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  Internet Draft
  Document: <draft-psamp-framework-04.txt>
  Expires: April 2004
                                                   Nick Duffield (Editor)
                                                     AT&T Labs – Research
 
                                                             October 2003
 
 
                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 RFC2026.
 
     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups. Note that
     other groups may also distribute working documents as Internet-
     Drafts. Internet-Drafts are draft documents valid for a maximum of
     six months and may be updated, replaced, or obsoleted by other
     documents at any time. It is inappropriate to use Internet-Drafts
     as reference material or to cite them other than as "work in
     progress."
 
     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt
 
     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.
 
  Abstract
 
     A wide range of traffic engineering and troubleshooting tasks rely
     on timely and detailed traffic measurements that can be
     consistently interpreted. This document describes a framework for
     packet sampling that is (a) general enough to serve as the basis
     for a wide range of operational tasks, and (b) needs only a small
     set of packet selectors that facilitate ubiquitous deployment in
     router interfaces or dedicated measurement devices, even at very
     high speeds.  The framework also covers reporting and exporting
     functions used by the sampling host, and configuration of the
     sampling PSAMP functions.
 
     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.   Motivation...................................................3
     2.   Elements, Terminology and Architecture.......................4
     3.   Requirements.................................................7
     3.1  Selection Process Requirements...............................7
     3.2  Reporting Process Requirements...............................8
     3.3  Export Process Requirements..................................8
     3.4  Configuration Requirements...................................9
     4.   Packet Selection.............................................9
     4.1  Packet Selection Terminology.................................9
     4.2  PSAMP Packet Selection Operations...........................11
     4.3  Input Sequence Numbers for Primitive Selection Processes....13
     4.4  Composite Selectors.........................................13
     4.5  Constraints on the Sampling Frequency.......................13
     4.6  Criteria for Choice of Selection Operations.................13
     5.   Reporting Process...........................................15
     5.1  Mandatory Contents of Packet Reports (MUST).................15
     5.2  Extended Packet Reports.....................................15
     5.3  PSAMP Extended Packet Reports in the Presence of IPFIX......16
     5.4  Report Interpretation.......................................16
     5.5  Report Timeliness...........................................17
     6.   Parallel Measurement Processes..............................17
     7.   Export Process..............................................18
     7.1  Collector Destination.......................................18
     7.2  Local Export................................................18
     7.3  Reliable vs. Unreliable Transport...........................18
     7.4  Limiting Delay for Export Packets...........................18
     7.5  Configurable Export Rate Limit..............................19
     7.6  Congestion-aware Unreliable Transport.......................19
     7.7  Collector-based Rate Reconfiguration........................20
     7.7.1 Changing the Export Rate and Other Rates...................20
     7.7.2 Notions of Fairness........................................21
     7.7.3 Behavior Under Overload and Failure........................21
     8.   Configuration and Management................................22
     9.   Feasibility and Complexity..................................22
     9.1  Feasibility.................................................22
     9.1.1 Filtering..................................................22
     9.1.2 Sampling...................................................23
     9.1.3 Hashing....................................................23
     9.1.4 Reporting..................................................23
     9.1.5 Export.....................................................23
     9.2  Potential Hardware Complexity...............................23
     10.  Applications................................................24
     10.1 Baseline Measurement and Drill Down.........................25
     10.2 Passive Performance Measurement.............................25
     10.3 Troubleshooting.............................................26
     11.  Security Considerations.....................................27
     12.  References..................................................27
     13.  Authors' Addresses..........................................28
 
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     14.  Intellectual Property Statement.............................29
     15.  Full Copyright Statement....................................30
 
 
 
     Copyright (C) The Internet Society (2003).  All Rights Reserved.
     This document is an Internet-Draft and is in full conformanc with
     all provisions of Section 10 of RFC2026.
 
     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups.  Note that
     other groups may also distribute working documents as Internet-
     Drafts.
 
     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other
     documents at any time.  It is inappropriate to use Internet-Drafts
     as reference material or to cite them other than as "work in
     progress."
 
     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt
 
     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.
 
     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
     "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
     this document are to be interpreted as described in RFC 2119.
 
