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   Internet Draft                               Nick Duffield (Editor)
   Category: Informational                        AT&T Labs - Research
   Document: <draft-ietf-psamp-framework-10.txt>          January 2005
   Expires: July 2005
                A Framework for Packet Selection and Reporting
   Status of this Memo
      This document is an Internet-Draft and is subject to all
      provisions of section 3 of RFC 3667. By submitting this
      Internet-Draft, each author represents that any applicable patent
      or other IPR claims of which he or she is aware have been or will
      be disclosed, and any of which he or she become aware will be
      disclosed, in accordance with RFC 3668.
      Internet-Drafts are working documents of the Internet Engineering
      Task Force (IETF), its areas, and its working groups. Note that
      other groups may also distribute working documents as
      Internet-Drafts. Internet-Drafts are draft documents valid for a
      maximum of six months and may be updated, replaced, or obsoleted
      by other documents at any time. It is inappropriate to use
      Internet-Drafts as reference material or to cite them other than
      as "work in progress."
      The list of current Internet-Drafts can be accessed at
      The list of Internet-Draft Shadow Directories can be accessed at
      This document specifies a framework for the PSAMP (Packet
      SAMPling) protocol. The functions of this protocol are to select
      packets from a stream according to a set of standardized
      selectors, to form a stream of reports on the selected packets,
      and to export the reports to a collector. This framework details
      the components of this architecture, then describes some generic
      requirements, motivated by the dual aims of ubiquitous deployment
      and utility of the reports for applications. Detailed
      requirements for selection, reporting and exporting are
      described, along with configuration requirements of the PSAMP
      Comments on this document should be addressed to the PSAMP
      Working Group mailing list: psamp@ops.ietf.org
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      To subscribe: psamp-request@ops.ietf.org, in body: subscribe
      Archive: https://ops.ietf.org/lists/psamp/
   Table of Contents
      1.   Introduction................................................3
      2.   PSAMP Documents Overview....................................4
      3.   Elements, Terminology and High-level Architecture...........4
      3.1  High-level description of the PSAMP Architecture............4
      3.2  Observation Points, Packet Streams and Packet Content.......5
      3.3  Selection Process...........................................6
      3.4  Reporting Process...........................................7
      3.5  Measurement Process.........................................8
      3.6  Exporting Process...........................................8
      3.7  PSAMP Device................................................8
      3.8  Collector...................................................8
      3.9  Possible Configurations.....................................9
      3.10 PSAMP and IPFIX Interaction................................10
      4.   Generic Requirements for PSAMP.............................11
      4.1  Generic Selection Process Requirements.....................11
      4.2  Generic Reporting Process Requirements.....................11
      4.3  Generic Exporting Process Requirements.....................12
      4.4  Generic Configuration Requirements.........................12
      5.   Packet Selection...........................................13
      5.1  Two Types of Selector......................................13
      5.2  PSAMP Packet Selectors.....................................14
      5.3  Selection Fraction Terminology.............................16
      5.4  Input Sequence Numbers for Primitive Selectors.............17
      5.5  Composite Selectors........................................18
      5.6  Constraints on the Selection Fraction......................18
      6.   Reporting Process..........................................18
      6.1  Mandatory Contents of Packet Reports: Basic Reports........19
      6.2  Extended Packet Reports....................................19
      6.3  Extended Packet Reports in the Presence of IPFIX...........20
      6.4  Report Interpretation......................................20
      7.   Parallel Measurement Processes.............................21
      8.   Exporting Process..........................................21
      8.1  Use of IPFIX...............................................21
      8.2  Congestion-aware Unreliable Transport......................22
      8.3  Configurable Export Rate Limit.............................22
      8.4  Limiting Delay for Export Packets..........................23
      8.5  Export Packet Compression..................................24
      8.6  Collector Destination......................................24
      8.7  Local Export...............................................24
      9.   Configuration and Management...............................24
      10.  Feasibility and Complexity.................................25
      10.1 Feasibility................................................25
      10.1.1 Filtering................................................25
      10.1.2 Sampling.................................................25
      10.1.3 Hashing..................................................26
      10.1.4 Reporting................................................26
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      10.1.5 Exporting................................................26
      10.2 Potential Hardware Complexity..............................26
      11.  Applications...............................................27
      11.1 Baseline Measurement and Drill Down........................28
      11.2 Trajectory Sampling........................................28
      11.3 Passive Performance Measurement............................29
      11.4 Troubleshooting............................................29
      12.  Security Considerations....................................30
      13.  IANA Considerations........................................30
      14.  Normative References.......................................30
      15.  Informative References.....................................31
      16.  Authors' Addresses.........................................33
      17.  Intellectual Property Statements...........................34
      18.  Full Copyright Statement...................................34
      19.  Disclaimers................................................35
      Copyright (C) The Internet Society (2004).  All Rights Reserved.
      This document is an Internet-Draft and is in full conformance
      with all provisions of Section 10 of RFC 2026.
      Internet-Drafts are working documents of the Internet Engineering
      Task Force (IETF), its areas, and its working groups.  Note that
      other groups may also distribute working documents as
      Internet-Drafts are draft documents valid for a maximum of six
      months and may be updated, replaced, or obsoleted by other
      documents at any time.  It is inappropriate to use
      Internet-Drafts as reference material or to cite them other than
      as "work in progress."
      The list of current Internet-Drafts can be accessed at
      The list of Internet-Draft Shadow Directories can be accessed at
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      "OPTIONAL" in this document are to be interpreted as described in
      RFC 2119.
   1. Introduction
      This document describes the PSAMP framework for network elements
      to select subsets of packets by statistical and other methods,
      and to export a stream of reports on the selected packets to a
      The motivation for the PSAMP standard comes from the need for
      measurement-based support for network management and control
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      across multivendor domains. This requires domain-wide consistency
      in the types of selection schemes available, and the manner in
      which the resulting measurements are presented and interpreted.
      The motivation for specific packet selection operations comes
      from the applications that they enable. Development of the PSAMP
      standard is open to influence by the requirements of standards in
      related IETF Working Groups, for example, IP Performance Metrics
      (IPPM) [RFC-2330] and Internet Traffic Engineering (TEWG).
      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.
      But PSAMP selection operations include random selection,
      deterministic selection (filtering), and deterministic
      approximations to random selection (hash-based selection).
   2. PSAMP Documents Overview
      PSAMP-FW: "A Framework for Packet Selection and Reporting" (this
      document). This document describes the PSAMP framework for
      network elements to select subsets of packets by statistical and
      other methods, and to export a stream of reports on the selected
      packets to a collector. Definitions of terminology and the use of
      the terms "must", "should" and "may" in this document are
      informational only.
      [PSAMP-TECH]: "Sampling and Filtering Techniques for IP Packet
      Selection", describes the set of packet selection techniques
      supported by PSAMP.
      [PSAMP-MIB]: "Definitions of Managed Objects for Packet Sampling"
      describes the PSAMP Management Information Base
      [PSAMP-PROTO]: "Packet Sampling (PSAMP) Protocol Specifications"
      specifies the export of packet information from a PSAMP Exporting
      Process to a PSAMP Colleting Process
      [PSAMP-INFO]: "Information Model for Packet Sampling Exports"
      defines an information and data model for PSAMP.
