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Network Working Group                                        S. Shalunov
Internet Draft                                                 Internet2
Expiration Date: May 2001                                  B. Teitelbaum
                               Advanced Network & Services and Internet2
                                                            M. Zekauskas
                                             Advanced Network & Services
                                                           November 2000



                  A One-way Delay Measurement Protocol
                     <draft-ietf-ippm-owdp-00.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 to date no 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 delay 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 OWDP 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 OWDP include stealth, security, logical
   separation of control and test functionality, and support for small
   test packets.

   Stealth is achieved by making test packet streams look as much as
   possible like ordinary Internet traffic.  Towards this goal, OWDP's
   test protocol is layered over UDP and allows for a wide range of
   packet sizes and port numbers.  Additionally, OWDP supports an
   encrypted mode that obscures all transmitted data, making detection
   of OWDP test activity by Internet service providers very difficult.

   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 OWDP test streams or who
   attempt to modify sender-generated timestamps to falsify test
   results.

   OWDP actually consists of two inter-related protocols: OWDP-Control
   and OWDP-Test with several roles logically separated to allow for
   broad flexibility in use.  Specifically, the following roles are
   logically separate: Control-Client, Retrieve-Client, Server, Session-
   Source, and Session-Receiver.  The relationships between these are
   shown below.













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       +----------------+              +------------------+
       | Session-Source |--OWDP-Test-->| Session-Receiver |
       +----------------+              +------------------+
              ^                                ^
              |                                |
              |                                |
              V                                |
       +----------------+<---------------------+
       |     Server     |<------------+
       +----------------+             |
              ^                       |
              |                       |
         OWDP-Control            OWDP-Control
              |                       |
              V                       V
       +----------------+     +-----------------+
       | Control-Client |     | Retrieve-Client |
       +----------------+     +-----------------+

   A Control-Client speaks to a Server and may request test session
   initiation and may request that accepted test sessions be started and
   stopped. A Retrieve-Client also speaks to a Server and may request
   the results of an OWDP test session. The test session itself consists
   of a stream of singleton OWDP-Test packets sent from Session-Source
   to Session-Receiver.

   Any combination these logical blocks may, in fact, be collocated.

   [FIXME: Insert interesting examples.]

   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, OWDP has been
   designed to allow for small test packets that would fit inside the
   payload of a single ATM cell.


3. Protocol Overview

   OWDP actually consists of two inter-related protocols: OWDP-Control
   and OWDP-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 OWDP-Test sessions.  IANA will be



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   requested to allocate a well-known port number for OWDP-Control
   sessions.  OWDP server SHOULD listen to this well-known port.

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

   The protocol allows negotiating three modes of operation of OWDP-
   Control and OWDP-Test: unauthenticated, authenticated, and encrypted.
   If authenticated or encrypted mode is desired, endpoints must possess
   a shared secret.


3.1. OWDP-Control

   The client opens a TCP connection to the server on a well-known port.

   The server responds with server greeting:
         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 (15 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 it is
   willing to support during this session. If Modes is 1, the Challenge
   field MAY be committed.

   If Modes octet is zero (server doesn't wish to communicate with this
   client), the server MAY close the connection after this message.  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                |              Unused           |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                              KID                              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                       Token (32 octets)                       .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                     Client-IV (16 octets)                     .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Here Mode is the mode that the client chooses to use during this
   OWDP-Control session.  It will also be used for all OWDP-Test
   sessions started under control of this OWDP-Control session.

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

   Otherwise, KID (key ID) is a 4-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 KID.

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

   The server 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
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                      Unused (15 octets)                       .
        .                                                               .
        .                                               +-+-+-+-+-+-+-+-+
        |                                               |   Yes/No      |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                     Server-IV (16 octets)                     .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Here "Yes/No" is either 1 or 0.  Yes (0) means that the server
   accepts the authentication and is willing to conduct further
   transactions.  No (any non-zero value) means that the server doesn't
   accept authentication provided by the client, or for some other
   reason is not willing to conduct further transactions in this OWDP-
   Control session.

   If a "No" response is sent, the server MAY close the connection after
   this message.  The client SHOULD close the connection if it gets
   message that says "No" at this stage.

   The previous transactions constitute connection setup.

