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Keywords: [--------|p], unidirectional characteristics, one-way, gps, cdma
Network Working Group S. Shalunov
Request for Comments: 4656 B. Teitelbaum
Category: Standards Track A. Karp
J. Boote
M. Zekauskas
Internet2
September 2006
A One-way Active Measurement Protocol (OWAMP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The One-Way Active Measurement Protocol (OWAMP) measures
unidirectional characteristics such as one-way delay and one-way
loss. High-precision measurement of these one-way IP performance
metrics became possible with wider availability of good time sources
(such as GPS and CDMA). OWAMP enables the interoperability of these
measurements.
Table of Contents
1. Introduction ....................................................2
1.1. Relationship of Test and Control Protocols .................3
1.2. Logical Model ..............................................4
2. Protocol Overview ...............................................5
3. OWAMP-Control ...................................................6
3.1. Connection Setup ...........................................6
3.2. Integrity Protection (HMAC) ...............................11
3.3. Values of the Accept Field ................................11
3.4. OWAMP-Control Commands ....................................12
3.5. Creating Test Sessions ....................................13
3.6. Send Schedules ............................................18
3.7. Starting Test Sessions ....................................19
3.8. Stop-Sessions .............................................20
3.9. Fetch-Session .............................................24
Shalunov, et al. Standards Track [Page 1]
RFC 4656 One-way Active Measurement Protocol September 2006
4. OWAMP-Test .....................................................27
4.1. Sender Behavior ...........................................28
4.1.1. Packet Timings .....................................28
4.1.2. OWAMP-Test Packet Format and Content ...............29
4.2. Receiver Behavior .........................................33
5. Computing Exponentially Distributed Pseudo-Random Numbers ......35
5.1. High-Level Description of the Algorithm ...................35
5.2. Data Types, Representation, and Arithmetic ................36
5.3. Uniform Random Quantities .................................37
6. Security Considerations ........................................38
6.1. Introduction ..............................................38
6.2. Preventing Third-Party Denial of Service ..................38
6.3. Covert Information Channels ...............................39
6.4. Requirement to Include AES in Implementations .............39
6.5. Resource Use Limitations ..................................39
6.6. Use of Cryptographic Primitives in OWAMP ..................40
6.7. Cryptographic Primitive Replacement .......................42
6.8. Long-term Manually Managed Keys ...........................43
6.9. (Not) Using Time as Salt ..................................44
6.10. The Use of AES-CBC and HMAC ..............................44
7. Acknowledgements ...............................................45
8. IANA Considerations ............................................45
9. Internationalization Considerations ............................46
10. References ....................................................46
10.1. Normative References .....................................46
10.2. Informative References ...................................47
Appendix A: Sample C Code for Exponential Deviates ................49
Appendix B: Test Vectors for Exponential Deviates .................54
1. Introduction
The IETF IP Performance Metrics (IPPM) working group has defined
metrics for one-way packet delay [RFC2679] and loss [RFC2680] across
Internet paths. Although there are now several measurement platforms
that implement collection of these metrics [SURVEYOR] [SURVEYOR-INET]
[RIPE] [BRIX], there is not currently a standard that would permit
initiation of test streams or exchange of packets to collect
singleton metrics in an interoperable manner.
With the increasingly wide availability of affordable global
positioning systems (GPS) and CDMA-based time sources, hosts
increasingly have available to them very accurate time sources,
either directly or through their proximity to Network Time Protocol
(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
Shalunov, et al. Standards Track [Page 2]
RFC 4656 One-way Active Measurement Protocol September 2006
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. (Being hard to
detect makes interference with measurements more difficult for
intermediaries in the middle of the network.)
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, as well). OWAMP
also supports an encrypted mode that further obscures the traffic and
makes 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 attacks
that attempt to provide special treatment to OWAMP test streams or
that attempt to modify sender-generated timestamps to falsify test
results.
In this document, the key words "MUST", "REQUIRED", "SHOULD",
"RECOMMENDED", and "MAY" are to be interpreted as described in
[RFC2119].
1.1. 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 to fetch their results, whereas 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 RFC 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 ensuring a future in
which inter-domain one-way active measurement could become as
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
Shalunov, et al. Standards Track [Page 3]
RFC 4656 One-way Active Measurement Protocol September 2006
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 network characteristics across
differentiated services networks. Additionally, OWAMP-Control
supports per-session encryption and authentication for both test and
control traffic, measurement servers that can 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
Simple Network Management Protocol (SNMP) or proprietary network
management protocols is required, gateways may be created.
1.2. Logical Model
Several roles are logically separated to allow for broad flexibility
in use. Specifically, we define the following:
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;
and
Fetch-Client An end system that initiates requests to fetch
the results of completed OWAMP-Test sessions.
Shalunov, et al. Standards Track [Page 4]
RFC 4656 One-way Active Measurement Protocol September 2006
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 document 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 mode).
Shalunov, et al. Standards Track [Page 5]
RFC 4656 One-way Active Measurement Protocol September 2006
2. 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, 861, on the target point and this connection
remains open for the duration of the OWAMP-Test 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 are completed (with the
possible exception of an early Stop-Sessions message).
The OWAMP-Control and OWAMP-Test protocols support three modes of
operation: unauthenticated, authenticated, and encrypted. The
authenticated or encrypted modes require that endpoints possess a
shared secret.
All multi-octet quantities defined in this document are represented
as unsigned integers in network byte order unless specified
otherwise.
3. OWAMP-Control
The type of each OWAMP-Control message can be found after reading the
first 16 octets. The length of each OWAMP-Control message can be
computed upon reading its fixed-size part. No message is shorter
than 16 octets.
An implementation SHOULD expunge unused state to prevent denial-of-
service attacks, or unbounded memory usage, on the server. For
example, if the full control message is not received within some
number of minutes after it is expected, the TCP connection associated
with the OWAMP-Control session SHOULD be dropped. In absence of
other considerations, 30 minutes seems like a reasonable upper bound.
3.1. Connection Setup
Before either a Control-Client or a Fetch-Client can issue commands
to a Server, it has to establish a connection to the server.
First, a client opens a TCP connection to the server on a well-known
port 861. The server responds with a server greeting:
Shalunov, et al. Standards Track [Page 6]
RFC 4656 One-way Active Measurement Protocol September 2006
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) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Salt (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following Mode values are meaningful: 1 for unauthenticated, 2
for authenticated, and 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, the 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.)
Challenge is a random sequence of octets generated by the server; it
is used subsequently by the client to prove possession of a shared
secret in a manner prescribed below.
Salt and Count are parameters used in deriving a key from a shared
secret as described below.
Salt MUST be generated pseudo-randomly (independently of anything
else in this document).
Count MUST be a power of 2. Count MUST be at least 1024. Count
SHOULD be increased as more computing power becomes common.
Shalunov, et al. Standards Track [Page 7]
RFC 4656 One-way Active Measurement Protocol September 2006
If the Modes value is zero, the server does not wish to communicate
with the client and MAY close the connection immediately. The client
SHOULD close the connection if it receives a greeting with Modes
equal to zero. The client MAY close the connection if the client's
desired mode is unavailable.
Otherwise, the client MUST respond with the following Set-Up-Response
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. KeyID (80 octets) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Token (64 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. If it is
one bit that is set within the last three bits, this bit MUST
indicate a mode that the server agreed to use (i.e., the same bit
MUST have been set by the server in the server greeting). The first
29 bits of Mode MUST be zero. A server MUST ignore the values of the
first 29 bits. If zero Mode bits are set by the client, the client
indicates that it will not continue with the session; in this case,
the client and the server SHOULD close the TCP connection associated
with the OWAMP-Control session.
Shalunov, et al. Standards Track [Page 8]
RFC 4656 One-way Active Measurement Protocol September 2006
In unauthenticated mode, KeyID, Token, and Client-IV are unused.
Otherwise, KeyID is a UTF-8 string, up to 80 octets in length (if the
string is shorter, it is padded with zero octets), that tells the
server which shared secret the client wishes to use to authenticate
or encrypt, while Token is the concatenation of a 16-octet challenge,
a 16-octet AES Session-key used for encryption, and a 32-octet HMAC-
SHA1 Session-key used for authentication. The token itself is
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 derived from the shared
secret associated with KeyID. (Both the server and the client use
the same mappings from KeyIDs to shared secrets. The server, being
prepared to conduct sessions with more than one client, uses KeyIDs
to choose the appropriate secret key; a client would typically have
different secret keys for different servers. The situation is
analogous to that with passwords.)