   3. Elements, Terminology and High-level Architecture
   3.1 High-level description of the PSAMP Architecture
      Here is an informal high level description of the PSAMP protocol
      operating in a PSAMP device (all terms will be defined
      presently). A stream of packets is observed at an observation
      point. A selection process inspects each packet to determine
      whether it should be selected. A reporting process constructs a
      report on each selected packet, using the packet content, and
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      possibly other information such as the packet treatment or the
      arrival timestamp. An exporting process sends the reports to a
      collector, together with any subsidiary information needed for
      their interpretation.
      The following figure indicates the sequence of the three
      processes (selection, reporting, and exporting) within the PSAMP
      device. The composition of the selection process followed by the
      reporting process is known as the measurement process.
                 +---------+    +---------+    +---------+
       Observed  |Selection|    |Reporting|    |Exporting|
       Packet--->|Process  |--->|Process  |--->|Process  |--->Collector
       Stream    +---------+    +---------+    +---------+
               \----Measurement Process-----/
      The following sections give the detailed definitions of each of
      all the objects just named.
   3.2 Observation Points, Packet Streams and Packet Content
      This section contains the definition of terms relevant to
      obtaining the packet input to the selection process.
      * Observation Point
        An observation point is a location in the network where packets
        can be observed. Examples include:
             (i) a line to which a probe is attached;
             (ii) a shared medium, such as an Ethernet-based LAN;
             (iii) a single port of a router, or set of interfaces
             (physical or logical) of a router;
             (iv) an embedded measurement subsystem within an
        Note that one Observation Point may be a superset of several
        other Observation Points.  For example one Observation Point
        can be an entire line card.  This would be the superset of the
        individual Observation Points at the line card's interfaces.
      * 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 measurement
        process. An example of a Packet Stream is the output of the
        selection process.
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      * Packet Content
        The packet content denotes the union of its associated headers
        (including data link layer, network layer and other
        encapsulation headers) and the packet payload.
      Note that packets selected from a Packet 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 [RFC-3917].
   3.3 Selection Process
      This section defines the selection process and related objects.
      * 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 and/or the Reporting Process. The
           selection state may depend on the current packet, packets
           observed earlier, and other variables, for example:
                  (i) sequence numbers of packets at the input of
                  (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 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 from the selector.
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           The Selector can make use of the following information in
           determining whether a packet is selected:
           (i) the packet's 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:
           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.
   3.4 Reporting Process
      * Reporting Process:
           A reporting process creates a report stream from the packets
           selected by a Selection Process, in preparation for export.
           The input to the Reporting Process comprises that
           information available to the Selection Process per selected
           packet, specifically:
             (i) the selected packet's content;
             (ii) information derived from the selected packet's
             treatment at the Observation Point;
             (iii) any Selection State maintained by the inputting
             Selection Process, reflecting any modifications to the
             Selection State made during selection of the packet.
      * Report Stream:
           The report stream is the output of a reporting process,
           comprising two distinguished types of information: packet
           reports, and report interpretation.
      * Packet Reports:
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           Packet Reports comprise a configurable subset of a packet's
           input to the Reporting Process, including the packet's
           content, information relating to its treatment
           (for example, the output interface), and its associated
           Selection State (for example, a hash of the packet's
      * Report Interpretation:
           Report interpretation comprises subsidiary information,
           relating to one or more packets, that is used for
           interpretation of their Packet Reports. Examples include
           configuration parameters of the Selection Process and of the
           Reporting Process.
   3.5 Measurement Process
      * A Measurement Process is the composition of a Selection Process
        followed by a Reporting Process.
   3.6 Exporting Process
      * Exporting Process:
        An exporting process sends, in the form of export packet, the
        output of one or more Measurement Processes to one or more
        A Measurement Process may feed more that one Exporting Process.
        For example, the output of a Measurement Process may be
        exported locally to a measurement application execution at the
        observation point, with a copy also being exported to a remote
      * Export Packets:
        a combination of Report Interpretation and/or one or more
        Packet Reports are bundled by the Exporting Process into a
        export packet for exporting to a collector.
   3.7 PSAMP Device
      A PSAMP Device is a device hosting at least an Observation Point,
      a Measurement Process and an Exporting Process. Typically,
      corresponding Observation Point(s), Measurement Process(es) and
      Exporting Process(es) are co-located at this device, for example
      at a router.
   3.8 Collector
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      A collector receives a report stream exported by one or more
      Exporting Processes. In some cases, the host of the Measurement
      and/or Exporting Processes may also serve as the collector.
   3.9 Possible Configurations
      Various possibilities for the high level architecture of these
      elements are as follows.
          MP = Measurement Process, EP = Exporting process
          PSAMP Device
         +---------------------+                 +------------------+
         |Observation Point(s) |                 | Collector(1)     |
         |MP(s)--->EP----------+---------------->|                  |
         |MP(s)--->EP----------+-------+-------->|                  |
         +---------------------+       |         +------------------+
          PSAMP Device                 |
         +---------------------+       |         +------------------+
         |Observation Point(s) |       +-------->| Collector(2)     |
         |MP(s)--->EP----------+---------------->|                  |
         +---------------------+                 +------------------+
          PSAMP Device
         |Observation Point(s) |
         |MP(s)--->EP---+      |
         |              |      |
         |Collector(3)<-+      |
      The most generic Measurement Process configuration is composed
                | +----------+           +---------+ |
                | |Selection |           |         | |
       Observed | |Process   |  Packet   |Reporting| |
       Packet-->| |(primitive|- Stream ->|Process  |--> Report Stream
       Stream   | | selector)|           |         | |
                | +----------+           +---------+ |
                |          Measurement Process       |
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      A Measurement Process with a composite selector is composed of:
                | +-----------------------------------+
                | | +----------+         +----------+ |
                | | |Selection |         |Selection | |
       Observed | | |Process   |         |Process   | |
       Packet-->| | |(primitive|-Packet->|(primitive|---> Packet ...
       Stream   | | |selector1)| Stream  |selector2)| |   Stream
                | | +----------+         +----------+ |
                | |        Composite Selector         |
                | +-----------------------------------+
                |                   Measurement Process
                      +---------+ |
                      |         | |
                      |Reporting| |
                 ...  | Process |---> Report Stream
                      |         | |
                      +---------+ |
   3.10    PSAMP and IPFIX Interaction
      The PSAMP Measurement Process can be viewed as analogous to the
      IPFIX metering process. The PSAMP Measurement Process takes an
      Observed Packet Stream as its input, and produces Packet Reports
      as its output. The IPFIX metering process produces flow records
      as its output. The distinct name "Measurement Process" has been
      retained in order to avoid potential confusion in settings where
      IPFIX and PSAMP coexist, and in order to avoid the implicit
      requirement that the PSAMP version satisfy the requirements of an
      IPFIX metering process (at least while these are under
      development). The relationship between PSAMP and IPFIX is
      described more in [PSAMP-INFO].
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   4. Generic Requirements for PSAMP
      This section describes the generic requirements for the PSAMP
      protocol. A number of these are realized as specific requirements
      in later sections.
   4.1 Generic Selection Process Requirements.
      * Ubiquity: The Selectors must be simple enough to be implemented
        ubiquitously at maximal line rate.
