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Network Working Group                                 Stanislav Shalunov
Internet Draft                                                 Internet2
Expiration Date: February 2003                       Benjamin Teitelbaum
                               Advanced Network & Services and Internet2
                                                    Matthew J. Zekauskas
                                             Advanced Network & Services
                                                             August 2002



                 A One-way Active Measurement Protocol
                     <draft-ietf-ippm-owdp-05.txt>


1. 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

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


2. Motivation and Goals

   The IETF IP Performance Metrics (IPPM) working group has proposed
   draft standard metrics for one-way packet delay [RFC2679] and loss
   [RFC 2680] across Internet paths.  Although there are now several
   measurement platforms that implement collection of these metrics
   [SURVEYOR], [RIPE], there is not currently a standard that would
   permit initiation of test streams or exchange of packets to collect



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   singleton metrics in an interoperable manner.

   With the increasingly wide availability of affordable global
   positioning system (GPS) and CDMA based time sources, hosts
   increasingly have available to them very accurate time
   sources--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 IPPM 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 OWAMP servers
   that would make measurement of one-way delay as commonplace as
   measurement of round-trip time using an ICMP-based tool like ping.

   Additional design goals of OWAMP include being hard to detect and
   manipulate, security, logical separation of control and test
   functionality, and support for small test packets.

   OWAMP test traffic is hard to detect, because it is simply a stream
   of UDP packets from and to negotiated port numbers with potentially
   nothing static in the packets (size is negotiated, too).
   Additionally, OWAMP supports an encrypted mode, that further obscures
   the traffic, at the same time making it impossible to alter
   timestamps undetectably.

   Security features include optional authentication and/or encryption
   of control and test messages.  These features may be useful to
   prevent unauthorized access to results or man-in-the-middle attackers
   who attempt to provide special treatment to OWAMP test streams or who
   attempt to modify sender-generated timestamps to falsify test
   results.


2.1. Relationship of Test and Control Protocols

   OWAMP actually consists of two inter-related protocols: OWAMP-Control
   and OWAMP-Test.  OWAMP-Control is used to initiate, start and stop
   test sessions and fetch their results, while OWAMP-Test is used to
   exchange test packets between two measurement nodes.

   Although OWAMP-Test may be used in conjunction with a control
   protocol other than OWAMP-Control, the authors have deliberately
   chosen to include both protocols in the same draft to encourage the
   implementation and deployment of OWAMP-Control as a common
   denominator control protocol for one-way active measurements.  Having
   a complete and open one-way active measurement solution that is
   simple to implement and deploy is crucial to assuring a future in
   which inter-domain one-way active measurement could become as



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   commonplace as ping.  We neither anticipate nor recommend that OWAMP-
   Control form the foundation of a general purpose extensible
   measurement and monitoring control protocol.

   OWAMP-Control is designed to support the negotiation of one-way
   active measurement sessions and results retrieval in a
   straightforward manner. At session initiation, there is a negotiation
   of sender and receiver addresses and port numbers, session start
   time, session length, test packet size, the mean Poisson sampling
   interval for the test stream, and some attributes of the very general
   RFC 2330 notion of `packet type', including packet size and per-hop
   behavior (PHB) [RFC2474], which could be used to support the
   measurement of one-way active across diff-serv networks.
   Additionally, OWAMP-Control supports per-session encryption and
   authentication for both test and control traffic, measurement servers
   which may act as proxies for test stream endpoints, and the exchange
   of a seed value for the pseudo-random Poisson process that describes
   the test stream generated by the sender.

   We believe that OWAMP-Control can effectively support one-way active
   measurement in a variety of environments, from publicly accessible
   measurement `beacons' running on arbitrary hosts to network
   monitoring deployments within private corporate networks.  If
   integration with SNMP or proprietary network management protocols is
   required, gateways may be created.


2.2. Logical Model

   Several roles are logically separated to allow for broad flexibility
   in use.  Specifically, we define:

     Session-Sender     the sending endpoint of an OWAMP-Test session;

     Session-Receiver   the receiving endpoint of an OWAMP-Test session;

     Server             an end system that manages one or more OWAMP-Test
                        sessions, is capable of configuring per-session
                        state in session endpoints, and is capable of
                        returning the results of a test session;

     Control-Client     an end system that initiates requests for
                        OWAMP-Test sessions, triggers the start of a set
                        of sessions, and may trigger their termination;

     Fetch-Client       an end system that initiates requests to fetch
                        the results of completed OWAMP-Test sessions;




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   One possible scenario of relationships between these roles is shown
   below.