The shared secret is a passphrase; it MUST not contain newlines. The
secret key is derived from the passphrase using a password-based key
derivation function PBKDF2 (PKCS #5) [RFC2898]. The PBKDF2 function
requires several parameters: the PRF is HMAC-SHA1 [RFC2104]; the salt
and count are as transmitted by the server.
AES Session-key, HMAC Session-key and Client-IV are generated
randomly by the client. AES Session-key and HMAC Session-key MUST be
generated with sufficient entropy not to reduce the security of the
underlying cipher [RFC4086]. Client-IV merely needs to be unique
(i.e., it MUST never be repeated for different sessions using the
same secret key; a simple way to achieve that without the use of
cumbersome state is to generate the Client-IV values using a
cryptographically secure pseudo-random number source: if this is
done, the first repetition is unlikely to occur before 2^64 sessions
with the same secret key are conducted).
Shalunov, et al. Standards Track [Page 9]
RFC 4656 One-way Active Measurement Protocol September 2006
The server MUST respond with the following Server-Start 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (15 octets) |
| |
| +-+-+-+-+-+-+-+-+
| | Accept |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Server-IV (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-Time (Timestamp) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The MBZ parts MUST be zero. The client MUST ignore their value. MBZ
(MUST be zero) fields here and after have the same semantics: the
party that sends the message MUST set the field so that all bits are
equal to zero; the party that interprets the message MUST ignore the
value. (This way, the field could be used for future extensions.)
Server-IV is generated randomly by the server. In unauthenticated
mode, Server-IV is unused.
The Accept field indicates the server's willingness to continue
communication. A zero value in the Accept field means that the
server accepts the authentication and is willing to conduct further
transactions. Non-zero values indicate that the server does not
accept the authentication or, for some other reason, is not willing
to conduct further transactions in this OWAMP-Control session. The
full list of available Accept values is described in Section 3.3,
"Values of the Accept Field".
If a negative (non-zero) response is sent, the server MAY (and the
client SHOULD) close the connection after this message.
Start-Time is a timestamp representing the time when the current
instantiation of the server started operating. (For example, in a
multi-user general purpose operating system, it could be the time
when the server process was started.) If Accept is non-zero, Start-
Shalunov, et al. Standards Track [Page 10]
RFC 4656 One-way Active Measurement Protocol September 2006
Time SHOULD be set so that all of its bits are zeros. In
authenticated and encrypted modes, Start-Time is encrypted as
described in Section 3.4, "OWAMP-Control Commands", unless Accept is
non-zero. (Authenticated and encrypted mode cannot be entered unless
the control connection can be initialized.)
Timestamp format is described in Section 4.1.2. The same
instantiation of the server SHOULD report the same exact Start-Time
value to each client in each session.
The previous transactions constitute connection setup.
3.2. Integrity Protection (HMAC)
Authentication of each message (also referred to as a command in this
document) in OWAMP-Control is accomplished by adding an HMAC to it.
The HMAC that OWAMP uses is HMAC-SHA1 truncated to 128 bits. Thus,
all HMAC fields are 16 octets. An HMAC needs a key. The HMAC
Session-key is communicated along with the AES Session-key during
OWAMP-Control connection setup. The HMAC Session-key SHOULD be
derived independently of the AES Session-key (an implementation, of
course, MAY use the same mechanism to generate the random bits for
both keys). Each HMAC sent covers everything sent in a given
direction between the previous HMAC (but not including it) and up to
the beginning of the new HMAC. This way, once encryption is set up,
each bit of the OWAMP-Control connection is authenticated by an HMAC
exactly once.
When encrypting, authentication happens before encryption, so HMAC
blocks are encrypted along with the rest of the stream. When
decrypting, the order, of course, is reversed: first one decrypts,
then one checks the HMAC, then one proceeds to use the data.
The HMAC MUST be checked as early as possible to avoid using and
propagating corrupt data.
In open mode, the HMAC fields are unused and have the same semantics
as MBZ fields.
3.3. Values of the Accept Field
Accept values are used throughout the OWAMP-Control protocol to
communicate the server response to client requests. The full set of
valid Accept field values are as follows:
0 OK.
1 Failure, reason unspecified (catch-all).
Shalunov, et al. Standards Track [Page 11]
RFC 4656 One-way Active Measurement Protocol September 2006
2 Internal error.
3 Some aspect of request is not supported.
4 Cannot perform request due to permanent resource limitations.
5 Cannot perform request due to temporary resource limitations.
All other values are reserved. The sender of the message MAY use the
value of 1 for all non-zero Accept values. A message sender SHOULD
use the correct Accept value if it is going to use other values. The
message receiver MUST interpret all values of Accept other than these
reserved values as 1. This way, other values are available for
future extensions.
3.4. 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 AES Session-key (using
CBC mode) and authenticated with HMAC Session-key. The client
encrypts everything it sends through the just-established OWAMP-
Control connection using stream encryption with Client-IV as the IV.
Correspondingly, the server encrypts its side of the connection using
Server-IV as the IV.
The IVs themselves are transmitted in cleartext. Encryption starts
with the block immediately following the block containing the IV.
The two streams (one going from the client to the server and one
going back) are encrypted independently, each with its own IV, but
using the same key (the AES Session-key).
The following commands are available for the client: Request-Session,
Start-Sessions, Stop-Sessions, and Fetch-Session. The command Stop-
Sessions is available to both the client and the server. (The server
can also send other messages in response to commands it receives.)
After the client sends the Start-Sessions command and until it both
sends and receives (in an unspecified order) the Stop-Sessions
command, it is said to be conducting active measurements. Similarly,
the server is said to be conducting active measurements after it
receives the Start-Sessions command and until it both sends and
receives (in an unspecified order) the Stop-Sessions command.
While conducting active measurements, the only command available is
Stop-Sessions.
These commands are described in detail below.
Shalunov, et al. Standards Track [Page 12]
RFC 4656 One-way Active Measurement Protocol September 2006
3.5. 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.
Shalunov, et al. Standards Track [Page 13]
RFC 4656 One-way Active Measurement Protocol September 2006
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 | MBZ | IPVN | Conf-Sender | Conf-Receiver |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Schedule Slots |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Packets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Port | Receiver Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Sender Address (cont.) or MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Receiver Address (cont.) or MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Time |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timeout, (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-P Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Shalunov, et al. Standards Track [Page 14]
RFC 4656 One-way Active Measurement Protocol September 2006
This is immediately followed by one or more schedule slot
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 (7 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Slot Parameter (Timestamp) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
These are immediately followed by HMAC:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All these messages constitute one logical message: the Request-
Session command.
Above, the first octet (1) indicates that this is the Request-Session
command.
IPVN is the IP version numbers for Sender and Receiver. When the IP
version number is 4, 12 octets follow the 4-octet IPv4 address stored
in Sender Address and Receiver Address. These octets MUST be set to
zero by the client and MUST be ignored by the server. Currently
meaningful IPVN values are 4 and 6.
Conf-Sender and Conf-Receiver MUST be set to 0 or 1 by the client.
The server MUST interpret any non-zero value as 1. If the value is
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.)
Shalunov, et al. Standards Track [Page 15]
RFC 4656 One-way Active Measurement Protocol September 2006
Number of Schedule Slots, as mentioned before, specifies the number
of slot records that go between the two blocks of HMAC. 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
sent during this OWAMP-Test session (note that either the server or
the client can abort the session early).
If Conf-Sender is not set, Sender Port is the UDP port from which
OWAMP-Test packets will be sent. If Conf-Receiver is not set,
Receiver Port is the UDP port OWAMP-Test to which packets are
requested to be sent.
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 the 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 the 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 (or a loss threshold) 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 the Type-P Descriptor are 00, then the
subsequent six bits specify the requested Differentiated Services
Codepoint (DSCP) value of sent OWAMP-Test packets, as defined in
[RFC2474]. If the first two bits of Type-P descriptor are 01, then
the subsequent 16 bits specify the requested PHB Identification Code
(PHB ID), as defined in [RFC2836].
Therefore, the value of all zeros specifies the default best-effort
service.
Shalunov, et al. Standards Track [Page 16]
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If Conf-Sender is set, the Type-P Descriptor is to be used to
configure the sender to send packets according to its value. If
Conf-Sender is not set, the Type-P Descriptor is a declaration of how
the sender will be configured.
If Conf-Sender is set and the server does not recognize the Type-P
Descriptor, or it cannot or does not wish to set the corresponding
attributes on OWAMP-Test packets, it SHOULD reject the session
request. If Conf-Sender is not set, the server SHOULD accept or
reject the session, paying no attention to the value of the Type-P
Descriptor.
