Internet Draft                               Nick Duffield (Editor)
   Category: Informational                        AT&T Labs û Research
   Document: <draft-ietf-psamp-framework-08.txt>        September 2004
   Expires: March 2005
               A Framework for Packet Selection and Reporting
   Status of this Memo
      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. 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
      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 the dual aims of ubiquitous deployment
      and utility of the reports for applications. Detailed
      requirements for selection, reporting and exporting  processes
      are described, along with configuration requirements of the PSAMP
      Comments on this document should be addressed to the PSAMP
      Working Group mailing list:
      To subscribe:, in body: subscribe
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   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................................9
      4.   Generic Requirements for PSAMP.............................9
      4.1  Generic Selection Process Requirements....................10
      4.2  Generic Reporting Process Requirements....................10
      4.3  Generic Exporting process Requirements....................11
      4.4  Generic Configuration Requirements........................11
      5.   Packet Selection Operations...............................12
      5.1  Two Types of Selection Operation..........................12
      5.2  PSAMP Packet Selection Operations ........................12
      5.3  Selection Rate Terminology................................14
      5.4  Input Sequence Numbers for Primitive Selection Processes..15
      5.5  Composite Selectors.......................................15
      5.6  Constraints on the Sampling Frequency.....................16
      6.   Reporting Process ........................................16
      6.1  Mandatory Contents of Packet Reports......................16
      6.2  Extended Packet Reports...................................17
      6.3  Extended Packet Reports in the Presence of IPFIX .........17
      6.4  Report Interpretation.....................................17
      6.5  Export Packet Compression ................................18
      7.   Parallel Measurement Processes............................18
      8.   Exporting Process ........................................19
      8.1  Use of IPFIX..............................................19
      8.2  Congestion-aware Unreliable Transport.....................19
      8.3  Limiting Delay for Export Packets ........................19
      8.4  Configurable Export Rate Limit............................21
      8.5  Collector Destination.....................................21
      8.6  Local Export..............................................21
      9.   Configuration and Management..............................21
      10.  Feasibility and Complexity................................22
      10.1 Feasibility...............................................22
      10.1.1 Filtering...............................................22
      10.1.2 Sampling ...............................................22
      10.1.3 Hashing.................................................23
      10.1.4 Reporting...............................................23
      10.1.5 Export..................................................23
      10.2 Potential Hardware Complexity.............................23
      11.  Applications..............................................24
      11.1 Baseline Measurement and Drill Down.......................25
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      11.2 Trajectory Sampling.......................................25
      11.3 Passive Performance Measurement...........................25
      11.4 Troubleshooting...........................................26
      12.  Security Considerations...................................27
      13.  Normative References......................................27
      14.  Informative References....................................28
      15.  Authors' Addresses........................................29
      16.  Intellectual Property Statements..........................31
      17.  Full Copyright Statement..................................31
      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-
      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
      across multivendor domains. This requires domain wide consistency
      in the types of selection schemes available, the manner in which
      the resulting measurements are presented, and consequently,
      consistency of the interpretation that can be put on them.
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      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 ôsamplingö 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-FRAMEWORK: ôA Framework for Packet Selection and
      Reportingö: 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 ômustö, ôshouldö and ômayö
      in this document are informational only.
      [PSAMP-TECH]: ôSampling and Filtering Techniques for IP Packet
      Selectionö, describes the set of packet selection techniques
      supported by PSAMP.
      [PSAMP-MIB]: ôDefinitions of Managed Objects for Packet Samplingö
      describes the PSAMP Management Information Base
      [PSAMP-PROTO]: ôPacket Sampling (PSAMP) Protocol Specificationsö
      specifies the export of packet information from a PSAMP Exporting
      Process to a PSAMP Colleting Process
      [PSAMP-INFO]: ôInformation Model for Packet Sampling Exportsö
      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
      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.
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      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.
      * 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.
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      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 ôstreamö is favored over ôflowö, which is defined
      as set of packets with common properties [IPFIX-REQUIRE].
   3.3 Selection Process
      This section defines the selection process and related objects.