      * Applicability: the set of Selectors must be rich enough to
        support a range of existing and emerging measurement based
        applications and protocols. This requires a workable trade-off
        between the range of traffic engineering applications and
        operational tasks it enables, and the complexity of the set of
      * Extensibility: the protocol must be able to accommodate
        additional packet selectors not currently defined.
      * Flexibility: the protocol must support selection of packets
        using various network protocols or encapsulation layers,
        including Internet Protocol Version 4 (IPv4) [IPv4], Internet
        Protocol Version 6 (IPv6) [RFC-2460], and Multiprotocol Label
        Switching (MPLS) [RFC-3031].
      * Robust Selection: packet selection must be robust against
        attempts to craft an observed packet stream from which packets
        are selected disproportionately (e.g. to evade selection, or
        overload measurement systems).
      * Parallel Measurement Processes: the protocol must support
        simultaneous operation of multiple independent Measurement
        Processes at the same host.
      * Causality: the selection decision for each packet should depend
        only weakly, if at all, upon future packets arrivals. This
        promotes ubiquity by limiting the complexity of the selection
      * Encrypted Packets: Selectors that interpret packet fields must
        be configurable to ignore (i.e. not select) encrypted packets,
        when they are detected.
      Specific Selectors are outlined in Section 5, and described in
      more detail in the companion document [PSAMP-TECH].
   4.2 Generic Reporting Process Requirements
      * Self-defining: the Report Stream must be complete in the sense
        that no additional information need be retrieved from the
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        Observation Point in order to interpret and analyze the
      * Indication of Information Loss: the Report Stream must include
        sufficient information to indicate or allow the detection of
        loss occurring within the Selection, Reporting or Exporting
        Processes, or in transport. This may be achieved by the use of
        sequence numbers.
      * Accuracy: the Report Stream must include information that
        enables the accuracy of measurements to be determined.
      * Faithfulness: all reported quantities that relate to the packet
        treatment must reflect the router state and configuration
        encountered by the packet at the time it is received by the
        Measurement Process.
      * Privacy: selection of the content of Packet Reports will be
        cognizant of privacy and anonymity issues while being
        responsive to the needs of measurement applications, and in
        accordance with [RFC-2804].  Full packet capture of arbitrary
        packet streams is explicitly out of scope.
      A specific Reporting Process meeting these requirements, and the
      requirement for ubiquity, is described in Section 6.
   4.3 Generic Exporting Process Requirements
      * Timeliness: configuration must allow for limiting of buffering
        delays for the formation and transmission for Export Packets.
        See Section 8.4 for further details.
      * Congestion Avoidance: export of a Report Stream across a
        network must be congestion avoiding in compliance with [RFC-
        2914]. This is discussed further in Section 8.2.
      * Secure Export:
        (i) confidentiality: the option to encrypt exported data must
        be provided.
        (ii) integrity: alterations in transit to exported data must be
        detectable at the Collector
        (iii) authenticity: authenticity of exported data must be
        verifiable by the Collector in order to detect forged data.
      The motivation here is the same as for security in IPFIX export;
      see Sections 6.3 and 10 of [RFC-3917].
   4.4 Generic Configuration Requirements
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      * Ease of Configuration: of sampling and export parameters, e.g.
        for automated remote reconfiguration in response to collected
      * Secure Configuration: the option to configure via protocols
        that prevent unauthorized reconfiguration or eavesdropping on
        configuration communications must be available.  Eavesdropping
        on configuration might allow an attacker to gain knowledge that
        would be helpful in crafting a packet stream to evade
        subversion, or overload the measurement infrastructure.
      Configuration is discussed in Section 9. Feasibility and
      complexity of PSAMP operations is discussed in Section 10.
   5. Packet Selection
      This section details specific requirements for the Selection
      Process, motivated by the generic requirements of Section 3.3.
   5.1 Two Types of Selector
      PSAMP categorizes selectors into two types:
      * Filtering: a filter is a selector that selects a packet
        deterministically based on the Packet Content, the packet's
        treatment, and functions of these occurring in the Selection
        State. Two examples are:
           (i) Field-match filtering.
           (ii) Hash-based selection: a hash function is applied to the
           packet content, and the packet is selected if the result
           falls in a specified range.
      * 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.
        Sampling operations can be divided into two subtypes:
           (i) Content-independent Sampling, which does not use Packet
           Content in reaching sampling decisions. Examples include
           periodic 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.
           (ii) Content-dependent Sampling, in which the Packet Content
           is used in reaching selection decisions. An application is
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           pseudorandom selection according to a probability that
           depends on the contents of a packet field, e.g., sampling
           packets with a probability dependent on their TCP/UDP port
           numbers. Note that this is not a Filter.
   5.2 PSAMP Packet Selectors
       A spectrum of packet selectors is described in detail in [PSAMP-
       TECH]. Here we only briefly summarize the meanings for
      A PSAMP Selection Process must support at least one of the
      following Selectors.
      * Systematic Time Based Sampling: packet selection is triggered
        at periodic instants separated by a time called the spacing.
        All packets that arrive within a certain time of the trigger
        (called the interval length) are selected.
      * Systematic Count Based Sampling: similar to systematic time
        based expect that selection is reckoned with respect to packet
        count rather than time. Packet selection is triggered
        periodically by packet count, a number of successive packets
        being selected subsequent to each trigger.
      * Uniform Probabilistic Sampling: packets are selected
        independently with fixed sampling probability p.
      * Non-uniform Probabilistic Sampling: packets are selected
        independently with probability p that depends on packet
      * Probabilistic n-out-of-N Sampling: from each count-based
        successive block of N packets, n are selected at random.
      * Field Match Filtering
        Filtering schemes are based on the IPFIX flow definition. With
        this method a packet is selected if a specific field in the
        packet equals a predefined value. Possible filter fields are
        all IPFIX flow attributes specified in [IPFIX-INFO]. Further
        fields can be defined by vendor specific extensions.
        A packet is selected if Field=Value. Masks and ranges are only
        supported to the extent to which [IPFIX-INFO] allows them e.g.
        by providing explicit fields like the netmasks for source and
        destination addresses.
        AND operations are possible by concatenating filters, thus
        producing a composite selection operation. In this case, the
        ordering in which the filtering happens is implicitly defined
        (outer filters come after inner filters). However, as long as
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        the concatenation is on filters only, the result of the
        cascaded filter is independent from the order, 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
        OR operations are not supported with this basic model. More
        sophisticated filters (e.g. supporting bitmasks, ranges or OR
        operations etc.) can be realized as vendor specific schemes.
        Field match operations should be available for different
        protocol portions of the packet header:
           (i) the IP header (excluding options in IPv4, stacked
           headers in IPv6)
           (ii) transport header
           (iii) encapsulation headers (e.g. the MPLS label stack, if
        When the PSAMP device offers field match filtering, and, in its
        usual capacity other than in performing PSAMP functions,
        identifies or processes information from IP, transport or
        encapsulation protocols, then the information should be made
        available for filtering. For example, when a PSAMP device
        routes based on destination IP address, that field should be
        made available for filtering. Conversely, a PSAMP device that
        does not route is not expected to be able to locate an IP
        address within a packet, or make it available for filtering,
        although it may do so.
        Since packet encryption alters the meaning of encrypted fields,
        field match filtering must be configurable to ignore encrypted
        packets, when detected.
