scope Field Count = 1      |0|      selectorId = 302       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope 1 Length = 4        |0|     selectorAlgorithm = 304 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |0|  samplingTimeInterval = 307 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |0|   samplingTimeSpace = 308   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 2         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 264        |          Length = 12          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              16                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        2      |       100     |             900               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure I: Example of the Selector Report Interpretation,
                 For Systematic Time-Based Sampling
 
   Notes:
   * A selectorAlgorithm value of 2 represents systematic time-based
   Sampling.
   * samplingTimeInterval and samplingTimeSpace are of type unsigned32
   but are compressed down here.
 
 
 6.5.2.3 Random n-out-of-N Sampling
 
   In random n-out-of-N Sampling, n elements are selected out of the
   parent population that consists of N elements [PSAMP-TECH].  The
   REQUIRED algorithm specific Information Elements in case of random n-
   out-of-N Sampling are:
 
      samplingSize:       number of packets selected
      samplingPopulation: number of packets in selection population
 
   Example of a 1 out-of 10 random n-out-of-N Sampling Selector:
 
   IPFIX Options Template Record:
 
 
 
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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 3          |          Length = 26          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 265        |        Field Count = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0|      selectorId = 302       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope 1 Length = 4        |0|  selectorAlgorithm = 304    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |0|      samplingSize = 309     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |0|  samplingPopulation = 310   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Set ID = 265          |          Length = 11          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              17                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       3       |       1       |        10     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure J: Example of the Selector Report Interpretation,
                 For Random n-out-of-N Sampling
 
 
   Notes:
   * A selectorAlgorithm value of 3 represents Random n-out-of-N
   Sampling.
   * samplingSize and samplingPopulation are of type unsigned32 but are
   compressed down to one octet here.
 
 6.5.2.4 Uniform Probabilistic Sampling
 
   In uniform probabilistic Sampling, each element has the same
   probability p of being selected from the parent population [PSAMP-
   TECH].  The algorithm specific Information Element in case of uniform
   probabilistic Sampling is:
 
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
     samplingProbablility: a floating point number for the Sampling
                           probability.
 
   Example of a 15% uniform probability Sampling Selector:
 
   IPFIX Options Template Record:
 
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Set ID = 3           |             Length = 22       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 271       |         Field Count = 3       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0|      selectorId = 302       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 4         |0|   selectorAlgorithm = 304   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 1         |0| samplingProbabilility = 311 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Field Length = 4         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Associated IPFIX Data Record:
 
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 271        |          Length = 11          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              20                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      4        |                          0.15                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |
   +-+-+-+-+-+-+-+-+
 
      Figure K: Example of the Selector Report Interpretation,
                For Uniform Probabilistic Sampling
 
   Notes:
   * A selectorAlgorithm value of 4 represents Uniform Probabilistic
   Sampling.
   * samplingProbablility is of type float64 but is compressed down to a
   float32 here.
 
 
 
 
 
 
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 6.5.2.5 Property Match Filtering
 
   This classification includes match(es) on field(s) within a packet
   and/or on properties of the router state.  With this method, a packet
   is selected if a specific field in the packet equals a predefined
   value.
 
   The algorithm specific Information Elements defining configuration
   parameters for property match filtering are taken from the full range
   of available Information Elements.
 
   When multiple different Information Elements are defined, the filter
   acts as a logical AND.  Note that the logical OR is not covered by
   these PSAMP specifications.  The property match Filtering Options
   Template Record MUST NOT have multiple identical Information
   Elements.  The result of the filter is independent from the order of
   the Information Elements in the Option Template Record, but the order
   may be important for implementation purposes, as the first filter
   will have to work at a higher rate.  In any case, an implementation
   is not constrained to respect the filter ordering as long as the
   result is the same, and it may even implement the composite Filtering
   in Filtering in one single step.
 
