One-way Active Measurement Protocol (OWAMP) Requirements

Network Working Group                                        S. Shalunov
Request for Comments: 3763                                 B. Teitelbaum
Category: Informational                                        Internet2
                                                              April 2004


        One-way Active Measurement Protocol (OWAMP) Requirements

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   With growing availability of good time sources to network nodes, it
   becomes increasingly possible to measure one-way IP performance
   metrics with high precision.  To do so in an interoperable manner, a
   common protocol for such measurements is required.  This document
   specifies requirements for a one-way active measurement protocol
   (OWAMP) standard.  The protocol can measure one-way delay, as well as
   other unidirectional characteristics, such as one-way loss.

1.  Motivations and Goals

   The IETF IP Performance Metrics (IPPM) working group has proposed
   standards track metrics for one-way packet delay [RFC2679] and loss
   [RFC 2680] across Internet paths.  Although there are now several
   measurement platforms that implement the collection of these metrics
   ([CQOS], [BRIX], [RIPE], [SURVEYOR]), there is not currently a
   standard for interoperability.  This requirements document is aimed
   at defining a protocol that allows users to do measurements using
   devices from different vendors at both ends and get meaningful
   results.

   With the increasingly wide availability of affordable global
   positioning system (GPS) and CDMA based time sources, hosts
   increasingly have available to them time sources that allow hosts to
   time-stamp packets with accuracies substantially better than the
   delays seen on the Internet--either directly or through their
   proximity to NTP primary (stratum 1) time servers.  By standardizing
   a technique for collecting IPPM one-way active measurements, we hope
   to create an environment where these metrics may be collected across
   a far broader mesh of Internet paths than is currently possible.  One
   particularly compelling vision is of widespread deployment of open
   one-way active measurement beacons that would make measurements of
   one-way delay as commonplace as measurements of round-trip time are
   today using ICMP-based tools like ping.  Even without very accurate
   timestamps one can measure characteristics such as loss with quality
   acceptable for many practical purposes, e.g., network operations.

   To support interoperability between alternative OWAMP implementations
   and make possible a world where "one-way ping" could become
   commonplace, a standard is required that specifies how test streams
   are initiated, how test packets are exchanged, and how test results
   are retrieved.  Detailed functional requirements are given in the
   subsequent section.

2.  Functional Requirements

   The protocol(s) should provide the ability to measure, record, and
   distribute the results of measurements of one-way singleton network
   characteristics such as characteristics defined in [RFC2679] and
   [RFC2680].  Result reporting, sampling, and time stamps are to be
   within the framework of [RFC2330].

   It should be possible to measure arbitrary one-way singleton
   characteristics (e.g., loss, median delay, mean delay, jitter, 90th
   percentile of delay, etc.); this is achieved by keeping all the raw
   data for post-processing by the final data consumer, as specified in
   section 2.1.  Since RFC2679 and RFC2680 standardize metrics based on
   Poisson sampling processes, Poisson streams must be supported by the
   protocol(s).

   Non-singleton characteristics (such as those related to trains of
   packets, back-to-back tuples, and so forth) and application traffic
   simulation need not be addressed.  However, they may be addressed if
   considered practical and not in contradiction to other design goals.

2.1.  Keeping All Data for Post-processing

   To facilitate the broadest possible use of obtained measurement
   results, the protocol(s) should not necessitate any required post-
   processing.  (This does not apply to implementation details such as
   converting timestamps from ticks since midnight into a canonical form
   or applying calibration constants; such details should naturally be
   hidden.)  All data obtained during a measurement session should be
   available after the session is finished if desired by the data
   consumer so that various characteristics can be computed from the raw
   data using arbitrary algorithms.

2.2.  Result Distribution

   A means to distribute measurement results (between hosts
   participating in a measurement session and beyond) should be
   provided.  Since there can exist a wide variety of scenarios as to
   where the final data destination should be, these should be invoked
   separately from measurement requests (e.g., receiver should not have
   to automatically send measurement results to the sender, since it may
   be the receiver or a third host that are the ultimate data
   destination).

   At the same time, ability to transfer results directly to their
   destination (without need for potentially large intermediate
   transfers) should be provided.

2.3.  Protocol Separation

   Since measurement session setup and the actual measurement session
   (i) are different tasks; (ii) require different levels of
   functionality, flexibility, and implementation effort; (iii) may need
   to run over different transport protocols, there should exist two
   protocols: one for conducting the actual measurement session and
   another for session setup/teardown/confirmation/retrieval.  These
   protocols are further referred to as OWAMP-Test and OWAMP-Control,
   respectively.

   It should be possible to use devices that only support OWAMP-Test but
   not OWAMP-Control to conduct measurement sessions (such devices will
   necessarily need to support one form of session setup protocol or the
   other, but it doesn't have to be known to external parties).

   OWAMP-Control would thus become a common protocol for different
   administrative domains, which may or may not use it for session setup
   internally.

2.4.  Test Protocol

   The test protocol needs to be implemented on all measurement nodes
   and should therefore have the following characteristics:

   +  Be lightweight and easy to implement.

   +  Be suitable for implementation on a wide range of measurement
      nodes.

