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rfc:rfc7497

Internet Engineering Task Force (IETF) A. Morton Request for Comments: 7497 AT&T Labs Category: Informational April 2015 ISSN: 2070-1721

 Rate Measurement Test Protocol Problem Statement and Requirements

Abstract

 This memo presents a problem statement for access rate measurement
 for test protocols to measure IP Performance Metrics (IPPM).  Key
 rate measurement test protocol aspects include the ability to control
 packet characteristics on the tested path, such as asymmetric rate
 and asymmetric packet size.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7497.

Copyright Notice

 Copyright (c) 2015 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Morton Informational [Page 1] RFC 7497 Rate Problem Statement April 2015

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
 2.  Purpose and Scope . . . . . . . . . . . . . . . . . . . . . .   3
 3.  Active Rate Measurement . . . . . . . . . . . . . . . . . . .   6
 4.  Measurement Method Categories . . . . . . . . . . . . . . . .   7
 5.  Test Protocol Control and Generation Requirements . . . . . .   9
 6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
 7.  Operational Considerations  . . . . . . . . . . . . . . . . .  11
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
   8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1. Introduction

 There are many possible rate measurement scenarios.  This memo
 describes one rate measurement problem and presents a rate
 measurement problem statement for test protocols to measure IP
 Performance Metrics (IPPM).
 When selecting a form of access to the Internet, subscribers are
 interested in the performance characteristics of the various
 alternatives.  Standardized measurements can be a basis for
 comparison between these alternatives.  There is an underlying need
 to coordinate measurements that support such comparisons and to test
 control protocols to fulfill this need.  The figure below depicts
 some typical measurement points of access networks.
 User     /====== Fiber =======  Access Node \
 Device -|------ Copper -------  Access Node -|-- Infrastructure -- GW
 or Host  \------ Radio -------  Access Node /
                             GW = Gateway
 The access rate scenario or use case has received widespread
 attention of Internet-access subscribers and seemingly all Internet-
 industry players, including regulators.  This problem is being
 approached with many different measurement methods.  The eventual
 protocol solutions to this problem (and the systems that utilize the
 protocol) may not directly involve users, such as when tests reach
 from the infrastructure to a service-specific device, such as a
 residential gateway.  However, no aspect of the problem precludes
 users from developing a test protocol controlled via command line

Morton Informational [Page 2] RFC 7497 Rate Problem Statement April 2015

 interfaces on both ends.  Thus, a very wide range of test protocols,
 active measurement methods, and system solutions are the possible
 outcomes of this problem statement.

1.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

2. Purpose and Scope

 The scope and purpose of this memo is to define the measurement
 problem statement for test protocols conducting access rate
 measurement on production networks.  Relevant test protocols include
 [RFC4656] and [RFC5357], but the problem is stated in a general way
 so that it can be addressed by any existing test protocol, such as
 [RFC6812].
 This memo discusses possible measurement methods but does not specify
 exact methods that would normally be part of the solution.
 We are interested in access measurement scenarios with the following
 characteristics:
 o  The access portion of the network is the focus of this problem
    statement.  The user typically subscribes to a service with
    bidirectional access partly described by rates in bits per second.
    The rates may be expressed as raw capacity or restricted capacity,
    as described in [RFC6703].  These are the quantities that must be
    measured according to one or more standard metrics and for which
    measurement methods must also be agreed on as a part of the
    solution.
 o  Referring to the reference path illustrated below and defined in
    [RFC7398], possible measurement points include a subscriber's
    host, the access service demarcation point, intra IP access (where
    a globally routable address is present), or the gateway between
    the measured access network and other networks.
 Subsc. -- Private -- Private -- Access -- Intra IP -- GRA -- Transit
 device     Net #1     Net #2    Demarc.    Access     GW     GRA GW
             GRA = Globally Routable Address, GW = Gateway
 o  Rates at some links near the edge of the provider's network can
    often be several orders of magnitude less than link rates in the
    aggregation and core portions of the network.