       +----------------+               +------------------+
       | Session-Sender |--OWAMP-Test-->| Session-Receiver |
       +----------------+               +------------------+
         ^                                     ^
         |                                     |
         |                                     |
         |                                     |
         |  +----------------+<----------------+
         |  |     Server     |<-------+
         |  +----------------+        |
         |    ^                       |
         |    |                       |
         | OWAMP-Control         OWAMP-Control
         |    |                       |
         v    v                       v
       +----------------+     +-----------------+
       | Control-Client |     |   Fetch-Client  |
       +----------------+     +-----------------+

   (Unlabeled links in the figure are unspecified by this draft and may
   be proprietary protocols.)

   Different logical roles can be played by the same host.  For example,
   in the figure above, there could actually be only two hosts: one
   playing the roles of Control-Client, Fetch-Client, and Session-
   Sender, and the other playing the roles of Server and Session-
   Receiver. This is shown below.

       +-----------------+                   +------------------+
       | Control-Client  |<--OWAMP-Control-->| Server           |
       | Fetch-Client    |                   |                  |
       | Session-Sender  |---OWAMP-Test----->| Session-Receiver |
       +-----------------+                   +------------------+

   Finally, because many Internet paths include segments that transport
   IP over ATM, delay and loss measurements can include the effects of
   ATM segmentation and reassembly (SAR).  Consequently, OWAMP has been
   designed to allow for small test packets that would fit inside the
   payload of a single ATM cell (this is only achieved in
   unauthenticated and encrypted modes).








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3. Protocol Overview

   As described above, OWAMP consists of two inter-related protocols:
   OWAMP-Control and OWAMP-Test.  The former is layered over TCP and is
   used to initiate and control measurement sessions and to fetch their
   results.  The latter protocol is layered over UDP and is used to send
   singleton measurement packets along the Internet path under test.

   The initiator of the measurement session establishes a TCP connection
   to a well-known port on the target point and this connection remains
   open for the duration of the OWAMP-Test sessions.  IANA will be
   requested to allocate a well-known port number for OWAMP-Control
   sessions.  An OWAMP server SHOULD listen to this well-known port.

   OWAMP-Control messages are transmitted only before OWAMP-Test
   sessions are actually started and after they complete (with the
   possible exception of an early Stop-Session message).

   The OWAMP-Control and OWAMP-Test protocols support three modes of
   operation: unauthenticated, authenticated, and encrypted.  The
   authenticated or encrypted modes require endpoints to possess a
   shared secret.

   All multi-octet quantities defined in this document are represented
   as unsigned integers in network byte order unless specified
   otherwise.


4. OWAMP-Control

   Each type of OWAMP-Control message has a fixed length.  The recipient
   will know the full length of a message after examining first 16
   octets of it.  No message is shorter than 16 octets.

   If the full message is not received within 30 minutes after it is
   expected, connection SHOULD be dropped.


4.1. Connection Setup

   Before either a Control-Client or a Fetch-Client can issue commands
   of a Server, it must establish a connection to the server.

   First, a client opens a TCP connection to the server on a well-known
   port.  The server responds with a server greeting:






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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                      Unused (12 octets)                       |
        |                                                               |
        |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                            Modes                              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                     Challenge (16 octets)                     |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following mode values are meaningful: 1 for unauthenticated, 2
   for authenticated, 4 for encrypted.  The value of the Modes field
   sent by the server is the bit-wise OR of the mode values that it is
   willing to support during this session.  Thus, last three bits of the
   Modes 32-bit value are used.  The first 29 bits MUST be zero.  A
   client MUST ignore the values in the first 29 bits of the Modes
   value.  (This way, the bits are available for future protocol
   extensions.  This is the only intended extension mechanism.)

   If Modes value is zero, the server doesn't wish to communicate with
   the client and MAY close the connection immediately.  The client
   SHOULD close the connection if it gets a greeting with Modes equal to
   zero.

   Otherwise, the client MUST respond with the following message:





















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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                             Mode                              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                     Username (16 octets)                      .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                       Token (32 octets)                       .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                     Client-IV (16 octets)                     .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Here Mode is the mode that the client chooses to use during this
   OWAMP-Control session.  It will also be used for all OWAMP-Test
   sessions started under control of this OWAMP-Control session.  In
   Mode, one or zero bits MUST be set within last three bits.  The first
   29 bits of Mode MUST be zero.  A server MUST ignore the values of the
   first 29 bits.

   In unauthenticated mode, Username, Token, and Client-IV are unused.

   Otherwise, Username is a 16-octet indicator of which shared secret
   the client wishes to use to authenticate or encrypt and Token is the
   concatenation of a 16-octet challenge and a 16-octet Session-key,
   encrypted using the AES (Advanced Encryption Standard) [AES] in
   Cipher Block Chaining (CBC). Encryption MUST be performed using an
   Initialization Vector (IV) of zero and a key value that is the shared
   secret associated with Username.  The shared secret will typically be
   provided as a passphrase; in this case, not the actual passphrase
   SHOULD be used as a key for encryption by the client and decryption
   by the server, but the MD5 sum [RFC1321] of the passphrase (without
   possible newline character(s) at the end of the passphrase; the
   passphrase also SHOULD not contain newlines).