 
  1. Motivation
 
     This document describes a framework in which to define a standard
     set of capabilities for network elements to select subsets of
     packets by statistical and other methods. The framework
     accommodates ongoing work to (i) specify a set of selectors by
     which packets are sampled; (ii) specify the information that is to
     be made available for reporting on sampled packets; (iii) describe
     a protocol by which information on sampled packets is reported to
     applications; (iv) describe a protocol by which packet selection
     and reporting are configured.
 
     The motivation to standardize these capabilities 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 capabilities are positioned as suppliers of packet samples to
     higher level consumers, including both remote collectors and
 
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     applications, and on board measurement-based applications.  Indeed,
     development of the standards within the framework described here
     should be open to influence by the requirements of standards in
     related IETF Working Groups, for example, IP Performance Metrics
     (IPPM) [RFC2330] and Internet Traffic Engineering (TEWG) [LCTV02].
     Conversely, we expect that aspects of this framework not
     specifically concerned with the central issue of packet selection
     and report formation may be able to leverage work in other Working
     Groups. Potential examples are the format and export of reports on
     selected packets, which may leverage the information model and
     export protocols of IP Flow Information Export (IPFIX) [QZCZ03],
     and work in congestion aware unreliable transport in the Datagram
     Congestion Control Protocol (DCCP) [FHK02], and related work in The
     Stream Control Transmission Protocol (SCTP) [SCTP] and [PR-SCTP].
 
  2. Elements, Terminology and Architecture
 
     This section defines the basic elements of the PSAMP framework. At
     the highest level, the architecture comprises observation points
     (at which packets are observed), measurement processes (which
     select packets and construct reports on them) and export processes
     (which export reports to collectors). The full definitions of these
     terms now follow.
 
     * Observation Point: a location in the network where a packet
        stream is observed. Examples include:
 
          - a line to which a probe is attached;
 
          - a shared medium, such as an Ethernet-based LAN;
 
          - a single port of a router, or set of interfaces (physical or
             logical) of a router;
 
          - an embedded measurement subsystem within an interface.
 
     * Observed Packet Stream: the set of all packets observed at the
        observation point.
 
     * Packet Stream: either the observed packet stream, or a subset of
        it.
 
        Note that packets selected from a stream, e.g. by sampling, do
        not necessarily possess a property by which they can be
        distinguished from packets that have not been selected. For this
        reason the term “stream” is favored over “flow”, which is defined
        as set of packets with common properties [QuZC02].
 
     * Selection Process: takes a packet stream as its input and selects
        a subset of that stream as its output.
 
     * Packet Content: the union of the packet header (which includes
        link layer, network layer and other encapsulation headers) and
 
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        the packet payload.
 
     * 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:
 
          - sequence numbers of packets at the input of selectors;
 
          - a timestamp of observation of the packet at the observation
             points;
 
          - iterators for pseudorandom number generators;
 
          - hash values calculated during selection;
 
          - 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.
 
     * 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:
 
          - the packet’s content;
 
          - information derived from the packet's treatment at the
             observation point;
 
          - any selection state that may be maintained by the selection
             process.
 
     * Composite Selection Process: an ordered composition of selection
        processes, in which the output stream issuing from one component
        forms the input stream for the succeeding component.
 
     * Primitive Selection Process: a selection process that is not a
        composite selection process.
 
     * Composite Selector: the selector of a composite selection
        process.
 
     * Primitive Selector: the selector of a primitive selection
        process.
 
     * Reporting Process: creates a report stream on packets selected by
        a selection process, in preparation for export. The input to the
 
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        reporting process comprises that information available to the
        selection process per selected packet, specifically:
 
          - the selected packet’s content;
 
          - information derived from the selected packet's treatment at
             the observation point;
 
          - any selection state maintained by the inputting selection
             process, reflecting any modifications to the selection state
             made during selection of the packet.
 
     * Report Stream: the output of a reporting process is a report
        stream, comprising two distinguished types of information: packet
        reports, and report interpretation.
 
     * Packet Reports: a configurable subset of the per packet input to
        the reporting process.
 
     * Report Interpretation: 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.
 
     * Measurement Process: the composition of a selection process that
        takes the observed packet stream as its input, followed by a
        reporting process.
 
     * Export Process: sends the output of one or more reporting
        processes to one or more collectors.
 
     * 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.
 