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 | MBZ | Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this message, zero in the Accept field means that the server is
willing to conduct the session. A non-zero value indicates rejection
of the request. The full list of available Accept values is
described in Section 3.3, "Values of the Accept Field".
If the server rejects a Request-Session message, it SHOULD not close
the TCP connection. The client MAY close it if it receives a
negative response to the Request-Session message.
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, the Port field is unused. If only Conf-Sender was
set, Port is the port from which to expect OWAMP-Test packets. If
Shalunov, et al. Standards Track [Page 17]
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only Conf-Receiver was set, Port is the port to which OWAMP-Test
packets are sent.
If only Conf-Sender was set, the 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 the 4-octet IPv4 IP
number belonging to the generating machine, an 8-octet timestamp, and
a 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 four octets of an IPv6 address MAY be used instead. Note that
SID is always chosen by the receiver. If truly random values are not
available, it is important that the SID be made unpredictable, as
knowledge of the SID might be used for access control.
3.6. Send Schedules
The sender and the receiver both need to know the same send schedule.
This way, when packets are lost, the receiver knows when they were
supposed to be 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 slot 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 (fixed quantity) 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 an
exponentially distributed time with a 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.
The sender and the receiver need to be able to reproducibly execute
the entire schedule (so, if a packet is lost, the receiver can still
attach a send timestamp to it). Slots of type 1 are trivial to
Shalunov, et al. Standards Track [Page 18]
RFC 4656 One-way Active Measurement Protocol September 2006
reproducibly execute. To reproducibly execute slots of type 0, we
need to be able to generate pseudo-random exponentially distributed
quantities in a reproducible manner. The way this is accomplished is
discussed later in Section 5, "Computing Exponentially Distributed
Pseudo-Random Numbers".
Using this mechanism, one can easily specify common testing
scenarios. The following are some examples:
+ 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.
Further, 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.
3.7. 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 | |
+-+-+-+-+-+-+-+-+ |
| MBZ (15 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The server MUST respond with an Start-Ack message (which SHOULD be
sent as quickly as possible). Start-Ack messages have the following
format:
Shalunov, et al. Standards Track [Page 19]
RFC 4656 One-way Active Measurement Protocol September 2006
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 | |
+-+-+-+-+-+-+-+-+ |
| MBZ (15 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If Accept is non-zero, the Start-Sessions request was rejected; zero
means that the command was accepted. The full list of available
Accept values is described in Section 3.3, "Values of the Accept
Field". The server MAY, and the client SHOULD, close the connection
in the case of a rejection.
The server SHOULD start all OWAMP-Test streams immediately after it
sends the response or immediately after their specified start times,
whichever is later. If the client represents a Sender, the client
SHOULD start its OWAMP-Test streams immediately after it sees the
Start-Ack response from the Server (if the Start-Sessions command was
accepted) or immediately after their specified start times, whichever
is later. See more on OWAMP-Test sender behavior in a separate
section below.
3.8. 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 | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Sessions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is immediately followed by zero or more session description
records (the number of session description records is specified in
Shalunov, et al. Standards Track [Page 20]
RFC 4656 One-way Active Measurement Protocol September 2006
the "Number of Sessions" field above). The session description
record is used to indicate which packets were actually sent by the
sender process (rather than skipped). The header of the session
description record 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Seqno |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Skip Ranges |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is immediately followed by zero or more Skip Range descriptions
as specified by the "Number of Skip Ranges" field above. Skip Ranges
are simply two sequence numbers that, together, indicate a range of
packets that were not sent:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| First Seqno Skipped |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno Skipped |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Skip Ranges MUST be in order. The last (possibly full, possibly
incomplete) block (16 octets) of data MUST be padded with zeros, if
necessary. This ensures that the next session description record
starts on a block boundary.
Finally, a single block (16 octets) of HMAC is concatenated on the
end to complete the Stop-Sessions message.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All these records comprise one logical message: the Stop-Sessions
command.
Shalunov, et al. Standards Track [Page 21]
RFC 4656 One-way Active Measurement Protocol September 2006
Above, the first octet (3) indicates that this is the Stop-Sessions
command.
Non-zero Accept values indicate a failure of some sort. Zero values
indicate normal (but possibly premature) completion. The full list
of available Accept values is described in Section 3.3, "Values of
the Accept Field".
If Accept had a non-zero value (from either party), results of all
OWAMP-Test sessions spawned by this OWAMP-Control session SHOULD be
considered invalid, even if a Fetch-Session with SID from this
session works for a different OWAMP-Control session. If Accept was
not transmitted at all (for whatever reason, including the TCP
connection used for OWAMP-Control breaking), the results of all
OWAMP-Test sessions spawned by this OWAMP-control session MAY be
considered invalid.
Number of Sessions indicates the number of session description
records that immediately follow the Stop-Sessions header.
Number of Sessions MUST contain the number of send sessions started
by the local side of the control connection that have not been
previously terminated by a Stop-Sessions command (i.e., the Control-
Client MUST account for each accepted Request-Session where Conf-
Receiver was set; the Control-Server MUST account for each accepted
Request-Session where Conf-Sender was set). If the Stop-Sessions
message does not account for exactly the send sessions controlled by
that side, then it is to be considered invalid and the connection
SHOULD be closed and any results obtained considered invalid.
Each session description record represents one OWAMP-Test session.
SID is the session identifier (SID) used to indicate which send
session is being described.
Next Seqno indicates the next sequence number that would have been
sent from this send session. For completed sessions, this will equal
NumPackets from the Request-Session.
Number of Skip Ranges indicates the number of holes that actually
occurred in the sending process. This is a range of packets that
were never actually sent by the sending process. For example, if a
send session is started too late for the first 10 packets to be sent
and this is the only hole in the schedule, then "Number of Skip
Ranges" would be 1. The single Skip Range description will have
First Seqno Skipped equal to 0 and Last Seqno Skipped equal to 9.
This is described further in the "Sender Behavior" section.
Shalunov, et al. Standards Track [Page 22]
RFC 4656 One-way Active Measurement Protocol September 2006
If the OWAMP-Control connection breaks when the Stop-Sessions command
is sent, the receiver MAY not completely invalidate the session
results. It MUST discard all record of packets that follow (in other
words, that have greater sequence number than) the last packet that
was actually received before any lost packet records. This will help
differentiate between packet losses that occurred in the network and
packets the sending process may have never sent.
If a receiver of an OWAMP-Test session learns, through an OWAMP-
Control Stop-Sessions message, that the OWAMP-Test sender's last
sequence number is lower than any sequence number actually received,
the results of the complete OWAMP-Test session MUST be invalidated.
A receiver of an OWAMP-Test session, upon receipt of an OWAMP-Control
Stop-Sessions command, MUST discard any packet records -- including
lost packet records -- with a (computed) send time that falls between
the current time minus Timeout and the current time. This ensures
statistical consistency for the measurement of loss and duplicates in
the event that the Timeout is greater than the time it takes for the
Stop-Sessions command to take place.
To effect complete sessions, each side of the control connection
SHOULD wait until all sessions are complete before sending the Stop-
Sessions message. The completed time of each session is determined
as Timeout after the scheduled time for the last sequence number.
Endpoints MAY add a small increment to the computed completed time
for send endpoints to ensure that the Stop-Sessions message reaches
the receiver endpoint after Timeout.
To effect a premature stop of sessions, the party that initiates this
command MUST stop its OWAMP-Test send streams to send the Session
Packets Sent values before sending this command. That party SHOULD
wait until receiving the response Stop-Sessions message before
stopping the receiver streams so that it can use the values from the
received Stop-Sessions message to validate the data.
Shalunov, et al. Standards Track [Page 23]
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3.9. 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 | |
+-+-+-+-+-+-+-+-+ |
| MBZ (7 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Begin Seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End Seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (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 normally, 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).
Shalunov, et al. Standards Track [Page 24]
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The server MUST respond with a Fetch-Ack message. The format of this
server response 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Accept | Finished | MBZ (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Seqno |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Skip Ranges |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Records |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Again, non-zero in the Accept field means a rejection of command.
The server MUST specify zero for all remaining fields if Accept is
non-zero. The client MUST ignore all remaining fields (except for
the HMAC) if Accept is non-zero. The full list of available Accept
values is described in Section 3.3, "Values of the Accept Field".
Finished is non-zero if the OWAMP-Test session has terminated.
Next Seqno indicates the next sequence number that would have been
sent from this send session. For completed sessions, this will equal
NumPackets from the Request-Session. This information is only
available if the session has terminated. If Finished is zero, then
Next Seqno MUST be set to zero by the server.
