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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 5474

   Internet Draft
   Category: Informational
   Document: <draft-ietf-psamp-framework-06.txt>
   Expires: January 2005                             Nick Duffield(Editor)
                                                      AT&T Labs í Research
                                                                 July 2004
                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 reports, form ra stream
      of reports on the selected packets, and to export that stream 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 export are described, along with configuration of the PSAMP
      Comments on this document should be addressed to the PSAMP Working
      Group mailing list: psamp@ops.ietf.org
      To subscribe: psamp-request@ops.ietf.org, in body: subscribe
      Archive: https://ops.ietf.org/lists/psamp/
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   Table of Contents
      1.   PSAMP Documents Overview.....................................3
      2.   Introduction.................................................4
      3.   Elements, Terminology and Architecture.......................4
      3.1  High-level description of the PSAMP Architecture.............5
      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.................................................9
      3.8  Collector....................................................9
      3.9  Possible configurations......................................9
      3.10 PSAMP and IPFIX Interaction..................................9
      4.   Generic Requirements for PSAMP..............................10
      4.1  Generic Selection Process Requirements......................10
      4.2  Generic Reporting Process Requirements......................11
      4.3  Generic Export Process Requirements.........................11
      4.4  Generic Configuration Requirements..........................12
      5.   Packet Selection Operations.................................12
      5.1  Two Types of Selection Operation............................12
      5.2  PSAMP Packet Selection Operations...........................13
      5.3  Input Sequence Numbers for Primitive Selection Processes....15
      5.4  Composite Selectors.........................................15
      5.5  Constraints on the Sampling Frequency.......................16
      6.   Reporting Process...........................................16
      6.1  Mandatory Contents of Packet Reports........................16
      6.2  Extended Packet Reports.....................................16
      6.3  Extended Packet Reports in the Presence of IPFIX............17
      6.4  Report Interpretation.......................................17
      6.5  Report Timeliness...........................................18
      7.   Parallel Measurement Processes..............................19
      8.   Export Process..............................................20
      8.1  Use of IPFIX................................................20
      8.2  Congestion-aware Unreliable Transport.......................20
      8.3  Limiting Delay for Export Packets...........................20
      8.4  Configurable Export Rate Limit..............................20
      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....................................................22
      10.1.4 Reporting..................................................23
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      10.1.5 Export.....................................................23
      10.2 Potential Hardware Complexity...............................23
      11.  Applications................................................24
      11.1 Baseline Measurement and Drill Down.........................24
      11.2 Passive Performance Measurement.............................25
      11.3 Troubleshooting.............................................25
      12.  Security Considerations.....................................26
      13.  Normative References........................................27
      14.  Informative References......................................27
      15.  Authors' Addresses..........................................28
      16.  Intellectual Property Statement.............................30
      17.  Full Copyright Statement....................................30
      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
      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 NOT",
      this document are to be interpreted as described in RFC 2119.
   1. PSAMP Documents Overview
      The PSAMP protocol specifies how network elements are to sample or
      otherwise select a subset of packets passing through them, and how
      reports on the selected packets are to be exported. The following
      documents will describe the PSAMP protocol.
      PSAMP-FRAMEWORK: ŸA Framework for Packet Selection and Reporting÷.
      This document. This framework document is for informational
      purposes; the normative references for PSAMP are the four documents
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      listed below [PSAMP-TECH], [PSAMP-MIB], [PSAMP-PROTO], [PSAMP-
      INFO]. Definitions of terminology and the use of the terms Ÿmust÷,
      Ÿshould÷ and Ÿmay÷ in this document are informational only.
      [PSAMP-TECH]: ŸSampling and Filtering Techniques for IP Packet
      Selection÷, describes the set of packet selection techniques
      supported by PSAMP.
      [PSAMP-MIB]: ŸDefinitions of Managed Objects for Packet Sampling÷
      describes the PSAMP Management Information Base
      [PSAMP-PROTO]: ŸPacket Sampling (PSAMP) Protocol Specifications÷
      specifies the export of packet information from a PSAMP Exporting
      Process to a PSAMP Colleting Process
      [PSAMP-INFO]: ŸInformation Model for Packet Sampling Exports÷
      defines an information and data model for PSAMP.
   2. 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 collector.
      The motivation to codify 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.
      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 Ÿsampling÷ 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).