     * Export packets: one or packet reports, and perhaps report
        interpretation, are bundled by the export process into a export
        packet for export to a collector.
 
     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)     |
 
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        |MP(s)--->EP----------+---------------->|                  |
        +---------------------+                 +------------------+
 
        +---------------------+
        |Observation Point(s) |
        |MP(s)--->EP---+      |
        |              |      |
        |Collector(3)<-+      |
        +---------------------+
 
     The PSAMP measurement process can be viewed as analogous to the
     IPFIX metering process. The PSAMP measurement process takes an
     observed packet stream as its input, and produces packet reports as
     its output. The IPFIX metering process produces flow records as its
     output. The distinct name “measurement process” has been retained
     in order to avoid potential confusion in settings where IPFIX and
     PSAMP coexist, and in order to avoid the implicit requirement that
     the PSAMP version satisfy the requirements of an IPFIX metering
     process (at least while these are under development). The relation
     between PSAMP and IPFIX is further discussed in [QC03].
 
  3. Requirements
 
  3.1 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
        capabilities.
 
     * Extensibility: to allow for additional packet selectors to
        support future applications.
 
     * Flexibility: to support selection of packets using different
        network protocols or encapsulation layers (e.g. IPv4, IPv6, MPLS,
        etc).
 
     * Robust Selection: packet selection MUST be robust with respect to
        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: multiple independent measurement
        processes at the same host, able to operate simultaneously.
 
     * Non-contingency: in order to satisfy the ubiquity requirement,
        the selection decision for each packet MUST NOT depend on future
        packets.  Rather, the selection decision MUST be capable of being
 
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        made on the basis of the selection process input up to and
        including the packet in question. This excludes selection
        functions that require caching of packet for selection contingent
        on subsequent packets. See also the timeliness requirement
        following.
 
     Selectors are outlined in Section 4, and described in more detail
     in the companion document [ZMRD03].
 
  3.2 Reporting Process Requirements
 
     * Transparency: allow transparent interpretation of the report
        stream, without any need to obtain additional information
        concerning the observed packet stream.
 
     * Robustness to Information Loss: allow robust interpretation of
        the report stream with respect to packet reports missing due to
        data loss, e.g. in transport, or within the selection, reporting
        or exporting processes.  Inclusion in reporting of 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 [RFC2804].  Full packet capture of arbitrary packet
        streams is explicitly out of scope.
 
     A specific reporting processes meeting these requirements, and th e
     requirement for ubiquity, is described in Section 5.
 
  3.3 Export Process Requirements
 
     * Timeliness: packet reports SHOULD be made available to the
        collector quickly enough to support near real time applications.
        Specifically, any report on a packet SHOULD be dispatched within
        1 second of the time of receipt of the packet by the measurement
        process. See Section 5.5 for further discussion of this point
 
     * Congestion Avoidance: export of a report stream across a network
        MUST be congestion avoiding in compliance with RFC 2914 [RFC
        2914].
 
     * Secure Export:
 
          - confidentiality: the option to encrypt exported data MUST be
             provided. [MUST vs. SHOULD needs further WG discussion].
 
 
 
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          - integrity: alterations in transit to exported data MUST be
             detectable at the collector
 
          - 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 [QZCZ03].
 
  3.4 Configuration Requirements
 
     * Ease of Configuration: of sampling and export parameters, e.g.
        for automated remote reconfiguration in response to collected
        reports.
 
     * 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 (for example)
        evade subversion, or overload the measurement infrastructure.
 
     Configuration is discussed in Section 8. Feasibility and complexity
     of PSAMP operations is discussed in Section 9.
 
     Reuse of existing protocols will be encouraged provided the
     protocol capabilities are compatible with the requirements laid out
     in this document.
 
  4. Packet Selection
 
  4.1 Packet Selection Terminology.
 
     * 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. Examples include mask/match filtering, and hash-based
        selection.
 
     * 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.
 
     * Content-independent Sampling: a sampling operation that does not
        use packet content (or quantities derived from it) as the basis
        for selection is called a content-independent sampling operation.
        Examples include systematic sampling, and uniform pseudorandom
        sampling driven by a pseudorandom number whose generation is
        independent of packet content. Note that in content-independent
        sampling it is not necessary to access the packet content in
        order to make the selection decision.
 