   Session-key and Client-IV are generated randomly by the client.




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   The server MUST respond with the following message:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                      Unused, MBZ (15 octets)                  |
        |                                                               |
        |                                               +-+-+-+-+-+-+-+-+
        |                                               |   Accept      |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                     Server-IV (16 octets)                     |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Unused 15-octet part MUST be zero.  The server MUST ignore its
   value.

   A zero value in the Accept field means that the server accepts the
   authentication and is willing to conduct further transactions.  A
   value of 1 means that the server does not accept the authentication
   provided by the client or, for some other reason, is not willing to
   conduct further transactions in this OWAMP-Control session.  All
   other values are reserved.  The server MUST interpret all values of
   Accept other than 0 and 1 as 1.  This way, other values are available
   for future extensions.  If a negative response is sent, the server
   MAY and the client SHOULD close the connection after this message.

   The previous transactions constitute connection setup.


4.2. OWAMP-Control Commands

   In authenticated or encrypted mode (which are identical as far as
   OWAMP-Control is concerned, and only differ in OWAMP-Test) all
   further communications are encrypted with the Session-key, using CBC
   mode.  The client encrypts its stream using Client-IV.  The server
   encrypts its stream using Server-IV.

   The following commands are available for the client: Request-Session,
   Start-Sessions, Stop-Session, Fetch-Session.  The command Stop-
   Session is available to both client and server.

   After Start-Sessions is sent/received by the client/server, and
   before it both sends and receives Stop-Session (order unspecified),
   it is said to be conducting active measurements.



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   While conducting active measurements, the only command available is
   Stop-Session.

   These commands are described in detail below.


4.3. Creating Test Sessions

   Individual one-way active measurement sessions are established using
   a simple request/response protocol. An OWAMP client MAY issue zero or
   more Request-Session messages to an OWAMP server, which MUST respond
   to each with an Accept-Session message.  An Accept-Session message
   MAY refuse a request.

   The format of Request-Session message is as follows:




































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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |      1        |  MBZ  | IPVN  |  Conf-Sender  | Conf-Receiver |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                  Number of Schedule Slots                     |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                      Number of Packets                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |          Sender Port          |         Receiver Port         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Sender Address                         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Sender Address (cont.) or MBZ                    |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Receiver Address                       |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Receiver Address (cont.) or MBZ                  |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                        SID (16 octets)                        |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                         Padding Length                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                           Start Time                          |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                            Timeout                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                       Type-P Descriptor                       |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                              MBZ                              |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This is immediately followed by one or more schedule slot



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   descriptions (the number of schedule slots is specified in the
   `Number of Schedule Slots' field above):

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |    Slot Type  |                                               |
        +-+-+-+-+-+-+-+-+              MBZ                              |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                 Slot Parameter (Timestamp)                    |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   These are immediately followed by Integrity Zero Padding:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All these messages comprise one logical message: the Request-Session
   command.

   Above, the first octet (1) indicates that this is Request-Session
   command.

   IPVN is the IP version numbers for Sender and Receiver.  In the case
   of IP version number being 4, twelve unused octets follow the four-
   octet address.  Currently meaningful values are 4 and 6.

   Conf-Sender and Conf-Receiver can be 0 or 1.  If 1, the server is
   being asked to configure the corresponding agent (sender or
   receiver).  In this case, the corresponding Port value SHOULD be
   disregarded by the server.  At least one of Conf-Sender and Conf-
   Receiver MUST be 1.  (Both can be set, in which case the server is
   being asked to perform a session between two hosts it can configure.)

   Number of Schedule Slots, as mentioned before, specifies the number
   of slot records that go between the two blocks of Integrity Zero
   Padding.  It is used by the sender to determine when to send test
   packets (see next section).

   Number of Packets is the number of active measurement packets to be



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   sent during this OWAMP-Test session (note that both server and client
   can abort the session early).

   If Conf-Sender is not set, Sender Port is the UDP port OWAMP-Test
   packets will be sent from.  If Conf-Receiver is not set, Receiver
   Port is the UDP port OWAMP-Test packets are requested to be sent to.

   The Sender Address and Receiver Address fields contain respectively
   the sender and receiver addresses of the end points of the Internet
   path over which an OWAMP test session is requested.

   SID is the session identifier.  It can be used in later sessions as
   an argument for Fetch-Session command.  It is meaningful only if
   Conf-Receiver is 0.  This way, the SID is always generated by the
   receiving side.  See the end of the section for information on how
   the SID is generated.