Morton Informational [Page 3] RFC 7497 Rate Problem Statement April 2015

 o  Asymmetrical access rates on ingress and egress are prevalent.
 o  In many scenarios of interest, services of extremely large-scale
    access require low-complexity devices participating at the user
    end of the path, and those devices place limits on clock and
    control timing accuracy.
 This problem statement assumes that the most likely bottleneck device
 or link is adjacent to the remote (user-end) measurement device or is
 within one or two router/switch hops of the remote measurement
 device.
 Other use cases for rate measurement involve situations where the
 packet switching and transport facilities are leased by one operator
 from another, and the link capacity available cannot be directly
 determined (e.g., from device-interface utilization).  These
 scenarios could include mobile backhaul, Ethernet service access
 networks, and/or extensions of layer 2 or layer 3 networks.  The
 results of rate measurements in such cases could be employed to
 select alternate routing, investigate whether capacity meets some
 previous agreement, and/or adapt the rate of traffic sources if a
 capacity bottleneck is found via the rate measurement.  In the case
 of aggregated leased networks, available capacity may also be
 asymmetric.  In these cases, the tester is assumed to have a sender
 and receiver location under their control.  We refer to this scenario
 below as the aggregated leased-network case.
 This memo describes protocol support for active measurement methods
 consistent with the IPPM working group's traditional charter.  Active
 measurements require synthetic traffic streams dedicated to testing
 and do not make measurements on user traffic.  See Section 2 of
 [RFC2679], where the concept of a stream is first introduced in IPPM
 literature as the basis for collecting a sample (defined in
 Section 11 of [RFC2330]).
 As noted in [RFC2330], the focus of access traffic management may
 influence the rate measurement results for some forms of access, as
 it may differ between user and test traffic if the test traffic has
 different characteristics, primarily in terms of the packets
 themselves (see Section 13 of [RFC2330] for the considerations on
 packet type, or Type-P).
 There are several aspects of Type-P where user traffic may be
 examined and selected for special treatment that may affect
 transmission rates.  Various aspects of Type-P are known to influence

Morton Informational [Page 4] RFC 7497 Rate Problem Statement April 2015

 Equal-Cost Multipath (ECMP) routing with possible rate measurement
 variability across parallel paths.  Without being exhaustive, the
 possibilities include:
 o  Packet length
 o  IP addresses
 o  Transport protocol (e.g., where TCP packets may be routed
    differently from UDP)
 o  Transport-protocol port numbers
 This issue requires further discussion when specific solutions/
 methods of measurement are proposed; for this problem statement, it
 is sufficient to identify the problem and indicate that the solution
 may require an extremely close emulation of user traffic, in terms of
 one or more factors above.
 Although the user may have multiple instances of network access
 available to them, the primary problem scope is to measure one form
 of access at a time.  It is plausible that a solution for the single
 access problem will be applicable to simultaneous measurement of
 multiple access instances, but treatment of this scenario is beyond
 the current scope this document.
 A key consideration is whether or not active measurements will be
 conducted with user traffic present.  In-Service testing takes place
 with user traffic present.  Out-of-Service testing occurs during pre-
 service assessment or during maintenance that interrupts service
 temporarily.  Out-of-Service testing includes activities described as
 "service commissioning", "service activation", and "planned
 maintenance".  Opportunistic In-Service testing (when there is no
 user traffic present throughout the test interval, such as outside
 normal business hours) is essentially equivalent to Out-of-Service
 testing.  Both In-Service and Out-of-Service testing are within the
 scope of this problem.
 It is a non-goal to solve the measurement protocol specification
 problem in this memo.
 It is a non-goal to standardize methods of measurement in this memo.
 However, the problem statement mandates support for one category of
 rate measurement methods in the test protocol and adequate control
 features for the methods in the control protocol (assuming the
 control and test protocols are separate).

Morton Informational [Page 5] RFC 7497 Rate Problem Statement April 2015

3. Active Rate Measurement

 This section lists features of active measurement methods needed to
 measure access rates in production networks.
 Coordination between source and destination devices through control
 messages and other basic capabilities described in the methods of
 IPPM RFCs [RFC2679] [RFC2680], and assumed for test protocols such as
 [RFC5357] and [RFC4656], are taken as given.
 Most forms of active testing intrude on user performance to some
 degree, especially In-Service testing.  One key tenet of IPPM methods
 is to minimize test traffic effects on user traffic in the production
 network.  Section 5 of [RFC2680] lists the problems with high
 measurement traffic rates ("too much" traffic); the most relevant for
 rate measurement is the tendency for measurement traffic to skew the
 results, followed by the possibility of introducing congestion on the
 access link.  Section 4 of [RFC3148] provides additional
 considerations.  The user of protocols for In-Service testing MUST
 respect these traffic constraints.  Obviously, categories of rate
 measurement methods that use less active test traffic than others
 with similar accuracy are preferred for In-Service testing, and the
 specifications of this memo encourage traffic reduction through
 asymmetric control capabilities.
 Out-of-Service tests where the test path shares no links with In-
 Service user traffic, have none of the congestion or skew concerns.
 Both types should address practical matters common to all test
 efforts, such as conducting measurements within a reasonable time
 from the tester's point of view and ensuring that timestamp accuracy
 is consistent with the precision needed for measurement [RFC2330].
 Out-of-Service tests where some part of the test path is shared with
 In-Service traffic MUST respect the In-Service constraints described
 above.
 The intended metrics to be measured have strong influence over the
 categories of measurement methods required.  For example, using the
 terminology of [RFC5136], it may be possible to measure a path
 capacity metric while In-Service if the level of background (user)
 traffic can be assessed and included in the reported result.
 The measurement architecture MAY be either of one-way (e.g.,
 [RFC4656]) or two-way (e.g., [RFC5357]), but the scale and complexity
 aspects of end-user or aggregated access measurement clearly favor
 two-way (with a low-complexity user-end device and round-trip results
 collection, as found in [RFC5357]).  However, the asymmetric rates of
 many access services mean that the measurement system MUST be able to
 evaluate performance in each direction of transmission.  In the two-