      * Hash-based Selection: Hash-based selection will employ one or
        more hash functions to be standardized.  A hash function is
        applied to a subset of packet content, and the packet is
        selected of the resulting hash falls in a specified range. The
        stronger the hash function, the more closely hash-based
        selection approximates uniform random sampling. Privacy of hash
        selection range and hash function parameters obstructs
        subversion of the selector by packets that are crafted either
        to avoid selection or to be selected. Privacy of the hash
        function is not required. Robustness and security
        considerations of hash-based selection are further discussed in
        further in [PSAMP-TECH]. Applications of hash-based sampling
        are described in Section 11.
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      * Router State Filtering: the Selection Process may support
        Filtering based on the following conditions, which may be
        combined with the logical AND operator"and", "or" or "not"
           (i) Ingress interface at which packet arrives equals a
           specified value
           (ii) Egress interface to which packet is routed to equals a
           specified value
           (iii) Packet violated Access Control List (ACL) on the
           (iv) Failed Reverse Path Forwarding (RPF)
           (v) Failed Resource Reservation (RSVP)
           (vi) No route found for the packet
           (vii) Origin Border Gateway Protocol (BGP) Autonomous System
           (AS) equals a specified value or lies within a given range
           (viii) Destination BGP AS equals a specified value or lies
           within a given range
       Router architectural considerations may preclude some
       information concerning the packet treatment being available at
       line rate for selection of packets. For example, the Selection
       Process may not be implemented in the fast path that is able to
       access routing state at line rate. However, when filtering
       follows sampling (or some other selection operation) in a
       Composite Selector, the rate of the Packet Stream output from
       the sampler and input to the filter may be sufficiently slow
       that the filter could select based on routing state.
   5.3 Selection Fraction Terminology
      * 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
      * Population Size:
        The Population Size is the number of all packets in a
      * 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
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        Population Size, as based on the configured selection
      * 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 configured
      Selectors, the Attained Selection Fraction usually approaches the
      Configured Selection Fraction. In Hash-based Selection, the
      Expected Selection Fraction is the quotient of size of the Hash
      Selection Range by the size of the Hash Range.
      The notions of Configured/Attained Selection Fraction extend
      beyond Selectors. An illustrative example is the Configured
      Selection Fraction of the composition of the Measurement Process
      with the Exporting Process. Here the Population is the Observed
      Packet Stream or a subset thereof. The Configured Selection
      Fraction is the fraction of the Population for which Packet
      Reports which are expected to reach the Collector. This quantity
      may reflect additional parameters, not necessarily described in
      the PSAMP protocol, that determine the degree of loss suffered by
      packet reports en route to the collector, e.g., the transmission
      bandwidth available to the Exporting Process. In this example,
      the Attained Selection Fraction is the fraction of Population
      packets for which reports did actually reach the collector, and
      thus incorporates the effect of any loss of Packet Reports due,
      e.g, to resource contention at the Observation Point, or during
   5.4 Input Sequence Numbers for Primitive Selectors
      Each instance of a Primitive Selector must maintain a count of
      packets presented at its input. The counter value is to be
      included as a sequence number for selected packets. The sequence
      numbers are considered as part of the packet's Selection State.
      Use of input sequence numbers enables applications to determine
      the Attained Selection Fraction, and hence correctly normalize
      network usage estimates regardless of loss of information,
      regardless of whether this loss occurs because of discard of
      packet reports in the measurement or reporting process (e.g. due
      to resource contention in the host of these processes), or loss
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      of export packets in transmission or collection. See [RFC-3176]
      for further details.
      As an example, consider a set of n consecutive packet reports r1,
      r2,... , rn, selected by a sampling operation and received at a
      collector. Let s1, s2,..., sn be the input sequence numbers
      reported by the packets. The Attained Selection Fraction for the
      composite of the measurement and exporting processes, taking into
      account both packet sampling at the observation point and loss in
      transmission, is computed as R = (n-1)/(sn-s1). (Note R would be
      1 if all packets were selected and there were no transmission
      The Attained Selection Fraction can be used to estimate the
      number bytes present in a portion of the Observed Packet Stream.
      Let b1, b2,..., bn be the bytes reported in each of the packets
      that reached the Collector, and set B = b1+b2+...+bn. Then the
      total bytes present in packets in the Observed Packet Stream
      whose input sequence numbers lie between s1 and sn is estimated
      by B/R, i.e, scaling up the measured bytes through division by
      the Attained Selection Fraction
      With Composite Selectors, an input sequence number must be
      reported for each Selector in the composition.
   5.5 Composite Selectors
      The ability to compose Selectors in a Selection Process should be
      provided. The following combinations appear to be most useful for
      *  concatentation of Field Match filters. This is useful for
      constructing the AND of the component filters.
      * filtering followed by sampling.
      * sampling followed by filtering.
      Composite Selectors are useful for drill down applications. The
      first component of a composite selector can be used to reduce the
      load on the second component. In this setting, the advantage to
      be gained from a given ordering can depends on the composition of
      the packet stream.
   5.6 Constraints on the Selection Fraction
      Sampling at full line rate, i.e. with probability 1, is not
      excluded in principle, although resource constraints may not
      permit it in practice.
   6. Reporting Process
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      This section details specific requirements for the Reporting
      Process, motivated by the generic requirements of Section 3.4
   6.1 Mandatory Contents of Packet Reports: Basic Reports
      The Reporting Process must include the following in each Packet
           (i) the input sequence number(s) of any Selectors that acted
           on the packet in the instance of a Measurement Process of
           which the Reporting Process is a component.
           (ii) the identifier of the measurement process that produced
           the selected packet
      The Reporting Process must support inclusion of the following in
      each Packet Report, as a configurable option:
           (iii) a basic report on the packet, i.e., 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.
      Some devices hosting Reporting Processes may not have the
      resource capacity or functionality to provide more detailed
      packet reports that those in (i), (ii) and (iii) above. Using
      this minimum required reporting functionality, the reporting
      process places the burden of interpretation on the Collector, or
      on applications that it supplies. Some devices may have the
      capability to provide extended packet reports, described in the
      next section.
   6.2 Extended Packet Reports
      The reporting process may support inclusion in Packet Reports of
      the following information, inclusion any or all being
      configurable as an option.
           (iv) fields relating to the following protocols used in the
           packet: IPv4, IPV6, transport protocols, MPLS.
           (v) packet treatment, including:
            - identifiers for any input and output interfaces of the
           Observation Point that were traversed by the packet
            - source and destination BGP AS
           (vi) Selection State associated with the packet, including:
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           - the timestamp of observation of the packet at the
           Observation Point. The timestamp should be reported to
           microsecond resolution.
           - hashes, where calculated.
       It is envisaged that selection of fields for Extended Packet
       Reporting may be used to reduce reporting bandwidth, in which
       case the option to report information in (iii) may not be
   6.3 Extended Packet Reports in the Presence of IPFIX
      If an IPFIX metering process is supported at the Observation
      Point, then in order to be PSAMP compliant, Extended Packet
      Reports must be able to include all fields required in the IPFIX
      information model [IPFIX-INFO], with modifications appropriate to
      reporting on single packets rather than flows.
   6.4  Report Interpretation
      The Report Interpretation must include:
           (i) configuration parameters of the Selectors of the packets
           reported on.