   Since encryption alters the meaning of encrypted fields, when the
   Property Match Filtering classification is based on the encrypted
   field(s) in the packet, it MUST be able to recognize that the
   field(s) are not available and MUST NOT select those packets unless
   specifically directed by the Information Element description.
   Even if they are ignored, the encrypted packets MUST be accounted for
   in the Selector packetsObserved Information Element [PSAMP-INFO],
   part of the Selection Sequence Statistics Report Interpretation.
 
   Example of a match based filter Selector, whose rules are:
      IPv4 Source Address   = 192.0.2.1
      IPv4 Next-Hop Address = 192.0.2.129
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Set ID =  3       |          Length = 26          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 266      |       Field Count = 4         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0|     selectorId = 302        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 4       |0|   selectorAlgorithm = 304   |
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 1        |0|    sourceIPv4Address = 8    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|   ipNextHopIPv4Address = 15 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    Associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 266        |        Length = 11            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              21                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       5       |                        192.0.2 ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ... .1        |                        192.0.2 ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ... .129      |
   +-+-+-+-+-+-+-+-+
 
       Figure L: Example of the Selector Report Interpretation,
                 For match based and router state Filtering
 
   Notes:
   * A selectorAlgorithm value of 5 represents property match Filtering.
   * In this filter there is a mix of information from the packet and
   information from the router.
 
 6.5.2.6 Hash-Based Filtering
 
   In hash based selection a hash function is run on IPv4 traffic
   the following fields MUST be used as input to that hash function:
    - IP identification field
    - Flags field
    - Fragment offset
    - Source IP address
    - Destination IP address
    - A number of bytes from the IP payload.  The number of bytes and
   starting offset MUST be configurable if the hash function supports
   it.
 
   For the bytes taken from the IP payload, IPSX has a fixed offset
   of 0 bytes and a fixed size of 8 bytes.  The number and offset of
   payload bytes in the BOB function MUST be configurable.
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
 
   The minimum configuration ranges MUST be as follows:
    Number of bytes:  from 8 to 32
    Offset:           from 0 to 64
 
   If the selected payload bytes are not available and the hash function
   can take a variable sized input then the hash function MUST be run
   with the information which is available and a shorter size.  Passing
   0 as a substitute for missing payload bytes is only acceptable if
   the hash function takes a fixed size as is the case with IPSX.
 
   If the hash function can take an initialization value then this
   value MUST be configurable.
 
   A hash-based selection function MAY be configurable as a digest
   function.  Any selection process which is configured as a digest
   function MUST have the output value included in the basic packet
   report for any selected packet.
 
   Each hash function used as a hash-based selector requires its own
   value for the selectorAlgorithm. Currently we have BOB (6), IPSX (7)
   and CRC (8) defined and any MAY be used for either Filtering
   or creating a Packet Digest.  Only BOB is recommended though and
   SHOULD be used.
 
   The REQUIRED algorithm specific Information Elements in case of hash
   based selection are:
 
   hashIPPayloadOffset   - The payload offset used by a hash based
                          Selector
   hashIPPayloadSize     - The payload size used by a hash based
                          Selector
   hashOutputRangeMin    - One or more values for the beginning of
                          each potential output range.
   hashOutputRangeMax    - One or more values for the end of each
                          potential output range.
   hashSelectedRangeMin  - One or more values for the beginning of
                          each selected range.
   hashSelectedRangeMax  - One or more values for the end of each
                          selected range.
   hashDigestOutput      - A boolean value, TRUE if the output from
                          this selector has been configured to be
                          included in the packet report as a packet
                          digest.
 
   NOTE: If more than one selection or output range needs to be sent
   then the minimum and maximum elements may be repeated as needed.
   These MUST make one or more non-overlapping ranges.  The elements
   SHOULD be sent as pairs of minimum and maximum in ascending order,
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   however if they are sent out of order then there will only be one
   way to interpret the ranges to produce a non-overlapping range and
   the Collecting Process MUST be prepared to accept and decode this.
 