Morton Informational [Page 6] RFC 7497 Rate Problem Statement April 2015

 way architecture, both end devices MUST include the ability to launch
 test streams and collect the results of measurements in both (one-
 way) directions of transmission (this requirement is consistent with
 previous protocol specifications, and it is not a unique problem for
 rate measurements).
 The following paragraphs describe features for the roles of test
 packet SENDER, RECEIVER, and results REPORTER.
 SENDER:
 Generate streams of test packets with various characteristics as
 desired (see Section 4).  The SENDER MAY be located at the user end
 of the access path or elsewhere in the production network, such as at
 one end of an aggregated leased-network segment.
 RECEIVER:
 Collect streams of test packets with various characteristics (as
 described above), and make the measurements necessary to support rate
 measurement at the receiving end of an access or aggregated leased-
 network segment.
 REPORTER:
 Use information from test packets and local processes to measure
 delivered packet rates and prepare results in the required format
 (the REPORTER role may be combined with another role, most likely the
 SENDER).

4. Measurement Method Categories

 A protocol that addresses the rate measurement problem MUST serve the
 test stream generation and measurement functions (SENDER and
 RECEIVER).  The follow-up phase of analyzing the measurement results
 to produce a report is outside the scope of this problem and memo
 (REPORTER).
 For the purposes of this problem statement, we categorize the many
 possibilities for rate measurement stream generation as follows:
 1.  Packet pairs, with fixed intra-pair packet spacing and fixed or
     random time intervals between pairs in a test stream.
 2.  Multiple streams of packet pairs, with a range of intra-pair
     spacing and inter-pair intervals.

Morton Informational [Page 7] RFC 7497 Rate Problem Statement April 2015

 3.  One or more packet ensembles in a test stream, using a fixed
     ensemble size in packets and one or more fixed intra-ensemble
     packet spacings (including zero spacing, meaning that back-to-
     back burst ensembles and constant rate ensembles fall in this
     category).
 4.  One or more packet chirps (a set of packets with specified
     characteristics), where inter-packet spacing typically decreases
     between adjacent packets in the same chirp and each pair of
     packets represents a rate for testing purposes.
 The test protocol SHALL support test packet ensemble generation
 (category 3), as this appears to minimize the demands on measurement
 accuracy.  Other stream generation categories are OPTIONAL.
 For all supported categories, the following is a list of additional
 variables that the protocol(s) MUST be able to specify, control, and
 generate:
 a.  variable payload lengths among packet streams;
 b.  variable length (in packets) among packet streams or ensembles;
 c.  variable IP header markings among packet streams;
 d.  choice of UDP transport and variable port numbers, or choice of
     TCP transport and variable port numbers for two-way architectures
     only, or both (see below for additional requirements on TCP
     transport generation); and
 e.  variable number of packet pairs, ensembles, or streams used in a
     test session.
 The ability to revise these variables during an established test
 session is OPTIONAL, as multiple test sessions could serve the same
 purpose.  Another OPTIONAL feature is the ability to generate streams
 with VLAN tags and other markings.
 For measurement systems employing TCP as the transport protocol, the
 ability to generate specific stream characteristics requires a sender
 with the ability to establish and prime the connection such that the
 desired stream characteristics are allowed.  See [IPPM-METRICS] for
 more background.