           (ii) format of the Packet Report;
           (iii) indication of the inherent accuracy of the reported
           quantities, e.g., of the packet timestamp.
      The accuracy measure in (iii) is of fundamental importance for
      estimating the likely error attached to estimates formed from the
      Packet Reports by applications.
      Identifiers in (iv) are necessary, e.g., in order to match Packet
      Reports to the selection process that selected them. For example,
      when Packet Reports produced by a sampling operation suffer loss
      (either during export, or in transit) it may be desirable to
      reconfigure downwards the Configured Selection Fraction on the
      Selection Process that selected them.
      The requirements for robustness and transparency are motivations
      for including Report Interpretation in the Report Stream: it
      makes the Report Stream self-defining.  The PSAMP framework
      excludes reliance on an alternative model in which interpretation
      is recovered out of band. This latter approach is not robust with
      respect to undocumented changes in Selector configuration, and
      may give rise to future architectural problems for network
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      management systems to coherently manage both configuration and
      data collection.
      It is not envisaged that all Report Interpretation be included in
      every packet report. Many of the quantities listed above are
      expected to be relatively static; they could be communicated
      periodically, and upon change.
   7. Parallel Measurement Processes
      Because of the increasing number of distinct measurement
      applications, with varying requirements, it is desirable to set
      up parallel Measurement Processes on a given Observed Packet
      Stream. A device capable of hosting a Measurement Process should
      be able to support more than one independently configurable
      Measurement Process simultaneously. Each such Measurement Process
      should have the option of being equipped with its own Exporting
      Process; otherwise the parallel Measurement Processes may share
      the same Exporting Process.
      Each of the parallel Measurement Processes should be independent.
      However, resource constraints may prevent complete reporting on a
      packet selected by multiple Selection Processes. In this case,
      reporting for the packet must be complete for at least one
      Measurement Process; other measurement processes need only record
      that they selected the packet, e.g., by incrementing a counter.
      The priority amongst Measurement Processes under resource
      contention should be configurable.
      It is not proposed to standardize the number of parallel
      Measurement Processes.
   8. Exporting Process
      This section detailes specific requirements for the Exporting
      Process, motivated by the generic requirements of Section 3.6
   8.1 Use of IPFIX
      PSAMP will use the IP Flow Information eXport (IPFIX) protocol
      for export of the Report Stream. The IPFIX protocol is well
      suited for this purpose, because the IPFIX architecture matches
      the PSAMP architecture very well and the means provided by the
      IPFIX protocol are sufficient for PSAMP purposes. On the other
      hand, not all features of the IPFIX protocol will need to be
      implemented by some PSAMP devices. For example, a device that
      offers only content-independent sampling and basic PSAMP
      reporting has no need to support IPFIX capabilities based on
      packet fields.
   8.1 Export Packets
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      Export packets may contain one or more packet reports, and/or
      report interpretation. Export packets must also contain:
           (i) An identifier for the Exporting Process
           (ii) An export packet sequence number.
           An export packet sequence number enables the collector to
           identify loss of export packets in transit. Note that some
           transport protocols, e.g. UDP, do not provide sequence
           numbers. Moreover, having sequence numbers available at the
           application level enables the collector to calculate packet
           loss rate for use, e.g., in estimating original traffic
           volumes from export packet that reach the collector.
   8.2 Congestion-aware Unreliable Transport
      The export of the report stream does not require reliable export.
      Section 5.4 shows that the use of input sequence numbers in
      packet Selectors means that the ability to estimate traffic rates
      is not impaired by export loss. Export packet loss becomes
      another form of sampling, albeit a less desirable, and less
      controlled, form of sampling.
      In distinction, retransmission of lost Export Packets consumes
      additional network resources. The requirement to store
      unacknowledged data is an impediment to having ubiquitous support
      for PSAMP.
      In order to jointly satisfy the timeliness and congestion
      avoidance requirements of Section 4.3, a congestion-aware
      unreliable transport protocol may be used. IPFIX is compatible
      with this requirement, since it mandates support of the Stream
      Control Transmission Protocol (SCTP) [SCTP] and the SCTP Partial
      Reliability Extension [RFC-3758].
      IPFIX also allows the use of User Datagram Protocol (UDP) [RFC-
      768] although it is not a congestion-aware protocol. However, in
      this case, the Export Packets must remain wholly within the
      administrative domains of the operators [IPFIX-PROTO]. The PSAMP
      exporting process is equipped with a configurable export rate
      limit (see Section 8.3 following) that can be used to limit the
      export rate when a congestion aware transport protocol is not
      used. The collector, upon detection of export packet loss through
      missing export sequence numbers, may reconfigure the export rate
      limit downwards in order to avoid congestion.
   8.3 Configurable Export Rate Limit
      The exporting process must have an export rate limit,
      configurable per Exporting Process. This is useful for two
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           (i) Even without network congestion, the rate of packet
           selection may exceed the capacity of the Collector to
           process reports, particularly when many Exporting Processes
           feed a common Collector. Use of an Export Rate Limit allows
           control of the global input rate to the Collector.
           (ii) IPFIX provides export using UDP as the transport
           protocol in some circumstances. An Export Rate Limit allows
           the capping of the export rate to match both path link
           speeds and the capacity of the Collector.
   8.4 Limiting Delay for Export Packets
      Low measurement latency allows the traffic monitoring system to
      be more responsive to real-time network events, for example, in
      quickly identifying sources of congestion. Timeliness is
      generally a good thing for devices performing the sampling since
      it minimizes the amount of memory needed to buffer samples.
      Keeping the packet dispatching delay small has other benefits
      besides limiting buffer requirements. For many applications a
      resolution of 1 second is sufficient. Applications in this
      category would include: identifying sources associated with
      congestion, tracing denial of service attacks through the
      network, and constructing traffic matrices. Furthermore, keeping
      dispatch delay within the resolution required by applications
      eliminates the need for timestamping by synchronized clocks at
      observation points, or for the Observation Points and Collector
      to maintain bi-directional communication in order to track clock
      offsets. The collector can simply process Packet Reports in the
      order that they are received, using its own clock as a "global"
      time base. This avoids the complexity of buffering and reordering
      samples. See [DuGeGr02] for an example.
      The delay between observation of a packet and transmission of a
      Export Packet containing a report on that packet has several
      components. It is difficult to standardize a given numerical
      delay requirement, since in practice the delay may be sensitive
      to processor load at the Observation Point. Therefore, PSAMP aims
      to control that portion of the delay within the Observation Point
      that is due to buffering in the formation and transmission of
      Export Packets.
      In order to limit delay in the formation of Export Packets, the
      Exporting Process must provide the ability to close out and
      enqueue for transmission any Export Packet during formation as
      soon as it includes one Packet Report.
      In order to limit the delay in the transmission of Export
      Packets, a configurable upper bound to the delay of an Export
      Packet prior to transmission must be provided. If the bound is
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      exceeded the Export Packet is dropped. This functionality can be
      provided by the timed reliability service of the SCTP Partial
      Reliability Extension [RFC-3758].
      The Exporting Process may enqueue the Report Stream in order to
      export multiple Packet Reports in a single export packet. Any
      consequent delay must still allow for timely availability of
      Packet Reports as just described. The timed reliability service
      of the SCTP Partial Reliability Extension [RFC-3758] allows the
      dropping of packets from the export buffer once their age in the
      buffer exceeds a configurable bound. A suitable default value for
      the bound should be used in order to avoid a low transmission
      rate due to misconfiguration.