 
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     * Content-dependent Sampling: a sampling operation where selection
        is dependent on packet content is called a content-dependent
        sampling operation. Examples include pseudorandom selection
        according to a probability that depends on the contents of a
        packet field; note that this is not a filter.
 
     * Hash Domain: a subset of the packet content and the packet
        treatment, viewed as an N-bit string for some positive integer N.
 
     * Hash Range: a set of M-bit strings for some positive integer M.
 
     * Hash Function: a deterministic map from the hash domain into the
        hash range.
 
     * Hash Selection Range: a subset of the hash range. The packet is
        selected if the action of the hash function on the hash domain
        for the packet yields a result in the hash selection range.
 
     * Hash-based Selection: filtering specified by a hash domain, a
        hash function, and hash range and a hash selection range.
 
     * Approximative Selection: selection operations in any of the above
        categories may be approximated by operations in the same or
        another category for the purposes of implementation. For example,
        uniform pseudorandom sampling may be approximated by hash-based
        selection, using a suitable hash function and hash domain. In
        this case, the closeness of the approximation depends on the
        choice of hash function and hash domain.
 
     * Population size: the number of packets in a subset of a packet
        stream.
 
     * Sample size: the number of packets selected from a subset of a
        packet stream by a selection operation.
 
     * Attained Selection Frequency: the actual frequency with which
        packets are selected by a selection process. The attained
        sampling frequency is calculated as ratio of the size of a sample
        size to the size of the population from which it was selected.
 
     * Target Selection Frequency: the long-term frequency with which
        packets are expected to be selected, based on selector parameter
        settings. Depending on the selector, the target selection
        frequency may be count-based or time-based.
 
        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. In hash-based selection, the target selection
        frequency is the quotient of size of the hash selection range by
        the size of the hash range.
 
 
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  4.2 PSAMP Packet Selection Operations
 
     A spectrum of packet selection operations is described in detail in
     [ZMRD03]. Here we only briefly summarize the meanings for
     completeness.
 
     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:
 
          - the IP header (excluding options in IPv4, stacked headers in
             IPv6)
 
          - transport header
 
          - encapsulation headers (including MPLS label stack, ATOM, if
             present)
 
        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
 
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        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.
 
     * 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
        payload.
 
        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: all routers use the same hash selector;
             the hash domain includes only portions of the packet that do
             not change from hop to hop. (For example, in an IP packet,
             TTL is excluded.) Hence packets are consistently selected in
             the sense that they are selected at all routers on their
             path or none. Reports packets also include a second hash
             (the label hash) that distinguishes different packets.
             Reports of a given packet reaching the collector from
             different routers can be used to reconstruct the path taken
             by the packet. Trajectory sampling is proposed in [DuGr01];
             further description is found in [ZMRD03]; some applications
             are described in Section 10.
 
          - Consistent Flow Sampling: the hash domain is a flow key. For
             a given flow, either all or none of its packets are sampled.
             This is accomplished without the need to maintain flow
             state.
 
          Some applications need to calculate packet hashes for purpose
          other than selection (e.g. the label hash in trajectory
          sampling). This can be achieved by placing a calculated hash
          in the selection state, and setting the selection range to be
          the whole of the hash range.
 
     * 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:
 
          - Ingress interface at which packet arrives equals a specified
             value
          - Egress interface to which packet is routed to equals a
             specified value
          - Packet violated Access Control List (ACL) on the router
          - Failed Reverse Path Forwarding (RPF)
          - Failed Resource Reservation (RSVP)
 
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          - No route found for the packet
          - Origin Autonomous System (AS) equals a specified value or
             lies within a given  range
          - 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.
 
  4.3 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
     [RFC3176] for further details.
 
  4.4 Composite Selectors
 
     The ability to compose selectors in a selection process SHOULD be
     provided. The following combinations appear to be most useful for
     applications:
 
     * 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.
 
  4.5 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.
 
  4.6 Criteria for Choice of Selection Operations
 
 
 
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     In current practice, sampling has been performed using particular
     algorithms, including:
 
     * pseudorandom independent sampling with probability 1/N;
 
     * systematic sampling of every Nth packet.
 
     The question arises as to whether both of these should be
     standardized as distinct selection operations, or whether they can
     be regarded as different implementations of a single selection
     operation.
 