      * Selection Process
        A selection process takes a 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. 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
                  (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
      * Selector:
           A selector defines the action of a selection process on a
           single packet of its input. A selected packet becomes an
           element of the output packet stream of the selection
           The selector can make use of the following information in
           determining whether a packet is selected:
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           (i) the packetÆs 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 Selection Process:
           A composite selection process is an ordered composition of
           selection processes, in which the output stream issuing from
           one component forms the input stream for the succeeding
      * Composite Selector:
           A selector is composite if it defines a composite selection
      * Primitive Selection Process:
           A selection process is primitive if it is not a composite a
           selection process.
      * Primitive Selector:
           A selector is primitive if it defines a primitive selection
   3.4 Reporting Process
      * Reporting Process:
           A reporting process creates a report stream on 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 packetÆs 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.
      * Packet Reports:
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           Packet reports comprise a configurable subset of a packetÆs
           input to the reporting process, including the packetÆs
           content, information relating to its treatment
           (for example, the output interface), and its associated
           selection state (for example, a hash of the packetÆs
      * 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.
      * Report Stream:
           The report stream is the output of a reporting process,
           comprising two distinguished types of information: packet
           reports, and report interpretation.
   3.5 Measurement Process
      * A Measurement Process is the composition of a selection process
        that takes the observed packet stream as its input, 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
      * 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)<-+      |
   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 ômeasurement processö 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].
   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.
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   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.
      * Non-Contingency: the selection decision for each packet must
        not depend on future packets.
      * Encrypted Packets: selection operations based on interpretation
        of packet fields must be configurable to ignore (i.e. not
        select) encrypted packets, when they are detected.
      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
        observation point in order to interpret and analyze the
      * Indication of Information Loss: the reports 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.
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      * 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 reports.
        See Section Error! Reference source not found. for further
      * Congestion Avoidance: export of a report stream across a
        network must be congestion avoiding in compliance with [RFC-
      * 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 [IPFIX-REQUIRE].
   4.4 Generic Configuration Requirements
      * 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
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        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 Operations
   5.1 Two Types of Selection Operation
      PSAMP categorizes selection operations into two types:
      * Filtering: a filter is a selection operation that selects a
        packet deterministically based on the packet content, its
        treatment, and functions of these occurring in the selection
        state. Two examples are:
           (i) Mask/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 selection operation 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
        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. Examples include
             pseudorandom selection according to a probability that
             depends on the contents of a packet field; note that this
             is not a filter.
   5.2 PSAMP Packet Selection Operations
      A spectrum of packet selection operations is described in detail
      in [PSAMP-TECH]. Here we only briefly summarize the meanings for
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      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: form each count-based
        successive block of N packets, n are selected at random.
      * Mask/match Filtering: this entails taking the masking portions
        of the packet (i.e. taking the logical ôandö with a binary
        mask) and selecting the packet if the result falls in a range
        specified in the selection parameters of the filter.  This
        specification does not preclude the future definition of a high
        level syntax for defining filtering in a concise way (e.g. TCP
        port taking a particular value) providing that syntax can be
        compiled into the bitwise expression.
        Mask/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 mask/match filtering, and, in its
        usual capacity other than in performing PSAMP functions,
        identifies or processes information from one or more of the
        above 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
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        packet, or make it available for filtering, although it may do
        Since packet encryption alters the meaning of encrypted fields,
        Mask/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. With
        a suitable hash function, hash based selection approximates
        uniform random sampling. Applications of hash-based sampling
        are described in Section 11.
      * Router State Filtering: the selection process may support
        filtering based on the following conditions, which may be
        combined with the logical "and", "or" or "not" operators:
           (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, e.g. routing state,
       being available at line rate for selection of packets. However,
       if selection not based on routing state has reduced down from
       line rate, subselection based on routing state may be feasible.
       This section detailed specific requirements for the selection
       process, motivated by the generic requirement of Section 3.3.