   8.5 Export Packet Compression
      To conserve network bandwidth and resources at the Collector, the
      Export Packets may be compressed before export.  Compression is
      expected to be quite effective since the sampled packets may
      share many fields in common, e.g. if a filter focuses on packets
      with certain values in particular header fields. Using
      compression, however, could impact the timeliness of Packet
      Reports. Any consequent delay must not violate the timeliness
      requirement for availability of Packet Reports at the collector.
   8.6 Collector Destination
      When exporting to a remote Collector, the Collector is identified
      by IP address, transport protocol, and transport port number.
   8.7 Local Export
      The Report Stream may be directly exported to on-board
      measurement based applications, for example those that form
      composite statistics from more than one packet. Local export may
      be presented through an interface direct to the higher level
      applications, i.e., through an API, rather than employing the
      transport used for off-board export. Specification of such an API
      is outside the scope of the PSAMP framework.
      A possible example of Local Export could be that packets selected
      by the PSAMP measurement process serve as the input for the IPFIX
      protocol, which then forms flow records out of the stream of
      selected packets.
   9. Configuration and Management
      A key requirement for PSAMP is the easy reconfiguration of the
      parameters of the Measurement Process: those for selection,
      packet reports and export. An important example is to support
      measurement-based applications that want to adaptively drill-down
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      on traffic detail in real-time;
      To facilitate reconfiguration and retrieval of parameters, they
      are to reside in a Management Information Base (MIB). Mandatory
      configuration, capabilities and monitoring objects will cover all
      mandatory PSAMP functionality.
      Secondary objects will cover the recommended and optional PSAMP
      functionality, and must be provided when such functionality is
      offered by a PSAMP device. Such PSAMP functionality includes
      configuration of offered Selectors, multiple Measurement
      Processes, and report format including the choice of fields to be
      reported. For further details concerning the PSAMP MIB, see
      PSAMP requires a uniform mechanism with which to access and
      configure the MIB. SNMP access must be provided by the host of
      the MIB.
   10.       Feasibility and Complexity
      In order for PSAMP to be supported across the entire spectrum of
      networking equipment, it must be simple and inexpensive to
      implement.  One can envision easy-to-implement instances of the
      mechanisms described within this draft. Thus, for that subset of
      instances, it should be straightforward for virtually all system
      vendors to include them within their products. Indeed, sampling
      and filtering operations are already realized in available
      Here we give some specific arguments to demonstrate feasibility
      and comment on the complexity of hardware implementations. We
      stress here that the point of these arguments is not to favor or
      recommend any particular implementation, or to suggest a path for
      standardization, but rather to demonstrate that the set of
      possible implementations is not empty.
   10.1     Feasibility
   10.1.1  Filtering
      Filtering consists of a small number of mask (bit-wise logical),
      comparison and range (greater than) operations.  Implementation
      of at least a small number of such operations is straightforward.
      For example, filters for security access control lists (ACLs) are
      widely implemented. This could be as simple as an exact match on
      certain fields, or involve more complex comparisons and ranges.
   10.1.2  Sampling
      Sampling based on either counters (counter set, decrement, test
      for equal to zero) or range matching on the hash of a packet
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      (greater than) is possible given a small number of selectors,
      although there may be some differences in ease of implementation
      for hardware vs. software platforms.
   10.1.3  Hashing
      Hashing functions vary greatly in complexity.  Execution of a
      small number of sufficient simple hash functions is implementable
      at line rate. Concerning the input to the hash function,
      hop-invariant IP header fields (IP address, IP identification)
      and TCP/UDP header fields (port numbers, TCP sequence number)
      drawn from the first 40 bytes of the packet have been found to
      possess a considerable variability; see [DuGr01].
   10.1.4  Reporting
      The simplest packet report would duplicate the first n bytes of
      the packet. However, such an uncompressed format may tax the
      bandwidth available to the reporting process for high sampling
      rates; reporting selected fields would save on this bandwidth.
      Thus there is a trade-off between simplicity and bandwidth
   10.1.5  Exporting
      Ease of exporting export packets depends on the system
      architecture. Most systems should be able to support export by
      insertion of export packets, even through the software path.
   10.2    Potential Hardware Complexity
      We now comment on the complexity of possible hardware
      implementations. Achieving low constants for performance while
      minimizing hardware resources is, of course, a challenge,
      especially at very high clock frequencies. Most of the selectors,
      however, are very basic and their implementations very well
      understood; in fact, the average ASIC designer simply uses canned
      library instances of these operations rather than design them
      from scratch. In addition, networking equipment generally does
      not need to run at the fastest clock rates, further reducing the
      effort required to get reasonably efficient implementations.
      Simple bit-wise logical operations are easy to implement in
      hardware.  Such operations (NAND/NOR/XNOR/NOT) directly translate
      to four-transistor gates.  Each bit of a multiple-bit logical
      operation is completely independent and thus can be performed in
      parallel incurring no additional performance cost above a single
      bit operation.
      Comparisons (EQ/NEQ) take O(log(M)) stages of logic, where M is
      the number of bits involved in the comparison.  The log(M) is
      required to accumulate the result into a single bit.
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      Greater than operations, as used to determine whether a hash
      falls in a selection range, are a determination of the most
      significant not-equivalent bit in the two operands.  The operand
      with that most-significant-not-equal bit set to be one is greater
      than the other.  Thus, a greater than operation is also an
      O(log(M)) stages of logic operation. Optimized implementations of
      arithmetic operations are also O(log(M)) due to propagation of
      the carry bit.
      Setting a counter is simply loading a register with a state. Such
      an operation is simple and fast O(1).  Incrementing or
      decrementing a counter is a read, followed by an arithmetic
      operation followed by a store.  Making the register dual-ported
      does take additional space, but it is a well-understood
      technique.  Thus, the increment/decrement is also an O(log(M))
      Hashing functions come in a variety of forms.  The computation
      involved in a standard Cyclic Redundancy Code (CRC) for example
      are essentially a set of XOR operations, where the intermediate
      result is stored and XORed with the next chunk of data.  There
      are only O(1) operations and no log complexity operations.  Thus,
      a simple hash function, such as CRC or generalizations thereof,
      can be implemented in hardware very efficiently.
      At the other end of the range of complexity, the MD5 function
      uses a large number of bit-wise conditional operations and
      arithmetic operations.  The former are O(1) operations and the
      latter are O(log(M)). MD5 specifies 256 32b ADD operations per
      16B of input processed.  Consider processing 10Gb/sec at 100MHz
      (this processing rate appears to be currently available). This
      requires processing 12.5B/cycle, and hence at least 200 adders, a
      sizeable number. Because of data dependencies within the MD5
      algorithm, the adders cannot be simply run in parallel, thus
      requiring either faster clock rates and/or more advanced
      architectures. Thus, selection hashing functions as complex as
      MD5 may be precluded for ubiquitous use at full line rate. This
      motivates exploring the use of selection hash functions with
      complexity somewhere between that of MD5 and CRC. In some
      applications (see Section below) a second hash may be calculated
      on only selected packets; MD5 is feasible for this purpose if the
      rate of production of selected packets is sufficiently low.