Morton Informational [Page 8] RFC 7497 Rate Problem Statement April 2015

 Beyond a simple connection handshake and the options establishment,
 an "open-loop" TCP sender requires the SENDER ability to:
 o  generate TCP packets with well-formed headers (all fields valid),
    including Acknowledgement aspects;
 o  produce packet streams at controlled rates and variable inter-
    packet spacings, including packet ensembles (back-to-back at
    server rate); and
 o  continue the configured sending stream characteristics despite all
    control indications except receive-window exhaust.
 The corresponding TCP RECEIVER performs normally, having some ability
 to configure the receive window sufficiently large so as to allow the
 SENDER to transmit at will (up to a configured target).
 It may also be useful (for diagnostic purposes) to provide a control
 for the bulk transfer capacity measurement with fully-specified (and
 congestion-controlled) TCP senders and receivers, as envisioned in
 [RFC3148], but this would be a brute-force assessment, which does not
 follow the conservative tenets of IPPM measurement [RFC2330].
 Measurements for each UDP test packet transferred between SENDER and
 RECEIVER MUST be compliant with the singleton measurement methods
 described in IPPM RFCs [RFC2679][RFC2680].  The timestamp information
 or loss/arrival status for each packet MUST be available for
 communication to the REPORTER function.

5. Test Protocol Control and Generation Requirements

 In summary, the test protocol must support the measurement features
 described in the sections above.  This requires:
 1.  Communicating all test variables to the SENDER and RECEIVER;
 2.  Results collection in a one-way architecture;
 3.  Remote device control for both one-way and two-way architectures;
     and
 4.  Asymmetric packet rates in a two-way measurement architecture, or
     coordinated one-way test capabilities with the same effect
     (asymmetric rates may be achieved through directional control of
     packet rate or packet size).

Morton Informational [Page 9] RFC 7497 Rate Problem Statement April 2015

 The ability to control and generate asymmetric rates in a two-way
 architecture is REQUIRED.  Two-way architectures are RECOMMENDED to
 include control and generation capability for both asymmetric and
 symmetric packet sizes because packet size often matters in the scope
 of this problem and test systems SHOULD be equipped to detect
 directional size dependency through comparative measurements.
 Asymmetric packet size control is indicated when the result of a
 measurement may depend on the size of the packets used in each
 direction, i.e., when any of the following conditions hold:
 o  there is a link in the path with asymmetrical capacity in opposite
    directions (in combination with one or more of the conditions
    below, but their presence or specific details may be unknown to
    the tester);
 o  there is a link in the path that aggregates (or divides) packets
    into link-level frames and may have a capacity that depends on
    packet size, rate, or timing;
 o  there is a link in the path where transmission in one direction
    influences performance in the opposite direction;
 o  there is a device in the path where transmission capacity depends
    on packet header processing capacity (in other words, the capacity
    is sensitive to packet size);
 o  the target application stream is nominally MTU size packets in one
    direction versus ACK stream in the other (noting that there are a
    vanishing number of symmetrical rate application streams for which
    rate measurement is wanted or interesting but such streams might
    have some relevance at this time);
 o  the distribution of packet losses is critical to rate assessment;
 and possibly other circumstances revealed by measurements comparing
 streams with symmetrical size and asymmetrical size.
 Implementations may support control and generation for only symmetric
 packet sizes when none of the above conditions hold.
 The test protocol SHOULD enable measurement of the capacity metric
 [RFC5136] either Out-of-Service, In-Service, or both; other metrics
 [RFC5136] are OPTIONAL.

Morton Informational [Page 10] RFC 7497 Rate Problem Statement April 2015

6. Security Considerations

 The security considerations that apply to any active measurement of
 live networks are relevant here as well.  See [RFC4656] and
 [RFC5357].
 Privacy considerations for measurement systems, particularly when
 Internet users participate in the tests in some way, are described in
 [LMAP-FRAMEWORK].
 There may be a serious issue if a proprietary service level agreement
 involved with the access network segment provider were somehow leaked
 in the process of rate measurement.  To address this, test protocols
 SHOULD NOT convey this information in a way that could be discovered
 by unauthorized parties.

7. Operational Considerations

 All forms of testing originate network traffic, either through their
 communications for control and results collection, from dedicated
 measurement packet streams, or from a combination of both types of
 traffic.  Testing traffic primarily falls in one of two categories:
 subscriber traffic or network management traffic.  There is an
 ongoing need to engineer networks so that various forms of traffic
 are adequately served, and publication of this memo does not change
 this need.  Service subscribers and authorized users SHOULD obtain
 their network operator's or service provider's permission before
 conducting tests.  Likewise, a service provider or third party SHOULD
 obtain the subscriber's permission to conduct tests, since they might
 temporarily reduce service quality.  The protocol SHOULD communicate
 the permission status once the overall system has obtained it, either
 explicitly or through other means.
 Subscribers, their service providers and network operators, and
 sometimes third parties, all seek to measure network performance.
 Capacity testing with active traffic often affects the packet
 transfer performance of streams traversing shared components of the
 test path, to some degree.  The degradation can be minimized by
 scheduling such tests infrequently and restricting the amount of
 measurement traffic required to assess capacity metrics.  As a
 result, occasional short-duration estimates with minimal traffic are
 preferred to measurements based on frequent file transfers of many
 megabytes with similar accuracy.  New measurement methodologies
 intended for standardization should be evaluated individually for
 potential operational issues.  However, the scheduled frequency of
 testing is as important as the methods used (and schedules are not
 typically submitted for standardization).