   5.3 Selection Rate Terminology
      The proportion of packets that are selected by a selection
      operation is figured in two ways:
      * Attained Selection Frequency: the actual frequency with which
        packets are selected by a selection process. When packets are
        selected from a set of packets in a stream, the attained
        sampling frequency is calculated as ratio of the number of
        packets selected to the number of packets in the set.
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      * Target Selection Frequency: the average frequency with which
        packets are expected to be selected, based on selector
        parameter settings.
        For sampling operations, due to the inherent statistical
        variability of sampling decisions, the target and attained
        selection frequencies will not in general be equal, although
        they may be close in some circumstances, e.g., when the
        population size is large.
   5.4 Input Sequence Numbers for Primitive Selection Processes
      Each instance of a primitive selection process 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
      Use of input sequence numbers enables applications to determine
      the attained selection frequency, 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
      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 frequency, taking
      into account both packet sampling at the observation point and
      selection arising from loss in transmission, is R = (n-1)/(sn-
      s1). (Note R would be 1 if all packets were selected and there
      were no transmission loss).
      The attained selection frequency 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 frequency.
      With composite selectors, and input sequence number must be
      reported for each selector in the composition.
   5.5 Composite Selectors
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      The ability to compose selectors in a selection process should be
      provided. The following combinations appear to be most useful for
      * 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 depend on the composition of
      the packet stream.
   5.6 Constraints on the Sampling Frequency
      Sampling at full line rate, i.e. with probability 1, is not
      excluded in principle, although resource constraints may not
      support it in practice.
   6. Reporting Process
      This section detailed specific requirements for the reporting
      process, motivated by the generic requirement of Section 3.4
   6.1 Mandatory Contents of Packet Reports
      The reporting process must include the following in each packet
           (i) the input sequence number(s) of any sampling operation
             that acted on the packet in the instance of a measurement
             process of which the reporting process is a component.
      The reporting process must support inclusion of the following in
      each packet report, as a configurable option:
           (ii) 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) and (ii) 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.
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   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.
           (iii) fields relating to the following protocols used in the
           packet: IPv4, IPV6, transport protocols, MPLS.
           (iv) 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
           (v) selection state associated with the packet, including:
           - 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 (ii) 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
      Information for use in 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.
           (iv) identifiers for observation point, measurement process,
           and exporting process.
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      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 due to a sampling operation suffer loss
      (either during export, or in transit) it may be desirable to
      reconfigure downwards the sampling rate on the selection process
      that selected them.
      The requirements for robustness and transparency are motivations
      for including report interpretation in the report stream.
      Inclusion 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 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.
   6.5 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.
   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 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,
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      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 detailed 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.
   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 number 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.
      On the contrary, 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 must 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) [UDP] 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].
   8.3 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
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      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 in formation as soon
      as it includes one packet report. This could be achieved, for
      example, by the following means:
          -      the number of packet reports per export packet is not
                  to exceed a maximum value, which can be configured to
                  take the value 1.
          -      the ability to exclude report interpretation from any
                  export packet that contains a 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
      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 queue 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 from
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      the dropping of packets from the export buffer once their age in
      the buffer exceeds a configurable bound.
   8.4 Configurable Export Rate Limit
      The exporting process must have an export rate limit,
      configurable per exporting process. This is useful for two
           (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.
   8.5 Collector Destination
      When exporting to a remote collector, the collector is identified
      by IP address, transport protocol, and transport port number.
   8.6 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. Examples are
           (i) support of measurement-based applications that want to
           drill-down on traffic detail in real-time;
           (ii) collector-based rate reconfiguration.
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      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, composite selectors, multiple
      measurement processes, and report format including the choice of
      fields to be reported. For further details concerning the PSAMP
      MIB, see [PSAMP-MIB].
      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
      (greater than) is possible given a small number of selectors,
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      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  Export
      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 these
      operations, 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
      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(lg(M)) stages of logic, where M is
      the number of bits involved in the comparison.  The lg(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(lg(M)) stages of logic operation. Optimized implementations of
      arithmetic operations are also O(lg(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(lg(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(lg(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. However, identification
      hashing with MD5 on only selected packets is feasible at a
      sufficiently low sampling frequency.
