Network Working Group S. Shalunov
Internet Draft Internet2
Expiration Date: June 2001 B. Teitelbaum
Advanced Network & Services and Internet2
M. Zekauskas
Advanced Network & Services
December 2000
A One-way Delay Measurement Protocol
<draft-ietf-ippm-owdp-01.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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INTERNET-DRAFT One-way Delay Measurement Protocol December 2000
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. OWDP-Control is used to initiate, start, stop and
retrieve test sessions, while OWDP-Test is the actual one-way delay
test protocol that exchanges singleton test packets between two
measurement nodes.
Several roles are logically separated to allow for broad flexibility
in use. Specifically, we define:
Session-Sender the sending endpoint of an OWDP-Test session;
Session-Receiver the receiving endpoint of an OWDP-Test session;
Server an end system that manages one or more OWDP-Test
sessions, is capable of configuring per-session
state in session endpoints, and is capable of
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returning the results of a test session;
Control-Client an end system that initiates requests for
OWDP-Test sessions, triggers the start of a set
of sessions, and may trigger their termination;
Retrieve-Client an end system that initiates requests to retrieve
the results of completed OWDP-Test sessions;
One possible scenario of relationships between these roles is shown
below.
+----------------+ +------------------+
| Session-Sender |--OWDP-Test-->| Session-Receiver |
+----------------+ +------------------+
^ ^
| |
| |
| |
| +----------------+<----------------+
| | Server |<-------+
| +----------------+ |
| ^ |
| | |
| OWDP-Control OWDP-Control
| | |
v v v
+----------------+ +-----------------+
| Control-Client | | Retrieve-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, Retrieve-Client, and Session-
Sender, and the other playing the roles of Server and Session-
Receiver. This is shown below.
+-----------------+ +------------------+
| Control-Client |<--OWDP-Control-->| Server |
| Retrieve-Client | | |
| Session-Sender |---OWDP-Test----->| Session-Receiver |
+-----------------+ +------------------+
Finally, because many Internet paths include segments that transport
IP over ATM, delay and loss measurements can include the effects of
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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 (this is only achieved in
unauthenticated and encrypted modes).
3. Protocol Overview
OWDP 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
requested to allocate a well-known port number for OWDP-Control
sessions. An OWDP server SHOULD listen to this well-known port.
OWDP-Control messages are transmitted only before OWDP-Test sessions
are actually started and after they complete (with the possible
exception of an early Stop-Session message).
The OWDP-Control and OWDP-Test protocols support three modes of
operation: unauthenticated, authenticated, and encrypted. The
authenticated or encrypted modes require endpoints to possess a
shared secret.
4. OWDP-Control
4.1. Connection Setup
Before either a Control-Client or a Retrieve-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 (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 that it is
willing to support during this session.
If the Modes octet 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:
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) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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:
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) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A zero value in the "Yes/No" field means that the server accepts the
authentication and is willing to conduct further transactions. Any
non-zero value 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 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.
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4.2. OWDP-Control Commands
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, Stop-Session, Retrieve-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.
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 delay measurement sessions are established using a
simple request/response protocol. An OWDP client MAY issue zero 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:
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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 |IPVN-S | IPVN-R| Conf-Sender | Conf-Receiver |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Address (cont.) or Unused |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Address (cont.) or Unused |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Port | Receiver Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | Flags | PHB ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inv-Lambda |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Time |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Precision | Receiver Precision |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Zero Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Here the first octet (1) indicates that this is Request-Session
command.
IPVN-S and IPVN-R are IP version numbers for Sender and Receiver. In
the case of IP version number being 4, twelve unused octets follow
the four-octet address.
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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.
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 OWDP test session is requested.
SID is the session identifier. It can be used in later sessions as
an argument for Retrieve-Session command. It is meaningful only if
Conf-Receiver is 1.
The field Inv-Lambda is an unsigned integer and is the scaled
reciprocal of rate (in microseconds) 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).
Start Time is the time when the session is to be started (but not
before Start-Sessions command is issued).