   Padding length is the number of octets to be appended to normal
   OWAMP-Test packet (see more on padding in discussion of OWAMP-Test).

   Start Time is the time when the session is to be started (but not
   before Start-Sessions command is issued).  This timestamp is in the
   same format as OWAMP-Test timestamps.

   Timeout is an interval of time (expressed as a timestamp).  A packet
   belonging to the test session that is being set up by the current
   Request-Session command will be considered lost if it is not received
   during Timeout seconds after it is sent.

   Type-P Descriptor covers only a subset of (very large) Type-P space.
   If the first two bits of Type-P Descriptor are 00, then subsequent 6
   bits specify the requested Differentiated Services Codepoint (DSCP)
   value of sent OWAMP-Test packets as defined in RFC 2474.  If the
   first two bits of Type-P descriptor are 01, then subsequent 16 bits
   specify the requested Per Hop Behavior Identification Code (PHB ID)
   as defined in RFC 2836.

   Therefore, the value of all zeros specifies the default best-effort
   service.

   If Conf-Sender is set, Type-P Descriptor is to be used to configure
   the sender to send packets according to its value.  If Conf-Sender is
   not set, Type-P Descriptor is a declaration of how the sender will be
   configured.

   If Conf-Sender is set and the server doesn't recognize Type-P
   Descriptor, cannot or does not wish to set the corresponding
   attributes on OWAMP-Test packets, it SHOULD reject the session



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   request.  If Conf-Sender is not set, the server SHOULD accept the
   session regardless of the value of Type-P Descriptor.

   Integrity Zero Padding MUST be all zeros in this and all subsequent
   messages that use zero padding.  The recipient of a message where
   zero padding is not zero MUST reject the message as it is an
   indication of tampering with the content of the message by an
   intermediary (or brokenness).  If the message is part of OWAMP-
   Control, the session MUST be terminated and results invalidated.  If
   the message is part of OWAMP-Test, it MUST be silently ignored.  This
   will ensure data integrity.  In unauthenticated mode, Integrity Zero
   Padding is nothing more than a simple check.  In authenticated and
   encrypted modes, however, it ensures, in conjuction with properties
   of CBC chaining mode, that everything received before was not
   tampered with.  For this reason, it is important to check the
   Integrity Zero Padding Field as soon as possible, so that bad data
   doesn't get propagated.

   To each Request-Session message, an OWAMP server MUST respond with an
   Accept-Session message:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |    Accept     |  Unused       |            Port               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
        |                                                               |
        |                        SID (16 octets)                        |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (12 octets)               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   In this message, zero in the Accept field means that the server is
   willing to conduct the session.  A value of 1 indicates rejection of
   the request.  All other values are reserved.

   If the server rejects a Request-Session command, it SHOULD not close
   the TCP connection.  The client MAY close it if it gets negative
   response to Request-Session.

   The meaning of Port in the response depends on the values of Conf-
   Sender and Conf-Receiver in the query that solicited the response.
   If both were set, Port field is unused.  If only Conf-Sender was set,
   Port is the port to expect OWAMP-Test packets from.  If only Conf-



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   Receiver was set, Port is the port to send OWAMP-Test packets to.

   If only Conf-Sender was set, SID field in the response is unused.
   Otherwise, SID is a unique server-generated session identifier.  It
   can be used later as handle to fetch the results of a session.

   SIDs SHOULD be constructed by concatenation of 4-octet IPv4 IP number
   belonging to the generating machine, 8-octet timestamp, and 4-octet
   random value.  To reduce the probability of collisions, if the
   generating machine has any IPv4 addresses (with the exception of
   loopback), one of them SHOULD be used for SID generation, even if all
   communication is IPv6-based.  If it has no IPv4 addresses at all, the
   last 4 octets of an IPv6 address can be used instead.  Note that SID
   is always chosen by the receiver.  If truely random values are not
   available, it is important that SID be made unpredictable as
   knowledge of SID might be used for access control.


4.4. Send Schedules

   The sender and the receiver need to both know the same send schedule.
   This way, when packets are lost, the receiver knows when they were
   sent.  It is desirable to compress common schedules and still to be
   able to use an arbitrary one for the test sessions.  In many cases,
   the schedule will consist of repeated sequences of packets: this way,
   the sequence performs some test, and the test is repeated a number of
   times to gather statistics.

   To implement this, we have a schedule with a given number of `slots'.
   Each slots has a type and a parameter.  Two types are supported:
   exponentially distributed pseudo-random quantity (denoted by a code
   of 0) and a fixed quantity (denoted by a code of 1).  The parameter
   is expressed as a timestamp and specifies a time interval.  For a
   type 0 slot (exponentially distributed pseudo-random quantity) this
   interval is the mean value (or 1/lambda if the distribution density
   function is expressed as lambda*exp(-lambda*x) for positive values of
   x).  For a type 1 slot, the parameter is the delay itself.  The
   sender starts with the beginning of the schedule, and `executes' the
   instructions in the slots: for a slot of type 0, wait exponentially
   distributed time with mean of the specified parameter and then send a
   test packet (and proceed to the next slot); for a slot of type 1,
   wait the specified time and send a test packet (and proceed to the
   next slot).  The schedule is circular: when there are no more slots,
   the sender returns to the first slot.