     To determine the answer to this question, we need to consider
 
     (a) measured or assumed statistical properties of the packet
     stream, e.g., one or more of the following:
 
          - contents of different packets are statistically independent
 
          - correlations between contents of different packets decay at
             a specified rate
 
          - contents of certain fields within the same packet are
             significantly variable and exhibit small cross correlation
 
     (b) the desired reference sampling model, e.g., one of:
 
          - sample packets with long term probability 1/N
 
          - sample packets independent with probability 1/N
 
     (c) the set of possible alternatives and implementations, e.g., one
     of:
          - pseudorandom independent sampling with probability 1/N
 
          - systematic sampling with period N
 
          - hash-based sampling with target probability 1/N
 
     (d) the tolerance for error in the applications that use the
     collected packet reports.
 
     We can say that a given alternative from (c) reproduces a reference
     model (b) for the applications if the results obtained using them
     are sufficiently accurate in (d) for traffic satisfying an assumed
     statistical properties in (a). Clearly, application to evaluate
     methods in (c) requires developing agreement on the relevant
     properties in (a), (b) and (d).
 
     Example: systematic sampling with period N will not count the
     occurrence of closely space packets (less than N counts apart) from
     the same flow. Thus for applications that are concerned with the
     joint statistics of multiple packets within flows, systematic
 
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     sampling may not reproduce the results obtained with random
     sampling sufficiently accurately.
 
  5. Reporting Process
 
  5.1 Mandatory Contents of Packet Reports (MUST)
 
     The reporting process MUST include the following in each packet
     report:
 
          (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 be able to include the following in each
     packet report, as a configurable option:
 
          (ii) 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.
 
  5.2 Extended Packet Reports (MAY)
 
     The reporting process MAY provide for the inclusion in packet
     reports of the following information, inclusion any or all being
     configurable as a option.
 
          (iii) fields relating to the following protocols used in the
          packet, specifically: IPv4, IPV6, transport protocols, MPLS,
          ATOM. Note that optional reporting of field contents may be
          used to reduce reporting bandwidth, in which case the option
          to not report information in (ii) above would be exercised.
 
          (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
 
 
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          - hashes, where calculated.
 
  5.3 Extended Packet Reports in the Presence of IPFIX
 
     If IPFIX 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 [QZCZ03], with
     modifications appropriate to reporting on single packets rather
     than flows.
 
  5.4  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,
     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.
 
     To conserve network bandwidth and resources at the collector, the
     export packets may be compressed before export.  Compression is
 
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     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.
 
  5.5 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 to under 1 second has other
     benefits besides limiting buffer requirements. For many
     applications a 1 second time resolution 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.
 
     A dispatch delay of 1 second in these situations eliminates the
     need for timestamping by synchronized clocks at observation points
     devices, 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---
     avoiding the complexity of buffering and reordering samples. See
     [DuGeGr02] for an example.
 
  6. 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
     process.
 
     Each of the parallel measurement processes SHOULD be independent.
     However, resource constraints may prevent complete reporting on a
     packet selected by multiple selection processes. In this case,
     reporting for the packet MUST be complete for at least one
     measurement process; other measurement processes need only record
     that they selected the packet, e.g., by incrementing a counter. The
     priority amongst measurement processes under resource contention
     SHOULD be configurable.
 
 
 
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     It is not proposed to standardize the number of parallel
     measurement processes.
 
  7. Export Process
 
  7.1 Collector Destination
 
     When exporting to a remote collector, the collector is identified
     by IP address, transport protocol, and transport port number.
 
  7.2 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. Note that IPFIX being still developed; this is
     given only as a possible example.
 
  7.3 Reliable vs. Unreliable Transport
 
     The export of the report stream does not require reliable export.
     On the contrary, retransmission of lost export packets consumes
     additional network resources and requires maintenance of state by
     the export process. As such, the export process would have to be
     able to receive and process acknowledgments, and to store
     unacknowledged data. Furthermore, the host of the export process
     may not possess its own network address at which to receive
     acknowledgments. For example an autonomous embedded measurement
     subsystem in an interface may simply inject export packets into the
     interface packet stream, designating the interface address as the
     source address of the export packets). These requirements would be
     a significant impediment to having ubiquitous support PSAMP.
 