Number of Skip Ranges indicates the number of holes that actually
occurred in the sending process. This information is only available
if the session has terminated. If Finished is zero, then Skip Ranges
MUST be set to zero by the server.
Number of Records is the number of packet records that fall within
the requested range. 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.
If Accept was non-zero, this concludes the response to the Fetch-
Session message. If Accept was 0, the server then MUST immediately
send the OWAMP-Test session data in question.
Shalunov, et al. Standards Track [Page 25]
RFC 4656 One-way Active Measurement Protocol September 2006
The OWAMP-Test session data consists of the following (concatenated):
+ 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.
+ Zero or more (as specified) Skip Range descriptions. The last
(possibly full, possibly incomplete) block (16 octets) of Skip
Range descriptions is padded with zeros, if necessary.
+ 16 octets of HMAC.
+ Zero or more (as specified) packet records. The last (possibly
full, possibly incomplete) block (16 octets) of data is padded
with zeros, if necessary.
+ 16 octets of HMAC.
Skip Range descriptions are simply two sequence numbers that,
together, indicate a range of packets that were not sent:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| First Seqno Skipped |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno Skipped |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Skip Range descriptions should be sent out in order, as sorted by
First Seqno. If any Skip Ranges overlap or are out of order, the
session data is to be considered invalid and the connection SHOULD be
closed and any results obtained considered invalid.
Each packet record is 25 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, 2 octets of receive
timestamp error estimate, and 1 octet of Time To Live (TTL), or Hop
Limit in IPv6:
Shalunov, et al. Standards Track [Page 26]
RFC 4656 One-way Active Measurement Protocol September 2006
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
00| Seq Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
04| Send Error Estimate | Receive Error Estimate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
08| Send Timestamp |
12| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16| Receive Timestamp |
20| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
24| TTL |
+-+-+-+-+-+-+-+-+
Packet records are sent out in the same order the actual packets were
received. 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 as follows:
+ A send timestamp filled with the presumed send time (as computed
by the send schedule).
+ A send error estimate filled with Multiplier=1, Scale=64, and S=0
(see the OWAMP-Test description for definition of these quantities
and explanation of timestamp format and error estimate format).
+ A normal receive error estimate as determined by the error of the
clock being used to declare the packet lost. (It is declared lost
if it is not received by the Timeout after the presumed send time,
as determined by the receiver's clock.)
+ A receive timestamp consisting of all zero bits.
+ A TTL value of 255.
4. OWAMP-Test
This section describes OWAMP-Test protocol. It runs over UDP, using
sender and receiver IP and port numbers negotiated during the
Request-Session exchange.
Shalunov, et al. Standards Track [Page 27]
RFC 4656 One-way Active Measurement Protocol September 2006
As with OWAMP-Control, OWAMP-Test has three modes: unauthenticated,
authenticated, and encrypted. All OWAMP-Test sessions that are
spawned by an OWAMP-Control session inherit its mode.
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.)
4.1. Sender Behavior
4.1.1. Packet Timings
Send schedules based on slots, described previously, in conjunction
with scheduled session start time, enable the sender and the receiver
to compute the same exact packet sending schedule independently of
each other. These sending schedules are independent for different
OWAMP-Test sessions, even if they are governed by the same OWAMP-
Control session.
Consider any OWAMP-Test session. Once Start-Sessions exchange is
complete, the sender is ready to start sending packets. Under normal
OWAMP use circumstances, the time to send the first packet is in the
near future (perhaps a fraction of a second away). The sender SHOULD
send packets as close as possible to their scheduled time, with the
following exception: if the scheduled time to send is in the past,
and is separated from the present by more than Timeout time, the
sender MUST NOT send the packet. (Indeed, such a packet would be
considered lost by the receiver anyway.) The sender MUST keep track
of which packets it does not send. It will use this to tell the
receiver what packets were not sent by setting Skip Ranges in the
Stop-Sessions message from the sender to the receiver upon completion
of the test. The Skip Ranges are also sent to a Fetch-Client as part
of the session data results. These holes in the sending schedule can
happen if a time in the past was specified in the Request-Session
command, or if the Start-Sessions exchange took unexpectedly long, or
if the sender could not start serving the OWAMP-Test session on time
due to internal scheduling problems of the OS. Packets that are in
the past but are separated from the present by less than Timeout
value SHOULD be sent as quickly as possible. With normal test rates
and timeout values, the number of packets in such a burst is limited.
Nevertheless, hosts SHOULD NOT intentionally schedule sessions so
that such bursts of packets occur.
Regardless of any scheduling delays, each packet that is actually
sent MUST have the best possible approximation of its real time of
departure as its timestamp (in the packet).
Shalunov, et al. Standards Track [Page 28]
RFC 4656 One-way Active Measurement Protocol September 2006
4.1.2. OWAMP-Test Packet Format and Content
The sender sends the receiver a stream of packets with the schedule
specified in the Request-Session command. The sender SHOULD set the
TTL in IPv4 (or Hop Limit in IPv6) in the UDP packet to 255. 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 .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Shalunov, et al. Standards Track [Page 29]
RFC 4656 One-way Active Measurement Protocol September 2006
For authenticated and encrypted modes:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the timestamp is the same as in [RFC1305] and is as
follows: the first 32 bits represent the unsigned integer number of
seconds elapsed since 0h on 1 January 1900; the 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Shalunov, et al. Standards Track [Page 30]
RFC 4656 One-way Active Measurement Protocol September 2006
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, SHOULD be set if the party generating the timestamp
has a clock that is synchronized to UTC using an external source
(e.g., the 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 zero and are incremented by one for each
subsequent packet.
The minimum data segment length is, therefore, 14 octets in
unauthenticated mode, and 48 octets in both authenticated mode and
encrypted modes.
The OWAMP-Test packet layout is the same in authenticated and
encrypted modes. The encryption and authentication operations are,
however, different. The difference is that in encrypted mode both
the sequence number and the timestamp are protected to provide
maximum data confidentiality and integrity protection, whereas in
authenticated mode the sequence number is protected while the
timestamp is sent in clear text. Sending the timestamp in clear text
in authenticated mode allows one to reduce the time between when a
timestamp is obtained by a sender and when 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,
potentially improving accuracy (the sequence number can be encrypted
and authenticated before the timestamp is fetched).
In authenticated mode, the first block (16 octets) of each packet is
encrypted using AES Electronic Cookbook (ECB) mode.
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Similarly to each OWAMP-Control session, each OWAMP-Test session has
two keys: an AES Session-key and an HMAC Session-key. However, there
is a difference in how the keys are obtained: in the case of OWAMP-
Control, the keys are generated by the client and communicated (as
part of the Token) during connection setup as part of Set-Up-Response
message; in the case of OWAMP-Test, described here, the keys are
derived from the OWAMP-Control keys and the SID.
The OWAMP-Test AES Session-key is obtained as follows: the OWAMP-
Control AES Session-key (the same AES Session-key as is used for the
corresponding OWAMP-Control session, where it is used in a different
chaining mode) is encrypted, using AES, with the 16-octet session
identifier (SID) as the key; this is a single-block ECB encryption;
its result is the OWAMP-Test AES Session-key to use in encrypting
(and decrypting) the packets of the particular OWAMP-Test session.
Note that all of OWAMP-Test AES Session-key, OWAMP-Control AES
Session-key, and the SID are comprised of 16 octets.
The OWAMP-Test HMAC Session-key is obtained as follows: the OWAMP-
Control HMAC Session-key (the same HMAC Session-key as is used for
the corresponding OWAMP-Control session) is encrypted, using AES,
with the 16-octet session identifier (SID) as the key; this is a
two-block CBC encryption, always performed with IV=0; its result is
the OWAMP-Test HMAC Session-key to use in authenticating the packets
of the particular OWAMP-Test session. Note that all of OWAMP-Test
HMAC Session-key and OWAMP-Control HMAC Session-key are comprised of
32 octets, while the SID is 16 octets.
ECB mode used for encrypting the first block of OWAMP-Test packets in
authenticated mode does not involve any actual chaining; this way,
lost, duplicated, or reordered packets do not cause problems with
deciphering any packet in an OWAMP-Test session.
In encrypted mode, the first two blocks (32 octets) are encrypted
using AES CBC mode. The AES Session-key to use is obtained in the
same way as the key for authenticated mode. 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. The initialization vector
for the CBC encryption is a value with all bits equal to zero.
Implementation note: Naturally, the key schedule for each OWAMP-Test
session MAY be set up only once per session, not once per packet.