   Slots of type 1 can be trivially reproduceably executed by both the
   sender and the receiver (so if a packet is lost, the receiver can
   still attach a send timestamp to it).  To reproduceable execute slots



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   of type 0, we need to be able to generate pseudo-random exponentially
   distributed quantities is a reproduceable manner.  The way this is
   accomplished is discussed later.

   Using this mechanism one can easily specify common testing scenarios:


   +  Poisson stream: a single slot of type 0;

   +  Periodic stream: a single slot of type 1;

   +  Poisson stream of back-to-back packet pairs: two slots -- type 0
      with a non-zero parameter and type 1 with a zero parameter.


   A completely arbitrary schedule can be specified (albeit
   inefficiently) by making the number of test packets equal to the
   number of schedule slots.  In this case, the complete schedule is
   transmitted in advance of an OWAMP-Test session.


4.5. Starting Test Sessions

   Having requested one or more test sessions and received affirmative
   Accept-Session responses, an OWAMP client may start the execution of
   the requested test sessions by sending a Start-Sessions message to
   the server.

   The format of this message is as follows:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |      2        |                                               |
        +-+-+-+-+-+-+-+-+                                               |
        |                      Unused (15 octets)                       |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The server MUST respond with an Control-Ack message (which SHOULD be
   sent as quickly as possible). Control-Ack messages have the following
   format:



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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |     Accept    |                                               |
        +-+-+-+-+-+-+-+-+                                               |
        |                      Unused (15 octets)                       |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If Accept is 1, the Start-Sessions request was rejected; zero means
   that the command was accepted.  All other values are reserved.  The
   server MAY and the client SHOULD close the connection in the case of
   a negative response.

   The server SHOULD start all OWAMP-Test streams immediately after it
   sends the response or immediately after their specified start times,
   whichever is later.  (Note that a client can effect an immediate
   start by specifying in Request-Session a Start Time in the past.)  If
   the client represents a Sender, the client SHOULD start its OWAMP-
   Test streams immediately after it sees the Control-Ack response from
   the Server.


4.6. Stop-Sessions

   The Stop-Sessions message may be issued by either the Control-Client
   or the Server.  The format of this command is as follows:


















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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |      3        |    Accept     |                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
        |                       Unused (14 octets)                      |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Normally, the client SHOULD send this command after the OWAMP-Test
   streams have completed.  However, either client or server MAY send it
   prematurely.

   Value of 1 of Accept indicates a failure of some sort.  Zero values
   indicates normal (but possibly premature) completion.  All other
   values are reserved.  If Accept had non-zero value (from either
   party), or if it was not transmitted at all (for whatever reason,
   including TCP connection used for OWAMP-Control breaking), results of
   all OWAMP-Test sessions spawned by this OWAMP-Control session SHOULD
   be considered invalid, even if Fetch-Session with SID from this
   session works during a different OWAMP-Control session.

   If an OWAMP-Test receiver finishes recording packets of a session and
   the OWAMP-Control end of connection associated with the receiver
   (probably the receiver itself) sends a Stop-Sessions command that
   receives no response within a reasonable communication timeout, or if
   the OWAMP-Control connection breaks when the Stop-Sessions command is
   sent, the receiver MAY not completely invalidate the session results,
   but it MUST discard any records of lost packets that follow (in other
   words, have greater sequence number than) the last packet that was
   actually received.  This will help differentiate between packet
   losses that occured in the network and the sender crashing.  When the
   results of such an OWAMP-Test session or an OWAMP-Session that was
   prematurely aborted successfully (with confirmation) are later
   fetched using Fetch-Session, the original number of packets MUST be
   supplied in the reproduction of the Request-Session command.

   The party that receives this command MUST stop its OWAMP-Test streams
   and respond with a Stop-Sessions message.  Any non-zero value in
   Accept field means something went wrong.  A zero value means OWAMP-
   Test streams have been successfully stopped.




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4.7. Fetch-Session

   The format of this client command is as follows:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |      4        |                                               |
        +-+-+-+-+-+-+-+-+                                               |
        |                      Unused (7 octets)                       |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                         Begin Seq                             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          End Seq                              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                        SID (16 octets)                        |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (16 octets)               |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Begin Seq is the sequence number of the first requested packet.  End
   Seq is the sequence number of the last requested packet.  If Begin
   Seq is all zeros and End Seq is all ones, complete session is said to
   be requested.