   +  Allow UDP as the transport protocol, since the protocol needs to
      be able to measure individual packet delivery times and has to run
      on various machines (see the section "Support for Measurements
      with Different Packet Types" below for further discussion).

   +  Support varying packet sizes and network services (e.g., DSCP
      marking).

   +  Be as simple as possible, but no simpler than necessary to
      implement requirements set forth in this document; the OWAMP-Test
      packet format should include only universally meaningful fields,
      and minimum number of them.

   +  If practical, it should be possible to generate OWAMP-Test packets
      small enough, so that when encapsulated, each fits inside a single
      ATM cell.

   +  Data needed to calculate experimental errors on the final result
      should be included in every OWAMP-Test packet.

2.5.  Control Protocol

   Control protocol needs to provide the capability to:

   +  authenticate peers to each other using a common authentication
      method that doesn't require building any new authentication
      infrastructure, such as user ID and a shared secret;

   +  schedule zero or more OWAMP-Test sessions (which do not have to be
      between the peers of OWAMP-Control conversation);

   +  start OWAMP-Test sessions simultaneously or at a pre-scheduled
      per-session times;

   +  retrieve OWAMP-Test session results (of OWAMP-Test sessions
      scheduled in the current and other OWAMP-Control sessions);

   +  confirm graceful completion of sessions and allow either side to
      abort a session prematurely.

   The OWAMP-Control design should not preclude the ability to record
   extended periods of losses.  It should always provide peers with the
   ability to distinguish between network and peer failures.

2.6.  Support for Measurements with Different Packet Types

   Since the notion of a packet of type P from [RFC2330], section 13
   doesn't always imply precise definition of packet type, some
   decisions narrowing the scope of possible packet types need to be
   made at measurement protocol design stage.  Further, measurement with
   packets of certain types, while feasible in more closed settings than
   those implied by OWAMP, become very hard to perform in an open
   inter-domain fashion (e.g., measurements with particular packets with
   broken IP checksum or particular loose source routing options).

   In addition, very general packet type specification could result in
   several problems:

   +  Many OWAMP-Test speakers will be general purpose computers with a
      multitasking operating system that includes a socket interface.
      These will inevitably have higher losses when listening to raw
      network traffic.  Raw sockets will induce higher loss rate than
      one would have with UDP measurements.

   +  It's not at all clear (short of standardizing tcpdump syntax) how
      to describe formally the filter that a receiver should use to
      listen for test traffic.

   +  Suppose an identity of an authenticated user becomes compromised.
      Now the attacker could use that to run TCP sessions to the rlogin
      port of machines around servers that trust this user to perform
      measurements (or, less drastically, to send spam from that
      network).  The ability to perform measurements is transformed into
      an ability to generate arbitrary traffic on behalf of all the
      senders an OWAMP-Control server controls.

   +  Carefully crafted packets could cause disruption to some link-
      layer protocols.  Implementors can't know what to disallow
      (scrambling is different for different link-layer technologies).

   It appears that allowing one to ask a measurement server to generate
   arbitrary packets becomes an unmanageable security hole and a
   formidable specification and implementation hurdle.

   For these reasons, we only require OWAMP to support a small subspace
   of the whole packet type space.  Namely, it should be possible to
   conduct measurements with a given Differentiated Services Codepoint
   (DSCP) [RFC2474] or a given Per Hop Behavior Identification Code (PHB
   ID) [RFC3140].

3.  Scalability

   While some measurement architecture designs have inherent scalability
   problems (e.g., a full mesh of always-on measurements among N
   measurement nodes requires O(N^2) total resources, such as storage
   space and link capacity), OWAMP itself should not exaggerate the
   problem or make it impossible (where it is in principle possible) to
   design other architectures that are free of scalability deficiencies.

   It is the protocol user's responsibility to decide how to use the
   protocol and which measurements to conduct.

4.  Security Considerations

4.1.  Authentication

   It should be possible to authenticate peers to each other using a
   user ID and a shared secret.  It should be infeasible for any
   external party without knowledge of the shared secret to obtain any
   information about it by observing, initiating, or modifying protocol
   transactions.

   It should also be infeasible for such party to use any information
   obtained by observing, modifying or initiating protocol transactions
   to impersonate (other) valid users.

4.2.  Authorization

   Authorization shall normally be performed on the basis of the
   authenticated identity (such as username) and the specification shall
   require all implementations to support such a mode of authorization.
   Different identities (or classes of identities) can have different
   testing privileges.  The use of authorization for arriving at
   specific policy decisions (such as whether to allow a specific test
   with a specific source and destination and with a given test send
   schedule -- which would determine the average network capacity
   utilization -- at a given time) is up to the users.

4.3.  Being Hard to Interfere with by Applying Special Treatment to
     Measurement Packets

   The design of the protocol should make it possible to run sessions
   that would make it very difficult for any intermediate party to make
   results appear better than they would be if no interference was
   attempted.