   The following algorithm specific Information Element MAY be sent,
   but is optional for security considerations:
   hashInitialiserValue  - The initialiser value to the hash function.
 
   Since encryption alters the meaning of encrypted fields, when the
   Hash-Based Filtering classification is based on the encrypted
   field(s) in the packet, it MUST be able to recognize that the
   field(s) are not available and MUST NOT select those packets.  Even
   if they are ignored, the encrypted packets MUST be accounted in the
   Selector packetsObserved Information Element [PSAMP-INFO], part of
   the Selection Sequence Statistics Report Interpretation.
 
   Example of a hash based filter Selector, whose configuration is:
   Hash Function           = BOB
   Hash IP Payload Offset  = 0
   Hash IP Payload Size    = 16
   Hash Initialiser Value  = 0x9A3F9A3F
   Hash Output Range       = 0 to 0xFFFFFFFF
   Hash Selected Range     = 100 to 200 and 400 to 500
 
   IPFIX Options Template Record:
 
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Set ID =  3       |          Length = 50          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Template ID = 269      |       Field Count = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0|     selectorId = 300        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 4       |0|   selectorAlgorithm = 302   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 1        |0|  hashIPpayloadOffset = 327  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|   hashIPpayloadSize = 328   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|  hashInitialiserValue = 329 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|   hashOutputRangeMin = 330  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|   hashOutputRangeMax = 331  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|  hashSeletionRangeMin = 332 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   |       Field Length = 4        |0|  hashSeletionRangeMax = 333 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|  hashSeletionRangeMin = 332 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|  hashSeletionRangeMax = 333 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   Associated IPFIX Data Record:
 
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID = 266        |        Length = 45            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              22                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       6       |                            ...                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...   0       |                            ...                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...  16       |                      0x9A3F9A ...             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...  3F       |                            ...                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...   0       |                      0xFFFFFF ...             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...  FF       |                        ... 100                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |                        ... 200                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |                        ... 400                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |                        ... 500                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ...      |
   +-+-+-+-+-+-+-+-+
 
       Figure M: Example of the Selector Report Interpretation,
                 for Hash Based Filtering
 
   Notes:
   * A selectorAlgorithm value of 6 represents hash-based Filtering
   using the BOB algorithm.
 
 
 
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
 6.5.2.7 Other Selection Methods
 
   Some potential new selection methods MAY be added.  Some of the new
   selection methods, such as non-uniform probabilistic Sampling and
   flow state dependent Sampling, are described in [PSAMP-TECH], with
   further references.
 
   Each new selection method MUST be assigned a unique value for the
   selectorAlgorithm Information Element.  Its configuration
   parameter(s), along with the way to report it/them with an Options
   Template, MUST be clearly specified.
 
 
 6.5.3   Selection Sequence Statistics Report Interpretation
 
   A Selector MAY be used in multiple Selection Sequences.  However,
   each use of a Selector must be independent, so each separate logical
   instance of a Selector MUST maintain its own individual Selection
   State and statistics.
 
   The Selection Sequence Statistics Report Interpretation MUST include
   the number of observed packets (Population Size) and the number of
   packets selected (Sample Size) by each instance of its Primitive
   Selectors.
 
   Within a Selection Sequence composed of several Primitive Selectors,
   the number of packets selected for one Selector is equal to the
   number of packets seen by the next Selector.  The order of the
   Selectors in the Selection Sequence Statistics Report Interpretation
   MUST match the order of the Selectors in the Selection Sequence.
 