   3. Elements, Terminology and Architecture
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   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 arrival timestamps.
      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 process,
      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.
                 +---------+    +---------+    +---------+
       Packet    |Selection|    |Reporting|    |Exporting|
       Stream--->|Process  |--->|Process  |--->|Process  |--->Collector
                 +---------+    +---------+    +---------+
                     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 interface.
        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.
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        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
      * Packet Content
           The packet content denotes he union of the packet header
           (which includes link layer, network layer and other
           encapsulation headers) and the packet payload.
      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
      Ÿstream÷ is favored over Ÿflow÷, which is defined as set of packets
      with common properties [IPFIX-REQUIRE].
   3.3 Selection Process
      This section defines a 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;
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           Selection processes may change portions of the selection state
           as a result of processing a packet. Selection state for a
           packet is to reflect the state after processing the packet.
      * Selector:
           A selector defines the action of a selection process on a
           single packet of its input. A selected packet becomes an
           element of the output packet stream of the selection process.
           The selector can make use of the following information in
           determining whether a packet is selected:
           (i) the packetËs 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,
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             (i) the selected packetËs 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:
           Packet reports comprise a configurable subset of a packetËs
           input to the reporting process, including the packetËs
           content, information relating to its treatment, and its
           associated selection state.
      * 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 the output of one or more measurement
        processes to one or more collectors.
      * Export Packets:
        one or more packet reports, and perhaps report interpretation,
        are bundled by the export process into a export packet for export
        to a collector.
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   3.7 PSAMP Device
      A PSAMP Device is a device hosting at least a PSAMP 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
      A collector receives a report stream exported by one or more export
      processes. In some cases, the host of the measurement and/or export
      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 = Export Process
         +---------------------+                 +------------------+
         |Observation Point(s) |                 | Collector(1)     |
         |MP(s)--->EP----------+---------------->|                  |
         |MP(s)--->EP----------+-------+-------->|                  |
         +---------------------+       |         +------------------+
         +---------------------+       |         +------------------+
         |Observation Point(s) |       +-------->| Collector(2)     |
         |MP(s)--->EP----------+---------------->|                  |
         +---------------------+                 +------------------+
         |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 Ÿmeasurement 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
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      relationship between PSAMP and IPFIX is described fully in [PSAMP-
   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.
      * 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].
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   4.2 Generic Reporting Process Requirements
      * Self-defining: the report stream must be complete in the sense
        that no additional information need be retrived from the
        observation point in order to interpret and analyze the reports.
      * 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
      * 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 Export Process Requirements
      * Timeliness: configuration must allow for limiting of buffering
        delays for the formation and transmission for export reports. See
        Section 6.5for further details.
      * Congestion Avoidance: export of a report stream across a network
        must be congestion avoiding in compliance with [RFC-2914].
      * Secure Export:
        (i) confidentiality: the option to encrypt exported data must be
        (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].
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   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 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.
             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 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.
             Content-dependent Sampling, in which the packet content is
             used in reaching selection decisions Examples include
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             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
      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 content.
      * 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 bitwise AND 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
        doesn't 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
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           (iii) encapsulation headers (e.g. the MPLS label stack) if
        When the host of a selection process 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 host routes based on
        destination IP address, that field should be made available for
        filtering. Conversely, a host 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,
        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.  The hash domain is
        specified by a bitmaps on the IP packet header and the IP
        When the hash function is sufficiently good, hash-based selection
        can be used to approximate uniform random sampling over the hash
        domain. The target sampling frequency is then the ratio of the
        size of the selection range to the hash range. Applications of
        hash-based selection include Trajectory Sampling [DuGr01] and
        Consistent Flow Sampling. See[PSAMP-TECH] for further details.
      * Router State Filtering: the selection process may support
        filtering based on the following conditions, which may be
        combined with the 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 router
           (iv) Failed Reverse Path Forwarding (RPF)
           (v) Failed Resource Reservation (RSVP)
           (vi) No route found for the packet
           (vii) Origin Autonomous System (AS) equals a specified value
           or lies within a given  range
           (viii) Destination 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.
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      This section detailed specific requirements for the selection
      process, motivated by the generic requirement of Section 3.3.
   5.3 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 state.
      Use of input sequence numbers enables applications to determine the
      attained frequency at which packets are selected, 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 packet 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 will be
      reported for each selector in the composition.