   11. Applications
      We first describe several representative operational applications
      that require traffic measurements at various levels of temporal
      and spatial granularity. Some of the goals here appear similar to
      those of IPFIX, at least in the broad classes of applications
      supported. The major benefit of PSAMP is the support of new
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      network management applications, specifically, those enabled by
      the packet selectors that it supports.
   11.1    Baseline Measurement and Drill Down
      Packet sampling is ideally suited to determine the composition of
      the traffic across a network. The approach is to enable
      measurement on a cut-set of the network links such that each
      packet entering the network is seen at least once, for example,
      on all ingress links. Unfiltered sampling with a relatively low
      selection fraction establishes baseline measurements of the
      network traffic. Packet reports include packet attributes of
      common interest: source and destination address and port numbers,
      prefix, protocol number, type of service, etc. Traffic matrices
      are indicated by reporting source and destination AS matrices.
      Absolute traffic volumes are estimated by renormalizing the
      sampled traffic volumes through division by either the Configured
      Selection Fraction, or by the Attained Selection Fraction (as
      derived from input packet counters included in the report stream)
      Suppose an operator or a measurement-based application detects an
      interesting subset of a packet stream, as identified by a
      particular packet attribute. Real-time drill-down to that subset
      is achieved by instantiating a new Measurement Process on the
      same Observed Packet Stream from which the subset was reported.
      The Selection Process of the new Measurement Process filters
      according to the attribute of interest, and composes with
      sampling if necessary to manage the attained fraction of packets
   11.2    Trajectory Sampling
      The goal of trajectory sampling is the selection of a subset of
      packets at all enabled Observation Points at which they are
      observed in a network domain. Thus the selection decisions are
      consistent in the sense that each packet is selected either at
      all enabled Observation Points, or at none of them. Trajectory
      sampling is realized by hash-based selection if all enabled
      Observation Points apply a common hash function to a portion of
      the packet content that is invariant along the packet path.
      (Thus, fields such at TTL and CRC are excluded).
      The trajectory followed by a packet is reconstructed from packet
      reports on it that reach the collector. Reports on a given packet
      are associated either by matching a label comprising the
      invariant reported packet content, or possibly some digest of it.
      The reconstruction of trajectories, and methods for dealing with
      possible ambiguities due to label collisions (identical labels
      reported by different packets) and potential loss of reports in
      transmission are dealt with in [DuGr01], [DuGeGr02] and [DuGr04].
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   11.3    Passive Performance Measurement
      Trajectory sampling enables the tracking of the performance
      experience by customer traffic, customers identified by a list of
      source or destination prefixes, or by ingress or egress
      interfaces. Operational uses include the verification of Service
      Level Agreements (SLAs), and troubleshooting following a customer
      In this application, trajectory sampling is enabled at all
      network ingress and egress interfaces. Rates of loss in transit
      between ingress and egress are estimated from the proportion of
      trajectories for which no egress report is received. Note that
      loss of customer packets is distinguishable from loss of packet
      reports through use of report sequence numbers. Assuming
      synchronization of clocks between different entities, delay of
      customer traffic across the network may also be measured; see
      Extending hash-selection to all interfaces in the network would
      enable attribution of poor performance to individual network
   11.4    Troubleshooting
      PSAMP Packet Reports can also be used to diagnose problems whose
      occurrence is evident from aggregate statistics, per interface
      utilization and packet loss statistics.  These statistics are
      typically moving averages over relatively long time windows,
      e.g., 5 minutes, and serve as a coarse-grain indication of
      operational health of the network. The most common method of
      obtaining such measurements are through the appropriate SNMP MIBs
      (MIB-II [RFC-1213] and vendor-specific MIBs.)
      Suppose an operator detects a link that is persistently
      overloaded and experiences significant packet drop rates. There
      is a wide range of potential causes: routing parameters (e.g.,
      OSPF link weights) that are poorly adapted to the traffic matrix,
      e.g., because of a shift in that matrix; a denial of service
      attack or a flash crowd; a routing problem (link flapping). In
      most cases, aggregate link statistics are not sufficient to
      distinguish between such causes, and to decide on an appropriate
      corrective action. For example, if routing over two links is
      unstable, and the links flap between being overloaded and
      inactive, this might be averaged out in a 5 minute window,
      indicating moderate loads on both links.
      Baseline PSAMP measurement of the congested link, as described in
      Section 11.1, enables measurements that are fine grained in both
      space and time. The operator has to be able to determine how many
      bytes/packets are generated for each source/destination address,
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   Internet Draft      Packet Selection and Reporting     January 2005
      port number, and prefix, or other attributes, such as protocol
      number, MPLS forwarding equivalence class (FEC), type of service,
      etc. This allows the precise determination of the nature of the
      offending traffic. For example, in the case of a Distributed
      Denial of Service(DDoS) attack, the operator would see a
      significant fraction of traffic with an identical destination
      In certain circumstances, precise information about the spatial
      flow of traffic through the network domain is required to detect
      and diagnose problems and verify correct network behavior. In the
      case of the overloaded link, it would be very helpful to know the
      precise set of paths that packets traversing this link follow.
      This would readily reveal a routing problem such as a loop, or a
      link with a misconfigured weight. More generally, complex
      diagnosis scenarios can benefit from measurement of traffic
      intensities (and other attributes) over a set of paths that is
      constrained in some way. For example, if a multihomed customer
      complains about performance problems on one of the access links
      from a particular source address prefix, the operator should be
      able to examine in detail the traffic from that source prefix
      which also traverses the specified access link towards the
      While it is in principle possible to obtain the spatial flow of
      traffic through auxiliary network state information, e.g., by
      downloading routing and forwarding tables from routers, this
      information is often unreliable, outdated, voluminous, and
      contingent on a network model. For operational purposes, a direct
      observation of traffic flow provided by trajectory sampling is
      more reliable, as it does not depend on any such auxiliary
      information. For example, if there was a bug in a router's
      software, direct observation would allow the diagnosis the effect
      of this bug, while an indirect method would not.
   12.  Security Considerations
         Security considerations are addressed in:
         - Section 4.1: item Robust Selection
         - Section 4.3: item Secure Export
         - Section 4.4: item Secure Configuration
   13.  IANA Considerations
      This document has no actions for IANA
   14.  Normative References
           [PSAMP-TECH] T. Zseby, M. Molina, F. Raspall, N. G. Duffield,
              S. Niccolini, Sampling and Filtering Techniques for IP
              Packet Selection, RFC XXXX. [Currently Internet Draft,
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   Internet Draft      Packet Selection and Reporting     January 2005
              draft-ietf-psamp-sample-tech-05.txt, work in progress,
              October 2004.
           [PSAMP-MIB] T. Dietz, B. Claise, Definitions of Managed
              Objects for Packet Sampling, RFC XXXX. [Currently
              Internet Draft, draft-ietf-psamp-mib-03.txt, work in
              progress, July 2004.]
           [PSAMP-PROTO] B. Claise (Ed.) Packet Sampling (PSAMP)
              Protocol Specifications, RFC XXXX. [Currently Internet
              Draft draft-ietf-psamp-protocol-01.txt, work in progress,
              February 2004.]
           [PSAMP-INFO] T. Dietz, F. Dressler, G. Carle, B. Claise,
              Information Model for Packet Sampling Exports, RFC XXXX.