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HMAC in OWAMP-Test only covers the part of the packet that is also
encrypted. So, in authenticated mode, HMAC covers the first block
(16 octets); in encrypted mode, HMAC covers two first blocks (32
octets). In OWAMP-Test HMAC is not encrypted (note that this is
different from OWAMP-Control, where encryption in stream mode is
used, so everything including the HMAC blocks ends up being
encrypted).
In unauthenticated mode, no encryption or authentication 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 reproducible fashion. It is
discussed later in a separate section.
4.2. Receiver Behavior
The receiver knows when the sender will send packets. The following
parameter is defined: Timeout (from Request-Session). Packets that
are delayed by more than 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 do not travel for longer
than TTL seconds). In fact, in IPv6, the name of this field has
actually been changed to Hop Limit. 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
that.
As packets are received,
+ timestamp the received packet;
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+ in authenticated or encrypted mode, decrypt and authenticate as
necessary (packets for which authentication fails MUST be
discarded); and
+ store the packet sequence number, send time, receive time, and the
TTL for IPv4 (or Hop Limit for IPv6) from the packet IP header for
the results to be transferred.
Packets not received within the Timeout are considered lost. They
are recorded with their true sequence number, presumed send time,
receive time value with all bits being zero, and a TTL (or Hop Limit)
of 255.
Implementations SHOULD fetch the TTL/Hop Limit value from the IP
header of the packet. If an implementation does not fetch the actual
TTL value (the only good reason not to do so is an inability to
access the TTL field of arriving packets), it MUST record the TTL
value as 255.
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, the 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 sequence number.
+ In authenticated or encrypted mode, HMAC verification fails.
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5. Computing Exponentially Distributed Pseudo-Random Numbers
Here we describe the way exponential random quantities used in the
protocol are generated. While there is a fair number of algorithms
for generating exponential random variables, most of them rely on
having logarithmic function as a primitive, resulting in potentially
different values, depending on the particular implementation of the
math library. We use algorithm 3.4.1.S from [KNUTH], which is free
of the above-mentioned problem, and which guarantees the same output
on any implementation. The algorithm belongs to the ziggurat family
developed in the 1970s by G. Marsaglia, M. Sibuya, and J. H. Ahrens
[ZIGG]. It replaces the use of logarithmic function by clever bit
manipulation, still producing the exponential variates on output.
5.1. High-Level Description of the Algorithm
For ease of exposition, the algorithm is first described with all
arithmetic operations being interpreted in their natural sense.
Later, exact details on data types, arithmetic, and generation of the
uniform random variates used by the algorithm are given. It is an
almost verbatim quotation from [KNUTH], p.133.
Algorithm S: Given a real positive number "mu", produce an
exponential random variate with mean "mu".
First, the constants
Q[k] = (ln2)/(1!) + (ln2)^2/(2!) + ... + (ln2)^k/(k!), 1 <= k <= 11
are computed in advance. The exact values which MUST be used by all
implementations are given in the next section. This is necessary to
ensure that exactly the same pseudo-random sequences are produced by
all implementations.
S1. [Get U and shift.] Generate a 32-bit uniform random binary
fraction
U = (.b0 b1 b2 ... b31) [note the binary point]
Locate the first zero bit b_j and shift off the leading (j+1) bits,
setting U <- (.b_{j+1} ... b31)
Note: In the rare case that the zero has not been found, it is
prescribed that the algorithm return (mu*32*ln2).
S2. [Immediate acceptance?] If U < ln2, set X <- mu*(j*ln2 + U) and
terminate the algorithm. (Note that Q[1] = ln2.)
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S3. [Minimize.] Find the least k >= 2 such that U < Q[k]. Generate k
new uniform random binary fractions U1,...,Uk and set V <-
min(U1,...,Uk).
S4. [Deliver the answer.] Set X <- mu*(j + V)*ln2.
5.2. Data Types, Representation, and Arithmetic
The high-level algorithm operates on real numbers, typically
represented as floating point numbers. This specification prescribes
that unsigned 64-bit integers be used instead.
u_int64_t integers are interpreted as real numbers by placing the
decimal point after the first 32 bits. In other words, conceptually,
the interpretation is given by the following map:
u_int64_t u;
u |--> (double)u / (2**32)
The algorithm produces a sequence of such u_int64_t integers that,
for any given value of SID, is guaranteed to be the same on any
implementation.
We specify that the u_int64_t representations of the first 11 values
of the Q array in the high-level algorithm MUST be as follows:
#1 0xB17217F8,
#2 0xEEF193F7,
#3 0xFD271862,
#4 0xFF9D6DD0,
#5 0xFFF4CFD0,
#6 0xFFFEE819,
#7 0xFFFFE7FF,
#8 0xFFFFFE2B,
#9 0xFFFFFFE0,
#10 0xFFFFFFFE,
#11 0xFFFFFFFF
For example, Q[1] = ln2 is indeed approximated by 0xB17217F8/(2**32)
= 0.693147180601954; for j > 11, Q[j] is 0xFFFFFFFF.
Small integer j in the high-level algorithm is represented as
u_int64_t value j * (2**32).
Operation of addition is done as usual on u_int64_t numbers; however,
the operation of multiplication in the high-level algorithm should be
replaced by
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(u, v) |---> (u * v) >> 32.
Implementations MUST compute the product (u * v) exactly. For
example, a fragment of unsigned 128-bit arithmetic can be implemented
for this purpose (see the sample implementation in Appendix A).
5.3. Uniform Random Quantities
The procedure for obtaining a sequence of 32-bit random numbers (such
as U in algorithm S) relies on using AES encryption in counter mode.
To describe the exact working of the algorithm, we introduce two
primitives from Rijndael. Their prototypes and specification are
given below, and they are assumed to be provided by the supporting
Rijndael implementation, such as [RIJN].
+ A function that initializes a Rijndael key with bytes from seed
(the SID will be used as the seed):
void KeyInit(unsigned char seed[16]);
+ A function that encrypts the 16-octet block inblock with the
specified key, returning a 16-octet encrypted block. Here,
keyInstance is an opaque type used to represent Rijndael keys:
void BlockEncrypt(keyInstance key, unsigned char inblock[16]);
Algorithm Unif: given a 16-octet quantity seed, produce a sequence of
unsigned 32-bit pseudo-random uniformly distributed integers. In
OWAMP, the SID (session ID) from Control protocol plays the role of
seed.
U1. [Initialize Rijndael key] key <- KeyInit(seed) [Initialize an
unsigned 16-octet (network byte order) counter] c <- 0
U2. [Need more random bytes?] Set i <- c mod 4. If (i == 0) set s
<- BlockEncrypt(key, c)
U3. [Increment the counter as unsigned 16-octet quantity] c <- c + 1
U4. [Do output] Output the i_th quartet of octets from s starting
from high-order octets, converted to native byte order and
represented as OWPNum64 value (as in 3.b).
U5. [Loop] Go to step U2.
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6. Security Considerations
6.1. Introduction
The goal of authenticated mode is to let one passphrase-protect the
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.
An additional design objective of the 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
does not coincide with either sender or receiver.
Encryption of OWAMP-Control using AES CBC mode with blocks of HMAC
after each message aims to achieve two goals: (i) to provide secrecy
of exchange, and (ii) to provide authentication of each message.
6.2. Preventing Third-Party Denial of Service
OWAMP-Test sessions directed at an unsuspecting party could be used
for denial of service (DoS) attacks. In unauthenticated mode,
servers SHOULD limit receivers to hosts they control or to the OWAMP-
Control client.
Unless otherwise configured, the default behavior of servers MUST be
to decline requests where the Receiver Address field is not equal to
the address that the control connection was initiated from or an
address of the server (or an address of a host it controls). Given
the TCP handshake procedure and sequence numbers in the control
connection, this ensures that the hosts that make such requests are
actually those hosts themselves, or at least on the path towards
them. If either this test or the handshake procedure were omitted,
it would become possible for attackers anywhere in the Internet to
request that large amounts of test packets be directed against victim
nodes somewhere else.
In any case, OWAMP-Test packets with a given source address MUST only
be sent from the node that has been assigned that address (i.e.,
address spoofing is not permitted).
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6.3. Covert Information Channels
OWAMP-Test sessions could be used as covert channels of information.
Environments that are worried about covert channels should take this
into consideration.
6.4. Requirement to Include AES in Implementations
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.
6.5. Resource Use Limitations
An OWAMP server can consume resources of various kinds. The two most
important kinds of resources are network capacity and memory (primary
or secondary) for storing test results.