   If a complete session is requested and the session is still in
   progress, or has terminated in any way other than normal, the request
   to fetch session results MUST be denied.  If an incomplete session is
   requested, all packets received so far that fall into the requested
   range SHOULD be returned.  Note that since no commands can be issued
   between Start-Sessions and Stop-Sessions, incomplete requests can
   only happen on a different OWAMP-Control connection (from the same or
   different host as Control-Client).

   The server MUST respond with a Control-Ack message. Again, 1 in the
   Accept field means rejection of command.  Zero means that data will
   follow.  All other values are reserved.

   If Accept was 0, the server then MUST send the OWAMP-Test session
   data in question, followed by 16 octets of Integrity Zero Padding.

   The OWAMP-Test session data consists of the following (concatenated):



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   +  A reproduction of the Request-Session command that was used to
      start the session; it is modified so that actual sender and
      receiver port numbers that were used by the OWAMP-Test session
      always appear in the reproduction.

   +  The number of packet records that will follow represented as an
      unsigned 4-octet integer.  This number might be less than the
      Number of Packets in the reproduction of the Request-Session
      command because of a session that ended prematurely; or it might
      be greater because of duplicates.

   +  12 octets of Integrity Zero Padding.

   +  Zero or more (as specified) packet records.


   Each packet record is 24 octets, and includes 4 octets of sequence
   number, 8 octets of send timestamp, 2 octets of send timestamp error
   estimate, 8 octets of receive timestamp, and 2 octets of receive
   timestamp error estimate (in this order).  Packet records are sent
   out in the same order they are made when the results of the session
   are recorded.  Therefore, the data is in arrival order.

   Note that lost packets (if any losses were detected during the OWAMP-
   Test session) MUST appear in the sequence of packets.  They can
   appear either at the point when the loss was detected or at any later
   point.  Lost packet records are distinguished by the receive
   timestamp consisting of a string of zero bits and an error estimate
   with Multiplier=1, Scale=64, and S=0 (see OWAMP-Test description for
   definition of these quantities and explanation of timestamp format
   and error estimate format).

   The last (possibly full, possibly incomplete) block (16 octets) of
   data is padded with zeros if necessary.  (These zeros are simple
   padding and should be distinguished from the 16 octets of Integrity
   Zero Padding that follow the session data and conclude the response
   to Fetch-Session.)


5. OWAMP-Test

   This section describes OWAMP-Test protocol.  It runs over UDP using
   sender and receiver IP and port numbers negotiated during Session-
   Prepare exchange.

   As OWAMP-Control, OWAMP-Test has three modes: unauthenticated,
   authenticated, and encrypted.  All OWAMP-Test sessions spawned by an
   OWAMP-Control session inherit its mode.



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   OWAMP-Control client, OWAMP-Control server, OWAMP-Test sender, and
   OWAMP-Test receiver can potentially all be different machines.  (In a
   typical case we expect that there will be only two machines.)


5.1. Sender Behavior

   The sender sends the receiver a stream of packets with exponential
   distribution of times between packets.  The format of the body of a
   UDP packet in the stream depends on the mode being used.

   For unauthenticated mode:

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Sequence Number                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Timestamp                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |        Error Estimate         |                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
        |                                                               |
        .                                                               .
        .                         Packet Padding                        .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For authenticated and encrypted modes:




















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         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Sequence Number                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |              Integrity Zero Padding (12 octets)               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Timestamp                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |        Error Estimate         |                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
        |              Integrity Zero Padding (6 octets)                |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                        Packet Padding                         .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the timestamp is the same as in RFC 1305 and is as
   follows: first 32 bits represent the unsigned integer number of
   seconds elapsed since 0h on 1 January 1900; next 32 bits represent
   the fractional part of a second that has elapsed since then.

   So, Timestamp is represented as follows:
         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                   Integer part of seconds                     |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                 Fractional part of seconds                    |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Error Estimate specifies the estimate of the error and
   synchronization.  It has the following format:

         0                   1
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |S|Z|   Scale   |   Multiplier  |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The first bit S is set if the party generating the timestamp has a
   clock that is synchronized to UTC using an external source (e.g., the



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   bit should be set if GPS hardware is used and it indicates that it
   has acquired current position and time or if NTP is used and it
   indicates that it has synchronized to an external source, which
   includes stratum 0 source, etc.); if there is no notion of external
   synchronization for the time source, the bit SHOULD NOT be set.  The
   next bit has the same semantics as MBZ fields elsewhere: it MUST be
   set to zero by the sender and ignored by everyone else.  The next six
   bits Scale form an unsigned integer; Multiplier is an unsigned
   integer as well.  They are interpreted as follows: the error estimate
   is equal to Multiplier*2^(-32)*2^Scale (in seconds).  [Notation
   clarification: 2^Scale is two to the power of Scale.]  Multiplier
   MUST NOT be set to zero.  If Multiplier is zero, the packet SHOULD be
   considered corrupt and discarded.