     Instead, it is proposed that the export process support unreliable
     export.  Sequence numbers on the export packets would indicate when
     loss has occurred, and the analysis of the surviving report stream
     can be used to determine the degree of loss.  In some sense, packet
     loss becomes another form of sampling (albeit a less desirable, and
     less controlled, form of sampling).
 
  7.4 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
 
 
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     delay MUST still allow for timely availability of packet reports at
     the collector as described in Section 5.4.
 
  7.5 Configurable Export Rate Limit
 
     The export process MUST be able to limit its export rate; otherwise
     it could overload the network and/or the collector. Note this
     problem would be exacerbated using reliable transport mode, since
     any lost packets would be retransmitted, thereby imposing an
     additional load on the network.
 
     At times, the reporting process may generate new packet reports or
     report interpretation faster than the allowed export rate.  In this
     situation, the export process MUST discard the excess packet
     reports rather than transmitting them to the collector. Sequence
     numbers reported for selector input enable correction for lost
     packet reports. An additional sequence number for dispatched export
     packets enables the collector to determine the degree of loss in
     transmission.
 
     There are two options for a configurable rate limit. First, if the
     transport protocol has a configurable rate limit, that can be used.
     The second option is to limit the rate at which export packets are
     supplied to the transport protocol. A candidate for implementation
     of rate limiting is the leaky bucket, with tokens corresponding
     e.g. to bytes or packets.
 
     The export rate limit MUST be configurable per export process. Note
     that since congestion loss can occur at any link on the export
     path, it is not sufficient to limit rate simply as a function of
     the bandwidth of the interface out of which export takes place.
 
  7.6 Congestion-aware Unreliable Transport
 
     Export packets compete for resources with other Internet transfers.
     Congestion-aware export is important to ensure that the export
     packets do not overwhelm the capacity of the network or unduly
     degrade the performance of other applications, while making good
     use of available bandwidth resources.
 
     Choice of transport for PSAMP has to be made under the following
     constraints:
 
          (i) IESG has mandated that all transport in new protocols must
          be congestion aware
 
          (ii) reliable transport is too onerous for general entities
          that support PSAMP (see Section 7.3)
 
          (iii) there currently exists no IETF standardized unreliable
          congestion-aware transport
 
 
 
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     In the absence of an existing IETF standardized unreliable
     congestion-aware protocol, PSAMP will provisionally nominate the
     reliable congestion aware transport protocol TCP as the interim
     transport protocol for export. From the preceding arguments, TCP is
     unsatisfactory for final standardization in PSAMP. In the meantime,
     the PSAMP Working Group will evaluate (at least) the following
     alternatives for congestion aware unreliable transport, as they
     become available, with a view to selecting one of them and
     discarding TCP:
 
          (i) unreliable transport protocols adopted in the future by
          the IPFIX Working Group,
 
          (ii) the Datagram Congestion Control Protocol (DCCP);
          currently under development; see [FHK02]
 
          (iii) The Stream Control Transmission Protocol (SCTP) under
          development [SCTP]. SCTP is by default reliable, but has the
          capability to operate in unreliable and partially reliable
          modes [PR-SCTP]. See [D03] for description of its potential
          use in flow export.
 
          (iv) collector-based rate reconfiguration, described below.
 
 
  7.7 Collector-based Rate Reconfiguration
 
     Since collector-based rate reconfiguration is a new proposal, this
     draft will discuss it in some detail.
 
     The collector can detect congestion loss along the path from the
     exporting device to the collector by observing packet loss,
     manifest as gaps in the sequence numbers, or the absence of packets
     for a period of time. The server can run an appropriate congestion-
     control algorithm to compute a new export rate limit, then
     reconfigure the export process with the new rate.  This is an
     attractive alternative to requiring the export process to receive
     acknowledgment packets.  Implementing the congestion control
     algorithm in the collector has the added advantages of flexibility
     in adapting the sending rate and the ability to incorporate new
     congestion-control algorithms as they become available.
 
  7.7.1   Changing the Export Rate and Other Rates
 
     Forcing the export process to discard excess packet reports is an
     effective control under short term congestion. Alternatively, the
     selection process could be reconfigured to select fewer packets, or
     the reporting process could be reconfigured to send smaller reports
     on each selected packet. This may be a more appropriate reaction to
     long-term congestion. In some cases, a collector may receive export
     packets due to more than one export process, and could decide to
     reduce the export or other rates associated with one export process
     rather than another, in order to prioritize the export packets.
 