Any implementation of OWAMP server MUST include technical mechanisms
to limit the use of network capacity and memory. Mechanisms for
managing the resources consumed by unauthenticated users and users
authenticated with a KeyID and passphrase SHOULD be separate. The
default configuration of an implementation MUST enable these
mechanisms and set the resource use limits to conservatively low
values.
One way to design the resource limitation mechanisms is as follows:
assign each session to a user class. User classes are partially
ordered with "includes" relation, with one class ("all users") that
is always present and that includes any other class. The assignment
of a session to a user class can be based on the presence of
authentication of the session, the KeyID, IP address range, time of
day, and, perhaps, other factors. Each user class would have a limit
for usage of network capacity (specified in units of bit/second) and
memory for storing test results (specified in units of octets).
Along with the limits for resource use, current use would be tracked
by the server. When a session is requested by a user in a specific
user class, the resources needed for this session are computed: the
average network capacity use (based on the sending schedule) and the
maximum memory use (based on the number of packets and number of
octets each packet would need to be stored internally -- note that
outgoing sessions would not require any memory use). These resource
use numbers are added to the current resource use numbers for the
given user class; if such addition would take the resource use
outside of the limits for the given user class, the session is
rejected. When resources are reclaimed, corresponding measures are
subtracted from the current use. Network capacity is reclaimed as
soon as the session ends. Memory is reclaimed when the data is
Shalunov, et al. Standards Track [Page 39]
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deleted. For unauthenticated sessions, memory consumed by an OWAMP-
Test session SHOULD be reclaimed after the OWAMP-Control connection
that initiated the session is closed (gracefully or otherwise). For
authenticated sessions, the administrator who configures the service
should be able to decide the exact policy, but useful policy
mechanisms that MAY be implemented are the ability to automatically
reclaim memory when the data is retrieved and the ability to reclaim
memory after a certain configurable (based on user class) period of
time passes after the OWAMP-Test session terminates.
6.6. Use of Cryptographic Primitives in OWAMP
At an early stage in designing the protocol, we considered using
Transport Layer Security (TLS) [RFC2246, RFC3546] and IPsec [RFC2401]
as cryptographic security mechanisms for OWAMP; later, we also
considered DTLS. The disadvantages of those are as follows (not an
exhaustive list):
Regarding TLS:
+ TLS could be used to secure TCP-based OWAMP-Control, but it would
be difficult to use it to secure UDP-based OWAMP-Test: OWAMP-Test
packets, if lost, are not resent, so packets have to be
(optionally) encrypted and authenticated while retaining
individual usability. Stream-based TLS cannot be easily used for
this.
+ Dealing with streams, TLS does not authenticate individual
messages (even in OWAMP-Control). The easiest way out would be to
add some known-format padding to each message and to verify that
the format of the padding is intact before using the message. The
solution would thus lose some of its appeal ("just use TLS"). It
would also be much more difficult to evaluate the security of this
scheme with the various modes and options of TLS; it would almost
certainly not be secure with all. The capacity of an attacker to
replace parts of messages (namely, the end) with random garbage
could have serious security implications and would need to be
analyzed carefully. Suppose, for example, that a parameter that
is used in some form to control the rate were replaced by random
garbage; chances are that the result (an unsigned integer) would
be quite large.
+ Dependent on the mode of use, one can end up with a requirement
for certificates for all users and a PKI. Even if one is to
accept that PKI is desirable, there just isn't a usable one today.
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+ TLS requires a fairly large implementation. OpenSSL, for example,
is larger than our implementation of OWAMP as a whole. This can
matter for embedded implementations.
Regarding DTLS:
+ Duplication and, similarly, reordering are network phenomena that
OWAMP needs to be able to measure; yet anti-replay measures and
reordering protection of DTLS would prevent the duplicated and
reordered packets from reaching the relevant part of the OWAMP
code. One could, of course, modify DTLS so that these protections
are weakened or even specify examining the messages in a carefully
crafted sequence somewhere in between DTLS checks; but then, of
course, the advantage of using an existing protocol would not be
realized.
+ In authenticated mode, the timestamp is in the clear and is not
protected cryptographically in any way, while the rest of the
message has the same protection as in encrypted mode. This mode
allows one to trade off cryptographic protection against accuracy
of timestamps. For example, the APAN hardware implementation of
OWAMP [APAN] is capable of supporting authenticated mode. The
accuracy of these measurements is in the sub-microsecond range.
The errors in OWAMP measurements of Abilene [Abilene] (done using
a software implementation, in its encrypted mode) exceed 10us.
Users in different environments have different concerns, and some
might very well care about every last microsecond of accuracy. At
the same time, users in these same environments might care about
access control to the service. Authenticated mode permits them to
control access to the server yet to use unprotected timestamps,
perhaps generated by a hardware device.
Regarding IPsec:
+ What we now call authenticated mode would not be possible (in
IPsec you can't authenticate part of a packet).
+ The deployment paths of IPsec and OWAMP could be separate if OWAMP
does not depend on IPsec. After nine years of IPsec, only 0.05%
of traffic on an advanced backbone network, such as Abilene, uses
IPsec (for comparison purposes with encryption above layer 4, SSH
use is at 2-4% and HTTPS use is at 0.2-0.6%). It is desirable to
be able to deploy OWAMP on as large a number of different
platforms as possible.
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+ The deployment problems of a protocol dependent on IPsec would be
especially acute in the case of lightweight embedded devices.
Ethernet switches, DSL "modems", and other such devices mostly do
not support IPsec.
+ The API for manipulating IPsec from an application is currently
poorly understood. Writing a program that needs to encrypt some
packets, to authenticate some packets, and to leave some open --
for the same destination -- would become more of an exercise in
IPsec than in IP measurement.
For the enumerated reasons, we decided to use a simple cryptographic
protocol (based on a block cipher in CBC mode) that is different from
TLS and IPsec.
6.7. Cryptographic Primitive Replacement
It might become necessary in the future to replace AES, or the way it
is used in OWAMP, with a new cryptographic primitive, or to make
other security-related changes to the protocol. OWAMP provides a
well-defined point of extensibility: the Modes word in the server
greeting and the Mode response in the Set-Up-Response message. For
example, if a simple replacement of AES with a different block cipher
with a 128-bit block is needed, this could be accomplished as
follows: take two bits from the reserved (MBZ) part of the Modes word
of the server greeting; use one of these bits to indicate encrypted
mode with the new cipher and another one to indicate authenticated
mode with the new cipher. (Bit consumption could, in fact, be
reduced from two to one, if the client is allowed to return a mode
selection with more than a single bit set: one could designate a
single bit to mean that the new cipher is supported (in the case of
the server) or selected (in the case of the client) and continue to
use already allocated bits for authenticated and encrypted modes;
this optimization is unimportant conceptually, but it could be useful
in practice to make the best use of bits.) Then, if the new cipher
is negotiated, all subsequent operations simply use it instead of
AES. Note that the normal transition sequence would be used in such
a case: implementations would probably first start supporting and
preferring the new cipher, and then drop support for the old cipher
(presumably no longer considered secure).
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If the need arises to make more extensive changes (perhaps to replace
AES with a 256-bit-block cipher), this would be more difficult and
would require changing the layout of the messages. However, the
change can still be conducted within the framework of OWAMP
extensibility using the Modes/Mode words. The semantics of the new
bits (or single bit, if the optimization described above is used)
would include the change to message layout as well as the change in
the cryptographic primitive.
Each of the bits in the Modes word can be used for an independent
extension. The extensions signaled by various bits are orthogonal;
for example, one bit might be allocated to change from AES-128 to
some other cipher, another bit might be allocated to add a protocol
feature (such as, e.g., support for measuring over multicast), yet
another might be allocated to change a key derivation function, etc.
The progression of versions is not a linear order, but rather a
partial order. An implementation can implement any subset of these
features (of course, features can be made mandatory to implement,
e.g., new more secure ciphers if they are needed).
Should a cipher with a different key size (say, a 256-bit key) become
needed, a new key derivation function for OWAMP-Test keys would also
be needed. The semantics of change in the cipher SHOULD then in the
future be tied to the semantics of change in the key derivation
function (KDF). One KDF that might be considered for the purpose
might be a pseudo-random function (PRF) with appropriately sized
output, such as 256 bits (perhaps HMAC-SHA256, if it is then still
considered a secure PRF), which could then be used to derive the
OWAMP-Test session keys from the OWAMP-Control session key by using
the OWAMP-Control session key as the HMAC key and the SID as HMAC
message.