   Sequence numbers start with 0 and are incremented by 1 for each
   subsequent packet.

   The minimum data segment length is therefore 14 octets in
   unauthenticated mode, and 32 octets in authenticated mode and
   encrypted modes.

   The OWAMP-Test packet layout is the same in authenticated and
   encrypted modes.  The encryption operations are, however, different.
   The difference is that in encrypted mode both the sequence number and
   the timestamp are encrypted to provide maximum data integrity
   protection while in authenticated mode the sequence number is
   encrypted and the timestamp is sent in cleartext.  Sending the
   timestamp in cleartext in authenticated mode allows to reduce the
   time between a timestamp is obtained by a sender and the packet is
   shipped out.  In encrypted mode, the sender has to fetch the
   timestamp, encrypt it, and send it; in authenticated mode, the middle
   step is removed improving accuracy (the sequence number can be
   encrypted before the timestamp is fetched).

   In authenticated mode, the first block (16 octets) of each packet is
   encrypted using AES ECB mode.  The key to use is the same key as is
   used for the corresponding OWAMP-Control session (where it is used in
   a different chaining mode).  Electronic Cookbook (ECB) mode does not
   involve any actual chaining; this way, lost, duplicated, or reordered
   packets do not cause problems with decyphering any packet in an
   OWAMP-Test session.

   In encrypted mode, the first two blocks (32 octets) are encrypted
   using AES CBC mode.  The key to use is the same key as is used for
   the corresponding OWAMP-Control session.  Each OWAMP-Test packet is
   encrypted as a separate stream, with just one chaining operation;
   chaining does not span multiple packets so that lost, duplicated, or
   reordered packets do not cause problems.



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   In unauthenticated mode, no encryption is applied.

   Packet Padding in OWAMP-Test SHOULD be pseudo-random (it MUST be
   generated independently of any other pseudo-random numbers mentioned
   in this document).  However, implementations MUST provide a
   configuration parameter, an option, or a different means of making
   Packet Padding consist of all zeros.

   The time elapsed between packets is computed according to the slot
   schedule as mentioned in Request-Session command description.  At
   that point we skipped over the issue of computing exponentially
   distributed pseudo-random numbers in a repreduceable fashion.


6. Computing Exponentially Distributed Pseudo-Random Numbers

   [This section will describe the method based on the ziggurat
   algorithm to generate exponentially distributed PRNs without any
   machine-dependent operations (no floating point is used).]

   Pseudo-random stream of bits is obtained using AES with SID as the
   key, running in counter mode (first encrypted block is 0, second
   encrypted block is 1 in network octet order, etc.)  Each block of 64
   bits is used to obtain one pseudo-random number uniformly distributed
   between 0 and 1.  If the bits are Bj (j=1..64, numbered left to
   right), the resulting value is
        U = B1*2^{-1} + B2*2^{-2} + ... B64*2^{-64}


6.1. Receiver Behavior

   Receiver knows when the sender will send packets.  The following
   parameter is defined: Timeout (from Request-Session).  Packets that
   are delayed by more that Timeout are considered lost (or `as good as
   lost').  Note that there is never an actual assurance of loss by the
   network: a `lost' packet might still be delivered at any time.  The
   original specification for IPv4 required that packets be delivered
   within TTL seconds or never (with TTL having a maximum value of 255).
   To the best of the authors' knowledge, this requirement was never
   actually implemented (and of course only a complete and universal
   implementation would ensure that packets don't travel for longer than
   TTL seconds).  Further, IPv4 specification makes no claims about the
   time it takes the packet to traverse the last link of the path.

   The choice of a reasonable value of Timeout is a problem faced by a
   user of OWAMP protocol, not by an implementor.  A value such as two
   minutes is very safe.  Note that certain applications (such as
   interactive `one-way ping') might wish to obtain the data faster than



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   that.

   As packets are received,

   +  Timestamp the received packet.

   +  In authenticated or encrypted mode, decrypt first block (16
      octets) of packet body.

   +  Store the packet sequence number, send times, and receive times
      for the results to be transferred.

   +  Packets not received within the Timeout are considered lost.  They
      are recorded with their seqno, presumed send time, and receive
      time consisting of a string of zero bits.


   Packets that are actually received are recorded in the order of
   arrival.  Lost packet records serve as indications of the send times
   of lost packets.  They SHOULD be placed either at the point where the
   receiver learns about the loss or at any later point; in particular,
   one MAY place all the records that correspond to lost packets at the
   very end.