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     This type of flexibility is valuable for network operators that
     collect export packets from multiple locations to drive multiple
     applications.
 
  7.7.2   Notions of Fairness
 
     In some cases, it may be reasonable to allow the collector to have
     flexibility in deciding how aggressively to respond to congestion.
     For example, the host of the export process and the collector may
     have a very small round-trip time (RTT) relative to other traffic.
     Conventional TCP-friendly congestion control would allocate a very
     large share of the bandwidth to the PSAMP export traffic.  Instead,
     the collector could apply an algorithm that reacts more
     aggressively to congestion to give a larger share of the bandwidth
     to other traffic (with larger RTTs).
 
     In other cases, the export packets may require a larger share of
     the bandwidth than other flows.  For example, consider a link that
     carries tens of thousands of flows, including some non TCP-friendly
     DoS attack traffic.  Restricting the PSAMP traffic to a fair share
     allocation may be too restrictive, and might limit the collection
     of the data necessary to diagnose the DoS attack which overloads
     links over which export packets are carried. In order to maintain
     report collection during periods of congestion, PSAMP report
     streams may claim more than a fair share of link bandwidth,
     provided the number of report streams in competition with fair
     sharing traffic is limited. The collector could also employ
     policies that allocate bandwidth in certain proportions amongst
     different measurement processes.
 
     Note that the ability to control differential bandwidth usage in
     the manner described in this section may be partially or wholly
     lost if congestion control is performed by other means purely at
     the transport level.
 
  7.7.3   Behavior Under Overload and Failure
 
     The congestion control algorithm has to be robust to severe
     overload or complete loss of connectivity between the host of the
     export process and the collector, and also to the failure of host
     of the export process or the collector. For example, in a scenario
     where the collector is unable to reconfigure the export rate
     because of loss of reverse (collector to exporting host)
     connectivity, it is desirable for the exporting host to reduce the
     export rate autonomously.  Similarly, if no export packets reach
     the collector because of loss of forward connectivity, the
     collector should not react to this by increasing the export rate.
     This problem may be solved through periodic heartbeat packets in
     both directions (i.e., export packets in the forward direction,
     configuration refresh messages in the reverse direction). This
     allows each side to detect a loss in connectivity or outright
     failure and to react appropriately.
 
 
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  8. 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
     minimum required (MUST) PSAMP functionality.
 
     Secondary objects will cover the recommended PSAMP functionality
     (SHOULD), and MUST be provided only 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
     [DRC03].
 
     PSAMP requires a uniform mechanism with which to access and
     configure the MIB. SNMP access MUST be provided by the host of the
     MIB.
 
 
  9. 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.
 
  9.1  Feasibility
 
  9.1.1   Filtering
 
     Filtering consists of a small number of mask (bit-wise logical),
     comparison and range (greater than) operations.  Implementation of
 
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     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.
 
  9.1.2   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.
 
  9.1.3   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].
 
  9.1.4   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.
 
  9.1.5   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.
 
  9.2 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
 
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     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
     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
     frequency.
 
  10. 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
 
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     of IPFIX, at least in the broad classes of applications supported.
     However, there are two major differences:
 
          - PSAMP aims for ubiquitous deployment of packet measurement,
             including devices that are not expected to support IPFIX.
             This offers broader reach for existing applications.
 
          - PSAMP can support new applications through the type of
             packet selectors that it supports
 
  10.1    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 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.
 
  10.2    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
     complaint.
 
     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
 
 
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     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.
 
  10.3    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 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 10.1, 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
 
 
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     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
     not.
 
  11. Security Considerations
 
        Security considerations are addressed in:
 
        - Section 3.1: item Robust Selection
        - Section 3.3: item Secure Export
        - Section 3.4: item Secure Configuration
 
  12. 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
 
        [DRC03] T. Dietz, D. Romascanu, B. Claise, Definitions of
              Managed Objects for Packet Sampling, Internet Draft,
              draft-ietf-psamp-mib-00.txt, work in progress, June 2003.
 