Note that the replacement scheme outlined above is trivially
susceptible to downgrade attacks: a malicious party in the middle can
flip modes bits as the mode is negotiated so that the oldest and
weakest mode supported by the two parties is used. If this is deemed
problematic at the time of cryptographic primitive replacement, the
scheme might be augmented with a measure to prevent such an attack
(by perhaps exchanging the modes again once a secure communications
channel is established, comparing the two sets of mode words, and
dropping the connection should they not match).
6.8. Long-term Manually Managed Keys
OWAMP-Control uses long-term keys with manual management. These keys
are used to automatically negotiate session keys for each OWAMP-
Control session running in authenticated or encrypted mode. The
number of these keys managed by a server scales linearly with (and,
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in fact, is equal to) the number of administratively different users
(perhaps particular humans, roles, or robots representing sites) that
need to connect to this server. Similarly, the number of different
manual keys managed by each client is the number of different servers
that the client needs to connect to. This use of manual long-term
keys is compliant with [BCP107].
6.9. (Not) Using Time as Salt
A natural idea is to use the current time as salt when deriving
session keys. Unfortunately, this appears to be too limiting.
Although OWAMP is often run on hosts with well-synchronized clocks,
it is also possible to run it on hosts with clocks completely
untrained. The delays obtained thus are, of course, not directly
usable; however, some metrics, such as unidirectional loss,
reordering, measures of congestion such as the median delay minus
minimum, and many others are usable directly and immediately (and
improve upon the information that would have been provided by a
round-trip measurement). Further, even delay information can be
useful with appropriate post-processing. Indeed, one can even argue
that running the clocks free and post-processing the results of a
mesh of measurements will result in better accuracy, as more
information is available a posteriori and correlation of data from
different hosts is possible in post-processing, but not with online
clock training.
Given this, time is not used as salt in key derivation.
6.10. The Use of AES-CBC and HMAC
OWAMP relies on AES-CBC for confidentiality and on HMAC-SHA1
truncated to 128 bits for message authentication. Random IV choice
is important for prevention of a codebook attack on the first block
(it should also be noted that, with its 128-bit block size, AES is
more resistant to codebook attacks than are ciphers with shorter
blocks; we use random IV anyway).
HMAC MUST verify. It is crucial to check for this before using the
message; otherwise, existential forgery becomes possible. The
complete message for which HMAC verification fails MUST be discarded
(both for short messages consisting of a few blocks and potentially
for long messages, such as a response to the Fetch-Session command).
If such a message is part of OWAMP-Control, the connection MUST be
dropped.
Since OWAMP messages can have different numbers of blocks, the
existential forgery attack described in example 9.62 of [MENEZES]
Shalunov, et al. Standards Track [Page 44]
RFC 4656 One-way Active Measurement Protocol September 2006
becomes a concern. To prevent it (and to simplify implementation),
the length of any message becomes known after decrypting its first
block.
A special case is the first (fixed-length) message sent by the
client. There, the token is a concatenation of the 128-bit challenge
(transmitted by the server in the clear), a 128-bit AES Session-key
(generated randomly by the client, encrypted with AES-CBC with IV=0),
and a 256-bit HMAC-SHA1 Session-key used for authentication. Since
IV=0, the challenge (a single cipher block) is simply encrypted with
the secret key. Therefore, we rely on resistance of AES to chosen
plaintext attacks (as the challenge could be substituted by an
attacker). It should be noted that the number of blocks of chosen
plaintext an attacker can have encrypted with the secret key is
limited by the number of sessions the client wants to initiate. An
attacker who knows the encryption of a server's challenge can produce
an existential forgery of the session key and thus disrupt the
session; however, any attacker can disrupt a session by corrupting
the protocol messages in an arbitrary fashion. Therefore, no new
threat is created here; nevertheless, we require that the server
never issues the same challenge twice. (If challenges are generated
randomly, a repetition would occur, on average, after 2^64 sessions;
we deem this satisfactory as this is enough even for an implausibly
busy server that participates in 1,000,000 sessions per second to go
without repetitions for more than 500 centuries.) With respect to
the second part of the token, an attacker can produce an existential
forgery of the session key by modifying the second half of the
client's token while leaving the first part intact. This forgery,
however, would be immediately discovered by the client when the HMAC
on the server's next message (acceptance or rejection of the
connection) does not verify.
7. Acknowledgements
We would like to thank Guy Almes, Mark Allman, Jari Arkko, Hamid
Asgari, Steven Van den Berghe, Eric Boyd, Robert Cole, Joan
Cucchiara, Stephen Donnelly, Susan Evett, Sam Hartman, Kaynam
Hedayat, Petri Helenius, Scott Hollenbeck, Russ Housley, Kitamura
Yasuichi, Daniel H. T. R. Lawson, Will E. Leland, Bruce A. Mah,
Allison Mankin, Al Morton, Attila Pasztor, Randy Presuhn, Matthew
Roughan, Andy Scherrer, Henk Uijterwaal, and Sam Weiler for their
comments, suggestions, reviews, helpful discussion and proof-reading.
8. IANA Considerations
IANA has allocated a well-known TCP port number (861) for the OWAMP-
Control part of the OWAMP protocol.
Shalunov, et al. Standards Track [Page 45]
RFC 4656 One-way Active Measurement Protocol September 2006
9. Internationalization Considerations
The protocol does not carry any information in a natural language,
with the possible exception of the KeyID in OWAMP-Control, which is
encoded in UTF-8.
10. References
10.1. Normative References
[AES] Advanced Encryption Standard (AES),
http://csrc.nist.gov/encryption/aes/
[BCP107] Bellovin, S. and R. Housley, "Guidelines for
Cryptographic Key Management", BCP 107, RFC 4107,
June 2005.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
Keyed-Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May
1998.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-
way Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-
way Packet Loss Metric for IPPM", RFC 2680, September
1999.
[RFC2836] Brim, S., Carpenter, B., and F. Le Faucheur, "Per Hop
Behavior Identification Codes", RFC 2836, May 2000.
[RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography
Specification Version 2.0", RFC 2898, September 2000.
Shalunov, et al. Standards Track [Page 46]
RFC 4656 One-way Active Measurement Protocol September 2006
10.2. Informative References
[APAN] Z. Shu and K. Kobayashi, "HOTS: An OWAMP-Compliant
Hardware Packet Timestamper", In Proceedings of PAM
2005, http://www.springerlink.com/index/
W4GBD39YWC11GQTN.pdf
[BRIX] Brix Networks, http://www.brixnet.com/
[ZIGG] J. H. Ahrens, U. Dieter, "Computer methods for
sampling from the exponential and normal
distributions", Communications of ACM, volume 15,
issue 10, 873-882, 1972.
http://doi.acm.org/10.1145/355604.361593
[MENEZES] A. J. Menezes, P. C. van Oorschot, and S. A.
Vanstone, Handbook of Applied Cryptography, CRC
Press, revised reprint with updates, 1997.
[KNUTH] D. Knuth, The Art of Computer Programming, vol.2, 3rd
edition, 1998.
[Abilene] One-way Latency Measurement (OWAMP),
http://e2epi.internet2.edu/owamp/
[RIJN] Reference ANSI C Implementation of Rijndael,
http://www.esat.kuleuven.ac.be/~rijmen/
rijndael/rijndaelref.zip
[RIPE] RIPE NCC Test-Traffic Measurements home,
http://www.ripe.net/test-traffic/.
[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
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation and Analysis", RFC
1305, March 1992.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version
1.0", RFC 2246, January 1999.
Shalunov, et al. Standards Track [Page 47]
RFC 4656 One-way Active Measurement Protocol September 2006
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
[RFC3546] Blake-Wilson, S., Nystrom, M., Hopwood, D.,
Mikkelsen, J., and T. Wright, "Transport Layer
Security (TLS) Extensions", RFC 3546, June 2003.
[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC
4086, June 2005.
Shalunov, et al. Standards Track [Page 48]
RFC 4656 One-way Active Measurement Protocol September 2006
Appendix A: Sample C Code for Exponential Deviates
The values in array Q[] are the exact values that MUST be used by all
implementations (see Sections 5.1 and 5.2). This appendix only
serves for illustrative purposes.
/*
** Example usage: generate a stream of exponential (mean 1)
** random quantities (ignoring error checking during initialization).
** If a variate with some mean mu other than 1 is desired, the output
** of this algorithm can be multiplied by mu according to the rules
** of arithmetic we described.
** Assume that a 16-octet 'seed' has been initialized
** (as the shared secret in OWAMP, for example)
** unsigned char seed[16];
** OWPrand_context next;
** (initialize state)
** OWPrand_context_init(&next, seed);
** (generate a sequence of exponential variates)
** while (1) {
** u_int64_t num = OWPexp_rand64(&next);
<do something with num here>
...