   Packets that have send time in the future MUST be recorded normally,
   without changing their send timestamp, unless they have to be
   discarded.  (Send timestamps in the future would normally indicate
   clocks that differ by more than the delay.  Some data -- such as
   jitter -- can be extracted even without knowledge of time difference.
   For other kinds of data, the adjustment is best handled by the data
   consumer on the basis of the complete information in a measurement
   session as well as possibly external data.)

   Packets with a sequence number that was already observed (duplicate
   packets) MUST be recorded normally.  (Duplicate packets are sometimes
   introduced by IP networks.  The protocol has to be able to measure
   duplication.)

   If any of the following is true, packet MUST be discarded:

   +  Send timestamp is more than Timeout in the past or in the future.

   +  Send timestamp differs by more than Timeout from the time when the
      packet should have been sent according to its seqno.

   +  In authenticated or encrypted mode, any of the bits of zero
      padding inside the first 16 octets of packet body is non-zero.




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7. Security Considerations

   The goal of authenticated mode to let one passphrase-protect service
   provided by a particular OWAMP-Control server.  One can imagine a
   variety of circumstances where this could be useful.  Authenticated
   mode is designed to prohibit theft of service.

   Additional design objective of authenticated mode was to make it
   impossible for an attacker who cannot read traffic between OWAMP-Test
   sender and receiver to tamper with test results in a fashion that
   affects the measurements, but not other traffic.

   The goal of encrypted mode is quite different: To make it hard for a
   party in the middle of the network to make results look `better' than
   they should be.  This is especially true if one of client and server
   doesn't coincide with neither sender nor receiver.

   Encryption of OWAMP-Control using AES CBC mode with blocks of zeros
   after each message aims to achieve two goals: (i) to provide secrecy
   of exchange; (ii) to provide authentication of each message.

   OWAMP-Test sessions directed at an unsuspecting party could be used
   for denial of service (DoS) attacks.  In unauthenticated mode servers
   should limits receivers to hosts they control or to the OWAMP-Control
   client.

   OWAMP-Test sessions could be used as covert channels of information.
   Environments that are worried about covert channels should take this
   into consideration.

   Notice that AES in counter mode is used for pseudo-random number
   generation, so implementation of AES MUST be included even in a
   server that only supports unauthenticated mode.


8. IANA Considerations

   IANA is requested to allocate a well-known TCP port number for OWAMP-
   Control part of the OWAMP protocol.












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9. Internationalization Considerations

   The protocol does not carry any information in a natural language.


10. Normative References


   [AES] Advanced Encryption Standard (AES),
        http://csrc.nist.gov/encryption/aes/

   [RFC1305] D. Mills, `Network Time Protocol (Version 3) Specification,
        Implementation and Analysis', RFC 1305, March 1992.

   [RFC1321] R. Rivest, `The MD5 Message-Digest Algorithm', RFC 1321,
        April 1992.

   [RFC2026] S. Bradner, `The Internet Standards Process -- Revision 3',
        RFC 2026, October 1996.

   [RFC2119] S. Bradner, `Key words for use in RFCs to Indicate
        Requirement Levels', RFC 2119, March 1997.

   [RFC2330] V. Paxon, G. Almes, J. Mahdavi, M. Mathis, `Framework for
        IP Performance Metrics' RFC 2330, May 1998.

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

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

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

   [RFC2836] S. Brim, B. Carpenter, F. Le Faucheur, `Per Hop Behavior
        Identification Codes', RFC 2836, May 2000.


11. Informative References


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

   [RIPE-NLUUG] H. Uijterwaal and O. Kolkman, `Internet Delay
        Measurements Using Test-Traffic', Spring 1998 Dutch Unix User



Shalunov et al.                                                [Page 26]

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        Group Meeting, http://www.ripe.net/test-
        traffic/Talks/9805_nluug.ps.gz.

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

   [SURVEYOR-INET] S. Kalidindi and M. Zekauskas, `Surveyor: An
        Infrastructure for Network Performance Measurements',
        Proceedings of INET'99, June 1999.
        http://www.isoc.org/inet99/proceedings/4h/4h_2.htm


12. Authors' Addresses

   Stanislav Shalunov
   Internet2 / UCAID
   200 Business Park Drive
   Armonk, NY  10504
   USA

   Phone: +1 914 765 1182
   EMail: shalunov@internet2.edu


   Benjamin Teitelbaum
   Advanced Network & Services
   200 Business Park Drive
   Armonk, NY 10504
   USA

   Phone: +1 914 765 1118
   EMail: ben@advanced.org

   Matthew J. Zekauskas
   Advanced Network & Services, Inc.
   200 Business Park Drive
   Armonk, NY  10504
   USA

   Phone: +1 914 765 1112
   EMail: matt@advanced.org


   Expiration date: February 2003








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