        [D03] M. Djernaes, Cisco Systems NetFlow Services Export Version
              9 Transport, Internet Draft,
              draft-djernaes-netflow-9-transport-00.txt, work in
              progress, February 2003
 
        [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.
 
 
        [RFC2914] S. Floyd, Congestion Control Principles, RFC 2914,
              September 2000.
 
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  Internet Draft      Packet Selection and Reporting       October 2003
 
        [FHK02] S. Floyd, M. Handley. E. Kohler, Problem Statement for
              DCCP, Internet Draft draft-ietf-dccp-problem-00.txt, work
              in progress, October 2002.
 
        [RFC2804] IAB and IESG, Network Working Group, IETF Policy on
              Wiretapping, RFC 2804, May 2000
 
        [LCTV02] W.S. Lai, B.Christian, R.W. Tibbs, S. Van den Berghe, A
              Framework for Internet Traffic Engineering Measurement
              Internet Draft draft-ietf-tewg-measure-05.txt, work in
              progress, February 2003.
 
        [RFC3176] P. Phaal, S. Panchen, N. McKee, InMon Corporation's
              sFlow: A Method for Monitoring Traffic in Switched and
              Routed Networks, RFC 3176, September 2001
 
        [RFC2330] V. Paxson, G. Almes, J. Mahdavi, M. Mathis,  Framework
              for IP Performance Metrics, RFC 2330, May 1998
 
        [QC03] J. Quittek, B. Claise, On the Relationship between PSAMP
              and IPFIX, Internet Draft draft-quittek-psamp-ipfix-01.txt,
              work in progress, February 2003.
 
        [QZCZ03] J. Quittek, T. Zseby, B. Claise, S. Zander,
              Requirements for IP Flow Information Export, Internet Draft
              draft-ietf-ipfix-reqs-10.txt, work in progress, June 2003.
 
        [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.
 
        [RFC2960] Stewart, R. (ed.) "Stream Control Transmission
              Protocol", RFC 2960, October 2000
 
        [PR-SCTP] Stewart, R, "SCTP Partial Reliability Extension",
              Internet Draft, draft-stewart-tsvwg-prsctp-01.txt, work in
              progress, June 2003.
 
  13. Authors' Addresses
 
        Derek Chiou
        Avici Systems
        101 Billerica Ave
        North Billerica, MA 01862
        Phone: +1 978-964-2017
        Email: dchiou@avici.com
 
        Benoit Claise
        Cisco Systems
        De Kleetlaan 6a b1
        1831 Diegem
 
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  Internet Draft      Packet Selection and Reporting       October 2003
 
 
        Belgium
        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
        EPFL
        1015 Lausanne
        Switzerland
        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
        170 W. Tasman Drive
        San Jose, CA 95134
        Phone: (408) 527-0251
        Email: gsadasiv@cisco.com
 
 
  14. Intellectual Property Statement
 
 
 
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 Internet Draft      Packet Selection and Reporting       October 2003
 
     AT&T Corporation may own intellectual property applicable to this
     contribution. The IETF has been notified of AT&T's licensing intent
     for the specification contained in this document. See
     http://www.ietf.org/ietf/IPR/ATT-GENERAL.txt for AT&T's IPR
     statement.
 
  15. Full Copyright Statement
 
     Copyright (C) The Internet Society (2003).  All Rights Reserved.
 
     This document and translations of it may be copied and furnished to
     others, and derivative works that comment on or otherwise explain
     it or assist in its implementation may be prepared, copied,
     published and distributed, in whole or in part, without restriction
     of any kind, provided that the above copyright notice and this
     paragraph are included on all such copies and derivative works.
     However, this document itself may not be modified in any way, such
     as by removing the copyright notice or references to the Internet
     Society or other Internet organizations, except as needed for the
     purpose of developing Internet standards in which case the
     procedures for copyrights defined in the Internet Standards process
     must be followed, or as required to translate it into languages
     other than English.
 
     The limited permissions granted above are perpetual and will not be
     revoked by the Internet Society or its successors or assigns.
 
 
     This document and the information contained herein is provided on
     an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
     ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
     IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
     THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
     WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 
 
 
 
 
 
 
 
 
 
 
 
  Duffield (Ed.)            Expires April 2004                 [Page 30]
 

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