   5.4 Composite Selectors
      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
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      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.
   5.5 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, 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.
   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.
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           (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 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 exercised.
   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-REQUIRE], 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 export process.
      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,
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      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
      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
      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.
      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.
   6.5 Report Timeliness
      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.
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      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
      In order to limit delay in the formation of export packets, the
      export 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
   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 export process; otherwise
      the parallel measurement processes may share the same export
      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.
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   8. Export 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. The remainder of this section describes
   8.2 Congestion-aware Unreliable Transport
      The export of the report stream does not require reliable export.
      Section 5.3 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
      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 The Stream Control
      Transmission Protocol (SCTP) [SCTP] and the SCTP Partial
      Reliability Extension [RFC-3758].
   8.3 Limiting Delay for Export Packets
      The export 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 at
      the collector as described in Section 6.5. The timed reliability
      service of the SCTP Partial Reliability Extension [RFC-3758] allows
      from 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 export process must have an export rate limit, configurable per
      export process. This is useful for two reasons:
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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 export processes feed a common
           collector. Use of an export rate limit allows control of the
           global input rate to the collector.
           (ii) IPFIX provides for export using the User Datagram
           Protocol (UDP) as transport in some circumstance, although its
           use it deprecated. An export rate limit allows the capping of
           the export rate to match both path link speeds and the
           capacity of the collector.
      [Check: does IPFIX provide a configurable export rate limit?]
   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.
      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.
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      Secondary objects will cover the recommended and optional PSAMP
      functionality, and must be provided when such functionality is
      offered by a host. 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-
      PSAMP requires a uniform mechanism with which to access and
      configure the MIB. SNMP access must be provided by the host of the
      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 equipment.
      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, although there
      may be some differences in ease of implementation for hardware vs.
      software platforms.
   10.1.3  Hashing
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      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 limitations.
   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 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(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.
      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
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      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)) operation.
      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
      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 for PSAMP is the support of new 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 frequency
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      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 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
      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 selection.
   11.2    Passive Performance Measurement
      Hash-based 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. The label hash is used to match up
      ingress and egress samples. Rates of loss in transit between
      ingress and egress are estimated from the proportion of
      trajectories for which no egress report is received. Note 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.
      Extending hash-selection to all interfaces in the network would
      enable attribution of poor performance to individual network links.
   11.3    Troubleshooting
      PSAMP 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.)
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      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 DDoS attack, the
      operator would see a significant fraction of traffic with an
      identical destination address.
      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 customer.
      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 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
      Security Considerations
         Security considerations are addressed in:
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   Internet Draft      Packet Selection and Reporting          July 2004
         - Section 4.1: item Robust Selection
         - Section 4.3: item Secure Export
         - Section 4.4: item Secure Configuration
      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 2004.
           [PSAMP-MIB] T. Dietz, D. Romascanu, B. Claise, Definitions of
              Managed Objects for Packet Sampling, ,
              RFC XXXX. [Currently Internet Draft, draft-ietf-psamp-mib-
              02.txt, work in progress, February 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
           [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-01,
              February 2004
      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
           [IPFIX-PROTO]   B. Claise,  Mark Fullmer ,Paul Calato ,
              Reinaldo Penno, IPFIX Protocol Specifications , Internet
              Draft, draft-ietf-ipfix-protocol-3.txt, February 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
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   Internet Draft      Packet Selection and Reporting          July 2004
              Network Operations and Management Symposium 2002, Florence,
              Italy, April 15-19, 2002.
           [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.
           [IPFIX-REQUIRE] J. Quittek, T. Zseby, B. Claise, S. Zander,
              Requirements for IP Flow Information Export, Internet Draft
              draft-ietf-ipfix-reqs-12.txt, work in progress, November
           [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
      Authors' Addresses
         Derek Chiou
         Avici Systems
         101 Billerica Ave
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   Internet Draft      Packet Selection and Reporting          July 2004
         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 B-139
         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 A-161
         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
         Room A-169
         180 Park Ave
         Florham Park NJ 07932, USA
         Phone: +1 973-360-8728
         Email: jrex@research.att.com
         Ganesh Sadasivan
         Cisco Systems
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   Internet Draft      Packet Selection and Reporting          July 2004
         170 W. Tasman Drive
         San Jose, CA 95134
         Phone: (408) 527-0251
         Email: gsadasiv@cisco.com
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