   In authenticated or encrypted mode (which are identical as far as
   OWDP-Control is concerned, and only differ in OWDP-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, End-Sessions, Retrieve-Session.  The command End-
   Sessions is available to both client and server.

   [FIXME: move next two paragraphs below?]  After Start-Sessions is
   sent/received by the client/server, and before it both sends and
   receives End-Sessions (order unspecified), it is said to be
   conducting active measurements.

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





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3.2. Creating Test Sessions

   Individual one-way delay measurement sessions are established using a
   simple request/response protocol. An OWDP client, may issue one or
   more Request-Session messages to an OWDP 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:
         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        |   Represents  | IPVN |        Unused          |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Source Address                         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |              Source Address (cont.) or Unused                 |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |           Unused              |              Port             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                        SID (16 octets)                        |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Dest Address                         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |               Dest Address (cont.) or Unused                  |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Inv-Lambda                           |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                            Packets                            |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                         Padding Length                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                           Start Time                          |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                            Accuracy                           |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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




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   Represents can have three values: Source (0), Dest (1), and Third-
   Party(2).  It tells the server on whose behalf the client is
   speaking.

   The meaning of Port depends on the value of Represents.  If it is
   Source, Port is the port to expect OWDP-Test packets from.  Is it is
   Dest, Port is the port to send OWDP-Test packets to. Port is unused
   in the case of a Third-Party client.

   The Source Address and Dest Address fields contain respectively the
   source and destination addresses of the end points of the Internet
   path over which an OWDP test session is requested.  The IPVN field
   contains the IP version number of the source and destination
   addresses that follow. In the case of IPVN=4, twelve unused octets
   follow each address.

   SID is the session identifier.  It can be used in later sessions as
   an argument for Retrieve-Session command.  It is meaningful only if
   Represents is Dest.

   The field Inv-Lambda is an unsigned integer and is the scaled
   reciprocal in microseconds of rate at which the Poisson test stream
   is to be generated.  This allows the average Poisson sampling
   interval for the requested test session to be set to between 1
   microsecond and over an hour.

   The value Packets is the number of active measurement packets to be
   sent during this OWDP-Test session (note that both server and client
   can abort the session early).

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

   To each Request-Session message, an OWDP 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                            |
        |                                                               |
        |                                                               |
        |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |           Unused              |              Port             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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        |                                                               |
        |                        SID (16 octets)                        |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Zero Padding                         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Zero in the Accept field means that the server is willing to conduct
   the session.  Any non-zero indicates rejection of the request.

   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 depend on the value of Represents in the query
   that solicited the response.  If it was Dest, Port is the port to
   expect OWDP-Test packets from.  Is it was Source, Port is the port to
   send OWDP-Test packets to.  If is was Third-Party, the Port field is
   unused.

   SID is a locally-unique server-generated session identifier.  It can
   be used later as handle to retrieve the results of a session.  An
   OWDP server MUST return an SID, if Represents was Source or Third-
   Party.  It is not meaningful if Represents was Dest.


3.3. Starting Test Sessions

   Having requested one or more test sessions and received affirmative
   Accept-Session responses, an OWDP 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:
















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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
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |      2        |                                               |
        +-+-+-+-+-+-+-+-+                                               |
        |                             Unused                            |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                    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:

         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                            |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                    Zero Padding (16 octets)                   |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If Accept has any non-zero value, the Start-Sessions request was
   rejected; zero means that the command was accepted.  The server MAY
   and the client SHOULD close the connection in the case of a negative
   response.

   The server SHOULD start all OWDP-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.) The
   client represents a Source, the client SHOULD start its OWDP-Test
   streams immediately after it sees the Control-Ack response from the
   Server.





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3.4. 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:

         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        |                                               |
        +-+-+-+-+-+-+-+-+                                               |
        |                             Unused                            |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                    Zero Padding (16 octets)                   |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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


3.5. Retrieve-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                            |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                              SID                              |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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        |                                                               |
        |                    Zero Padding (16 octets)                   |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The server MUST respond with a Control-Ack message. Again, any non-
   zero value in the Accept field means rejection of command.  Zero
   means that data will follow.

   If Yes/No was 0, the server then MUST send the OWDP-Test session data
   in question, followed by 16 octets of zero padding.

