RFC 4656
A One-way Active Measurement Protocol (OWAMP)
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
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 .................541. 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
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
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.
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).
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:
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.
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.
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).
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-
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).
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.
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.
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) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.)
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.
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
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
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:
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
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.
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.
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.
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).
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.
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:
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.
(page 27 continued on part 2)