   This is different from cryptographic assurance of data integrity,
   because one can manipulate the results without changing any data in
   the packets.  For example, if OWAMP-Test packets are easy to identify
   (e.g., they all come to a well-known port number), an intermediate
   party might place OWAMP-Test traffic into a priority queue at a
   congested link thus ensuring that the results of the measurement
   appear better than what would be experienced by other traffic.  It
   should not be easy for intermediate parties to identify OWAMP-Test
   packets (just as it should not be easy for restaurants to identify
   restaurant critics).

4.4.  Secrecy/Confidentiality

   It should be possible to make it infeasible for any outside party
   without knowledge of the shared secret being used to learn what
   information is exchanged using OWAMP-Control by inspecting an OWAMP-
   Control stream or actively modifying it.

   (It is recognized that some information will inevitably leak from the
   mere fact of communication and from the presence and timing of
   concurrent and subsequent OWAMP-Test traffic.)

4.5.  Integrity

   So that it is possible to detect any interference during a
   conversation (other than the detention of some messages), facility
   must be provided to authenticate each message of the OWAMP-Control
   protocol, its attribution to a given session, and its exact placement
   in the sequence of control protocol exchanges.

   It must also be possible to authenticate each message of the test
   protocol and its attribution to a specific session, so that
   modifications of OWAMP-Test messages can be detected.  It must be
   possible to do this in a fashion that does not require timestamps
   themselves to be encrypted; in this case, security properties are
   valid only when an attacker cannot observe valid traffic between the
   OWAMP-Test sender and receiver.

4.6.  Replay Attacks

   OWAMP-Control must be resistant to any replay attacks.

   OWAMP-Test, on the other hand, is a protocol for network measurement.
   One of the attributes of networks is packet duplication.  OWAMP-Test
   has to be suitable for measurement of duplication.  This would make
   it vulnerable to attacks that involve replaying a recent packet.  For
   the recipient of such a packet it is impossible to determine whether
   the duplication is malicious or naturally occurring.

   OWAMP-Test should measure all duplication -- malicious or otherwise.
   Note that this is similar to delay attacks: an attacker can hold up a
   packet for some short period of time and then release it to continue
   on its way to the recipient.  There's no way such delay can be
   reliably distinguished from naturally occurring delay by the
   recipient.

   OWAMP-Test should measure the network as it was.  Note, however, that
   this does not prevent the data from being sanitized at a later stage
   of processing, analysis, or consumption.  Some sanity checks (those
   that are deemed reliable and erring on the side of inclusion) should
   be performed by OWAMP-Test recipient immediately.

4.7.  Modes of Operation

   Since the protocol(s) will be used in widely varying circumstances
   using widely varying equipment, it is necessary to be able to support
   varying degrees of security modes of operation.  The parameters to be
   considered include: confidentiality, data origin authentication,
   integrity and replay protection.

   It should also be possible to operate in a mode where all security
   mechanisms are enabled and security objectives are realized to the
   fullest extent possible.  We call this "encrypted mode".

   Since timestamp encryption takes a certain amount of time, which may
   be hard to predict on some devices (with a time-sharing OS), a mode
   should be provided that is similar to encrypted mode, but in which
   timestamps are not encrypted.  In this mode, all security properties
   of the encrypted mode that can be retained without timestamp
   encryption should be present.  We call this "authenticated mode".

   It should be possible to operate in a completely "open" mode, where
   no cryptographic security mechanisms are used.  We call this
   "unauthenticated mode".  In this mode, mandatory-to-use mechanisms
   must be specified that prevent the use of the protocol for network
   capacity starvation denial-of-service attacks (e.g., only sending
   test data back to the client that requested them to be sent with the
   request delivered over a TCP connection), and that prevent a worm
   from using the protocol to send test data to a very large number of
   hosts in a short time (e.g., ensuring that open mode requests can
   only be made by humans, rate-limiting the acceptance of open mode
   requests).

   To make implementation more manageable, the number of other options
   and modes should be kept to the absolute practical minimum.  Where
   choosing a single mechanism for achieving anything related to
   security is possible, such choice should be made at specification
   phase and be put into the standard.

5.  IANA Considerations

   Relevant IANA considerations will be placed into the protocol
   specification document itself, and not into the requirements
   document.

6.  References

6.1.  Normative References

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J. and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330, May
              1998.

   [RFC2474]  Nichols, K., Blake, S., Baker, F. and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474, December
              1998.

   [RFC2679]  Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, September 1999.

   [RFC2680]  Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way
              Packet Loss Metric for IPPM", RFC 2680, September 1999.

   [RFC3140]  Black, D., Brim, S., Carpenter, B. and F. Le Faucheur,
              "Per Hop Behavior Identification Codes", RFC 3140, June
              2001.

6.2.  Informative References

   [BRIX]     Brix 1000 Verifier,
              http://www.brixnet.com/products/brix1000.html

   [CQOS]     CQOS Home Page, http://www.cqos.com/

   [RIPE]     RIPE NCC Test-Traffic Measurements home,
              http://www.ripe.net/test-traffic/

   [SURVEYOR] Surveyor Home Page, http://www.advanced.org/surveyor/

7.  Authors' Addresses

   Stanislav Shalunov

   EMail: shalunov@internet2.edu


   Benjamin Teitelbaum

   EMail: ben@internet2.edu

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