   If the full set of statistics is not sent as part of the Basic Packet
   Reports, the PSAMP Device MUST export a Selection Sequence Statistics
   Report Interpretation for every Selection Sequence, using an Options
   Template containing the following Information Elements:
 
    Scope:         selectionSequenceId
    Non-scope:     packetsObserved
                   packetsSelected (first)
                   ...
                   packetsSelected (last)
 
   The packetsObserved Information Element [PSAMP-INFO] MUST contain the
   number of packets seen at the Observation Point, and as a consequence
   passed to the first Selector in the Selection Sequence.  The
   packetsSelected Information Element [PSAMP-INFO] contains the number
   of packets selected by a Selector in the Selection Sequence.
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   The Attained Selection Fraction for the Selection Sequence is
   calculated by dividing the number of selected packets
   (packetsSelected Information Element) for the last Selector by the
   number of observed packets (packetsObserved Information Element).
   The Attained Selection Fraction can be calculated for each Selector
   by dividing the number of packets selected for that Selector by the
   value for the previous Selector.
 
   The statistics for the whole sequence SHOULD be taken at a single
   logical point in time; the input value for a Selector MUST equal the
   output value of the previous selector.
 
   The Selection Sequence Statistics Report Interpretation MUST be
   exported periodically.
 
   Example of Selection Sequence Statistics Report Interpretation:
 
    Selection Sequence 7 (Filter->Sampling):
 
      Observed   100  (observationPointId  1, Interface 5)
      Selected    50  (selectorId  5, match IPV4SourceAddress 192.0.2.1)
      Selected     6  (selectorId 10, Sampler: Random one out-of ten)
 
    Selection Sequence 9 (Sampling->Filtering):
 
      Observed   100  (observationPointId  1, Interface 5)
      Selected    10  (selectorId 10, Sampler: Random one out-of ten)
      Selected     3  (selectorId  5, match IPV4SourceAddress 192.0.2.1)
 
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Set ID = 3         |           Length = 26         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 267       |        Field Count = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0|  selectionSequenceId = 301  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 4       |0|    packetsObserved = 318    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|    packetsSelected = 319    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |0|    packetsSelected = 319    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
 
   The associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID =  267       |          Length = 36          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               7                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              100                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              50                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               6                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               9                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              100                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              10                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               3                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure N: Example of the Selection Sequence Statistics Report
                 Interpretation
 
   Notes:
   * The Attained Sampling Fractions for Selection Sequence 7 are:
            Filter 10: 50/100
            Sampler 5: 6/50
            Number of samples selected: 6
 
   * The Attained Sampling Fractions for Selection Sequence 9 are:
            Sampler 5: 10/100
            Filter 10: 3/10
            Number of samples selected: 3
 
 
 6.5.4   Accuracy Report Interpretation
   In order for the Collecting Process to determine the inherent
   accuracy of the reported quantities (for example timestamps), the
   PSAMP Device SHOULD send an Accuracy Report Interpretation.
 
   The Accuracy Report Interpretation MUST be exported by an Option
   Template Record with a scope that contains the Information Element
   for which the accuracy is required.  In case the accuracy is specific
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   to a template, a second scope containing the templateId value MUST be
   added to the Option Template Record.  The accuracy SHOULD be reported
   either with the fixedError Information Element [PSAMP-INFO], or with
   the relativeError Information Element [PSAMP-INFO].
 
   Accuracy Report Interpretation using the fixedError Information
   Element:
    Scope:     informationElementId
    Non-scope: fixedError
 
   Accuracy Report Interpretation using the fixedError Information
   Element and a double scope:
    Scope:     templateId
               informationElementId
    Non-scope: fixedError
 
   Accuracy Report Interpretation using the relativeError Information
   Element:
    Scope:     informationElementId
    Non-scope: relativeError
 
   Accuracy Report Interpretation using the relativeError Information
   Element and a double scope:
    Scope:     templateId
               informationElementId
    Non-scope: relativeError
 
   For example, the accuracy of an Information Element whose Abstract
   Data Type is dateTimeMilliseconds [IPFIX-INFO], for which the unit is
   specified as milliseconds, can be specified with the fixedError
   Information Element with the milliseconds units.  In this case, the
   error interval is the Information Element value +/- the value
   reported in the fixedError.
 
   For example, the accuracy of an Information Element to estimate the
   accuracy of a sampled flow, for which the unit would be specified in
   octets, can be specified with the relativeError Information Element
   with the octet units.  In this case, the error interval is the
   Information Element value +/- the value reported in the relativeError
   times the reported Information Element value.
 