   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
      network management applications, specifically, those enabled by
      the packet selectors that it supports.
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   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
      frequency 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 target
      sampling frequency, or by the attained sampling frequency (as
      derived by interface packet counters included in the report
      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 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 frequency of packet
   11.2    Trajectory Sampling
      Trajectory sampling is the selection of a subset of packets at
      either all of a set of observation points or none of them.
      Trajectory sampling is realized by hash-based sampling if all
      observation points in the set 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 PSAMP
      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].
   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
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      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 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,
      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
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      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.       Normative References
           [PSAMP-TECH] T. Zseby, M. Molina, F. Raspall, N. G. Duffield,
              Sampling and Filtering Techniques for IP Packet
              Selection, RFC XXXX. [Currently Internet Draft, draft-
              ietf-psamp-sample-tech-04.txt, work in progress, February
           [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.]
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           [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
   14.       Informative References
           [B88] R.T. Braden, A pseudo-machine for packet monitoring
              and statistics, in Proc ACM SIGCOMM 1988
           [IPFIX-INFO] Calato, P, Meyer, J, Quittek, J, "Information
              Model for IP Flow Information Export" draft-ietf-ipfix-
              info-04, November 2003
           [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
           [IPFIX-PROTO]   B. Claise,  B. Stewart, G. Sadasivan, M.
              Fullmer,P. Calato , R. Penno, IPFIX Protocol
              Specifications , Internet Draft, draft-ietf-ipfix-
              protocol-05.txt, August 2004.
           [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.
           [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.
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   Internet Draft      Packet Selection and Reporting     September 2004
           [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.
           [UDP]  Postel, J., "User Datagram Protocol" RFC 768, August
           [IPFIX-REQUIRE] J. Quittek, T. Zseby, B. Claise, S. Zander,
              Requirements for IP Flow Information Export, Internet
              Draft draft-ietf-ipfix-reqs-16.txt, work in progress,
              June 2004.
           [RFC1771]   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.
           [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.
           [Zs02] T. Zseby, ``Deployment of Sampling Methods for SLA
              Validation with Non-Intrusive Measurements'', Proceedings
              of Passive and Active Measurement Workshop (PAM 2002),
              Fort Collins, CO, USA, March 25-26, 2002
   15.       Authors' Addresses
   Duffield (Ed.)            Expires March 2005                [Page 29]

   Internet Draft      Packet Selection and Reporting     September 2004
         Derek Chiou
         Avici Systems
         101 Billerica Ave
         North Billerica, MA 01862
         Phone: +1 978-964-2017
         Benoit Claise
         Cisco Systems
         De Kleetlaan 6a b1
         1831 Diegem
         Phone: +32 2 704 5622
         Nick Duffield
         AT&T Labs - Research
         Room B-139
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8726
         Albert Greenberg
         AT&T Labs - Research
         Room A-161
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8730
         Matthias Grossglauser
         School of Computer and Communication Sciences
         1015 Lausanne
         Peram Marimuthu
         Cisco Systems
         170, W. Tasman Drive
         San Jose, CA 95134
         Phone: (408) 527-6314
         Jennifer Rexford
         AT&T Labs - Research
         Room A-169
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8728
   Duffield (Ed.)            Expires March 2005                [Page 30]

   Internet Draft      Packet Selection and Reporting     September 2004
         Ganesh Sadasivan
         Cisco Systems
         170 W. Tasman Drive
         San Jose, CA 95134
         Phone: (408) 527-0251
   16.       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.
      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,
   17.       Full Copyright Statement
      Copyright (C) The Internet Society (2004).  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
      This document and translations of it may be copied and furnished
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      explain it or assist in its implementation may be prepared,
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      The limited permissions granted above are perpetual and will not
      be revoked by the Internet Society or its successors or assigns.
   Duffield (Ed.)            Expires March 2005                [Page 31]

   Internet Draft      Packet Selection and Reporting     September 2004
      This document and the information contained herein is provided on
   Duffield (Ed.)            Expires March 2005                [Page 32]