              [Currently Internet Draft, draft-ietf-psamp-info-02, July
           [IPFIX-PROTO]   B. Claise (Ed.) IPFIX Protocol
              Specifications , Internet Draft,
              draft-ietf-ipfix-protocol-06.txt, October 2004.
           [IPFIX-INFO] J. Meyer, J. Quittek, S. Bryant, "Information
              Model for IP Flow Information Export"
              draft-ietf-ipfix-info-06, October 2004
           [RFC-2960] R. Stewart, (ed.) "Stream Control Transmission
              Protocol", RFC 2960, October 2000.
           [RFC-3758] R. Stewart, M. Ramalho, Q. Xie, M. Tuexen, P.
              Conrad, "SCTP Partial Reliability Extension", RFC 3758,
              May 2004.
   15. Informative References
           [B88] R.T. Braden, A pseudo-machine for packet monitoring
              and statistics, in Proc ACM SIGCOMM 1988
           [ClPB93] K.C. Claffy, G.C. Polyzos, H.-W. Braun, Application
              of Sampling Methodologies to Network Traffic
              Characterization, Proceedings of ACM SIGCOMM'93, San
              Francisco, CA, USA, September 13-17, 1993
           [RFC-2460] S. Deering, R. Hinden, Internet Protocol, Version
             6 (IPv6) Specification, RFC 2460, December 1998.
           [DuGr01] N. G. Duffield and M. Grossglauser, Trajectory
              Sampling for Direct Traffic Observation, IEEE/ACM Trans.
              on Networking, 9(3), 280-292, June 2001.
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    Internet Draft      Packet Selection and Reporting     January 2005
           [DuGeGr02] N.G. Duffield, A. Gerber, M. Grossglauser,
              Trajectory Engine: A Backend for Trajectory Sampling,
              IEEE Network Operations and Management Symposium 2002,
              Florence, Italy, April 15-19, 2002.
           [DuGr04] N. G. Duffield and M. Grossglauser, Trajectory
              Sampling with Unreliable Reporting, Proc IEEE Infocom
              2004, Hong Kong, March 2004,
           [RFC-2914] S. Floyd, Congestion Control Principles, RFC
              2914, September 2000.
           [RFC-2804] IAB and IESG, Network Working Group, IETF Policy
              on Wiretapping, RFC 2804, May 2000
           [RFC-1213] K. McCloghrie, M. Rose, Management Information
              Base for Network Management of TCP/IP-based
              internets:MIB-II, RFC 1213, March 1991.
           [RFC-3176] P. Phaal, S. Panchen, N. McKee, InMon
              Corporation's sFlow: A Method for Monitoring Traffic in
              Switched and Routed Networks, RFC 3176, September 2001
           [RFC-2330] V. Paxson, G. Almes, J. Mahdavi, M. Mathis,
              Framework for IP Performance Metrics, RFC 2330, May 1998
           [RFC-791] J. Postel, "Internet Protocol", STD 5, RFC 791,
              September 1981.
           [RFC-768]  Postel, J., "User Datagram Protocol" RFC 768,
              August 1980
           [RFC-3917] J. Quittek, T. Zseby, B. Claise, S. Zander,
              Requirements for IP Flow Information Export, RFC 3917,
              October 2004.
           [RFC-1771]   Rekhter, Y. and T. Li, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 1771, March 1995.
           [RFC-3031]  Rosen, E., Viswanathan, A. and R. Callon,
              "Multiprotocol Label Switching Architecture", RFC 3031,
              January 2001.
           [SPSJTKS01] A. C. Snoeren, C. Partridge, L. A. Sanchez, C.
              E. Jones, F. Tchakountio, S. T. Kent, W. T. Strayer,
              Hash-Based IP Traceback, Proc. ACM SIGCOMM 2001, San
              Diego, CA, September 2001.
           [Zs02] T. Zseby, ``Deployment of Sampling Methods for SLA
              Validation with Non-Intrusive Measurements'', Proceedings
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              of Passive and Active Measurement Workshop (PAM 2002),
              Fort Collins, CO, USA, March 25-26, 2002
   16. Authors' Addresses
         Derek Chiou
         Avici Systems
         101 Billerica Ave
         North Billerica, MA 01862
         Phone: +1 978-964-2017
         Email: dchiou@avici.com
         Benoit Claise
         Cisco Systems
         De Kleetlaan 6a b1
         1831 Diegem
         Phone: +32 2 704 5622
         Email: bclaise@cisco.com
         Nick Duffield
         AT&T Labs - Research
         Room B139
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8726
         Email: duffield@research.att.com
         Albert Greenberg
         AT&T Labs - Research
         Room A161
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8730
         Email: albert@research.att.com
         Matthias Grossglauser
         School of Computer and Communication Sciences
         1015 Lausanne
         Email: matthias.grossglauser@epfl.ch
         Peram Marimuthu
         Cisco Systems
         170, W. Tasman Drive
         San Jose, CA 95134
         Phone: (408) 527-6314
         Email: peram@cisco.com
         Jennifer Rexford
         AT&T Labs - Research
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   Internet Draft      Packet Selection and Reporting     January 2005
         Room A139
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8728
         Email: jrex@research.att.com
         Ganesh Sadasivan
         Cisco Systems
         170 W. Tasman Drive
         San Jose, CA 95134
         Phone: (408) 527-0251
         Email: gsadasiv@cisco.com
   17. Intellectual Property Statements
      By submitting this Internet-Draft, each author represents that
      any applicable patent or other IPR claims of which he or she is
      aware have been or will be disclosed, and any of which he or she
      becomes aware will be disclosed, in accordance with Section 6 of
      RFC 3668.
      Copies of IPR disclosures made to the IETF Secretariat and any
      assurances of licenses to be made available, or the result of an
      attempt made to obtain a general license or permission for the
      use of such proprietary rights by implementers or users of this
      specification can be obtained from the IETF on-line IPR
      repository at http://www.ietf.org/ipr.
      The IETF invites any interested party to bring to its attention
      any copyrights, patents or patent applications, or other
      proprietary rights that may cover technology that may be required
      to implement this standard.  Please address the information to
      the IETF at ietf-ipr@ietf.org.
      The IETF has been notified by AT&T Corp. of intellectual property
      rights claimed in regard to some or all of the specification
      contained in this document. For more information, see
      The IETF has been notified by Cisco Corp. of intellectual
      property rights claimed in regard to some or all of the
      specification contained in this document. For more information,
   18.       Full Copyright Statement
      Copyright (C) The Internet Society (2004).  This document is
      subject to the rights, licenses and restrictions contained in BCP
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    Internet Draft      Packet Selection and Reporting     January 2005
      78 and except as set forth therein, the authors retain all their
      This document and translations of it may be copied and furnished
      to others, and derivative works that comment on or otherwise
      explain it or assist in its implementation may be prepared,
      copied, published and distributed, in whole or in part, without
      restriction of any kind, provided that the above copyright notice
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     Standards process must be followed, or as required to translate
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      The limited permissions granted above are perpetual and will not
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   19.  Disclaimers
      The IETF takes no position regarding the validity or scope of any
      Intellectual Property Rights or other rights that might be
      claimed to pertain to the implementation or use of the technology
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      This document and the information contained herein are provided
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