   Alternatively to reporting either the fixedError Information Element
   or the relativeError Information Element in the Accuracy Report
   Interpretation, both Information Elements MAY be present.  This
   scenario could help in more complex situations where the system clock
   drifts, on the top of having its own accuracy, during the duration of
   a measurement.
 
   If the accuracy of a reported quantity changes on the Metering
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   Process, a new Accuracy Report Interpretation MUST be generated.  The
   Collecting Process MUST keep the accuracy of the latest Accuracy
   Report Interpretation.
 
   Example of an Accuracy Report Interpretation using the fixedError
   Information Element and a double scope: the timeMicroseconds
   contained in the Template 5 has an accuracy of +/- 2 ms, represented
   by the fixedError Information Element.
    Scope:     templateId = 6
               informationElementId = timeMicroseconds
    Non-scope: fixedError = 2 ms
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Set ID = 3         |           Length = 22         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 267       |        Field Count = 3        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 2     |0|       templateId = 145      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 2       |0| InformationElementId = 303  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 2 Length = 2       |0|      fixedError = 320       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
   The associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID =  267       |          Length = 12          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              5                |             324               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    2  (encoded as a float32)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure O: Example of the Selection Sequence Statistics Report
                 Interpretation
 
   Notes:
   * fixedError is of type float64 but is compressed down to a float32
   here.
 
 
 Claise, et. al            Standard Track                   [Page 38]
 

                  PSAMP Protocol Specifications           December 2007
 
 
 
   The second example displays an Accuracy Report Interpretation using
   the relativeError Information Element and a single scope: the
   timeMicroseconds has an error of 5 percents, represented by the
   proportionalAccuracy Information Element.
    Scope:     informationElementId = timeMicroseconds
    Non-scope: relativeError = 0.05
 
   IPFIX Options Template Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Set ID = 3         |           Length = 18         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Template ID = 268       |        Field Count = 2        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Scope Field Count = 1     |0| InformationElementId = 303  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Scope 1 Length = 2       |0|      relativeError= 321     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Field Length = 4        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
   The associated IPFIX Data Record:
 
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Set ID =  267       |          Length = 10          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             324               |                     0.05 ...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ...(encoded as a float32)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
       Figure P: Example of the Selection Sequence Statistics Report
                 Interpretation
 
   Notes:
   * relativeError is of type float64 but is compressed down to a
   float32 here.
 
 
 7.    Security Considerations
 
   As IPFIX has been selected as the PSAMP export protocol and as the
   PSAMP security requirements are not stricter than the IPFIX security
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   requirements, refer to the IPFIX export protocol [IPFIX-PROTO] for
   the security considerations.
 
   In the basic Packet Report, a PSAMP Device exports some number of
   contiguous bytes from the start of the packet, including the packet
   header (which includes link layer, network layer and other
   encapsulation headers) and some subsequent bytes of the packet
   payload. The PSAMP Device SHOULD NOT export the full payload of
   conversations, as this would mean wiretapping [RFC2804].  The PSAMP
   Device MUST respect local privacy laws.
 
 8.    IANA Considerations
 
   The PSAMP Protocol, as set out in this document, has two sets of
   assigned numbers.  Considerations for assigning them are discussed
   in this section, using the example policies as set out in the
   "Guidelines for IANA Considerations" document IANA-RFC [RFC2434].
 
 8.1      IPFIX Related Considerations
 
   As the PSAMP protocol uses the IPFIX protocol, refer to the IANA
   considerations section in [IPFIX-PROTO] for the assignments of
   numbers used in the protocol and for the numbers used in the
   information model.
 
 8.2      PSAMP Related Considerations
 
   Each new selection method MUST be assigned a unique value for the
   selectorAlgorithm Information Element [PSAMP-INFO].  Initial
   contents of this registry are found section 8.2.4 in [PSAMP-INFO].
   Its configuration parameter(s), along with the way to report it/them
   with an Options Template, MUST be clearly specified.
 