Morton Informational [Page 11] RFC 7497 Rate Problem Statement April 2015

 The new test protocol feature of asymmetrical packet size generation
 in two-way testing is recommended in this memo.  It can appreciably
 reduce the load and packet processing demands of each test and
 therefore reduce the likelihood of degradation in one direction of
 the tested path.  Current IETF standardized test protocols (e.g.,
 [RFC5357] and [RFC6812]) do not possess the asymmetric size
 generation capability with two-way testing.

8. References

8.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
            "Framework for IP Performance Metrics", RFC 2330, May
            1998, <http://www.rfc-editor.org/info/rfc2330>.
 [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
            Delay Metric for IPPM", RFC 2679, September 1999,
            <http://www.rfc-editor.org/info/rfc2679>.
 [RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
            Packet Loss Metric for IPPM", RFC 2680, September 1999,
            <http://www.rfc-editor.org/info/rfc2680>.
 [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
            Zekauskas, "A One-way Active Measurement Protocol
            (OWAMP)", RFC 4656, September 2006,
            <http://www.rfc-editor.org/info/rfc4656>.
 [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
            Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
            RFC 5357, October 2008,
            <http://www.rfc-editor.org/info/rfc5357>.
 [RFC6703]  Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
            IP Network Performance Metrics: Different Points of View",
            RFC 6703, August 2012,
            <http://www.rfc-editor.org/info/rfc6703>.

Morton Informational [Page 12] RFC 7497 Rate Problem Statement April 2015

8.2. Informative References

 [IPPM-METRICS]
            Mathis, M. and A. Morton, "Model Based Bulk Performance
            Metrics", Work in Progress, draft-ietf-ippm-model-based-
            metrics-04, March 2015.
 [LMAP-FRAMEWORK]
            Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
            Aitken, P., and A. Akhter, "A framework for Large-Scale
            Measurement of Broadband Performance (LMAP)", Work in
            Progress, draft-ietf-lmap-framework-12, March 2015.
 [RFC3148]  Mathis, M. and M. Allman, "A Framework for Defining
            Empirical Bulk Transfer Capacity Metrics", RFC 3148, July
            2001, <http://www.rfc-editor.org/info/rfc3148>.
 [RFC5136]  Chimento, P. and J. Ishac, "Defining Network Capacity",
            RFC 5136, February 2008,
            <http://www.rfc-editor.org/info/rfc5136>.
 [RFC6812]  Chiba, M., Clemm, A., Medley, S., Salowey, J., Thombare,
            S., and E. Yedavalli, "Cisco Service-Level Assurance
            Protocol", RFC 6812, January 2013,
            <http://www.rfc-editor.org/info/rfc6812>.
 [RFC7398]  Bagnulo, M., Burbridge, T., Crawford, S., Eardley, P., and
            A. Morton, "A Reference Path and Measurement Points for
            Large-Scale Measurement of Broadband Performance", RFC
            7398, February 2015,
            <http://www.rfc-editor.org/info/rfc7398>.

Acknowledgements

 Dave McDysan provided comments and text for the aggregated leased use
 case.  Yaakov Stein suggested many considerations to address,
 including the In-Service vs. Out-of-Service distinction and its
 implication on test traffic limits and protocols.  Bill Cerveny,
 Marcelo Bagnulo, Kostas Pentikousis (a persistent reviewer), and
 Joachim Fabini have contributed insightful, clarifying comments that
 made this a better document.  Barry Constantine also provided
 suggestions for clarification.

Morton Informational [Page 13] RFC 7497 Rate Problem Statement April 2015

Author's Address

 Al Morton
 AT&T Labs
 200 Laurel Avenue South
 Middletown, NJ  07748
 United States
 Phone: +1 732 420 1571
 Fax:   +1 732 368 1192
 EMail: acmorton@att.com
 URI:   http://home.comcast.net/~acmacm/

Morton Informational [Page 14]

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