** }
*/
#include <stdlib.h>
typedef u_int64_t u_int64_t;
/* (K - 1) is the first k such that Q[k] > 1 - 1/(2^32). */
#define K 12
#define BIT31 0x80000000UL /* See if first bit in the lower
32 bits is zero. */
#define MASK32(n) ((n) & 0xFFFFFFFFUL)
#define EXP2POW32 0x100000000ULL
typedef struct OWPrand_context {
unsigned char counter[16];/* Counter (network byte order).*/
keyInstance key; /* Key to encrypt the counter.*/
unsigned char out[16]; /* The encrypted block.*/
Shalunov, et al. Standards Track [Page 49]
RFC 4656 One-way Active Measurement Protocol September 2006
} OWPrand_context;
/*
** The array has been computed according to the formula:
**
** Q[k] = (ln2)/(1!) + (ln2)^2/(2!) + ... + (ln2)^k/(k!)
**
** as described in algorithm S. (The values below have been
** multiplied by 2^32 and rounded to the nearest integer.)
** These exact values MUST be used so that different implementation
** produce the same sequences.
*/
static u_int64_t Q[K] = {
0, /* Placeholder - so array indices start from 1. */
0xB17217F8,
0xEEF193F7,
0xFD271862,
0xFF9D6DD0,
0xFFF4CFD0,
0xFFFEE819,
0xFFFFE7FF,
0xFFFFFE2B,
0xFFFFFFE0,
0xFFFFFFFE,
0xFFFFFFFF
};
/* this element represents ln2 */
#define LN2 Q[1]
/*
** Convert an unsigned 32-bit integer into a u_int64_t number.
*/
u_int64_t
OWPulong2num64(u_int32_t a)
{
return ((u_int64_t)1 << 32) * a;
}
/*
** Arithmetic functions on u_int64_t numbers.
*/
/*
** Addition.
*/
u_int64_t
OWPnum64_add(u_int64_t x, u_int64_t y)
Shalunov, et al. Standards Track [Page 50]
RFC 4656 One-way Active Measurement Protocol September 2006
{
return x + y;
}
/*
** Multiplication. Allows overflow. Straightforward implementation
** of Algorithm 4.3.1.M (p.268) from [KNUTH].
*/
u_int64_t
OWPnum64_mul(u_int64_t x, u_int64_t y)
{
unsigned long w[4];
u_int64_t xdec[2];
u_int64_t ydec[2];
int i, j;
u_int64_t k, t, ret;
xdec[0] = MASK32(x);
xdec[1] = MASK32(x>>32);
ydec[0] = MASK32(y);
ydec[1] = MASK32(y>>32);
for (j = 0; j < 4; j++)
w[j] = 0;
for (j = 0; j < 2; j++) {
k = 0;
for (i = 0; ; ) {
t = k + (xdec[i]*ydec[j]) + w[i + j];
w[i + j] = t%EXP2POW32;
k = t/EXP2POW32;
if (++i < 2)
continue;
else {
w[j + 2] = k;
break;
}
}
}
ret = w[2];
ret <<= 32;
return w[1] + ret;
}
/*
Shalunov, et al. Standards Track [Page 51]
RFC 4656 One-way Active Measurement Protocol September 2006
** Seed the random number generator using a 16-byte quantity 'seed'
** (== the session ID in OWAMP). This function implements step U1
** of algorithm Unif.
*/
void
OWPrand_context_init(OWPrand_context *next, unsigned char *seed)
{
int i;
/* Initialize the key */
rijndaelKeyInit(next->key, seed);
/* Initialize the counter with zeros */
memset(next->out, 0, 16);
for (i = 0; i < 16; i++)
next->counter[i] = 0UL;
}
/*
** Random number generating functions.
*/
/*
** Generate and return a 32-bit uniform random value (saved in the
**less significant half of the u_int64_t). This function implements
**steps U2-U4 of the algorithm Unif.
*/
u_int64_t
OWPunif_rand64(OWPrand_context *next)
{
int j;
u_int8_t *buf;
u_int64_t ret = 0;
/* step U2 */
u_int8_t i = next->counter[15] & (u_int8_t)3;
if (!i)
rijndaelEncrypt(next->key, next->counter, next->out);
/* Step U3. Increment next.counter as a 16-octet single
quantity in network byte order for AES counter mode. */
for (j = 15; j >= 0; j--)
if (++next->counter[j])
break;
/* Step U4. Do output. The last 4 bytes of ret now contain
Shalunov, et al. Standards Track [Page 52]
RFC 4656 One-way Active Measurement Protocol September 2006
the random integer in network byte order */
buf = &next->out[4*i];
for (j=0; j<4; j++) {
ret <<= 8;
ret += *buf++;
}
return ret;
}
/*
** Generate an exponential deviate with mean 1.
*/
u_int64_t
OWPexp_rand64(OWPrand_context *next)
{
unsigned long i, k;
u_int32_t j = 0;
u_int64_t U, V, J, tmp;
/* Step S1. Get U and shift */
U = OWPunif_rand64(next);
while ((U & BIT31) && (j < 32)) { /* Shift until first 0. */
U <<= 1;
j++;
}
/* Remove the 0 itself. */
U <<= 1;
U = MASK32(U); /* Keep only the fractional part. */
J = OWPulong2num64(j);
/* Step S2. Immediate acceptance? */
if (U < LN2) /* return (j*ln2 + U) */
return OWPnum64_add(OWPnum64_mul(J, LN2), U);
/* Step S3. Minimize. */
for (k = 2; k < K; k++)
if (U < Q[k])
break;
V = OWPunif_rand64(next);
for (i = 2; i <= k; i++) {
tmp = OWPunif_rand64(next);
if (tmp < V)
V = tmp;
}
/* Step S4. Return (j+V)*ln2 */
Shalunov, et al. Standards Track [Page 53]
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return OWPnum64_mul(OWPnum64_add(J, V), LN2);
}
Appendix B: Test Vectors for Exponential Deviates
It is important that the test schedules generated by different
implementations from identical inputs be identical. The non-trivial
part is the generation of pseudo-random exponentially distributed
deviates. To aid implementors in verifying interoperability, several
test vectors are provided. For each of the four given 128-bit values
of SID represented as hexadecimal numbers, 1,000,000 exponentially
distributed 64-bit deviates are generated as described above. As
they are generated, they are all added to each other. The sum of all
1,000,000 deviates is given as a hexadecimal number for each SID. An
implementation MUST produce exactly these hexadecimal numbers. To
aid in the verification of the conversion of these numbers to values
of delay in seconds, approximate values are given (assuming
lambda=1). An implementation SHOULD produce delay values in seconds
that are close to the ones given below.
SID = 0x2872979303ab47eeac028dab3829dab2
SUM[1000000] = 0x000f4479bd317381 (1000569.739036 seconds)
SID = 0x0102030405060708090a0b0c0d0e0f00
SUM[1000000] = 0x000f433686466a62 (1000246.524512 seconds)
SID = 0xdeadbeefdeadbeefdeadbeefdeadbeef
SUM[1000000] = 0x000f416c8884d2d3 (999788.533277 seconds)
SID = 0xfeed0feed1feed2feed3feed4feed5ab
SUM[1000000] = 0x000f3f0b4b416ec8 (999179.293967 seconds)
Shalunov, et al. Standards Track [Page 54]
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Authors' Addresses
Stanislav Shalunov
Internet2
1000 Oakbrook Drive, Suite 300
Ann Arbor, MI 48104
EMail: shalunov@internet2.edu
WWW: http://www.internet2.edu/~shalunov/
Benjamin Teitelbaum
Internet2
1000 Oakbrook Drive, Suite 300
Ann Arbor, MI 48104
EMail: ben@internet2.edu
WWW: http://people.internet2.edu/~ben/
Anatoly Karp
Computer Sciences Department
University of Wisconsin-Madison
Madison, WI 53706
EMail: akarp@cs.wisc.edu
Jeff W. Boote
Internet2
1000 Oakbrook Drive, Suite 300
Ann Arbor, MI 48104
EMail: boote@internet2.edu
Matthew J. Zekauskas
Internet2
1000 Oakbrook Drive, Suite 300
Ann Arbor, MI 48104
EMail: matt@internet2.edu
Shalunov, et al. Standards Track [Page 55]
RFC 4656 One-way Active Measurement Protocol September 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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This document and the information contained herein are provided on an
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Shalunov, et al. Standards Track [Page 56]