   New assignments for the PSAMP selection method will be administered
   by IANA, on a First Come First Served basis [RFC2434], subject to
   Expert Review [RFC2434].  The group of experts must double check the
   Information Elements definitions with already defined Information
   Elements for completeness, accuracy and redundancy.  Those experts
   will initially be drawn from the Working Group Chairs and document
   editors of the IPFIX and PSAMP Working Groups.
 
 9.    References
 
 9.1      Normative References
 
   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   [RFC2434] H. Alvestrand, T. Narten, "Guidelines for Writing an IANA
   Considerations Section in RFCs", RFC 2434, October 1998
 
   [PSAMP-TECH] T. Zseby, M. Molina, N. Duffield, S. Niccolini, F.
   Raspall, "Sampling and Filtering Techniques for IP Packet Selection"
   draft-ietf-psamp-sample-tech-10.txt
 
   [PSAMP-INFO] T. Dietz, F. Dressler, G. Carle, B. Claise, "Information
   Model for Packet Sampling Exports", draft-ietf-psamp-info-07.txt
 
   [IPFIX-INFO] J. Quittek, S. Bryant, B. Claise, J. Meyer, "Information
   Model for IP Flow Information Export" draft-ietf-ipfix-info-15.txt
 
   [IPFIX-PROTO] B. Claise (Editor) "Specification of the IPFIX Protocol
   for the Exchange of IP Traffic Flow Information", draft-ietf-ipfix-
   protocol-26.txt
 
 9.2     Informative References
 
   [IPFIX-ARCH] G. Sadasivan, N. Brownlee, B. Claise, J. Quittek,
   "Architecture Model for IP Flow Information Export" draft-ietf-ipfix-
   architecture-12.txt"
 
   [PSAMP-FMWK] D. Chiou, B. Claise, N. Duffield, A. Greenberg, M.
   Grossglauser, P. Marimuthu, J. Rexford, G. Sadasivan,  "A Framework
   for Passive Packet Measurement" draft-ietf-psamp-framework-12.txt
 
   [RFC4271] Y. Rekhter, T. Li, Hares, S. "A Border Gateway Protocol 4
   (BGP-4)", RFC 4271, January 2006
 
   [RFC2804] IAB, IESG, "IETF Policy on Wiretapping", RFC 2804, May 2000
 
   [RFC3917] J. Quittek, T. Zseby, B. Claise, S. Zander, "Requirements
   for IP Flow Information Export", RFC 3917, October 2004
 
 10.     Acknowledgments
 
   The authors would like to thank the PSAMP group, especially Paul
   Aitken for fruitful discussions and for proofreading the document
   several times.
 
   Authors' Addresses
 
   Benoit Claise
   Cisco Systems
   De Kleetlaan 6a b1
   1831 Diegem
   Belgium
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   Phone: +32 2 704 5622
   E-mail: bclaise@cisco.com
 
   Juergen Quittek
   NEC Europe Ltd.
   Network Laboratories
   Kurfuersten-Anlage 36
   69115 Heidelberg
   Germany
   Phone: +49 6221 90511-15
   Email: quittek@nw.neclab.eu
 
   Andrew Johnson
   Cisco Systems
   96 Commercial Quay
   Edinburgh EH6 6LX
   Scotland
   Phone: +44 131 561 3641
   Email: andrjohn@cisco.com
 
 
 11.     Intellectual Property Statement
 
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 12.     Copyright Statement
 
   Copyright (C) The IETF Trust (2007).
 
 
 
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                  PSAMP Protocol Specifications           December 2007
 
 
   This document is subject to the rights, licenses and
   restrictions contained in BCP 78, and except as set forth
   therein, the authors retain all their rights.
 
 13.     Disclaimer
 
   This document and the information contained herein are provided
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   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY,
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