   Each packet is represented with 20 octets, and includes 4 octets of
   sequence number, 8 octets of send timestamp, and 8 octets of receive
   timestamp.

   The last (possibly full, possibly incomplete) block (16 octets) of
   data is padded with zeros.  A zero padding consisting of 16 octets is
   then appended.


4. OWDP-Test

   This section describes OWDP-Test protocol.  It runs over UDP using
   source and destination IP and port numbers negotiated during Session-
   Prepare exchange.

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

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


4.1. Sender Behavior

   The sender sends the receiver a stream of packets with Poisson
   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:







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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                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Timestamp                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                   Zero padding (0-65515 octets)               .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For authenticated 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                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                         Zero Padding                          |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Timestamp                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                                                               .
        .                   Zero padding (0-65503 octets)               .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For encrypted 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                            |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                         Zero Padding                          |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Shalunov et al.                                                [Page 13]

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        |                                                               |
        .                                                               .
        .                   Zero padding (0-65511 octets)               .
        .                                                               .
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of timestamp is the same as that of NTP v3 protocol
   [RFC958]. Quoting from RFC 958:

      NTP timestamps are represented as a 64-bit fixed-point number, in
      seconds relative to 0000 UT on 1 January 1900.  The integer part
      is in the first 32 bits and the fraction part in the last 32 bits,
      as shown in the following diagram.

       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                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Fraction Part                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      This format allows convenient multiple-precision arithmetic and
      conversion to Time Protocol representation (seconds), but does
      complicate the conversion to ICMP Timestamp message representation
      (milliseconds).  The low-order fraction bit increments at about
      0.2-nanosecond intervals, so a free-running one-millisecond clock
      will be in error only a small fraction of one part per million, or
      less than a second per year.

   Sequence numbers start with 0.

   The minimum data segment length is therefore 12 octets in
   unauthenticated mode, 24 octets in authenticated mode, and 16 octets
   in encrypted mode.

   In authenticated and encrypted mode, the first block (16 octets) of
   each packet is encrypted using AES ECB mode.

   In unauthenticated mode, no encryption is applied.

   The time elapsed between packets is (pseudo) random, with exponential
   (Poisson) distribution. As suggested in RFC 2330, the ith sampling
   interval Ei may be computed using inverse transform:

        Ei = -log(Ui) / lambda




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   where Ui is uniformly distributed between 0 and 1 and 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.)
   and lambda is the desired mean rate of the sampling distribution.
   [FIXME: should state precisely how the 16 byte block is interpreted
   as a number between 0 and 1].

   The parameter lambda is has the value requested in the Request-Session
   message of the OWDP-Control negotiation that spawned the session.

   The logarithm and division in the formula above MUST be computed using
   IEEE 754 standard floating point arithmetic. [HELP WANTED!: Someone
   with a stronger background in numerical analysis to specify how to
   compute the sampling intervals precisely and portably!]


4.2. Receiver Behavior

   FIXME: Expand this sketch.

   As packets are received,

   +  Timestamp the received packet.

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

   +  Packets not received within parameter Tl, the loss threshold are
      considered lost.  FIXME: loss threshold not mentioned above.  also
      need to decide if the receiver knows which packets are lost, and
      if so how is it represented in the results perhaps (seqno presumed
      send time, receive time of 0).



5. Security Considerations

   The goal of authenticated mode to let one be able to password-protect
   service provided by a particular OWDP-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 OWDP-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



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   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 OWDP-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.

   FIXME: More stuff to go here.

   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.


6. References

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

   [RFC958]D. Mills, "Network Time Protocol (NTP)", RFC 958, September
        1985.

   [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.

   [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.

   [RIPE]     Ripe Test-Traffic Home page, http://www.ripe.net/test-
        traffic/.

   [RIPE-NLUUG]H. Uijterwaal and O. Kolkman, "Internet Delay
        Measurements Using Test-Traffic", Spring 1998 Dutch Unix User
        Group Meeting, http://www.ripe.net/ripencc/mem-
        services/ttm/Talks/9805_nluug.ps.gz.  (NOTE: it's actually
        postscript, not gzip'd postscript.)

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



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   [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


7. 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: kalidindi@advanced.org


   Expiration date: May 2001













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