Sender Precision and Receiver Precision are signed integers in the
range +32 to -32 indicating the precision of the corresponding
clocks, in seconds to the nearest power of two, as described in
RFC 958. Sender Precision is meaningful only if Conf-Sender is not
set. Receiver Precision is meaningful only if Conf-Receiver is not
set.
To each Request-Session message, an OWDP server MUST respond with an
Accept-Session 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Accept | Unused | Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Precision | Receiver Precision |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Zero Padding |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Zero in the Accept field means that the server is willing to conduct
the session. Any non-zero value 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 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 OWDP-Test packets from. If only Conf-Receiver was set,
Port is the port to send OWDP-Test packets to.
If only Conf-Sender was set, SID is unused. Otherwise, SID is a
unique server-generated session identifier. It can be used later as
handle to retrieve 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.
Sender Precision and Receiver Precision have the same meaning as in
Request-Session command. Sender Precision is meaningful only if
Conf-Sender is set. Receiver Precision is meaningful only if Conf-
Receiver is set.
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4.4. 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:
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.
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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.) If
the client represents a Sender, the client SHOULD start its OWDP-Test
streams immediately after it sees the Control-Ack response from the
Server.
4.5. 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 | Accept | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| 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.
Non-zero value of Accept indicates a failure of some sort. Zero
values indicates normal (but possibly premature) completion. 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 OWDP-Control breaking), results of all OWDP-Test sessions
spawned by this OWDP-Control session SHOULD be considered invalid,
even if Retrieve-Session with SID from this session works during a
different OWDP-Control session.
The party that receives this command MUST stop its OWDP-Test streams
and respond with a Stop-Sessions message. Any non-zero value in
Accept field means something went wrong. A zero value means OWDP-
Test streams have been successfully stopped.
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4.6. 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 |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| 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.
The transmission starts with 4 octets that contain the number of
records that will follow, each record representing one received
packet. This is followed by 2 octets of Sender Precision, 2 octets
of Receiver precision, and 8 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.
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5. OWDP-Test
This section describes OWDP-Test protocol. It runs over UDP using
sender and receiver 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.)
5.1. 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:
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 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet padding (0-65515 octets) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For authenticated 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Zero Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet 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.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
distribution (resulting in a Poisson stream of packets). As
suggested in RFC 2330, the ith sampling interval Ei may be computed
using inverse transform:
Ei = -ln(Ui) * Inv-Lambda
where Ui is uniformly distributed between 0 and 1 and lambda is the
desired mean time between packets.
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}
The parameter lambda is has the value requested in the Request-
Session message of the OWDP-Control negotiation that spawned the
session.
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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!]
Finally, Packet Padding SHOULD be pseudo-random (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.
5.2. Receiver Behavior
Receiver knows when the sender will send packets. The following
parameter is defined: loss threshold. It SHOULD be 10 minutes and
MAY be more, but not more than 60 minutes.
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 loss threshold are considered
lost. They are recorded with their seqno, presumed send time, and
receive time consisting of a string of zero bits.
Packets that have send time in the future MUST be recorded normally,
without changing their send timestamp, unless they have to be
discarded.
If any of the following is true, packet MUST be discarded:
+ Send timestamp is more than loss threshold in the past or in the
future.
+ Send timestamp differs by more than loss threshold 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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6. Security Considerations
The goal of authenticated mode to let one 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
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.
OWDP-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 OWDP-Control
client.
OWDP-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.
7. 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.
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INTERNET-DRAFT One-way Delay Measurement Protocol December 2000
[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.
[RFC2836]S. Brim, B. Carpenter, F. Le Faucheur, "Per Hop Behavior
Identification Codes", RFC 2836, May 2000.
[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/.
[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
8. Authors' Addresses
Stanislav Shalunov
Internet2 / UCAID
200 Business Park Drive
Armonk, NY 10504
USA
Phone: +1 914 765 1182
EMail: shalunov@internet2.edu
Shalunov et al. [Page 19]
INTERNET-DRAFT One-way Delay Measurement Protocol December 2000
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: June 2001
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